Discussion
The purpose of our scoping review was to summarise the literature published since 2000 on long-term function, body composition and cardiometabolic health in former athletes and to make recommendations for future research areas. We identified 20 published articles that met our criteria. In summary, our findings suggest that prior engagement in elite sport does not necessarily position individuals for optimal long-term health and function. The available data suggest that former national and international class endurance athletes may have higher aerobic capacity (ie, higher VO2 max), better cardiometabolic indicators and leaner body compositions than non-athlete controls. Data from a few studies54 57 58 suggest former athletes who maintain higher activity patterns (ie, self-reported exercise frequency of at least 3×/week) in midlife are healthier than former athletes who lead more sedentary lives and controls. Though limited by quantity of studies and samples, our findings suggest that former team sport athletes—who also have a much higher prevalence of former time-loss injury60—have poorer physical function and cardiometabolic health than individuals who were recreationally active during young adulthood.
Our findings that few studies included females or evaluated sex differences are well supported by prior literature demonstrating inequalities in research conducted on female versus male athletes.61 While some sports (eg, American football) are not widely practiced among both sexes, including both males and females in studies and evaluating sex differences when possible is essential and may have substantial clinical implications. Female sports participation has seen drastic increases since the passage of Title IX, furthering the need for sports medicine research to actively include female athletes in research studies to enable appropriate investigation of sex-based differences. Most of the former athletes in the included studies evaluated European males at a previous professional/elite level of competition, thus the findings may not generalise to females or athletes at lower competition levels. Four studies included only female participants,44 45 49 59 though two had sample sizes totalling less than 50 participants, including controls.49 59 Future studies should include female and male athletes to evaluate long-term health in both sexes and evaluate sex differences in long-term health among athletes in similar sports.
Current physical activity patterns in former athletes may be a key consideration for later health outcomes. Three studies54 57 58 compared male former athletes who led a more active lifestyle in midlife with former athletes who were sedentary in midlife, consistently finding that greater exercise in midlife was correlated with better functional performance,57 higher VO2 max54 57 and better body composition.54 57 58 While these athletes were male endurance athletes57 58 and male soccer players,54 limiting generalisability, substantial literature supports the benefit of physical activity and exercise on health outcomes.10 62 63 The included studies54 57 58 also relied exclusively on self-reported exercise frequency, rather than quantifying physical activity patterns. Important physical activity patterns include varying levels of physical activity (ie, light, moderate and vigorous) and sedentary behaviour, which is high in current male professional soccer players.64 Future studies should quantify activity patterns via continuous wear accelerometer protocols in current and former athletes and healthy non-athlete controls to determine more precisely the impact of activity patterns on long-term health in athletes.
Despite noted limitations, the importance of current health practices (ie, physical activity) on current health is clear, highlighting a reality for former athletes: prior engagement in high levels of exercise through elite sport does not provide athletes with lifelong protection for function, body composition and cardiometabolic health. Prior research on long-term cardiovascular health in former athletes has focused heavily on American football players.9 50–52 65 McHugh et al9 performed a systematic review and meta-analysis on cardiovascular health in male team-sport athletes (ie, American football (12 studies) and soccer (1 study)), finding that some factors (eg, fasting glucose, triglycerides) were better in former athletes whereas others (eg, systolic blood pressure, LDL cholesterol) were better in controls. While former NFL players who have higher BMI at time of professional sport participation have significantly greater cardiovascular disease risk,65 current behaviours including physical activity, exercise, diet and sleep, likely influence not only cardiovascular disease risk but also function, body composition, and other health outcomes. Future research should explore biopsychosocial factors for why some former athletes engage in healthy behaviours and others do not.
While it is well known that athletes sustain musculoskeletal injuries at much higher rates than non-athletes, one notable finding of our scoping review was that the included studies did not rigorously control for prior injury. Given the well-established link between traumatic joint injury, particularly intra-articular knee injury and subsequent risk for early OA,29 30 future research must compare former athletes with and without prior injury/surgery. To illustrate this point, Simon and Docherty found poorer functional performance and higher body fat percentage in former NCAA college athletes compared with controls, but 78/100 of the former athletes sustained a time-loss injury compared with just 20/100 controls.33 In short, prior injury likely influences long-term health in athletes and should be evaluated thoroughly in future research.
One of the best datasets on long-term athlete health evaluated Finnish former athletes who competed in national/international competitions from 1920 to 1965.46–48 66–72 While several of these studies were published prior to 2000 or did not meet other inclusion criteria, three were included in our scoping review.46–48 Collectively, these studies suggest former athletes may be fitter, healthier and stronger well into midlife and older age,73 despite high rates of radiographic OA.72 It is possible that former athletes benefit from persistently greater quadriceps muscle strength, which could help preserve better function,74 and/or high cardiorespiratory fitness, which could (partially) counteract deleterious consequences of higher OA prevalence.6 7 72 75 Future studies could investigate the effect of prior sports participation on cardiorespiratory fitness and function in midlife and older adults who have OA. In recent decades, however, sports have changed dramatically,24 including higher injury rates, differences in training and competition times and expectations, and artificial playing field surfaces.24 These factors limit the applicability of studies on athletes from many years ago to today’s athletes.
Limitations
A scoping review was pursued instead of a systematic review for several reasons, so our conclusions are limited primarily to summarising general findings, discussing gaps in the literature and identifying areas of future research. While we synthesised outcomes when possible, we did not perform meta-analyses or quality assessments of included studies in line with scoping review guidelines.40 Most studies evaluated male participants only and athletes who competed at the professional/elite competition levels, thus the findings may not generalise to females or athletes at lower competition levels. Most studies also used a cross-sectional study design, limiting the ability to determine cause and effect. Prior injury, the type and level of sport, subsequent and current physical activity patterns, and outcome measures likely influence the findings and generalisability. Finally, we did not consider atrial fibrillation or other cardiac arrythmias or abnormalities, though there has already been considerable research including a systematic review and meta-analysis on atrial fibrillation in athletes.76 Further research is needed in many areas (eg, standardised functional performance tests, inclusion of females, study of sex differences) before a systematic review(s) would be feasible, although systematically evaluating BMI, body composition and blood lipids—at least in male former athletes—may be possible.