Effects of prior very-heavy intensity exercise on indices of aerobic function and high-intensity exercise tolerance

The Effects of a 90-km Outdoor Cycling Ride on Performance Outcomes Derived From Ramp-Incremental and 3-Minute All-Out Tests

ABSTRACT

Bitel, M, Keir, DA, Grossman, K, Barnes, M, Murias, JM, and Belfry, GR. The effects of a 90-km outdoor cycling ride on performance outcomes derived from ramp-incremental and 3-minute all-out tests. J Strength Cond Res 38(3): 540-548, 2024-The purpose of this study was to determine whether laboratory-derived exercise intensity and performance demarcations are altered after prolonged outdoor cycling. Male recreational cyclists ( n = 10; RIDE) performed an exhaustive ramp-incremental test (RAMP) and a 3-minute all-out test (3MT) on a cycle ergometer before and after a 90-km cycling ride. RAMP-derived maximal oxygen uptake (V̇O 2max ), gas exchange threshold (GET), respiratory compensation point (RCP), and associated power output (PO), as well as 3MT-derived critical power (CP) and work performed above CP, were compared before and after ∼3 hours of outdoor cycling. Six active men served as "no-exercise" healthy controls (CON), who, instead, rested for 3 hours between repeated RAMP and 3MT tests. During the 90-km ride, the duration within the moderate-intensity, heavy-intensity, and severe-intensity domains was 59 ± 24%, 40 ± 24%, and 1 ± 1%, respectively. Compared with pre-90 km, post-RAMP exhibited reductions in (a) V̇O 2max (4.04 ± 0.48 vs. 3.80 ± 0.38 L·min -1 ; p = 0.026) and associated PO (392 ± 30 W vs. 357 ± 26 W; p = 0.002); (b) the V̇O 2 and PO at RCP (3.49 ± 0.46 vs. 3.34 ± 0.43 L·min -1 ; p = 0.040 and 312 ± 40 W vs. 292 ± 24 W; p = 0.023); and (c) the PO (214 ± 32 W vs. 198 ± 25 W; p = 0.027), but not the V̇O 2 at GET (2.52 ± 0.44 vs. 2.44 ± 0.38 L·min -1 ; p = 0.388). Pre-90 km vs. post-90 km 3MT variables showed reduced W' (9.8 ± 3.4 vs. 6.8 ± 2.6 kJ; p = 0.002) and unchanged CP (304 ± 26 W and 297 ± 34 W; p = 0.275). In the CON group, there were no differences in V̇O 2max , GET, RCP, W', CP, or associated power outputs ( p > 0.05) pre-to-post 3 hours of rest. The preservation of critical power demonstrates that longer-duration maximal efforts may be sustained after long-duration cycle. However, shorter sprints and higher-intensity efforts eliciting V̇O 2max will exhibit decreased PO after 3 hours of a predominantly moderate-intensity cycle.

How Priming Exercise Affects Oxygen Uptake Kinetics: From Underpinning Mechanisms to Endurance Performance

The observation that prior heavy or severe-intensity exercise speeds overall oxygen uptake ([Formula: see text]O₂) kinetics, termed the "priming effect", has garnered significant research attention and its underpinning mechanisms have been hotly debated. In the first part of this review, the evidence for and against (1) lactic acidosis, (2) increased muscle temperature, (3) O₂ delivery, (4) altered motor unit recruitment patterns and (5) enhanced intracellular O₂ utilisation in underpinning the priming effect is discussed. Lactic acidosis and increased muscle temperature are most likely not key determinants of the priming effect. Whilst priming increases muscle O₂ delivery, many studies have demonstrated that an increased muscle O₂ delivery is not a prerequisite for the priming effect. Motor unit recruitment patterns are altered by prior exercise, and these alterations are consistent with some of the observed changes in [Formula: see text]O₂ kinetics in humans. Enhancements in intracellular O₂ utilisation likely play a central role in mediating the priming effect, probably related to elevated mitochondrial calcium levels and parallel activation of mitochondrial enzymes at the onset of the second bout. In the latter portion of the review, the implications of priming on the parameters of the power-duration relationship are discussed. The effect of priming on subsequent endurance performance depends critically upon which phases of the [Formula: see text]O₂ response are altered. A reduced [Formula: see text]O₂ slow component or increased fundamental phase amplitude tend to increase the work performable above critical power (i.e. W´), whereas a reduction in the fundamental phase time constant following priming results in an increased critical power.

Identifying the Optimal Arm Priming Exercise Intensity to Improve Maximal Leg Sprint Cycling Performance

Priming exercises improve subsequent motor performance; however, their effectiveness may depend on the workload and involved body areas. The present study aimed to estimate the effects of leg and arm priming exercises performed at different intensities on maximal sprint cycling performance. Fourteen competitive male speed-skaters visited a lab eight times, where they underwent a body composition measurement, two V̇O_2max measurements (leg and arm ergometers), and five sprint cycling sessions after different priming exercise conditions. The five priming exercise conditions included 10-minute rest (Control); 10-minute arm ergometer exercise at 20% V̇O_2max (Arm 20%); 10-minute arm ergometer exercise at 70% V̇O_2max (Arm 70%); 1-min maximal arm ergometer exercise at 140% V̇O_2max (Arm 140%); and 10-min leg ergometer exercise at 70% V̇O_2max (Leg 70%). Power outputs of 60-s maximal sprint cycling, blood lactate concentration, heart rate, muscle and skin surface temperature, and rating of perceived exertion were compared between the priming conditions at different measurement points. Our results showed that the Leg 70% was the optimal priming exercise among our experimental conditions. Priming exercise with the Arm 70% also tended to improve subsequent motor performance, while Arm 20% and Arm 140% did not. Mild elevation in blood lactate concentration by arm priming exercise may improve the performance of high-intensity exercise.

Bioenergetic Mechanisms Linking V˙O2 Kinetics and Exercise Tolerance

We hypothesize that the V˙O2 time constant (τV˙O2) determines exercise tolerance by defining the power output associated with a "critical threshold" of intramuscular metabolite accumulation (e.g., inorganic phosphate), above which muscle fatigue and work inefficiency are apparent. Thereafter, the V˙O2 "slow component" and its consequences (increased pulmonary, circulatory, and neuromuscular demands) determine performance limits.

W' reconstitution rate at different intensities above critical torque: the role of muscle size and maximal strength

NEW FINDINGS

What is the central question of this study? Do muscle size, maximal force and exercise intensity influence the recovery time constant for the finite impulse above critical torque (τ_IET' )? What is the main finding and its importance? Muscle size and maximal strength have different influences on the parameters of the hyperbolic torque-time to task failure relationship. Greater muscle size and maximal strength, as well as exercise at an intensity of 60% MVC, prolong τ_IET' during intermittent isometric exercise.

ABSTRACT

Muscle perfusion and O₂ delivery limitations through muscle force generation appear to play a major role in defining the hyperbolic torque-time to task failure (T_lim ) relationship. Therefore, we aimed to determine the influence of muscle size and maximal strength on the recovery time constant for the finite impulse above critical torque (τ_IET' ). Ten men participated in the study and performed intermittent isometric tests until task-failure (T_lim ) for the knee-extensors (KE) (35% and 60% maximal voluntary contraction (MVC)) and plantar flexors (PF) (60% MVC). The τ_IET' was determined for each of these T_lim tests using the IET'_BAL model. The IET' (9738 ± 3080 vs. 2959 ± 1289 N m s) and end-test torque (ET)(84.5 ± 7.1 vs. 74.3 ± 12.7 N m) were significantly lower for PF compared to KE (P < 0.05). Exercise tolerance (T_lim ) was significantly longer for PF (239 ± 81 s) than KE (150 ± 55 s) at 60% MVC, and significantly longer for KE at 35% MVC (641 ± 158 s) than 60% MVC. The τ_IET' was significantly faster at 35% MVC (641 ± 177 s) than 60% MVC (1840 ± 354 s) for KE, both of which were significantly slower than PF at 60% MVC (317 ± 102 s). This study showed that τ_IET' during intermittent isometric exercise is slower with greater muscle size and maximal strength.

Effects of Prior Voluntary Hyperventilation on the 3-min All-Out Cycling Test in Men

INTRODUCTION

The ergogenic effects of respiratory alkalosis induced by prior voluntary hyperventilation (VH) are controversial. This study examined the effects of prior VH on derived parameters from the 3-min all-out cycling test (3MT).

METHODS

Eleven men ( = 46 ± 8 mL·kg-1·min-1) performed a 3MT preceded by 15 min of rest (CONT) or VH ( = 38 ± 5 L·min-1) with PETCO2 reduced to 21 ± 1 mm Hg (HYP). End-test power (EP; synonymous with critical power) was calculated as the mean power output over the last 30 s of the 3MT, and the work done above EP (WEP; synonymous with W') was calculated as the power-time integral above EP.

RESULTS

At the start of the 3MT, capillary blood PCO2 and [H+] were lower in HYP (25.2 ± 3.0 mm Hg, 27.1 ± 2.6 nmol·L-1) than CONT (43.2 ± 2.0 mm Hg, 40.0 ± 1.5 nmol·L-1) (P < 0.001). At the end of the 3MT, blood PCO2 was still lower in HYP (35.7 ± 5.4 mm Hg) than CONT (40.6 ± 5.0 mm Hg) (P < 0.001). WEP was 10% higher in HYP (19.4 ± 7.0 kJ) than CONT (17.6 ± 6.4 kJ) (P = 0.006), whereas EP was 5% lower in HYP (246 ± 69 W) than CONT (260 ± 74 W) (P = 0.007). The ΔWEP (J·kg-1) between CONT and HYP correlated positively with the PCO2 immediately before the 3MT in HYP (r = 0.77, P = 0.006).

CONCLUSION

These findings suggest that acid-base changes elicited by prior VH increase WEP but decrease EP during the all-out 3MT.

A 30-Min Rest Protocol Does Not Affect W', Critical Power, and Systemic Response

PURPOSE

This study aimed to assess and compare the systemic response of oxygen uptake kinetics and muscle deoxygenation between a 30-min rest protocol and a multivisit protocol on the parameters of the power-duration relationship (i.e., critical power [CP] and W').

METHODS

Nine endurance-trained triathletes reported to the laboratory on five occasions: a preliminary graded exercise test and a familiarization, a 30-min single-visit protocol (time trials of 10, 5, and 2 min in that order interspersed with 30 min rest), and a multivisit protocol (time trials of 10, 5, and 2 min in randomized order interspersed by >24 h rest). Heart rate (HR) was recorded continuously, respiratory gases were measured breath by breath, and deoxygenation was recorded at 10 Hz using near-infrared spectroscopy (NIRS) during all tests. Blood lactate (BLa-) concentration was measured before all time trials. Maximal HR (HRmax), oxygen uptake (V˙O2) during the first 2 min (V˙O2onset), mean response time, end-exercise V˙O2 (V˙O2peak), V˙O2 amplitude (amplV˙O2), O2 deficit, NIRS τ, amplitude (amplNIRS), and time delay were assessed. To compare the two protocols and to assess the differences in W' and CP, a paired sample t-test was used as well as a two-way ANOVA to assess the differences between trials and/or protocols, including trial-protocol interactions.

RESULTS

No significant differences, and trivial effect sizes, were found for W' and CP between protocols (P = 0.106-0.114, d < 0.01-0.08). Furthermore, no significant differences between protocols were found for all parameters, except for [BLa-]. Significant differences between trials were found for V˙O2ampl, V˙O2onset, NIRS τ, amplNIRS, [BLa-], and HRmax.

CONCLUSION

Results suggest that W' and CP can be determined using the 30-min rest protocol without confounding effects of previous severe exercise compared with the multivisit protocol.

Modeling the depletion and reconstitution of W': Effects of prior exercise on cycling tolerance

Thirteen healthy male subjects (age 28 ± 7 years) performed tests for critical power and W' determination and two square-wave high-intensity exercises until exhaustion either with prior very-heavy intensity cycling (EXP) or without (CON). Prior exercise bout induced a depletion of 60 % of W'. After 10 min of recovery, W' reconstitution was not fully achieved (∼ 92 %). Time to exhaustion and Δ blood lactate concentration were significantly lower in EXP compared to CON (595 ± 118 s vs. 683 ± 148 s; 3.5 ± 1.2 mmol.L^-1 vs. 8.8 ± 2.3 mmol.L^-1; p < 0.05, respectively). Oxygen uptake (VO₂) and heart rate were significantly higher in EXP, during the first 150 s of exercise (p < 0.05). The carbon dioxide production kinetics was significantly slower in EXP (mean response time = 87.8 ± 17.8 s vs. 73.7 ± 16.6 s in CON; p < 0.05). Thus, prior exercise impairs high-intensity cycling performance which can partly be explained by physiological disturbances linked to W' depletion.

The Effects of a Short Specific Versus a Long Traditional Warm-Up on Time-Trial Performance in Cross-Country Skiing Sprint

PURPOSE

To compare the effects of a short specific and a long traditional warm-up on time-trial performance in cross-country skiing sprint using the skating style, as well as related differences in pacing strategy and physiological responses.

METHODS

In total, 14 (8 men and 6 women) national-level Norwegian cross-country skiers (age 20.4 [3.1] y; VO2max 65.9 [5.7] mL/kg/min) performed 2 types of warm-up (short, 8 × 100 m with gradual increase from 60% to 95% of maximal speed with a 1-min rest between sprints, and long, ∼35 min at low intensity, including 5 min at moderate and 3 min at high intensity) in a randomized order with 1 hour and 40 minutes of rest between tests. Each warm-up was followed by a 1.3-km sprint time trial, with continuous measurements of speed and heart rate.

RESULTS

No difference in total time for the time trial between the short and long warm-ups (199 [17] vs 200 [16] s; P = .952), or average speed and heart rate for the total course, or in the 6 terrain sections (all P < .41, η2 < .06) was found. There was an effect of order, with total time-trial time being shorter during test 2 than test 1 (197 [16] vs 202 [16] s; P = .004). No significant difference in blood lactate and rating of perceived exertion was found between the short versus long warm-ups or between test 1 and test 2 at any of the measurement points during the test day (P < .58, η2 > .01).

CONCLUSIONS

This study indicates that a short specific warm-up could be as effective as a long traditional warm-up during a sprint time trial in cross-country skiing.

Effect of intensive prior exercise on muscle fiber activation, oxygen uptake kinetics, and oxygen uptake plateau occurrence

Purpose

We tested the hypothesis that the described increase in oxygen uptake (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{2}}$$\end{document}V˙O2)-plateau incidence following a heavy-severe prior exercise is caused by a steeper increase in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{2}}$$\end{document}V˙O2 and muscle fiber activation in the submaximal intensity domain.

Methods

Twenty-one male participants performed a standard ramp test, a \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{{\text{2max}}}}$$\end{document}V˙O2max verification bout, an unprimed ramp test with an individualized ramp slope and a primed ramp test with the same ramp slope, which was preceded by an intensive exercise at 50% of the difference between gas exchange threshold and maximum workload. Muscle fiber activation was recorded from vastus lateralis, vastus medialis, and gastrocnemius medialis using a surface electromyography (EMG) device in a subgroup of 11 participants. Linear regression analyses were used to calculate the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{2}}$$\end{document}V˙O2-(\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta \dot{V}{\text{O}}_{{2}} /\Delta P$$\end{document}ΔV˙O2/ΔP) and EMG-(∆RMS/∆P) ramp test kinetics.

Results

Twenty out of the 21 participants confirmed their \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{{\text{2max}}}}$$\end{document}V˙O2max in the verification bout. The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{2}}$$\end{document}V˙O2-plateau incidence in these participants did not differ between the unprimed (n = 8) and primed (n = 7) ramp test (p = 0.500). The \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\Delta \dot{V}{\text{O}}_{{2}} /\Delta P$$\end{document}ΔV˙O2/ΔP was lower in the primed compared to the unprimed ramp test (9.40 ± 0.66 vs. 10.31 ± 0.67 ml min⁻¹ W⁻¹, p < 0.001), whereas the ∆RMS/∆P did not differ between the ramp tests (0.62 ± 0.15 vs. 0.66 ± 0.14% W⁻¹; p = 0.744).

Conclusion

These findings do not support previous studies, which reported an increase in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{2}}$$\end{document}V˙O2-plateau incidence as well as steeper increases in \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{{2}}$$\end{document}V˙O2 and muscle fiber activation in the submaximal intensity domain following a heavy-severe prior exercise.

Priming exercise increases Wingate cycling peak power output

PURPOSE

The aim of the present study was to investigate the effect of priming exercise on Wingate performance and fatigue.

METHODS

Twelve recreationally active young male volunteers participated in the study (age: 25 ± 5 years; weight: 75.0 ± 7.5 kg; height: 177 ± 6 cm; BMI: 24.0 ± 1.7). During a first visit, participants performed a typical V˙O2max test and a supramaximal assessment of V˙O2max on a cycle ergometer, while during the next three visits, the participants performed in a random order a Wingate test (i) with no priming exercise, (ii) after priming exercise followed by a 15-min recovery (Priming15) and (iii) after priming exercise followed by a 30-min recovery (Priming30). Priming exercise lasted 6 min, at work rate corresponding to the gas exchange threshold (GET) plus 70% of the difference between the GET and V˙O2max.

RESULTS

The Priming 30 condition exhibited greater peak power output (595 ± 84 W) compared to the control (567 ± 85 W) and the Priming15 condition (569 ± 95 W) (P < .05). Regarding fatigue index, a tendency towards increased resistance to fatigue was observed in the Priming30 condition compared to the control and the Priming15 conditions (P = .072). Pre-Wingate lactate levels were found to be significantly different between the Priming15 (7.18 ± 3.09 mmol/L) and the Priming30 (4.87 ± 2.11 mmol/L) conditions (P < .05).

CONCLUSIONS

Priming exercise of high intensity followed by a prolonged recovery leads to increased peak power in a subsequent Wingate test. Moreover, our data are consistent with the idea that a priming exercise-induced modest increase in blood lactate concentration at the onset of the following criterion bout is a key factor of performance.

Effects of Prior Upper Body Exercise on the 3-min All-Out Cycling Test in Men

INTRODUCTION

Prior upper body exercise reduces the curvature constant (W') of the hyperbolic power-duration relationship without affecting critical power. This study tested the hypothesis that prior upper body exercise reduces the work done over the end-test power (WEP; analog of W') during a 3-min all-out cycling test (3MT) without affecting the end-test power (EP; analog of critical power).

METHODS

Ten endurance-trained men (V˙O2max = 62 ± 5 mL·kg·min) performed a 3MT without (CYC) and with (ARM-CYC) prior severe-intensity, intermittent upper body exercise. EP was calculated as the mean power output over the last 30 s of the 3MT, whereas WEP was calculated as the power-time integral above EP.

RESULTS

At the start of the 3MT, plasma [La] (1.8 ± 0.4 vs 14.1 ± 3.4 mmol·L) and [H] (42.8 ± 3.1 vs 58.6 ± 5.5 nmol·L) were higher, whereas the strong ion difference (41.4 ± 2.2 vs 30.9 ± 4.6 mmol·L) and [HCO3] (27.0 ± 1.9 vs 16.9 ± 3.2 mmol·L) were lower during ARM-CYC than CYC (P < 0.010). EP was 12% lower during the 3MT of ARM-CYC (298 ± 52 W) than CYC (338 ± 60 W; P < 0.001), whereas WEP was not different (CYC: 12.8 ± 3.3 kJ vs ARM-CYC: 13.5 ± 4.1 kJ, P = 0.312). EP in CYC was positively correlated with the peak [H] (r = 0.78, P = 0008) and negatively correlated with the lowest [HCO3] (r = -0.74, P = 0.015).

CONCLUSIONS

These results suggest that EP during a 3MT in endurance-trained men is sensitive to fatigue-related ionic perturbation.

Chronotropic incompetence and myocardial injury after noncardiac surgery: planned secondary analysis of a prospective observational international cohort study

BACKGROUND

Physiological measures of heart failure are common in surgical patients, despite the absence of a diagnosis. Heart rate (HR) increases during exercise are frequently blunted in heart failure (termed chronotropic incompetence), which primarily reflects beta-adrenoreceptor dysfunction. We examined whether chronotropic incompetence was associated with myocardial injury after noncardiac surgery.

METHODS

This was a predefined analysis of an international cohort study where participants aged ≥40 yr underwent symptom-limited cardiopulmonary exercise testing before noncardiac surgery. Chronotropic incompetence was defined as the ratio of increase in HR during exercise to age-predicted maximal increase in HR <0.6. The primary outcome was myocardial injury within 3 days after surgery, defined by high-sensitivity troponin assays >99th centile. Explanatory variables were biomarkers for heart failure (ventilatory efficiency slope [minute ventilation/carbon dioxide production] ≥34; peak oxygen consumption ≤14 ml kg-1 min-1; HR recovery ≤6 beats min-1 decrease 1 min post-exercise; preoperative N-terminal pro-B-type natriuretic peptide [NT pro-BNP] >300 pg ml-1). Myocardial injury was compared in the presence or absence of sympathetic (i.e. chronotropic incompetence) or parasympathetic (i.e. impaired HR recovery after exercise) thresholds indicative of dysfunction. Data are presented as odds ratios (ORs) (95% confidence intervals).

RESULTS

Chronotropic incompetence occurred in 396/1325 (29.9%) participants; only 16/1325 (1.2%) had a heart failure diagnosis. Myocardial injury was sustained by 162/1325 (12.2%) patients. Raised preoperative NT pro-BNP was more common when chronotropic incompetence was <0.6 (OR: 1.57 [1.11-2.23]; P=0.011). Chronotropic incompetence was not significantly associated with myocardial injury (OR: 1.05 [0.74-1.50]; P=0.78), independent of rate-limiting therapy. HR recovery <12 beats min-1 decrease after exercise was associated with myocardial injury in the presence (OR: 1.62 [1.05-2.51]; P=0.03) or absence (OR: 1.60 [1.06-2.39]; P=0.02) of chronotropic incompetence.

CONCLUSIONS

Chronotropic incompetence is common in surgical patients. In contrast to parasympathetic dysfunction which was associated with myocardial injury, preoperative chronotropic incompetence (suggestive of sympathetic dysfunction) was not associated with postoperative myocardial injury.

Handgrip fatiguing exercise can provide objective assessment of cancer-related fatigue: a pilot study

PURPOSE

As a subjective symptom, cancer-related fatigue is assessed via patient-reported outcomes. Due to the inherent bias of such evaluation, screening and treatment for cancer-related fatigue remains suboptimal. The purpose is to evaluate whether objective cancer patients' hand muscle mechanical parameters (maximal force, critical force, force variability) extracted from a fatiguing handgrip exercise may be correlated to the different dimensions (physical, emotional, and cognitive) of cancer-related fatigue.

METHODS

Fourteen women with advanced breast cancer, still under or having previously received chemotherapy within the preceding 3 months, and 11 healthy women participated to the present study. Cancer-related fatigue was first assessed through the EORTC QLQ-30 and its fatigue module. Fatigability was then measured during 60 maximal repeated handgrip contractions. The maximum force, critical force (asymptote of the force-time evolution), and force variability (root mean square of the successive differences) were extracted. Multiple regression models were performed to investigate the influence of the force parameters on cancer-related fatigue's dimensions.

RESULTS

The multiple linear regression analysis evidenced that physical fatigue was best explained by maximum force and critical force (r = 0.81; p = 0.029). The emotional fatigue was best explained by maximum force, critical force, and force variability (r = 0.83; p = 0.008). The cognitive fatigue was best explained by critical force and force variability (r = 0.62; p = 0.035).

CONCLUSION

The handgrip maximal force, critical force, and force variability may offer objective measures of the different dimensions of cancer-related fatigue and could provide a complementary approach to the patient reported outcomes.

W' expenditure and reconstitution during severe intensity constant power exercise: mechanistic insight into the determinants of W'

The sustainable duration of severe intensity exercise is well-predicted by critical power (CP) and the curvature constant (W'). The development of the W'BAL model allows for the pattern of W' expenditure and reconstitution to be characterized and this model has been applied to intermittent exercise protocols. The purpose of this investigation was to assess the influence of relaxation phase duration and exercise intensity on W' reconstitution during dynamic constant power severe intensity exercise. Six men (24.6 ± 0.9 years, height: 173.5 ± 1.9 cm, body mass: 78.9 ± 5.6 kg) performed severe intensity dynamic handgrip exercise to task failure using 50% and 20% duty cycles. The W'BAL model was fit to each exercise test and the time constant for W' reconstitution (τW') was determined. The τW' was significantly longer for the 50% duty cycle (1640 ± 262 sec) than the 20% duty cycle (863 ± 84 sec, P = 0.02). Additionally, the relationship between τW' and CP was well described as an exponential decay (r(2) = 0.90, P < 0.0001). In conclusion, the W'BAL model is able to characterize the expenditure and reconstitution of W' across the contraction-relaxation cycles comprising severe intensity constant power handgrip exercise. Moreover, the reconstitution of W' during constant power severe intensity exercise is influenced by the relative exercise intensity, the duration of relaxation between contractions, and CP.

Warm-Up Exercises May Not Be So Important for Enhancing Submaximal Running Performance

Takizawa, K, Yamaguchi, T, and Shibata, K. Warm-up exercises may not be so important for enhancing submaximal running performance. J Strength Cond Res 32(5): 1383-1390, 2018-The purpose of this study was to determine an appropriate warm-up intensity for enhancing performance in submaximal running at 90% vV[Combining Dot Above]O2max (it assumes 3,000-5,000 m in track events). Seven trained male university athletes took part in this study (age: 21.3 ± 2.1 years, height: 169.3 ± 4.7 cm, body mass: 58.4 ± 5.6 kg, V[Combining Dot Above]O2max: 73.33 ± 5.46 ml·kg·min). Each subject ran on a treadmill at 90% vV[Combining Dot Above]O2max until exhaustion after 1 of 4 warm-up treatments. The 4 warm-up treatments were no warm-up, 15 minutes running at 60% vV[Combining Dot Above]O2max, at 70% vV[Combining Dot Above]O2max, and at 80% vV[Combining Dot Above]O2max. The running performance was evaluated by time to exhaustion (TTE). V[Combining Dot Above]O2, and vastus lateralis muscle temperature were also measured. There were no significant differences in TTE among the warm-up exercises (p > 0.05). V[Combining Dot Above]O2 in no warm-up showed slower reaction than the other warm-up exercises. Regarding, the vastus lateralis muscle temperature immediately after warm-up, no warm-up was significantly (p < 0.01) lower compared with the other warm-up exercises. Our results suggested that submaximal running performance was not affected by the presence or absence of a warm-up or by warm-up intensity, although physiological changes occurred.

Comparison of inter-trial recovery times for the determination of critical power and W' in cycling

Critical Power (CP) and W' are often determined using multi-day testing protocols. To investigate this cumbersome testing method, the purpose of this study was to compare the differences between the conventional use of a 24-h inter-trial recovery time with those of 3 h and 30 min for the determination of CP and W'.

METHODS

9 moderately trained cyclists performed an incremental test to exhaustion to establish the power output associated with the maximum oxygen uptake (p[Formula: see text]_max), and 3 protocols requiring time-to-exhaustion trials at a constant work-rate performed at 80%, 100% and 105% of p[Formula: see text]_max. Design: Protocol A utilised 24-h inter-trial recovery (CP₂₄/W'₂₄), protocol B utilised 3-h inter-trial recovery (CP₃/W'₃), and protocol C used 30-min inter-trial recovery period (CP_0.5/W'_0.5). CP and W' were calculated using the inverse time (1/t) versus power (P) relation (P = W'(1/t) + CP).

RESULTS

95% Limits of Agreement between protocol A and B were -9 to 15 W; -7.4 to 7.8 kJ (CP/W') and between protocol A and protocol C they were -27 to 22 W; -7.2 to 15.1 kJ (CP/W'). Compared to criterion protocol A, the average prediction error of protocol B was 2.5% (CP) and 25.6% (W'), whilst for protocol C it was 3.7% (CP) and 32.9% (W').

CONCLUSION

3-h and 30-min inter-trial recovery time protocols provide valid methods of determining CP but not W' in cycling.

Warm-Up Strategies for Sport and Exercise: Mechanisms and Applications

It is widely accepted that warming-up prior to exercise is vital for the attainment of optimum performance. Both passive and active warm-up can evoke temperature, metabolic, neural and psychology-related effects, including increased anaerobic metabolism, elevated oxygen uptake kinetics and post-activation potentiation. Passive warm-up can increase body temperature without depleting energy substrate stores, as occurs during the physical activity associated with active warm-up. While the use of passive warm-up alone is not commonplace, the idea of utilizing passive warming techniques to maintain elevated core and muscle temperature throughout the transition phase (the period between completion of the warm-up and the start of the event) is gaining in popularity. Active warm-up induces greater metabolic changes, leading to increased preparedness for a subsequent exercise task. Until recently, only modest scientific evidence was available supporting the effectiveness of pre-competition warm-ups, with early studies often containing relatively few participants and focusing mostly on physiological rather than performance-related changes. External issues faced by athletes pre-competition, including access to equipment and the length of the transition/marshalling phase, have also frequently been overlooked. Consequently, warm-up strategies have continued to develop largely on a trial-and-error basis, utilizing coach and athlete experiences rather than scientific evidence. However, over the past decade or so, new research has emerged, providing greater insight into how and why warm-up influences subsequent performance. This review identifies potential physiological mechanisms underpinning warm-ups and how they can affect subsequent exercise performance, and provides recommendations for warm-up strategy design for specific individual and team sports.

The mechanistic bases of the power-time relationship: muscle metabolic responses and relationships to muscle fibre type

KEY POINTS

The power-asymptote (critical power; CP) of the hyperbolic power-time relationship for high-intensity exercise defines a threshold between steady-state and non-steady-state exercise intensities and the curvature constant (W') indicates a fixed capacity for work >CP that is related to a loss of muscular efficiency. The present study reports novel evidence on the muscle metabolic underpinnings of CP and W' during whole-body exercise and their relationships to muscle fibre type. We show that the W' is not correlated with muscle fibre type distribution and that it represents an elevated energy contribution from both oxidative and glycolytic/glycogenolytic metabolism. We show that there is a positive correlation between CP and highly oxidative type I muscle fibres and that muscle metabolic steady-state is attainable <CP but not >CP. Our findings indicate a mechanistic link between the bioenergetic characteristics of muscle fibre types and the power-time relationship for high-intensity exercise.

ABSTRACT

We hypothesized that: (1) the critical power (CP) will represent a boundary separating steady-state from non-steady-state muscle metabolic responses during whole-body exercise and (2) that the CP and the curvature constant (W') of the power-time relationship for high-intensity exercise will be correlated with type I and type IIx muscle fibre distributions, respectively. Four men and four women performed a 3 min all-out cycling test for the estimation of CP and constant work rate (CWR) tests slightly >CP until exhaustion (Tlim ), slightly <CP for 24 min and until the >CP Tlim isotime to test the first hypothesis. Eleven men performed 3 min all-out tests and donated muscle biopsies to test the second hypothesis. Below CP, muscle [PCr] [42.6 ± 7.1 vs. 49.4 ± 6.9 mmol (kg d.w.)(-1) ], [La(-) ] [34.8 ± 12.6 vs. 35.5 ± 13.2 mmol (kg d.w.)(-1) ] and pH (7.11 ± 0.08 vs. 7.10 ± 0.11) remained stable between ∼12 and 24 min (P > 0.05 for all), whereas these variables changed with time >CP such that they were greater [[La(-) ] 95.6 ± 14.1 mmol (kg d.w.)(-1) ] and lower [[PCr] 24.2 ± 3.9 mmol (kg d.w.)(-1) ; pH 6.84 ± 0.06] (P < 0.05) at Tlim (740 ± 186 s) than during the <CP trial. The CP (234 ± 53 W) was correlated with muscle type I (r = 0.67, P = 0.025) and inversely correlated with muscle type IIx fibre proportion (r = -0.76, P = 0.01). There was no relationship between W' (19.4 ± 6.3 kJ) and muscle fibre type. These data indicate a mechanistic link between the bioenergetic characteristics of different muscle fibre types and the power-duration relationship. The CP reflects the bioenergetic characteristics of highly oxidative type I muscle fibres, such that a muscle metabolic steady-state is attainable below and not above CP.

Measurement of Exercise Tolerance before Surgery (METS) study: a protocol for an international multicentre prospective cohort study of cardiopulmonary exercise testing prior to major non-cardiac surgery

INTRODUCTION

Preoperative functional capacity is considered an important risk factor for cardiovascular and other complications of major non-cardiac surgery. Nonetheless, the usual approach for estimating preoperative functional capacity, namely doctors' subjective assessment, may not accurately predict postoperative morbidity or mortality. 3 possible alternatives are cardiopulmonary exercise testing; the Duke Activity Status Index, a standardised questionnaire for estimating functional capacity; and the serum concentration of N-terminal pro-B-type natriuretic peptide (NT pro-BNP), a biomarker for heart failure and cardiac ischaemia.

METHODS AND ANALYSIS

The Measurement of Exercise Tolerance before Surgery (METS) Study is a multicentre prospective cohort study of patients undergoing major elective non-cardiac surgery at 25 participating study sites in Australia, Canada, New Zealand and the UK. We aim to recruit 1723 participants. Prior to surgery, participants undergo symptom-limited cardiopulmonary exercise testing on a cycle ergometer, complete the Duke Activity Status Index questionnaire, undergo blood sampling to measure serum NT pro-BNP concentration and have their functional capacity subjectively assessed by their responsible doctors. Participants are followed for 1 year after surgery to assess vital status, postoperative complications and general health utilities. The primary outcome is all-cause death or non-fatal myocardial infarction within 30 days after surgery, and the secondary outcome is all-cause death within 1 year after surgery. Both receiver-operating-characteristic curve methods and risk reclassification table methods will be used to compare the prognostic accuracy of preoperative subjective assessment, peak oxygen consumption during cardiopulmonary exercise testing, Duke Activity Status Index scores and serum NT pro-BNP concentration.

ETHICS AND DISSEMINATION

The METS Study has received research ethics board approval at all sites. Participant recruitment began in March 2013, and 1-year follow-up is expected to finish in 2016. Publication of the results of the METS Study is anticipated to occur in 2017.

Physiological responses at the lactate-minimum-intensity with and without prior high-intensity exercise

This study examined the physiological responses during exercise-to-exhaustion at the lactate-minimum-intensity with and without prior high-intensity exercise. Eleven recreationally trained males performed a graded exercise test, a lactate minimum test and two constant-load tests at lactate-minimum-intensity until exhaustion, which were applied with or without prior hyperlactatemia induction (i.e., 30-s Wingate test). The physiological responses were significantly different (P < 0.05) between constant-load tests for pulmonary ventilation ([Formula: see text]), blood-lactate-concentration ([La(-)]), pH, bicarbonate concentration ([HCO3]) and partial pressure of carbon dioxide during the initial minutes. The comparisons within constant-load tests showed steady state behaviour for oxygen uptake and the respiratory exchange ratio, but heart rate and rating of perceived exertion increased significantly during both exercise conditions, while the [Formula: see text] increased only during constant-load effort. During effort performed after high-intensity exercise: [Formula: see text], [La(-)], pH and [HCO3] differed at the start of exercise compared to another condition but were similar at the end (P > 0.05). In conclusion, the constant-load exercises performed at lactate-minimum-intensity with or without prior high-intensity exercise did not lead to the steady state of all analysed parameters; however, variables such as [La(-)], pH and [HCO3] - altered at the beginning of effort performed after high-intensity exercise - were reestablished after approximately 30 min of exercise.

The effect of resting blood flow occlusion on exercise tolerance and W'

It has previously been postulated that the anaerobic work capacity (W') may be utilized during resting blood flow occlusion in the absence of mechanical work. We tested the hypothesis that W' would not be utilized during an initial range of time following the onset of resting blood flow occlusion, after which W' would be utilized progressively more. Seven men completed blood flow occlusion constant power severe intensity handgrip exercise to task failure following 0, 300, 600, 900, and 1,200 s of resting blood flow occlusion. The work performed above critical power (CP) was not significantly different between the 0-, 300-, and 600-s conditions and was not significantly different from the total W' available. Significantly less work was performed above CP during the 1,200-s condition than the 900-s condition (P < 0.05), while both conditions were significantly less than the 0-, 300-, and 600-s conditions (P < 0.05). The work performed above CP during these conditions was significantly less than the total W' available (P < 0.05). The utilization of W' during resting blood flow occlusion did not begin until 751 ± 118 s, after which time W' was progressively utilized. The current findings demonstrate that W' is not utilized during the initial ∼751 s of resting blood flow occlusion, but is progressively utilized thereafter, despite no mechanical work being performed. Thus, the utilization of W' is not exclusive to exercise, and a constant amount of work that can be performed above CP is not the determining mechanism of W'.

Influence of blood flow occlusion on muscle oxygenation characteristics and the parameters of the power-duration relationship

It was previously (Monod H, Scherrer J. Ergonomics 8: 329-338, 1965) postulated that blood flow occlusion during exercise would reduce critical power (CP) to 0 Watts (W), while not altering the curvature constant (W'). We empirically assessed the influence of blood flow occlusion on CP, W', and muscle oxygenation characteristics. Ten healthy men (age: 24.8 ± 2.6 yr; height: 180 ± 5 cm; weight: 84.6 ± 10.1 kg) completed four constant-power handgrip exercise tests during both control blood flow (control) and blood flow occlusion (occlusion) for the determination of the power-duration relationship. Occlusion CP (-0.7 ± 0.4 W) was significantly (P < 0.001) lower than control CP (4.1 ± 0.7 W) and significantly (P < 0.001) lower than 0 W. Occlusion W' (808 ± 155 J) was significantly (P < 0.001) different from control W' (558 ± 129 J), and all 10 subjects demonstrated an increased occlusion W' with a mean increase of ∼49%. The present findings support the aerobic nature of CP. The findings also demonstrate that the amount of work that can be performed above CP is constant for a given condition, but can vary across conditions. Moreover, this amount of work that can be performed above CP does not appear to be the determinant of W', but rather a consequence of the depletion of intramuscular energy stores and/or the accumulation of fatigue-inducing metabolites, which limit exercise tolerance and determine W'.

Prior upper body exercise reduces cycling work capacity but not critical power

PURPOSE

This study examined whether metabolite accumulation, induced by prior upper body exercise, affected the power-duration relationship for leg cycle ergometry.

METHODS

Seven males performed, to the limit of tolerance and both without (L) and with (AL) prior severe-intensity arm-cranking exercise, an incremental cycling test and four constant power cycling tests to determine the parameters of the power-duration relationship: critical power (CP) and W'.

RESULTS

At the onset of cycling exercise plasma lactate (L vs AL: 1.2 ± 0.1 vs 11.6 ± 2.9 mEq · L) and hydrogen ion (40.4 ± 1.3 vs 53.1 ± 4.3 nEq · L), concentrations were higher during AL compared with L, whereas the strong ion difference (37.8 ± 1.8 vs 32.4 ± 2.0 mEq · L) and bicarbonate concentration (25.7 ± 0.7 vs 18.3 ± 1.9 mEq · L) were lower during AL compared with L (P < 0.01). During incremental exercise, maximum cycling power (358 ± 15 vs 332 ± 21 W) and peak oxygen uptake (VO2peak) (4.31 ± 0.36 vs 3.71 ± 0.44 L · min) were lower during AL compared with L (P < 0.05). The rate of increase in plasma potassium concentration during constant power cycling was greater during AL compared with L (0.09 ± 0.08 vs 0.14 ± 0.13 mEq · L · min) (P < 0.05), and exercise duration was 35 ± 15% shorter (P < 0.01). CP was not different between L and AL (267 ± 19 vs 264 ± 20 W), whereas W' was lower in AL (17.3 ± 5.7 vs 11.8 ± 4.2 kJ) (P < 0.01).

CONCLUSION

The reduced W' after prior upper body exercise indicates that the magnitude of W' is partly dependent on metabolite accumulation.

Prior heavy-intensity exercise's enhancement of oxygen-uptake kinetics and short-term high-intensity exercise performance independent of aerobic-training status

Prior high-intensity exercise can improve exercise performance during severe-intensity exercise. These positive alterations have been attributed, at least in part, to enhancement of overall oxygen-uptake (VO2) kinetics.

PURPOSE

To determine the effects of prior heavy-intensity exercise on VO2 kinetics and short-term high-intensity exercise performance in individuals with different aerobic-training statuses.

METHODS

Fifteen active subjects (UT; VO2max = 43.8 ± 6.3 mL · kg-1 · min-1) and 10 well-trained endurance cyclists (T; VO2max = 66.7 ± 6.7 mL · kg-1 · min-1) performed the following protocols: an incremental test to determine lactate threshold and VO2max, 4 maximal constant-load tests to estimate critical power, and two 3-min bouts of cycle exercise, involving 2 min of constant-work-rate exercise at severe intensity followed by a 1-min all-out sprint test. This trial was performed without prior intervention and 10 min after prior heavy-intensity exercise (ie, 6 min at 90% critical power).

RESULTS

The mean response time of VO2 was shortened after prior exercise for both UT (30.7 ± 9.2 vs 24.1 ± 7.2 s) and T (31.8 ± 5.2 vs 25.4 ± 4.3 s), but no group-by-condition interaction was detected. The end-sprint performance (ie, mean power output) was improved in both groups (UT ~4.7%, T ~2.0%; P < .05) by prior exercise.

CONCLUSION

The effect of prior heavy-intensity exercise on overall VO2 kinetics and short-term high-intensity exercise performance is independent of aerobic-training status.

The effect of prior upper body exercise on subsequent wingate performance

It has been reported previously that the upper body musculature is continually active during high intensity cycle ergometry. The aim of this study was to examine the effects of prior upper body exercise on subsequent Wingate (WAnT) performance. Eleven recreationally active males (20.8 ± 2.2 yrs; 77.7 ± 12.0 kg; 1.79 ± 0.04 m) completed two trials in a randomised order. In one trial participants completed 2 × 30 s WAnT tests (WAnT1 and WAnT2) with a 6 min recovery period; in the other trial, this protocol was preceded with 4 sets of biceps curls to induce localised arm fatigue. Prior upper body exercise was found to have a statistically significant detrimental effect on peak power output (PPO) during WAnT1 (P < 0.05) but no effect was observed for mean power output (MPO) (P > 0.05). Handgrip (HG) strength was also found to be significantly lower following the upper body exercise. These results demonstrate that the upper body is meaningfully involved in the generation of leg power during intense cycling.

Influence of prior exercise on VO2 kinetics subsequent exhaustive rowing performance

Prior exercise has the potential to enhance subsequent performance by accelerating the oxygen uptake (VO₂) kinetics. The present study investigated the effects of two different intensities of prior exercise on pulmonary VO₂ kinetics and exercise time during subsequent exhaustive rowing exercise. It was hypothesized that in prior heavy, but not prior moderate exercise condition, overall VO₂ kinetics would be faster and the VO₂ primary amplitude would be higher, leading to longer exercise time at VO_2max. Six subjects (mean ± SD; age: 22.9±4.5 yr; height: 181.2±7.1 cm and body mass: 75.5±3.4 kg) completed square-wave transitions to 100% of VO_2max from three different conditions: without prior exercise, with prior moderate and heavy exercise. VO₂ was measured using a telemetric portable gas analyser (K4b², Cosmed, Rome, Italy) and the data were modelled using either mono or double exponential fittings. The use of prior moderate exercise resulted in a faster VO₂ pulmonary kinetics response (τ₁ = 13.41±3.96 s), an improved performance in the time to exhaustion (238.8±50.2 s) and similar blood lactate concentrations ([La⁻]) values (11.8±1.7 mmol.L⁻¹) compared to the condition without prior exercise (16.0±5.56 s, 215.3±60.1 s and 10.7±1.2 mmol.L⁻¹, for τ₁, time sustained at VO_2max and [La⁻], respectively). Performance of prior heavy exercise, although useful in accelerating the VO₂ pulmonary kinetics response during a subsequent time to exhaustion exercise (τ₁ = 9.18±1.60 s), resulted in a shorter time sustained at VO_2max (155.5±46.0 s), while [La⁻] was similar (13.5±1.7 mmol.L⁻¹) compared to the other two conditions. Although both prior moderate and heavy exercise resulted in a faster pulmonary VO₂ kinetics response, only prior moderate exercise lead to improved rowing performance.

Influence of duty cycle on the power-duration relationship: observations and potential mechanisms

The highest sustainable rate of aerobic metabolism [critical power (CP)] and the finite amount of work that can be performed above CP (W' [curvature constant]) were determined under two muscle contraction duty cycles. Eight men completed at least three constant-power handgrip tests to exhaustion to determine CP and W' for 50% and 20% duty cycles, while brachial artery blood flow (Q̇BA) and deoxygenated-[hemoglobin + myoglobin] (deoxy-[Hb+Mb]) were measured. CP was lower for the 50% duty cycle (3.9 ± 0.9 W) than the 20% duty cycle (5.1 ± 0.8 W; p < 0.001), while W' was not significantly different (50% duty cycle: 452 ± 141 J vs. 20% duty cycle: 432 ± 130 J; p > 0.05). At the same power output, Q̇BA and deoxy-[Hb + Mb] achieved higher end-exercise values for the 20% duty cycle (9.87 ± 1.73 ml·s(-1); 51.7 ± 4.7 μM) than the 50% duty cycle (7.37 ± 1.76 ml·s(-1), p < 0.001; 44.3 ± 2.4 μM, p < 0.03). These findings indicate that blood flow influences CP, but not W'.

Application of the speed-duration relationship to normalize the intensity of high-intensity interval training

The tolerable duration of continuous high-intensity exercise is determined by the hyperbolic Speed-tolerable duration (S-tLIM) relationship. However, application of the S-tLIM relationship to normalize the intensity of High-Intensity Interval Training (HIIT) has yet to be considered, with this the aim of present study. Subjects completed a ramp-incremental test, and series of 4 constant-speed tests to determine the S-tLIM relationship. A sub-group of subjects (n = 8) then repeated 4 min bouts of exercise at the speeds predicted to induce intolerance at 4 min (WR4), 6 min (WR6) and 8 min (WR8), interspersed with bouts of 4 min recovery, to the point of exercise intolerance (fixed WR HIIT) on different days, with the aim of establishing the work rate that could be sustained for 960 s (i.e. 4×4 min). A sub-group of subjects (n = 6) also completed 4 bouts of exercise interspersed with 4 min recovery, with each bout continued to the point of exercise intolerance (maximal HIIT) to determine the appropriate protocol for maximizing the amount of high-intensity work that can be completed during 4×4 min HIIT. For fixed WR HIIT tLIM of HIIT sessions was 399±81 s for WR4, 892±181 s for WR6 and 1517±346 s for WR8, with total exercise durations all significantly different from each other (P<0.050). For maximal HIIT, there was no difference in tLIM of each of the 4 bouts (Bout 1: 229±27 s; Bout 2: 262±37 s; Bout 3: 235±49 s; Bout 4: 235±53 s; P>0.050). However, there was significantly less high-intensity work completed during bouts 2 (153.5±40. 9 m), 3 (136.9±38.9 m), and 4 (136.7±39.3 m), compared with bout 1 (264.9±58.7 m; P>0.050). These data establish that WR6 provides the appropriate work rate to normalize the intensity of HIIT between subjects. Maximal HIIT provides a protocol which allows the relative contribution of the work rate profile to physiological adaptations to be considered during alternative intensity-matched HIIT protocols.

Exercise: Kinetic considerations for gas exchange

The activities of daily living typically occur at metabolic rates below the maximum rate of aerobic energy production. Such activity is characteristic of the nonsteady state, where energy demands, and consequential physiological responses, are in constant flux. The dynamics of the integrated physiological processes during these activities determine the degree to which exercise can be supported through rates of O₂ utilization and CO₂ clearance appropriate for their demands and, as such, provide a physiological framework for the notion of exercise intensity. The rate at which O₂ exchange responds to meet the changing energy demands of exercise--its kinetics--is dependent on the ability of the pulmonary, circulatory, and muscle bioenergetic systems to respond appropriately. Slow response kinetics in pulmonary O₂ uptake predispose toward a greater necessity for substrate-level energy supply, processes that are limited in their capacity, challenge system homeostasis and hence contribute to exercise intolerance. This review provides a physiological systems perspective of pulmonary gas exchange kinetics: from an integrative view on the control of muscle oxygen consumption kinetics to the dissociation of cellular respiration from its pulmonary expression by the circulatory dynamics and the gas capacitance of the lungs, blood, and tissues. The intensity dependence of gas exchange kinetics is discussed in relation to constant, intermittent, and ramped work rate changes. The influence of heterogeneity in the kinetic matching of O₂ delivery to utilization is presented in reference to exercise tolerance in endurance-trained athletes, the elderly, and patients with chronic heart or lung disease.

The effect of priming exercise on O2 uptake kinetics, muscle O2 delivery and utilization, muscle activity, and exercise tolerance in boys

This study used priming exercise in young boys to investigate (i) how muscle oxygen delivery and oxygen utilization, and muscle activity modulate oxygen uptake kinetics during exercise; and (ii) whether the accelerated oxygen uptake kinetics following priming exercise can improve exercise tolerance. Seven boys that were aged 11.3 ± 1.6 years completed either a single bout (bout 1) or repeated bouts with 6 min of recovery (bout 2) of very heavy-intensity cycling exercise. During the tests oxygen uptake, muscle oxygenation, muscle electrical activity and exercise tolerance were measured. Priming exercise most likely shortened the oxygen uptake mean response time (change, ±90% confidence limits; -8.0 s, ±3.0), possibly increased the phase II oxygen uptake amplitude (0.11 L·min(-1), ±0.09) and very likely reduced the oxygen uptake slow component amplitude (-0.08 L·min(-1), ±0.07). Priming resulted in a likely reduction in integrated electromyography (-24% baseline, ±21% and -25% baseline, ±19) and a very likely reduction in Δ deoxyhaemoglobin/Δoxygen uptake (-0.16, ±0.11 and -0.09, ±0.05) over the phase II and slow component portions of the oxygen uptake response, respectively. A correlation was present between the change in tissue oxygenation index during bout 2 and the change in the phase II (r = -0.72, likely negative) and slow component (r = 0.72, likely positive) oxygen uptake amplitudes following priming exercise, but not for muscle activity. Exercise tolerance was likely reduced (change -177 s, ±180) following priming exercise. The altered phase II and slow component oxygen uptake amplitudes in boys following priming exercise are linked to an improved localised matching of muscle oxygen delivery to oxygen uptake and not muscle electrical activity. Despite more rapid oxygen uptake kinetics following priming exercise, exercise tolerance was not enhanced.

Determining Anaerobic Capacity in Sporting Activities

Anaerobic capacity/anaerobically attributable power is an important parameter for athletic performance, not only for short high-intensity activities but also for breakaway efforts and end spurts during endurance events. Unlike aerobic capacity, anaerobic capacity cannot be easily quantified. The 3 most commonly used methodologies to quantify anaerobic capacity are the maximal accumulated oxygen deficit method, the critical power concept, and the gross efficiency method. This review describes these methods, evaluates if they result in similar estimates of anaerobic capacity, and highlights how anaerobic capacity is used during sporting activities. All 3 methods have their own strengths and weaknesses and result in more or less similar estimates of anaerobic capacity but cannot be used interchangeably. The method of choice depends on the research question or practical goal.

Modeling the expenditure and reconstitution of work capacity above critical power

PURPOSE

The critical power (CP) model includes two constants: the CP and the W' [P = (W' / t) + CP]. The W' is the finite work capacity available above CP. Power output above CP results in depletion of the W' complete depletion of the W' results in exhaustion. Monitoring the W' may be valuable to athletes during training and competition. Our purpose was to develop a function describing the dynamic state of the W' during intermittent exercise.

METHODS

After determination of V˙O(2max), CP, and W', seven subjects completed four separate exercise tests on a cycle ergometer on different days. Each protocol comprised a set of intervals: 60 s at a severe power output, followed by 30-s recovery at a lower prescribed power output. The intervals were repeated until exhaustion. These data were entered into a continuous equation predicting balance of W' remaining, assuming exponential reconstitution of the W'. The time constant was varied by an iterative process until the remaining modeled W' = 0 at the point of exhaustion.

RESULTS

The time constants of W' recharge were negatively correlated with the difference between sub-CP recovery power and CP. The relationship was best fit by an exponential (r = 0.77). The model-predicted W' balance correlated with the temporal course of the rise in V˙O(2) (r = 0.82-0.96). The model accurately predicted exhaustion of the W' in a competitive cyclist during a road race.

CONCLUSIONS

We have developed a function to track the dynamic state of the W' during intermittent exercise. This may have important implications for the planning and real-time monitoring of athletic performance.

A single test for the determination of parameters of the speed-time relationship for running

A validated expeditious method is needed to determine critical speed (CS) and the finite distance that can be covered above CS (D'). We tested the hypothesis that a single all-out 3-min running test would accurately determine CS and D'. Seven healthy subjects completed three constant-speed runs on a treadmill for the determination of CS and D', as well as an all-out 3-min test on a track for the determination of end-test speed (ES) and the distance above end-test speed (DES). ES (13.4 ± 2.8 km h(-1)) was not significantly different from the speed-1/time model CS (13.3 ± 2.8 km h(-1)). While DES (141 ± 34 m) was not significantly different from D' (204 ± 103 m), it underestimated D' in 5 of 7 subjects. Thus, the speed-1/time model CS can be accurately determined using a single 3-min test, while caution should be used in relating DES to D'.

Effect of aerobic training status on both maximal lactate steady state and critical power

This study aimed at assessing the sensitivity of both maximal lactate steady state (MLSS) and critical power (CP) in populations of different aerobic training status to ascertain whether CP is as sensitive as MLSS to a change in aerobic fitness. Seven untrained subjects (UT) (maximal oxygen uptake = 37.4 ± 6.5 mL·kg–1·min–1) and 7 endurance cyclists (T) (maximal oxygen uptake = 62.4 ± 5.2 mL·kg–1·min–1) performed an incremental test for maximal oxygen uptake estimation and several constant work rate tests for MLSS and CP determination. MLSS, whether expressed in mL·kg–1·min–1 (T: 51.8 ± 5.7 vs. UT: 29.0 ± 6.1) or % maximal oxygen uptake (T: 83.1 ± 6.8 vs. UT: 77.1 ± 4.5), was significantly higher in the T group. CP expressed in mL·kg–1·min–1 (T: 56.8 ± 5.1 vs. UT: 33.1 ± 6.3) was significantly higher in the T group as well but no difference was found when expressed in % maximal oxygen uptake (T: 91.1 ± 4.8 vs. UT: 88.3 ± 3.6). Whether expressed in absolute or relative values, MLSS is sensitive to aerobic training status and a good measure of aerobic endurance. Conversely, the improvement in CP with years of training is proportional to those of maximal oxygen uptake. Thus, CP might be less sensitive than MLSS for depicting an enhancement in aerobic fitness.

Improvement of 800-m running performance with prior high-intensity exercise

Prior high-intensity exercise increases the oxidative energy contribution to subsequent exercise and may enhance exercise tolerance. The potential impact of a high-intensity warm-up on competitive performance, however, has not been investigated.

PURPOSE

To test the hypothesis that a high-intensity warm-up would speed VO2 kinetics and enhance 800-m running performance in well-trained athletes.

METHODS

Eleven highly trained middle-distance runners completed two 800-m time trials on separate days on an indoor track, preceded by 2 different warm-up procedures. The 800-m time trials were preceded by a 10-min self-paced jog and standardized mobility drills, followed by either 6 × 50-m strides (control [CON]) or 2 × 50-m strides and a continuous high-intensity 200-m run (HWU) at race pace. Blood [La] was measured before the time trials, and VO2 was measured breath by breath throughout exercise.

RESULTS

800-m time-trial performance was significantly faster after HWU (124.5 ± 8.3 vs CON, 125.7 ± 8.7 s, P < .05). Blood [La] was greater after HWU (3.6 ± 1.9 vs CON, 1.7 ± 0.8 mM; P < .01). The mean response time for VO2 was not different between conditions (HWU, 27 ± 6 vs CON, 28 ± 7 s), but total O2 consumed (HWU, 119 ± 18 vs CON, 109 ± 28 ml/kg, P = .05) and peak VO2 attained (HWU, 4.21 ± 0.85 vs CON, 3.91 ± 0.63 L/min; P = .08) tended to be greater after HWU.

CONCLUSIONS

These data indicate that a sustained high-intensity warm-up enhances 800-m time-trial performance in trained athletes.

Slow component of VO2 kinetics: mechanistic bases and practical applications

The V·O₂ slow component, a slowly developing increase in V·O₂ during constant-work-rate exercise performed above the lactate threshold, represents a progressive loss of skeletal muscle contractile efficiency and is associated with the fatigue process. This brief review outlines the current state of knowledge concerning the mechanistic bases of the V·O₂ slow component and describes practical interventions that can attenuate the slow component and thus enhance exercise tolerance. There is strong evidence that, during constant-work-rate exercise, the development of the V·O₂ slow component is associated with the progressive recruitment of additional (type II) muscle fibers that are presumed to have lower efficiency. Recent studies, however, indicate that muscle efficiency is also lowered (resulting in a "mirror-image" V·O₂ slow component) during fatiguing, high-intensity exercise in which additional fiber recruitment is unlikely or impossible. Therefore, it seems that muscle fatigue underpins the V·O₂ slow component, although the greater fatigue sensitivity of recruited type II fibers might still play a crucial role in the loss of muscle efficiency in both situations. Several interventions can reduce the magnitude of the V·O₂ slow component, and these are typically associated with an enhanced exercise tolerance. These include endurance training, inspiratory muscle training, priming exercise, dietary nitrate supplementation, and the inspiration of hyperoxic gas. All of these interventions reduce muscle fatigue development either by improving muscle oxidative capacity and thus metabolic stability or by enhancing bulk muscle O2 delivery or local Q·O₂-to-V·O₂ matching. Future honing of these interventions to maximize their impact on the V·O₂ slow component might improve sports performance in athletes and exercise tolerance in the elderly or in patient populations.

Application of critical power in sport

The critical power (CP) is mathematically defined as the power-asymptote of the hyperbolic relationship between power output and time-to-exhaustion. Physiologically, the CP represents the boundary between the steady-state and nonsteady state exercise intensity domains and therefore may provide a more meaningful index of performance than other well-known landmarks of aerobic fitness such as the lactate threshold and the maximal O2 uptake. Despite the potential importance to sports performance, the CP is often misinterpreted as a purely mathematical construct which lacks physiological meaning and only in recent years has this concept begun to emerge as valid and useful technique for monitoring endurance fitness. This commentary defines the basic principles of the CP concept, outlines its importance to high-intensity exercise performance, and provides an overview of the current methods available for its assessment. Interventions including training, pacing and prior exercise can be used to alter the parameters of the power-time relationship. A future challenge lies in optimizing such interventions in order to positively affect the parameters of the power-time relationship and thereby enhance sports performance in specific events.

Influence of moderate hypoxia on tolerance to high-intensity exercise

It remains uncertain as how the reduction in systemic oxygen transport limits high-intensity exercise tolerance. 11 participants (5 males; age 35 ± 10 years; peak [Formula: see text] 3.5 ± 0.4 L min(-1)) performed cycle ergometry to the limit of tolerance: (1) a ramp test to determine ventilatory threshold (VT) and peak [Formula: see text]; (2) three to four constant-load tests in order to model the linear P-t (-1) relationship for estimation of intercept (critical power; CP) and slope (AWC). All tests were performed in a random order under moderate hypoxia (FiO(2) = 0.15) and normoxia. The linearity of the P-t (-1) relationship was retained under hypoxia, with a systematic reduction in CP (220 ± 25 W vs. 190 ± 28 W; P < 0.01) but no significant difference in AWC (11.7 ± 5.5 kJ vs. 12.1 ± 4.4 kJ; P > 0.05). However, large individual variations in the change of the latter were observed (-36 to +66%). A significant relationship was found between the % change in CP (r = 0.80, P < 0.01) and both peak [Formula: see text] (CP: r = -0.65, P < 0.05) and VT values recorded under normoxia (CP: r = -0.65, P < 0.05). The present study demonstrates the aerobic nature of the intercept of the P-t (-1) relationship, i.e. CP. However, the extreme within-individual changes in AWC do not support the original assumption that AWC reflects a finite energy store. Lower hypoxia-induced decrements in CP were observed in aerobically fitter participants. This study also demonstrates the greater ability these participants have to exercise at supra-CP but close to CP workloads under moderate hypoxia.

Pulmonary O2 uptake kinetics as a determinant of high-intensity exercise tolerance in humans

Tolerance to high-intensity constant-power (P) exercise is well described by a hyperbola with two parameters: a curvature constant (W') and power asymptote termed "critical power" (CP). Since the ability to sustain exercise is closely related to the ability to meet the ATP demand in a steady state, we reasoned that pulmonary O(2) uptake (Vo(2)) kinetics would relate to the P-tolerable duration (t(lim)) parameters. We hypothesized that 1) the fundamental time constant (τVo(2)) would relate inversely to CP; and 2) the slow-component magnitude (ΔVo(2sc)) would relate directly to W'. Fourteen healthy men performed cycle ergometry protocols to the limit of tolerance: 1) an incremental ramp test; 2) a series of constant-P tests to determine Vo(2max), CP, and W'; and 3) repeated constant-P tests (WR(6)) normalized to a 6 min t(lim) for τVo(2) and ΔVo(2sc) estimation. The WR(6) t(lim) averaged 365 ± 16 s, and Vo(2max) (4.18 ± 0.49 l/min) was achieved in every case. CP (range: 171-294 W) was inversely correlated with τVo(2) (18-38 s; R(2) = 0.90), and W' (12.8-29.9 kJ) was directly correlated with ΔVo(2sc) (0.42-0.96 l/min; R(2) = 0.76). These findings support the notions that 1) rapid Vo(2) adaptation at exercise onset allows a steady state to be achieved at higher work rates compared with when Vo(2) kinetics are slower; and 2) exercise exceeding this limit initiates a "fatigue cascade" linking W' to a progressive increase in the O(2) cost of power production (Vo(2sc)), which, if continued, results in attainment of Vo(2max) and exercise intolerance. Collectively, these data implicate Vo(2) kinetics as a key determinant of high-intensity exercise tolerance in humans.