If your goal is to have killer arms, but you have been neglecting other body parts, such as your legs, this study is for you. Danish scientists at Odense University performed some pretty interesting research with a group of students which were assigned different exercise regimes (Hansen et al, 2001). One group trained only their biceps on one arm, while the other group trained their biceps on one arm, together with their legs.
As expected, both groups experienced an increase in the strength of their trained biceps. However, those who trained their legs experienced a much greater increase in arm strength. In addition, the leg training group also experienced an increase in strength of the arm they did not train.
The scientists attributed this difference to the hormonal effect from training large muscle groups. Simply put, leg training causes a higher release of growth hormone, which leads to more overall muscle growth throughout the body.
In summary, if you want huge arms, you may think that spending all your time training your arms is the right way to go. But this couldn’t be further from the truth. If you are training only arms, you could be robbing yourself of some serious gains. Training larger muscle groups gives a better hormone response, which can be critical to help you grow. Even if you are only interested in growing arms, try to train them together with your chest, back, or legs.
Hansen et al (2001), The effect of short-term strength training on human skeletal muscle: the importance of physiologically elevated hormone levels. Scand J Med Sci Sports. 11(6):347-54