Showing papers by "Barry Drust published in 2008"

Muscle Fatigue during Football Match-Play

Abstract: One of the consequences of sustaining exercise for 90 minutes of football match-play is that the capability of muscle to generate force declines. This impairment is reflected in the decline of work-rate towards the late part of the game. Causes of this phenomenon, which is known as fatigue, and some of its consequences are considered in this article. The stores of muscle glycogen may be considerably reduced by the end of the game, especially if there has not been a tapering of the training load. Thermoregulatory strain may also be encountered, resulting in a fall in physical performance, or there may be a reduced central drive from the nervous system. The decline in muscle strength may increase the predisposition to injury in the lower limbs. Central fatigue may also occur with implications for muscle performance. Strategies to offset fatigue include astute use of substitutions, appropriate nutritional preparation and balancing pre-cooling and warm-up procedures. There is also a role for endurance training and for a pacing strategy that optimizes the expenditure of energy during match-play.

Trained men display increased basal heat shock protein content of skeletal muscle.

Abstract: Purpose: 1) To compare the baseline levels of heat shock and antioxidant protein content in the skeletal muscle of trained and untrained humans and 2) to characterize the exercise-induced stress response of aerobically trained human skeletal muscle to an acute exercise challenge. Methods: Resting muscle biopsies were obtained from the vastus lateralis muscle of six untrained and six aerobically trained young males. To characterize the stress response of a trained population, the trained subjects also performed a 45-min nondamaging running exercise protocol at an intensity corresponding to 75% of V[spacing dot above]O2max. Muscle biopsies were obtained from the vastus lateralis muscle at 48 h and 7 d after exercise. Results: Trained subjects displayed significantly higher (P 0.05) in resting levels of HSP70 (16%), HSC70 (13%), and total superoxide dismutase (SOD) activity (46%) compared with untrained subjects. Resting HSP27 levels were unaffected by exercise training (P > 0.05). In the trained subjects, exercise failed to induce significant increases (P>0.05)in muscle content of HSP70, HSC70, HSP60, HSP27, [alpha]B-crystallin, and MnSOD protein content or in the activity of SOD at any time point after exercise. Conclusion: This study demonstrates for the first time that trained men display a selective up-regulation of basal heat shock and antioxidant protein content and do not exhibit a stress response to customary running exercise. It is suggested that an increase in these protective systems functions to maintain homeostasis during the stress of exercise by protecting against disruptions to the cytoskeleton/contractile machinery, by maintaining redox balance, and by facilitating mitochondrial biogenesis.

Fluid provision and metabolic responses to soccer-specific exercise

Abstract: The present study aimed to investigate the impact on metabolism of altering the timing and volume of ingested carbohydrate during soccer-specific exercise. Twelve soccer players performed a soccer-specific protocol on three occasions. On two, 7 ml kg−1 carbohydrate–electrolyte or placebo were ingested at 0 and 45 min. On a third, the same total volume of carbohydrate–electrolyte was consumed but at 0, 15, 30, 45, 60 and 75 min. Carbohydrate–electrolyte ingestion increased blood glucose, insulin and carbohydrate oxidation, whilst suppressing NEFA, glycerol and fat oxidation (P 0.05). However, consuming fluid in small volumes reduced the sensation of gut fullness (P < 0.05). The results demonstrated that when the total volume of carbohydrate consumed is equal, manipulating the timing and volume of ingestion elicits similar metabolic responses. Furthermore, consuming a small volume of fluid at regular intervals reduces the sensation of gut fullness.

Heat shock factor activation in human muscles following a demanding intermittent exercise protocol is attenuated with hyperthermia.

Abstract: AIM The present study investigated whether increased activation of heat shock factors (HSF) following exercise relates primarily to the increased muscle temperature or to exercise in general. METHODS Six subjects completed 40 min of intermittent cycling (15s:15s exercise:recovery at 300 +/- 22 W) at an ambient temperature of either 20.0 +/- 1.3 or 40.3 +/- 0.7 degrees C. Muscle biopsies were taken prior to and immediately following the exercise protocol with samples analysed for HSF DNA binding by electrophoretic mobility shift assay. RESULTS Exercise at 40 degrees C resulted in significantly increased oesophageal (39.3 +/- 0.2 degrees C) and muscle temperature (40.0 +/- 0.2 degrees C) at the end of the exercise protocol compared with 20 degrees C (oesophageal, 38.1 +/- 0.1 degrees C; muscle, 38.9 +/- 0.2 degrees C). However, an increased DNA binding of HSF was not evident following exercise at 40 degrees C (reduced by 21 +/- 22%) whereas it increased by 29 +/- 51% following exercise at 20 degrees C. CONCLUSION It appears that increased temperature is not the major factor responsible for activation of HSF DNA binding.

Bright Light and Thermoregulatory Responses to Exercise

Abstract: The thermoregulatory responses to morning exercise after exposure to different schedules of bright light were examined. At 07:00 h, six males ran on two occasions in an environmental chamber (temperature = 31.4 +/- 1.0 degrees C, humidity = 66 +/- 6 %) for 40 min at 60 % of maximal oxygen uptake. Participants were exposed to bright light (10,000 lux) either between 22:00 - 23:00 h (BT (low)) or 06:00 - 07:00 h (BT (high)). Otherwise, participants remained in dim light (< 50 lux). It was hypothesized that BT (low) attenuates core temperature during morning exercise via the phase-delaying properties of evening bright light and by avoiding bright light in the morning. Evening bright light in BT (low) suppressed (p = 0.037) the increase in melatonin compared to dim light (1.1 +/- 11.4 vs. 15.2 +/- 19.7 pg x ml (-1)) and delayed (p = 0.034) the core temperature minimum by 1.46 +/- 1.24 h. Core temperature was 0.20 +/- 0.17 degrees C lower in BT (low) compared to BT (high) during the hour before exercise (p = 0.036), with evidence (p = 0.075) that this difference was maintained during exercise. Conversely, mean skin temperature was 1.0 +/- 1.7 degrees C higher during the first 10 min of exercise in BT (low) than in BT (high) (p = 0.030). There was evidence that the increase in perceived exertion was attenuated in BT (low) (p = 0.056). A chronobiologically-based light schedule can lower core temperature before and during morning exercise in hot conditions.

Is it time for sports performance researchers to adopt a clinical-type research framework?

Abstract: For this editorial, my invited co-authors and I would like to highlight a manuscript in this issue of Int J Sports Med entitled “The effects of exercise upon symptoms and quality of life in patients diagnosed with irritable bowel syndrome: a randomised controlled trial” [5]. Not only do the authors address an interesting and important research question, but they also provide a reasonable template for anyone who might be contemplating a randomised controlled trial in the sport and exercise sciences. The study by Daley et al. [5] is obviously more relevant to human health than to sports performance. Health researchers and clinicians have worked hard over the last 20 years to set down gold-standard research practices and methods for other researchers to adopt. For example, there is a logical and accepted “roadmap” in clinical research governing how a particular treatment or intervention should be examined for efficacy and effectiveness. Efficacy is a measure of the ability of a treatment to improve whatever condition it is indicated for, whereas effectiveness is a measure of how well a treatment works in the “real world” with the target population [6]. To cite an example that is relevant to sports performance, it is known that some substances (e.g., sodium bicarbonate) are efficacious in manipulating the acid-base balance during repeated bouts of intense exercise [4]. Nevertheless, the effectiveness of these substances for improving real athletic performance might be less clear due to the potential for inducing gastrointestinal disturbances. The exploration of issues like efficacy and effectiveness is inherent within the “phased” framework for clinical trials [12]. Alongside this framework, there are also published regulations covering how an individual randomised controlled trial should be managed and reported in a scientific journal. These regulations are laid down in the so-called “CONSORT” statement, which can be found at: http://www.consortstatement.org/. We delimit this editorial to any study in which the primary variable is performance (or some component of athletic performance) and the research participants are competitive athletes. It is clear that there are sound studies published in the literature of this type and, in this editorial, we are able to cite some examples which have been published in past issues of Int J Sports Med. Nevertheless, we are unaware of any parallel procedures to phased clinical trials and the CONSORT statement, which have been set down by sports performance researchers to formalise the