Article Review: Training one limb results in opposing limb increasing in strength
Article: Munn, J., Herbert, R.D., Hancock, M.J. and Gandevia, S.C., 2005. Training with unilateral resistance exercise increases contralateral strength. Journal of Applied Physiology, 99(5), pp.1880-1884.
Design: 111 participants completed training on one limb, whilst resting the other limb completely. They either trained 3 sets at fast speed, 3 sets at a slow speed, 1 set at a fast speed, 1 set at a slow speed or were a control group (no training either limb).
Findings: There was a 7% increase in strength in the untrained limb when 3 sets were performed (Note the strength improvement on the trained limb was 48%). When 1 set was performed there was no improvement in the untrained limb, as well as being no statistical difference between slow or fast training affecting the untrained limb. There was no change in muscle size in the untrained limb, showing that the improvement must be on a neurological level and not a hypertrophy change.
Limitations: This is quite a large sample size providing strong evidence. The measurement of muscle size was via tape measure which isn't very sensitive to small changes in size however.
My Thoughts: When a beginner is exposed to exercise there is a vast improvement in strength in the initial few weeks, regardless in change in muscle size. This has been studied to be due to a neurological improvement causing the improvement in strength. The study here was clearly due to a neurological level as there was no muscle size change. Why the increase is thought to be due to either an overflow of signalling to the limb. So as the signal to squeeze your right bicep goes down your spine, when it goes to turn to the right hand side bicep, a little signal spills over to the lefthand side causing a neurological stimulus and an improvement in motor unit firing. This provides a strong reasoning that if an injury occurs and a limb is immobilised, there is a valid reason to continue training the working limb.