Exercise variety

Using more exercise variety during a strength training program seems to lead to greater gains in the maximum strength of a target exercise, which to contradict the principle of specificity. Nevertheless, if we consider the underlying physiology, we can appreciate why this happens.

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#1. Greater exercise variety leads to greater strength gains

Given that the principle of specificity is a very well-established element of strength training programming, it can be surprising to discover that greater exercise variety is very likely better for strength gains in a given exercise than performing the same exercise constantly.

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#2. Hypertrophy after training with a given exercise is very regional

Muscle hypertrophy displays regional differences, with some regions growing more than others. Moreover, this regional hypertrophy differs between exercises for a variety of reasons that cause either differences in motor unit recruitment or in passive mechanical tension between the muscle regions (read more).

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#3. Regional hypertrophy contributes substantially to exercise-specific gains in maximum strength

As we might expect, whenever a muscle region contributes substantially to a specific exercise and therefore experiences meaningful hypertrophy after training with that exercise, the hypertrophy in turn contributes to the gains in strength. We can see this happening in the literature when increases in the size of some muscle regions are strongly associated with increases in maximum strength of the trained exercise while others are not so strongly associated.

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#4. Regional hypertrophy after strength training with an exercise alters the relative leverages of the muscle regions in future exercises

Importantly, when we generate regional hypertrophy, this changes the relative leverages of our individual muscle regions, causing us to use the hypertrophied muscle region to a greater extent than other regions within the the same muscle in future exercises. As we repeatedly perform the same exercise, we therefore become more and more dependent upon that single muscle region, and this likely eventually leads to it reaching plateau in size, which subsequently then causes an early plateau in the maximum strength of the trained exercise. Increasing exercise variety can help address this problem by causing increases in leverage of other muscle regions, thereby allowing the exercise to depend upon the contributions of multiple muscle regions for maximum strength instead of relying upon one.

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Conclusions

Using more exercise variety during a strength training program often leads to greater gains in the maximum strength of the primary exercise, which seems to contradict the principle of specificity. Nevertheless, if we consider the underlying physiology, we can appreciate why this happens. Firstly, strength training with any exercise causes more hypertrophy to occur in some regions of the prime mover muscle than in others. Which regions experience the most hypertrophy depends upon the exercise, according to [1] the principle of neuromechanical matching, [2] the two-joint muscle principle, and [3] regional variations in passive mechanical tension due to local muscle fiber strains. Secondly, while whole muscle hypertrophy is not strongly associated with increases in the maximum strength of the trained exercise, the hypertrophy of specific muscle regions is far more closely associated. Thirdly, when a muscle region increases in size after training, its leverage simultaneously increases and this increases its relative contribution to the trained exercise due to the principle of neuromechanical matching. This means that this muscle region will receive more of the overall central motor command during future repetitions of the same exercise. In other words, the performance of that exercise becomes ever more dependent on that muscle region over time, unless other exercises are done with the same muscle to increase the sizes (and therefore the leverages) of other regions within the same muscle. When only one region grows (or grows more than the other regions), this will cause a plateau in strength of the trained exercise to occur once that muscle region reaches its maximum possible size but continues to be the most strongly activated region of the muscle.​