Physiological response to brief maximal intermittent exercise: with particular reference to testing procedures and performance determinants

Purpose: The activity patterns of many sports are intermittent in nature, fluctuating randomly from brief periods of maximal or near maximal work to longer periods of moderate and low intensity activity. Attempts to examine the complex energy demands of this type of work have typically utilised repeated bouts of brief (< 6-s) maximal work interspersed with relatively short (< 60-s) recovery periods. However, despite years of research, many issues concerning the physiological response to this type of activity remain unresolved. The principal aim of the present thesis was to focus on one of these issues, namely the influence of aerobic fitness on sport-specific repeat sprint ability. Methods: Physically active students from the University of Edinburgh were used in all studies. Each investigation utilised two distinct maximal intermittent (20 x 5-s) test protocols with contrasting recovery periods (10-s or 30-s). The protocols were designed to simulate the range of work to rest ratios often experienced in sports such as badminton, rugby, soccer, and squash. All tests were conducted on a friction-braked cycle ergometer. Results: Both of the intermittent test protocols were found to have good degrees of test-retest reliability in measures of power output and fatigue. Moreover, the highest degrees of test-retest reliability were found to occur after the administration of two familiarisation trials. Although the quantification of fatigue during intermittent work had received a number of different approaches, the percentage decrement score was determined as the most valid and reliable means of assessing this parameter. Differences in recovery duration between the two intermittent test protocols had considerable effects on measures of maximum power output, mean power output, blood lactate, and fatigue. Between-protocol differences in maximum power output were attributed to the potentiation effect associated with Protocol 2 (30-s rest periods). In contrast, differences in mean power output, blood lactate and fatigue were most likely the result of between-protocol differences in the magnitude of the phosphocreatine (PCr) contribution to each sprint. Relative to controls, training-induced improvements in aerobic fitness, as evidenced by a 10.2% increase in V02max, corresponded with substantial improvements in intermittent performance measures of maximum and mean power output (range: 3.2 to 8.2%). Endurance training also impacted on the ability to resist fatigue, the magnitude of which increased with increasing recovery duration. Correlations between V02max and fatigue were also dependent on recovery duration supporting the idea that the principle role of aerobic metabolism during brief maximal intermittent work is in the iii restoration of homeostasis during intervening rest periods. Conclusions: The ability to produce and maintain high power outputs during prolonged periods of brief maximal intermittent work is an important determinant of performance in many sports. The results of the present thesis demonstrate the considerable influence of aerobic fitness in this respect, the magnitude of the effects being largely determined by the duration of the intervening rest periods. Although the precise mechanisms of action require further investigation, the improvements in repeat sprint performance that accompany increases in aerobic fitness are likely to be the result of enhancements in the recovery of power output via improved offtransient inorganic phosphate and PCr kinetics

A comparison of methods to estimate anaerobic capacity: Accumulated oxygen deficit and W' during constant and all-out work-rate profiles.

This document is the Pre-Print version of an article first published by Taylor & Francis Group in Journal of Sports Sciences, on December 2016, available online at:http://www.tandfonline.com/doi/full/10.1080/02640414.2016.1267386. The Accepted Manuscript version is under embargo. Embargo end date: 26 June 2018.This study investigated (i) whether the accumulated oxygen deficit (AOD) and curvature constant of the power-duration relationship (W') are different during constant work-rate to exhaustion (CWR) and 3-min all-out (3MT) tests and (ii) the relationship between AOD and W' during CWR and 3MT. Twenty-one male cyclists (age: 40 ± 6 years; maximal oxygen uptake [V̇O2max]: 58 ± 7 ml · kg-1 · min-1) completed preliminary tests to determine the V̇O2-power output relationship and V̇O2max. Subsequently, AOD and W' were determined as the difference between oxygen demand and oxygen uptake and work completed above critical power, respectively, in CWR and 3MT. There were no differences between tests for duration, work, or average power output (P ≥ 0.05). AOD was greater in the CWR test (4.18 ± 0.95 vs. 3.68 ± 0.98 L; P = 0.004), whereas W' was greater in 3MT (9.55 ± 4.00 vs. 11.37 ± 3.84 kJ; P = 0.010). AOD and W' were significantly correlated in both CWR (P < 0.001, r = 0.654) and 3MT (P < 0.001, r = 0.654). In conclusion, despite positive correlations between AOD and W' in CWR and 3MT, between-test differences in the magnitude of AOD and W', suggest that both measures have different underpinning mechanisms.Peer reviewe

Moderate-intensity oxygen uptake kinetics: is a mono-exponential function always appropriate to model the response?

Purpose: This study investigated the existence of the oxygen uptake () overshoot and the effects of exercise intensity and fitness status on the response during moderate-intensity exercise. Methods: Twelve “high-fitness” (Mage = 26 ± 5 years; Mheight = 184.1 ± 5.4 cm; Mbody mass = 76.6 ± 8.9 kg; mean peak oxygen uptake (peak) = 59.0 ± 3.3 mL·kg−1·min·−1) and 11 “moderate-fitness” (Mage = 29 ± 5 years; Mheight = 178.7 ± 7.5 cm; Mbody mass = 81.7 ± 10.9 kg; MV̇O2peak = 45.2 ± 3.1 mL·kg−1·min·−1) participants performed square-wave transitions from unloaded cycling to 3 different intensities (70%, 82.5%, and 95% of the gas exchange threshold). The data were modeled using both a mono-exponential function (Model 1) and a function that included a switch-on component (Model 2). The overshoot was computed by subtracting the steady state from the peak of the modeled response and by calculating the area of the curve that was above steady state. Results: The goodness of fit was affected by model type (p = .002) and exercise intensity (p < .001). High-fitness participants displayed a smaller τ (p < .05) and a larger amplitude (p < .05) and were more likely to overshoot the steady state (p = .035). However, while exercise intensity did affect the amplitude (p < .001), it did not affect τ (p ≥ .05) or the likelihood of an overshoot occurring (p = .389). Conclusion: While exercise intensity did not alter the response, fitness status affected τ and the likelihood of an overshoot occurring. The overshoot questions the traditional approach to modeling moderate-intensity data

Influence of Work-Interval Intensity and Duration on Time Spent at a High Percentage VO2max During Intermittent Supramaximal Exercise

The purpose of this study was to examine the effect of work-interval duration (WID) and intensity on the time spent at, or above, 95% V̇O2max (T95 V̇O2max) during intermittent bouts of supramaximal exercise. Over a 5-week period, 7 physically active men with a mean (±SD) age, height, body mass, and V̇O2max of 22 ± 5 years, 181.5 ± 5.6 cm, 86.4 ± 11.4 kg, and 51.5 ± 1.5 ml·kg−1·min−1, respectively, attended 7 testing sessions. After completing a submaximal incremental test on a treadmill to identify individual oxygen uptake/running velocity relationships, subjects completed a maximal incremental test to exhaustion to establish V̇O2max and subsequently (from the aforementioned relationship) the minimum velocity required to elicit V̇O2max (vV̇O2max). In a random order, subjects then carried out 3 intermittent runs to exhaustion at both 105% and 115% vV̇O2max. Each test used a different WID (20 s, 25 s, or 30 s) interspersed with 20-second passive recovery periods. Results revealed no significant difference in T95 vV̇O2max for intermittent runs at 105% versus 115% vV̇O2max (p = 0.142). There was, however, a significant effect (p < 0.001) of WID on T95 V̇O2max, with WIDs of 30 seconds enabling more time relative to WIDs of 20 seconds (p = 0.018) and 25 seconds (p = 0.009). Moreover, there was an interaction between intensity and duration such that the effect of WID was magnified at the lower exercise intensity (p = 0.046). In conclusion, despite a number of limitations, the results of this investigation suggest that exercise intensities of approximately 105% vV̇O2max combined with WIDs greater than 25 seconds provide the best way of optimizing T95 V̇O2max when using fixed 20-second stationary rest periods

The influence of aerobic fitness on the recovery of peak power output

Purpose The aims of this study were to evaluate the recovery kinetics of peak power output (PPO) following a maximal sprint, and to evaluate the influence of aerobic fitness on that recovery process. Methods On separate occasions, 16 well-trained men (age: 21 ± 3 years; height: 1.84 ± 0.05 m; and body mass: 78.8 ± 7.8 kg) performed a 30 s maximal sprint on a cycle ergometer, followed by a predetermined stationary rest period (5, 10, 20, 40, 80, and 160 s) and a subsequent 5 s sprint to determine PPO recovery kinetics. On another occasion, V ˙ O 2 was monitored during recovery from a 30 s sprint to provide a comparison with the recovery of PPO. Finally, subjects completed a V ˙ O 2max test to evaluate the influence of aerobic fitness on the recovery of PPO. Results Despite following similar time courses (F = 0.36, p = 0.558), and being well described by double-exponential models, the kinetic parameters of PPO and V ˙ O 2 in recovery were significantly different (p < 0.05). There was no significant relationship (r = 0.15; p = 0.578) between V ˙ O 2max and the time to achieve 50 % recovery of PPO. Moreover, there was no difference (p = 0.61) between the recovery kinetics of participants classified according to their V ˙ O 2max (59.4 ± 1.3 vs 48.5 ± 2.2 ml·kg−1·min−1). Conclusion Despite similar overall recovery kinetics, V ˙ O 2 and PPO show differences in key model parameters. Moreover, the recovery of PPO does not appear to be affected by aerobic fitness

The Reliability and Validity of Fatigue Measures During Multiple-Sprint Work: An Issue Revisited

The ability to repeatedly produce a high-power output or sprint speed is a key fitness component of most field and court sports. The aim of this study was to evaluate the validity and reliability of eight different approaches to quantify this parameter in tests of multiple-sprint performance. Ten physically active men completed two trials of each of two multiple-sprint running protocols with contrasting recovery periods. Protocol 1 consisted of 12 × 30-m sprints repeated every 35 seconds; protocol 2 consisted of 12 × 30-m sprints repeated every 65 seconds. All testing was performed in an indoor sports facility, and sprint times were recorded using twin-beam photocells. All but one of the formulae showed good construct validity, as evidenced by similar within-protocol fatigue scores. However, the assumptions on which many of the formulae were based, combined with poor or inconsistent test-retest reliability (coefficient of variation range: 0.8-145.7%; intraclass correlation coefficient range: 0.09-0.75), suggested many problems regarding logical validity. In line with previous research, the results support the percentage decrement calculation as the most valid and reliable method of quantifying fatigue in tests of multiple-sprint performance

Perceptual and Physiological Responses to Recovery from a Maximal 30-Second Sprint

The aims of this study were to evaluate perceptions of post-exercise recovery and to compare patterns of perceived recovery with those of several potential mediating physiological variables. Seventeen well-trained men (age: 22 ± 4 years; height: 1.83 ± 0.05 m; body mass: 78.9 ± 7.6 kg; and body fat: 11.1 ± 2.2%) completed 10 sprint trials on an electromagnetically braked cycle ergometer. Trial 1 evaluated peak power via a 5-second sprint. The remaining trials evaluated (a) the recovery of peak power after a maximal 30-second sprint using rest intervals of 5, 10, 20, 40, 80, and 160 seconds; (b) perceived recovery via visual analog scales; and (c) physiological responses during recovery. The time point in recovery at which individuals perceived they had fully recovered was 163.3 ± 57.5 seconds. Power output at that same time point was 83.6 ± 5.2% of peak power. There were no significant differences between perceived recovery and the recovery processes of VO2 or minute ventilation (VE). Despite differences in the time courses of perceived recovery and the recovery of power output, individuals were able to closely predict full recovery without the need for external timepieces. Moreover, the time course of perceived recovery is similar to that of VO2 and VE

Methodological Approaches and Related Challenges Associated With the Determination of Critical Power and Curvature Constant

The relationship between exercise intensity and time to task-failure (P-T relationship) is hyperbolic, and characterised by its asymptote (critical power, CP) and curvature constant (W’). The determination of these parameters is of interest for researchers and practitioners, but the testing protocol for CP and W’ determination has not yet been standardised. Conventionally, a series of constant work-rate tests (CWR) to task-failure have been used to construct the P-T relationship. However, the duration, number, and recovery between predictive CWR, and the mathematical model (hyperbolic or derived linear models) are known to affect CP and W’. Moreover, repeating CWR may be deemed as a cumbersome and impractical protocol. Recently, CP and W’ have been determined in field and laboratory settings using time-trials, but the validity of these methods has raised concerns. Alternatively, a 3-min all-out test (3MT) has been suggested, as it provides a simpler method for the determination of CP and W’, whereby power output at the end of the test represents CP, and the amount of work performed above this end-test power equates to W’. However, the 3MT still requires an initial incremental test, and may overestimate CP. The aim of this review is, therefore, to appraise current methods to estimate CP and W’, providing guidelines and suggestions for future research where appropriate

The Effect of Ischemic Preconditioning on Repeated Sprint Cycling Performance

Purpose: Ischemic preconditioning enhances exercise performance. We tested the hypothesis that ischemic preconditioning would improve intermittent exercise in the form of a repeated sprint test during cycling ergometry.Methods: In a single-blind, crossover study, 14 recreationally active men (mean ± SD age, 22.9 ± 3.7 yr; height, 1.80 ± 0.07 m; and mass, 77.3 ± 9.2 kg) performed twelve 6-s sprints after four 5-min periods of bilateral limb occlusion at 220 mm Hg (ischemic preconditioning) or 20 mm Hg (placebo).Results: Ischemic preconditioning resulted in a 2.4% ± 2.2%, 2.6% ± 2.7%, and 3.7% ± 2.4% substantial increase in peak power for sprints 1, 2, and 3, respectively, relative to placebo, with no further changes between trials observed for any other sprint. Similar findings were observed in the first three sprints for mean power output after ischemic preconditioning (2.8% ± 2.5%, 2.6% ± 2.5%, and 3.4% ± 2.1%, for sprints 1, 2, and 3, respectively), relative to placebo. Fatigue index was not substantially different between trials. At rest, tissue saturation index was not different between the trials. During the ischemic preconditioning/placebo stimulus, there was a -19.7% ± 3.6% decrease in tissue saturation index in the ischemic preconditioning trial, relative to placebo. During exercise, there was a 5.4% ± 4.8% greater maintenance of tissue saturation index in the ischemic preconditioning trial, relative to placebo. There were no substantial differences between trials for blood lactate, electromyography (EMG) median frequency, oxygen uptake, or rating of perceived exertion (RPE) at any time points.Conclusion: Ischemic preconditioning improved peak and mean power output during the early stages of repeated sprint cycling and may be beneficial for sprint sports