Increase of aerobic capacity by submaximal training and high-fat diets.

Forty male Long-Evans rats were used in an 8-week experiment designed to study the possibilities of using fats to increase aerobic work capacity and to elucidate the mechanisms of aerobic adaptation. The animals were divided into four groups: group SD comprised control rats kept on a standard diet and sedentary regimen; group HFD were given a high-fat diet (78 en.% of fats) and no training; group SDT consumed standard diet and were trained submaximally; group HFDT was on a high-fat diet and submaximal training. Submaximal running endurance (SRE) and maximum oxygen uptake (VO2max) tests were carried out in all groups. To clarify some of the mechanisms of aerobic adaptation we measured the glycogen content in m. gastrocnemius and the activity of key enzymes for the carbohydrate and fat metabolism, citrate synthase (CS), 3-hydroxiacetyl-CoA-dehydrogenase (3-HAD), and carnitine palmitoyl transferase (CPT) in muscle homogenates. It was found that a high-fat diet (HFD) improved the submaximal running endurance and if combined with submaximal training increased its effect several-fold. HFD increased the maximum oxygen uptake, training made it even greater, but the effect on VO2max the greatest when the two were used in combination. CS activity in m. soleus in HFD-fed rats was 23% greater than that in group SD, while 3-HAD activity was 27% higher than that in group SD. CPT activity in group HFDT was twice as great as that of the control group. Under the influence of HFD the muscle fibres underwent a shift of the energy substrate from carbohydrates to fats which was proved by the economical muscle glycogen depletion during physical exercise.