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W G Hopkins

Publications and source records attributed to W G Hopkins.

At least 19 recordsLinked to original sources
PubMed2002

Effect of tapered normal and interval training on performance of Standardbred pacers.

Human athletes taper or reduce their training load before a race to enhance performance, apparently because recovery from the effects of fatigue occurs faster than the loss of fitness from the reduced training. However, there appear to be no previous studies of tapering of equine athletes. Our aim in the present study was, therefore, to investigate the efficacy of tapering with Standardbred pacers. We determined the effect of repeated cycles of tapered training on performance of Standardbred pacers. After 8 weeks of jogging and 3 x 2 week cycles of pace work, 19 horses were randomised to a taper and a control group. The taper group completed 5 consecutive 2 week cycles, each incorporating a 7 day taper; some cycles included high-intensity interval training. The control group continued with 5 more cycles of pace work. All horses completed a 2400 m individual time trial after each cycle. Peak and mean speed of the taper group were faster than those of the control group in all cycles; the differences were clear-cut in all cycles for peak speed (overall 4.4%, 95% confidence interval 1.7 to 7.1%), but only in one of the interval-training cycles for mean speed (2.4%, 0.3 to 4.7%). Four horses in the taper group were injured during interval training. Repeated tapering produces a worthwhile enhancement of performance in Standardbreds, but the addition of interval training appears to increase the risk of injury.

Animals↗
PubMed2002

Changes in physiological parameters in overtrained Standardbred racehorses.

Various changes in physiological parameters are associated with overtraining, which can be a serious problem for human and equine athletes. A 34 week longitudinal study was conducted to investigate the effects of an acute training overload on physiological parameters in 10 Standardbred racehorses. After 24 weeks of training, horses received 8 weeks of increased workload, followed by 2 weeks recovery. Horses performed a 2400 m time trial and a progressive submaximal exercise test on alternate weeks. By the end of the heavy training period, the average time for the final 1200 m of the time trial increased by 4.0% (95% probable range of true value 1.7-5.8) and peak velocity decreased by 6.9% (4.7-8.9), indicating that overtraining had occurred. Acute overtraining coincided with an increase in blood lactate concentration after the time trial and submaximal test. There were also substantial decreases in bodyweight, plasma cortisol concentration and packed cell volume after the time trial, and in the velocity at a heart rate of 200/min (V200). Parameters that showed no clear-cut change with overtraining included maximal and recovery heart rate, basal plasma cortisol, plasma and red cell volume, and markers of skeletal damage (plasma concentrations of creatine kinase and aspartate aminotransferase). Bodyweight, V200, postexercise blood lactate and plasma cortisol concentrations may all be useful for detecting acute overtraining in equine athletes.

Animals↗
PubMed2001

Little effect of caffeine ingestion on repeated sprints in team-sport athletes.

PURPOSE: The effect of caffeine ingestion on sprint performance is unclear. We have therefore investigated its effect on performance in a test that simulates the repeated sprints of team sports. METHODS: In a randomized double-blind crossover experiment, 16 male team-sport athletes ingested either caffeine (6 mg.kg-1 of body mass) or a placebo 60 min before performing a repeated 20-m sprint test. The test consisted of 10 sprints, each performed within 10 s and followed by rest for the remainder of each 10 s. The caffeine and placebo trials followed a familiarization trial, and the time between consecutive trials was 2-3 d. To allow estimation of variation in treatment effects between individuals, nine subjects performed three more trials without a supplement 7-14 d later. We estimated the smallest worthwhile effect on sprint time in a team sport to be approximately 0.8%. RESULTS: Mean time to complete 10 sprints increased by 0.1% (95% likely range -1.5 to 1.7%) with caffeine ingestion relative to placebo. Individual variation in this effect was a standard deviation of 0.7% (-2.7 to 2.9%). Time to complete the 10th sprint was 14.4% longer than the first; caffeine increased this time by 0.7% (-1.8 to 3.2%) relative to placebo, and individual variation in this effect was 2.4% (-3.4 to 4.9%). CONCLUSION: The observed effect of caffeine ingestion on mean sprint performance and fatigue over 10 sprints was negligible. The true effect on mean performance could be small at most, although the true effects on fatigue and on the performance of individuals could be somewhat larger. Pending confirmatory research, team-sport athletes should not expect caffeine to enhance sprint performance.

Adult↗
PubMed2001

Variability of competitive performance of distance runners.

PURPOSE: The typical variation in an athlete's performance from race to race sets a benchmark for assessing the utility of performance tests and the magnitude of factors affecting medal prospects. We report here the typical variation in competitive performance of endurance runners. METHODS: Repeated-measures analysis of log-transformed official race times provided the typical within-athlete variation in performance as coefficients of variation (CV). The types of race were cross-country runs (4 races over 9 wk), summer road runs (5 races over 4 wk), winter road runs (4 races over 9 wk), half marathons (3 races over 13 wk and 2 races over 22 wk), and marathons (2 races over 22 wk). RESULTS: Typical variation of times for the fastest quartile of male runners was 1.2-1.9% in the cross-country and road runs, 2.7% and 4.2% in half marathons, and 2.6% in marathons. Times for the slower half of runners in most events were more variable than those of the faster half (ratio of slower/faster CV, 1.0-2.3). Times of younger adult runners were more variable than times of older runners (ratio of younger/older CV, 1.1-1.8). Times of male runners were generally more variable than those of female runners (ratio of male/female CV, 0.9-1.7). CONCLUSION: Tests of endurance power suitable for assessing the smallest worthwhile changes in running performance for top runners need CV < or = 2.5% and < or = 1.5% for tests simulating half or full marathons and shorter running races, respectively. Most of the differences in variability of race times between types of race, ability groups, age groups, and sexes probably arise from differences in competitive experience and attitude toward competing.

Adolescent↗
PubMed2001

Reliability of power in physical performance tests.

The reliability of power in tests of physical performance affects the precision of assessment of athletes, patients, clients and study participants. In this meta-analytic review we identify the most reliable measures of power and the factors affecting reliability. Our measures of reliability were the typical (standard) error of measurement expressed as a coefficient of variation (CV) and the percent change in the mean between trials. We meta-analysed these measures for power or work from 101 studies of healthy adults. Measures and tests with the smallest CV in exercise of a given duration include field tests of sprint running (approximately 0.9%), peak power in an incremental test on a treadmill or cycle ergometer (approximately 0.9%), equivalent mean power in a constant-power test lasting 1 minute to 3 hours on a treadmill or cycle ergometer (0.9 to 2.0%), lactate-threshold power (approximately 1.5%), and jump height or distance (approximately 2.0%). The CV for mean power on isokinetic ergometers was relatively large (> 4%). CV were larger for nonathletes versus athletes (1.3 x), female versus male nonathletes (1.4 x), shorter (approximately 1-second) and longer (approximately 1-hour) versus 1-minute tests (< or = 1.6 x), and respiratory- versus ergometer-based measures of power (1.4 to 1.6 x). There was no clear-cut effect of time between trials. The importance of a practice trial was evident in studies with > 2 trials: the CV between the first 2 trials was 1.3 times the CV between subsequent trials; performance also improved by 1.2% between the first 2 trials but by only 0.2% between subsequent trials. These findings should help exercise practitioners and researchers select or design good measures and protocols for tests of physical performance.

Ergometry↗
PubMed2001

Tests of cycling performance.

Performance tests are an integral component of assessment for competitive cyclists in practical and research settings. Cycle ergometry is the basis of most of these tests. Most cycle ergometers are stationary devices that measure power while a cyclist pedals against sliding friction (e.g. Monark), electromagnetic braking (e.g. Lode), or air resistance (e.g. Kingcycle). Mobile ergometers (e.g. SRM cranks) allow measurement of power through the drive train of the cyclist's own bike in real or simulated competitions on the road, in a velodrome or in the laboratory. The manufacturers' calibration of all ergometers is questionable; dynamic recalibration with a special rig is therefore desirable for comparison of cyclists tested on different ergometers. For monitoring changes in performance of a cyclist, an ergometer should introduce negligible random error (variation) in its measurements; in this respect, SRM cranks appear to be the best ergometer, but more comparison studies of ergometers are needed. Random error in the cyclist's performance should also be minimised by choice of an appropriate type of test. Tests based on physiological measures (e.g. maximum oxygen uptake, anaerobic threshold) and tests requiring self-selection of pace (e.g. constant-duration and constant-distance tests) usually produce random error of at least approximately 2 to 3% in the measure of power output. Random error as low as approximately 1% is possible for measures of power in 'all-out' sprints, incremental tests, constant-power tests to exhaustion and probably also time trials in an indoor velodrome. Measures with such low error might be suitable for tracking the small changes in competitive performance that matter to elite cyclists.

Bicycling↗
PubMed2000

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↗
PubMed2000

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↗
PubMed2000

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↗
PubMed2000

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↗
PubMed2000

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↗
PubMed2000

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↗
PubMed2000

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↗
PubMed1999

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↗
PubMed1999

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↗
PubMed1999

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↗
PubMed1999

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↗