The Effects of Combined Strength and Endurance Training

There are several marked adaptations associated with the regular performance of endurance training. Aerobic endurance training produces increases in VO2 max (13, 7, 8), but has no hypertrophy effect on muscle (6). Muscle fibre size has actually been shown to decrease (15, 11). Capillary supply to the muscles has been shown to change in response to endurance training through an increase in the capillary to muscle fibre ratio (16, 9). There is an increase in the number as well as the size of mitochondria, the latter of which is associated with an increase in certain enzymes (8). These increases are most apparent in the type I fibres as they have the highest content of mitochondria. Smaller increases in muscle and blood lactate levels are produced at the same relative exercise intensity after completing an endurance training program (8, 7). Glycogen is depleted less rapidly when trained than when untrained (8). The decreased use of carbohydrate during submaximal exercise is compensated for by a proportional increase in fat oxidation (8, 9). There is also a decrease in heart rate response during submaximal exercise (7). Several of these adaptations are in direct contrast to those associated with strength training.