Influence of carbohydrate-electrolyte drinks on muscle metabolism and endurance running performance in man
2013-02-20T14:34:07Z (GMT) by
Prolonged running is an activity associated with a wide range of sports and improvement in' running endurance is therefore important for those involved, The aims of the first and second studies were to investigate the effect of carbohydrate ingestion on endurance running capacity and performance, In the first study (Chapter 4), seven experienced endurance runners ingested either water (W), a 6.9% carbohydrate (CHO) solution (B) or a 5.5% CHO solution (A) during 3 randomly assigned 42.2-km treadmill runs, 4 weeks apart. Running times for W, B and A trials were 193.9 ± 5.0 min, 192.4 ± 3.3 min and 190.0 ± 3.9 min, respectively. Performance time for the A trial was faster (p < 0.05) compared with that of the W trial. In the second study (Chapter 5), eleven recreational runners completed 3 randomly assigned treadmill runs at 70% V02 max to exhaustion, one week apart. On the first and second occasions a 5.5% (A) and 6.9% (C) CHO solutions were ingested for the first hour of exercise, water was then ingested until exhaustion. On the third occasion water (W) was ingested throughout the run. Performance times for the W, A and C trials were 109.6 ± 9.6 min, , 124.5 ± 8.4 min and 121.4 ± 9.4 min, respectively. Running time to exhaustion for the A trial was significantly longer (p < 0.05) compared with the W trial. The results of these studies suggested that the ergogenic effect of the 5.5% CHO solution was not associated with the prevention of a declining blood glucose concentration and CHO oxidation rate. In the third study (Chapter 6), the possibility that sparing of muscle glycogen could be the mechanism by which CHO ingestion exerts its ergogenic effect was investigated. Seven subjects consumed either a 5.5% carbohydrate solution (CHO) or water (W) during two 60-min treadmill runs at 70% V02 max a week apart. Biopsy samples from the vastus lateralis muscle were obtained at rest and 60 min for glycogen determination. A28% reduction in glycogen utilization was observed as a result of CHO ingestion when compared with W ingestion 008.7 ± 16.3 mmol.kg dry muscle (dm)-l vs 150.9 ± 19.9 mmol.kgdm-1 respectively, p < 0.01). In order to investigate the site of glycogen sparing, individual fibres were dissected and analysed for glycogen. The ingestion of the CHO solution resulted in sparing of glycogen in Type I (slow twitch) fibres only (38.1 % degradation of glycogen as opposed to 66.2% during the W trial, p = 0.01). This glycogen sparing in Type I fibres would only explain the delay in the onset of fatigue observed in the first two studies if glycogen depletion in these fibres was associated with fa tigue during prolonged running. In the fourth study (Chapter 7), eight subjects consumed either a 5.5% carbohydrate solution (CHO) or placebo (PL) during two treadmill runs at 75% V02 max to exhaustion performed one week apart. Biopsy samples from the vastus lateralis muscle were obtained at rest and exhaustion in the PL trial and at rest, the point coinciding with PL exhaustion and exhaustion in the CHO trial. Running times to exhaustion in the PL and CHO trials were 104.3 ± 8.6 min and 132.4 ± 12.3 min (p < 0.01). Higher glycogen concentration was observed at the point coinciding with PL exhaustion in the CHO trial when compared with the value measured at the point of exhaustion in the PL trial 025.6 ± 22.3 mmol.kg dm-1 vs 59.8 ± 7.9 mmol.kg dm -1 p < 0.05, respectively). This sparing of muscle glycogen was almost totally restricted to Type I fibres (87.1 ± 18 mmol.kg dm-1 in the CHO trial vs 31.6 ± 10.3 mmol.kg dm-1 in the PL trial, p < 0.01, respectively). In both the CHO and PL trials, fatigue coincided with glycogen depletion in Type I fibres (28.1 ± 7.1 mmol.kg dm-1 and 31.6 ± 10.3 mmol.kg dm-1, respectively). It was suggested, that the spared glycogen became available during the latter stages of the run and, therefore, could account for the improved endurance capacity and performance observed in studies I, 2 and 4 when the 5.5% CHO solution was ingested.