Biomedical subjects

William G Hopkins

Publications and source records attributed to William G Hopkins.

7 recordsLinked to original sources

PubMed2006

Effect of post-exercise sauna bathing on the endurance performance of competitive male runners.

The physiological adaptations to sauna bathing could enhance endurance performance. We have therefore performed a cross-over study in which six male distance runners completed 3 wk of post-training sauna bathing and 3 wk of control training, with a 3 wk washout. During the sauna period, subjects sat in a humid sauna at 89.9+/-2.0 degrees C (mean+/-standard deviation) immediately post-exercise for 31+/-5 min on 12.7+/-2.1 occasions. The performance test was a approximately 15 min treadmill run to exhaustion at the runner's current best speed over 5 km. The test was performed on the 1st and 2nd day following completion of the sauna and control periods, and the times were averaged. Plasma, red-cell and total blood volume were measured via Evans blue dye dilution immediately prior to the first run to exhaustion for each period. Relative to control, sauna bathing increased run time to exhaustion by 32% (90% confidence limits 21-43%), which is equivalent to an enhancement of approximately 1.9% (1.3-2.4%) in an endurance time trial. Plasma and red-cell volumes increased by 7.1% (5.6-8.7%) and 3.5% (-0.8% to 8.1%) respectively, after sauna relative to control. Change in performance had high correlations with change in plasma volume (0.96, 0.76-0.99) and total blood volume (0.94, 0.66-0.99), but the correlation with change in red cell volume was unclear (0.48, -0.40 to 0.90). We conclude that 3 wk of post-exercise sauna bathing produced a worthwhile enhancement of endurance running performance, probably by increasing blood volume.

Adaptation, Physiological↗

PubMed2005

Combining explosive and high-resistance training improves performance in competitive cyclists.

In several recent studies, athletes experienced substantial gains in sprint and endurance performance when explosive training or high-intensity interval training was added in the noncompetitive phase of a season. Here we report the effect of combining these 2 types of training on performance in the competitive phase. We randomized 18 road cyclists to an experimental (n = 9) or control (n = 9) group for 4-5 weeks of training. The experimental group replaced part of their usual training with twelve 30-minute sessions consisting of 3 sets of explosive single-leg jumps (20 for each leg) alternating with 3 sets of high-resistance cycling sprints (5 x 30 seconds at 60-70 min(-1) with 30-second recoveries between repetitions). Performance measures, obtained over 2-3 days on a cycle ergometer before and after the intervention, were mean power in a 1- and 4-km time trial, peak power in an incremental test, and lactate-profile power and oxygen cost determined from 2 fixed submaximal workloads. The control group showed little mean change in performance. Power output sampled in the training sprints of the experimental group indicated a plateau in the training effect after 8-12 sessions. Relative to the control group, the mean changes (+/-90% confidence limits) in the experimental group were: 1-km power, 8.7% (+/-2.5%); 4-km power, 8.1% (+/-4.1%); peak power, 6.8% (+/-3.6); lactate-profile power, 3.7% (+/-4.8%); and oxygen cost, -3.0% (+/-2.6%). Individual responses to the training were apparent only for 4-km and lactate-profile power (standard deviations of 2.5% and 2.8%, respectively). The addition of explosive training and high-resistance interval training to the programs of already well-trained cyclists produces major gains in sprint and endurance performance, partly through improvements in exercise efficiency and anaerobic threshold.

Adult↗

PubMed2004

Relationship between world-ranking and Olympic performance of swimmers.

Coaches believe world-ranking lists are a reliable tool for predicting international swimming performance. To examine the relationship between world-ranking and Olympic performance, we modelled world-ranking time and best time from the 2000 Olympic Games for 407 top-50 world-ranked swimmers. Analysis of log-transformed times yielded within-athlete and between-athlete coefficients of variation (CV) and percent changes in performance from world-rankings to Olympics. Variations and performance progressions were compared across sex, stroke, distance, nation and medal status. The within-athlete coefficient of variation of performance for all swimmers was 0.8% (95% confidence limits: 0.7 to 0.9%). Females were slightly less consistent, although not substantially different to males (ratio of female/male within-athlete CV: 1.1; 95% confidence limits: 1.0 to 1.2) and had a wider range of talent (ratio of female/male between-athlete CV: 1.2; 95% confidence limits: 1.1 to 1.4). Swimmers from Australia (AUS) were more consistent than those from the United States (USA) and other nations (OTHER) (ratio of within-athlete CV, USA/AUS: 1.5; 95% confidence limits: 1.0 to 2.2; OTHER/ AUS: 1.6; 95% confidence limits: 1.2 to 2.1). Most Olympic medallists (87%) had a top-10 world-ranking. Overall performance time at the Olympics was slower than world-ranking time by 0.3% (95% confidence limits: 0.2 to 0.4%), medallists improved by 0.6% (95% confidence limits: 0.4 to 0.9%) and non-medallists swam 0.6% slower (95% confidence limits: 0.5 to 0.7%). We conclude that a top-10 ranked swimmer who can improve performance time by 0.6%, equivalent to 0.13 s in the men's 50-m freestyle, will substantially increase their chance of an Olympic medal (the difference between first and fourth place).

Achievement↗

PubMed2004

Effects of ingestion of bicarbonate, citrate, lactate, and chloride on sprint running.

PURPOSE: Ingestion of sodium bicarbonate is known to enhance sprint performance, probably via increased buffering of intracellular acidity. The goal was to compare the effect of ingestion of sodium bicarbonate with that of other potential buffering agents (sodium citrate and sodium lactate) and of a placebo (sodium chloride) on sprinting. METHODS: In a double-blind randomized crossover trial, 15 competitive male endurance runners performed a run to exhaustion 90 min after ingestion of each of the agents in the same osmolar dose relative to body mass (3.6 mosmol x kg) on separate days. The agents were packed in gelatin capsules and ingested with 750 mL of water over 90 min. During each treatment we assayed serial finger-prick blood samples for lactate and bicarbonate. A familiarization trial was used to set a treadmill speed for each runner's set of runs. We converted changes in run time between treatments into changes in a time trial of similar duration using the critical-power model, and we estimated likelihood of practical benefit using 0.5% as the smallest worthwhile change in time-trial performance. RESULTS: The mean run times to exhaustion for each treatment were: bicarbonate 82.3 s, lactate 80.2 s, citrate 78.2 s, and chloride 77.4 s. Relative to bicarbonate, the effects on equivalent time-trial time were lactate 1.0%, citrate 2.2%, and chloride 2.7% (90% likely limits +/- 2.1%). Ingested lactate and citrate both appeared to be converted to bicarbonate before the run. There were no substantial differences in gut discomfort between the buffer treatments. CONCLUSION: Bicarbonate is possibly more beneficial to sprint performance than lactate and probably more beneficial than citrate or chloride. We recommend ingestion of sodium bicarbonate to enhance sprint performance.

Adult↗

PubMed2003

Variability in estimation of self-reported dietary intake data from elite athletes resulting from coding by different sports dietitians.

A routine activity for a sports dietitian is to estimate energy and nutrient intake from an athlete's self-reported food intake. Decisions made by the dietitian when coding a food record are a source of variability in the data. The aim of the present study was to determine the variability in estimation of the daily energy and key nutrient intakes of elite athletes, when experienced coders analyzed the same food record using the same database and software package. Seven-day food records from a dietary survey of athletes in the 1996 Australian Olympic team were randomly selected to provide 13 sets of records, each set representing the self-reported food intake of an endurance, team, weight restricted, and sprint/power athlete. Each set was coded by 3-5 members of Sports Dietitians Australia, making a total of 52 athletes, 53 dietitians, and 1456 athlete-days of data. We estimated within- and between- athlete and dietitian variances for each dietary nutrient using mixed modeling, and we combined the variances to express variability as a coefficient of variation (typical variation as a percent of the mean). Variability in the mean of 7-day estimates of a nutrient was 2- to 3-fold less than that of a single day. The variability contributed by the coder was less than the true athlete variability for a 1-day record but was of similar magnitude for a 7-day record. The most variable nutrients (e.g., vitamin C, vitamin A, cholesterol) had approximately 3-fold more variability than least variable nutrients (e.g., energy, carbohydrate, magnesium). These athlete and coder variabilities need to be taken into account in dietary assessment of athletes for counseling and research.

Diet Records↗

PubMed2003

Eating patterns and meal frequency of elite Australian athletes.

We undertook a dietary survey of 167 Australian Olympic team athletes (80 females and 87 males) competing in endurance sports (n = 41), team sports (n = 31), sprint- or skill-based sports (n = 67), and sports in which athletes are weight-conscious (n = 28). Analysis of their 7-day food diaries provided mean energy intakes, nutrient intakes, and eating patterns. Higher energy intakes relative to body mass were reported by male athletes compared with females, and by endurance athletes compared with other athletes. Endurance athletes reported substantially higher intakes of carbohydrate (CHO) than other athletes, and were among the athletes most likely to consume CHO during and after training sessions. Athletes undertaking weight-conscious sports reported relatively low energy intakes and were least likely to consume CHO during a training session or in the first hour of recovery. On average, athletes reported eating on approximately 5 separate occasions each day, with a moderate relationship between the number of daily eating occasions and total energy intake. Snacks, defined as food or drink consumed between main meals, provided 23% of daily energy intake and were chosen from sources higher in CHO and lower in fat and protein than foods chosen at meals. The dietary behaviors of these elite athletes were generally consistent with guidelines for sports nutrition, but intakes during and after training sessions were often sub-optimal. Although it is of interest to study the periodicity of fluid and food intake by athletes, it is difficult to compare across studies due to a lack of standardized terminology.

Adult↗

PubMed2003

Velocity specificity of weight training for kayak sprint performance.

PURPOSE: Athletes often use weight training to prepare for sprint events, but the effectiveness of different types of weight training for sprinting is unclear. We have therefore investigated the effect of slow and explosive weight training on kayak sprint performance. METHODS: Twenty-seven male and 11 female experienced sprint kayakers were randomized to slow weight training, explosive weight training, or control (usual training) groups. Weight training consisted of two sessions per week for 6 wk; in each session the athletes performed 3-4 sets of two sport-specific exercises with a load of 80% 1-repetition-maximum. The two training programs differed only in the time taken to complete the concentric phase of the exercises: slow, 1.7 s; explosive, <0.85 s. To determine the effects of training on sprint acceleration and speed maintenance, the athletes performed 15-m kayaking sprints pre- and posttraining; an electronic timing system provided sprint times at 3.75-, 7.5-, and 15-m marks. RESULTS: Relative to control, both types of weight training substantially improved strength and sprint performance. The improvements in mean sprint time over 15 m in each group were: slow, 3.4%; explosive, 2.3%; control, -0.2% (90% confidence limits for pairwise differences, approximately +/-1.4%). Over the first 3.75 m, the improvements were: slow, 7.1%; explosive, 3.2%; control, 1.4% ( approximately +/-2.6%). Over the last 7.5 m, the improvements were: slow, 2.1%; explosive, 3.0%; control, -0.8% ( approximately +/-1.9%). CONCLUSIONS: Slow weight training is likely to be more effective than explosive training for improving the acceleration phase of sprinting, when force is high throughout the length of the stroke. Explosive weight training may be more effective in speed maintenance, when forces are developed rapidly over a short period at the start of the stroke.

Adolescent↗