Most studies show that you get a more efficient anabolic hormone response by training larger muscle groups, such as the back or legs. That doesn’t mean that training smaller muscles, such as biceps or triceps, doesn’t stimulate more hormone release but that the magnitude of the effect is greater when you train larger muscle groups. A new study, however, shows that training smaller muscle groups can have a surprising effect on the secretion of various muscle hormone growth factors.1
The study involved 10 healthy men, ages 20 to 36, who did one-arm wrist curls. The researchers wanted to determine whether various growth factors that have previously been identified with weight training, such as fibroblast growth factor 2 (FGF-2), insulinlike growth factor 1 (IGF-1) and growth hormone (GH), originated in locally worked muscle tissue or were released systemically as a result of the exercise stimulus.
The authors placed blood catheters in both the exercising and nonexercising arms of the subjects, who did wrist curls for 10 minutes. Only the exercised arms showed increases in lactate levels. FGF-2 disappeared altogether shortly after the subjects started exercising, which the authors surmised may be due to its being ‘absorbed’ into the muscle itself. FGF-2 may work in tandem with IGF-1 in the muscle to promote muscular hypertrophy as well as increase internal muscle vascularity, thus increasing blood flow.
Both the exercised and resting arms showed increases in IGF-1 and its major binding protein in blood. Growth hormone also increased in both arms of the exercising men. The fact that both the exercised and resting arms showed increases in IGF-1 led the authors to conclude that the increased IGF-1 wasn’t produced locally in the muscle but systemically.
The increase in growth hormone was a surprise, since most previous studies found that it took either a high volume or exercising a larger muscle group to produce any type of GH response during training. The authors suggest that the psychological stress associated with perceived exertion during exercise may have accounted for the small rise in GH. Another possibility is that exercise may stimulate certain nerve tracts that directly communicate with the portion of the brain where GH is secreted. The major point of this study is that you can get a significant anabolic hormonal response from training any size muscle. IM
1 Eliakim, A., et al. (2000). Effect of single-wrist exercise on fibroblast growth factor 2, insulin-like growth factor and growth hormone. American J Physiology. 279:R548-R553.