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Male Wistar rats were treadmill-trained for 8 weeks using one of the two regimens: with the constant running speed or with alternating high-speed and low-speed intervals. Both training regimens led to an increase of rat aerobic capacities and to a higher citrate synthase activity in the medial head of gastrocnemius muscle. No differences between the effects of two training regimens were observed. However, in contrast to constant-speed training the interval one resulted in myocardium hypertrophy and also in less pronounced changes in diaphragm muscle, such as slow-direction shift of myosin phenotype and reduction of muscle fiber cross-sectional area. Neither of the training regimens had an effect on corticosterone and thyroid hormones levels in rat blood, whereas the interval training resulted in a higher level of testosterone. Anabolic influence of testosterone during interval aerobic training may be favorable for heart hemodynamic capacity and force characteristics of the diaphragm.
Borzykh et al. (Sat,) studied this question.