Oxygen uptake dynamics: from muscle to mouth--an introduction to the symposium

Modelling the optimization of world-class 400 m and 1,500 m running performances using high-resolution data

The 400 m and 1,500 m are track events that rely on different but important contributions from both the aerobic and anaerobic energy systems. The purpose of this study is to model men's and women's 400 m and 1,500 m championship performances to gain a deeper understanding of the key mechanical and physiological factors affecting running speed and bend running using high-resolution data from live competition (10 Hz). To investigate World-class athletes' instantaneous speeds, propulsive forces and aerobic and anaerobic energy, we model and simulate the performances of the men's and women's European Athletics 400 m champions, Matthew Hudson-Smith and Femke Bol, as well as the men's European Athletics 1,500 m champion, Jakob Ingebrigtsen, and the women's European Athletics U23 1,500 m champion, Gaia Sabbatini. The simulations show that a fast start is essential in both the 400 m and 1,500 m because of the need for fast oxygen kinetics, with peak running speeds occurring within the first ∼50 m in both events. Subsequently, 400 m athletes slow continually from this maximum speed to the finish, and a total anaerobic contribution of ∼77% is found for both male and female champions. The key to faster 400 m racing is to reduce the decrease in velocity: this comes from both a high VO2 and a high anaerobic contribution. Ingebrigtsen's winning tactic in the European 1,500 m final is to adopt a very fast cruising pace from 300 m onwards that is possible because he is able to maintain a high VO2 value until the end of the race and has a large anaerobic contribution. He has fast VO2 kinetics that does not require as fast a start as his opponents, but then he speeds up in the last two laps, without a fast sprint finish. The comparison between Sabbatini's slower and quicker races (∼8 s difference) shows that it is the improvement of aerobic metabolism that has the greatest effect on 1,500 m performance. Coaches should note in particular that the all-out pacing nature of the 400 m requires the prioritization of anaerobic energy system development, and those who coach the 1,500 m should note the differing energy contributions between even-paced races and championship racing.

Effect of Pulsed Electromagnetic Fields (PEMFs) on Muscular Activation during Cycling: A Single-Blind Controlled Pilot Study

PURPOSE

PEMF stimulation results in a higher O₂ muscle supply during exercise through increased O₂ release and uptake. Given the importance of oxygen uptake in sport activity, especially in aerobic disciplines such as cycling, we sought to investigate the influence of PEMF on muscle activity when subjects cycled at an intensity between low and severe.

METHODS

Twenty semi-professional cyclists performed a constant-load exercise with randomized active (ON) or inactive (OFF) PEMF stimulation. Each subject started the recording session with 1 min of cycling without load (warm-up), followed by an instantaneous increase in power, as the individualized workload (constant-load physical effort). PEMF loops were applied on the vastus medialis and biceps femoris of the right leg. We recorded the electromyographic activity from each muscle and measured blood lactate prior the exercise and during the constant-load physical effort.

RESULTS

PEMF stimulation caused a significant increase in muscle activity in the warm-up condition when subjects cycled without load (p < 0.001). The blood lactate concentration was higher during PEMF stimulation (p < 0.001), a possible consequence of PEMF's influence on glycolytic metabolism.

CONCLUSION

PEMF stimulation augmented the activity and the metabolism of muscular fibers during the execution of physical exercise. PEMF stimulation could be used to raise the amplitude of muscular responses to physical activity, especially during low-intensity exercise.

Prescription of High-intensity Aerobic Interval Training Based on Oxygen Uptake Kinetics

Endurance training results in diverse adaptations that lead to increased performance and health benefits. A commonly measured training response is the analysis of oxygen uptake kinetics, representing the demand of a determined load (speed/work) on the cardiovascular, respiratory, and metabolic systems, providing useful information for the prescription of constant load or interval-type aerobic exercise. There is evidence that during high-intensity aerobic exercise some interventions prescribe brief interval times (<1-min), which may lead to a dissociation between the load prescribed and the oxygen uptake demanded, potentially affecting training outcomes. Therefore, this review explored the time to achieve a close association between the speed/work prescribed and the oxygen uptake demanded after the onset of high-intensity aerobic exercise. The evidence assessed revealed that at least 80% of the oxygen uptake amplitude is reached when phase II of oxygen uptake kinetics is completed (1 to 2 minutes after the onset of exercise, depending on the training status). We propose that the minimum work-time during high-intensity aerobic interval training sessions should be at least 1 minute for athletes and 2 minutes for non-athletes. This suggestion could be used by coaches, physical trainers, clinicians and sports or health scientists for the prescription of high-intensity aerobic interval training.

The Effect of a Hydroxytyrosol-Rich, Olive-Derived Phytocomplex on Aerobic Exercise and Acute Recovery

There is current scientific interest in naturally sourced phenolic compounds and their potential benefits to health, as well as the effective role polyphenols may provide in an exercise setting. This study investigated the chronic effects of supplementation with a biodynamic and organic olive fruit water phytocomplex (OliPhenolia® [OliP]), rich in hydroxytyrosol (HT), on submaximal and exhaustive exercise performance and respiratory markers of recovery. Twenty-nine recreationally active participants (42 ± 2 yrs; 71.1 ± 2.1 kg; 1.76 ± 0.02 m) consumed 2 × 28 mL∙d−1 of OliP or a taste- and appearance-matched placebo (PL) over 16 consecutive days. Participants completed a demanding, aerobic exercise protocol at ~75% maximal oxygen uptake (V˙O2max) for 65 min 24 h before sub- and maximal performance exercise tests prior to and following the 16-day consumption period. OliP reduced the time constant (τ) (p = 0.005) at the onset of exercise, running economy (p = 0.015) at lactate threshold 1 (LT1), as well as the rating of perceived exertion (p = 0.003) at lactate turnpoint (LT2). Additionally, OliP led to modest improvements in acute recovery based upon a shorter time to achieve 50% of the end of exercise V˙O2 value (p = 0.02). Whilst OliP increased time to exhaustion (+4.1 ± 1.8%), this was not significantly different to PL (p > 0.05). Phenolic compounds present in OliP, including HT and related metabolites, may provide benefits for aerobic exercise and acute recovery in recreationally active individuals. Further research is needed to determine whether dose-response or adjunct use of OliP alongside longer-term training programs can further modulate exercise-associated adaptations in recreationally active individuals, or indeed support athletic performance.

Machine Learning Models for the Automatic Detection of Exercise Thresholds in Cardiopulmonary Exercising Tests: From Regression to Generation to Explanation

The cardiopulmonary exercise test (CPET) constitutes a gold standard for the assessment of an individual's cardiovascular fitness. A trend is emerging for the development of new machine-learning techniques applied to the automatic process of CPET data. Some of these focus on the precise task of detecting the exercise thresholds, which represent important physiological parameters. Three are the major challenges tackled by this contribution: (A) regression (i.e., the process of correctly identifying the exercise intensity domains and their crossing points); (B) generation (i.e., the process of artificially creating a CPET data file ex-novo); and (C) explanation (i.e., proving an interpretable explanation about the output of the machine learning model). The following methods were used for each challenge: (A) a convolutional neural network adapted for multi-variable time series; (B) a conditional generative adversarial neural network; and (C) visual explanations and calculations of model decisions have been conducted using cooperative game theory (Shapley's values). The results for the regression, generation, and explanatory techniques for AI-assisted CPET interpretation are presented here in a unique framework for the first time: (A) machine learning techniques reported an expert-level accuracy in the classification of exercise intensity domains; (B) experts are not able to substantially differentiate between a real vs an artificially generated CPET; and (C) Shapley's values can provide an explanation about the choices of the algorithms in terms of ventilatory variables. With the aim to increase their technology-readiness level, all the models discussed in this contribution have been incorporated into a free-to-use Python package called pyoxynet (ver. 12.1). This contribution should therefore be of interest to major players operating in the CPET device market and engineering.

Priming exercise accelerates oxygen uptake kinetics during high-intensity cycle exercise in middle-aged individuals with type 2 diabetes

Background: The primary phase time constant of pulmonary oxygen uptake kinetics (V · O 2 τ p) during submaximal efforts is longer in middle-aged people with type 2 diabetes (T2D), partly due to limitations in oxygen supply to active muscles. This study examined if a high-intensity "priming" exercise (PE) would speedV · O 2 τ p during a subsequent high-intensity cycling exercise in T2D due to enhanced oxygen delivery. Methods: Eleven (4 women) middle-aged individuals with type 2 diabetes and 11 (4 women) non-diabetic controls completed four separate cycling bouts each starting at an 'unloaded' baseline of 10 W and transitioning to a high-intensity constant-load. Two of the four cycling bouts were preceded by priming exercise. The dynamics of pulmonaryV · O 2 and muscle deoxygenation (i.e. deoxygenated haemoglobin and myoglobin concentration [HHb + Mb]), were calculated from breath-by-breath and near-infrared spectroscopy data at the vastus lateralis, respectively. Results: At baselineV · O 2 τ p, was slower (p < 0.001) in the type 2 diabetes group (48 ± 6 s) compared to the control group (34 ± 2 s) but priming exercise significantly reducedV · O 2 τ p (p < 0.001) in type 2 diabetes (32 ± 6 s) so that post priming exercise it was not different compared with controls (34 ± 3 s). Priming exercise reduced the amplitude of theV · O 2 slow component (As) in both groups (type 2 diabetes: 0.26 ± 0.11 to 0.16 ± 0.07 L/min; control: 0.33 ± 0.13 to 0.25 ± 0.14 L/min, p < 0.001), while [HHb + Mb] kinetics remained unchanged. Conclusion: These results suggest that in middle-aged men and women with T2D, PE speedsV · O 2 τ p likely by a better matching of O2 delivery to utilisation and reduces theV · O 2 As during a subsequent high-intensity exercise.

Capillary hemodynamics and contracting skeletal muscle oxygen pressures in male rats with heart failure: Impact of soluble guanylyl cyclase activator

In heart failure with reduced ejection fraction (HFrEF), nitric oxide-soluble guanylyl cyclase (sGC) pathway dysfunction impairs skeletal muscle arteriolar vasodilation and thus capillary hemodynamics, contributing to impaired oxygen uptake (V̇O2) kinetics. Targeting this pathway with sGC activators offers a new treatment approach to HFrEF. We tested the hypotheses that sGC activator administration would increase the O2 delivery (Q̇O2)-to-V̇O2 ratio in the skeletal muscle interstitial space (PO2is) of HFrEF rats during twitch contractions due, in part, to increases in red blood cell (RBC) flux (fRBC), velocity (VRBC), and capillary hematocrit (Hctcap). HFrEF was induced in male Sprague-Dawley rats via myocardial infarction. After 3 weeks, rats were treated with 0.3 mg/kg of the sGC activator BAY 60-2770 (HFrEF + BAY; n = 11) or solvent (HFrEF; n = 9) via gavage b.i.d for 5 days prior to phosphorescence quenching (PO2is, in contracting muscle) and intravital microscopy (resting) measurements in the spinotrapezius muscle. Intravital microscopy revealed higher fRBC (70 ± 9 vs 25 ± 8 RBC/s), VRBC (490 ± 43 vs 226 ± 35 μm/s), Hctcap (16 ± 1 vs 10 ± 1%) and a greater number of capillaries supporting flow (91 ± 3 vs 82 ± 3%) in HFrEF + BAY vs HFrEF (all P < 0.05). Additionally, PO2is was especially higher during 12-34s of contractions in HFrEF + BAY vs HFrEF (P < 0.05). Our findings suggest that sGC activators improved resting Q̇O2 via increased fRBC, VRBC, and Hctcap allowing for better Q̇O2-to-V̇O2 matching during the rest-contraction transient, supporting sGC activators as a potential therapeutic to target skeletal muscle vasomotor dysfunction in HFrEF.

Benchmarking occupational exoskeletons: An evidence mapping systematic review

OBJECTIVES

To provide an overview of protocols assessing the effect of occupational exoskeletons on users and to formulate recommendations towards a literature-based assessment framework to benchmark the effect of occupational exoskeletons on the user.

METHODS

PubMed (MEDLINE), Web of Science database and Scopus were searched (March 2, 2021). Studies were included if they investigated the effect of one or more occupational exoskeletons on the user.

RESULTS

In total, 139 eligible studies were identified, encompassing 33, 25 and 18 unique back, shoulder and other exoskeletons, respectively. Device validation was most frequently conducted using controlled tasks while collecting muscle activity and biomechanical data. As the exoskeleton concept matures, tasks became more applied and the experimental design more representative. With that change towards realistic testing environments came a trade-off with experimental control, and user experience data became more valuable.

DISCUSSION

This evidence mapping systematic review reveals that the assessment of occupational exoskeletons is a dynamic process, and provides literature-based assessment recommendations. The homogeneity and repeatability of future exoskeleton assessment experiments will increase following these recommendations. The current review recognises the value of variability in evaluation protocols in order to obtain an overall overview of the effect of exoskeletons on the users, but the presented framework strives to facilitate benchmarking the effect of occupational exoskeletons on the users across this variety of assessment protocols.

Steady-state [Formula: see text] above MLSS: evidence that critical speed better represents maximal metabolic steady state in well-trained runners

The metabolic boundary separating the heavy-intensity and severe-intensity exercise domains is of scientific and practical interest but there is controversy concerning whether the maximal lactate steady state (MLSS) or critical power (synonymous with critical speed, CS) better represents this boundary. We measured the running speeds at MLSS and CS and investigated their ability to discriminate speeds at which \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 was stable over time from speeds at which a steady-state \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 could not be established. Ten well-trained male distance runners completed 9–12 constant-speed treadmill tests, including 3–5 runs of up to 30-min duration for the assessment of MLSS and at least 4 runs performed to the limit of tolerance for assessment of CS. The running speeds at CS and MLSS were significantly different (16.4 ± 1.3 vs. 15.2 ± 0.9 km/h, respectively; P < 0.001). Blood lactate concentration was higher and increased with time at a speed 0.5 km/h higher than MLSS compared to MLSS (P < 0.01); however, pulmonary \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 did not change significantly between 10 and 30 min at either MLSS or MLSS + 0.5 km/h. In contrast, \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 increased significantly over time and reached \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2\,\,\max }$$\end{document}V˙O2max at end-exercise at a speed ~ 0.4 km/h above CS (P < 0.05) but remained stable at a speed ~ 0.5 km/h below CS. The stability of \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 at a speed exceeding MLSS suggests that MLSS underestimates the maximal metabolic steady state. These results indicate that CS more closely represents the maximal metabolic steady state when the latter is appropriately defined according to the ability to stabilise pulmonary \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.

Estimation of Metabolic Energy Expenditure during Short Walking Bouts

Assessment of metabolic energy expenditure from indirect calorimetry is currently limited to sustained (>4 min) cyclic activities, because of steady-state requirements. This is problematic for patient populations who are unable to perform such sustained activities. Therefore, this study explores validity and reliability of a method estimating metabolic energy expenditure based on oxygen consumption (V̇O₂) during short walking bouts. Twelve able-bodied adults twice performed six treadmill walking trials (1, 2 and 6 min at 4 and 5 km/h), while V̇O₂ was measured. Total V̇O₂ was calculated by integrating net V̇O₂ over walking and recovery. Concurrent validity with steady-state V̇O₂ was assessed with Pearson's correlations. Test-retest reliability was assessed using intra-class correlation coefficients (ICC) and Bland-Altman analyses. Total V̇O₂ was strongly correlated with steady-state V̇O₂ (r=0.91-0.99), but consistently higher. Test-retest reliability of total V̇O₂ (ICC=0.65-0.92) was lower than or comparable to steady-state V̇O₂ (ICC=0.83-0.92), with lower reliability for shorter trials. Total V̇O₂ discriminated between gait speeds. Total oxygen uptake provides a useful measure to estimate metabolic load of short activities from oxygen consumption. Although estimates are less reliable than steady-state measurements, they can provide insight in the yet unknown metabolic demands of daily activities for patient populations unable to perform sustained activities.

Time-course of V̇o2 kinetics responses during moderate-intensity exercise subsequent to HIIT versus moderate-intensity continuous training in type 2 diabetes

We assessed the time-course of changes in oxygen uptake (V̇o₂) and muscle deoxygenation (i.e., deoxygenated hemoglobin and myoglobin, [HHb + Mb]) kinetics during transitions to moderate-intensity cycling following 12 wk of low-volume high-intensity interval training (HIIT) vs. moderate-intensity continuous training (MICT) in adults with type 2 diabetes (T2D). Participants were randomly assigned to MICT (n = 10, 50 min of moderate-intensity cycling), HIIT (n = 9, 10 × 1 min at ∼90% maximal heart rate), or nonexercising control (n = 9) groups. Exercising groups trained three times per week, and measurements were taken every 3 wk. [HHb + Mb] kinetics were measured by near-infrared spectroscopy at the vastus lateralis muscle. The local matching of O₂ delivery to O₂ utilization was assessed by the Δ[HHb + Mb]/ΔV̇o₂ ratio. The pretraining time constant of the primary phase of V̇o₂ (τV̇o_2p) decreased (P < 0.05) at wk 3 of training in both MICT (from 44 ± 12 to 32 ± 5 s) and HIIT (from 42 ± 8 to 32 ± 4 s) with no further changes thereafter, whereas no changes were reported in controls. The pretraining overall dynamic response of muscle deoxygenation (τ'[HHb + Mb]) was faster than τV̇o_2p in all groups, resulting in Δ[HHb + Mb]/V̇o_2p showing a transient "overshoot" relative to the subsequent steady-state level. After 3 wk, the Δ[HHb + Mb]/V̇o_2p overshoot was eliminated only in the training groups, so that τ'[HHb + Mb] was not different to τV̇o_2p in MICT and HIIT. The enhanced V̇o₂ kinetics response consequent to both MICT and HIIT in T2D was likely attributed to a training-induced improvement in matching of O₂ delivery to utilization.NEW & NOTEWORTHY High-intensity interval training and moderate-intensity continuous training elicited faster pulmonary oxygen uptake (V̇o₂) kinetics during moderate-intensity cycling within 3 wk of training with no further changes thereafter in individuals with type 2 diabetes. These adaptations were accompanied by unaltered near-infrared spectroscopy-derived muscle deoxygenation (i.e. deoxygenated hemoglobin and myoglobin concentration, [HHb+Mb]) kinetics and transiently reduced Δ[HHb+Mb]-to-ΔV̇o₂ ratio, suggesting an enhanced blood flow distribution within the active muscles subsequent to both training interventions.

Validity of Heart Rate-Based Models for Estimating Oxygen Uptake During Tennis Play

Baiget, E, Iglesias, X, and Rodríguez, FA. Validity of heart rate-based models for estimating oxygen uptake during tennis play. J Strength Cond Res 34(11): 3208-3216, 2020-This study aimed to assess the validity of an on-court tennis test (specific endurance tennis test [SET-Test]) and 2 heart rate (HR)-based methods for estimating oxygen uptake (V[Combining Dot Above]O2) in competitive tennis players. Thirty-five male players performed a SET-Test to relate test duration (minutes) and V[Combining Dot Above]O2. Two weeks later, 16 players performed a simulated match play set where HR and V[Combining Dot Above]O2 (V[Combining Dot Above]O2-PLAY, criterion value) were measured and then compared with V[Combining Dot Above]O2 values predicted from the HR/V[Combining Dot Above]O2 linear regression equations derived from the SET-Test (pV[Combining Dot Above]O2-TEST) and from the one set match play (pV[Combining Dot Above]O2-PLAY). Test duration and V[Combining Dot Above]O2-TEST were strongly correlated (r = 0.821, p < 0.001, SEE = 5.6 ml·kg·min), indicating that SET-Test outcome is a somewhat good indicator of aerobic fitness in tennis players, likely to be useful for training purposes. pV[Combining Dot Above]O2-PLAY and V[Combining Dot Above]O2-PLAY (criterion value) were strongly correlated (r = 0.832, p < 0.001) and SEE was moderate (3.5 ml·kg·min = 11.5%). pV[Combining Dot Above]O2-TEST differed from the criterion (32.4 ± 10.7 vs. 30.8 ± 8.6 ml·kg·min, p < 0.001) and, although strongly correlated (r = 0.689, p < 0.001), an overestimation occurred (mean Δ = 1.6 ml·kg·min = 4.9%), yielding a high SEE (4.8 ml·kg·min = 15.6%). We conclude that (a) SET-Test performance is a valid and moderately accurate predictor of V[Combining Dot Above]O2; and (b) the individual HR-V[Combining Dot Above]O2 regression equation generated during tennis match play predicts V[Combining Dot Above]O2 with greater accuracy than the regression derived from the SET-Test.

Priming exercise accelerates pulmonary oxygen uptake kinetics during "work-to-work" cycle exercise in middle-aged individuals with type 2 diabetes

PURPOSE

The time constant of phase II pulmonary oxygen uptake kinetics ([Formula: see text]) is increased when high-intensity exercise is initiated from an elevated baseline (work-to-work). A high-intensity priming exercise (PE), which enhances muscle oxygen supply, does not reduce this prolonged [Formula: see text] in healthy active individuals, likely because [Formula: see text] is limited by metabolic inertia (rather than oxygen delivery) in these individuals. Since [Formula: see text] is more influenced by oxygen delivery in type 2 diabetes (T2D), this study tested the hypothesis that PE would reduce [Formula: see text] in T2D during work-to-work cycle exercise.

METHODS

Nine middle-aged individuals with T2D and nine controls (ND) performed four bouts of constant-load, high-intensity work-to-work transitions, each commencing from a baseline of moderate-intensity. Two bouts were completed without PE and two were preceded by PE. The rate of muscle deoxygenation ([HHb + Mb]) and surface integrated electromyography (iEMG) were measured at the right and left vastus lateralis, respectively.

RESULTS

Subsequent to PE, [Formula: see text] was reduced (P = 0.001) in T2D (from 59 ± 17 to 37 ± 20 s) but not (P = 0.24) in ND (44 ± 10 to 38 ± 7 s). The amplitude of the [Formula: see text] slow component ([Formula: see text]₂ A_s) was reduced (P = 0.001) in both groups (T2D: 0.16 ± 0.09 to 0.11 ± 0.04 l/min; ND: 0.21 ± 0.13 to 0.13  ± 0.09 l/min). This was accompanied by a reduction in ΔiEMG from the onset of [Formula: see text] slow component to end-exercise in both groups (P < 0.001), while [HHb + Mb] kinetics remained unchanged.

CONCLUSIONS

PE accelerates [Formula: see text] in T2D, likely by negating the O₂ delivery limitation extant in the unprimed condition, and reduces the [Formula: see text]A_s possibly due to changes in muscle fibre activation.

Effect of an acute blood donation on oxygen uptake kinetics in moderate and heavy domains over a period of 96 hours

BACKGROUND

Studies determining the effects of blood donation (BD) on oxygen uptake kinetics are limited. This study aims to ascertain the effects of BD (~470 mL) over a period of 96 hours on oxygen uptake kinetics in moderate and heavy exercise domains.

STUDY DESIGN AND METHODS

Twelve participants (nine males and three females; 31.1 ± 11.7 years, mass 79.9 ± 12.8 kg, height 175.5 ± 7.5 cm) completed four consecutive days (24-96 hours) of moderate and heavy V˙O₂ on-kinetics trials pre BD and post BD. Visit one (0 hour), pre BD established hematological levels, V˙O_2max and Gas Exchange Threshold (GET). Subsequent visits comprised two 6-minute moderate (∆ 50% rest-GET) and 1 heavy (∆ 20% GET-V˙O_2max ) trial. Post BD 0 hour the participants donated blood post hematological testing only.

RESULTS

Despite non-significances for V˙O₂ amplitude, time constant-2 (tau₂ ) for V˙O₂ showed significant decreases at 24 and 48 hours, and tau₃ showed significant increases at 72 and 96 hours pre to post BD (P < .05). Hemoglobin (Hb) values reduced (P < .05) pre (14.48 ± 0.16 g·dL^-1 ) to post BD (13.47 ± 0.66 g·dL^- 1). Hb significantly decreased at 24, 48, 72, and 96 hours compared to 0 hour post BD (P < .05).

CONCLUSION

BD has no effect on V˙O₂ amplitude, but time-based components show sensitivity to reduced circulating O₂ ; with a decreased PO₂ a slower O₂ exchange across the blood myocyte barrier could result in altering O₂ kinetics.

Yo-Yo Intermittent Recovery Level 1 Test for Estimation of Peak Oxygen Uptake: Use Without Restriction?

Purpose: This study analyzed the physiological response during Yo-Yo Intermittent Recovery Level 1 (YYIR1) test and re-test by in-field ergospirometry and time-series analyses of respiratory parameters. Methods: Ten moderately trained males (23.4 ± 2.01 years, VO_2peak= 56.81 ± 10.75 mL·kg^-1·min^-1) completed three running trials including two separate YYIR1 tests and an independent maximal performance running test with time-series analyses of gas exchange parameters. Physiological response was assessed during all tests by determination of blood lactate levels (including calculation of individual lactate threshold), heart rate, oxygen consumption and respiratory exchange ratio (RER). Results: Modeling of YYIR1 test mean VO₂ uptake kinetics over all participants revealed that VO₂ increased rapidly after the individual lactate threshold (11.49 ± 0.66 km∙h^-1 at 3.83 ± 0.42 mmol∙L^-1) was reached with ~95% VO_2peak at ~50% of the test duration (test, VO₂ ^50%= 95.17 ± 8.74% of VO_2peak; re-test, VO₂ ^50%= 96.78 ± 7.04% of VO_2peak). However, and despite identical YYIR1 test performance (1568 ± 364.6 m vs. 1568 ± 449.7 m, CV = 4.59%), mean VO_2peak during YYIR1 test was 8.81 ± 5.6% higher than YYIR1 re-test (p = .027). Importantly, correlation of VO_2peak with YYIR1 test performance was weak (R² = 0.28, p = .115). Conclusions: We conclude that the YYIR1 test should not be used to estimate VO_2peak. Further studies on direct determination of gas exchange parameters during different YYI test variants are warranted.

VO2 Steady State at and Just Above Maximum Lactate Steady State Intensity

Over recent decades the association between metabolic and gas exchange parameters during exercise has become evident. Different "thresholds" (such as lactate thresholds, critical power, EMG thresholds) and intensity domains appear to be linked to an upper limit of oxygen uptake steady state (V̇O_2SS). The aim of this study was to investigate whether MLSS is associated with the upper limit for a V̇O_2SS. Forty-five subjects underwent one incremental test and 4-6 30-minute MLSS tests on a cycle ergometer. A three-component model was used to describe V̇O₂ response at P_MLSS and just above P_MLSS+1. To evaluate the results, breath-by-breath V̇O₂ and lactate (LA) values were analyzed using the intraclass correlation coefficient (ICC), increasing (k-) values and the Wilcoxon test. According to the calculated k-values of LA and VO₂ at P_MLSS and P_MLSS+1, no significant increase of VO₂ occurred during both intensities (P_MLSS and P_MLSS+1) from minute 10 to minute 30, confirming the existence of a V̇O_2SS. Additionally, the ICC of 0.94 confirmed high accordance of the VO₂ kinetics at both intensities (P_MLSS and P_MLSS+1). This study shows that power output at MLSS workload does not represent an accurate cut for an upper limit of V̇O_2SS.

Estimating an individual's oxygen uptake during cycling exercise with a recurrent neural network trained from easy-to-obtain inputs: A pilot study

Measurement of oxygen uptake during exercise ([Formula: see text]) is currently non-accessible to most individuals without expensive and invasive equipment. The goal of this pilot study was to estimate cycling [Formula: see text] from easy-to-obtain inputs, such as heart rate, mechanical power output, cadence and respiratory frequency. To this end, a recurrent neural network was trained from laboratory cycling data to predict [Formula: see text] values. Data were collected on 7 amateur cyclists during a graded exercise test, two arbitrary protocols (Prot-1 and -2) and an "all-out" Wingate test. In Trial-1, a neural network was trained with data from a graded exercise test, Prot-1 and Wingate, before being tested against Prot-2. In Trial-2, a neural network was trained using data from the graded exercise test, Prot-1 and 2, before being tested against the Wingate test. Two analytical models (Models 1 and 2) were used to compare the predictive performance of the neural network. Predictive performance of the neural network was high during both Trial-1 (MAE = 229(35) mlO2min-1, r = 0.94) and Trial-2 (MAE = 304(150) mlO2min-1, r = 0.89). As expected, the predictive ability of Models 1 and 2 deteriorated from Trial-1 to Trial-2. Results suggest that recurrent neural networks have the potential to predict the individual [Formula: see text] response from easy-to-obtain inputs across a wide range of cycling intensities.

Influence of priming exercise on oxygen uptake and muscle deoxygenation kinetics during moderate-intensity cycling in type 2 diabetes

The pulmonary oxygen uptake (V̇o2) kinetics during the transition to moderate-intensity exercise is slowed in individuals with type 2 diabetes (T2D), at least in part because of limitations in O2 delivery. The present study tested the hypothesis that a prior heavy-intensity warm-up or “priming” exercise (PE) bout would accelerate V̇o2 kinetics in T2D, because of a better matching of O2 delivery to utilization. Twelve middle-aged individuals with T2D and 12 healthy controls (ND) completed moderate-intensity constant-load cycling bouts either without (Mod A) or with (Mod B) prior PE. The rates of muscle deoxygenation (i.e., deoxygenated hemoglobin and myoglobin concentration, [HHb+Mb]) and oxygenation (i.e., tissue oxygenation index) were continuously measured by near-infrared spectroscopy at the vastus lateralis muscle. The local matching of O2 delivery to O2 utilization was assessed by the Δ[HHb+Mb]-to-ΔV̇o2 ratio. Both groups demonstrated an accelerated V̇O2 kinetics response during Mod B compared with Mod A (T2D, 32 ± 9 vs. 42 ± 12 s; ND, 28 ± 9 vs. 34 ± 8 s; means ± SD) and an elevated muscle oxygenation throughout Mod B, whereas the [HHb+Mb] amplitude was greater during Mod B only in individuals with T2D. The [HHb+Mb] kinetics remained unchanged in both groups. In T2D, Mod B was associated with a decrease in the “overshoot” relative to steady state in the Δ[HHb+Mb]-to-ΔV̇o2 ratio (1.17 ± 0.17 vs. 1.05 ± 0.15), whereas no overshoot was observed in the control group before (1.04 ± 0.12) or after (1.01 ± 0.12) PE. Our findings support a favorable priming-induced acceleration of the V̇o2 kinetics response in middle-aged individuals with uncomplicated T2D attributed to an enhanced matching of microvascular O2 delivery to utilization.

NEW & NOTEWORTHY Heavy-intensity “priming” exercise (PE) elicited faster pulmonary oxygen uptake (V̇o2) kinetics during moderate-intensity cycling exercise in middle-aged individuals with type 2 diabetes (T2D). This was accompanied by greater near-infrared spectroscopy-derived muscle deoxygenation (i.e., deoxygenated hemoglobin and myoglobin concentration, [HHb+Mb]) responses and a reduced Δ[HHb+Mb]-to-ΔV̇o2 ratio. This suggests that the PE-induced acceleration in oxidative metabolism in T2D is a result of greater O2 extraction and better matching between O2 delivery and utilization.

Identifying Physically Demanding Tasks Performed by the Royal Australian Navy for the Development of a Physical Employment Standard

OBJECTIVE

The aim of this study was to determine an appropriate method to characterize Royal Australian Navy intermittent intensity tasks.

METHOD

Sixteen personnel performed four scenarios: (1) storing: repeatedly handle a 10 to 15 kg crate; (2) firefighting: walk 45 m wearing protective equipment and fighting a fire; (3) and (4) toxic hazard response: casualty evacuation tasks wearing protective equipment. Heart rate and oxygen consumption ((Equation is included in full-text article.)) were measured continuously. Mean and peak values and time spent in incremental zones were calculated.

RESULTS

Scenario 2 elicited the highest oxygen cost (18.1 L, mean (Equation is included in full-text article.)1.5 L.min, time >2.5 L.min: 0.8%), yet scenario 4 elicited the highest mean (Equation is included in full-text article.)(1.8 L.min, oxygen cost 14.4 L), and participants spent a greater duration >2.5 L.min(Equation is included in full-text article.)(23.3% or 1 minute 55 seconds).

CONCLUSIONS

A small difference (0.3 L.min) was observed between scenarios 2 and 4 for mean (Equation is included in full-text article.), yet (Equation is included in full-text article.)>2.5 L.min demonstrated scenario 4 had a higher metabolic demand.

Relationship between muscle metabolic rate and muscle torque complexity during fatiguing intermittent isometric contractions in humans

To test the hypothesis that a system's metabolic rate and the complexity of fluctuations in the output of that system are related, thirteen healthy participants performed intermittent isometric knee extensor contractions at intensities where a rise in metabolic rate would (40% maximal voluntary contraction, MVC) and would not (20% MVC) be expected. The contractions had a 60% duty factor (6 sec contraction, 4 sec rest) and were performed until task failure or for 30 min, whichever occurred sooner. Torque and surface EMG signals were sampled continuously. Complexity and fractal scaling of torque were quantified using approximate entropy (ApEn) and the detrended fluctuation analysis (DFA) α scaling exponent. Muscle metabolic rate was determined using near-infrared spectroscopy. At 40% MVC, task failure occurred after (mean ± SD) 11.5 ± 5.2 min, whereas all participants completed 30 min of contractions at 20% MVC. Muscle metabolic rate increased significantly after 2 min at 40% MVC (2.70 ± 1.48 to 4.04 ± 1.23 %·s-1 , P < 0.001), but not at 20% MVC. Similarly, complexity decreased significantly at 40% MVC (ApEn, 0.53 ± 0.19 to 0.15 ± 0.09; DFA α, 1.37 ± 0.08 to 1.60 ± 0.09; both P < 0.001), but not at 20% MVC. The rates of change of torque complexity and muscle metabolic rate at 40% MVC were significantly correlated (ApEn, ρ = -0.63, P = 0.022; DFA, ρ = 0.58, P = 0.037). This study demonstrated that an inverse relationship exists between muscle torque complexity and metabolic rate during high-intensity contractions.

Wavelet and principal component analysis of electromyographic activity and slow component of oxygen uptake during heavy and severe cycling exercise

The aim of the study was to investigate whether the slow component of oxygen uptake was concurrent with the recruitment of large α-motoneuron muscle fibres by using wavelet and principal component analysis (PCA) of electromyography (EMG) during heavy and severe cycling exercise. Eleven male subjects participated in the study. After establishing each subject's maximum value of oxygen uptake through an incremental test on the cycle ergometer, the subjects performed 6-min cycling tests at heavy and severe intensity. EMG signals were collected from rectus femoris, biceps femoris long head, tibialis anterior, and medial gastrocnemius and processed by combined use of wavelet and PCA analysis. The time delays to the onset of slow component occurred significantly earlier during severe (105.22 ± 5.45 s) compared with during heavy (138.78 ± 15.09 s) exercise. ANOVA with repeated measures showed that for all muscles tested, the angle θ formed by the first and second principal components decreased significantly between time windows during heavy and severe exercise. However, significant increases of EMG mean power frequency (MPF) were found only during heavy exercise. Our results show the concurrence of the oxygen uptake slow component with the additional recruitment of muscle fibres, presumably less efficient large α-motoneuron fibres. Novelty The expected rise in MPF may be offset by muscle fatigue occurring in the later time windows of the slow component during severe exercise. The gradual shift to higher EMG frequencies throughout the slow-component phase was reflected in the progressive and significant decrease of angle θ.

Cardiopulmonary exercise testing for evaluation of a randomized exercise training intervention following aortic valve replacement

Aortic valve surgery is the definitive treatment for aortic stenosis (AS). No specific recommendation is available on how exercise training should be conducted and evaluated after aortic valve replacement (AVR). This study aimed to examine the effect of aerobic exercise training on exercise capacity following AVR. In addition to our primary outcome variable, peak oxygen uptake (peakVO₂ ), the effect on submaximal cardiopulmonary variables including oxygen uptake kinetics (tau), oxygen uptake efficiency slope (OUES) and ventilatory efficiency (VE/VCO₂ slope) was evaluated. Following AVR due to AS, 12 patients were randomized to either a group receiving 12 weeks of supervised aerobic exercise training (EX) or a control group (CON). Exercise capacity was assessed by a maximal cardiopulmonary exercise test (CPET). There was a significant increase in peak load (+28%, P = 0·031) and in peakVO₂ (+23%, P = 0·031) in EX, corresponding to an increase in achieved percentage of predicted peakVO₂ from 88 to 104% (P = 0·031). For submaximal variables, there were only non-statistically significant trends in improvement between CPETs in EX. In CON, there were no significant differences in any maximal or submaximal variable between CPETs. We conclude that 12 weeks of supervised aerobic exercise training induces significant adaptations in cardiopulmonary function following AVR, especially in regard to maximal variables including peakVO₂ . In addition, we provide novel data on the effect on several submaximal variables following exercise training in this group of patients.

Lack of age-specific influence on leg blood flow during incremental calf plantar-flexion exercise in men and women

PURPOSE

Age-related exercising leg blood flow (LBF) responses during dynamic knee-extension exercise and forearm blood flow responses during handgrip exercise are preserved in normally active men but attenuated in activity-matched women. We explored whether these age- and sex-specific effects are also apparent during isometric calf plantar-flexion incremental exercise.

METHODS

Normally active young men (YM, n = 15, 24 ± 2 years), young women (YW, n = 8, 22 ± 1 years), older men (OM, n = 13, 70 ± 7 years) and older women (OW, n = 10, 64 ± 7 years) were tested. LBF was measured between contractions using venous occlusion plethysmography.

RESULTS

Peak force obtained was higher (P < 0.05) in men compared with women and in young compared with older individuals. However, peak LBF (YM; 971 ± 328 ml min^-1, OM; 985 ± 504 ml min^-1, YW; 844 ± 366 ml min^-1, OW; 960 ± 244 ml min^-1) and peak leg vascular conductance [LVC = LBF/(MAP + hydrostatic pressure)] responses (YM; 6.0 ± 1.8 ml min^-1 mmHg^-1, OM; 5.5 ± 2.8 ml min^-1 mmHg^-1, YW; 5.3 ± 2.1 ml min^-1 mmHg^-1, OW; 5.5 ± 1.6 ml min^-1 mmHg^-1) were similar among the four groups. Furthermore, the hyperaemic (YM; 8.8 ± 3.7 ml min^-1 %F_peak^-1 OM; 8.3 ± 5.4 ml min^-1 %F_peak^-1, YW; 8.2 ± 3.5 ml min^-1 %F_peak^-1, OW; 9.6 ± 2.2 ml min^-1 %F_peak^-1) and vasodilatory responses (YM; 0.053 ± 0.020 ml min^-1 mmHg^-1 %F_peak^-1, OM; 0.048 ± 0.028 ml min^-1 mmHg^-1 %F_peak^-1, YW; 0.051 ± 0.019 ml min^-1 mmHg^-1 %F_peak^-1, OW; 0.055 ± 0.014 ml min^-1 mmHg^-1 %F_peak^-1) were not different among the four groups. These results were accompanied by similar resting LBF responses among groups and were not affected when data were normalised to estimated leg muscle mass.

CONCLUSIONS

Our results demonstrate that exercising LBF responses during isometric incremental calf muscle exercise are preserved in older men and women, suggesting that the previously observed age-related attenuations in leg and forearm hyperaemia among women may be muscle-group specific.

Improvements in fitness are not obligatory for exercise training-induced improvements in CV risk factors

The purpose of this study was to assess whether changes in physical fitness relate to changes in cardiovascular risk factors following standardized, center-based and supervised exercise training programs in subjects with increased cardiovascular risk. We pooled data from exercise training studies of subjects with increased cardiovascular risk (n = 166) who underwent 8-52 weeks endurance training. We determined fitness (i.e., peak oxygen uptake) and traditional cardiovascular risk factors (body mass index, blood pressure, total cholesterol, high-density lipoprotein cholesterol), before and after training. We divided subjects into quartiles based on improvement in fitness, and examined whether these groups differed in terms of risk factors. Associations between changes in fitness and in cardiovascular risk factors were further tested using Pearson correlations. Significant heterogeneity was apparent in the improvement of fitness and individual risk factors, with nonresponder rates of 17% for fitness, 44% for body mass index, 33% for mean arterial pressure, 49% for total cholesterol, and 49% for high-density lipoprotein cholesterol. Neither the number, nor the magnitude, of change in cardiovascular risk factors differed significantly between quartiles of fitness change. Changes in fitness were not correlated with changes in cardiovascular risk factors (all P > 0.05). Our data suggest that significant heterogeneity exists in changes in peak oxygen uptake after training, while improvement in fitness did not relate to improvement in cardiovascular risk factors. In subjects with increased cardiovascular risk, improvements in fitness are not obligatory for training-induced improvements in cardiovascular risk factors.

Effect of acute nitrate ingestion on V̇O2 response at different exercise intensity domains

While nitrate supplementation influences oxygen uptake (V̇O2) response to exercise, this effect may be intensity dependent. The purpose of this study was to investigate the effect of acute nitrate supplementation on V̇O2 response during different exercise intensity domains in humans. Eleven men ingested 10 mg·kg−1 body mass (8.76 ± 1.35 mmol) of sodium nitrate or sodium chloride (placebo) 2.5 h before cycling at moderate (90% of gas exchange threshold; GET), heavy (GET + 40% of the difference between GET and peak oxygen uptake (V̇O2peak), Δ 40) or severe (GET + 80% of the difference between GET and V̇O2peak, Δ 80) exercise intensities. Volunteers performed exercise for 10 min (moderate), 15 min (heavy) or until exhaustion (severe). Acute nitrate supplementation had no effect on any V̇O2 response parameters during moderate and severe exercise intensities. However, the V̇O2 slow amplitude (nitrate: 0.93 ± 0.36 L·min−1 vs. placebo: 1.13 ± 0.59 L·min−1, p = 0.04) and V̇O2 slow gain (nitrate: 5.81 ± 2.37 mL·min–1·W−1 vs. placebo: 7.09 ± 3.67 mL·min–1·W−1, p = 0.04) were significantly lower in nitrate than in placebo during the heavy exercise intensity. There was no effect of nitrate on plasma lactate during any exercise intensity (p > 0.05). Time to exhaustion during the severe exercise intensity was also not affected by nitrate (p > 0.05). In conclusion, acute nitrate supplementation reduced the slow component of V̇O2 only when performing heavy-intensity exercise, which might indicate an intensity-dependent effect of nitrate on V̇O2 response.

Effects of continuous and intermittent exercise on executive function in children aged 8-10 years

Understanding the effects of acute exercise on executive function in prepubescent children may be important for the enhancement of school performance. This study assessed the effect of an acute bout of continuous (CONT) or intermittent (INT), moderate-intensity treadmill exercise on executive function in young children. Twenty healthy children, mean (SD); age: 8.8 (0.8) years; height: 140 (9) cm; weight: 36 (11) kg; boys: n = 9, performed a graded-exercise test to determine maximal oxygen uptake, and two 15-min submaximal bouts of treadmill exercise; protocols were either CONT or INT. During CONT, participants ran at 90% of gas exchange threshold. During INT, participants performed six consecutive 2.5 min blocks of exercise, which were designed to reflect children's typical activity patterns, comprising 45 s at a heavy intensity, 33 s at a moderate intensity, 10 s at a severe intensity, and 62 s at a low intensity. Participants performed the Stroop task before the submaximal exercise bouts and after, at 1-, 15-, and 30-min intervals. Near-infrared spectroscopy (NIRS) measured cerebral perfusion and oxygenation. Regardless of condition, Stroop performance was improved at 1 min after compared to before, 54.9 (9.8) s versus 57.9 (11) s, respectively, p < .01, and improvements were maintained until 30 min after. NIRS (oxyhemoglobin, total hemoglobin) explained a significant amount of variance in the change in Stroop performance for INT only (49%, p < .05). An acute bout of exercise, of either an intermittent or continuous nature, improves executive function in children, and effects are maintained for ≤ 30 min following exercise cessation. Accordingly, it is recommended that children should engage in physical activity during periods of school recess.

Maximal Aerobic Frequency of Ball Hitting: A New Training Load Parameter in Tennis

Baiget, E, Iglesias, X, and Rodríguez, FA. Maximal aerobic frequency of ball hitting: a new training load parameter in tennis. J Strength Cond Res 31(1): 106-114, 2017-This study aimed (a) to evaluate a new training load parameter in tennis based on the ball-hitting frequency (Ballf) at V[Combining Dot Above]O2max occurs (maximal aerobic frequency of ball hitting, MAF) and (b) to assess the accuracy of a specific endurance tennis test (SET-Test) for predicting MAF. Thirty-five male competitive tennis players performed the SET-Test and selected physiological and performance parameters at maximal workload (MAX), and last completed stage (LS) and MAF were compared. Performance parameters (Ballf, time, stage, and hits per test) at LS were higher than at MAF (20.2 ± 1.7 vs. 18.1 ± 1.5 shots·min, 6.6 ± 0.8 vs. 5.6 ± 0.8 stages, and 189 ± 33 vs. 147 ± 27 hits; p < 0.001), and highly correlated (r = 0.72-0.77; p < 0.001). The mean difference between Ballf and stage at MAF and LS were 2.1 ± 1.1 shots·min and 1.1 ± 0.6 stages, respectively. The main physiological parameters (heart rate, V[Combining Dot Above]O2, and V[Combining Dot Above]CO2 at LS) were higher than at MAF (191 ± 9 vs. 186 ± 8 beats·min, 55.5 ± 5.9 vs. 55.0 ± 6.0 ml·kg·min and 4,724 ± 880 vs. 4,253 ± 739 ml·min; p < 0.005), and were very strongly correlated (r = 0.93-0.99; p < 0.001). We conclude that MAF can be used as a practical performance parameter to prescribe tennis-specific training, and that the SET-Test is a valid method for assessing MAF. Gas exchange measurements not being available, as a rule of thumb, most players reach their MAF at ∼1 stage (95% confidence interval: 0.9-1.2) and ∼2 shots·min (95% confidence interval: 1.7-2.5) less than their completed LS. A model for specific on-court training protocols for optimizing aerobic fitness in competitive tennis player is proposed.

The Yo-Yo IE2 test: physiological response for untrained men versus trained soccer players

PURPOSE

This study aimed to examine the physical capacity and physiological response to the Yo-Yo Intermittent Endurance level 2 test (IE2) for untrained individuals (UTR) and trained male soccer players (TR) and to investigate the determinants of intense intermittent exercise performance.

METHODS

Thirty-four healthy UTR males and 15 age-matched TR performed a maximal incremental treadmill test and a Yo-Yo IE2 test. Muscle biopsies and blood samples were obtained, and heart rate (HR) was measured before, during, and after tests.

RESULTS

UTR had a 67% lower (P < 0.01) Yo-Yo IE2 performance (665 ± 271 vs 2027 ± 298 m; effect size (ES), 4.8), 34% lower V˙O2max (P < 0.01), and 19% lower resting muscle glycogen (P < 0.05) than those of TR. Blood lactate concentration and HR during the first 560 m of the Yo-Yo IE2 test were higher (P < 0.01) in UTR than those in TR (560 m, 7.4 ± 2.8 vs 2.4 ± 0.8 mM; ES, 1.7-2.8; 188 ± 11 vs 173 ± 8 bpm; ES, 0.9-1.5), with no differences at exhaustion. Time >95% HRmax was lower (P < 0.01) in UTR than that in TR (1.0 ± 1.1 vs 6.3 ± 2.9 min; ES, 3.1). Mean rates of muscle creatine phosphate utilization (16.5 ± 9.5 vs 4.3 ± 2.7 mmol·kg d.w·min), muscle lactate accumulation (16.8 ± 9.1 vs 4.2 ± 2.9 mmol·kg d.w.·min), and glycogen breakdown (29.6 ± 14.2 vs 7.7 ± 5.4 mmol·kg d.w.·min) were fourfold higher (P < 0.01; ES, 1.4-1.7) in UTR than those in TR. For UTR, correlations (P < 0.01) were observed between Yo-Yo IE2 performance and V˙O2max (r = 0.77), incremental treadmill test performance (r = 0.79), and muscle citrate synthase activity (r = 0.57) but not for TR (r = -0.12 to 0.50; P > 0.05).

CONCLUSIONS

The Yo-Yo IE2 test was shown to possess high construct validity by showing large differences in performance, HR, and anaerobic metabolism between UTR and TR. In addition, V˙O2max seemed to be important for intermittent exercise performance in UTR but not for TR.

A short period of high-intensity interval training improves skeletal muscle mitochondrial function and pulmonary oxygen uptake kinetics

The aim of the present study was to examine whether improvements in pulmonary oxygen uptake (V̇o2) kinetics following a short period of high-intensity training (HIT) would be associated with improved skeletal muscle mitochondrial function. Ten untrained male volunteers (age 26 ± 2 yr; mean ± SD) performed six HIT sessions (8-12 × 60 s at incremental test peak power; 271 ± 52 W) over a 2-wk period. Before and after the HIT period, V̇o2 kinetics was modeled during moderate-intensity cycling (110 ± 19 W). Mitochondrial function was assessed with high-resolution respirometry (HRR), and maximal activities of oxidative enzymes citrate synthase (CS) and cytochrome c oxidase (COX) were accordingly determined. In response to HIT, V̇o2 kinetics became faster (τ: 20.4 ± 4.4 vs. 28.9 ± 6.1 s; P < 0.01) and fatty acid oxidation (ETFP) and leak respiration (LN) both became elevated (P < 0.05). Activity of CS and COX did not increase in response to training. Both before and after the HIT period, fast V̇o2 kinetics (low τ values) was associated with large values for ETFP, electron transport system capacity (ETS), and electron flow specific to complex II (CIIP) (P < 0.05). Collectively, these findings support that selected measures of mitochondrial function obtained with HRR are important for fast V̇o2 kinetics and better markers than maximal oxidative enzyme activity in describing the speed of the V̇o2 response during moderate-intensity exercise.

Unchanged content of oxidative enzymes in fast-twitch muscle fibers and V˙O2 kinetics after intensified training in trained cyclists

The present study examined if high intensity training (HIT) could increase the expression of oxidative enzymes in fast-twitch muscle fibers causing a faster oxygen uptake () response during intense (INT), but not moderate (MOD), exercise and reduce the slow component and muscle metabolic perturbation during INT. Pulmonary kinetics was determined in eight trained male cyclists (-max: 59 ± 4 (means ± SD) mL min⁻¹ kg⁻¹) during MOD (205 ± 12 W ∼65% -max) and INT (286 ± 17 W ∼85% -max) exercise before and after a 7-week HIT period (30-sec sprints and 4-min intervals) with a 50% reduction in volume. Both before and after HIT the content in fast-twitch fibers of CS (P < 0.05) and COX-4 (P < 0.01) was lower, whereas PFK was higher (P < 0.001) than in slow-twitch fibers. Content of CS, COX-4, and PFK in homogenate and fast-twitch fibers was unchanged with HIT. Maximal activity (μmol g DW⁻¹ min⁻¹) of CS (56 ± 8 post-HIT vs. 59 ± 10 pre-HIT), HAD (27 ± 6 vs. 29 ± 3) and PFK (340 ± 69 vs. 318 ± 105) and the capillary to fiber ratio (2.30 ± 0.16 vs. 2.38 ± 0.20) was unaltered following HIT. kinetics was unchanged with HIT and the speed of the primary response did not differ between MOD and INT. Muscle creatine phosphate was lower (42 ± 15 vs. 66 ± 17 mmol kg DW⁻¹) and muscle lactate was higher (40 ± 18 vs. 14 ± 5 mmol kg DW⁻¹) at 6 min of INT (P < 0.05) after compared to before HIT. A period of intensified training with a volume reduction did not increase the content of oxidative enzymes in fast-twitch fibers, and did not change kinetics.

Efeito do exercício prévio no ciclismo de curta duração

INTRODUÇÃO: O exercício prévio tem importantes implicações na preparação de atletas antes de competições.OBJETIVO: Analisar o efeito de um exercício prévio realizado no domínio pesado no pico de torque (PTORQUE) medido após exercício severo.MÉTODOS: Participaram deste estudo 14 homens ativos (idade: 26 ± 4 anos, VO2max: 44 ± 6 mLO2.min-1.kg-1) que realizaram sete testes em dias diferentes: a) teste progressivo de rampa para determinação do VO2max e da potência pico; b) quatro testes de carga constante para determinação da potência crítica, capacidade de trabalho anaeróbio e potência correspondente ao tempo de exaustão de 3 min (PTLim3min) e; c) dois testes de carga constante de 2 min na PTLim3min seguidos por um sprint all outde 10 s, a fim de medir o PTORQUE. Este último protocolo foi realizado com (EP) e sem (CON) a realização de um exercício prévio pesado.RESULTADOS: O PTORQUE foi significantemente maior após o EP (101 ± 30 Nm) em relação à condição CON (95 ± 23 Nm). O tempo da resposta médio (TRM) do VO2foi significantemente menor após o EP (24 ± 7 s) em relação à condição CON (32 ± 10 s). A amplitude primária do VO2aumentou significantemente após o EP (2598 ± 421 mLO2.min-1) em relação à condição CON (2184 ± 246 mLO2.min-1). O déficit de O2 foi significantemente menor após o exercício prévio (980 ± 432 mLO2) em relação à condição CON (1273 ± 398 mLO2). Houve correlação significante entre a variação do déficit de O2 com a do PTORQUE (r = 0,53) e da variação do TRM com a do PTORQUE (r = 0,53).CONCLUSÃO: Pode-se concluir que o PTORQUE é maior após exercício aeróbio de curta duração precedido do EP. Deste modo, esta estratégia pode ser interessante como preparação para algumas competições esportivas.

Muscle metabolic responses during high-intensity intermittent exercise measured by (31)P-MRS: relationship to the critical power concept

We investigated the responses of intramuscular phosphate-linked metabolites and pH (as assessed by (31)P-MRS) during intermittent high-intensity exercise protocols performed with different recovery-interval durations. Following estimation of the parameters of the power-duration relationship, i.e., the critical power (CP) and curvature constant (W'), for severe-intensity constant-power exercise, nine male subjects completed three intermittent exercise protocols to exhaustion where periods of high-intensity constant-power exercise (60 s) were separated by different durations of passive recovery (18 s, 30 s and 48 s). The tolerable duration of exercise was 304 ± 68 s, 516 ± 142 s, and 847 ± 240 s for the 18-s, 30-s, and 48-s recovery protocols, respectively (P < 0.05). The work done >CP (W>CP) was significantly greater for all intermittent protocols compared with the subjects' W', and this difference became progressively greater as recovery-interval duration was increased. The restoration of intramuscular phosphocreatine concentration during recovery was greatest, intermediate, and least for 48 s, 30 s, and 18 s of recovery, respectively (P < 0.05). The W>CP in excess of W' increased with greater durations of recovery, and this was correlated with the mean magnitude of muscle phosphocreatine reconstitution between work intervals (r = 0.61; P < 0.01). The results of this study show that during intermittent high-intensity exercise, recovery intervals allow intramuscular homeostasis to be restored, with the degree of restoration being related to the duration of the recovery interval. Consequently, and consistent with the intermittent CP model, the ability to perform W>CP during intermittent high-intensity exercise and, therefore, exercise tolerance, increases when recovery-interval duration is extended.

Cinética do VO2 durante o exercício realizado na potência crítica em ciclistas e indivíduos não-treinados no ciclismo

O objetivo foi analisar a cinética do consumo de oxigênio (VO2) na potência crítica (PC), em indivíduos com diferentes níveis de aptidão aeróbia no ciclismo. Seis ciclistas treinados (GT) e sete indivíduos não-treinados (GNT) realizaram os seguintes protocolos em cicloergômetro: (a) progressivo até a exaustão para determinação do VO2max e sua respectiva intensidade (IVO2max); (b) três testes em cargas constantes até a exaustão a 95-110%IVO2max para determinação da PC; e (c) um teste em carga constante até a exaustão a 100%PC. No exercício a 100%PC, o componente lento expresso em valor absoluto (GT: 342,4±165,8 ml.min-1 vs. GNT: 571,3±170,1 ml.min-1) e relativo ao aumento do VO2 em exercício (GT: 10,0±4,6% vs. GNT: 26,6±7,3%) foram menores para GT. O VO2 ao final do exercício (GT: 89,8±8,4%VO2max vs. GNT: 97,4±2,8%VO2max) foi significativamente menor no grupo GT (ρ = 0,045), sendo similar ao VO2max no grupo GNT. Portanto, o nível de aptidão aeróbia pode influenciar as respostas do VO2 ao exercício em PC.

Muscle metabolic determinants of exercise tolerance following exhaustion: relationship to the "critical power"

We tested the hypothesis that muscle high-energy phosphate compounds and metabolites related to the fatigue process would be recovered after exhaustion during recovery exercise performed below but not above critical power (CP) and that these changes would influence the capacity to continue exercise. Eight male subjects completed single-leg, knee-extension exercise to exhaustion (for ∼180 s) on three occasions, followed by a work-rate reduction to severe-intensity exercise, heavy-intensity exercise (<CP), or a 10-min passive recovery period, in random order. The muscle metabolic responses to exercise were assessed using (31)P magnetic resonance spectroscopy. There was a significant difference between the sustainable exercise duration during the recovery from exhaustive exercise between the <CP and >CP conditions (at least 10 min and 39 ± 31 s, respectively; P < 0.05). During passive recovery and <CP recovery exercise, muscle phosphocreatine concentration ([PCr]) increased rapidly after the exhaustion point, reaching ∼96% and ∼76% of baseline values, respectively, after 10 min (P < 0.05). Moreover, pH increased abruptly, reaching 7.0 ± 0.0 and 7.0 ± 0.2, respectively, after 10 min recovery (P < 0.05). However, during >CP recovery exercise, neither muscle [PCr] nor pH recovered, reaching ∼37% of the initial baseline and 6.6 ± 0.2, respectively. These results indicate that the muscle metabolic dynamics in recovery from exhaustive >CP differ according to whether the recovery exercise is performed below or above the CP. These findings confirm the importance of the CP as an intramuscular metabolic threshold that dictates the accumulation of fatigue-related metabolites and the capacity to tolerate high-intensity exercise.

Effects of short-term dietary nitrate supplementation on blood pressure, O2 uptake kinetics, and muscle and cognitive function in older adults

Dietary nitrate (NO3−) supplementation has been shown to reduce resting blood pressure and alter the physiological response to exercise in young adults. We investigated whether these effects might also be evident in older adults. In a double-blind, randomized, crossover study, 12 healthy, older (60–70 yr) adults supplemented their diet for 3 days with either nitrate-rich concentrated beetroot juice (BR; 2 × 70 ml/day, ∼9.6 mmol/day NO3−) or a nitrate-depleted beetroot juice placebo (PL; 2 × 70 ml/day, ∼0.01 mmol/day NO3−). Before and after the intervention periods, resting blood pressure and plasma [nitrite] were measured, and subjects completed a battery of physiological and cognitive tests. Nitrate supplementation significantly increased plasma [nitrite] and reduced resting systolic (BR: 115 ± 9 vs. PL: 120 ± 6 mmHg; P < 0.05) and diastolic (BR: 70 ± 5 vs. PL: 73 ± 5 mmHg; P < 0.05) blood pressure. Nitrate supplementation resulted in a speeding of the V̇o2 mean response time (BR: 25 ± 7 vs. PL: 28 ± 7 s; P < 0.05) in the transition from standing rest to treadmill walking, although in contrast to our hypothesis, the O2 cost of exercise remained unchanged. Functional capacity (6-min walk test), the muscle metabolic response to low-intensity exercise, brain metabolite concentrations, and cognitive function were also not altered. Dietary nitrate supplementation reduced resting blood pressure and improved V̇o2 kinetics during treadmill walking in healthy older adults but did not improve walking or cognitive performance. These results may have implications for the enhancement of cardiovascular health in older age.

Influence of exercise intensity on skeletal muscle blood flow, O2 extraction and O2 uptake on-kinetics

Following the start of low-intensity exercise in healthy humans, it has been established that the kinetics of skeletal muscle O(2) delivery is faster than, and does not limit, the kinetics of muscle O(2) uptake (V(O(2)(m))). Direct data are lacking, however, on the question of whether O(2) delivery might limit (V(O(2)(m))) kinetics during high-intensity exercise. Using multiple exercise transitions to enhance confidence in parameter estimation, we therefore investigated the kinetics of, and inter-relationships between, muscle blood flow (Q(m)), a-(V(O(2))) difference and (V(O(2)(m))) following the onset of low-intensity (LI) and high-intensity (HI) exercise. Seven healthy males completed four 6 min bouts of LI and four 6 min bouts of HI single-legged knee-extension exercise. Blood was frequently drawn from the femoral artery and vein during exercise and Q(m), a-(V(O(2))) difference and (V(O(2)(m))) were calculated and subsequently modelled using non-linear regression techniques. For LI, the fundamental component mean response time (MRT(p)) for Q(m) kinetics was significantly shorter than (V(O(2)(m))) kinetics (mean ± SEM, 18 ± 4 vs. 30 ± 4 s; P < 0.05), whereas for HI, the MRT(p) for Q(m) and (V(O(2)(m))) was not significantly different (27 ± 5 vs. 29 ± 4 s, respectively). There was no difference in the MRT(p) for either Q(m) or (V(O(2)(m))) between the two exercise intensities; however, the MRT(p)for a-(V(O(2)) difference was significantly shorter for HI compared with LI (17 ± 3 vs. 28 ± 4 s; P < 0.05). Excess O(2), i.e. oxygen not taken up (Q(m) x (V(O(2))), was significantly elevated within the first 5 s of exercise and remained unaltered thereafter, with no differences between LI and HI. These results indicate that bulk O(2) delivery does not limit (V(O(2)(m))) kinetics following the onset of LI or HI knee-extension exercise.

Exercise tolerance in intermittent cycling: application of the critical power concept

PURPOSE

This study tested the relevance of the critical power (CP) model for explaining exercise tolerance during intermittent high-intensity exercise with different recovery intensities.

METHODS

After estimation of CP and W' from a 3-min all-out test, seven male subjects completed, in randomized order, a cycle test to exhaustion at a severe-intensity constant-work-rate (S-CWR) and four cycle tests to exhaustion using different intermittent ("work-recovery") protocols (i.e., severe-severe (S-S), severe-heavy (S-H), severe-moderate (S-M), and severe-light (S-L)).

RESULTS

The tolerable duration of exercise in S-CWR was 384 ± 48 s, and this was increased by 47%, 100%, and 219% for S-H, S-M, and S-L, respectively (all P < 0.05). Consistent with this, compared with S-CWR (22.9 ± 7.4 kJ), the work done above the CP was significantly greater by 46%, 98%, and 220% for S-H, S-M, and S-L, respectively (all P < 0.05). The slope of the relationship between V˙O₂ and time was significantly reduced for S-H, S-M, and S-L (0.09 ± 0.02, 0.09 ± 0.01, and 0.07 ± 0.02 L·min⁻², respectively) compared with S-CWR (0.16 ± 0.03 L·min⁻², P < 0.05). In addition, the slope of the relationship between integrated EMG and time showed a systematic decline for S-H, S-M, and S-L compared with S-CWR (P < 0.05).

CONCLUSIONS

These results indicate that, when recovery intervals during intermittent exercise are performed below the CP, exercise tolerance is improved in proportion to the reconstitution of the finite W'. The enhanced exercise tolerance with the lower-intensity recovery intervals was associated with a blunted increase in both V˙O₂ and integrated EMG with time.

Older Type 2 diabetic males do not exhibit abnormal pulmonary oxygen uptake and muscle oxygen utilization dynamics during submaximal cycling exercise

There are reports of abnormal pulmonary oxygen uptake (V̇o2) and deoxygenated hemoglobin ([HHb]) kinetics in individuals with Type 2 diabetes (T2D) below 50 yr of age with disease durations of <5 yr. We examined the V̇o2 and muscle [HHb] kinetics in 12 older T2D patients with extended disease durations (age: 65 ± 5 years; disease duration 9.3 ± 3.8 years) and 12 healthy age-matched control participants (CON; age: 62 ± 6 years). Maximal oxygen uptake (V̇o2max) was determined via a ramp incremental cycle test and V̇o2 and [HHb] kinetics were determined during subsequent submaximal step exercise. The V̇o2max was significantly reduced ( P < 0.05) in individuals with T2D compared with CON (1.98 ± 0.43 vs. 2.72 ± 0.40 l/min, respectively) but, surprisingly, V̇o2 kinetics was not different in T2D compared with CON (phase II time constant: 43 ± 17 vs. 41 ± 12 s, respectively). The Δ[HHb]/ΔV̇o2 was significantly higher in T2D compared with CON (235 ± 99 vs. 135 ± 33 AU·l−1·min−1; P < 0.05). Despite a lower V̇o2max, V̇o2 kinetics is not different in older T2D compared with healthy age-matched control participants. The elevated Δ[HHb]/ΔV̇o2 in T2D individuals possibly indicates a compromised muscle blood flow that mandates a greater O2 extraction during exercise. Longer disease duration may result in adaptations in the O2 extraction capabilities of individuals with T2D, thereby mitigating the expected age-related slowing of V̇o2 kinetics.

Dietary nitrate supplementation reduces the O2cost of walking and running: a placebo-controlled study

Dietary supplementation with beetroot juice (BR) has been shown to reduce resting blood pressure and the O2cost of submaximal exercise and to increase tolerance to high-intensity cycling. We tested the hypothesis that the physiological effects of BR were consequent to its high NO3−content per se, and not the presence of other potentially bioactive compounds. We investigated changes in blood pressure, mitochondrial oxidative capacity (Qmax), and physiological responses to walking and moderate- and severe-intensity running following dietary supplementation with BR and NO3−-depleted BR [placebo (PL)]. After control (nonsupplemented) tests, nine healthy, physically active male subjects were assigned in a randomized, double-blind, crossover design to receive BR (0.5 l/day, containing ∼6.2 mmol of NO3−) and PL (0.5 l/day, containing ∼0.003 mmol of NO3−) for 6 days. Subjects completed treadmill exercise tests on days 4 and 5 and knee-extension exercise tests for estimation of Qmax(using31P-magnetic resonance spectroscopy) on day 6 of the supplementation periods. Relative to PL, BR elevated plasma NO2−concentration (183 ± 119 vs. 373 ± 211 nM, P < 0.05) and reduced systolic blood pressure (129 ± 9 vs. 124 ± 10 mmHg, P < 0.01). Qmaxwas not different between PL and BR (0.93 ± 0.05 and 1.05 ± 0.22 mM/s, respectively). The O2cost of walking (0.87 ± 0.12 and 0.70 ± 0.10 l/min in PL and BR, respectively, P < 0.01), moderate-intensity running (2.26 ± 0.27 and 2.10 ± 0.28 l/min in PL and BR, respectively, P < 0.01), and severe-intensity running (end-exercise O2uptake = 3.77 ± 0.57 and 3.50 ± 0.62 l/min in PL and BL, respectively, P < 0.01) was reduced by BR, and time to exhaustion during severe-intensity running was increased by 15% (7.6 ± 1.5 and 8.7 ± 1.8 min in PL and BR, respectively, P < 0.01). In contrast, relative to control, PL supplementation did not alter plasma NO2−concentration, blood pressure, or the physiological responses to exercise. These results indicate that the positive effects of 6 days of BR supplementation on the physiological responses to exercise can be ascribed to the high NO3−content per se.

Muscle fiber recruitment and the slow component of O2 uptake: constant work rate vs. all-out sprint exercise

The slow component of pulmonary O(2) uptake (Vo(2)) during constant work rate (CWR) high-intensity exercise has been attributed to the progressive recruitment of (type II) muscle fibers. We tested the following hypotheses: 1) the Vo(2) slow component gain would be greater in a 3-min all-out cycle test than in a work-matched CWR test, and 2) the all-out test would be associated with a progressive decline, and the CWR test with a progressive increase, in muscle activation, as estimated from the electromyogram (EMG) of the vastus lateralis muscle. Eight men (aged 21-39 yr) completed a ramp incremental test, a 3-min all-out test, and a work- and time-matched CWR test to exhaustion. The maximum Vo(2) attained in an initial ramp incremental test (3.97 ± 0.83 l/min) was reached in both experimental tests (3.99 ± 0.84 and 4.03 ± 0.76 l/min for all-out and CWR, respectively). The Vo(2) slow component was greater (P < 0.05) in the all-out test (1.21 ± 0.31 l/min, 4.2 ± 2.2 ml·min(-1)·W(-1)) than in the CWR test (0.59 ± 0.22 l/min, 1.70 ± 0.5 ml·min(-1)·W(-1)). The integrated EMG declined by 26% (P < 0.001) during the all-out test and increased by 60% (P < 0.05) during the CWR test from the first 30 s to the last 30 s of exercise. The considerable reduction in muscle efficiency in the all-out test in the face of a progressively falling integrated EMG indicates that progressive fiber recruitment is not requisite for development of the Vo(2) slow component during voluntary exercise in humans.

Acute and chronic effects of dietary nitrate supplementation on blood pressure and the physiological responses to moderate-intensity and incremental exercise

Dietary nitrate (NO3−) supplementation with beetroot juice (BR) over 4–6 days has been shown to reduce the O2cost of submaximal exercise and to improve exercise tolerance. However, it is not known whether shorter (or longer) periods of supplementation have similar (or greater) effects. We therefore investigated the effects of acute and chronic NO3−supplementation on resting blood pressure (BP) and the physiological responses to moderate-intensity exercise and ramp incremental cycle exercise in eight healthy subjects. Following baseline tests, the subjects were assigned in a balanced crossover design to receive BR (0.5 l/day; 5.2 mmol of NO3−/day) and placebo (PL; 0.5 l/day low-calorie juice cordial) treatments. The exercise protocol (two moderate-intensity step tests followed by a ramp test) was repeated 2.5 h following first ingestion (0.5 liter) and after 5 and 15 days of BR and PL. Plasma nitrite concentration (baseline: 454 ± 81 nM) was significantly elevated (+39% at 2.5 h postingestion; +25% at 5 days; +46% at 15 days; P < 0.05) and systolic and diastolic BP (baseline: 127 ± 6 and 72 ± 5 mmHg, respectively) were reduced by ∼4% throughout the BR supplementation period ( P < 0.05). Compared with PL, the steady-state V̇o2during moderate exercise was reduced by ∼4% after 2.5 h and remained similarly reduced after 5 and 15 days of BR ( P < 0.05). The ramp test peak power and the work rate at the gas exchange threshold (baseline: 322 ± 67 W and 89 ± 15 W, respectively) were elevated after 15 days of BR (331 ± 68 W and 105 ± 28 W; P < 0.05) but not PL (323 ± 68 W and 84 ± 18 W). These results indicate that dietary NO3−supplementation acutely reduces BP and the O2cost of submaximal exercise and that these effects are maintained for at least 15 days if supplementation is continued.

Acute L-arginine supplementation reduces the O2 cost of moderate-intensity exercise and enhances high-intensity exercise tolerance

It has recently been reported that dietary nitrate (NO(3)(-)) supplementation, which increases plasma nitrite (NO(2)(-)) concentration, a biomarker of nitric oxide (NO) availability, improves exercise efficiency and exercise tolerance in healthy humans. We hypothesized that dietary supplementation with L-arginine, the substrate for NO synthase (NOS), would elicit similar responses. In a double-blind, crossover study, nine healthy men (aged 19-38 yr) consumed 500 ml of a beverage containing 6 g of l-arginine (Arg) or a placebo beverage (PL) and completed a series of "step" moderate- and severe-intensity exercise bouts 1 h after ingestion of the beverage. Plasma NO(2)(-) concentration was significantly greater in the Arg than the PL group (331 ± 198 vs. 159 ± 102 nM, P < 0.05) and systolic blood pressure was significantly reduced (123 ± 3 vs. 131 ± 5 mmHg, P < 0.01). The steady-state O(2) uptake (VO(2)) during moderate-intensity exercise was reduced by 7% in the Arg group (1.48 ± 0.12 vs. 1.59 ± 0.14 l/min, P < 0.05). During severe-intensity exercise, the Vo(2) slow component amplitude was reduced (0.58 ± 0.23 and 0.76 ± 0.29 l/min in Arg and PL, respectively, P < 0.05) and the time to exhaustion was extended (707 ± 232 and 562 ± 145 s in Arg and PL, respectively, P < 0.05) following consumption of Arg. In conclusion, similar to the effects of increased dietary NO(3)(-) intake, elevating NO bioavailability through dietary L-Arg supplementation reduced the O(2) cost of moderate-intensity exercise and blunted the VO(2) slow component and extended the time to exhaustion during severe-intensity exercise.

Physiological monitoring of the Olympic athlete

As the winning margin in Olympic competition is so small, there is a continuous quest for improvements in the preparation of athletes at this standard. Therefore, even the smallest physiological improvements that result from modifications in training strategy, preparation regime or ergogenic aids are potentially useful. Unfortunately, there is a lack of research data on elite competitors, which limits our interpretation of current literature to the elite sporting environment. This places extra responsibility on the physiologist to carefully consider the most appropriate physiological variables to monitor, the best protocols to assess those variables, and the accurate interpretation of the test results. In this paper, we address the key issues of ecological validity, measurement error, and interpretation for the most commonly monitored physiological variables. Where appropriate, we also indicate areas that would benefit from further research.

Dietary nitrate supplementation enhances muscle contractile efficiency during knee-extensor exercise in humans

The purpose of this study was to elucidate the mechanistic bases for the reported reduction in the O2cost of exercise following short-term dietary nitrate (NO3−) supplementation. In a randomized, double-blind, crossover study, seven men (aged 19–38 yr) consumed 500 ml/day of either nitrate-rich beetroot juice (BR, 5.1 mmol of NO3−/day) or placebo (PL, with negligible nitrate content) for 6 consecutive days, and completed a series of low-intensity and high-intensity “step” exercise tests on the last 3 days for the determination of the muscle metabolic (using31P-MRS) and pulmonary oxygen uptake (V̇o2) responses to exercise. On days 4–6, BR resulted in a significant increase in plasma [nitrite] (mean ± SE, PL 231 ± 76 vs. BR 547 ± 55 nM; P < 0.05). During low-intensity exercise, BR attenuated the reduction in muscle phosphocreatine concentration ([PCr]; PL 8.1 ± 1.2 vs. BR 5.2 ± 0.8 mM; P < 0.05) and the increase in V̇o2(PL 484 ± 41 vs. BR 362 ± 30 ml/min; P < 0.05). During high-intensity exercise, BR reduced the amplitudes of the [PCr] (PL 3.9 ± 1.1 vs. BR 1.6 ± 0.7 mM; P < 0.05) and V̇o2(PL 209 ± 30 vs. BR 100 ± 26 ml/min; P < 0.05) slow components and improved time to exhaustion (PL 586 ± 80 vs. BR 734 ± 109 s; P < 0.01). The total ATP turnover rate was estimated to be less for both low-intensity (PL 296 ± 58 vs. BR 192 ± 38 μM/s; P < 0.05) and high-intensity (PL 607 ± 65 vs. BR 436 ± 43 μM/s; P < 0.05) exercise. Thus the reduced O2cost of exercise following dietary NO3−supplementation appears to be due to a reduced ATP cost of muscle force production. The reduced muscle metabolic perturbation with NO3−supplementation allowed high-intensity exercise to be tolerated for a greater period of time.