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Title: Influence of nutrition on muscle metabolism and performance during prolonged intermittent high intensity shuttle running
Authors: Nicholas, Ceri W.
Issue Date: 1996
Publisher: © C.W. Nicholas
Abstract: The purpose of this thesis was to study the effects of I) carbohydrate intake, either during or in the recovery from exhaustive intermittent exercise, and 2) oral creatine supplementation for 5 days, on metabolism, performance and endurance capacity during a prolonged intermittent high intensity shuttle run test (PIHSRT). Prolonged intermittent high intensity running is an activity pattern which is typical of the multiple sprint sports such as soccer, hockey and rugby. Understanding the physiological and metabolic responses to this type of activity can improve our understanding of the aetiology of fatigue and how training and nutritional intervention can improve performance during prolonged intermittent high intensity running. The aims of the first and second studies were to investigate the effect of increased carbohydrate availability, by ingesting additional carbohydrate in the recovery from (Chapter 4) and by drinking a carbohydrate-electrolyte solution immediately prior to, and during (Chapter 5), prolonged intermittent high intensity running. In the first study (Chapter 4), six games players performed two prolonged intermittent high intensity shuttle run tests (PIHSRT) consisting of a fixed 70 min period of intermittent exercise (Part A) followed by high intensity intermittent running to fatigue (Part B), separated by 22 h recovery, on two occasions, separated by one week. During the 22 h recovery, subjects were prescribed their normal dietary intake of carbohydrate plus the additional energy needed to consume the equivalent of 10 g.kg·1bm.day·l. This extra energy was consumed either in the form of carbohydrate (the CHO trial) or as fat and protein (the CON trial). No differences in sprint performance were observed 22 h following either recovery diet. High intensity running capacity was improved after 22 h in the CHO trial (T2) by 16% (P<O.OI). No such improvement was observed in T2 following the CON diet. No differences were observed in the blood metabolic responses to the PIHSRT. In the second study (Chapter 5), nine games players performed the PIHSRT on two occasions, separated by one week. Subjects were randomly assigned to ingest either a 6.9% CHO-E beverage (CHO trial) immediately prior to and at regular intervals throughout the PIHSRT or a non-CHO placebo (CON trial). The PIHSRT comprised a fixed period of 75 min of variable intensity exercise (Part A) followed by intermittent high intensity running until fatigue (Part B). Sprint performance was similar during both trials and was not affected by treatment. High intensity running capacity was improved by 33% following CHO-E ingestion (P<0.05). Blood glucose concentration was higher after 30 min (P<0.05) and after the cessation of exercise (P<O.05) in the CHO-E trial but similar concentrations were observed after 75 min of exercise, immediately prior to the exhaustive bout of high intensity running. The results of these two initial studies showed that the ergogenic effect of higher pre-exercise muscle glycogen stores (Chapter 4) and drinking a 6.9% CHO-E solution during exercise was not associated with the prevention of a declining blood glucose concentration over the duration of the exercise trials. The hypothesis that the underlying mechanism for the increased running capacity was the sparing of muscle glycogen was investigated in the third study (Chapter 6). Six games players completed 90 min of the PIHSRT twice in a random order, separated by one week. Subjects consumed either a 6.9% CHO-E solution (CHO trial) or a non-CHO placebo (CON trial). Biopsy samples were obtained from the vastus lateralis muscle at rest and immediately following the end of exercise for the determination of mixed and single muscle fibre glycogen concentration. A 22% reduction was observed in the CHO trial compared with the CON trial [ 192.5± 26.3 mmol (kg DM) -1 vs. 245.3 ± 22.9 mmol (kg DM) -1 , respectively; P<0.05]. Single fibre analysis revealed a reduced glycogen concentration in both fibre types, but that there was a greater amount of glycogen utilised in the type II fibres compared with the type I fibres during 90 min of intermittent high intensity exercise in the CON [287.4± 41.2 mmol (kg DM)·1 vs. 182.2 ± 34.5 mmol (kg DM) ·1 ,respectively; P<O.Oll. Results indicate that there was a greater amount of glycogen utilised in both type I and type II fibres in the CON nial compared with ingesting a CHO-E solution, although no conclusive statement can be made due to the small sample size. A reduction in the amount of glycogen utilised was associated with a higher serum insulin concentration after 30 min in the CHO trial. The apparent sparing of muscle glycogen may be due to a reduction in the amount of glycogen utilised per se , or the result of glycogen resynthesis in the inactive fibres during variable intensity exercise. In suppon of a reduction in the breakdown of muscle glycogen was the lower blood lactate concentration observed after 30 min in the CHO trial . The aim of the next section (Chapter 6, Pan B) was to investigate whether the reduced concentration of muscle glycogen in type I and II muscle fibres following 90 min of the PIHSRT would affect muscle function. The influence of drinking a carbohydrateelectrolyte beverage during exercise, which was previously found to reduce the amount of glycogen utilised (Chapter 6, Pan A), on muscle function was also examined. The same 6 subjects panicipated in the second pan of the study as did in Pan A. An assessment of muscle function was made by measuring peak torque, total work and average power at angular velocities of 600/s and at 2400 /s in the knee extensors (concennically and eccentrically) and flexors (concennically) before and after 90 min of the PIHSRT. Muscle function was reduced after 90 min of shuttle running at 60° /sec in both nials, although the differences were attenuated following the ingestion of a carbohydrate-electrolyte beverage at regular intervals throughout exercise. In the previous study (Chapter 6, Pan A), the post-exercise muscle concentration of PCr was lower after 90 min of shuttle running in the CON trial than the CHO trial (P<0.05). Thus, the purpose of the next study (Chapter 7) was to investigate the effect of oral creatine supplementation on sprint performance and endurance capacity during the PIHSRT. Sixteen male games players performed the PIHSRT for 75 min (Pan A) followed by intermittent running to exhaustion (Pan B) on two occasions, separated by one week. Following the first, pre-supplementation trial (Tl) subjects were randomly assigned to either a placebo (Plac) or creatine (Cr) group in a double blind design. The supplementation regime was three 6 g doses of either 3 g of creatine monohydrate and 1.5 g maltodextrin, plus 1.5 g glucose (Cr group), or 6 g glucose (Plac group) for 5 days. The second trial (T2) was performed immediately following the end of the 5 day supplementation period. There were no differences in sprint times or running time to exhaustion between trials. Plasma ammonia concentrations were lower after 60 min and 75 min of exercise in T2 compared with T2 in the Cr group (P<0.05). Similar physiological and metabolic responses were observed between nials (within groups) for all other variables measured. Increasing the availability of carbohydrate, either by increasing the normal carbohydrate intake to the equivalent of 10 g.kg·1bm per day, or by ingesting a carbohydrateelectrolyte beverage which provides 47 g carbohydrate per hour immediately prior to and at regular intervals during exercise, enhances endurance running capacity following a fixed period of prolonged intermittent high intensity shuttle running. No such improvement was observed following an oral creatine supplementation period. Sprint performance during the PIHSRT did not change either following carbohydrate or creatine supplementation. The mechanism for the improved performance may be the sparing of muscle glycogen in the type I and type II fibres during intermittent high intensity exercise when a carbohydrate-electrolyte solution is ingested.
Description: A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.
URI: https://dspace.lboro.ac.uk/2134/13905
Appears in Collections:PhD Theses (Sport, Exercise and Health Sciences)

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