Submaximal Endurance Exercise Research Articles

Exercise-induced glycogen utilization by the respiratory muscles.

Some controversy exists in the literature as to whether or not diaphragmatic glycogen is utilized during exercise. In this study male Sprague-Dawley rats were used to determine whether prolonged treadmill exercise would result in a significant reduction of glycogen concentration in the respiratory muscles. Untrained rats were run to exhaustion at a speed of 24 m/min, up a 10% grade. Run time averaged 48:30 min. After exercise a significant reduction in glycogen was observed in the diaphragm (43% of control), intercostals (43%), heart (39%), and plantaris (76%). In the diaphragm a significant reduction was shown in both types I and II fibers using the periodic acid-Schiff (PAS) stain for glycogen. These findings show that muscles with vastly different aerobic capacities utilize endogenous glycogen during moderately intense submaximal endurance exercise and that the costal diaphragm muscle is not an exception as has recently been suggested.

Ventilatory muscle training improves exercise capacity in chronic obstructive pulmonary disease patients.

We examined the effect of a 6-wk period of ventilatory muscle endurance training on the maximal sustained ventilatory capacity (MSVC) and on exercise tolerance in 10 patients with chronic obstructive pulmonary disease (COPD). No significant changes occurred in lung volumes or spirometric indices. After training, the MSVC increased from 32 +/- 11 to 42 +/- 13 l/min (P less than 0.001) and the MSVC/FEV1 ratio from 40.2 +/- 8.8 to 47.8 +/- 8.0 (P less than 0.001). Oxygen consumption during the MSVC increased from 460 +/- 94 to 647 +/- 107 ml/min (P less than 0.001), and MSVC heart rate increased from 99 +/- 15 to 114 +/- 15 (P less than 0.001). The post MSVC blood lactate increased from 1.55 +/- 1.29 to 2.85 +/- 1.05 mM/l (P less than 0.001). Maximal exercise ventilation measured by an incremental ergometer test increased from 32 +/- 8 to 36 +/- 11.5 l/min for leg exercise and from 30.4 +/- 8.4 to 33.7 +/- 8.9 l/min (P less than 0.01) for arm exercise. Endurance time at a constant submaximal load increased from 6.98 +/- 4.30 to 10.76 +/- 6.00/min (P less than 0.01) for leg exercise and from 5.76 +/- 3.53 to 10.47 +/- 6.57/min (P less than 0.01) for arm exercise. The maximal distance covered in a 12-min walk increased from 1,058 +/- 161 to 1,188 +/- 201 m (P less than 0.01). We concluded that ventilatory muscle training in patients with COPD improved the ventilatory muscle performance, as indicated by the increased MSVC, oxygen consumption during the MSVC, and the maximal exercise ventilation. There was a substantial increase in submaximal exercise endurance for both arm and leg work.

Selective glycogen depletion pattern in human muscle fibres after exercise of varying intensity and at varying pedalling rates.

1. Glycogen depletion pattern in human skeletal muscle fibres was studied after bicycle exercise of varying intensity performed at different pedalling rates. Work intensities studied were equivalent to 30-150% of V(O) (2) max. with pedalling rates of 30-120 rev/min.2. Glycogen depletion increased dramatically with increasing exercise intensity; depletion was 2.7 and 7.4 times greater respectively at workloads demanding 64 and 84% V(O) (2) max. than at workloads calling for 31% V(O) (2) max. Even greater rates of glycogen utilization occurred at supramaximal loads.3. Slow twitch, high oxidative (ST) fibres were the first to lose glycogen (reduced PAS staining) at all workloads below V(O) (2) max. Progressive glycogen depletion occurred in fast twitch (FT) fibres as work continued. Large quantities of glycogen remained in the muscle after 3 hr of exercise at low exercise intensity. This was almost exclusively found in FT fibres. At workloads exceeding maximal aerobic power, there was an initial depletion of glycogen in both fibre types. Varying the pedalling rate and, thus, the total force exerted in each pedal thrust had no effect on the pattern of glycogen depletion in the fibres.4. Results point to primary reliance upon ST fibres during submaximal endurance exercise, FT fibres being recruited after ST fibres are depleted of glycogen. During exertion requiring energy expenditure greater than the maximal aerobic power, both fibre types appeared to be continuously involved in carrying out the exercise.

Glycogen depletion pattern in human skeletal muscle fibers after heavy exercise.

Glycogen depletion pattern in human skeletal muscle fibers after heavy exercise.