Irisin may explain why some teens benefit from exercise, while others do not.

Former DREAM trainee Dr. Martin Senechal discovers that a muscle protein may explain why some teens benefit from exercise, while others don’t.

It’s well established that the benefits of exercise can vary greatly between different people. For example, among the group overweight adolescents involved in the 6-month POWER trial; we found that on average exercise training led to improvements in fitness and modest changes in body composition compared to those that did not exercise. However, the individual response to exercise varied dramatically. Some children lost 10kg of fat mass while others gained 6kg (Figure 2). The mechanisms underlying these individual responses to exercise are not entirely clear, however data from Dr. Senechal’s lab suggest it may be related to the amount of a muscle-specific hormone released during each exercise session.

In a pilot trial conducted at CHRIM, 11 obese teens performed a single session of aerobic exercise (running) and a single session of resistance exercise (various weight lifting exercises) and had their blood measured throughout. Afterwards, all 11 teens performed a 6-week resistance training program, where they exercised 3 times/week for 45 minutes lifting weights up to 65% of their body weight. At the end of the training, Martin and his team measured changes in how well the teens handled a sugar drink and how sensitive their bodies were to insulin. Similar to our previous work, the response to exercise varied significantly, with some teens experiencing big improvements in insulin sensitivity while others saw their insulin sensitivity worsen. Overall however, the individual changes were related to how much of the muscle-borne hormone, named Irisin, was released during the single-session exercise they performed before the trial (Figure 2).

Together, the study provides, on a small scale, novel information to explain why some teens respond well to exercise, while others do not (or respond less well). They provide a new window into our understanding of the complex interactions between muscle and other organs, particularly during an exercise training intervention. Future, large-scale studies are needed to confirm and expand on these observations.