By Kavindra Sahabir ‘21
One commonality between the average gym goer and competitive bodybuilders is the goal of stimulating muscle growth. Researchers led by Sarah J. Lessard from the Joslin Diabetes Center have aimed to understand how to stimulate muscle growth by investigating the effects of resistance training, or training using weights, and endurance training, or running and other aerobic exercises, on JNK. JNK, or c-Jun N-terminal kinase, serves as a molecular switch; when activated, JNK stimulates muscle growth, but when suppressed, JNK stimulates greater muscular oxidative capacity, or stamina (1).
To ensure a greater understanding of mammalian muscle growth, their study tested mouse and human subjects, both of which were split up into two groups: one that underwent resistance training and another which underwent endurance training. For the mice, in order to directly observe the effects that the expression of JNK had on resistance and endurance training, they compared mice with JNK suppressed and without JNK suppression. In the mice, their resistance training involved the removal of a muscle to force the strengthening of another muscle, their endurance training involved running in wheel running cages. Then, to relate the study to humans, they measured the expression of JNK and other proteins activated within human test subjects as a result of resistance and endurance training.
From this study, it was found in the mice group, that by inhibiting JNK, the mice experienced an increase in stamina and endurance and a decrease in muscle gain. It was also found that whereas engaging in resistance exercises led to an increase in JNK activation and increased muscle growth, engaging in endurance exercise led to a suppression of JNK activation and increased muscle endurance. According to the research team, these findings will also help pave the way to find solutions for muscular wasting diseases, which involve a degeneration of muscle, as through JNK activation, patients with these diseases may be able to regain muscle mass.