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

Abstract

SUMMARY1. 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 70o, max. with pedalling rates of 30-120 rev/mi.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 % ro2 max. than at workloads calling for 31 % 1702 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 T°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.

Effect of carbohydrate availability on time to exhaustion in exercise performed at two different intensities

“…Although we did not directly measure the pre-exercise carbohydrate store, several observations made during the experimental exercise strongly suggested that the carbohydrate stores of the subjects were significantly reduced under the CHO low condition: 1) the RER values during the CHO low -aboveLT 2 trial in this study were significantly lower than those for the CHO mod -aboveLT 2 trial, indicating a greater utilization of fat as fuel; 2) blood lactate tended to be lower during the CHO low -aboveLT 2 trial than during the CHO mod -aboveLT 2 trial, and 3) all subjects confirmed that they followed the recommended diets as demonstrated by their own records. These results are in accordance with other studies that utilized a similar protocol intended to reduce the carbohydrate store (10,(14)(15)(16).…”

“…Exercise was terminated when subjects could not complete 1 min of exercise at 125% VO 2max . This protocol for muscle glycogen depletion was previously validated by Gollnick et al (14,15) and Heigenhauser et al (16) who demonstrated a decreased muscle glycogen content in both fast and slow-twitch fibers. In addition, Gollnick et al (15) have demonstrated that, when intermittent heavy exercise is performed until exhaustion, glycogen from both types of fibers is depleted independently of the intensity used (120 to 150% of maximal aerobic power).…”

Relationship between motor corticospinal excitability and ventilatory response during intense exercise

“…Therefore, in the present study, using the glycogen-reduction procedure adopted in our previous study (Yamanaka et al 2012), we examined the relationship between effort-mediated ventilatory response and corticospinal excitability of lower limb muscle during IE. It has been shown that moderate-intensity exercise decreased muscle glycogen content to half of the pre-exercise level in about 45 min (Gollnick et al 1974). In the present experiment, IE was repeated twice, and 45-min moderate-intensity exercise was performed between the two IEs in order to reduce the muscle glycogen content.…”

“…This hyperventilatory response is considered to be respiratory compensation to minimize a decrease in blood pH (Kowalchuk et al 1988;Rausch et al 1991;Ward 2007;Wasserman et al 1986;Yunoki et al 1999), and the decrease in blood pH per se has been regarded as an important factor enhancing ventilation during exercise above the lactate threshold (Stringer et al 1992;Wasserman et al 1975). However, by using a glycogen-reduction procedure (Gollnick et al 1974;Heigenhauser et al 1983; Sabapathy et al 2006), which can manipulate the degree of metabolic acidosis, we found that hyperventilatory response to IE is not dependent on blood pH but is associated with effort sense of exercising muscle (Yamanaka et al 2011;Yamanaka et al 2012). …”

“…During the two IEs, the subjects were constrained to maintain pedaling frequency at 60 rpm against the workload (3.4 ± 0.2 kp) corresponding to 75-85% of W max (202 ± 34 W). After 10-min resting recovery following IE 1st , each subject performed 45-min submaximal exercise at the workload (2.1 ± 0.4 kp, 60 rpm) corresponding to T vent (129 ± 26 W) in order to reduce muscle glycogen content (Gollnick et al 1974). Pedaling frequency during the two IEs and a submaximal exercise was averaged over a 30-s interval.…”