We thank Shrier et al. for a thoughtful expansion on the topic of non-linearity.1 The comments from the authors provide valuable insights and detail to both the handling and the interpretation of fractional polynomials and splines, and may interest readers who seek more information than the short introduction in Bache-Mathiesen, et al. 2.
We are especially grateful for elaborating on the interpretation of restricted cubic splines, and the solution of adding a small constant (i.e. 0.1) to all values to handle the value “0” when using fractional polynomials. These topics could not be sufficiently addressed within the limited wordcount of the original article, and we encourage readers to consider these comments.
Conflict of Interest:
None declared.
References
1. Shrier I, Wang C, Stokes T, et al. Important Nuances for Non-Linear Modeling. BMJ Open Sport & Exercise Medicine 2021
2. Bache-Mathiesen LK, Andersen TE, Dalen-Lorentsen T, et al. Not straightforward: modelling non-linearity in training load and injury research. BMJ Open Sport & Exercise Medicine 2021;7(3):e001119. doi: 10.1136/bmjsem-2021-001119
We would like to thank Bache-Matiesen et al.(1) for their thoughtful article on non-linear modelling in sport medicine. Our own study on the non-linear relationship between acute: chronic workload ratio (ACWR) and injury risk in children was published as a preprint (2) and recently accepted by the American Journal of Epidemiology.(3) Below, we highlight some additional underlying principles in non-linear modelling that readers should understand.
GENERAL CONCEPTS
Models are based on information, which includes both data and assumptions. Simple linear models are more prone to bias because they assume a data generating process that is likely incorrect. The flexibility of non-linear models leads to less risk of bias, but also less precision. The optimal choice between bias and uncertainty depends on the context.(4)
Bache-Matiesen describe three non-linear modelling options: quadratic modelling, fractional polynomials (FP), and restricted cubic splines (RCS, where knots are determined by either data driven or a priori methods). These all fall under generalized additive models (GAMs), or generalized additive mixed models (GAMMs; if one uses “random effects” to adjust for repeated measures on participants).
FP methods use a single polynomial function over the entire range of exposures to predict the outcome. Quadratic models are special cases of FP (with exponents of 0, 1 and 2) and are too restrictive to be generally recommended. RCS separate data i...
We would like to thank Bache-Matiesen et al.(1) for their thoughtful article on non-linear modelling in sport medicine. Our own study on the non-linear relationship between acute: chronic workload ratio (ACWR) and injury risk in children was published as a preprint (2) and recently accepted by the American Journal of Epidemiology.(3) Below, we highlight some additional underlying principles in non-linear modelling that readers should understand.
GENERAL CONCEPTS
Models are based on information, which includes both data and assumptions. Simple linear models are more prone to bias because they assume a data generating process that is likely incorrect. The flexibility of non-linear models leads to less risk of bias, but also less precision. The optimal choice between bias and uncertainty depends on the context.(4)
Bache-Matiesen describe three non-linear modelling options: quadratic modelling, fractional polynomials (FP), and restricted cubic splines (RCS, where knots are determined by either data driven or a priori methods). These all fall under generalized additive models (GAMs), or generalized additive mixed models (GAMMs; if one uses “random effects” to adjust for repeated measures on participants).
FP methods use a single polynomial function over the entire range of exposures to predict the outcome. Quadratic models are special cases of FP (with exponents of 0, 1 and 2) and are too restrictive to be generally recommended. RCS separate data into sections by “knots”, determine which polynomials best predict the observed data within the sections defined by the knots, and apply a smoothing function to join the polynomials. The placement of the knots is important. In simulations, we know the true data generating process. In real-world observational data, we do not. Although we believe subjective a priori knot placement is sometimes better than data driven methods, researchers should be aware that gross errors may occur if the assumptions are incorrect.
RCS methods are more flexible than FP because they allow the functions between knots to be different from each other. We highlight two technical points. First, the “restriction” in the RCS method used by Bache-Matiesen appears restricted to using linear functions before the first knot and after the last knot. RCS can include other types of restrictions as well. Second, FP and RCS are just two forms of GAM(M)s. Two other popular forms are penalized regression spline and thin plate regression spline (e.g. default in mgcv package in the statistical program R (5)). The major difference between RCS and the penalized/thin plate regression splines is the shape of the polynomial that is used. The optimal choice depends partly on the research question and partly on the observed data.
SPECIFIC COMMENTS ON RECOMMENDATIONS BY BACHE-MATIESEN
1. Based on their simulations, Bache-Matiesen suggests RCS performs better than FP for predictive modeling. We believe the conclusion is too strong. RCS can be used in situations when there is a more complex underlying structure than FP. However, fitting more complex structure requires more data. When there is limited data and less complex structure, FP could outperform RCS.
2. Bache-Matiesen claim that RCS allowed the authors to model the relationship at high training loads where there were few data points. We caution against this due to the limited information. In our own study on children,(3) we restricted our conclusions about the relationship between acute:chronic workload ratio (ACWR) and injury risk to ACWR <3 where there were enough data. We show the full range of the relationship in the supplementary material to be fully transparent and to help generate hypotheses for future studies but did not feel it appropriate to make inferences.
3. We disagree with Bache-Matiesen that FP is more interpretable than RCS for causal effects, and that RCS results “can only be interpreted in the form of p values and visualisation”. First, we hope that most sport medicine researchers have moved beyond making inferences on p-values because of its severe limitations.(6, 7) Second, for causal questions, we generally estimate the difference in outcome when exposure is set to two different levels. When causal inference assumptions are reasonable, one estimates the causal effect with g-computation using predicted data from the model;(8) this is applicable for both linear and non-linear models. In brief, the magnitude of the causal effect in a non-linear model necessarily depends on the two chosen exposure levels. Although FP has only a single function over its entire range, the causal effect between the chosen exposure levels still requires using g-computation and the predicted values from the FP function. The causal effect using other GAM(M) methods is obtained with the same process; one uses the predicted values provided by the statistical software over the chosen exposure range.
4. The authors discuss the need to add a small constant to training load when it can equal 0, in order to allow for analyses on the log scale. The choice should have theoretical justification. For example, if activity (i.e. training load) is a proxy for time at risk (e.g. game injuries and a game was not played), adding a constant is inconsistent with the research question. However, in the ACWR, activity is a proxy for fatigue in the numerator and a proxy for fitness in the denominator. Both fatigue and fitness are affected by activities of daily living (e.g. occupation, transportation) outside of regular sports. In our analysis on children, we added a constant of 0.1 to activity to reflect our belief that activities of daily living might contribute 10% to each of fatigue and fitness. In supplementary analyses, we explored the effects if the contribution were 25% or 50%.
5. Finally, if we believe tripling the activity will triple the injury risk (e.g. 3 games vs 1 game), then activity (or ACWR) should be plotted on the log scale.(3)
REFERENCES
1. Bache-Mathiesen LK, Andersen TE, Dalen-Lorentsen T, et al. Not straightforward: modelling non-linearity in training load and injury research. BMJ Open Sport Exerc Med. 2021;7(3):e001119.
2. Wang C, Stokes T, Vargas JT, et al. Injury risk increases minimally over a large range of changes in activity level in children. arXiv. 2021;2010.02952v2 [q-bio.QM].
3. Wang C, Stokes T, Vargas JT, et al. Injury risk increases minimally over a large range of changes in activity level in children (In Press). Am J Epidemiol. 2021.
4. Kaufman JS. Commentary: Why are we biased against bias? Int J Epidemiol. 2008;37(3):624-626.
5. Wood S. mgcv. In: R: A language and environment for statistical computing R Foundation for Statistical Computing Vienna, Austria; 2021.
6. Amrhein V, Greenland S, McShane B. Scientists rise up against statistical significance. Nature. 2019;567(7748):305-307.
7. Wasserstein RL, Lazar NA. The ASA statement on p-values: context, process, and purpose. Am Stat. 2019;70(2):129-133.
8. Hernán MA, Robins JM. Causal inference: What if. Boca Raton: Chapman & Hall/CRC, 2020.
Thanks to the authors for providing some preliminary data on the potential effectiveness of bike-fitting to reduce pain and discomfort in cycling.
Very interesting study, but probably some questions are worth comments from authors:
1- Was there a proper ethics approval for this study? It seems that data was obtained retrospectively from clinical records.
2- How transferable to training is 100W of cycling?
3- Would authors be able to disclose the source of the 'measurement reference values'? Elaborating the criteria used for changes in bike-fit is critical to understand how and why cyclists improved their posture on the bike.
It would have been nice to see a control group to determine how much of the perceived changes are from placebo-effect.
Thank you for your e-letter of 5th April 2021 regarding our publication ‘Diagnostic accuracy of MRI for identifying posterior element bone stress injury in athletes with low back pain: a systematic review and narrative synthesis. BMJ Open Sport & Exercise Medicine 2020;0:e000764. doi:10.1136/ bmjsem-2020-000764’. We welcome your comments and interest in this research as it further highlights the importance of evidence based safe and ethical practice. Our own interest and rationale for this review stems from extensive working with young adults and adolescents involved in elite sport with low back pain.
We take on board your comments, although where good evidence to support one modality over another is lacking, the merits of different approaches concerning risk v benefit must be central to clinical decision making. In this instance, evidence based practice in the UK overwhelmingly supports the use of MRI as the first line investigation; recognising SPECT/CT involves ionising radiation, and that a safe alternative exists with MRI. When undertaken and interpreted correctly, MRI permits the sensitive detection of posterior element bone stress injury in the vast majority of cases and should therefore be used as the first line investigation. SPECT/CT should therefore be reserved for those small minority of cases where (following MRI) diagnostic doubt remains, where there are underlying complexities (such as previous same-level stress injuries)...
Thank you for your e-letter of 5th April 2021 regarding our publication ‘Diagnostic accuracy of MRI for identifying posterior element bone stress injury in athletes with low back pain: a systematic review and narrative synthesis. BMJ Open Sport & Exercise Medicine 2020;0:e000764. doi:10.1136/ bmjsem-2020-000764’. We welcome your comments and interest in this research as it further highlights the importance of evidence based safe and ethical practice. Our own interest and rationale for this review stems from extensive working with young adults and adolescents involved in elite sport with low back pain.
We take on board your comments, although where good evidence to support one modality over another is lacking, the merits of different approaches concerning risk v benefit must be central to clinical decision making. In this instance, evidence based practice in the UK overwhelmingly supports the use of MRI as the first line investigation; recognising SPECT/CT involves ionising radiation, and that a safe alternative exists with MRI. When undertaken and interpreted correctly, MRI permits the sensitive detection of posterior element bone stress injury in the vast majority of cases and should therefore be used as the first line investigation. SPECT/CT should therefore be reserved for those small minority of cases where (following MRI) diagnostic doubt remains, where there are underlying complexities (such as previous same-level stress injuries) or when the stakes are unusually high and uncertainty persists (such as in some professional athletes). Moreover, young elite athletes may need repeated imaging for lumbar stress injuries, further supporting the use of MRI over SPECT/CT and repeated exposure to ionising radiation.
We readily acknowledge that radiation doses from SPECT/CT have decreased in recent years, however this does not compare with ‘zero’ exposure for MRI. To continue to endorse SPECT/CT as a routine first line investigation condemns a cohort of predominantly young individuals to unnecessary exposure to ionising radiation, something that basic principles of radiation protection advocate against.
Thank you again for your interest and points raised to allow us to respond.
Dear colleagues, I have read with a great interest this systematic review “Esh R, Grødahl LHJ, Kerslake R, et al. Diagnostic accuracy of MRI for identifying posterior element bone stress injury in athletes with low back pain: a systematic review and narrative synthesis”[1] and would like to make some comments. Further research, as authors concluded, are always desired and I wish there are appropriate studies in the next future to decide if MRI could be a modality of choice for diagnosing PEBSI and not SPECT/CT as it is by now. But the referred articles from this review do not support this assertion for the following reasons.
First, there are just 2 articles from 4 included in this review compared MRI and SPECT/CT and just in 1 of them (Juvenil spondilolysis: a comparative analysis of CT, SPECT and MRI) the results of both techniques were concordant, although the main causes of discrepancy were between MRI and SPECT/CT for diagnoses of stress reaction in absence of overt fracture and distinguishing incomplete fracture from intact pars of complete defects (22 patients and 40 pars defect) [2].
Second, in the 2nd article the authors mention that sensitivity and specificity of MRI was 80 and 100% respectively skipping the SPECT/CT results and author’s conclusion that in the original article was following: “These results suggest that there is a high rate of active spondylolysis in active athletes with low back pain. MRI is inferior to bone scintigraphy (with SPECT)/c...
Dear colleagues, I have read with a great interest this systematic review “Esh R, Grødahl LHJ, Kerslake R, et al. Diagnostic accuracy of MRI for identifying posterior element bone stress injury in athletes with low back pain: a systematic review and narrative synthesis”[1] and would like to make some comments. Further research, as authors concluded, are always desired and I wish there are appropriate studies in the next future to decide if MRI could be a modality of choice for diagnosing PEBSI and not SPECT/CT as it is by now. But the referred articles from this review do not support this assertion for the following reasons.
First, there are just 2 articles from 4 included in this review compared MRI and SPECT/CT and just in 1 of them (Juvenil spondilolysis: a comparative analysis of CT, SPECT and MRI) the results of both techniques were concordant, although the main causes of discrepancy were between MRI and SPECT/CT for diagnoses of stress reaction in absence of overt fracture and distinguishing incomplete fracture from intact pars of complete defects (22 patients and 40 pars defect) [2].
Second, in the 2nd article the authors mention that sensitivity and specificity of MRI was 80 and 100% respectively skipping the SPECT/CT results and author’s conclusion that in the original article was following: “These results suggest that there is a high rate of active spondylolysis in active athletes with low back pain. MRI is inferior to bone scintigraphy (with SPECT)/computed tomography. Bone scintigraphy (with SPECT) should remain the first-line investigation of active athletes with low back pain followed by limited computed tomography if bone scintigraphy is positive” [3], 39 subjects and 50 pars interarticularis were included. The authors of the review make the opposite conclusion, that there were no false negative results of MRI, but false positive results of SPECT/CT due to SPECT´s high sensitivity of ongoing bone turnover activity and lacked classification system for SPECT.
Regarding to metabolic bone turnover activity I would like kindly remind a metabolism of 99mTc-diphosphonates, which is used for scintigraphy. The incorporation of diphosphonates is carried out in the hydroxyapatite crystals, in such a way that the degree of uptake will be proportional to the presence of those crystals, which, will be proportional to the osteoblastic activity and, therefore, to the metabolic turnover bone activity. The metabolism cannot be deceived, if it is increased focally or diffusely, there are more crystals that will bind with more diphosphonates in the exact localization [4].
Third, the authors mention that there is no established grading system defining SPECT abnormality in lumbar spine. System which normally used in Nuclear Medicine for defining an uptake in scintigraphy with/without SPECT is a semi-quantitative scale or a color scale of ROI (region of interest) lesion. Also nowadays quantitative SPECT has been commercially available for several years [5].
Forth, the authors mention possible false positive results of SPECT/TC, saying that scintigraphy uptake occurs frequently in athletes (34-45.2%) in non-painful sites, making a conclusion that such false positive cases are commonly regarded as adaptive changes and are perceived normal, giving as a link an article “Assessment o a clinical significance of asymptomatic lower extremity uptake abnormality in Young Athletes” [6]. Skipping the fact that in this study was used planar scintigraphy of lower extremities and not SPECT/CT of spine, there is a huge difference between false positive and asymptomatic abnormality, which can be translate into some irrelevant for treatment or following but present detection, and this is really frequent in athletes, that’s why it is not recommended to make scintigraphy in the absence of pain [6]. As you can check the images of this article, there are uptakes which are not considered as false positives, the authors are discussing its origin and relevance, but not calling in question the fact of the uptakes.
And the last, the risk of cancer development using nuclear medicine techniques is very low, even if the authors mention that “The effective dose from a single course of X-ray and SPECT-CT scans is 10X more, than what UK dwellings get in a year from natural background radiation exposure”. I can suppose that the authors took an effective dose of ionizing radiation 1mSv per year for UK dwelling and compared with approximately 10mSv received from SPECT/CT. There are epidemiological studies on populations exposed to radiation, such as atomic bomb survivors or radiotherapy patients, showed a significant increase of cancer risk at doses above 100 mSv [7] and despite intensive study, evidence to prove an increased cancer risk associated with radiation doses below ~100 mSv is lacking; however, concerns about ionizing radiation in medical imaging remain and can affect patient care [8]. Also nowadays it is used a lower dose CT protocols when performing SPECT-CT, permitting a reduction in the mean effective dose to 1.8 mSv from 4.0 mSv without a loss of CT image quality [9]. As an effective dose of an adult bone scintigraphy is between 2.9-4mSv [10], so the final effective dose of SPECT/CT is much lower than considered as risky for human health.
As a conclusion, with the analysed studies of this systematic review we can make a conclusion, that SPECT/CT has better sensitivity (100%), than MRI (80%) in 1 study [3], which means a loss of the fifth part of pathology, not detected by MRI and concordant results in the other article [2]. The SPECT/CT is still a technique of choice in patients with PEBSI without neurological symptoms. In the absence of risk, it would be preferably to use more sensible technique, although further research is desired to find out the best test for diagnosing PEBSI.
1) Esh R, Grødahl LHJ, Kerslake R, et al. Diagnostic accuracy of MRI for identifying posterior element bone stress injury in athletes with low back pain: a systematic review and narrative synthesis. BMJ Open Sport & Exercise Medicine 2020;0:e000764. doi:10.1136/ bmjsem-2020-000764
2) Campbell et al. Juvenil spondilolysis: a comparative analysis of CT, SPECT and MRI. Skeletal Radiology volume 34, pages63–73(2005) https://link.springer.com/article/10.1007/s00256-004-0878-3
3) Masci et al. 2005. Use of the one-legged hyperextension test and magnetic resonance imaging in the diagnosis of active spondylolysis. Br J Sports Med 2006; 40:940–946. doi: 10.1136/bjsm.2006.030023 https://www.researchgate.net/publication/6812831_Use_of_the_one-legged_h...
4) Yuda, H., Wakao, H. 99mTc-MDP accumulation mechanisms in bone: Basic study on the adsorption onto hydroxyapatite. Oral Radiol. 12, 27–32 (1996) https://link.springer.com/article/10.1007/BF02351579
5) Kangasmaa, T.S., Constable, C. & Sohlberg, A.O. Quantitative bone SPECT/CT reconstruction utilizing anatomical information. EJNMMI Phys 8, 2 (2021). https://doi.org/10.1186/s40658-020-00348-1
6) Laura A. Drubach, Leonard P. Connolly, Pierre A. D’Hemecourt and S. Ted Treves. Assessment of the Clinical Significance of Asymptomatic Lower Extremity Uptake Abnormality in Young Athletes Journal of Nuclear Medicine February 2001, 42 (2) 209-212. https://jnm.snmjournals.org/content/42/2/209
7) https://www.who.int/news-room/fact-sheets/detail/ionizing-radiation-heal...
8) Ferrero A. et al. Understanding, justifying, and optimizing radiation exposure for CT imaging in nephrourology. Nature reviews. Urology, 01 Apr 2019, 16(4):231-244 https://scite.ai/reports/10.1038/s41585-019-0148-8
9) Sandeep Kumar Gupta et al. Radionuclide bone scan SPECT-CT: lowering the dose of CT significantly reduces radiation dose without impacting CT image quality. Am J Nucl Med Mol Imaging 2017;7(2):63-73 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5435612/pdf/ajnmmi0007-0063...
10) The EANM practice guidelines for bone scintigraphy. T. Van den Wyngaert, K. Strobel, W. U. Kampen, T. Kuwert, W. van der Bruggen, H. K. Mohan, G. Gnanasegaran, R. Delgado-Bolton, W. A. Weber, M. Beheshti, W. Langsteger, F. Giammarile, F. M. Mottaghy, F. Paycha, On behalf of the EANM Bone & Joint Committee and the Oncology Committee. Eur J Nucl Med Mol Imaging. 2016; 43: 1723–1738. Published online 2016 Jun 4. doi: 10.1007/s00259-016-3415-4. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4932135/pdf/259_2016_Articl...
Nice study, and great to see you including dog ownership in your COI statements! A plea from a veterinary surgeon interested in dog walking though: please collect and report data about the dogs. A dog isn't a standardised intervention like a Fitbit. Their exercise capacity and exercise desire will vary with breed, age, comorbidities, body condition score, behaviour yet no data about the dogs is included in this publication. In addition, research suggests that owning an ill or behaviourally problematic dog can be very stressful. These canine attributes may have introduced a level of unaccounted for heterogeneity into your intervention arm which may have confounded your results. I'd be happy to point any researchers in this field towards the relevant canine literature, or assist with dog aspects of a study design.
Dear authors, I have read your paper with interest, and I have a couple of remarks that I think needs to be discussed to hopefully stimulate to more studies in this important field.
It is a weakness that there are very few randomised trials on surgical treatment of tendinopathy. To then draw conclusions from few studies is difficult and not always possible.
From this systematic review it is shown that 10 out 12 trials are on tendinopathy in the upper extremities (shoulder and elbow-althogether 998 tendinopathies) and only 2 on tendinopathy in the lower extremities (patellar and Achilles-althogeteher 60 tendinopathies). The authors have unfortunately missed to include 2 randomised studies on surgical treatment of patellar tendinopathy, published by Dr Willberg et al. Althogether, most information is about the shoulder and elbow, and very little about the Achilles and patellar tendons. Anyhow, when conclusions are drawn I get the impression that the authors put all tendinopathies in one group. This might be strongly misleading since there is very little information about the lower extremity tendons (only 2 studies), and conclusions cannot be drawn for Achilles and patellar tendinopathy. Furthermore, such conclusions might lead to that we miss possible differences in load response between upper and lower extremity tendons? The upper extremity non weight-bearing tendons might respond different compared to the lower extremity weight bearing tendons, as it is fo...
Dear authors, I have read your paper with interest, and I have a couple of remarks that I think needs to be discussed to hopefully stimulate to more studies in this important field.
It is a weakness that there are very few randomised trials on surgical treatment of tendinopathy. To then draw conclusions from few studies is difficult and not always possible.
From this systematic review it is shown that 10 out 12 trials are on tendinopathy in the upper extremities (shoulder and elbow-althogether 998 tendinopathies) and only 2 on tendinopathy in the lower extremities (patellar and Achilles-althogeteher 60 tendinopathies). The authors have unfortunately missed to include 2 randomised studies on surgical treatment of patellar tendinopathy, published by Dr Willberg et al. Althogether, most information is about the shoulder and elbow, and very little about the Achilles and patellar tendons. Anyhow, when conclusions are drawn I get the impression that the authors put all tendinopathies in one group. This might be strongly misleading since there is very little information about the lower extremity tendons (only 2 studies), and conclusions cannot be drawn for Achilles and patellar tendinopathy. Furthermore, such conclusions might lead to that we miss possible differences in load response between upper and lower extremity tendons? The upper extremity non weight-bearing tendons might respond different compared to the lower extremity weight bearing tendons, as it is for skeletal bones. Therefore, until we have more knowledge, I suggest that conclusions about tendinopathies are separated to upper and lower extremity.
-The conclusion in the abstract that tendinopathies should be treated with physiotherapy for at least 12 months before the option of surgery is seriously entertained cannot be stated based on the material in this systematic review. Although I myself is a strong promoter of exercise treatment for tendinopathy, at least for the Achilles and patellar tendons there is not enough research backing up such a statement.
-The conclusion that surgery is not superior to sham surgery in patients with tendinopathy is not correct-this can maybe be indicated considering the shoulder and elbow (based on very few studies), but for the lower extremity there are no such studies to refer to.
Althogether, this review clearly shows that much more research is needed in this field.
In their recent viewpoint and article, Stöllberger and Finsterer 1 2 criticize the inadequate regulation of “whole body-electromyostimulation” (WB-EMS), potentially responsible for a variety of adverse effects recently reported. 3-6 Indeed, in contrast to locally applied EMS, the stimulation of all, or at least most, major muscle groups characterizes WB-EMS. Consequently, given that even locally applied EMS might cause severe rhabdomyolysis and hospitalization 7, it is obvious that a technology able to stimulate simultaneously up to 2600 cm2 of muscular area entails a much larger risk of triggering unintended side effects 3-6 at least when inadequately applied. 8
Particularly with regard to the WB-EMS safety guidelines published in 2016 by our national WB-EMS consortium8, Stöllberger and Finsterer2 complain that the enquiring about contraindications and the requirements for a licensed WB-EMS trainer are not adequately specified. Overlapping with the publication of the article of Stöllberger and Finsterer, however it should be noted, that a German standard (DIN 33961-5, 9) was recently released which includes both contraindications for WB-EMS application in commercial, non-medical settings 10 and the requirements for the qualification of EMS trainers. Of importance, the latter was also specified by the 2019 revised German Radiation Protection Statutes (NiSV) a mandatory guideline published by the German “Bundesministerium für Umwelt, Naturschutz und nukleare Sicherhei...
In their recent viewpoint and article, Stöllberger and Finsterer 1 2 criticize the inadequate regulation of “whole body-electromyostimulation” (WB-EMS), potentially responsible for a variety of adverse effects recently reported. 3-6 Indeed, in contrast to locally applied EMS, the stimulation of all, or at least most, major muscle groups characterizes WB-EMS. Consequently, given that even locally applied EMS might cause severe rhabdomyolysis and hospitalization 7, it is obvious that a technology able to stimulate simultaneously up to 2600 cm2 of muscular area entails a much larger risk of triggering unintended side effects 3-6 at least when inadequately applied. 8
Particularly with regard to the WB-EMS safety guidelines published in 2016 by our national WB-EMS consortium8, Stöllberger and Finsterer2 complain that the enquiring about contraindications and the requirements for a licensed WB-EMS trainer are not adequately specified. Overlapping with the publication of the article of Stöllberger and Finsterer, however it should be noted, that a German standard (DIN 33961-5, 9) was recently released which includes both contraindications for WB-EMS application in commercial, non-medical settings 10 and the requirements for the qualification of EMS trainers. Of importance, the latter was also specified by the 2019 revised German Radiation Protection Statutes (NiSV) a mandatory guideline published by the German “Bundesministerium für Umwelt, Naturschutz und nukleare Sicherheit (BMU)” that includes WB-EMS, magnetic resonance imaging (MRI) and other types of “applications of non-ionizing radiation to humans”.11 However, apart from the mandatory instructor training, we are not fully convinced that the formal requirements specified by the NiSV will contribute to higher safety standards or increased effectiveness of WB-EMS.
Surprisingly, one key aspect of safe and effective WB-EMS application addressed by the DIN 33951-5 is rarely given sufficient attention in the discussion about regulating WB-EMS: the close supervision and interaction during WB-EMS application. Based on the safety guidelines 8, the DIN 33961-5 9 set the supervision ratio for WB-EMS applications to a maximum of two participants per licensed and qualified trainer and training unit. We think that this safety standard contributes significantly to reducing the risk of adverse effects as outlined by Stöllberger et al. 1 2 and boost the effectiveness of WB-EMS on various outcome 12 To comprehend this conclusion, it is crucial to consider the nature of WB-EMS and to separate the technology of "WB-EMS" from other types of EMS. We define WB-EMS as a simultaneous application of electric stimuli via at least six current channels or participation of all major muscle groups with a current impulse effective to trigger muscular adaptations. Apart from the large stimulated area, it should be noted that EMS-technology, be it locally or globally applied, enables a supramaximal workload without voluntary effort. Correspondingly, physiological mechanisms that protect against overloading during conventional training (e.g., muscular fatigue 13) do not come into play during EMS. Additionally, there is no objective parameter for prescribing impulse intensity during WB-EMS; and the sensitivity of the areas stimulated vary considerably. Consequently, the present WB-EMS application strategy focused on extensive feedback about perceived exertion for each area of stimulation consistently requested from the participant and adjusted by the trainer throughout the recommended 20 min session. 8 In order to apply an adequate WB-EMS stimulus without negative impact there is an undisputed consensus among WB-EMS experts that a trainer should supervise no more than two participants simultaneously. 8 14 We justify this narrow ratio of supervision with the need for close attention that includes intense verbal, visual and, when necessary, haptic interaction between licensed trainer and participants. Asking about individual load and readjustment of the current intensity at short intervals is essential for applying an adequate impulse intensity. We conclude that query and adjustment of the individual load must be conducted at least three times per current channel or muscle group during a 20 min training session. Further, a permanent visual control of the participant and eye contact is essential to check participant strain, avoid overload and to react immediately to the first signs of cardiorespiratory or metabolic side effect (e.g., change of face color in the case of stress-induced syncope). Additionally, the distance between trainer and participant has to be close enough to enable visual control, verbal interaction, movement corrections (“spotting”) and rapid assistance in cases of emergency, including cutting off power supply of the device and preventing fall-related injuries. We consider a maximum space of 120 cm between trainer and participants for just sufficient to permit these complex goals. Summing up, taking this key relevance and indispensable role of the physically present, well-trained and attentive WB-EMS trainer for safety and effectiveness into account, it is clear and logical that the optimum WB-EMS application cannot be anything but personal training (1:1 supervision). However, a ratio of two participants per licensed trainer and session, as implemented by most commercial WB-EMS providers, can be still considered as acceptable supervision. But having more than two participants simultaneously supervised by one trainer definitely prevents frequent regulation of workload, spotting, consistent visual control, frequent verbal interaction, and rapid reaction in case of emergency, and would mean low effectiveness and limited safety during WB-EMS application.
In conclusion: although several specifications on WB-EMS safety and effectiveness were published in 2019, we admit that there are still some features and limitations that have to be specified in the nearest future. This refers not only to an obligatory supervision ratio of one trainer and a maximum of two participants, but also to a mandatory commitment by commercial, non-medical WB-EMS institutions to adhere to the safety guideline and to fully respect contraindications 9 10 for WB-EMS. Considering further the rapid international development and dissemination of this novel technology, we fully agree with Stöllberger et al. 2 that initiatives to increase safety of WB-EMS should be implemented at an international level.
References
1. Stollberger C, Finsterer J. Side effects of whole-body electromyostimulation. Wien Med Wochenschr 2019;169(7-8):173-80. doi: 10.1007/s10354-018-0655-x
2. Stollberger C, Finsterer J. Side effects of and contraindications for whole-body electro-myo-stimulation: a viewpoint. BMJ open sport & exercise medicine 2019;5(1):e000619. doi: 10.1136/bmjsem-2019-000619 [published Online First: 2020/01/08]
3. Kastner A, Braun M, Meyer T. Two Cases of Rhabdomyolysis After Training With Electromyostimulation by 2 Young Male Professional Soccer Players. Clin J Sport Med 2014;25(6):71-73. doi: 10.1097/JSM.0000000000000153
4. Teschler M, Weissenfels A, Bebenek M, et al. Very high creatine kinase CK levels after WB_EMS. Are there implications for health. Int J Clin Exp Med 2016;9(11):22841-50.
5. Malnick SD, Band Y, Alin P, et al. It's time to regulate the use of whole body electrical stimulation. BMJ 2016;352:i1693. doi: 10.1136/bmj.i1693
6. Finsterer J, Stollberger C. Severe rhabdomyolysis after MIHA-bodytec(R) electrostimulation with previous mild hyper-CK-emia and noncompaction. Int J Cardiol 2015;180:100-2. doi: 10.1016/j.ijcard.2014.11.148
7. Johannsen AD, Krogh TK. Rhabdomyolysis in an elite dancer after training with electromyostimulation: A case report. Transl Sports Med 2019;2:288-91. doi: 10.1002/tsm2.91
8. Kemmler W, Froehlich M, von Stengel S, et al. Whole-Body Electromyostimulation – The Need for Common Sense! Rationale and Guideline for a Safe and Effective Training. Dtsch Z Sportmed 2016;67(9):218-21. doi: 10.5960/dzsm.2016.246.
9. DIN. DIN 33961-5. Fitness-Studio - Anforderungen an Studioausstattung und -betrieb – Teil 5: Elektromyostimulationstraining. Berlin: Beuth 2019.
10. Kemmler W, Weissenfels A, Willert S, et al. Recommended Contraindications for the Use of Non-Medical WB-Electromyostimulation. Dtsch Z Sportmed 2019;70(11):278-81.
11. BMU, editor. Verordnung zum Schutz vor schädlichen Wirkungen nichtionisierender Strahlung bei der Anwendung am Menschen (NiSV). Bonn: Bundesanzeiger Verlag, 2019.
12. Kemmler W, Weissenfels A, Willert S, et al. Efficacy and safety of low frequency Whole-Body Electromyostimulation (WB-EMS) to improve health-related outcomes in non-athletic adults. A systematic review. Front Physiol 2018;9:573. :doi: 10.3389/fphys.2018.0057.
13. Wan JJ, Qin Z, Wang PY, et al. Muscle fatigue: general understanding and treatment. Exp Mol Med 2017;49(10):e384. doi: 10.1038/emm.2017.194 [published Online First: 2017/10/07]
14. Kemmler W, Kleinöder H, Fröhlich M, et al. Leitlinien WB-EMS-Training: „Safety First“ – Sicherheit beim EMS Training. 2016 [accessed 11.02.2020 2019.
The article Mortality of Japanese Olympic athletes: 1952 – 2017 cohort study currently fails to account for a probable source of non-negligible bias. Whilst the main finding, stating that there is a decreased mortality rate among Japanese Olympians appears to be methodologically reliable, the authors also state that “higher mortality was observed among those who participated in the Olympics twice and three times or more compared with those who participated just once,” which we believe to be a potentially inaccurate finding.
A delayed entry exists at baseline, as those with longer careers tend to be older than those with shorter careers. For instance, someone who has participated in 3 Olympic Games started her/his Olympic career 12 years before those who have participated only once. Thus, there might be an important period effect underlying these findings. Even if the authors have adjusted the analysis by age, this is not equivalent to adjusting for period, as earlier periods in time are related with higher mortality rates, which could explain the findings.
Additionally, another problem often seen in survival studies is ignoring when a death event occurs. This is problematic because deaths will be observed more frequently in subjects with longer follow-up times. In the presence of time-dependent bias, the hazard ratio is artificially underestimated and the length bias leads to an artificial underestimation of the overall hazard [2]. Therefore, faulty interpretat...
The article Mortality of Japanese Olympic athletes: 1952 – 2017 cohort study currently fails to account for a probable source of non-negligible bias. Whilst the main finding, stating that there is a decreased mortality rate among Japanese Olympians appears to be methodologically reliable, the authors also state that “higher mortality was observed among those who participated in the Olympics twice and three times or more compared with those who participated just once,” which we believe to be a potentially inaccurate finding.
A delayed entry exists at baseline, as those with longer careers tend to be older than those with shorter careers. For instance, someone who has participated in 3 Olympic Games started her/his Olympic career 12 years before those who have participated only once. Thus, there might be an important period effect underlying these findings. Even if the authors have adjusted the analysis by age, this is not equivalent to adjusting for period, as earlier periods in time are related with higher mortality rates, which could explain the findings.
Additionally, another problem often seen in survival studies is ignoring when a death event occurs. This is problematic because deaths will be observed more frequently in subjects with longer follow-up times. In the presence of time-dependent bias, the hazard ratio is artificially underestimated and the length bias leads to an artificial underestimation of the overall hazard [2]. Therefore, faulty interpretation may result from the underlying assumptions, which is potentially the case in this study.
The authors argue that the higher mortality rate found among those who participated in multiple Olympics could be related to longer periods of intense training. Yet, this is contradictory to their main finding which demonstrates far lower mortality rates among Olympians in comparison to the general population.
Finally, the higher mortality found among those engaged in multiple Games could also be explained by the missing life status confirmations. There were 1324 Olympians who were assumed to be alive when missing date of death. Previous studies that dealt with the same data source and the submission of life status to national data certification for confirmation found that there was more reliable data for well-known athletes [3]. Thus, date of death is probably more widespread for athletes engaged in multiple games and therefore less well-known athletes, participating in only one Games, may have been mislabeled alive when death information was missing.
The main findings that demonstrate lower mortality rates among Japanese Olympians compared to the general population rely on standard methods and seem to be reliable. The secondary findings that compare mortality among Olympians engaged in multiple games should be revised accounting for the biases described in this letter.
1 Zwiener I, Blettner M, Hommel G. Survival analysis: part 15 of a series on evaluation of scientific publications. Dtsch Ärztebl Int 2011;108:163–9. doi:10.3238/arztebl.2010.0163
2 Wolkewitz M, Allignol A, Harbarth S, et al. Time-dependent study entries and exposures in cohort studies can easily be sources of different and avoidable types of bias. J Clin Epidemiol 2012;65:1171–80. doi:10.1016/j.jclinepi.2012.04.008
3 Antero-Jacquemin J, Pohar-Perme M, Rey G, et al. The heart of the matter: years-saved from cardiovascular and cancer deaths in an elite athlete cohort with over a century of follow-up. Eur J Epidemiol Published Online First: 5 May 2018. doi:10.1007/s10654-018-0401-0
We have read with interest the article by Radenkovic D et al. (1) As final year medical students having experienced both pre-clinical and clinical training, we agree that there is a significant gap in lifestyle medicine training. We appreciate the authors highlighting the gap in formal training and assessment of motivational interviewing. Evidence suggests there is a strong positive correlation in using motivational interviewing and the transtheoretical model of behaviour change as counselling strategies to achieve improved patient outcomes in lifestyle changes. (2)
While this study focused primarily on physical exercise guidelines, it is important to define lifestyle medicine holistically, as it incorporates not only physical exercise but also nutrition, sleep, smoking as well as stress management. It would also be interesting to see how well trained medical students are in these other aspects of lifestyle medicine and how that correlates to lifestyle habits of students across various years of training. This could be done in the form or student welfare surveys throughout the academic year which would allow a more longitudinal holistic analysis of the representation of lifestyle medicine knowledge and student lifestyle habits. This can further inform targeted changes to medical school curriculum and student wellness interventions to ensure students are well equipped to maintain their own well-being and increase their confidence in counselling p...
We have read with interest the article by Radenkovic D et al. (1) As final year medical students having experienced both pre-clinical and clinical training, we agree that there is a significant gap in lifestyle medicine training. We appreciate the authors highlighting the gap in formal training and assessment of motivational interviewing. Evidence suggests there is a strong positive correlation in using motivational interviewing and the transtheoretical model of behaviour change as counselling strategies to achieve improved patient outcomes in lifestyle changes. (2)
While this study focused primarily on physical exercise guidelines, it is important to define lifestyle medicine holistically, as it incorporates not only physical exercise but also nutrition, sleep, smoking as well as stress management. It would also be interesting to see how well trained medical students are in these other aspects of lifestyle medicine and how that correlates to lifestyle habits of students across various years of training. This could be done in the form or student welfare surveys throughout the academic year which would allow a more longitudinal holistic analysis of the representation of lifestyle medicine knowledge and student lifestyle habits. This can further inform targeted changes to medical school curriculum and student wellness interventions to ensure students are well equipped to maintain their own well-being and increase their confidence in counselling patient about lifestyle changes. (3)
As explained in your article seven UK medical schools were contacted with the online Google survey yielded a response rate of 11.6%, this may result in a recruitment bias which would mean that the results of the survey may not represent the wider medical student population who did not participate in the survey. Contacting more medical schools, at various points in the year with a greater window to complete the survey, would increase the probability of more responses. In light of survey design, it may have been interesting to analyse qualitative responses to open questions regarding students’ opinions of how confident they would be in counselling patients regarding lifestyle changes and suggestions on how this could be improved in medical school training.
Ultimately, we applaud the efforts of this article in highlighting the inadequate physical exercise education in medical school curriculum, and we hope to see further work on strategies to bridge this knowledge gap. Going forward, there should be future research into training of other aspects of lifestyle including stress management, nutrition and mental health awareness, in addition to counselling-strategy training in large multicentre cross-sectional studies. This will produce further insight into areas of improvement to ultimately increase confidence and resilience amongst doctors of the future in counselling patients about lifestyle changes.
References:
1. Radenkovic D, Aswani R, Ahmad I, Kreindler J, Robinson R. Lifestyle medicine and physical activity knowledge of final year UK medical students. BMJ Open Sport Exerc Med. 2019;5(1):e000518. Published 2019 Jun 14. doi:10.1136/bmjsem-2019-000518
2. Stonerock GL, Blumenthal JA. Role of Counseling to Promote Adherence in Healthy Lifestyle Medicine: Strategies to Improve Exercise Adherence and Enhance Physical Activity. Prog Cardiovasc Dis. 2017;59(5):455–462. doi:10.1016/j.pcad.2016.09.003
3. Ludwig AB, Burton W, Weingarten J, Milan F, Myers DC, Kligler B. Depression and stress amongst undergraduate medical students. BMC Med Educ. 2015;15:141. Published 2015 Aug 27. doi:10.1186/s12909-015-0425-z
We thank Shrier et al. for a thoughtful expansion on the topic of non-linearity.1 The comments from the authors provide valuable insights and detail to both the handling and the interpretation of fractional polynomials and splines, and may interest readers who seek more information than the short introduction in Bache-Mathiesen, et al. 2.
We are especially grateful for elaborating on the interpretation of restricted cubic splines, and the solution of adding a small constant (i.e. 0.1) to all values to handle the value “0” when using fractional polynomials. These topics could not be sufficiently addressed within the limited wordcount of the original article, and we encourage readers to consider these comments.
Conflict of Interest:
None declared.
References
1. Shrier I, Wang C, Stokes T, et al. Important Nuances for Non-Linear Modeling. BMJ Open Sport & Exercise Medicine 2021
2. Bache-Mathiesen LK, Andersen TE, Dalen-Lorentsen T, et al. Not straightforward: modelling non-linearity in training load and injury research. BMJ Open Sport & Exercise Medicine 2021;7(3):e001119. doi: 10.1136/bmjsem-2021-001119
We would like to thank Bache-Matiesen et al.(1) for their thoughtful article on non-linear modelling in sport medicine. Our own study on the non-linear relationship between acute: chronic workload ratio (ACWR) and injury risk in children was published as a preprint (2) and recently accepted by the American Journal of Epidemiology.(3) Below, we highlight some additional underlying principles in non-linear modelling that readers should understand.
GENERAL CONCEPTS
Models are based on information, which includes both data and assumptions. Simple linear models are more prone to bias because they assume a data generating process that is likely incorrect. The flexibility of non-linear models leads to less risk of bias, but also less precision. The optimal choice between bias and uncertainty depends on the context.(4)
Bache-Matiesen describe three non-linear modelling options: quadratic modelling, fractional polynomials (FP), and restricted cubic splines (RCS, where knots are determined by either data driven or a priori methods). These all fall under generalized additive models (GAMs), or generalized additive mixed models (GAMMs; if one uses “random effects” to adjust for repeated measures on participants).
FP methods use a single polynomial function over the entire range of exposures to predict the outcome. Quadratic models are special cases of FP (with exponents of 0, 1 and 2) and are too restrictive to be generally recommended. RCS separate data i...
Show MoreThanks to the authors for providing some preliminary data on the potential effectiveness of bike-fitting to reduce pain and discomfort in cycling.
Very interesting study, but probably some questions are worth comments from authors:
1- Was there a proper ethics approval for this study? It seems that data was obtained retrospectively from clinical records.
2- How transferable to training is 100W of cycling?
3- Would authors be able to disclose the source of the 'measurement reference values'? Elaborating the criteria used for changes in bike-fit is critical to understand how and why cyclists improved their posture on the bike.
It would have been nice to see a control group to determine how much of the perceived changes are from placebo-effect.
Dear Dr Obedkova
Thank you for your e-letter of 5th April 2021 regarding our publication ‘Diagnostic accuracy of MRI for identifying posterior element bone stress injury in athletes with low back pain: a systematic review and narrative synthesis. BMJ Open Sport & Exercise Medicine 2020;0:e000764. doi:10.1136/ bmjsem-2020-000764’. We welcome your comments and interest in this research as it further highlights the importance of evidence based safe and ethical practice. Our own interest and rationale for this review stems from extensive working with young adults and adolescents involved in elite sport with low back pain.
We take on board your comments, although where good evidence to support one modality over another is lacking, the merits of different approaches concerning risk v benefit must be central to clinical decision making. In this instance, evidence based practice in the UK overwhelmingly supports the use of MRI as the first line investigation; recognising SPECT/CT involves ionising radiation, and that a safe alternative exists with MRI. When undertaken and interpreted correctly, MRI permits the sensitive detection of posterior element bone stress injury in the vast majority of cases and should therefore be used as the first line investigation. SPECT/CT should therefore be reserved for those small minority of cases where (following MRI) diagnostic doubt remains, where there are underlying complexities (such as previous same-level stress injuries)...
Show MoreDear colleagues, I have read with a great interest this systematic review “Esh R, Grødahl LHJ, Kerslake R, et al. Diagnostic accuracy of MRI for identifying posterior element bone stress injury in athletes with low back pain: a systematic review and narrative synthesis”[1] and would like to make some comments. Further research, as authors concluded, are always desired and I wish there are appropriate studies in the next future to decide if MRI could be a modality of choice for diagnosing PEBSI and not SPECT/CT as it is by now. But the referred articles from this review do not support this assertion for the following reasons.
Show MoreFirst, there are just 2 articles from 4 included in this review compared MRI and SPECT/CT and just in 1 of them (Juvenil spondilolysis: a comparative analysis of CT, SPECT and MRI) the results of both techniques were concordant, although the main causes of discrepancy were between MRI and SPECT/CT for diagnoses of stress reaction in absence of overt fracture and distinguishing incomplete fracture from intact pars of complete defects (22 patients and 40 pars defect) [2].
Second, in the 2nd article the authors mention that sensitivity and specificity of MRI was 80 and 100% respectively skipping the SPECT/CT results and author’s conclusion that in the original article was following: “These results suggest that there is a high rate of active spondylolysis in active athletes with low back pain. MRI is inferior to bone scintigraphy (with SPECT)/c...
Nice study, and great to see you including dog ownership in your COI statements! A plea from a veterinary surgeon interested in dog walking though: please collect and report data about the dogs. A dog isn't a standardised intervention like a Fitbit. Their exercise capacity and exercise desire will vary with breed, age, comorbidities, body condition score, behaviour yet no data about the dogs is included in this publication. In addition, research suggests that owning an ill or behaviourally problematic dog can be very stressful. These canine attributes may have introduced a level of unaccounted for heterogeneity into your intervention arm which may have confounded your results. I'd be happy to point any researchers in this field towards the relevant canine literature, or assist with dog aspects of a study design.
Dear authors, I have read your paper with interest, and I have a couple of remarks that I think needs to be discussed to hopefully stimulate to more studies in this important field.
Show MoreIt is a weakness that there are very few randomised trials on surgical treatment of tendinopathy. To then draw conclusions from few studies is difficult and not always possible.
From this systematic review it is shown that 10 out 12 trials are on tendinopathy in the upper extremities (shoulder and elbow-althogether 998 tendinopathies) and only 2 on tendinopathy in the lower extremities (patellar and Achilles-althogeteher 60 tendinopathies). The authors have unfortunately missed to include 2 randomised studies on surgical treatment of patellar tendinopathy, published by Dr Willberg et al. Althogether, most information is about the shoulder and elbow, and very little about the Achilles and patellar tendons. Anyhow, when conclusions are drawn I get the impression that the authors put all tendinopathies in one group. This might be strongly misleading since there is very little information about the lower extremity tendons (only 2 studies), and conclusions cannot be drawn for Achilles and patellar tendinopathy. Furthermore, such conclusions might lead to that we miss possible differences in load response between upper and lower extremity tendons? The upper extremity non weight-bearing tendons might respond different compared to the lower extremity weight bearing tendons, as it is fo...
In their recent viewpoint and article, Stöllberger and Finsterer 1 2 criticize the inadequate regulation of “whole body-electromyostimulation” (WB-EMS), potentially responsible for a variety of adverse effects recently reported. 3-6 Indeed, in contrast to locally applied EMS, the stimulation of all, or at least most, major muscle groups characterizes WB-EMS. Consequently, given that even locally applied EMS might cause severe rhabdomyolysis and hospitalization 7, it is obvious that a technology able to stimulate simultaneously up to 2600 cm2 of muscular area entails a much larger risk of triggering unintended side effects 3-6 at least when inadequately applied. 8
Show MoreParticularly with regard to the WB-EMS safety guidelines published in 2016 by our national WB-EMS consortium8, Stöllberger and Finsterer2 complain that the enquiring about contraindications and the requirements for a licensed WB-EMS trainer are not adequately specified. Overlapping with the publication of the article of Stöllberger and Finsterer, however it should be noted, that a German standard (DIN 33961-5, 9) was recently released which includes both contraindications for WB-EMS application in commercial, non-medical settings 10 and the requirements for the qualification of EMS trainers. Of importance, the latter was also specified by the 2019 revised German Radiation Protection Statutes (NiSV) a mandatory guideline published by the German “Bundesministerium für Umwelt, Naturschutz und nukleare Sicherhei...
The article Mortality of Japanese Olympic athletes: 1952 – 2017 cohort study currently fails to account for a probable source of non-negligible bias. Whilst the main finding, stating that there is a decreased mortality rate among Japanese Olympians appears to be methodologically reliable, the authors also state that “higher mortality was observed among those who participated in the Olympics twice and three times or more compared with those who participated just once,” which we believe to be a potentially inaccurate finding.
Show MoreA delayed entry exists at baseline, as those with longer careers tend to be older than those with shorter careers. For instance, someone who has participated in 3 Olympic Games started her/his Olympic career 12 years before those who have participated only once. Thus, there might be an important period effect underlying these findings. Even if the authors have adjusted the analysis by age, this is not equivalent to adjusting for period, as earlier periods in time are related with higher mortality rates, which could explain the findings.
Additionally, another problem often seen in survival studies is ignoring when a death event occurs. This is problematic because deaths will be observed more frequently in subjects with longer follow-up times. In the presence of time-dependent bias, the hazard ratio is artificially underestimated and the length bias leads to an artificial underestimation of the overall hazard [2]. Therefore, faulty interpretat...
Dear Editor,
We have read with interest the article by Radenkovic D et al. (1) As final year medical students having experienced both pre-clinical and clinical training, we agree that there is a significant gap in lifestyle medicine training. We appreciate the authors highlighting the gap in formal training and assessment of motivational interviewing. Evidence suggests there is a strong positive correlation in using motivational interviewing and the transtheoretical model of behaviour change as counselling strategies to achieve improved patient outcomes in lifestyle changes. (2)
While this study focused primarily on physical exercise guidelines, it is important to define lifestyle medicine holistically, as it incorporates not only physical exercise but also nutrition, sleep, smoking as well as stress management. It would also be interesting to see how well trained medical students are in these other aspects of lifestyle medicine and how that correlates to lifestyle habits of students across various years of training. This could be done in the form or student welfare surveys throughout the academic year which would allow a more longitudinal holistic analysis of the representation of lifestyle medicine knowledge and student lifestyle habits. This can further inform targeted changes to medical school curriculum and student wellness interventions to ensure students are well equipped to maintain their own well-being and increase their confidence in counselling p...
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