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Biomedical subjects

W G Hopkins

Publications and source records attributed to W G Hopkins.

At least 37 records · Page 2Linked to original sources

Seasonal training and performance of competitive swimmers.

To determine the relationship between prescribed training and seasonal-best swimming performance, we surveyed 24 swim coaches and 185 of their age-group and open-class swimmers specializing in sprint (50 and 100 m) and middle-distance (200 and 400 m) events in a summer and winter season. We expressed effects on training as either multiples of swimmers' standard deviations (effect size, ES) or as correlations (r). Coaches prescribed higher mileage and longer repetitions of lower intensity to middle-distance swimmers than to sprinters (ES = 0.4-1.5); as competitions approached, repetition intensity and duration of rest intervals increased (ES = 0.5-0.9), whereas session and repetition distances decreased (ES = 0.4-1.3). The 95% likely ranges of the true values for these effects were about +/- 0.3. Weekly mileage swum at an easy or moderate pace remained at almost 60% of the total throughout both seasons. Interval training reduced gradually from 40% of total distance in the build-up to 30% at the end of tapering. Older swimmers had shorter rests and swam more miles (r = 0.5-0.8). After partialling out the effects of age on performance (r = 0.7-0.8), better performance was significantly associated only with greater weekly mileage (r = 0.5-0.8) and shorter duration of rest intervals (r = 0.6-0.7) in middle-distance swimmers. We conclude that periodization of training and differences in training between sprint and middle-distance events were broadly in accord with principles of specificity. Strong effects of specificity on performance were not apparent, but weak effects might have been detected with a larger sample.

Adolescent↗

Consistency of swimming performance within and between competitions.

PURPOSE: The consistency of performance between events impacts how athletes should specialize in events, how competitions should be structured, and how changes in performance affect an athlete's placing in an event. We have therefore determined the consistency of swimming performance in events within and between two national-level competitions. METHODS: We used mixed linear modeling to analyze official performance times of 149 male and 162 female swimmers at a junior national championship, and of 117 male and 104 female swimmers at an open national championship 20 d later. The events differed in stroke (backstroke, breaststroke, butterfly, freestyle, and individual medley) or distance (50-1500 m). RESULTS: Swimmers were most consistent in their performance for the same event between the two competitions (typical variation between competitions, 1.4%; 95% likely range of true value, 1.3-1.5%). They were less consistent between distances of a given stroke within each competition (1.7%; 1.5-1.9%) and least consistent between strokes for a given distance (2.7%; 2.3-3.1%). Variation in performance between the longest continuous freestyle distances (400, 800, and 1500 m) in the open competition was half that between widely spaced freestyle distances (50, 200, and 800 m). Faster swimmers were more consistent (1.1%; 0.9-1.4%) for the same event between competitions than slower swimmers (1.5%; 1.3-1.9%). CONCLUSIONS: (a) Swimmers are stroke specialists rather than distance specialists; with the present set of events in competitions, they should concentrate training and competing on a particular stroke rather than a particular distance. (b) More swimmers would have a chance of winning a medal if events of a given stroke differed more widely in distance. (c) Factors that affect performance time by as little as 0.5% will affect the placing of a top junior swimmer.

Adolescent↗

Placebo effect of carbohydrate feedings during a 40-km cycling time trial.

PURPOSE: The placebo effect, a favorable outcome from belief that one has received a beneficial treatment, may be an important phenomenon in athletic performance. We have therefore investigated the placebo effect of a carbohydrate supplement on endurance performance. METHODS: Forty-three competitive endurance cyclists (2 female, 41 male) performed two simulated 40-km time trials on an air-braked ergometer. In the first trial they ingested water to establish baseline performance (mean power 265 +/- 46 W for 58 +/- 4 min, mean +/- SD). For the second trial 6-8 d later they were randomized to two groups: one group ingested 16 mL x kg(-1) of a drink containing 7.6 g x 100 mL(-1) carbohydrate; the other ingested an indistinguishable noncaloric placebo drink. Cyclists in each group were further randomized to three subgroups according to whether they were told the drink contained carbohydrate, placebo, or either (not told). RESULTS: Changes in mean power in the second trial were: told carbohydrate, 4.3 +/- 4.8%; told placebo, 0.5 +/- 5.8%; and not told, -1.1 +/- 8.5%. The difference between the told-carbohydrate and told-placebo groups was 3.8% (95% likely range 7.9 to -0.2%). The change in performance in the not-told group was more variable than that of the told groups by a factor of 1.6 (2.6 to 1.0). The real effect of carbohydrate was a slight reduction in power of 0.3% (4.4 to -3.8%). CONCLUSIONS: (a) The placebo effect of a potentially ergogenic treatment during unblinded laboratory time trials lasting approximately 1 h is probably a small but worthwhile increase in endurance power. (b) Blinding subjects to the treatment increases individual differences in endurance effort, which may reduce precision of performance outcomes in controlled trials.

Adult↗

Enhancement of 2000-m rowing performance after caffeine ingestion.

PURPOSE: To investigate the effect of caffeine ingestion on short-term endurance performance in competitive rowers. METHODS: In this randomized double-blind crossover study, eight competitive oarsmen (peak oxygen uptake [VO2peak] 4.7+/-0.4 L x min(-1), mean +/- SD) performed three familiarization trials of a 2000-m rowing test on an air-braked ergometer, followed by three experimental trials at 3- to 7-d intervals, each 1 h after ingesting caffeine (6 or 9 mg x kg(-1) body mass) or placebo. Trials were preceded by a standardized warm-up (6 min at 225+/-39 W; 75+/-7.7% VO2peak). RESULTS: Urinary caffeine concentration was similar before ingestion (approximately 1 mg x L(-1)) but rose to 6.2+/-3.6 and 14.5+/-7.0 mg x L(-1) for the low and high caffeine doses, respectively. Plasma free fatty acid concentration before exercise was higher after caffeine ingestion (0.29+/-0.17 and 0.39+/-0.20 mM for 6 and 9 mg x kg(-1), respectively) than after placebo (0.13+/-0.05 mM). Respiratory exchange ratio during the warm-up was also substantially lower with caffeine (0.94+/-0.09 and 0.93+/-0.06 for the low and high dose) than with placebo (0.98+/-0.12). Subjects could not distinguish between treatments before or after the exercise test. Both doses of caffeine had a similar ergogenic effect relative to placebo: performance time decreased by a mean of 1.2% (95% likely range 0.4-1.9%); the corresponding increase in mean power was 2.7% (0.4-5.0%). Performance time showed some evidence of individual differences in the effect of caffeine (SD 0.9%; 95% likely range 1.5 to -0.9%). CONCLUSIONS: Ingestion of 6 or 9 mg x kg(-1) of caffeine produces a worthwhile enhancement of short-term endurance performance in a controlled laboratory setting.

Caffeine↗

Improved 2000-meter rowing performance in competitive oarswomen after caffeine ingestion.

Eight competitive oarswomen (age, 22 +/- 3 years; mass, 64.4 +/- 3.8 kg) performed three simulated 2,000-m time trials on a rowing ergometer. The trials, which were preceded by a 24-hour dietary and training control and 72 hours of caffeine abstinence, were conducted 1 hour after ingesting caffeine (6 or 9 mg á kg-1 body mass) or placebo. Plasma free fatty acid concentrations before exercise were higher with caffeine than placebo (0.67 +/- 0.34 vs. 0.72 +/- 0.36 vs. 0.30 +/- 0.10 mM for 6 and 9 mg á kg-1 caffeine and placebo, respectively; p <.05). Performance time improved 0.7% (95% confidence interval [CI] 0 to 1.5%) with 6 mg á kg-1 caffeine and 1. 3% (95% CI 0.5 to 2.0%) with 9 mg á kg-1 caffeine. The first 500 m of the 2,000 m was faster with the higher caffeine dose compared with placebo or the lower dose (1.53 +/- 0.52 vs.1.55 +/- 0.62 and 1. 56 +/- 0.43 min; p =.02). We concluded that caffeine produces a worthwhile enhancement of performance in a controlled laboratory setting, primarily by improving the first 500 m of a 2,000-m row.

Adult↗

Measures of reliability in sports medicine and science.

Reliability refers to the reproducibility of values of a test, assay or other measurement in repeated trials on the same individuals. Better reliability implies better precision of single measurements and better tracking of changes in measurements in research or practical settings. The main measures of reliability are within-subject random variation, systematic change in the mean, and retest correlation. A simple, adaptable form of within-subject variation is the typical (standard) error of measurement: the standard deviation of an individual's repeated measurements. For many measurements in sports medicine and science, the typical error is best expressed as a coefficient of variation (percentage of the mean). A biased, more limited form of within-subject variation is the limits of agreement: the 95% likely range of change of an individual's measurements between 2 trials. Systematic changes in the mean of a measure between consecutive trials represent such effects as learning, motivation or fatigue; these changes need to be eliminated from estimates of within-subject variation. Retest correlation is difficult to interpret, mainly because its value is sensitive to the heterogeneity of the sample of participants. Uses of reliability include decision-making when monitoring individuals, comparison of tests or equipment, estimation of sample size in experiments and estimation of the magnitude of individual differences in the response to a treatment. Reasonable precision for estimates of reliability requires approximately 50 study participants and at least 3 trials. Studies aimed at assessing variation in reliability between tests or equipment require complex designs and analyses that researchers seldom perform correctly. A wider understanding of reliability and adoption of the typical error as the standard measure of reliability would improve the assessment of tests and equipment in our disciplines.

Algorithms↗

Reliability of two 2,400-m time-trial protocols for assessing performance of Standardbred racehorses.

OBJECTIVE: To evaluate the reliability of 2 time-trial protocols, 1 that involved use of a pacemaker and 1 that did not, for assessing performance of Standardbred racehorses. ANIMALS: 3- to 7-year-old Standardbred maiden pacers. PROCEDURE: 11 Standardbred pacers were used to determine the reliability of a time-trial protocol that involved use of a galloping pacemaker. All tests were performed by a single driver. Horses were paced for an initial 1,600 m then raced and timed for the final 800 m. They were retested 9 days later. Twenty-two horses were used to determine the reliability of a time-trial protocol that did not involve use of a pacemaker. All tests were performed by a second driver. Horses were paced for the first 1,200 m then raced and timed for the final 1,200 m. They were retested 3 and 8 days later. RESULTS: Reliability of performance time, expressed as the coefficient of variation (ie, the typical percentage variation in a horse's time between trials), was similar for the 2 protocols (1.0% and 1.3%, respectively). CONCLUSIONS: The small variations in performance times for the 2 time-trial protocols were similar to those of the best comparable laboratory and field tests of human and equine performance. Both protocols would be suitable for investigating factors affecting performance of Standardbred racehorses.

Analysis of Variance↗

Metabolic adaptations to a high-fat diet in endurance cyclists.

We examined the time course of metabolic adaptations to 15 days of a high-fat diet (HFD). Sixteen endurance-trained cyclists were assigned randomly to a control (CON) group, who consumed their habitual diet (30% +/- 8% mJ fat), or a HFD group, who consumed a high-fat isocaloric diet (69% +/- 1% mJ fat). At 5-day intervals, the subjects underwent an oral glucose tolerance test (OGTT); on the next day, they performed a 2.5-hour constant-load ride at 70% peak oxygen consumption (VO2peak), followed by a simulated 40-km cycling time-trial while ingesting a 10% 14C-glucose + 3.44% medium-chain triglyceride (MCT) emulsion at a rate of 600 mL/h. In the OGTT, plasma glucose concentrations at 30 minutes increased significantly after 5 days of the HFD and remained elevated at days 10 and 15 versus the levels measured prior to the HFD (P < .05). The activity of carnitine acyltransferase (CAT) in biopsies of the vastus lateralis muscle also increased from 0.45 to 0.54 micromol/g/min over days 0 to 10 of the HFD (P < .01) without any change in citrate synthase (CS) or 3-hydroxyacyl-coenzyme A dehydrogenase (3-HAD) activities. Changes in glucose tolerance and CAT activity were associated with a shift from carbohydrate (CHO) to fat oxidation during exercise (P < .001), which occurred within 5 to 10 days of the HFD. During the constant-load ride, the calculated oxidation of muscle glycogen was reduced from 1.5 to 1.0 g/min (P < .001) after 15 days of the HFD. Ingestion of a HFD for as little as 5 to 10 days significantly altered substrate utilization during submaximal exercise but did not attenuate the 40-km time-trial performance.

Adaptation, Physiological↗

High reliability of performance of well-trained rowers on a rowing ergometer.

High retest reliability is desirable in tests used to monitor athletic performance, but the reliability of many popular tests has not been established. The aim of this study was to determine the reliability of performance of a 2000-m time-trial lasting approximately 7 min performed on a Concept II rowing ergometer. Eight well-trained rowers (peak oxygen uptake 61+/-5 ml x kg(-1) x min(-1); mean +/- standard deviation) performed the time-trials on three occasions at 3-day intervals. Mean power (313+/-38 W in trial 1) improved by 2.3% (95% confidence interval 0.1 to 4.5%) in trial 2 and by a further 0.9% (-1.4 to 3.3%) in trial 3. The variability of performance for individual rowers expressed as a coefficient of variation for mean power was 2.0% (1.3 to 3.1%), and the retest correlation was 0.96 (0.87 to 0.99). Variability and changes in performance expressed as time to complete the test were approximately one-third those of mean power, apparently because simulated velocity is proportional to the cube root of power on this ergometer. Such high reliability makes this combination of ergometer, athlete and test protocol very suitable for monitoring rowing performance and for investigating factors that affect performance in short, high-intensity endurance events.

Adolescent↗

Design and analysis of research on sport performance enhancement.

PURPOSE: The purpose of this study was to assess research aimed at measuring performance enhancements that affect success of individual elite athletes in competitive events. ANALYSIS: Simulations show that the smallest worthwhile enhancement of performance for an athlete in an international event is 0.7-0.4 of the typical within-athlete random variation in performance between events. Using change in performance in events as the outcome measure in a crossover study, researchers could delimit such enhancements with a sample of 16-65 athletes, or with 65-260 in a fully controlled study. Sample size for a study using a valid laboratory or field test is proportional to the square of the within-athlete variation in performance in the test relative to the event; estimates of these variations are therefore crucial and should be determined by repeated-measures analysis of data from reliability studies for the test and event. Enhancements in test and event may differ when factors that affect performance differ between test and event; overall effects of these factors can be determined with a validity study that combines reliability data for test and event. A test should be used only if it is valid, more reliable than the event, allows estimation of performance enhancement in the event, and if the subjects replicate their usual training and dietary practices for the study; otherwise the event itself provides the only dependable estimate of performance enhancement. Publication of enhancement as a percent change with confidence limits along with an analysis for individual differences will make the study more applicable to athletes. Outcomes can be generalized only to athletes with abilities and practices represented in the study. CONCLUSION: estimates of enhancement of performance in laboratory or field tests in most previous studies may not apply to elite athletes in competitive events.

Humans↗

Effects of different interval-training programs on cycling time-trial performance.

PURPOSE: We have investigated the effect of varying the intensity of interval training on 40-km time-trial performance in 20 male endurance cyclists (peak oxygen uptake 4.8+/-0.6 L x min(-1), mean +/- SD). METHODS: Cyclists performed a 25-kJ sprint test, an incremental test to determine peak aerobic power (PP) and a simulated 40-km time-trial on a Kingcycle ergometer. They were then randomly assigned to one of five types of interval-training session: 12x30 s at 175% PP, 12x60 s at 100% PP, 12x2 min at 90% PP, 8x4 min at 85% PP, or 4x8 min at 80% PP. Cyclists completed 6 sessions over 3 wk, in addition to their usual aerobic base training. All laboratory tests were then repeated. RESULTS: Performances in the time trial were highly reliable when controlled for training effects (coefficient of variation = 1.1%). The percent improvement in the time trial was modeled as a polynomial function of the rank order of the intensity of the training intervals, a procedure validated by simulation. The cubic trend was strong and statistically significant (overall correlation = 0.70, P = 0.005) and predicted greatest enhancement for the intervals performed at 85% PP (2.8%, 95% CI = 4.3-1.3%) and at 175% PP (2.4%, 95% CI = 4.0-0.7%). Intervals performed at 100% PP and 80% PP did not produce statistically significant enhancements of performance. Quadratic and linear trends were weak or insubstantial. CONCLUSIONS: Interval training with work bouts close to race-pace enhance 1-h endurance performance; work bouts at much higher intensity also appear to improve performance, possibly by a different mechanism.

Adult↗

Investigation of the side pain "stitch" induced by running after fluid ingestion.

PURPOSE: Text books attribute the side pain "stitch" during exercise to changes in blood flow to the viscera, but the little available research favors stretching of visceral ligaments. We therefore induced and modified stitch experimentally to investigate its cause and possible treatments. METHODS: Ten active healthy young men reported the intensity of stitch during sessions of intermittent exercise after drinking either no fluid (control) or a body-mass-adjusted volume (14 mL x kg(-1)) of each of four fluids: water, Exceed, decarbonated Coca-Cola, and a hypertonic solution of the nonabsorbable sugar lactulose. Each exercise session consisted of five 5-min bouts of hard running on a treadmill, with 10-min rests between each bout. In another experiment, seven subjects reported the effect of several physical maneuvers on stitch during exercise after drinking decarbonated Coca-Cola. RESULTS: Stitch developed to a similar intensity with all fluids during the first two bouts of running; thereafter, stitch declined only with Exceed, reaching the intensity with no fluid by the last two bouts. Bending forward while tightening abdominal muscles, tightening a belt around the waist, or breathing through pursed lips with increased lung volume alleviated stitch within seconds, but attempting to relax abdominal muscles or increasing the impact of foot strike had little effect. CONCLUSIONS: Our observations cannot be explained readily by mechanisms involving digestion-induced changes in blood flow but are consistent with the notion that stitch arises when the fluid-engorged gut tugs on visceral ligaments.

Adult↗

Reproducibility of self-paced treadmill performance of trained endurance runners.

The reproducibility of performance in a laboratory test impacts on the statistical power of that test to detect changes of performance in experiments. The purpose of this study was to determine the reproducibility of performance of distance runners completing a 60 min time trial (TT) on a motor-driven treadmill. Eight trained distance runners (age 27 +/- 7yrs, peak oxygen consumption [VO2peak] 66 +/- 5 ml x min(-1) x kg(-1), mean +/- SD) performed the TT on three occasions separated by 7-10 days. Throughout each TT the runners controlled the speed of the treadmill and could view current speed and elapsed time, but they did not know the elapsed or final distance. On the basis of heart-rate, it is estimated that the subjects ran at an average intensity equivalent to 80-83% of VO2peak. The distance run in 1 h did not vary substantially between trials (16.2 +/- 1.4 km, 15.9 +/- 1.4 km, and 16.1 +/- 1.2 km for TTs 1-3 respectively, p = 0.5). The coefficient of variation (CV) for individual runners was 2.7% (95% Cl = 1.8-4.0%) and the test-retest reliability expressed as an intraclass correlation coefficient was 0.90 (95% Cl = 0.72-0.98). Reproducibility of performance in this test was therefore acceptable. However, higher reproducibility is required for experimental studies aimed at detecting the smallest worthwhile changes in performance with realistic sample sizes.

Adult↗

A new reliable laboratory test of endurance performance for road cyclists.

PURPOSE: The purpose of this study was to devise and evaluate a laboratory test of cycling performance that simulates the variable power demands of competitive road racing. The test is a 100-km time trial interspersed with four 1-km and four 4-km sprints. METHODS: On three occasions separated by 5-7 d, eight endurance-trained cyclists (peak oxygen uptake 5.0 +/- 0.7 L.min-1, peak power output 411 +/- 43 W, mean +/- SD) performed the test on their own bikes mounted on an air-braked Kingcycle ergometer. Subjects were free to regulate their power output but were asked to complete each sprint and the full distance as quickly as possible. The only feedback given to the cyclists during each test was elapsed distance. RESULTS: In the first test, time for the 100 km and mean times for the 1-km and 4-km sprints were 151:42 +/- 10:36, 1:16 +/- 0:06, and 5:31 +/- 0:16 min:s, respectively; these times improved by 1.6-2.2% in the second test, but there was little further improvement in the third test (0.7 to -0.5%). The between-test correlation for 100-km time was 0.93 (95% CI 0.79 to 0.98), and the within-cyclist coefficient of variation was 1.7% (95% CI 1.1 to 2.5%). Mean sprint performance showed similar good reliability (within-subject variation and correlations for the 1-km and 4-km sprint times of 1.9%, 2.0%, 0.93, and 0.81, respectively). CONCLUSIONS: The high reliability of this laboratory test will make the test useful for research on performance of competitive road cyclists.

Adult↗

Swimmers' compliance with training prescription.

The purpose of this study was to determine how closely competitive swimmers complied with their coaches' prescriptions when training in squads. A training session early in the buildup phase of the season was observed for each of 24 coaches who had been randomized to two groups: an experimental, high-intensity, low-distance program (E) and a control (usual) program (C). Swim distances, rest durations, and swim durations for at least one set of prescribed repetitions (reps) were recorded for each of 47 swimmers (87 sets, 429 reps) in E and for 49 swimmers (79 sets, 402 reps) in C. The pace of each rep, expressed as percent of the swimmer's current personal best pace for the distance of the rep, represented observed intensity. There was almost perfect agreement between the prescribed and observed swim distances for the set of reps (Spearman r = 0.99 in both groups). Prescribed and observed rest intervals were also closely matched in E and C (Spearman r = 0.87 and 0.77 respectively). Four coaches in E and 10 coaches in C prescribed intensity subjectively as easy, moderate, hard, or race-pace; mean +/- SD observed intensities (%) for their swimmers were 79 +/- 6, 81 +/- 3, 91 +/- 2, and 93 +/- 5, respectively. The relationship between these coaches' subjective training prescription and individual swimmers' interpretations of these intensities was poor (Cohen's kappa = 0.39). Nine coaches in E prescribed intensity as percent of personal best pace. Although the mean prescribed and observed intensities for their swimmers were similar (89 +/- 4 and 90 +/- 7, respectively), the relationship between individual values was poor (Pearson r = 0.30). We conclude that swimmers complied with prescribed distances and rest intervals but were less effective in judging the intensity of swim training. We recommend that coaches monitor training intensity more closely.

Humans↗

Specificity of training and its relation to the performance of distance runners.

Validated six-month retrospective questionnaires were completed by 119 female and 234 male coached distance runners (59% compliance) for a descriptive study of relationships between specificity of training and best performance in a summer season. Runners were aged 26 +/- 10 y (mean +/- SD), specialising in distances from 800 m to the marathon, with seasonal best paces of 82 +/- 7% of sex- and age-group world records. They reported typical weekly durations of interval and strength training, and typical weekly durations and paces of moderate and hard continuous running, for build-up, precompetition, competition, and postcompetition phases of the season. The training programs showed some evidence of specificity, especially for runners preparing for longer events. A potentially beneficial effect of specificity was evident in a significant (p < 0.01) correlation between performance and seasonal mean weekly duration of moderate continuous running for runners specialising in longer distances (r = 0.29). The only other significant correlates of performance were seasonal mean relative training paces of moderate (r = -0.18) and hard (r = -0.42) continuous running, which exemplified detrimental effects of specificity for most runners. Thus, the training of better runners is not characterised strongly by greater specificity.

Adult↗

Prescribed and self-reported seasonal training of distance runners.

A survey of 123 distance-running coaches and their best runners was undertaken to describe prescribed seasonal training and its relationship to the performance and self-reported training of the runners. The runners were 43 females and 80 males, aged 24 +/- 8 years (mean +/- S.D.), training for events from 800 m to the marathon, with seasonal best paces of 86 +/- 6% of sex- and age-group world records. The coaches and runners completed a questionnaire on typical weekly volumes of interval and strength training, and typical weekly volumes and paces of moderate and hard continuous running, for build-up, pre-competition, competition and post-competition phases of a season. Prescribed training decreased in volume and increased in intensity from the build-up through to the competition phase, and had similarities with 'long slow distance' training. Coaches of the faster runners prescribed longer build-ups, greater volumes of moderate continuous running and slower relative paces of continuous running (r = 0.19-0.36, P < 0.05), suggesting beneficial effects of not training close to competition pace. The mean training volumes and paces prescribed by the coaches were similar to those reported by the runners, but the correlations between prescribed and reported training were poor (r = 0.2-0.6). Coaches may therefore need to monitor their runners' training more closely.

Adult↗