Influence of liquid and solid meals on muscle glycogen resynthesis, plasma fuel hormone response, and maximal physical working capacity.
AbstractThe effect of forced liquid (L) or solid (S) carbohydrate (CHO)-rich feedings on plasma glucose, insulin, and glycogenesis after glycogen depletion was investigated. The relationship between glycogen restoration and maximal physical working capacity (MPWC) was studied as well. Eight males performed two experiments, with 2 weeks interval, on a bicycle ergometer. In each experiment, MPWC was determined in a graded test, which was immediately followed by interval work until exhaustion. After exercise cessation (EC), the subjects started to consume a standardized amount of concentrated L or CHO-rich food. Insulin and glucose concentration in blood were determined. Muscle glycogen was determined before, immediately after, 5 h after, and 22 h after EC. MPWC was determined again 22 h after EC. Four subjects performed a third experiment, in which solid food consumption was left ad libitum (AL). A rapid glycogen repletion was found 5 h after EC, i.e., from 72 +/- 40 to 198 +/- 38 mmol/kg in the S, and from 69 +/- 39 to 192 +/- 40 mmol/kg in the L experiment. The higher plasma glucose and insulin levels (P less than 0.05) during the 5 h after EC in the S experiments did not elicit a difference in glycogen repletion. Glycogen synthesis rate in the AL experiment was lower (P less than 0.05) than in the L and S experiments. Glycogen restoration in the L and S experiments was complete 22 h after depletion. However, despite repletion of glycogen, MPWC was decreased (P less than 0.05) in both experiments.
Muscle glycogen concentration during recovery after prolonged severe exercise in fasting subjects.
The influence of 12 h of fasting after prolonged severe exercise on the muscle glycogen concentration was studed in 5 normal subjects. The subjects exercised in the post absorptive state at 70% of max. Vo2 till exhaustion, then rested for 12 h. No food was allowed during recovery. Blood samples and muscle biopsies were obtained before exercise, immediately after the cessation of exercise, and after 2, 4, 6, 9 and 12 h of recovery. Muscle glycogen content decreased from 70.4 +/- 3.0 to 21.6 +/- 3.9 mmol glucosyl units/kg w.w. in response to exercise. After 4 h of recovery muscle glycogen had increased to 28.8 +/- 3.6 mmol glucosyl units/kg (P less than 0.025). During the next 8 h of recovery no further increase in glycogen concentration was observed. Mean plasma glucose concentration was observed. Mean plasma glucose concentration decreased from 5.25 +/- 0.16 to 4.37 +/- 0.18 mmol/l during exercise (P less than 0.001). No change in the plasma glucose level was observed during recovery. Immunoreactive insulin (IRI) concentration decreased from 15.9 +/- 1.0 to 10.2 +/- 0.5 micromicron/ml (P less than 0.001) during exercise, and remained at this level during recovery. It is concluded that some muscle glycogen repletion may occur after prolonged, severe exercise even under fasting conditions. It is suggested that this may proceed through an increased hepatic gluconeogenesis.