Intensive endurance training immediately before or after power training can reduce the effect of improving muscle strength. Athletes who do power training to increase maximal strength, should opt for a rest period of at least 3 hours between strength and endurance training or for endurance training with low exercise intensity (<70% VO2max).
The way in which the muscles of athletes adapt, depends on the nature of the effort. Power training leads to an increase in the number of muscle fibers and of the muscle volume. Endurance training leads to other changes, such as improving the function of mitochondria (the energy factories in muscle). Recent research has shown that power training can enhance endurance performance. In some cases, however, endurance training seems to have a negative effect on an explosive sports performance.
The question is in which cases different forms of exercise affect muscle adaptations after power and endurance training. The American researcher Baar therefore includes in this review article how the processes in the muscle cells are influenced by endurance training and strength training.
PROCESSES REQUIRED TO STRENGTH DEVELOPMENT
When power training is properly executed certain processes in the muscle provide for an increase in muscle mass and muscle strength. According to research the activation of the mTORC1 enzyme is required for these processes. If the activation fails for some reason, the power training has less or no effect. Also in case of insufficient protein in the diet or a high-fat and low carbohydrate diet the processes needed for power gain will be disrupted.
The studies summarized by Baar show no negative effect of power training on endurance performance. However, it has been found that intensive endurance training (for example, in the form of interval training) counteracts the increase in volume after the muscle strength training. This can be explained by certain types of duration effort to prevent the activation of mTORC1, even if athletes also do power training.
For example, it appears that doing a short sprint interval training of 10 sprints of 6 seconds on a bike, 15 minutes before a strength training, can block the activation of mTORC1. Immediately after a power training such sprints cause a rapid deactivation of the enzyme. If there are more than 3 hours between the two forms of training, however, no negative effects were found.
A combined training can limit the force increase, when the intensity of the endurance or interval training is high. Also, a shortage of carbohydrates or proteins in the body could deteriorate the strength gain. Athletes, who want to increase their muscle strength and volume, but also want to perform endurance or interval training, should take account all these effects. Adequate nutrition and a rest period of at least 3 hours between workouts is therefore advisable. For athletes who want to improve their endurance performance, combining different forms of training, however, is highly recommended because of the increase of performance.