Search Results

You are looking at 1 - 10 of 473 items for :

  • "exercise performance" x
Clear All
Restricted access

Matthew David Cook and Mark Elisabeth Theodorus Willems

nuclear factor erythroid 2-related factor 2 (Nrf2) pathway ( Cimino et al., 2013 ; Yan et al., 2017 ). Nrf2 is a transcription factor regulating gene expression of antioxidant proteins. Oh et al. ( 2017 ) observed upregulation of Nrf2 in mice and increased endurance exercise performance, and similar

Restricted access

Daniel G. Hursh, Marissa N. Baranauskas, Chad C. Wiggins, Shane Bielko, Timothy D. Mickleborough and Robert F. Chapman

Endurance exercise performance in hypoxia is impaired partly due to declines in arterial oxyhemoglobin saturation (S p O 2 ), 1 which may limit the delivery of oxygen to exercising muscle. A well-established mechanism of defending S p O 2 during hypoxic exercise is to increase minute ventilation

Restricted access

Oliver R. Barley, Dale W. Chapman, Georgios Mavropalias and Chris R. Abbiss

performance effects associated with heat stress. 14 – 15 Heat acclimation can be achieved both through passive or active thermal exposure, though the benefits of passive acclimation on exercise performance have been less clear. 16 Interestingly, the effects of short-term heat acclimation protocols have been

Restricted access

Caitlin Campbell, Diana Prince, Marlia Braun, Elizabeth Applegate and Gretchen A. Casazza

Numerous studies have shown that ingesting carbohydrate in the form of a drink can improve exercise performance by maintaining blood glucose levels and sparing endogenous glycogen stores. The effectiveness of carbohydrate gels or jellybeans in improving endurance performance has not been examined. On 4 separate days and 1–2 hr after a standardized meal, 16 male (8; 35.8 ± 2.5 yr) and female (8; 32.4 ± 2.4 yr) athletes cycled at 75% VO2peak for 80 min followed by a 10-km time trial. Participants consumed isocaloric (0.6 g of carbohydrate per kg per hour) amounts of randomly assigned sports beans, sports drink, gel, or water only, before, during, and after exercise. Blood glucose concentrations were similar at rest between treatments and decreased significantly during exercise with the water trial only. Blood glucose concentrations for all carbohydrate supplements were significantly, p < .05, higher than water during the 80-min exercise bout and during the time trial (5.7 ± 0.2 mmol/L for sports beans, 5.6 ± 0.2 mmol/L for sports drink, 5.7 ± 0.3 mmol/L for gel, and 4.6 ± 0.3 mmol/L for water). There were no significant differences in blood glucose between carbohydrate treatments. The 10-km time trials using all 3 carbohydrate treatments were significantly faster (17.2 ± 0.6 min for sports beans, 17.3 ± 0.6 min for sports drink, and 17.3 ± 0.6 min for gel) than water (17.8 ± 0.7 min). All carbohydrate-supplement types were equally effective in maintaining blood glucose levels during exercise and improving exercise performance compared with water only.

Restricted access

Jessica M. Stephens, Shona L. Halson, Joanna Miller, Gary J. Slater, Dale W. Chapman and Christopher D. Askew

-cooling threshold appears to hold true for TT performance, the same does not appear to apply to all types of exercise performance, in particular shorter-duration explosive muscle function. The present study examined a number of aspects of muscle function (CMJ, IMTP) to gain a broader understanding of the effect of

Restricted access

Catherine Applegate, Mackenzie Mueller and Krystle E. Zuniga

Diet composition can affect systemic pH and acid-base regulation, which may in turn influence exercise performance. An acidic environment in the muscle impairs performance and contributes to fatigue; therefore, current trends in sports nutrition place importance on maximizing the alkalinity of the body with ergogenic aids and dietary strategies. This review examines the evidence on the effects of dietary manipulations on acid load and exercise performance. Ten studies that investigated the effect of high versus low dietary acid loads on athletic performance generally identified that low dietary acid loads increased plasma pH, but did not consistently improve exercise performance at maximal or submaximal exercise intensities. In addition, the few studies conducted have several limitations including lack of female subjects and use of exercise tests exclusive to cycling or treadmill running. Although the research does not strongly support a performance benefit from low dietary acid loads, a more alkaline dietary pattern may be beneficial for overall health, as dietary induced acidosis has been associated with greater risk of cardiovascular disease and bone disease. The review includes dietary recommendations for athletes to reduce dietary acid load while still meeting sports nutrition recommendations.

Restricted access

Lawrence E. Armstrong

Recreational enthusiasts and athletes often are advised to abstain from consuming caffeinated beverages (CB). The dual purposes of this review are to (a) critique controlled investigations regarding the effects of caffeine on dehydration and exercise performance, and (b) ascertain whether abstaining from CB is scientifically and physiologically justifiable. The literature indicates that caffeine consumption stimulates a mild diuresis similar to water, but there is no evidence of a fluid-electrolyte imbalance that is detrimental to exercise performance or health. Investigations comparing caffeine (100-680 mg) to water or placebo seldom found a statistical difference in urine volume. In the 10 studies reviewed, consumption of a CB resulted in 0-84% retention of the initial volume ingested, whereas consumption of water resulted in 0-81% retention. Further, tolerance to caffeine reduces the likelihood that a detrimental fluid-electrolyte imbalance will occur. The scientific literature suggests that athletes and recreational enthusiasts will not incur detrimental fluid-electrolyte imbalances if they consume CB in moderation and eat a typical U.S. diet. Sedentary members of the general public should be at less risk than athletes because their fluid losses via sweating are smaller.

Restricted access

Joel B. Mitchell, Paul C. DiLauro, Francis X. Pizza and Daniel L. Cavender

The purpose of this study was to determine the effect of a high vs. a low preexercise carbohydrate (CHO) diet on performance during multiple sets of resistance exercise. Eleven resistance-trained males performed cycle ergometry to deplete quadriceps muscle glycogen stores, followed by 48 hr of a high (HICHO) or a low (LOCHO) CHO diet. Subjects then performed five sets each of squats, leg presses, and knee extensions (resistance = 15 RM) to failure. Blood samples were taken before and during exercise for determination of glucose and lactate (LA). No differences in performance (repetitions X weight lifted) were observed (HICHO = 15,975±1,381 and LOCHO = 15,723±1,231 kg). Blood glucose was significantly higher after exercise for HICHO compared to LOCHO (HICHO = 4.8 ± 0.2 vs. LOCHO = 3.9 ± 0.2 mmol·L−1). No differences in LA accumulation were observed. The data indicated that preexercise CHO status did not affect resistance exercise performance. Further, the differences in blood glucose and the similarity in LA responses suggest that glycolysis was maintained in the LOCHO condition, and there may have been an increased reliance on blood glucose when preexercise CHO status was low.

Restricted access

Andrew M. Jones and Mark Burnley

The rate at which VO2 adjusts to the new energy demand following the onset of exercise strongly influences the magnitude of the “O2 defcit” incurred and thus the extent to which muscle and systemic homeostasis is perturbed. Moreover, during continuous high-intensity exercise, there is a progressive loss of muscle contractile efficiency, which is reflected in a “slow component” increase in VO2. The factors that dictate the characteristics of these fast and slow phases of the dynamic response of VO2 following a step change in energy turnover remain obscure. However, it is clear that these features of the VO2 kinetics have the potential to influence the rate of muscle fatigue development and, therefore, to affect sports performance. This commentary outlines the present state of knowledge on the characteristics of, and mechanistic bases to, the VO2 response to exercise of different intensities. Several interventions have been reported to speed the early VO2 kinetics and/or reduce the magnitude of the subsequent VO2 slow component, and the possibility that these might enhance exercise performance is discussed.

Restricted access

Costas A. Anastasiou, Stavros A. Kavouras, Christina Koutsari, Charalambos Georgakakis, Katerina Skenderi, Michael Beer and Labros S. Sidossis

This study examined the effect of maltose-containing sports drinks on exercise performance. Ten subjects completed 4 trials. Each trial consisted of a glycogen depletion protocol, followed by a 15-min refueling, after which subjects performed an 1-h performance test while consuming one of the experimental drinks (HGlu, glucose; HMal, maltose; MalMix, sucrose, maltose, and maltodextrin; Plac, placebo). Drinks provided 0.65 g/kg body weight carbohydrates during refueling and 0.2 g/kg every 15 min during the performance test. Although no significant differences were found in performance (HGlu: 67.2 ± 2.0; HMal: 68.6 ± 1.7; MalMix: 66.7 ± 2.0; Plac: 69.4 ± 3.0 min, P > 0.05), subjects completed the MalMix trial 3.9% faster than the Plac. Carbohydrate drinks caused comparable plasma glucose values that were significantly higher during refueling and at the end of exercise, compared to Plac. The data suggest that although carbohydrate drinks help to maintain plasma glucose at a higher level, no differences in performance could be detected after glycogen-depleting exercise.