Editors' ChoiceCARDIORESPIRATORY FITNESS

Exercise adaptations: A red herring?

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Science Translational Medicine  01 Jul 2015:
Vol. 7, Issue 294, pp. 294ec110
DOI: 10.1126/scitranslmed.aac8104

The widely accepted dogma that physically active people are healthier than sedentary ones is difficult to refute because of a massive body of supportive empirical evidence. Inspired by these promising observations, many are motivated to adopt exercise into their daily routines but then become discouraged or frustrated by seemingly modest returns on investment. Now, solid scientific data have verified that some people respond robustly to exercise whereas others do not. These so-called “nonresponders” are estimated to encompass 15 to 30% of the population and are classified on the basis of their lack of improvement in cardiorespiratory fitness or metabolic function—even when exercise interventions are painstakingly controlled. In a recent analysis of data from the Health Benefits of Aerobic and Resistance Training in Individuals with Type 2 Diabetes (HART-D) Study, Pandey and colleagues provide a new perspective on the concept of exercise resistance in people with type 2 diabetes.

The HART-D study involved 262 men and women with type 2 diabetes who were randomized to control, resistance exercise training, aerobic exercise training, or combined resistance and aerobic training groups. After 9 months, only 37% of participants in the exercise-intervention groups demonstrated meaningful improvements in whole-body fitness, whereas 43% exhibited no improvement in fitness. On the surface, these findings are staggering, because the exercise interventions were performed at the high end of the current U.S. National Institutes of Health recommendations (12 kcal/kg/week). But before we resign in frustration to a sedentary existence, it is important to consider the health benefits beyond physical performance.

Pandey and colleagues did exactly that, focusing on glycosylated hemoglobin (HbA1c), a blood test that represents an index of average blood sugar over the prior 3 months. This metabolic parameter is important to diabetic individuals because it reflects how well their diabetes is controlled. The authors found that exercise lowered HbA1c equally well in exercise responders and nonresponders. This study provides a great example of how important health benefits of exercise can be completely dissociated from the parameters that are commonly used to gauge the success of an exercise intervention. The vast majority of people exercise to become healthier, not to jump higher or run faster. Therefore, it makes sense that the metrics for evaluating exercise responsiveness focus less on physical performance and body composition and more on the health outcomes most relevant to a particular population, such as HbA1c in type 2 diabetes.

A. Pandey et al., Metabolic effects of exercise training among fitness nonresponsive patients with type 2 diabetes mellitus: The HART-D study. Diabetes Care 10.2337/dc14-2378 (2015). [Abstract]

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