Pulmonary oxygen uptake and muscle deoxygenation kinetics during recovery in trained and untrained male adolescents

Previous studies have demonstrated faster pulmonary oxygen uptake ( [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} ) kinetics in the trained state during the transition to and from moderate-intensity exercise in adults. Whilst a similar effect of training status has previously been observed during the on-transition in adolescents, whether this is also observed during recovery from exercise is presently unknown. The aim of the present study was therefore to examine [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics in trained and untrained male adolescents during recovery from moderate-intensity exercise. 15 trained (15 ± 0.8 years, [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max} 54.9 ± 6.4 mL kg⁻¹ min⁻¹) and 8 untrained (15 ± 0.5 years, [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } 44.0 ± 4.6 mL kg⁻¹ min⁻¹) male adolescents performed two 6-min exercise off-transitions to 10 W from a preceding “baseline” of exercise at a workload equivalent to 80% lactate threshold; [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} (breath-by-breath) and muscle deoxyhaemoglobin (near-infrared spectroscopy) were measured continuously. The time constant of the fundamental phase of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} off-kinetics was not different between trained and untrained (trained 27.8 ± 5.9 s vs. untrained 28.9 ± 7.6 s, P = 0.71). However, the time constant (trained 17.0 ± 7.5 s vs. untrained 32 ± 11 s, P < 0.01) and mean response time (trained 24.2 ± 9.2 s vs. untrained 34 ± 13 s, P = 0.05) of muscle deoxyhaemoglobin off-kinetics was faster in the trained subjects compared to the untrained subjects. [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics was unaffected by training status; the faster muscle deoxyhaemoglobin kinetics in the trained subjects thus indicates slower blood flow kinetics during recovery from exercise compared to the untrained subjects.     

Oxygen uptake kinetics during exercise in adults with Down syndrome

Persons with Down syndrome (DS) have diminished submaximal and peak work capacity. This study evaluated the dynamic response of oxygen uptake at onset and recovery (VO₂ kinetics) of constant-load exercise (moderate intensity 45% VO_2peak) in adults with DS. A total of 27 healthy participants aged 18–50 years performed graded treadmill exercise to assess peak VO₂: 14 with DS (9 males and 5 females) and 13 controls without disabilities (9 males and 4 females). Subjects also performed constant-load exercise tests at 45% VO_2peak to determine VO₂ on-transient and VO₂ off-transient responses. Peak VO₂ was lower in participants with DS as compared to controls (DS 30.2 ± 7.1; controls 46.1 ± 9.6 mL kg⁻¹ min⁻¹, P < 0.05). In contrast, at 45% VO_2peak, the time constants for the VO₂ on-transients (DS 34.6 ± 9.1; controls 37.6 ± 9.0 s) and VO₂ off-transients (DS 36.5 ± 12.3; controls 37.7 ± 7.0 s) were not significantly different between the groups. Additionally, there were no differences between on-transient and off-transient time constants in participants with DS or controls. These data demonstrate that the VO₂ kinetics at onset and recovery of moderate intensity exercise is similar between adults with DS and controls. Therefore, the submaximal exercise performance of these individuals is not affected by slowed VO₂ kinetics.     

<Emphasis Type="Italic">V</Emphasis>O<Subscript>2</Subscript>max during successive maximal efforts

The concept of VO₂max has been a defining paradigm in exercise physiology for >75 years. Within the last decade, this concept has been both challenged and defended. The purpose of this study was to test the concept of VO₂max by comparing VO₂ during a second exercise bout following a preliminary maximal effort exercise bout. The study had two parts. In Study #1, physically active non-athletes performed incremental cycle exercise. After 1-min recovery, a second bout was performed at a higher power output. In Study #2, competitive runners performed incremental treadmill exercise and, after 3-min recovery, a second bout at a higher speed. In Study #1 the highest VO₂ (bout 1 vs. bout 2) was not significantly different (3.95 ± 0.75 vs. 4.06 ± 0.75 l min⁻¹). Maximal heart rate was not different (179 ± 14 vs. 180 ± 13 bpm) although maximal V _E was higher in the second bout (141 ± 36 vs. 151 ± 34 l min⁻¹). In Study #2 the highest VO₂ (bout 1 vs. bout 2) was not significantly different (4.09 ± 0.97 vs. 4.03 ± 1.16 l min⁻¹), nor was maximal heart rate (184 + 6 vs. 181 ± 10 bpm) or maximal V _E (126 ± 29 vs. 126 ± 34 l min⁻¹). The results support the concept that the highest VO₂ during a maximal incremental exercise bout is unlikely to change during a subsequent exercise bout, despite higher muscular power output. As such, the results support the “classical” view of VO₂max.     

Energetics of karate (<Emphasis Type="Italic">kata</Emphasis> and <Emphasis Type="Italic">kumite</Emphasis> techniques) in top-level athletes

Breath-by-breath O₂ uptake ( [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} , L min⁻¹) and blood lactate concentration were measured before, during exercise, and recovery in six kata and six kumite karate Word Champions performing a simulated competition. [(V)\dot]_{\textO 2 \textmax} , \dot{V}_{{{\text{O}}_{{ 2 {\text{max}}}} }} , maximal anaerobic alactic, and lactic power were also assessed. The total energy cost ( V_{\textO 2 \textTOT} , V_{{{\text{O}}_{{ 2 {\text{TOT}}}} }} , mL kg⁻¹ above resting) of each simulated competition was calculated and subdivided into aerobic, lactic, and alactic fractions. Results showed that (a) no differences between kata and kumite groups in [(V)\dot]_{\textO 2 \textmax} , \dot{V}_{{{\text{O}}_{{ 2 {\text{max}}}} }} , height of vertical jump, and Wingate test were found; (b) V_{\textO 2 \textTOT} V_{{{\text{O}}_{{ 2 {\text{TOT}}}} }} were 87.8 ± 6.6 and 82.3 ± 12.3 mL kg⁻¹ in kata male and female with a performance time of 138 ± 4 and 158 ± 14 s, respectively; 189.0 ± 14.6 mL kg⁻¹ in kumite male and 155.8 ± 38.4 mL kg⁻¹ in kumite female with a predetermined performance time of 240 ± 0 and 180 ± 0 s, respectively; (c) the metabolic power was significantly higher in kumite than in kata athletes (p ≤ 0.05 in both gender); (d) aerobic and anaerobic alactic sources, in percentage of the total, were significantly different between gender and disciplines (p < 0.05), while the lactic source was similar; (e) HR ranged between 174 and 187 b min⁻¹ during simulated competition. In conclusion, kumite appears to require a much higher metabolic power than kata, being the energy source with the aerobic contribution predominant.     

Validity of the Oxycon Mobile metabolic system under field measuring conditions

Abstract  

This study aimed to validate a portable metabolic system in field measuring conditions, such as prolonged moderate exercise at low temperatures, high humidity and with external wind. VO₂, VCO₂, RER and V _E were measured using the Oxycon Mobile (OM), with a windshield, during cycle ergometer exercise: (1) indoors at three submaximal workloads with no wind or with external wind (13–20 m s⁻¹) from front, side and back; (2) at two submaximal workloads outdoors (12 ± 2°C; 86 ± 7% relative humidity (RH)), with and without a system for drying the ambient air around the air sampling tube; and (3) at one workload outdoors for 45 min (5 ± 4°C; 69 ± 16.5% RH). Any physiological drift was checked for with pre- and postmeasurements by the Douglas bag method (DBM). A minor effect of external wind from behind was noted in RER and V _E (−2 and −3%). The system for drying the ambient air around the gas sampling tube had no effect on the measured levels. A small difference in VCO₂ drift between the OM and DBM (1.5 mL min⁻²) was noted in the stability test. The results indicated that heavy external wind applied from different directions generally does not affect the measurements of the OM and further that, when using a unit for drying the ambient air around the gas sampling tube, the OM can accurately measure VO₂, RER and V _E at submaximal workloads for at least 45 min under challenging conditions with regard to humidity and temperature.     

Myocardial function and aerobic fitness in adolescent females

A recent report indicated that variations in myocardial functional (systolic and diastolic) responses to exercise do not contribute to inter-individual differences in aerobic fitness (peak VO₂) among young males. This study was designed to investigate the same question among adolescent females. Thirteen highly fit adolescent football (soccer) players (peak VO₂ 43.5 ± 3.4 ml kg⁻¹ min⁻¹) and nine untrained girls (peak VO₂ 36.0 ± 5.1 ml kg⁻¹ min⁻¹) matched for age underwent a progressive cycle exercise test to exhaustion. Cardiac variables were measured by standard echocardiographic techniques. Maximal stroke index was greater in the high-fit group (50 ± 5 vs. 41 ± 4 ml m⁻²), but no significant group differences were observed in maximal heart rate or arterial venous oxygen difference. Increases in markers of both systolic (ejection rate, tissue Doppler S′) and diastolic (tissue Doppler E′, mitral E velocity) myocardial functions at rest and during the acute bout of exercise were similar in the two groups. This study suggests that among healthy adolescent females, like young males, myocardial systolic and diastolic functional capacities do not contribute to inter-individual variability in physiologic aerobic fitness.     

The validity and reliability of predicting maximal oxygen uptake from a treadmill-based sub-maximal perceptually regulated exercise test

The purpose of this study was to determine for the first time whether [(V)\dot]\textO _2max {\dot{V}}{\text{O}}_{ 2\hbox{max}} could be predicted accurately and reliably from a treadmill-based perceptually regulated exercise test (PRET) incorporating a safer and more practical upper limit of RPE 15 (“Hard”) than used in previous investigations. Eighteen volunteers (21.7 ± 2.8 years) completed three treadmill PRETs (each separated by 48 h) and one maximal graded exercise test. Participants self-regulated their exercise at RPE levels 9, 11, 13 and 15 in a continuous and incremental fashion. Oxygen uptake ( [(V)\dot]\textO ₂ ) \left( {{\dot{V}}{\text{O}}_{ 2} } \right) was recorded continuously during each 3 min bout. [(V)\dot]\textO₂ {\dot{V}}{\text{O}}_{2} values for the RPE range 9–15 were extrapolated to RPE₁₉ and RPE₂₀ using regression analysis to predict individual [(V)\dot]\textO_2max {\dot{V}}{\text{O}}_{2\hbox{max}} scores. The optimal limits of agreement (LoA) between actual (48.0 ± 6.2 ml kg⁻¹ min⁻¹) and predicted scores were −0.6 ± 7.1 and −2.5 ± 9.4 ml^.kg⁻¹ min⁻¹ for the RPE₂₀ and RPE₁₉ models, respectively. Reliability analysis for the [(V)\dot]\textO_2max {\dot{V}}{\text{O}}_{2\hbox{max}} predictions yielded LoAs of 1.6 ± 8.5 (RPE₂₀) and 2.7 ± 9.4 (RPE₁₉) ml kg⁻¹ min⁻¹ between trials 2 and 3. These findings demonstrate that (with practice) a novel treadmill-based PRET can yield predictions of [(V)\dot]\textO_2max {\dot{V}}{\text{O}}_{2\hbox{max}} that are acceptably reliable and valid amongst young, healthy, and active adults.     

Walking economy in male adults with Down syndrome

The purpose of this study was to investigate walking economy in response to steady-state locomotion in adult males with Down syndrome (DS) and in healthy controls. Twelve participants with DS (34.5 ± 7.0 years) and 11 non-disabled controls (34.3 ± 8.7 years) performed submaximal (0% grade, 2.5 km h⁻¹ for 8 min) and maximal treadmill tests with metabolic and heart-rate measurements. For submaximal walking, submaximal oxygen uptake (VO₂) (9.1 vs. 9.5 mL kg⁻¹ min⁻¹), net VO₂ (5.9 vs. 5.4 mL kg⁻¹ min⁻¹) were not different between the groups (P > 0.05). However, oxygen-pulse (6.6 vs. 8.6 mL/beat) was lower and relative work intensity (44.6 vs. 19.9% of max) was higher in individuals with DS compared to controls (P < 0.05). Findings indicate similar walking economy between groups. Nevertheless, participants with DS exercised at lower submaximal oxygen-pulse and higher percentage of VO_2peak. Therefore, despite similar walking economy, participants with DS have lower cardiorespiratory function than controls for a given steady-state treadmill speed.     

Is the balance between skeletal muscular metabolic capacity and oxygen supply capacity the same in endurance trained and untrained subjects?

We attempted to test whether the balance between muscular metabolic capacity and oxygen supply capacity in endurance-trained athletes (ET) differs from that in a control group of normal physically active subjects by using exercises with different muscle masses. We compared maximal exercise in nine ET subjects [Maximal oxygen uptake (VO₂max) 64 ml kg⁻¹ min⁻¹ ± SD 4] and eight controls (VO₂max 46 ± 4 ml kg⁻¹ min⁻¹) during one-legged knee extensions (1-KE), two-legged knee extensions (2-KE) and bicycling. Maximal values for power output (P), VO₂max, concentration of blood lactate ([La⁻]), ventilation (VE), heart rate (HR), and arterial oxygen saturation of haemoglobin (SpO₂) were registered. P was 43 (2), 89 (3) and 298 (7) W (mean ± SE); and VO₂max: 1,387 (80), 2,234 (113) and 4,115 (150) ml min⁻¹) for controls in 1-KE, 2-KE and bicycling, respectively. The ET subjects achieved 126, 121 and 126% of the P of controls (p < 0.05) and 127, 124, and 117% of their VO₂max (p < 0.05). HR and [La⁻] were similar for both groups during all modes of exercise, while VE in ET was 147 and 114% of controls during 1-KE and bicycling, respectively. For mass-specific VO₂max (VO₂max divided by the calculated active muscle mass) during the different exercises, ET achieved 148, 141, and 150% of the controls’ values, respectively (p < 0.05). During bicycling, both groups achieved 37% of their mass-specific VO₂ during 1-KE. Finally we conclude that ET subjects have the same utilization of the muscular metabolic capacity during whole body exercise as active control subjects.     

Kinetics of skeletal muscle O2 delivery and utilization at the onset of heavy-intensity exercise in pulmonary arterial hypertension

Impaired O₂ delivery relative to O₂ demands at the onset of exercise might influence the response profile of muscle fractional O₂ extraction (≅Δ[deoxy-Hb/Mb] by near-infrared spectroscopy) either by accelerating its rate of increase or creating an “overshoot” (OS) in patients with pulmonary arterial hypertension (PAH). We therefore assessed the kinetics of O₂ uptake ( [(V)\dot]\textO₂ ), \left( {\dot{V}{\text{O}}_{2} } \right), Δ[deoxy-Hb/Mb] in the vastus lateralis, and heart rate (HR) at the onset of heavy-intensity exercise in 14 females with PAH (connective tissue disease, IPAH, portal hypertension, and acquired immunodeficiency syndrome) and 11 age- and gender-matched controls. Patients had slower [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and HR dynamics than controls (τ [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2}  = 62.7 ± 15.2 s vs. 41.0 ± 13.8 s and t ^1/2-HR = 61.3 ± 16.6 s vs. 43.4 ± 8.8 s, respectively; p < 0.01). No study participant had a significant reduction in oxyhemoglobin saturation. In OS(−) subjects (6 patients and 7 controls), the kinetics of Δ[deoxy-Hb/Mb] relative to [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} were faster in patients (p = 0.05). Larger area under the OS and slower kinetics (MRT) of the “downward” component indicated greater O₂ delivery-to-utilization mismatch in OS(+) patients versus OS(+) controls (477.4 ± 330.0 vs. 78.1 ± 65.6 a.u. and 74.6 ± 18.8 vs. 46.0 ± 17.0 s, respectively; p < 0.05). Resting pulmonary vascular resistance was higher in OS(+) than OS(−) patients (23.1 ± 12.0 vs. 10.7 ± 4.0 Woods, respectively; p < 0.05). We conclude that microvascular O₂ delivery-to-utilization inequalities slowed the rate of adaptation of aerobic metabolism at the start of heavy-intensity exercise in women with PAH.     

Effects of aerobic fitness on oxygen uptake kinetics in heavy intensity swimming

This study aimed to characterise both the [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics within constant heavy-intensity swimming exercise, and to assess the relationships between [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics and other parameters of aerobic fitness, in well-trained swimmers. On separate days, 21 male swimmers completed: (1) an incremental swimming test to determine their maximal oxygen uptake ([(V)\dot]\textO_2max ) (\dot{V}{\text{O}}_{2\max } ) , first ventilatory threshold (VT), and the velocity associated with [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } (v[(V)\dot]\textO_2max ) (v\dot{V}{\text{O}}_{2\max } ) and (2) two square-wave transitions from rest to heavy-intensity exercise, to determine their [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics. All the tests involved breath-by-breath analysis of freestyle swimming using a swimming snorkel. [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics was modelled with two exponential functions. The mean values for the incremental test were 56.0 ± 6.0 ml min⁻¹ kg⁻¹, 1.45 ± 0.08 m s⁻¹; and 42.1 ± 5.7 ml min⁻¹ kg⁻¹ for [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } , v[(V)\dot]\textO_2max v\dot{V}{\text{O}}_{2\max } and VT, respectively. For the square-wave transition, the time constant of the primary phase (τ_p) averaged 17.3 ± 5.4 s and the relevant slow component (A′_sc) averaged 4.8 ± 2.9 ml min⁻¹ kg⁻¹ [representing 8.9% of the end-exercise [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} (%A′_sc)]. τ_p was correlated with v[(V)\dot]\textO_2max v\dot{V}{\text{O}}_{2\max } (r = −0.55, P = 0.01), but not with either [(V)\dot]\textO _{2 \textmax} \dot{V}{\text{O}}_{{ 2 {\text{max}}}} (r = 0.05, ns) or VT (r = 0.14, ns). The %A′_sc did not correlate with either [(V)\dot]\textO _{2 \textmax} \dot{V}{\text{O}}_{{ 2 {\text{max}}}} (r = −0.14, ns) or v[(V)\dot]\textO_2max v\dot{V}{\text{O}}_{2\max } (r = 0.06, ns), but was inversely related with VT (r = −0.61, P < 0.01). This study was the first to describe the [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics in heavy-intensity swimming using specific swimming exercise and appropriate methods. As has been demonstrated in cycling, faster [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics allow higher aerobic power outputs to be attained. The slow component seems to be reduced in swimmers with higher ventilatory thresholds.     

Skin microvascular reactivity in trained adolescents

Whilst endothelial dysfunction is associated with a sedentary lifestyle, enhanced endothelial function has been documented in the skin of trained individuals. The purpose of this study was to investigate whether highly trained adolescent males possess enhanced skin microvascular endothelial function compared to their untrained peers. Seventeen highly and predominantly soccer trained boys ( [(V)\dot]\textO_2 \textpeak \dot{V}{\text{O}}_{{2\,{\text{peak}}}} : 55 ± 6 mL kg⁻¹ min⁻¹) and nine age- and maturation-matched untrained controls ( [(V)\dot]\textO_2 \textpeak \dot{V}{\text{O}}_{{2\,{\text{peak}}}} : 43 ± 5 mL kg⁻¹ min⁻¹) aged 13–15 years had skin microvascular endothelial function assessed using laser Doppler flowmetry. Baseline and maximal thermally stimulated skin blood flow (SkBF) responses were higher in forearms of trained subjects compared to untrained participants [baseline SkBF: 11 ± 4 vs. 9 ± 3 perfusion units (PU), p < 0.05; SkBF_max: 282 ± 120 vs. 204 ± 68 PU, p < 0.05]. Similarly, cutaneous vascular conductance (CVC) during local heating was superior in the forearm skin of trained versus untrained individuals (CVC_max: 3 ± 1 vs. 2 ± 1 PU mmHg⁻¹, p < 0.05). Peak hyperaemia following arterial occlusion and area under the reactive hyperaemia curve were also greater in forearm skin of the trained group (peak hyperaemia: 51 ± 21 vs. 35 ± 15 PU, p < 0.05; area under curve: 1596 ± 739 vs. 962 ± 796 PUs, p < 0.05). These results suggest that chronic exercise training in adolescents is associated with enhanced microvascular endothelial vasodilation in non-glabrous skin.     

Are the parameters of VO2, heart rate and muscle deoxygenation kinetics affected by serial moderate-intensity exercise transitions in a single day?

This study compared the parameter estimates of pulmonary oxygen uptake (VO_2p), heart rate (HR) and muscle deoxygenation (Δ[HHb]) kinetics when several moderate-intensity exercise transitions (MODs) were performed during a single visit versus several MODs performed during separate visits. Nine subjects (24 ± 5 years, mean ± SD) each completed two successive cycling MODs on six occasions (1-6A and 1-6B) from 20 W to a work rate corresponding to 80% estimated lactate threshold with 6 min recovery at 20 W. During one visit, subjects completed two series of three MODs (6A-F), separated by 20 min rest. VO_2p time constants (τVO_2p; 27 ± 10 s, 25 ± 12 s, 25 ± 11 s) were similar (p > 0.05) for MODs 1-6A, 1-6B and 6A-F, respectively. τVO_2p had reproducibility 95% confidence intervals (CI₉₅) of 8.3, 8.2, 4.7, 4.9 and 4.7 s when comparing single (1A vs. 2A), the average of two (1-2A vs. 3-4A), three (1-3A vs. 4-6A), four (1-2AB vs. 3-4AB) and six (1-3AB vs. 4-6AB) MODs, respectively. The effective Δ[HHb] response time (τ′Δ[HHb]) was unaffected across conditions (1-6A: 19 ± 2 s, 1-6B: 19 ± 3 s, 6A-F: 17 ± 4 s) with reproducibility CI₉₅ of 5.3, 4.5, 3.1, 2.9 and 3.3 s when a single, two, three, four and six MODs were compared, respectively. τHR was reduced in MODs 6A-F compared to 1-6A and 1-6B (23 ± 5 s, 25 ± 5 s, 27 ± 6 s, respectively). This study showed that parameter estimates of VO_2p, HR and Δ[HHb] kinetics are largely unaffected by data collection sequence, and the day-to-day reproducibility of τVO_2p and τ′Δ[HHb] estimates, as determined by the CI₉₅, was appreciably improved by averaging of at least three MODs.     

Kinetics of VO2 limb blood flow and regional muscle deoxygenation in young adults during moderate intensity, knee-extension exercise

The kinetics of pulmonary O₂ uptake ( [(V)\dot]\textO _2 \textp ), \left( {\dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} } \right), limb blood flow (LBF) and deoxygenation (ΔHHb) of the vastus lateralis (VL) and vastus medialis (VM) muscles during the transition to moderate-intensity knee-extension exercise (MOD) was examined. Seven males (27 ± 5 years; mean ± SD) performed repeated step transitions (n = 4) from passive exercise to MOD. Breath by breath [(V)\dot]\textO _2 \textp , \dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} , femoral artery LBF, and VL and VM muscle ∆HHb were measured, respectively, by mass spectrometer and volume turbine, Doppler ultrasound and near-infrared spectroscopy. Phase 2 [(V)\dot]\textO _2 \textp , \dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} , LBF, and ∆HHb data were fit with a mono-exponential model. The time constant (τ) of the [(V)\dot]\textO _2 \textp \dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} and LBF response were not different ( t[(V)\dot]\textO _2 \textp , \tau \dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} , 24 ± 6 s; τLBF, 23 ± 8 s). The ∆HHb response did not differ between VL and VM in amplitude (VL 6.97 ± 4.22 a.u.; VM 7.24 ± 3.99 a.u.), time delay (∆HHb_TD: VL 17 ± 2 s; VM 15 ± 1 s), time constant (τ∆HHb: VL 11 ± 6 s; VM 13 ± 4 s), or effective time constant [τ′∆HHb (= ∆HHb_TD + τ∆HHb): VL 28 ± 7 s; VM 28 ± 4 s]. Adjustments in ∆HHb in VL and VM depict a similar balance of regional O₂ delivery and utilization within the quadriceps muscle group. The τ′∆HHb and t[(V)\dot]\textO _2 \textp \tau \dot{V}{{{\text{O}}_{{ 2\,{\text{p}}}} }} were similar, however, the ∆HHb displayed an “overshoot” relative to the steady-state levels reflecting a slower alteration of microvascular blood flow (O₂ delivery) relative to O₂ utilization, necessitating a greater reliance on O₂ extraction.     

Oxygen uptake, cardiac output and muscle deoxygenation at the onset of moderate and supramaximal exercise in humans

[(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , [(Q)\dot] \dot{Q} and muscular deoxyhaemoglobin (HHb) kinetics were determined in 14 healthy male subjects at the onset of constant-load cycling exercise performed at 80% of the ventilatory threshold (80%_VT) and at 120% of [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } (120%_Wmax). An innovative approach was applied to calculate the time constant (τ₂) of the primary phase of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and [(Q)\dot] \dot{Q} kinetics at 120%_Wmax. Data were linearly interpolated after a semilogarithmic transformation of the difference between required/steady state and measured values. Furthermore, [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , \mathop Q ^· \mathop Q\limits^{ \cdot } and HHb data were fitted with traditional exponential models. τ₂ of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics was longer (62.5 ± 20.9 s) at 120%_Wmax than at 80%_VT (27.8 ± 10.4 s). The τ₂ of [(Q)\dot] \dot{Q} kinetics was unaffected by exercise intensity and, at 120% of [(V)\dot]\textO_2max , \dot{V}{\text{O}}_{2\max } , it was significantly faster (τ₂ = 35.7 ± 28.4 s) than that of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} response. The time delay of HHb kinetics was shorter (4.3 ± 1.7 s) at 120%_Wmax than at 80%_VT (8.5 ± 2.6 s) suggesting a larger mismatch between O₂ uptake and delivery at 120%_Wmax. These results suggest that [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} at the onset of exercise is not regulated/limited by muscle’s O₂ utilisation and that a slower adaptation of capillary perfusion may cause the deceleration of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics observed during supramaximal exercise.     

Aerobically trained individuals have greater increases in rectal temperature than untrained ones during exercise in the heat at similar relative intensities

To determine if the increases in rectal temperature (T _REC) during exercise in the heat at a given percent of [(V)\dot]O_2 \textpeak \dot{V}\hbox{O}_{{2\,{\text{peak}}}} depend on a subject’s aerobic fitness level. On three occasions, 10 endurance-trained (Tr) and 10 untrained (UTr) subjects ([(V)\dot]O_2 peak \dot{V}\hbox{O}_{2\,{\rm peak}} : 60 ± 6 vs. 44 ± 3 mL kg⁻¹ min⁻¹, P < 0.05) cycled in a hot-dry environment (36 ± 1°C; 25 ± 2% humidity, airflow 2.5 m s⁻¹) at three workloads (40, 60, and 80% [(V)\dot]O_2 peak \dot{V}\hbox{O}_{2\,{\rm peak}} ). At the same percent of [(V)\dot]O_2 peak \dot{V}\hbox{O}_{2\,{\rm peak}} , on average, Tr had 28 ± 5% higher heat production but also higher skin blood flow (29 ± 3%) and sweat rate (20 ± 7%; P = 0.07) and lower skin temperature (0.5°C; P < 0.05). Pre-exercise T _REC was lower in the Tr subjects (37.4 ± 0.2 vs. 37.6 ± 0.2; P < 0.05) but similar to the UTr at the end of 40 and 60% [(V)\dot]O_2 peak \dot{V}\hbox{O}_{2\,{\rm peak}} trials. Thus, exercise T _REC increased more in the Tr group than in the UTr group (0.6 ± 0.1 vs. 0.3 ± 0.1°C at 40% [(V)\dot]O_2 peak \dot{V}\hbox{O}_{2\,{\rm peak}} and 1.0 ± 0.1 vs. 0.6 ± 0.3°C at 60% [(V)\dot]O_2 peak \dot{V}\hbox{O}_{2\,{\rm peak}} ; P < 0.05). At 80% [(V)\dot]O_2 peak \dot{V}\hbox{O}_{2\,{\rm peak}} not only the increase in T _REC (1.7 ± 0.1 vs. 1.3 ± 0.3°C) but also the final T _REC was larger in Tr than in UTr subjects (39.15 ± 0.1 vs. 38.85 ± 0.1°C; P < 0.05). During exercise in the heat at the same relative intensity, aerobically trained individuals have a larger rise in T _REC than do the untrained ones which renders them more hyperthermic after high-intensity exercise.     

Effectiveness of intermittent training in hypoxia combined with live high/train low

Elite athletes often undertake altitude training to improve sea-level athletic performance, yet the optimal methodology has not been established. A combined approach of live high/train low plus train high (LH/TL+TH) may provide an additional training stimulus to enhance performance gains. Seventeen male and female middle-distance runners with maximal aerobic power ( [(V)\dot]\textO_{2 max} ) \left( {\dot{V}{\text{O}}_{{2{ \max }}} } \right) of 65.5 ± 7.3 mL kg⁻¹ min⁻¹ (mean ± SD) trained on a treadmill in normobaric hypoxia for 3 weeks (2,200 m, 4 week⁻¹). During this period, the train high (TH) group (n = 9) resided near sea-level (~600 m) while the LH/TL+TH group (n = 8) stayed in normobaric hypoxia (3,000 m) for 14 hours day⁻¹. Changes in 3-km time trial performance and physiological measures including [(V)\dot]\textO_{2 max} , \dot{V}{\text{O}}_{{2{ \max }}} , running economy and haemoglobin mass (Hb_mass) were assessed. The LH/TL+TH group substantially improved [(V)\dot]\textO_{2 max} \dot{V}{\text{O}}_{{2{ \max }}} (4.8%; ±2.8%, mean; ±90% CL), Hb_mass (3.6%; ±2.4%) and 3-km time trial performance (−1.1%; ±1.0%) immediately post-altitude. There was no substantial improvement in time trial performance 2 weeks later. The TH group substantially improved [(V)\dot]\textO_{2 max} \dot{V}{\text{O}}_{{2{ \max }}} (2.2%; ±1.8%), but had only trivial changes in Hb_mass and 3-km time-trial performance. Compared with TH, combined LH/TL+TH substantially improved [(V)\dot]\textO_{2 max} \dot{V}{\text{O}}_{{2{ \max }}} (2.6%; ±3.2%), Hb_mass (4.3%; ±3.2%), and time trial performance (−0.9%; ±1.4%) immediately post-altitude. LH/TL+TH elicited greater enhancements in physiological capacities compared with TH, however, the transfer of benefits to time-trial performance was more variable.     

High-intensity exercise and carbohydrate-reduced energy-restricted diet in obese individuals

Continuous high glycemic load and inactivity challenge glucose homeostasis and fat oxidation. Hyperglycemia and high intramuscular glucose levels mediate insulin resistance, a precursor state of type 2 diabetes. The aim was to investigate whether a carbohydrate (CHO)-reduced diet combined with high-intensity interval training (HIIT) enhances the beneficial effects of the diet alone on insulin sensitivity and fat oxidation in obese individuals. Nineteen obese subjects underwent 14 days of CHO-reduced and energy-restricted diet. Ten of them combined the diet with HIIT (4 min bouts at 90% VO_2peak up to 10 times, 3 times a week). Oral glucose insulin sensitivity (OGIS) increased significantly in both groups; [diet–exercise (DE) group: pre 377 ± 70, post 396 ± 68 mL min⁻¹ m⁻²; diet (D) group: pre 365 ± 91, post 404 ± 87 mL min⁻¹ m⁻²; P < 0.001]. Fasting respiratory exchange ratio (RER) decreased significantly in both groups (DE group: pre 0.91 ± 0.06, post 0.88 ± 0.06; D group: pre 0.92 ± 0.07, post 0.86 ± 0.07; P = 0.002). VO_2peak increased significantly in the DE group (pre 27 ± 5, post 32 ± 6 mL kg⁻¹ min⁻¹; P < 0.001), but not in the D group (pre 26 ± 9, post 26 ± 8 mL kg⁻¹ min⁻¹). Lean mass and resistin were preserved only in the DE group (P < 0.05). Fourteen days of CHO-reduced diet improved OGIS and fat oxidation (RER) in obese subjects. The energy-balanced HIIT did not further enhance these parameters, but increased aerobic capacity (VO_2peak) and preserved lean mass and resistin.