Background: The improvement of exercise capacity in patients with chronic heart failure (CHF) by physical training has been connected with reversal of the abnormalities in muscle fiber distribution and with the reduced activity of the enzymes of oxidative metabolism in skeletal muscle. However, the change in fiber type distribution induced by training is controversial and in previous studies the activities of the rate-limiting enzymes of the metabolic pathways have not been measured.
Aims: To examine the effect of dynamic training on percentage distribution of muscle fibers, on activities of the rate-limiting enzymes of the metabolic pathways and on electrophysiology in skeletal muscle.
Methods: A total of 27 patients with stable CHF (NYHA class II-III) were randomized to a training (N=12) or a control (N=15) group. The training group exercised on a bicycle ergometer for 30 min three times a week for 3 months using a load corresponding to 50-60% of their peak oxygen consumption. This was followed by a 3-month training period at home according to personal instructions. The control group did not change its physical activities. We studied muscle histology and measured the activities of the rate-limiting enzymes of anaerobic glycolysis (phosphofructokinase, PFK), glycogenolysis (phosphorylase), citric acid cycle (alpha-ketoglurate dehydrogenase, KGDH) and fatty acid oxidation (carnitinepalmitoyl transferase I and II, CPT I and II) from biopsies of the vastus lateralis muscle at baseline and after 3 and 6 months. Muscle strength and strength endurance with surface EMG and macro EMG of the right knee extensors were also determined.
Results: Exercise capacity, particularly submaximal, improved in the training group. The activity of PFK rose significantly but that of the other enzymes did not when compared with the change in the controls. Training had no effect on the percentage distribution of slow-twitch and fast-twitch muscle fibers or on capillary density around these fibers in skeletal muscle. Maximum voluntary force, strength endurance and the function of motor units remained unaffected.
Conclusions: Dynamic training results in improved exercise endurance in CHF. In skeletal muscle, the capacity of anaerobic glycolysis is increased but that of the citric acid cycle and fatty acid oxidation is not. Furthermore, the improvement in exercise endurance seems to be independent of changes in the percentage distribution of muscle fibers, capillarity or electrophysiological factors.