Elske J. Schabort

Reliability of Power in Physical Performance Tests

AbstractThe 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 (∼0.9%), peak power in an incremental test on a treadmill or cycle ergometer (∼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 (∼1.5%), and jump height or distance (∼2.0%). The CV for mean power on isokinetic ergometers was relatively large (>4%). CV were larger for nonathletes versus athletes (1.3 ×), female versus male nonathletes (1.4 ×), shorter (∼1-second) and longer (∼1-hour) versus 1-minute tests (≤1.6 ×), and respiratory- versus ergometer-based measures of power (1.4 to 1.6 ×). 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.

Carbohydrate-loading and exercise performance. An update.

SummaryThis review suggests that there is little or no effect of elevating pre-exercise muscle glycogen contents above normal resting values on a single exhaustive bout of high-intensity exercise lasting less than 5 minutes. Nor is there any benefit of increasing starting muscle glycogen content on moderate-intensity running or cycling lasting 60 to 90 minutes. In such exercise substantial quantities of glycogen remain in the working muscles at the end of exercise. However, elevated starting muscle glycogen content will postpone fatigue by ≈20% in endurance events lasting more than 90 minutes. During this type of exercise, exhaustion usually coincides with critically low (25 mmol/kg wet weight) muscle glycogen contents, suggesting the supply of energy from glycogen utilisation cannot be replaced by an increased oxidation of blood glucose. Glycogen supercompensation may also improve endurance performance in which a set distance is covered as quickly as possible. In such exercise, high carbohydrate diets have been reported to improve performance by 2 to 3%.

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.

Prediction of triathlon race time from laboratory testing in national triathletes

PURPOSE Four days after competing in an Olympic-distance National Triathlon Championship (1500-m swim, 40-km cycle, 10-km run), five male and five female triathletes underwent comprehensive physiological testing in an attempt to determine which physiological variables accurately predict triathlon race time. METHODS All triathletes underwent maximal swimming tests over 25 and 400 m, the determination of peak sustained power output (PPO) and peak oxygen uptake (VO2peak) during an incremental cycle test to exhaustion, and a maximal treadmill running test to assess peak running velocity and VO2peak. In addition, submaximal steady-state measures of oxygen uptake (VO2), blood [lactate], and heart rate (HR) were determined during the cycling and running tests. RESULTS The five most significant (P < 0.01) predictors of triathlon performance were blood lactate measured during steady-state cycling at a workload of 4 W x kg(-1) body mass (BM) (r = 0.92), blood lactate while running at 15 km x h(-1) (r = 0.89), PPO (r = 0.86), peak treadmill running velocity (r = 0.85), and VO2peak during cycling (r = 0.85). Stepwise multiple regression analysis revealed a highly significant (r = 0.90, P < 0.001) relationship between predicted race time (from laboratory measures) and actual race time, from the following calculation: race time (s) = - 129 (peak treadmill velocity [km x h(-1)]) + 122 ([lactate] at 4 W x kg(-1) BM) + 9456. CONCLUSION The results of this study show that race time for top triathletes competing over the Olympic distance can be accurately predicted from the results of maximal and submaximal laboratory measures.

The effect of a preexercise meal on time to fatigue during prolonged cycling exercise.

PURPOSE AND METHODS Seven subjects exercised to exhaustion on a bicycle ergometer at a workload corresponding to an intensity of 70% maximal oxygen uptake (VO2max). On one occasion (FED), subjects consumed a preexercise carbohydrate (CHO) containing breakfast (100 g CHO) 3 h before exercise. On the other occasion (FASTED), subjects exercised after an overnight fast. Exercise time to fatigue was significantly longer (P < 0.05) when subjects consumed the breakfast (136+/-14 min) compared with when they exercised in the fasted state (109+/-12 min). RESULTS Pre- and post-exercise muscle glycogen concentrations, respiratory exchange ratio, carbohydrate and fat oxidation, and lactate and insulin concentrations were not significantly different between the two trials. Insulin concentrations decreased significantly (P < 0.05) from 4.7+/-0.05 microIU.mL(-1) to 2.8+/-0.4 microIU.mL(-1) in FED and from 6.6+/-0.6 microIU.mL(-1) to 3.7+/-0.6 microIU.mL(-1) in FASTED subjects and free fatty acid concentrations (FFA) increased significantly (P < 0.05) from 0.09+/-0.02 mmol.L(-1) to 1.4+/-0.6 mmol.L(-1) in FED and from 0.17+/-0.02 mmol.L(-) to 0.74+/-0.27 mmol.L(-1) in FASTED subjects over the duration of the trials. CONCLUSIONS In conclusion, the important finding of this study is the increased time to fatigue when subjects ingested the CHO meal with no negative effects ascribed to increased insulin concentrations and decreased FFA concentrations after CHO ingestion.

Dose-related elevations in venous pH with citrate ingestion do not alter 40-km cycling time-trial performance.

Abstract The purpose of the current investigation was to determine whether sodium citrate enhances endurance cycling performance and, if so, what dosage(s) produces this effect. Eight trained [peak power output: 362 (48) W; power:weight: 5.1 (0.4) W · kg−1, mean (SD)] male cyclists were requested to complete four, 40-km time-trials, each separated by 3–7 days, on their own bicycles, mounted on a Kingcycle ergometer. To mimic the stochastic nature of cycle road races, the time-trials included four 500-m, four 1-km and two 2-km sprints. The experimental conditions involved the ingestion of three dosages of sodium citrate dissolved in 400 ml water: 0.2 g · kg−1, 0.4 g · kg−1 and 0.6 g · kg−1 body mass (b.m.) and a placebo (calcium carbonate, 0.1 g · kg−1 b.m.). Subjects were asked to complete both the sprints and total distance in the fastest time possible. Venous blood samples were collected before, as well as at 10-km intervals during the trials for the analysis of plasma lactate and glucose concentrations and for the measurement of blood pH and PCO2 levels. Immediately before, as well as during exercise, pH was significantly higher in the group ingesting the highest citrate dose (range 7.36–7.45) compared to the placebo (range 7.31–7.39) and the two lower citrate dosages. Despite this, no significant differences in power output (P=0.886) or time taken to complete the 40 km (P=0.754) were measured between the four trials. The average performance times (in min:s, with SD in parentheses) and average power output (in W) for the 40-km time-trials were: 58:46 (5:06) [265 (62) W], 60:24 (6:07) [251 (59) W], 61:47 (5:07) [243 (44) W] and 60:02 (5.05) [255 (55) W] for the 0.2, 0.4, 0.6 g · kg−1 b.m. sodium citrate and placebo trials, respectively. There were also no significant differences measured between treatments in terms of time, power output, speed or heart rate during the 500-m, 1-km and 2-km sprints. The ingestion of increasing sodium citrate dosages before exercise produced dose-dependent changes in pH, base excess and HCO−3 concentrations before and during the 40-km time-trial. However, these changes influenced neither the time-trial time nor the sprinting performance times.

Brain activity and perceived exertion during cycling exercise: an fMRI study

Background/aim Currently, the equipment and techniques available to assess brain function during dynamic exercise are limited, which has restricted our knowledge of how the brain regulates exercise. This study assessed the brain areas activated during cycling by making use of a novel cycle ergometer, constructed to measure functional MRI (fMRI) brain images during dynamic exercise. Furthermore, we compared brain activation at different levels of ratings of perceived exertion (RPE) generated during the exercise. Methods Seven healthy adults performed cycling exercise in a novel MRI compatible cycle ergometer while undergoing brain fMRI. Participants completed a cycling block protocol comprising six trials of 2 min cycling with 16-s intervals between trials. Participants reported their RPE every minute through an audio link. The MRI cycling ergometer transferred the torque generated on the ergometer through a cardan system to a cycling ergometer positioned outside the MRI room. For data analysis, the effects of cycling as opposed to rest periods were examined after motion correction. Results The multiparticipant analysis revealed in particular the activation of the cerebellar vermis and precentral and postcentral gyrus when periods of cycling versus rest were compared. Single participant analysis in four participants revealed that activation of the posterior cingulate gyrus and precuneus occurred in cycling blocks perceived as ‘hard’ compared with exercise blocks that were less demanding. Conclusions The present study offers a new approach to assess brain activation during dynamic cycling exercise, and suggests that specific brain areas could be involved in the sensations generating the rating of perceived exertion.

Potential myogenic stem cell populations: sources, plasticity, and application for cardiac repair.

The ability of unspecialized stem cells to differentiate into mature, specialized cell types has made them attractive as potential agents for enhanced tissue repair and regenerative medicine. This is especially true of diseases and disorders for which no or only partially effective treatments are currently available. Recently, increased focus has been placed on the regenerative potential of satellite cells (myogenic precursor cells found in the adult skeletal muscle) in various muscular disorders, such as dystrophy and myocardial injury following ischemia. Animal studies and clinical trials are in progress using satellite cells as cellular candidates; however, this early rollout in the clinical setting has deflected attention from the potential of other less specialized, but potentially more maliable, stem cell sources. Published data is still lacking on the best methods for identification, isolation, and further expansion or nuclear manipulation of these cells in vitro. Also, although differentiation capacity has been proven in terms of protein expression patterns characteristic of myogenesis, proof of contractile and energetic compatibility between graft and host is more difficult to establish. In this regard, although future animal model studies will be invaluable, they must be designed with short- and long-term functional outcomes in mind. This review moves beyond initial excitement regarding the acknowledged potential of cell therapy and provides a realistic exposition of the themes and specific issues that should be considered in current experimental research study designs.

Physiological and subjective measures of workload when shovelling with a conventional and two-handled ('levered') shovel.

Previous studies have suggested that the two-handled (levered) shovel is advantageous over the conventional spade from a biomechanical point of view. The aim of this experiment was to determine whether less energy was consumed while shovelling a load of sand with this shovel compared to a conventional tool. Accordingly, an experiment was designed in which subjects (n = 10) shovelled 1815 kg sand under laboratory conditions using either a conventional or a levered shovel. Heart rate and oxygen consumption were measured continuously during the trial and subjective data on perceived exertion, general fatigue and body discomfort were recorded after the trial. Although total energy expenditure was similar under both conditions (120 +/- 20 and 125 +/- 25 kcal; conventional versus two-handled spade), average heart rate was 4% higher when the two-handled shovel was used (p < 0.05). In addition, the mass of sand per scoop was 4% less with the two-handled shovel (p < 0.05). In conclusion, subjects used similar energy expenditure to shovel 1815 kg sand with the conventional shovel and the two-handled tool despite lower mass of sand per scoop with the latter. This can be explained by the fact that the increased mass of the additional handle compensated for the lower mass of sand per scoop. The higher average heart rate while shovelling with the two-handled shovel can be explained by the more erect posture.