It has long been known that large compound exercises such as squats stimulate a short term increase in testosterone production. It has always been assumed that this increased testosterone would act systemically to produce greater muscle growth in all muscles.
For this reason many bodybuilders perform exercises such as 20 rep squats every workout to ensure the maximum possible testosterone production, or always train small muscles such as biceps with other larger body parts so the biceps can benefit from the higher testosterone levels stimulated by training the larger muscle.
However a recent study shows that this practice is probably ineffective.
To test the theory a group of men trained their left and right biceps separately for 15 weeks. One bicep was trained alone and then two days later the other bicep was trained together with legs.
Higher levels of GH, IGF-1, and total and free testosterone on the leg days were confirmed by blood tests.
At the end of the study there were no differences between biceps in strength or type I or type II muscle fibre size.
The authors of the study conclude that local muscle growth factors and signalling mechanisms are responsible for muscle hypertrophy following training.
A sustained basal level of testosterone is required to support anabolism once the growth stimulus has been produced and higher constant basal levels such as those produced by taking anabolic steroids clearly have a potent effect. However small transient increases in systemic testosterone levels produced following exercise do not contribute to muscle growth.
Then why does the body increase testosterone and levels of other hormones such as GH following intense resistance training? Probably for reasons related to fuel mobilization and as a response to metabolic stress.
In conclusion this study gives you more freedom to organize your workouts without always having to train large and small muscles together. If you just want to train arms one day your guns will be just as impressive !
West DW et al. Elevations in ostensibly anabolic hormones with resistance exercise enhance neither training-induced muscle hypertrophy nor strength of the elbow flexors. J Appl Physiol. 2010 Jan;108(1):60-7
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