scholarly journals Cocoa-flavanols enhance moderate-intensity pulmonary $$\dot{V}{\text{O}}_{2}$$ kinetics but not exercise tolerance in sedentary middle-aged adults

2021 ◽  
Author(s):  
Daniel G. Sadler ◽  
Richard Draijer ◽  
Claire E. Stewart ◽  
Helen Jones ◽  
Simon Marwood ◽  
...  
Keyword(s):  
Exercise Tolerance ◽  
Slow Component ◽  
Moderate Intensity ◽  
Moderate Activity ◽  
Middle Aged ◽  
Moderate Intensity Exercise ◽  
Exercise Tests ◽  
Severe Intensity ◽  
Middle Aged Adults ◽  
Cocoa Flavanols

Abstract Introduction Cocoa flavanols (CF) may exert health benefits through their potent vasodilatory effects, which are perpetuated by elevations in nitric oxide (NO) bioavailability. These vasodilatory effects may contribute to improved delivery of blood and oxygen (O2) to exercising muscle. Purpose Therefore, the objective of this study was to examine how CF supplementation impacts pulmonary O2 uptake ($$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 ) kinetics and exercise tolerance in sedentary middle-aged adults. Methods We employed a double-blind cross-over, placebo-controlled design whereby 17 participants (11 male, 6 female; mean ± SD, 45 ± 6 years) randomly received either 7 days of daily CF (400 mg) or placebo (PL) supplementation. On day 7, participants completed a series of ‘step’ moderate- and severe-intensity exercise tests for the determination of $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 kinetics. Results During moderate-intensity exercise, the time constant of the phase II $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 kinetics ($$\tau \dot{V}{\text{O}}_{2}$$ τ V ˙ O 2 ) was decreased by 15% in CF as compared to PL (mean ± SD; PL 40 ± 12 s vs. CF 34 ± 9 s, P = 0.019), with no differences in the amplitude of $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 (A$$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 ; PL 0.77 ± 0.32 l min−1 vs. CF 0.79 ± 0.34 l min−1, P = 0.263). However, during severe-intensity exercise, $$\tau \dot{V}{\text{O}}_{2}$$ τ V ˙ O 2 , the amplitude of the slow component ($${\text{SC}}\dot{V}{\text{O}}_{2}$$ SC V ˙ O 2 ) and exercise tolerance (PL 435 ± 58 s vs. CF 424 ± 47 s, P = 0.480) were unchanged between conditions. Conclusion Our data show that acute CF supplementation enhanced $$\dot{V}{\text{O}}_{2}$$ V ˙ O 2 kinetics during moderate-, but not severe-intensity exercise in middle-aged participants. These novel effects of CFs, in this demographic, may contribute to improved tolerance of moderate-activity physical activities, which appear commonly present in daily life. Trial registration Registered under ClinicalTrials.gov Identifier no. NCT04370353, 30/04/20 retrospectively registered

scholarly journals Cocoa-flavanols enhance moderate-intensity pulmonary V̇O2 kinetics but not exercise tolerance in sedentary middle-aged adults: A randomised controlled trial

2020 ◽  
Author(s):  
Daniel Sadler ◽  
Richard Draijer ◽  
Claire E. Stewart ◽  
Helen Jones ◽  
Simon Marwood ◽  
...  
Keyword(s):  
Oxygen Uptake ◽  
Exercise Tolerance ◽  
Oxygen Uptake Kinetics ◽  
Uptake Kinetics ◽  
Moderate Intensity ◽  
Moderate Activity ◽  
Middle Aged ◽  
Severe Intensity ◽  
Middle Aged Adults ◽  
Cocoa Flavanols

Abstract Background: Cocoa flavanols (CF) may exert health benefits through their potent vasodilatory effects which are perpetuated by elevations in nitric oxide (NO) bioavailability. These vasodilatory effects may contribute to improved delivery of blood and oxygen to exercising muscle.Objective: Therefore, the objective of this study was to examine how CF supplementation impacts pulmonary oxygen uptake (V̇O2) kinetics and exercise tolerance in sedentary middle-aged adults.Methods: We employed a double-blind cross-over, placebo-controlled design whereby 17 participants (11 male, 6 female; mean±SD, 45±6 years) randomly received either 7 days of daily CF (400 mg) or placebo (PL) supplementation. On day 7, participants completed a series of ‘step’ moderate- and severe-intensity exercise tests for the determination of oxygen uptake kinetics.Results: During moderate-intensity exercise, the time constant of the fundamental phase of V̇O2 kinetics (τV̇O2) was decreased by 15% in CF as compared to PL (mean±SD; PL: 40±12 vs. CF: 34±9 s, P=0.019), with no differences in the amplitude of V̇O2 (AV̇O2; PL: 0.77±0.32 vs. CF: 0.79±0.34 l min−1, P=0.263). However, during severe-intensity exercise, τV̇O2,the amplitude of the slow component (SCV̇O2) and exercise tolerance (PL: 435±58 vs. CF: 424±47 s, P=0.480) were unchanged between conditions.Conclusions: Our data show that acute CF supplementation enhanced oxygen uptake kinetics during moderate-, but not severe-intensity exercise in middle-aged participants. These novel effects of CFs, in this demographic, may contribute to improved tolerance of moderate-activity physical activities, which appear commonly present in daily life.Registered under ClinicalTrials.gov Identifier no. NCT04370353

Dietary nitrate supplementation: effects on plasma nitrite and pulmonary O2 uptake dynamics during exercise in hypoxia and normoxia

2014 ◽  
Vol 307 (7) ◽  
pp. R920-R930 ◽  
Author(s):  
James Kelly ◽  
Anni Vanhatalo ◽  
Stephen J. Bailey ◽  
Lee J. Wylie ◽  
Christopher Tucker ◽  
...  
Keyword(s):  
Exercise Tolerance ◽  
Moderate Intensity ◽  
Beetroot Juice ◽  
Moderate Intensity Exercise ◽  
Exercise Tests ◽  
Double Blind ◽  
Dietary Nitrate ◽  
Severe Intensity ◽  
Rate Of Decline ◽  
Plasma Nitrite

We investigated the effects of dietary nitrate (NO3−) supplementation on the concentration of plasma nitrite ([NO2−]), oxygen uptake (V̇o2) kinetics, and exercise tolerance in normoxia (N) and hypoxia (H). In a double-blind, crossover study, 12 healthy subjects completed cycle exercise tests, twice in N (20.9% O2) and twice in H (13.1% O2). Subjects ingested either 140 ml/day of NO3−-rich beetroot juice (8.4 mmol NO3; BR) or NO3−-depleted beetroot juice (PL) for 3 days prior to moderate-intensity and severe-intensity exercise tests in H and N. Preexercise plasma [NO2−] was significantly elevated in H-BR and N-BR compared with H-PL ( P < 0.01) and N-PL ( P < 0.01). The rate of decline in plasma [NO2−] was greater during severe-intensity exercise in H-BR [−30 ± 22 nM/min, 95% confidence interval (CI); −44, −16] compared with H-PL (−7 ± 10 nM/min, 95% CI; −13, −1; P < 0.01) and in N-BR (−26 ± 19 nM/min, 95% CI; −38, −14) compared with N-PL (−1 ± 6 nM/min, 95% CI; −5, 2; P < 0.01). During moderate-intensity exercise, steady-state pulmonary V̇o2 was lower in H-BR (1.91 ± 0.28 l/min, 95% CI; 1.77, 2.13) compared with H-PL (2.05 ± 0.25 l/min, 95% CI; 1.93, 2.26; P = 0.02), and V̇o2 kinetics was faster in H-BR (τ: 24 ± 13 s, 95% CI; 15, 32) compared with H-PL (31 ± 11 s, 95% CI; 23, 38; P = 0.04). NO3− supplementation had no significant effect on V̇o2 kinetics during severe-intensity exercise in hypoxia, or during moderate-intensity or severe-intensity exercise in normoxia. Tolerance to severe-intensity exercise was improved by NO3− in hypoxia (H-PL: 197 ± 28; 95% CI; 173, 220 vs. H-BR: 214 ± 43 s, 95% CI; 177, 249; P = 0.04) but not normoxia. The metabolism of NO2− during exercise is altered by NO3− supplementation, exercise, and to a lesser extent, hypoxia. In hypoxia, NO3− supplementation enhances V̇o2 kinetics during moderate-intensity exercise and improves severe-intensity exercise tolerance. These findings may have important implications for individuals exercising at altitude.

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

2010 ◽  
Vol 109 (5) ◽  
pp. 1394-1403 ◽  
Author(s):  
Stephen J. Bailey ◽  
Paul G. Winyard ◽  
Anni Vanhatalo ◽  
Jamie R. Blackwell ◽  
Fred J. DiMenna ◽  
...  
Keyword(s):  
Exercise Tolerance ◽  
Slow Component ◽  
Moderate Intensity ◽  
Time To Exhaustion ◽  
Moderate Intensity Exercise ◽  
Double Blind ◽  
Healthy Humans ◽  
Severe Intensity ◽  
Component Amplitude ◽  
Plasma Nitrite

It has recently been reported that dietary nitrate (NO3−) supplementation, which increases plasma nitrite (NO2−) 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 NO2− 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 O2 uptake (V̇o2) 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 V̇o2 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 NO3− intake, elevating NO bioavailability through dietary l-Arg supplementation reduced the O2 cost of moderate-intensity exercise and blunted the V̇o2 slow component and extended the time to exhaustion during severe-intensity exercise.

scholarly journals Dietary nitrate supplementation attenuates the reduction in exercise tolerance following blood donation

2016 ◽  
Vol 311 (6) ◽  
pp. H1520-H1529 ◽  
Author(s):  
Sinead T. J. McDonagh ◽  
Anni Vanhatalo ◽  
Jonathan Fulford ◽  
Lee J. Wylie ◽  
Stephen J. Bailey ◽  
...  
Keyword(s):  
Exercise Tolerance ◽  
Peak Power ◽  
Blood Donation ◽  
Hemoglobin Concentration ◽  
Moderate Intensity ◽  
Beetroot Juice ◽  
Moderate Intensity Exercise ◽  
Exercise Tests ◽  
Dietary Nitrate ◽  
Nitrate Supplementation

We tested the hypothesis that dietary nitrate (NO3−)-rich beetroot juice (BR) supplementation could partially offset deteriorations in O2transport and utilization and exercise tolerance after blood donation. Twenty-two healthy volunteers performed moderate-intensity and ramp incremental cycle exercise tests prior to and following withdrawal of ∼450 ml of whole blood. Before donation, all subjects consumed seven 70-ml shots of NO3−-depleted BR [placebo (PL)] in the 48 h preceding the exercise tests. During the 48 h after blood donation, subjects consumed seven shots of BR (each containing 6.2 mmol of NO3−, n = 11) or PL ( n = 11) before repeating the exercise tests. Hemoglobin concentration and hematocrit were reduced by ∼8–9% following blood donation ( P < 0.05), with no difference between the BR and PL groups. Steady-state O2uptake during moderate-intensity exercise was ∼4% lower after than before donation in the BR group ( P < 0.05) but was unchanged in the PL group. The ramp test peak power decreased from predonation (341 ± 70 and 331 ± 68 W in PL and BR, respectively) to postdonation (324 ± 69 and 322 ± 66 W in PL and BR, respectively) in both groups ( P < 0.05). However, the decrement in performance was significantly less in the BR than PL group (2.7% vs. 5.0%, P < 0.05). NO3−supplementation reduced the O2cost of moderate-intensity exercise and attenuated the decline in ramp incremental exercise performance following blood donation. These results have implications for improving functional capacity following blood loss.

scholarly journals Beetroot juice supplementation speeds O2uptake kinetics and improves exercise tolerance during severe-intensity exercise initiated from an elevated metabolic rate

2013 ◽  
Vol 305 (12) ◽  
pp. R1441-R1450 ◽  
Author(s):  
Brynmor C. Breese ◽  
Melitta A. McNarry ◽  
Simon Marwood ◽  
Jamie R. Blackwell ◽  
Stephen J. Bailey ◽  
...  
Keyword(s):  
Metabolic Rate ◽  
Exercise Tolerance ◽  
Near Infrared ◽  
Order Type ◽  
Moderate Intensity ◽  
Type Ii ◽  
Beetroot Juice ◽  
Moderate Intensity Exercise ◽  
Double Blind ◽  
Severe Intensity

Recent research has suggested that dietary nitrate (NO3−) supplementation might alter the physiological responses to exercise via specific effects on type II muscle. Severe-intensity exercise initiated from an elevated metabolic rate would be expected to enhance the proportional activation of higher-order (type II) muscle fibers. The purpose of this study was, therefore, to test the hypothesis that, compared with placebo (PL), NO3−-rich beetroot juice (BR) supplementation would speed the phase II V̇o2kinetics (τp) and enhance exercise tolerance during severe-intensity exercise initiated from a baseline of moderate-intensity exercise. Nine healthy, physically active subjects were assigned in a randomized, double-blind, crossover design to receive BR (140 ml/day, containing ∼8 mmol of NO3−) and PL (140 ml/day, containing ∼0.003 mmol of NO3−) for 6 days. On days 4, 5, and 6 of the supplementation periods, subjects completed a double-step exercise protocol that included transitions from unloaded to moderate-intensity exercise (U→M) followed immediately by moderate to severe-intensity exercise (M→S). Compared with PL, BR elevated resting plasma nitrite concentration (PL: 65 ± 32 vs. BR: 348 ± 170 nM, P < 0.01) and reduced the V̇o2τpin M→S (PL: 46 ± 13 vs. BR: 36 ± 10 s, P < 0.05) but not U→M (PL: 25 ± 4 vs. BR: 27 ± 6 s, P > 0.05). During M→S exercise, the faster V̇o2kinetics coincided with faster near-infrared spectroscopy-derived muscle [deoxyhemoglobin] kinetics (τ; PL: 20 ± 9 vs. BR: 10 ± 3 s, P < 0.05) and a 22% greater time-to-task failure (PL: 521 ± 158 vs. BR: 635 ± 258 s, P < 0.05). Dietary supplementation with NO3−-rich BR juice speeds V̇o2kinetics and enhances exercise tolerance during severe-intensity exercise when initiated from an elevated metabolic rate.

Beetroot juice and exercise: pharmacodynamic and dose-response relationships

2013 ◽  
Vol 115 (3) ◽  
pp. 325-336 ◽  
Author(s):  
Lee J. Wylie ◽  
James Kelly ◽  
Stephen J. Bailey ◽  
Jamie R. Blackwell ◽  
Philip F. Skiba ◽  
...  
Keyword(s):  
Dose Response ◽  
Cardiovascular Health ◽  
Physiological Responses ◽  
Moderate Intensity ◽  
Dependent Manner ◽  
Beetroot Juice ◽  
Moderate Intensity Exercise ◽  
Exercise Tests ◽  
Severe Intensity ◽  
Plasma Nitrite

Dietary supplementation with beetroot juice (BR), containing approximately 5–8 mmol inorganic nitrate (NO3−), increases plasma nitrite concentration ([NO2−]), reduces blood pressure, and may positively influence the physiological responses to exercise. However, the dose-response relationship between the volume of BR ingested and the physiological effects invoked has not been investigated. In a balanced crossover design, 10 healthy men ingested 70, 140, or 280 ml concentrated BR (containing 4.2, 8.4, and 16.8 mmol NO3−, respectively) or no supplement to establish the effects of BR on resting plasma [NO3−] and [NO2−] over 24 h. Subsequently, on six separate occasions, 10 subjects completed moderate-intensity and severe-intensity cycle exercise tests, 2.5 h postingestion of 70, 140, and 280 ml BR or NO3−-depleted BR as placebo (PL). Following acute BR ingestion, plasma [NO2−] increased in a dose-dependent manner, with the peak changes occurring at approximately 2–3 h. Compared with PL, 70 ml BR did not alter the physiological responses to exercise. However, 140 and 280 ml BR reduced the steady-state oxygen (O2) uptake during moderate-intensity exercise by 1.7% ( P = 0.06) and 3.0% ( P < 0.05), whereas time-to-task failure was extended by 14% and 12% (both P < 0.05), respectively, compared with PL. The results indicate that whereas plasma [NO2−] and the O2 cost of moderate-intensity exercise are altered dose dependently with NO3−-rich BR, there is no additional improvement in exercise tolerance after ingesting BR containing 16.8 compared with 8.4 mmol NO3−. These findings have important implications for the use of BR to enhance cardiovascular health and exercise performance in young adults.

scholarly journals Ergogenic effects of beetroot juice supplementation during severe-intensity exercise in obese adolescents

2018 ◽  
Vol 315 (3) ◽  
pp. R453-R460 ◽  
Author(s):  
Letizia Rasica ◽  
Simone Porcelli ◽  
Mauro Marzorati ◽  
Desy Salvadego ◽  
Alessandra Vezzoli ◽  
...  
Keyword(s):  
Exercise Tolerance ◽  
Healthy Subjects ◽  
Slow Component ◽  
Moderate Intensity ◽  
Time To Exhaustion ◽  
Beetroot Juice ◽  
Obese Adolescents ◽  
Physiological Variables ◽  
Severe Intensity ◽  
Ergogenic Effects

Previous studies showed a higher O2 cost of exercise, and therefore, a reduced exercise tolerance in patients with obesity during constant work rate (CWR) exercise compared with healthy subjects. Among the ergogenic effects of dietary nitrate ([Formula: see text]) supplementation in sedentary healthy subjects, a reduced O2 cost and enhanced exercise tolerance have often been demonstrated. The aim of this study was to evaluate the effects of beetroot juice (BR) supplementation, rich in [Formula: see text], on physiological variables associated with exercise tolerance in adolescents with obesity. In a double-blind, randomized crossover study, 10 adolescents with obesity (8 girls, 2 boys; age = 16 ± 1 yr; body mass index = 35.2 ± 5.0 kg/m2) were tested after 6 days of supplementation with BR (5 mmol [Formula: see text] per day) or placebo (PLA). Following each supplementation period, patients carried out two repetitions of 6-min moderate-intensity CWR exercise and one severe-intensity CWR exercise until exhaustion. Plasma [Formula: see text] concentration was significantly higher in BR versus PLA (108 ± 37 vs. 15 ± 5 μM, P < 0.0001). The O2 cost of moderate-intensity exercise was not different in BR versus PLA (13.3 ± 1.7 vs. 12.9 ± 1.1 ml·min−1·W−1, P = 0.517). During severe-intensity exercise, signs of a reduced amplitude of the O2 uptake slow component were observed in BR, in association with a significantly longer time to exhaustion (561 ± 198 s in BR vs. 457 ± 101 s in PLA, P = 0.0143). In obese adolescents, short-term dietary [Formula: see text] supplementation is effective in improving exercise tolerance during severe-intensity exercise. This may prove to be useful in counteracting early fatigue and reduced physical activity in this at-risk population.

Pulmonary oxygen uptake kinetics

2017 ◽  
Author(s):  
Alan R Barker ◽  
Neil Armstrong
Keyword(s):  
Oxygen Uptake ◽  
Oxidative Phosphorylation ◽  
Children And Adolescents ◽  
Phase Ii ◽  
Slow Component ◽  
Moderate Intensity ◽  
Heavy Exercise ◽  
Moderate Intensity Exercise ◽  
Pulmonary Oxygen Uptake ◽  
Age Related

The pulmonary oxygen uptake (pV̇O2) kinetic response to exercise provides valuable non-invasive insight into the control of oxidative phosphorylation and determinants of exercise tolerance in children and adolescents. Few methodologically robust studies have investigated pV̇O2 kinetics in children and adolescents, but age- and sex-related differences have been identified. There is a clear age-related slowing of phase II pV̇O2 kinetics during heavy and very heavy exercise, with a trend showing during moderate intensity exercise. During heavy and very heavy exercise the oxygen cost is higher for phase II and the pV̇O2 component is truncated in children. Sex-related differences occur during heavy, but not moderate, intensity exercise, with boys having faster phase II pV̇O2 kinetics and a smaller pV̇O2 slow component compared to girls. The mechanisms underlying these differences are likely related to changes in phosphate feedback controllers of oxidative phosphorylation, muscle oxygen delivery, and/or muscle fibre recruitment strategies.

scholarly journals The effect of breaking up prolonged sitting on paired associative stimulation-induced plasticity

2020 ◽  
Vol 238 (11) ◽  
pp. 2497-2506 ◽  
Author(s):  
E. Bojsen-Møller ◽  
M. M. Ekblom ◽  
O. Tarassova ◽  
D. W. Dunstan ◽  
O. Ekblom
Keyword(s):  
Physical Activity ◽  
Motor Cortex ◽  
Fixed Effects ◽  
Primary Motor Cortex ◽  
Short Interval ◽  
Moderate Intensity ◽  
Middle Aged ◽  
Moderate Intensity Exercise ◽  
Abductor Pollicis Brevis ◽  
Paired Associative Stimulation

Abstract Paired associative stimulation (PAS) can induce plasticity in the motor cortex, as measured by changes in corticospinal excitability (CSE). This effect is attenuated in older and less active individuals. Although a single bout of exercise enhances PAS-induced plasticity in young, physically inactive adults, it is not yet known if physical activity interventions affect PAS-induced neuroplasticity in middle-aged inactive individuals. Sixteen inactive middle-aged office workers participated in a randomized cross-over design investigating how CSE and short-interval intracortical inhibition (SICI) were affected by PAS preceded by 3 h of sitting (SIT), 3 h of sitting interrupted every 30 min by 3 min of frequent short bouts of physical activity (FPA) and 2.5 h of sitting followed by 25 min of moderate-intensity exercise (EXE). Transcranial magnetic stimulation was applied over the primary motor cortex (M1) of the dominant abductor pollicis brevis to induce recruitment curves before and 5 min and 30 min post-PAS. Linear mixed models were used to compare changes in CSE using time and condition as fixed effects and subjects as random effects. There was a main effect of time on CSE and planned within-condition comparisons showed that CSE was significantly increased from baseline to 5 min and 30 min post-PAS, in the FPA condition, with no significant changes in the SIT or EXE conditions. SICI decreased from baseline to 5 min post-PAS, but this was not related to changes in CSE. Our findings suggest that in middle-aged inactive adults, FPAs may promote corticospinal neuroplasticity. Possible mechanisms are discussed.

The Effect of Prior Moderate- and Heavy-Intensity Running on the VO2 Response to Exhaustive Severe-Intensity Running

2006 ◽  
Vol 1 (4) ◽  
pp. 361-374 ◽  
Author(s):  
Stephen B. Draper ◽  
Dan M. Wood ◽  
Jo Corbett ◽  
David V.B. James ◽  
Christopher R. Potter
Keyword(s):  
Oxygen Uptake ◽  
Slow Component ◽  
Maximum Oxygen Uptake ◽  
Moderate Intensity ◽  
Time To Exhaustion ◽  
Heavy Exercise ◽  
Square Wave ◽  
Severe Intensity ◽  
The Difference ◽  
Trained Runners

We tested the hypothesis that prior heavy-intensity exercise reduces the difference between asymptotic oxygen uptake (VO2) and maximum oxygen uptake (VO2max) during exhaustive severe-intensity running lasting ≍2 minutes. Ten trained runners each performed 2 ramp tests to determine peak VO2 (VO2peak) and speed at venti-latory threshold. They performed exhaustive square-wave runs lasting ≍2 minutes, preceded by either 6 minutes of moderate-intensity running and 6 minutes rest (SEVMOD) or 6 minutes of heavy-intensity running and 6 minutes rest (SEVHEAVY). Two transitions were completed in each condition. VO2 was determined breath by breath and averaged across the 2 repeats of each test; for the square-wave test, the averaged VO2 response was then modeled using a monoexponential function. The amplitude of the VO2 response to severe-intensity running was not different in the 2 conditions (SEVMOD vs SEVHEAVY; 3925 ± 442 vs 3997 ± 430 mL/min, P = .237), nor was the speed of the response (τ; 9.2 ± 2.1 vs 10.0 ± 2.1 seconds, P = .177). VO2peak from the square-wave tests was below that achieved in the ramp tests (91.0% ± 3.2% and 92.0% ± 3.9% VO2peak, P < .001). There was no difference in time to exhaustion between conditions (110.2 ± 9.7 vs 111.0 ± 15.2 seconds, P = .813). The results show that the primary VO2 response is unaffected by prior heavy exercise in running performed at intensities at which exhaustion will occur before a slow component emerges.

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