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Abstract
Aim To investigate the suitability of metabolic equivalents (METs) for determining exercise intensity in phase-IV post-myocardial infarction (MI) men during the modified Bruce treadmill walking test (MBWT).
Methods Twenty phase-IV post-MI men (mean±SD, aged 64.4±5.8 years) and 20 healthy non-cardiac male controls (59.8±7.6 years) participated. Participants performed a MBWT. Throughout the participants’ heart rate (HR), heart rhythm, expired air parameters and ratings of perceived exertion (RPEs) were measured. MET values were compared between groups and those currently ascribed to each stage of the MBWT.
Results General linear model analysis found no significant differences between groups during the MBWT for VO2, VCO2, HR, METs or RPEs (Borg 6–20 scale). Ascribed METs did not differ from mean METs of post-MIs or controls other than at stage 5 where post-MI METs were significantly lower. Irrespective, the post-MI group worked at a higher percentage of their anaerobic threshold (AT) (respiratory exchange ratio, RER=1.0) (F (2,5)=7.22, p<0.008), higher RER (F (2,5)=11.25, p<0.001) with increased breathing frequency (F (2,5)=7.22, p<0.001). Regression analysis revealed AT to be VO2 25.6 (mL/kg/min) for post-MI versus VO2 31.1 (mL/kg/min) for controls. Gross energy expenditure (kcal/min) was greater for the post-MI group compared with controls (F (2,5)=11.22, p<0.001). Throughout the MBWT, post-MI group worked at a higher %AT/MET than controls (F (2,196)=211.76, p<0.01). Body composition did not strongly influence %AT/MET, parameters of VO2, METs or RPE.
Conclusion During the MBWT, post-MI men worked more anaerobically per MET (%AT/MET) than controls. Therefore, current METs based on non-cardiac individuals appear unsuitable in determining the full metabolic load of the exercise intensity for cardiac patients during the MBWT.
- Anaerobic threshold
- RPE
- VO2
- VCO2
- cardiac
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Footnotes
Acknowledgements Acknowledgements to statistician Dr Sabina Hulbert for advice and verification of the statistical analysis.
Contributors Dr Woolf-May, Dr Meadows and Mr Kearney developed the research protocol. Dr Meadows, Debbie Ferrett and Anna Upton conducted data collection. Dr Woolf-May conducted data analysis and report writing. Dr Woolf-May, Dr Meadows and Mr Kearney contributed to editing, gaining ethical approval and administrative procedures.
Funding Funding for this study was provided by East Kent Hospital University NHS Foundation Trust Cardiovascular Disease Research Grant Award.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
Data sharing statement Additional data are available upon request.