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This study was undertaken to examine the effects of ingestion of different concentrations of carbohydrate (CHO) (H20, 6, 12, and 18 g/100ml- WP, CHO-6, CH0-12, and CH0--18, respectively) on gastric emptying, muscle glycogen metabolism, and performance. Ten trained male cyclists performed four trials of 105 min of continuous cycling at 70% of VO2max. In a fifth trial the subjects completed seven 15-min rides at 70% of VO2max with three min rest between each ride. In all five trials the submaximal rides were followed by an all-out, self-paced 15-min "performance" ride on an isokinetic ergometer (Fitron) interfaced with a computer which calculated the total work output. Every 15 min the men consumed approximately 150 ml (8.5 ml/kg/hr) of one of the four test solutions (in the intermittent trial the men consumed the CHO-12 solution). Blood samples were taken every 15 min for glucose and insulin determination. Muscle biopsies were obtained from the vastus lateralis at 0 and 105 min in the WP, and the CHO-12 continuous and intermittent trials. Biopsy samples were assayed for glycogen, and sectioned and stained for myosin ATPase and glycogen to determine single fiber depletion patterns. Gastric residue was determined by intubation following the performance ride. The volume of drink emptied in the CHO-12 and CHO-18 trials was significantly less compared to both the WP and CHO-6 trials, and the volume emptied in the CHO-18 trial was less than in the CHO-12. There were no differences in glycogen use between the water and the two CHO-12 trials. Single fiber depletion patterns showed a trend toward a greater depletion of type I fibers but were not influenced by CHO ingestion. Blood glucose was significantly elevated at 105 min in both CHO-12 and the CHO-18 trials compared to the WP trial. CHO oxidation in both CHO-12 and the CHO-18 trials was significantly higher in the performance ride. Work output in both the CHO-12 trials was significantly elevated compared to the WP. These data demonstrate that 12 and 18% CHO solutions retarded gastric emptying, but that adequate CHO was delivered to enable enhanced performance in the CHO-12 trials. The fact that glycogen sparing was not observed suggests that the improved performance may have been due to the maintenance of blood glucose. Single fiber depletion patterns did not explain the performance benefits observed with CHO ingestion. / Human Performance Laboratory

This study was designed to investigate the relationship between dietary carbohydrate consumption and muscle glycogen storage during five days of intense training. Ten highly trained distance runners performed two diet-training regimens. Training consisted of running 1.5 times each runner's average daily training distance (~20 km) at ~80% Vo2 max. During one of these intense training periods the runners ate slightly more carbohydrate (8.0 g•kg•d-1) than was required to meet the energy requirements of exercise and normal activity (EQ-CHO). During the second regimen (LO-CHO) the runners ate approximately half (3.9 g•kg•d-1) as much carbohydrate as in the previous regimen. Each regimen was preceded by a three day control period during which carbohydrate intake was maintained at 6.2 g•kg•d-1 and training was reduced to 80% of the runners normal training distance. At the end of each regimen the runners rested for three days and carbohydrate consumption was maintained at 3.8 g•kg•d-1.Compared to the EQ-CHO regimen oxygen consumption measured during standard exercise tests performed at 65% (SET 80) and 80% (SET80) of Vo2 max was greater during the LO-CHO regimen. Corresponding respiratory exchange ratios were lower during these tests. Overall (12.9 + 0.4 vs 13.7+ 0.5 units) and leg (13.3 + 0.3 vs 14.4 + 0.5 units) ratings of perceived exertion were higher during the SET80 at the end of the LO-CHO regimen. Total muscle glycogen levels were lower following the LO-CHO regimen (90.6 + 8.8 vs 66.4 + 7.8 mmol•kg-1 w.w. for the EQ-CHO vs LO-CHO regimens). A linear relationship was observed between histochemical and direct chemical analysis of muscle glycogen content (r=0.93). Resting muscle glycogen content was the same in type I, IIA and IIB fibers before the intense training period of both regimens. The glycogen content of type I, IIA and IIB fibers was lower after the LO-CHO regimen. Frequency distribution analysis of the glycogen content in individual fibers revealed that ~27% of type I fibers, 17% of type IIA fibers and 0% type IIB fibers had optical densities below 0.2 units (54 g•kg•d-1) following the intense training period of the LO-CHO regimen. Glycogen repletion during the three days of rest was greater after the LO-CHO regimen (22.2 vs 56.5 mmol•kg-1 w.w. for the EQ-CHO vs LO-CHO regimens).These data indicate that inadequate dietary carbohydrate consumption during successive days of intense training leads to incomplete glycogen repletion and selective glycogen depletion from type I muscle fibers. These events produce a greater perception of effort and decreased running economy during exercise. / Human Performance Laboratory

Thesis (M.S.)--Purdue University, 2005. / Includes bibliographical references (leaves 56-60). Also available online (PDF file) by a subscription to the set or by purchasing the individual file.

Thesis (M.S.)--Purdue University, 2005. / Includes bibliographical references (leaves 56-60).

Typescript (photocopy). / Digitized by Kansas Correctional Industries

In an attempt to determine the extent to which well-trained endurance athletes practice the dietary recommendations for maximizing muscle glycogen resynthesis, twenty-four collegiate cross-country runners (14 males and 10 females) were chosen as subjects. The athletes kept four-day food and activity records during both a training and competitive period in the regular season. Energy intake was shown to be adequate in both phases. Total calories from carbohydrate, primarily complex, were found to be inadequate (<60%) for male runners and desirable (>60%) for females. Approximately 50% or less of the time carbohydrate was ingested immediately post-exercise, with even far less taken in suggested quantities (-1 g CHO/kg body weight). While the male athletes consumed primarily a combined solid and liquid form of carbohydrate immediately post-exercise, the females chose solid sources. Cereals and other breads were the most popular types of carbohydrate chosen immediately following exercise, in addition to commercial sports drinks/bars which were frequently ingested. An even more unfavorable trend in the distance runners was the infrequency of additional carbohydrate being ingested at two hour intervals following exercise. There were no significant differences in dietary trends between training and competitive phases. Overall these endurance athletes were not practicing the recommended feeding regimen for optimal muscle glycogen restoration. / Department of Home Economics

A dose response relationship between carbohydrate (CHO) ingestion and exercise performance has not been consistently reported. Additionally the underlying metabolic and neuromuscular explanations for an improvement in performance with increasing doses of CHO have not been fully explained. In Chapter 2 of this thesis 20 male cyclists completed 2 h of submaximal exercise followed by a time trial task (531 ± 48KJ). Three CHO electrolyte beverages, plus a control (water), were administered during a 2 h ride providing 0, 20, 39 or 64 g CHO·h-1 at a fluid intake rate of 1 L·h-1. Performance was assessed by time to complete the time trial task, mean power output sustained, and pacing strategy used. Mean task completion time (min:sec ± SD) for 39 g·h-1 (34:19.5 ± 03:07.1, p=0.006) and 64 g·h-1 (34:11.3 ± 03:08.5 p=0.004) of CHO were significantly faster than control (37:01.9 ± 05:35.0). The mean percentage improvement from control was -6.1% (95% CI: -11.3 to -1.0) and -6.5% (95% CI: -11.7 to -1.4) in the 39 and 64 g·h-1 trials respectively. The 20 g·h-1 (35:17.6 ± 04:16.3) treatment did not reach statistical significance compared to control (p = 0.126) despite a mean improvement of -3.7% (95% CI -8.8 to 1.5%). These data demonstrate that consuming CHO at a rate between 39 to 64 g·h-1 is likely to be optimal for most individuals looking to utilise a single source CHO as an ergogenic aid during endurance performances lasting less than 3 hrs. Attempts have been made to try and understand the acute metabolic regulation that occurs when ingesting increasing amounts of CHO. However, no one study has fully investigated the metabolic mechanisms underlying graded increments of CHO ingestion. In Chapter 3 we aimed to utilise stable isotopes and blood metabolite profiles to examine the integrated physiological responses to CHO ingestion when ingested at rates throughout the range where performance gains appear greatest. Twenty well-trained male cyclists completed 2 h constant load ride (95% lactate threshold, 185 ± 25W) where one of three CHO beverages, or a control (water), were administered every 15 min, providing participants with 0, 20, 39 or 64 g CHO·h-1 at a fixed fluid intake rate of 1L·h-1. Dual glucose tracer techniques (6,6,2H2 glucose and U13C labelled glucose) were used to determine glucose kinetics and exogenous carbohydrate oxidation (EXO) during exercise. Endogenous CHO contribution was suppressed in the second hour of exercise when consuming 39 and 64 g·h-1 in comparison to 0 g·h-1 (-7.3%, 95%CI: -13.1 to -1.6 and -11.2%, 95%CI: -16.9 to -5.5 respectively). Additionally, consuming 64 g·h-1 suppressed the endogenous CHO contribution by -7.2% (95%CI: -1.5 to -13.0) compared to the 20 g·h-1 treatment. Exogenous CHO oxidation rate increased by 0.13 g·min-1 (95%CI: 0.10 to 0.15) and 0.29 g·min-1 (95%CI: 0.27 to 0.31) when consuming 39 and 64 g·h-1 in comparison to 20 g·h-1 of CHO. Peak exogenous CHO oxidation rates were 0.34 (0.06), 0.54 (0.09) and 0.78 (0.19) g·min-1 for 20, 39 and 64 g·h-1 respectively. Plasma NEFA concentration was 0.10 (95%CI: 0.07 to 0.13), 0.12 (95%CI: 0.10 to 0.16) and 0.16 (95%CI: 0.13 to 0.19) mmol.L-1 higher when consuming 0 g·h-1 in comparison to 20, 39 and 64 g·h-1 respectively. Both 39 and 64 g·h-1 were effective at sparing endogenous CHO stores of which it is estimated that most of this is liver glycogen sparing, but the measured response was highly variable between individuals. Consuming 39 g·h-1 of CHO appears to be the minimum ingestion rate required to have a significant metabolic effect that results in an increase in performance. Recent research has indicated a key role of endogenous CHO sensing and oral glucose sensing in maintaining central drive and peripheral function during endurance exercise tasks. Consuming 39 and 64 g·h-1 of CHO elicits the greatest improvements in performance and also demonstrate a similar metabolic response. The improvement in subsequent time trial performance when consuming 39 and 64 g·h-1 coincided with significant alterations in whole body substrate usage that lead to endogenous CHO sparing at the same ingestion rates. In Chapter 4 we aimed to utilise gold standard neuromuscular function assessment techniques, alongside novel measures, to investigate the effect of consuming different rates of CHO on neuromuscular function during and following prolonged cycling exercise. In a double-blind, randomised cross-over design, well-trained male cyclists (n=20, mean±SD, age 34 ± 10 y, mass 75.8 ± 9 kg, peak power output 394 ± 36 W, V̇O2max 62 ± 9 ml·kg-1·min-1) completed 2 familiarisation trials then 4 experimental trials. Trials involved a 2 h submaximal ride followed by a high intensity time trial task lasting approx. 35 min with each of 0, 20, 39 and 64 g·h-1 CHO ingestion rates during submaximal exercise. Each trial involved pre and post exercise assessments (MVC, Mwave twitch potentiation and force, motor unit recruitment and firing rate assessment using high density EMG) and during exercise (gross EMG amplitude). MVC peak torque values were reduced post exercise by -20.4 nM (95%CI: -26.5 to -14.4) in comparison to pre value on all trials with no differences between trials. The firing rates of early recruited motor units significantly increased by 1.55 pps (95%CI: 0.51 to 2.59) following exercise in comparison to pre-exercise rates. Gross EMG during the 2 h cycling bout revealed a main effect of treatment (p<0.01) but post hoc comparisons provided no clarity and likely reflect methodological issues. Consuming CHO at ingestion rates between 20 and 64 g·h-1 had little to no impact on the neuromuscular function of well-trained cyclists when comparing pre and post fatiguing exercise values. Despite differences in time trial completion time between trials, following exercise to fatigue in an endurance task, no post exercise differences were detected.