AIM: Dietary nitrate (NO3 - ) supplementation increases nitric oxide bioavailability and can enhance exercise performance. We investigated the distribution and metabolic fate of ingested NO3 - at rest and during exercise with a focus on skeletal muscle. METHODS: in a randomized, crossover study, 10 healthy volunteers consumed 12.8 mmol 15 N-labeled potassium nitrate (K15 NO3 ; NIT) or potassium chloride placebo (PLA). Muscle biopsies were taken at baseline, at 1- and 3-h post-supplement ingestion, and immediately following the completion of 60 maximal intermittent contractions of the knee extensors. Muscle, plasma, saliva, and urine samples were analyzed using chemiluminescence to determine absolute [NO3 - ] and [NO2 - ], and by mass spectrometry to determine the proportion of NO3 - and NO2 - that was 15 N-labeled. RESULTS: Neither muscle [NO3 - ] nor [NO2 - ] were altered by PLA. Following NIT, muscle [NO3 - ] (but not [NO2 - ]) was elevated at 1-h (from ~35 to 147 nmol/g, p 

PURPOSE: This study aimed 1) to examine the accuracy with which W' reconstitution (W' REC ) is estimated by the W' balance (W' BAL ) models after a 3-min all-out cycling test (3MT), 2) to determine the effects of a 3MT on the power-duration relationship, and 3) to assess whether accounting for changes in the power-duration relationship during exercise improved estimates of W' REC. METHODS: the power-duration relationship and the actual and estimated W' REC were determined for 12 data sets extracted from our laboratory database where participants had completed two 3MT separated by 1-min recovery (i.e. control [C-3MT] and fatigued [F-3MT]). RESULTS: Actual W' REC (6.3 ± 1.4 kJ) was significantly overestimated by the W' BAL·ODE (9.8 ± 1.3 kJ; P < 0.001) and the W' BAL·MORTON (16.9 ± 2.6 kJ; P < 0.001) models but was not significantly different to the estimate provided by the W' BAL·INT (7.5 ± 1.5 kJ; P > 0.05) model. End power (EP) was 7% lower in the F-3MT (263 ± 40 W) compared with the C-3MT (282 ± 44 W; P < 0.001), and work done above EP (WEP) was 61% lower in the F-3MT (6.3 ± 1.4 kJ) compared with the C-3MT (16.9 ± 3.2 kJ). The size of the error in the estimated W' REC was correlated with the reduction in WEP for the W' BAL·INT and W' BAL·ODE models (both r > -0.74, P < 0.01) but not the W' BAL·MORTON model ( r = -0.18, P > 0.05). Accounting for the changes in the power-duration relationship improved the accuracy of the W' BAL·ODE and W' BAL·MORTON , but they remained significantly different to actual W' REC. CONCLUSIONS: These findings demonstrate that the power-duration relationship is altered after a 3MT, and accounting for these changes improves the accuracy of the W' BAL·ODE and the W' BAL·MORTON , but not W' BAL·INT models. These results have important implications for the design and use of mathematical models describing the energetics of exercise performance.

Dietary nitrate (NO3-) supplementation can enhance nitric oxide (NO) bioavailability and lower blood pressure (BP) in humans. The nitrite concentration ([NO2-]) in the plasma is the most commonly used biomarker of increased NO availability. However, it is unknown to what extent changes in other NO congeners, such as S-nitrosothiols (RSNOs), and in other blood components, such as red blood cells (RBC), also contribute to the BP lowering effects of dietary NO3-. We investigated the correlations between changes in NO biomarkers in different blood compartments and changes in BP variables following acute NO3- ingestion. Resting BP was measured and blood samples were collected at baseline, and at 1, 2, 3, 4 and 24 h following acute beetroot juice (∼12.8 mmol NO3-, ∼11 mg NO3-/kg) ingestion in 20 healthy volunteers. Spearman rank correlation coefficients were determined between the peak individual increases in NO biomarkers (NO3-, NO2-, RSNOs) in plasma, RBC and whole blood, and corresponding decreases in resting BP variables. No significant correlation was observed between increased plasma [NO2-] and reduced BP, but increased RBC [NO2-] was correlated with decreased systolic BP (rs = -0.50, P = 0.03). Notably, increased RBC [RSNOs] was significantly correlated with decreases in systolic (rs = -0.68, P = 0.001), diastolic (rs = -0.59, P = 0.008) and mean arterial pressure (rs = -0.64, P = 0.003). Fisher's z transformation indicated no difference in the strength of the correlations between increases in RBC [NO2-] or [RSNOs] and decreased systolic blood pressure. In conclusion, increased RBC [RSNOs] may be an important mediator of the reduction in resting BP observed following dietary NO3- supplementation.

The parameters of the power-duration relationship, critical power (CP) and W′ can be used to accurately predict severe-intensity (>CP) exercise performance. Both endurance-based sports such as cycling and team sports involve severe-intensity exercise. Thus, the optimization of severe-intensity exercise performance is highly relevant. It is advantageous if athletes can monitor their energy usage and energy availability either during an event or in retrospect, in order to inform tactics and pacing strategy. Mathematical models of energy expenditure have been developed, based on the CP concept and designed to measure the dynamic balance of W′ (W′BAL) during exercise. The accuracy of the current W′BAL models is equivocal and may be influenced by day-to-day variability in estimates of CP and W′. Additionally, it is known that dynamic changes in the power-duration parameters can occur during exercise – such changes are currently unaccounted for in the W′BAL models. The purpose of this thesis was two-fold. Firstly, to investigate the accuracy with which the current W′BAL models were able to characterise W′BAL and the influence of inherent variability in CP and W′ on the accuracy of the W′BAL models. Secondly, to examine whether dynamic changes in the power-duration parameters occurred during team sport type exercise. Study 1: W′BAL was modelled for a 16.1-km road TT, using both the point (Best individual fit; BIF) estimates of CP and W′ and the upper and lower 95% CIs of both parameters. Upon completion of the 16.1-km TT, predicted end W′BAL was -14.7 ± 26.4, - 0.82 ± 5.52, and -14.2 ± 20.0 kJ for Morton’s W′BAL model (W′BAL-MORTON), the integral W′BAL model (W′BAL-INT) and the differential W′BAL model (W′BAL-ODE) respectively, with no significant differences (P > 0.05) between models. When accounting for the 95% CIs of CP and W′, the ‘bandwidth’ in predicted end W′BAL was equivalent to 278, 134 and 292% of starting W′ (W′0) for the W′BAL-MORTON, W′BAL-INT and W′BAL-ODE models respectively. These results indicate that: (i) the current W′BAL models have poor predictive accuracy and; (ii) That inherent variability in the power-duration parameters significantly influences the accuracy of the W′BAL models. Study 2: CP, W′ and the speed at which W′ recovered following full depletion (W′REC) were measured in a fresh condition (no exercise prior to fatiguing bout) and following; (i) one 40 min block and; (ii) two 40 min blocks separated by a 15 minute ‘half-time’ interval, of simulated match play. CP and W′REC did not significantly decline (P > 0.05) relative to the fresh condition following either 40 or 80 min of match play. W′ was significantly lower (P < 0.05) in comparison to baseline in

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both the 40- and 80-min conditions but did not significantly differ (P > 0.05) between the 40- and 80-min conditions, indicating that the 15-minute recovery interval permitted full recovery of W′. The above results indicate that significant dynamic changes in the power-duration parameters do not occur during team sport type exercise. Taken collectively, the findings of both studies inform us of potential sources of error in W′BAL modelling.

PURPOSE: We tested the hypotheses that a highly cushioned running shoe (HCS) would 1) improve incremental exercise performance and reduce the oxygen cost (Oc) of submaximal running, and 2) attenuate the deterioration in Oc elicited by muscle damage consequent to a downhill run. METHODS: Thirty-two recreationally active participants completed an incremental treadmill test in an HCS and a control running shoe (CON) for the determination of Oc and maximal performance. Subsequently, participants were pair matched and randomly assigned to one of the two footwear conditions to perform a moderate-intensity running bout before and 48 h after a 30-min downhill run designed to elicit muscle damage. RESULTS: Incremental treadmill test performance was improved (+5.7%; +1:16 min:ss; P < 0.01) in the HCS when assessed in the nondamaged state, relative to CON. This coincided with a significantly lower Oc (-3.2%; -6 mL·kg-1·km-1; P < 0.001) at a range of running speeds and an increase in the speed corresponding to 3 mM blood lactate (+3.2%; +0.4 km·h-1; P < 0.05). As anticipated, the downhill run resulted in significant changes in biochemical, histological, and perceptual markers of muscle damage, and a significant increase in Oc (+5.2%; 10.1 mL·kg-1·km-1) was observed 48 h post. In the presence of muscle damage, Oc was significantly lower in HCS (-4.6%; -10 mL·kg-1·km-1) compared with CON. CONCLUSIONS: These results indicate that HCS improved incremental exercise performance and Oc in the absence of muscle damage and show, for the first time, that despite worsening of Oc consequent to muscle damage, improved Oc in HCS is maintained.

The purpose of this study was to investigate effects of concurrent and independent administration of dietary nitrate (NO3-), administered as NO3--rich beetroot juice (BR; ~12.4 mmol of NO3-), and N-acetylcysteine (NAC; 70 mg·kg-1) on physiological responses during prolonged exercise and subsequent high-intensity exercise tolerance. Sixteen recreationally active males supplemented with NO3--depleted beetroot juice (PL) or BR for 6 days and ingested an acute dose of NAC or maltodextrin (MAL) 1 h prior to performing 1 h of heavy-intensity cycling exercise immediately followed by a severe-intensity time-to-exhaustion (TTE) test in four conditions: 1) PL+MAL, 2) PL+NAC, 3) BR+MAL and 4) BR+NAC. Pre-exercise plasma [NO3-] and nitrite ([NO2-]) were elevated following BR+NAC  and BR+MAL (both P

Dietary nitrate (NO3-) ingestion can be beneficial for health and exercise performance. Recently, based on animal and limited human studies, a skeletal muscle NO3- reservoir has been suggested to be important in whole body nitric oxide (NO) homeostasis. The purpose of this study was to determine the time course of changes in human skeletal muscle NO3- concentration ([NO3-]) following the ingestion of dietary NO3-. Sixteen participants were allocated to either an experimental group (NIT: n = 11) which consumed a bolus of ∼1300 mg (12.8 mmol) potassium nitrate (KNO3), or a placebo group (PLA: n = 5) which consumed a bolus of potassium chloride (KCl). Biological samples (muscle (vastus lateralis), blood, saliva and urine) were collected shortly before NIT or PLA ingestion and at intervals over the course of the subsequent 24 h. At baseline, no differences were observed for muscle [NO3-] and [NO2-] between NIT and PLA (P > 0.05). In PLA, there were no changes in muscle [NO3-] or [NO2-] over time. In NIT, muscle [NO3-] was significantly elevated above baseline (54 ± 29 nmol/g) at 0.5 h, reached a peak at 3 h (181 ± 128 nmol/g), and was not different to baseline from 9 h onwards (P > 0.05). Muscle [NO2-] did not change significantly over time. Following ingestion of a bolus of dietary NO3-, skeletal muscle [NO3-] increases rapidly, reaches a peak at ∼3 h and subsequently declines towards baseline values. Following dietary NO3- ingestion, human m. vastus lateralis [NO3-] expressed a slightly delayed pharmacokinetic profile compared to plasma [NO3-].

UNLABELLED: the influence of anthropometry and body composition on running economy is unclear, with previous investigations involving small relatively homogeneous groups of runners and limited anthropometric/composition measurements. PURPOSE: to comprehensively investigate the relationships of anthropometry and body composition with running economy within a large heterogeneous sample of runners. METHODS: Eighty-five runners (males [M], n = 45; females [F], n = 40), of diverse competitive standard, performed a discontinuous protocol of incremental treadmill running (4-min stages, 1 km·h increments) to establish locomotory energy cost (LEc) of running at submaximal speeds (averaged across 10-12 km·h; the highest common speed < lactate turnpoint). Measurements of anthropometry, including segment lengths, perimeters, masses and moments of inertia, and body composition were obtained using tape-based measurements and dual-energy x-ray absorptiometry. RESULTS: Absolute LEc (ABSLEc, kcal·km) was positively correlated with 21 (of 27) absolute anthropometric variables in both male and female cohorts. Multiple-regression analyses revealed that one variable (mean perimeter z score) explained 49.4% (M) and 68.9% (F) of the variance in ABSLEc. Relative LEc (RELLEc, kcal·kg·km) was also correlated with five (M) and seven (F) normalized anthropometric variables, and regression analyses explained 31.6% (M; percentage bone mass and normalized hip perimeter) and 33.3% (F, normalized forearm perimeter) of the variance in RELLEc. CONCLUSIONS: These findings provide novel and robust evidence that anthropometry and body composition variables, predominantly indicative of relative slenderness, explain a considerable proportion of the variance in running economy (i.e. more slender, lower energy cost). We, therefore, recommend that runners and coaches are attentive to relative slenderness in selecting and training athletes with the aim of enhancing running economy, and improving distance running performance.

We tested the hypotheses that the parameters of the power-duration relationship, estimated as the end-test power (EP) and work done above EP (WEP) during a 3-min all-out exercise test (3MT), would be reduced progressively after 40 min, 80 min, and 2 h of heavy-intensity cycling and that carbohydrate (CHO) ingestion would attenuate the reduction in EP and WEP. Sixteen participants completed a 3MT without prior exercise (control), immediately after 40 min, 80 min, and 2 h of heavy-intensity exercise while consuming a placebo beverage, and also after 2 h of heavy-intensity exercise while consuming a CHO supplement (60 g/h CHO). There was no difference in EP measured without prior exercise (260 ± 37 W) compared with EP after 40 min (268 ± 39 W) or 80 min (260 ± 40 W) of heavy-intensity exercise; however, after 2 h EP was 9% lower compared with control (236 ± 47 W; P < 0.05). There was no difference in WEP measured without prior exercise (17.9 ± 3.3 kJ) compared with after 40 min of heavy-intensity exercise (16.1 ± 3.3 kJ), but WEP was lower (P < 0.05) than control after 80 min (14.7 ± 2.9 kJ) and 2 h (13.8 ± 2.7 kJ). Compared with placebo, CHO ingestion negated the reduction of EP following 2 h of heavy-intensity exercise (254 ± 49 W) but had no effect on WEP (13.5 ± 3.4 kJ). These results reveal a different time course for the deterioration of EP and WEP during prolonged endurance exercise and indicate that EP is sensitive to CHO availability.NEW & NOTEWORTHY the parameters of the power-duration relationship [critical power (CP) and the curvature constant (W')] have typically been considered to be static. Here we report the time course for reductions in CP and W', as estimated with the 3-min all-out cycle test, during 2 h of heavy-intensity exercise. We also show that carbohydrate ingestion during exercise preserves CP, but not W', without altering muscle glycogen depletion. These results provide new mechanistic and practical insight into the power-duration curve and its relationship to exercise-related fatigue development.

KEY POINTS: Nitric oxide (NO), a potent vasodilator and a regulator of many physiological processes, is produced in mammals both enzymatically and by reduction of nitrite and nitrate ions. We have previously reported that, in rodents, skeletal muscle serves as a nitrate reservoir, with nitrate levels greatly exceeding those in blood or other internal organs, and with nitrate being reduced to NO during exercise. In the current study, we show that nitrate concentration is substantially greater in skeletal muscle than in blood and is elevated further by dietary nitrate ingestion in human volunteers. We also show that high-intensity exercise results in a reduction in the skeletal muscle nitrate store following supplementation, likely as a consequence of its reduction to nitrite and NO. We also report the presence of sialin, a nitrate transporter, and xanthine oxidoreductase in human skeletal muscle, indicating that muscle has the necessary apparatus for nitrate transport, storage and metabolism. ABSTRACT: Rodent skeletal muscle contains a large store of nitrate that can be augmented by the consumption of dietary nitrate. This muscle nitrate reservoir has been found to be an important source of nitrite and nitric oxide (NO) via its reduction by tissue xanthine oxidoreductase. To explore if this pathway is also active in human skeletal muscle during exercise, and if it is sensitive to local nitrate availability, we assessed exercise-induced changes in muscle nitrate and nitrite concentrations in young healthy humans, under baseline conditions and following dietary nitrate consumption. We found that baseline nitrate and nitrite concentrations were far higher in muscle than in plasma (∼4-fold and ∼29-fold, respectively), and that the consumption of a single bolus of dietary nitrate (12.8 mmol) significantly elevated nitrate concentration in both plasma (∼19-fold) and muscle (∼5-fold). Consistent with these observations, and with previous suggestions of active muscle nitrate transport, we present western blot data to show significant expression of the active nitrate/nitrite transporter sialin in human skeletal muscle. Furthermore, we report an exercise-induced reduction in human muscle nitrate concentration (by ∼39%), but only in the presence of an increased muscle nitrate store. Our results indicate that human skeletal muscle nitrate stores are sensitive to dietary nitrate intake and may contribute to NO generation during exercise. Together, these findings suggest that skeletal muscle plays an important role in the transport, storage and metabolism of nitrate in humans.

We reinforce the key messages in our earlier review paper that critical power, rather than maximal lactate steady state, provides the better index for defining steady-state vs non-steady state physiological behaviour during exercise.

Purpose: to determine the accuracy of critical power (CP) and Wʹ (the curvature constant of the power-duration relationship) derived from self-paced time-trial (TT) prediction trials using mobile power meters to predict 16.1-km road cycling TT performance. This study also aimed to assess the agreement between functional threshold power (FTP) and CP. Methods: Twelve competitive male cyclists completed an incremental test to exhaustion, a FTP test and 4–5 self-paced TT bouts on a stationary bike within the lab, and a 16.1 km road TT, using mobile power meters. Results: CP and Wʹ derived from the power-duration relationship closely predicted TT performance. The 16.1-km road TT completion time (26.7 ± 2.2 min) was not significantly different from and was significantly correlated with the predicted time-to-completion (27.5 ± 3.3 min, r = 0.89, P  0.05); however, the limits of agreement between CP and FTP were 30 to -36 W. Discussion: the findings of this study indicate that CP and Wʹ determined using mobile power meters during maximal, self-paced TT prediction trials can be used to accurately predict 16.1-km cycling performance, supporting the application of the CP and Wʹ for performance prediction. However, the limits of agreement were too large to consider FTP and CP interchangeable.

The maximal lactate steady state (MLSS) and the critical power (CP) are two widely used indices of the highest oxidative metabolic rate that can be sustained during continuous exercise and are often considered to be synonymous. However, while perhaps having similarities in principle, methodological differences in the assessment of these parameters typically result in MLSS occurring at a somewhat lower power output or running speed and exercise at CP being sustainable for no more than approximately 20-30 min. This has led to the view that CP overestimates the 'actual' maximal metabolic steady state and that MLSS should be considered the 'gold standard' metric for the evaluation of endurance exercise capacity. In this article we will present evidence consistent with the contrary conclusion: i.e. that (1) as presently defined, MLSS naturally underestimates the actual maximal metabolic steady state; and (2) CP alone represents the boundary between discrete exercise intensity domains within which the dynamic cardiorespiratory and muscle metabolic responses to exercise differ profoundly. While both MLSS and CP may have relevance for athletic training and performance, we urge that the distinction between the two concepts/metrics be better appreciated and that comparisons between MLSS and CP, undertaken in the mistaken belief that they are theoretically synonymous, is discontinued. CP represents the genuine boundary separating exercise in which physiological homeostasis can be maintained from exercise in which it cannot, and should be considered the gold standard when the goal is to determine the maximal metabolic steady state.

PURPOSE: to investigate whether oxygen-uptake ([Formula: see text]) kinetics and simulated 4-km cycling performance are synergistically improved by prior "priming" exercise and an all-out starting strategy. METHODS: Nine men completed 4 target work trials (114 ± 17 kJ) to assess [Formula: see text] kinetics and cycling performance in a repeated-measures, crossover experimental design. Trials were initiated with either a 12-s all-out start or a self-selected start and preceded by prior severe-intensity (70%Δ) priming exercise or no priming exercise. RESULTS: the [Formula: see text] mean response time (MRT) was lower (indicative of faster [Formula: see text] kinetics) in the all-out primed condition (20 ± 6 s) than in the all-out unprimed (23 ± 6 s), self-paced-unprimed (42 ± 13 s), and self-paced-primed (42 ± 11 s) trials (P 

The influence of running speed and sex on running economy is unclear and may have been confounded by measurements of oxygen cost that do not account for known differences in substrate metabolism, across a limited range of speeds, and differences in performance standard. Therefore, this study assessed the energy cost of running over a wide range of speeds in high-level and recreational runners to investigate the effect of speed (in absolute and relative terms) and sex (men vs women of equivalent performance standard) on running economy. To determine the energy cost (kcal · kg?1 · km?1) of submaximal running, speed at lactate turn point (sLTP), and maximal rate of oxygen uptake, 92 healthy runners (high-level men, n = 14; high-level women, n = 10; recreational men, n = 35; recreational women, n = 33) completed a discontinuous incremental treadmill test. There were no sex-specific differences in the energy cost of running for the recreational or high-level runners when compared at absolute or relative running speeds (P >. 05). The absolute and relative speed–energy cost relationships for the high-level runners demonstrated a curvilinear U shape with a nadir reflecting the most economical speed at 13 km/h or 70% sLTP. The high-level runners were more economical than the recreational runners at all absolute and relative running speeds (P <. 05). These findings demonstrate that there is an optimal speed for economical running, there is no sex-specific difference, and high-level endurance runners exhibit better running economy than recreational endurance runners.

Purpose: to investigate the influence of β-alanine (BA) supplementation on muscle carnosine content, muscle pH and the power-duration relationship (i.e. critical power and W'). Methods: in a double-blind, randomized, placebo-controlled study, 20 recreationally-active males (22 ± 3 y, V°O2peak 3.73 ± 0.44 L·min-1) ingested either BA (6.4 g/d for 28 d) or placebo (PL) (6.4 g/d) for 28 d. Subjects completed an incremental test and two 3-min all-out tests separated by 1-min on a cycle ergometer pre- and post-supplementation. Muscle pH was assessed using 31P-magnetic resonance spectroscopy (MRS) during incremental (INC KEE) and intermittent knee-extension exercise (INT KEE). Muscle carnosine content was determined using 1H-MRS. Results: There were no differences in the change in muscle carnosine content from pre- to post-intervention (PL: 1 ± 16% vs. BA: -4 ± 25%) or in muscle pH during INC KEE or INT KEE (P > 0.05) between PL and BA, but blood pH (PL: -0.06 ± 0.10 vs. BA: 0.09 ± 0.13) during the incremental test was elevated post-supplementation in the BA group only (P < 0.05). The changes from pre- to post-supplementation in critical power (PL: -8 ± 18 W vs. BA: -6 ± 17 W) and W' (PL: 1.8 ± 3.3 kJ vs. BA: 1.5 ± 1.7 kJ) were not different between groups. No relationships were detected between muscle carnosine content and indices of exercise performance. Conclusions: BA supplementation had no significant effect on muscle carnosine content and no influence on intramuscular pH during incremental or high-intensity intermittent knee-extension exercise. The small increase in blood pH following BA supplementation was not sufficient to significantly alter the power-duration relationship or exercise performance.

This study investigated the relationship between challenge and threat states and anaerobic power, core affect, perceived exertion, and self-focused attention during a competitive sprint cycling task. Thirty-five participants completed familiarization, baseline, and pressurized Wingate tests. Before the pressurized test, challenge and threat states were measured via self-report (demand resource evaluation score) and cardiovascular reactivity (challenge/threat index). After the pressurized test, relative peak power, core affect, perceived exertion, and self-focused attention were assessed. Evaluating the pressurized test as more of a challenge (i.e. coping resources match or exceed task demands) was associated with greater increases in relative peak power (vs. the baseline test) and more positive affect, as well as marginally lower perceived exertion and less self-focused attention. However, challenge/threat index failed to predict any variable. Although the findings raise questions about the value of the physiological pattern underlying a challenge state for anaerobic power, they highlight the benefits of evaluating a physically-demanding task as a challenge.

We hypothesized that 4 wk of dietary nitrate supplementation would enhance exercise performance and muscle metabolic adaptations to sprint interval training (SIT). Thirty-six recreationally active subjects, matched on key variables at baseline, completed a series of exercise tests before and following a 4-wk period in which they were allocated to one of the following groups: 1) SIT and [Formula: see text]-depleted beetroot juice as a placebo (SIT+PL); 2) SIT and [Formula: see text]-rich beetroot juice (~13 mmol [Formula: see text]/day; SIT+BR); or 3) no training and [Formula: see text]-rich beetroot juice (NT+BR). During moderate-intensity exercise, pulmonary oxygen uptake was reduced by 4% following 4 wk of SIT+BR and NT+BR (P < 0.05) but not SIT+PL. The peak work rate attained during incremental exercise increased more in SIT+BR than in SIT+PL (P < 0.05) or NT+BR (P < 0.001). The reduction in muscle and blood [lactate] and the increase in muscle pH from preintervention to postintervention were greater at 3 min of severe-intensity exercise in SIT+BR compared with SIT+PL and NT+BR (P < 0.05). However, the change in severe-intensity exercise performance was not different between SIT+BR and SIT+PL (P > 0.05). The relative proportion of type IIx muscle fibers in the vastus lateralis muscle was reduced in SIT+BR only (P < 0.05). These findings suggest that BR supplementation may enhance some aspects of the physiological adaptations to SIT.NEW & NOTEWORTHY We investigated the influence of nitrate-rich and nitrate-depleted beetroot juice on the muscle metabolic and physiological adaptations to 4 wk of sprint interval training. Compared with placebo, dietary nitrate supplementation reduced the O2 cost of submaximal exercise, resulted in greater improvement in incremental (but not severe-intensity) exercise performance, and augmented some muscle metabolic adaptations to training. Nitrate supplementation may facilitate some of the physiological responses to sprint interval training.

Lactate or gas exchange threshold (GET) and critical power (CP) are closely associated with human exercise performance. We tested the hypothesis that the limit of tolerance (Tlim) during cycle exercise performed within the exercise intensity domains demarcated by GET and CP is linked to discrete muscle metabolic and neuromuscular responses. Eleven men performed a ramp incremental exercise test, 4-5 severe-intensity (SEV; >CP) constant-work-rate (CWR) tests until Tlim, a heavy-intensity (HVY; GET) CWR test until Tlim, and a moderate-intensity (MOD;. 0.05) muscle metabolic milieu (i.e. low pH and [PCr] and high [lactate]) was attained at Tlim (approximately 2-14 min) for all SEV exercise bouts. The muscle metabolic perturbation was greater at Tlim following SEV compared with HVY, and also following SEV and HVY compared with MOD (all P < 0.05). The normalized M-wave amplitude for the vastus lateralis (VL) muscle decreased to a similar extent following SEV (-38 ± 15%), HVY (-68 ± 24%), and MOD (-53 ± 29%), (P > 0.05). Neural drive to the VL increased during SEV (4 ± 4%; P < 0.05) but did not change during HVY or MOD (P > 0.05). During SEV and HVY, but not MOD, the rates of change in M-wave amplitude and neural drive were correlated with changes in muscle metabolic ([PCr], [lactate]) and blood ionic/acid-base status ([lactate], [K+]) (P < 0.05). The results of this study indicate that the metabolic and neuromuscular determinants of fatigue development differ according to the intensity domain in which the exercise is performed.NEW & NOTEWORTHY the gas exchange threshold and the critical power demarcate discrete exercise intensity domains. For the first time, we show that the limit of tolerance during whole-body exercise within these domains is characterized by distinct metabolic and neuromuscular responses. Fatigue development during exercise greater than critical power is associated with the attainment of consistent "limiting" values of muscle metabolites, whereas substrate availability and limitations to muscle activation may constrain performance at lower intensities.

Although a number of algorithms exist for estimating ground contact events (GCEs) from kinematic data during running, they are typically only applicable to heelstrike running, or have only been evaluated at a single running speed. The purpose of this study was to investigate the accuracy of four kinematics-based algorithms to estimate GCEs over a range of running speeds and footstrike types. Subjects ran over a force platform at a range of speeds; kinetic and kinematic data was captured at 1000 Hz, and kinematic data was downsampled to 250 Hz. A windowing process initially identified reduced time windows containing touchdown and toe-off. Algorithms based on acceleration and jerk signals of the foot markers were used to estimate touchdown (2 algorithms), toe-off (2 algorithms), and ground contact time (GCT) (4 algorithms), and compared to synchronous ‘gold standard’ force platform data. An algorithm utilising the vertical acceleration peak of either the heel or first metatarsal marker (whichever appeared first) for touchdown, and the vertical jerk peak of the hallux marker for toe-off, resulted in the lowest offsets (+3.1 ms, 95% Confidence Interval (CI): −11.8 to +18.1 ms; and +2.1 ms, CI: −8.1 to +12.2 ms respectively). This method also resulted in the smallest offset in GCT (−1.1 ms, CI: −18.6 to +16.4 ms). Offsets in GCE and GCT estimates from all algorithms were typically negatively correlated to running speed, with offsets decreasing as speed increased. Assessing GCEs and GCT using this method may be useful when a force platform is unavailable or impractical.

PURPOSE: the parameters of the power-duration relationship (i.e. the critical power, CP, and the curvature constant, W') may theoretically predict maximal performance capability for exercise above the CP. The CP and W' are associated with the parameters of oxygen uptake ([Formula: see text]O2) kinetics, which can be altered by manipulation of the work-rate forcing function. We tested the hypothesis that the CP and W' derived from constant work-rate (CWR) prediction trials would overestimate ramp incremental exercise performance. METHODS: Thirty subjects (males, n = 28; females, n = 2) performed a ramp incremental test, and 3-5 CWR prediction trials for the determination of the CP and W'. Multiple ramp incremental tests and corresponding CP and W' estimates were available for some subjects such that in total 51 ramp test performances were predicted. RESULTS: the ramp incremental test performance (729 ± 113 s) was overestimated by the CP and W' estimates derived from the best (751 ± 114 s, P 

We hypothesised 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 W′ (curvature constant 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 Tlim isotime to test hypothesis 1. Eleven men performed 3-min all-out tests and donated muscle biopsies to test hypothesis 2. Below CP, muscle [PCr] (42.6±7.1 vs 49.4±6.9 mmol/kgDW), [La-] (34.8±12.6 vs 35.5±13.2 mmol/kgDW) 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/kgDW) and lower ([PCr] 24.2±3.9 mmol/kgDW; pH 6.84±0.06) (P

UNLABELLED: it is possible that dietary nitrate (NO3 (-)) supplementation may improve both physical and cognitive performance via its influence on blood flow and cellular energetics. PURPOSE: to investigate the effects of dietary NO3 (-) supplementation on exercise performance and cognitive function during a prolonged intermittent sprint test (IST) protocol, which was designed to reflect typical work patterns during team sports. METHODS: in a double-blind randomised crossover study, 16 male team-sport players received NO3 (-)-rich (BR; 140 mL day(-1); 12.8 mmol of NO3 (-)), and NO3 (-)-depleted (PL; 140 mL day(-1); 0.08 mmol NO3 (-)) beetroot juice for 7 days. On day 7 of supplementation, subjects completed the IST (two 40-min "halves" of repeated 2-min blocks consisting of a 6-s "all-out" sprint, 100-s active recovery and 20 s of rest), on a cycle ergometer during which cognitive tasks were simultaneously performed. RESULTS: Total work done during the sprints of the IST was greater in BR (123 ± 19 kJ) compared to PL (119 ± 17 kJ; P < 0.05). Reaction time of response to the cognitive tasks in the second half of the IST was improved in BR compared to PL (BR first half: 820 ± 96 vs. second half: 817 ± 86 ms; PL first half: 824 ± 114 vs. second half: 847 ± 118 ms; P < 0.05). There was no difference in response accuracy. CONCLUSIONS: These findings suggest that dietary NO3 (-) enhances repeated sprint performance and may attenuate the decline in cognitive function (and specifically reaction time) that may occur during prolonged intermittent exercise.

The parameters of the power-duration relationship for severe-intensity exercise (i.e. the critical power (CP) and the curvature constant (W')) are related to the kinetics of pulmonary O2 uptake, which may be altered by pacing strategy. We tested the hypothesis that the CP would be higher when derived from a series of self-paced time-trials (TT) than when derived from the conventional series of constant work-rate (CWR) exercise tests. Ten male subjects (age, 21.5 ± 1.9 years; mass, 75.2 ± 11.5 kg) completed 3-4 CWR and 3-4 TT prediction trial protocols on a cycle ergometer for the determination of the CP and W'. The CP derived from the TT protocol (265 ± 44 W) was greater (P < 0.05) than the CP derived from the CWR protocol (250 ± 47 W), while the W' was not different between protocols (TT: 18.1 ± 5.7 kJ, CWR: 20.6 ± 7.4 kJ, P > 0.05). The mean response time of pulmonary O2 uptake was shorter during the TTs than the CWR trials (TT: 34 ± 16, CWR: 39 ± 19 s, P < 0.05). The CP was correlated with the total O2 consumed in the first 60 s across both protocols (r = 0.88, P < 0.05, n = 20). These results suggest that in comparison with the conventional CWR exercise protocol, a self-selected pacing strategy enhances CP and improves severe-intensity exercise performance. The greater CP during TT compared with CWR exercise has important implications for performance prediction, suggesting that TT completion times may be overestimated by CP and W' parameters derived from CWR protocols.

It has been shown that the critical power (CP) in cycling estimated using a novel 3-min all-out protocol is reliable and closely matches the CP derived from conventional procedures. The purpose of this study was to assess the predictive validity of the all-out test CP estimate. We hypothesised that the all-out test CP would be significantly correlated with 16.1-km road time-trial (TT) performance and more strongly correlated with performance than the gas exchange threshold (GET), respiratory compensation point (RCP) and V̇O2 max. Ten club-level male cyclists (mean±SD: age 33.8±8.2 y, body mass 73.8±4.3 kg, V̇O2 max 60±4 ml·kg-1·min-1) performed a 10-mile road TT, a ramp incremental test to exhaustion, and two 3-min all-out tests, the first of which served as familiarisation. The 16.1-km TT performance (27.1±1.2 min) was significantly correlated with the CP (309±34 W; r=-0.83, P

It has been shown that the critical power (CP) in cycling estimated using a novel 3-min all-out protocol is reliable and closely matches the CP derived from conventional procedures. The purpose of this study was to assess the predictive validity of the all-out test CP estimate. We hypothesised that the all-out test CP would be significantly correlated with 16.1-km road time-trial (TT) performance and more strongly correlated with performance than the gas exchange threshold (GET), respiratory compensation point (RCP) and VO2 max. Ten club-level male cyclists (mean±SD: age 33.8±8.2 y, body mass 73.8±4.3 kg, VO2 max 60±4 ml·kg(-1)·min(-1)) performed a 10-mile road TT, a ramp incremental test to exhaustion, and two 3-min all-out tests, the first of which served as familiarisation. The 16.1-km TT performance (27.1±1.2 min) was significantly correlated with the CP (309±34 W; r = -0.83, P

Recent studies have suggested that dietary inorganic nitrate (NO 3- ) supplementation may improve muscle efficiency and endurance exercise tolerance but possible effects during team sport-specific intense intermittent exercise have not been examined. We hypothesized that NO 3- supplementation would enhance high-intensity intermittent exercise performance. Fourteen male recreational team-sport players were assigned in a double-blind, randomized, crossover design to consume 490 mL of concentrated, nitrate-rich beetroot juice (BR) and nitrate-depleted placebo juice (PL) over ∼30 h preceding the completion of a Yo-Yo intermittent recovery level 1 test (Yo-Yo IR1). Resting plasma nitrite concentration ([NO 2- ]) was ∼400 % greater in BR compared to PL. Plasma [NO 2- ] declined by 20 % in PL (P < 0.05) and by 54 % in BR (P < 0.05) from pre-exercise to end-exercise. Performance in the Yo-Yo IR1 was 4.2 % greater (P < 0.05) with BR (1,704 ± 304 m) compared to PL (1,636 ± 288 m). Blood [lactate] was not different between BR and PL, but the mean blood [glucose] was lower (3.8 ± 0.8 vs. 4.2 ± 1.1 mM, P < 0.05) and the rise in plasma [K + ] tended to be reduced in BR compared to PL (P = 0.08). These findings suggest that NO 3- supplementation may promote NO production via the nitrate-nitrite-NO pathway and enhance Yo-Yo IR1 test performance, perhaps by facilitating greater muscle glucose uptake or by better maintaining muscle excitability. Dietary NO 3- supplementation improves performance during intense intermittent exercise and may be a useful ergogenic aid for team sports players. © 2013 Springer-Verlag Berlin Heidelberg.

Recent studies have suggested that dietary inorganic nitrate (NO₃(-)) supplementation may improve muscle efficiency and endurance exercise tolerance but possible effects during team sport-specific intense intermittent exercise have not been examined. We hypothesized that NO₃(-) supplementation would enhance high-intensity intermittent exercise performance. Fourteen male recreational team-sport players were assigned in a double-blind, randomized, crossover design to consume 490 mL of concentrated, nitrate-rich beetroot juice (BR) and nitrate-depleted placebo juice (PL) over ~30 h preceding the completion of a Yo-Yo intermittent recovery level 1 test (Yo-Yo IR1). Resting plasma nitrite concentration ([NO₂(-)]) was ~400% greater in BR compared to PL. Plasma [NO₂(-)] declined by 20% in PL (P < 0.05) and by 54 % in BR (P < 0.05) from pre-exercise to end-exercise. Performance in the Yo-Yo IR1 was 4.2% greater (P < 0.05) with BR (1,704 ± 304 m) compared to PL (1,636 ± 288 m). Blood [lactate] was not different between BR and PL, but the mean blood [glucose] was lower (3.8 ± 0.8 vs. 4.2 ± 1.1 mM, P < 0.05) and the rise in plasma [K(+)] tended to be reduced in BR compared to PL (P = 0.08). These findings suggest that NO₃(-) supplementation may promote NO production via the nitrate-nitrite-NO pathway and enhance Yo-Yo IR1 test performance, perhaps by facilitating greater muscle glucose uptake or by better maintaining muscle excitability. Dietary NO₃(-) supplementation improves performance during intense intermittent exercise and may be a useful ergogenic aid for team sports players.