MacDougall, J. D., Ward, G. R., Sale, D. G., & Sutton, J. R. (1977). Biochemical adaptation of human skeletal muscle to heavy resistance training and immobilization. Journal of Applied Physiology, 43, 700-703.

Low-resistance repeated contractions develop significant increases in the capacity of muscle to oxidize pyruvate and fatty acids as a result of both increased mitochondrial enzyme activity and an increase in number and size of mitochondria.

Brief, maximal contractions associated with heavy-resistance strength training require a very high rate of energy production which can be met only by the muscle's high-energy phosphate reserves and to a lesser extent glycolysis.

Although an increase in the total content of the high-energy phosphate pool would not be expected to affect the maximal rate of power output from a muscle, it would increase the total energy available from this source, and thus prolong the time that this rate of power output could be sustained.

Implications.

1. High repetition weight training produces aerobic changes. However, since aerobic adaptation is specific that would not be useful for competitive aerobic activities. Aerobic adaptation would be achieved better by doing the activity itself.
2. Weight training with high loads produces changes in stored energy sources for maximum power output. No change in rate should be expected, just stored energy.
3. Weight training is possibly useful for only strength and power activities.

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