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To establish the test–retest reliability of pulmonary oxygen uptake (VO2), muscle deoxygenation (deoxy[haem]) and tissue oxygen saturation (StO2) kinetics in youth elite-cyclists. From baseline pe...

We tested the hypothesis that acute supplementation with nitrate (NO3−)-rich beetroot juice (BR) would improve quadriceps muscle oxygenation, pulmonary oxygen uptake ( V ˙ O 2 ) kinetics and exercise tolerance (Tlim) in normoxia and that these improvements would be augmented in hypoxia and attenuated in hyperoxia. In a randomised, double-blind, cross-over study, ten healthy males completed two-step cycle tests to Tlim following acute consumption of 210 mL BR (18.6 mmol NO3−) or NO3−-depleted beetroot juice placebo (PL; 0.12 mmol NO3−). These tests were completed in normobaric normoxia [fraction of inspired oxygen (FIO2): 21%], hypoxia (FIO2: 15%) and hyperoxia (FIO2: 40%). Pulmonary V ˙ O 2 and quadriceps tissue oxygenation index (TOI), derived from multi-channel near-infrared spectroscopy, were measured during all trials. Plasma [nitrite] was higher in all BR compared to all PL trials (P V ˙ O 2 in hypoxia (P 0.05). These findings indicate that BR supplementation is more likely to improve Tlim and peak V ˙ O 2 in situations when skeletal muscle is more hypoxic.

We investigated the influence of inorganic nitrate ( $${\text{NO}}_{3}^{ - }$$ ) supplementation on local sweating and cutaneous vascular responses during exercise in hot conditions. Eight healthy, young subjects were assigned in a randomized, double-blind, crossover design to receive $${\text{NO}}_{3}^{ - }$$ -rich beetroot (BR) juice (140 mL/day, containing ~ 8 mmol of $${\text{NO}}_{3}^{ - }$$ ) and $${\text{NO}}_{3}^{ - }$$ -depleted placebo (PL) juice (140 mL/day, containing ~ 0.003 mmol of $${\text{NO}}_{3}^{ - }$$ ) for 3 days. On day 3 of supplementation, subjects cycled at an intensity corresponding to 55% of $$\dot{V}$$ O2max for 30 min in hot conditions (30 °C, 50% relative humidity). Chest and forearm sweat rate (SR) and skin blood flow (SkBF), were measured continuously. Cutaneous vascular conductance (CVC) was calculated by SkBF/mean arterial pressure (MAP). Prior to exercise, plasma $${\text{NO}}_{3}^{ - }$$ (21 ± 6 and 581 ± 161 µM) and nitrite ( $${\text{NO}}_{2}^{ - }$$ , 87 ± 28 and 336 ± 156 nM) concentrations were higher after BR compared to PL supplementation (P ≤ 0.011, n = 6). Oesophageal, mean skin, and mean body temperatures during exercise were not different between conditions. In addition, BR supplementation did not affect SR, SkBF, and CVC during exercise. A lower MAP was found after 30 min of exercise following BR supplementation (112 ± 6 and 103 ± 6 mmHg for PL and BR, respectively, P = 0.021). These results suggest that inorganic $${\text{NO}}_{3}^{ - }$$ supplementation, which increases the potential for O2-independent NO production, does not affect local sweating and cutaneous vascular responses, but attenuates blood pressure in young healthy subjects exercising in a hot environment.

We tested the hypothesis that acute supplementation with nitrate (NO

NEW FINDINGS What is the central question of this study? Do the phase II parameters of pulmonary oxygen uptake ( VO2 ) kinetics display linear, first-order behaviour in association with alterations in skeletal muscle oxygenation during step cycling of different intensities or when exercise is initiated from an elevated work rate in youths. What is the main finding and its importance? Both linear and non-linear features of phase II VO2 kinetics may be determined by alterations in the dynamic balance between microvascular O2 delivery and utilization in 11-15 year olds. The recruitment of higher-order (i.e. type II) muscle fibres during 'work-to-work' cycling might be responsible for modulating VO2 kinetics with chronological age. ABSTRACT This study investigated in 19 male youths (mean age: 13.6 ± 1.1 years, range: 11.7-15.7 years) the relationship between pulmonary oxygen uptake ( VO2 ) and muscle deoxygenation kinetics during moderate- and very heavy-intensity 'step' cycling initiated from unloaded pedalling (i.e. U → M and U → VH) and moderate to very heavy-intensity step cycling (i.e. M → VH). Pulmonary VO2 was measured breath-by-breath along with the tissue oxygenation index (TOI) of the vastus lateralis using near-infrared spectroscopy. There were no significant differences in the phase II time constant ( τVO2p ) between U → M and U → VH (23 ± 6 vs. 25 ± 7 s; P = 0.36); however, the τVO2p was slower during M → VH (42 ± 16 s) compared to other conditions (P

This study aimed to characterize changes in deoxyhemoglobin ([HHb]) response dynamics in boys and girls during ramp incremental exercise to investigate whether the reduced peak oxygen uptake (peak V˙O2) in girls is associated with poorer matching of muscle O2 delivery to muscle O2 utilization, as evidenced by a more rapid increase in [HHb].Fifty-two children (31 boys, 9.9 ± 0.6 yr, 1.38 ± 0.07 m, 31.70 ± 5.78 kg) completed ramp incremental exercise on a cycle ergometer during which pulmonary gas exchange and muscle oxygenation parameters were measured.When muscle [HHb] was expressed against absolute work rate and V˙O2, girls had an earlier change in [HHb], as evidenced by the lower c/d parameter (girls, 54 ± 20 W, vs boys, 67 ± 19 W, P = 0.023; girls, 0.82 ± 0.28 L·min(-1), vs boys, 0.95 ± 0.19 L·min(-1), P = 0.055) and plateau (girls, 85 ± 12 W, vs boys, 99 ± 18 W, P = 0.031; girls, 1.02 ± 0.25 L·min(-1), vs boys, 1.22 ± 0.28 L·min(-1), P = 0.014). However, when expressed against relative work rate or V˙O2, there were no sex differences in ([HHb]) response dynamics (all P0.20). Significant correlations were observed between absolute and fat-free mass normalized peak V˙O2 and the HHb c/d and plateau parameters when expressed against absolute work rate or V˙O2. Furthermore, when entered into a multiple regression model, the [HHb] plateau against absolute V˙O2 contributed 12% of the variance in peak V˙O2 after adjusting for fat-free mass, gas exchange threshold, and body fatness (model R2 = 0.81, P0.001).The sex difference in peak V˙O2 in 9- to 10-yr-old children is, in part, related to sex-specific changes in muscle O2 extraction dynamics during incremental exercise.

We tested the hypothesis that inorganic nitrate (NO3−) supplementation would improve muscle oxygenation, pulmonary oxygen uptake (V̇o2) kinetics, and exercise tolerance (Tlim) to a greater extent when cycling at high compared with low pedal rates. In a randomized, placebo-controlled cross-over study, seven subjects (mean ± SD, age 21 ± 2 yr, body mass 86 ± 10 kg) completed severe-intensity step cycle tests at pedal cadences of 35 rpm and 115 rpm during separate nine-day supplementation periods with NO3−-rich beetroot juice (BR) (providing 8.4 mmol NO3−/day) and placebo (PLA). Compared with PLA, plasma nitrite concentration increased 178% with BR ( P < 0.01). There were no significant differences in muscle oxyhemoglobin concentration ([O2Hb]), phase II V̇o2kinetics, or Tlim between BR and PLA when cycling at 35 rpm ( P > 0.05). However, when cycling at 115 rpm, muscle [O2Hb] was higher at baseline and throughout exercise, phase II V̇o2kinetics was faster (47 ± 16 s vs. 61 ± 25 s; P < 0.05), and Tlim was greater (362 ± 137 s vs. 297 ± 79 s; P < 0.05) with BR compared with PLA. These results suggest that short-term BR supplementation can increase muscle oxygenation, expedite the adjustment of oxidative metabolism, and enhance exercise tolerance when cycling at a high, but not a low, pedal cadence in healthy recreationally active subjects. These findings support recent observations that NO3−supplementation may be particularly effective at improving physiological and functional responses in type II muscle fibers.

During constant work rate exercise above the lactate threshold (LT), the initial rapid phase of pulmonary oxygen uptake ( $$\dot{V}$$ O2) kinetics is supplemented by an additional $$\dot{V}$$ O2 slow component ( $$\dot{V}$$ O2Sc) which reduces the efficiency of muscular work. The $$\dot{V}$$ O2Sc amplitude has been shown to increase with maturation but the mechanisms are poorly understood. We utilized the transverse relaxation time (T 2) of muscle protons from magnetic resonance imaging (MRI) to test the hypothesis that a lower $$\dot{V}$$ O2 slow component ( $$\dot{V}$$ O2Sc) amplitude in children would be associated with a reduced muscle recruitment compared to adults. Eight boys (mean age 11.4 ± 0.4) and eight men (mean age 25.3 ± 3.3 years) completed repeated step transitions of unloaded-to-very heavy-intensity (U → VH) exercise on a cycle ergometer. MRI scans of the thigh region were acquired at rest and after VH exercise up to the $$\dot{V}$$ O2Sc time delay (ScTD) and after 6 min. T 2 for each of eight muscles was adjusted in relation to cross-sectional area and then summed to provide the area-weighted ΣT 2 as an index of thigh recruitment. There were no child/adult differences in the relative $$\dot{V}$$ O2Sc amplitude [Boys 14 ± 7 vs. Men 18 ± 3 %, P = 0.15, effect size (ES) = 0.8] during which the change (∆) in area-weighted ΣT 2 between the ScTD and 6 min was not different between groups (Boys 1.6 ± 1.2 vs. Men 2.3 ± 1.1 ms, P = 0.27, ES = 0.6). A positive and strong correlation was found between the relative $$\dot{V}$$ O2Sc amplitude and the magnitude of the area-weighted ∆ΣT 2 in men (r = 0.92, P = 0.001) but not in boys (r = 0.09, P = 0.84). This study provides evidence to show that progressive muscle recruitment (as inferred from T 2 changes) contributes to the development of the $$\dot{V}$$ O2Sc during intense submaximal exercise independent of age.

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

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.

Nimmerichter, A, Novak, N, Triska, C, Prinz, B, and Breese, BC. Validity of treadmill-derived critical speed on predicting 5,000-meter track-running performance. J Strength Cond Res 31(3): 706-714, 2017-To evaluate 3 models of critical speed (CS) for the prediction of 5,000-m running performance, 16 trained athletes completed an incremental test on a treadmill to determine maximal aerobic speed (MAS) and 3 randomly ordered runs to exhaustion at the [INCREMENT]70% intensity, at 110% and 98% of MAS. Critical speed and the distance covered above CS (D') were calculated using the hyperbolic speed-time (HYP), the linear distance-time (LIN), and the linear speed inverse-time model (INV). Five thousand meter performance was determined on a 400-m running track. Individual predictions of 5,000-m running time (t = [5,000-D']/CS) and speed (s = D'/t + CS) were calculated across the 3 models in addition to multiple regression analyses. Prediction accuracy was assessed with the standard error of estimate (SEE) from linear regression analysis and the mean difference expressed in units of measurement and coefficient of variation (%). Five thousand meter running performance (speed: 4.29 ± 0.39 m·s; time: 1,176 ± 117 seconds) was significantly better than the predictions from all 3 models (p < 0.0001). The mean difference was 65-105 seconds (5.7-9.4%) for time and -0.22 to -0.34 m·s (-5.0 to -7.5%) for speed. Predictions from multiple regression analyses with CS and D' as predictor variables were not significantly different from actual running performance (-1.0 to 1.1%). The SEE across all models and predictions was approximately 65 seconds or 0.20 m·s and is therefore considered as moderate. The results of this study have shown the importance of aerobic and anaerobic energy system contribution to predict 5,000-m running performance. Using estimates of CS and D' is valuable for predicting performance over race distances of 5,000 m.

This study tested the hypothesis that pulmonary VO₂ kinetics would be slowed during 'work-to-work' exercise in adults but not in children. Eight boys (mean age=12.5 ± 0.5 years) and nine men completed very heavy step transitions initiated from either 'unloaded' pedalling (U→VH) or unloaded-to-moderate cycling (i.e. U→M to M→VH). The phase II τ was significantly (p

This study tested the hypothesis that the VO2 kinetic response would be slowed in untrained (UT) but not trained (T) teenage participants whilst cycling at 115 rev min(-1) compared to 50 rev min(-1). Eight UT and seven T boys completed two square-wave transitions to very heavy-intensity exercise pedalling at 50 rev min(-1) and 115 rev min(-1). In UT at the higher pedal rate, the phase II VO2 was significantly (P0.01) slower (50 rev min(-1): 32 ± 5 vs. 115 rev min(-1): 42 ± 11 s) and the relative VO2 slow component was significantly (P0.01) elevated (50 rev min(-1): 10 ± 3 vs. 115 rev min(-1): 16 ± 5%). The phase II VO2 (50 rev min(-1): 26 ± 4 vs. 115 rev min(-1): 22 ± 6s) and relative VO2 slow component (50 rev min(-1): 14 ± 5 vs. 115 rev min(-1): 17 ± 3%) were unaltered by pedal rate in T (P0.05). These data are consistent with the notion that VO2 kinetics are influenced by muscle fibre recruitment in youth but this effect is attenuated in endurance trained teenage boys.

This study investigated the influence of dietary inorganic nitrate (NO 3 −) supplementation on pulmonary O2 uptake (V˙O2) and muscle deoxyhemoglobin/myoglobin (i.e. deoxy [Hb + Mb]) kinetics during submaximal cycling exercise. In a randomized, placebo‐controlled, cross‐over study, eight healthy and physically active male subjects completed two step cycle tests at a work rate equivalent to 50% of the difference between the gas exchange threshold and peak V˙O2 over separate 4‐day supplementation periods with NO 3 −‐rich (BR; providing 8.4 mmol NO 3 −∙day−1) and NO 3 −‐depleted (placebo; PLA) beetroot juice. Pulmonary V˙O2 was measured breath‐by‐breath and time‐resolved near‐infrared spectroscopy was utilized to quantify absolute deoxy [Hb + Mb] and total [Hb + Mb] within the rectus femoris, vastus lateralis, and vastus medialis. There were no significant differences (P > 0.05) in the primary deoxy [Hb + Mb] mean response time or amplitude between the PLA and BR trials at each muscle site. BR significantly increased the mean (three‐site) end‐exercise deoxy [Hb + Mb] (PLA: 91 ± 9 vs. BR: 95 ± 12 μmol/L, P

We tested the hypothesis that inorganic nitrate (NO3 (-)) supplementation would improve muscle oxygenation, pulmonary oxygen uptake (V̇o2) kinetics, and exercise tolerance (Tlim) to a greater extent when cycling at high compared with low pedal rates. In a randomized, placebo-controlled cross-over study, seven subjects (mean ± SD, age 21 ± 2 yr, body mass 86 ± 10 kg) completed severe-intensity step cycle tests at pedal cadences of 35 rpm and 115 rpm during separate nine-day supplementation periods with NO3 (-)-rich beetroot juice (BR) (providing 8.4 mmol NO3 (-)/day) and placebo (PLA). Compared with PLA, plasma nitrite concentration increased 178% with BR (P0.01). There were no significant differences in muscle oxyhemoglobin concentration ([O2Hb]), phase II V̇o2 kinetics, or Tlim between BR and PLA when cycling at 35 rpm (P0.05). However, when cycling at 115 rpm, muscle [O2Hb] was higher at baseline and throughout exercise, phase II V̇o2 kinetics was faster (47 ± 16 s vs. 61 ± 25 s; P0.05), and Tlim was greater (362 ± 137 s vs. 297 ± 79 s; P0.05) with BR compared with PLA. These results suggest that short-term BR supplementation can increase muscle oxygenation, expedite the adjustment of oxidative metabolism, and enhance exercise tolerance when cycling at a high, but not a low, pedal cadence in healthy recreationally active subjects. These findings support recent observations that NO3 (-) supplementation may be particularly effective at improving physiological and functional responses in type II muscle fibers.

During constant work rate exercise above the lactate threshold (LT), the initial rapid phase of pulmonary oxygen uptake (VO₂) kinetics is supplemented by an additional VO₂ slow component (VO₂Sc) which reduces the efficiency of muscular work. The VO₂Sc amplitude has been shown to increase with maturation but the mechanisms are poorly understood. We utilized the transverse relaxation time (T₂) of muscle protons from magnetic resonance imaging (MRI) to test the hypothesis that a lower VO₂ slow component (VO₂Sc) amplitude in children would be associated with a reduced muscle recruitment compared to adults.Eight boys (mean age 11.4 ± 0.4) and eight men (mean age 25.3 ± 3.3 years) completed repeated step transitions of unloaded-to-very heavy-intensity (U → VH) exercise on a cycle ergometer. MRI scans of the thigh region were acquired at rest and after VH exercise up to the VO₂Sc time delay (ScTD) and after 6 min. T₂ for each of eight muscles was adjusted in relation to cross-sectional area and then summed to provide the area-weighted ΣT₂ as an index of thigh recruitment.There were no child/adult differences in the relative VO₂Sc amplitude [Boys 14 ± 7 vs. Men 18 ± 3 %, P = 0.15, effect size (ES) = 0.8] during which the change (∆) in area-weighted ΣT₂ between the ScTD and 6 min was not different between groups (Boys 1.6 ± 1.2 vs. Men 2.3 ± 1.1 ms, P = 0.27, ES = 0.6). A positive and strong correlation was found between the relative VO₂Sc amplitude and the magnitude of the area-weighted ∆ΣT₂ in men (r = 0.92, P = 0.001) but not in boys (r = 0.09, P = 0.84).This study provides evidence to show that progressive muscle recruitment (as inferred from T₂ changes) contributes to the development of the VO₂Sc during intense submaximal exercise independent of age.

This study tested the hypothesis that pulmonary VO₂ kinetics would be slowed during 'work-to-work' exercise in adults but not in children. Eight boys (mean age=12.5 ± 0.5 years) and nine men completed very heavy step transitions initiated from either 'unloaded' pedalling (U→VH) or unloaded-to-moderate cycling (i.e. U→M to M→VH). The phase II τ was significantly (p0.05) lengthened in M→VH compared to U→M and U→VH in boys (30 ± 5 vs. 19 ± 5 vs. 21 ± 5 s) and men (49 ± 14 vs. 30 ± 5 vs. 34 ± 8 s). In U→VH, a greater relative VO₂ slow component temporally coincided with an increased linear iEMG slope in men compared boys (VO₂ slow component: 16 ± 3 vs. 11 ± 4%; iEMG slope: 0.19 ± 0.24 vs. -0.06 ± 0.14%, p0.05). These results suggest that an age-linked modulation of VO₂ kinetics might be influenced by alterations in muscle fibre recruitment following the onset of exercise.

This study examined longitudinal changes in the pulmonary oxygen uptake (pV̇O2) kinetic response to heavy-intensity exercise in 14–16 yr old boys. Fourteen healthy boys (age 14.1 ± 0.2 yr) completed exercise testing on two occasions with a 2-yr interval. Each participant completed a minimum of three ‘step’ exercise transitions, from unloaded pedalling to a constant work rate corresponding to 40% of the difference between the pV̇O2 at the gas exchange threshold and peak pV̇O2 (40% Δ). Over the 2-yr period a significant increase in the phase II time constant (25 ± 5 vs. 30 ± 5 s; p = .002, ω2 = 0.34), the relative amplitude of the pV̇O2 slow component (9 ± 5 vs. 13 ± 4%; p = .036, ω2 = 0.14) and the pV̇O2 gain at end-exercise (11.6 ± 0.6 vs. 12.4 ± 0.7 mL·min−1·W−1; p < .001, ω2 = 0.42) were observed. These data indicate that the control of oxidative phosphorylation in response to heavy-intensity cycling exercise is age-dependent in teenage boys.