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.     

Oxygen uptake and blood metabolic responses to a 400-m run

This study aimed to investigate the oxygen uptake and metabolic responses during a 400-m run reproducing the pacing strategy used in competition. A portable gas analyser was used to measure the oxygen uptake ( [(V)\dot]\textO ₂ ) \left( {\dot{V}{{{\text{O}}_{ 2} }} } \right) of ten specifically trained runners racing on an outdoor track. The tests included (1) an incremental test to determine maximal [(V)\dot]\textO ₂  ( [(V)\dot]\textO _{2 \textmax} ) \dot{V}{{{\text{O}}_{ 2} }} \,\left( {\dot{V}{{{\text{O}}_{{ 2 {\text{max}}}} }} } \right) and the velocity associated with [(V)\dot]\textO _{2 \textmax} ( \textv-[(V)\dot]\textO _{2 \textmax} ), \dot{V}{{{\text{O}}_{{ 2 {\text{max}}}} }} \left( {{\text{v}}-\dot{V}{{{\text{O}}_{{ 2 {\text{max}}}} }} } \right), (2) a maximal 400-m (400T) and 3) a 300-m running test (300T) reproducing the exact pacing pattern of the 400T. Blood lactate, bicarbonate concentrations [ \textHCO ₃ ^- ], \left[ {{\text{HCO}}_{ 3}^{ - } } \right], pH and arterial oxygen saturation were analysed at rest and 1, 4, 7, 10 min after the end of the 400 and 300T. The peak [(V)\dot]\textO ₂ \dot{V}{{{\text{O}}_{ 2} }} recorded during the 400T corresponded to 93.9 ± 3.9% of [(V)\dot]\textO_2max \dot{V}{{{\text{O}}_{2\max } }} and was reached at 24.4 ± 3.2 s (192 ± 22 m). A significant decrease in [(V)\dot]\textO ₂ \dot{V}{{{\text{O}}_{ 2} }} (P < 0.05) was observed in all subjects during the last 100 m, although the velocity did not decrease below \textv-[(V)\dot]_{\textO 2 \textmax} . {\text{v}}-\dot{V}_{{{\text{O}}_{{ 2 {\text{max}}}} }} . The [(V)\dot]\textO ₂ \dot{V}{{{\text{O}}_{ 2} }} in the last 5 s was correlated with the pH (r = 0.86, P < 0.0005) and [ \textHCO ₃ ^- ] \left[ {{\text{HCO}}_{ 3}^{ - } } \right] (r = 0.70, P < 0.05) measured at the end of 300T. Additionally, the velocity decrease observed in the last 100 m was inversely correlated with [ \textHCO ₃ ^- ] \left[ {{\text{HCO}}_{ 3}^{ - } } \right] and pH at 300T (r = −0.83, P < 0.001, r = −0.69, P < 0.05, respectively). These track running data demonstrate that acidosis at 300 m was related to both the [(V)\dot]\textO ₂ \dot{V}{{{\text{O}}_{ 2} }} response and the velocity decrease during the final 100 m of a 400-m run.     

Performance and physiological responses during a sprint interval training session: relationships with muscle oxygenation and pulmonary oxygen uptake kinetics

The purpose of this study was to examine the cardiorespiratory and muscle oxygenation responses to a sprint interval training (SIT) session, and to assess their relationships with maximal pulmonary O₂ uptake ([(V)\dot]\textO _{2 \textp} \textmax) (\dot{V}{\text{O}}_{{ 2 {\text{p}}}} {\text{max)}} , on- and off- [(V)\dot]\textO _{2 \textp} \dot{V}{\text{O}}_{{ 2 {\text{p}}}} kinetics and muscle reoxygenation rate (Reoxy rate). Ten male cyclists performed two 6-min moderate-intensity exercises (≈90–95% of lactate threshold power output, Mod), followed 10 min later by a SIT session consisting of 6 × 30-s all out cycling sprints interspersed with 2 min of passive recovery. [(V)\dot]\textO _{2 \textp} \dot{V}{\text{O}}_{{ 2 {\text{p}}}} kinetics at Mod onset ( [(V)\dot]\textO _{2 \textp} t_\texton \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \tau_{\text{on}} ) and cessation ( [(V)\dot]\textO _{2 \textp} t_\textoff \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \tau_{\text{off}} ) were calculated. Cardiorespiratory variables, blood lactate ([La]_b) and muscle oxygenation level of the vastus lateralis (tissue oxygenation index, TOI) were recorded during SIT. Percentage of the decline in power output (%Dec), time spent above 90% of [(V)\dot]\textO _{2 \textp} max \dot{V}{\text{O}}_{{ 2 {\text{p}}}} { \max } (t > 90% [(V)\dot]\textO _{2 \textp} max \dot{V}{\text{O}}_{{ 2 {\text{p}}}} { \max } ) and Reoxy rate after each sprint were also recorded. Despite a low mean [(V)\dot]\textO _{2 \textp} \dot{V}{\text{O}}_{{ 2 {\text{p}}}} (48.0 ± 4.1% of [(V)\dot]\textO _{2 \textp} max \dot{V}{\text{O}}_{{ 2 {\text{p}}}} { \max } ), SIT performance was associated with high peak [(V)\dot]\textO _{2 \textp} \dot{V}{\text{O}}_{{ 2 {\text{p}}}} (90.4 ± 2.8% of [(V)\dot]\textO _{2 \textp} max \dot{V}{\text{O}}_{{ 2 {\text{p}}}} { \max } ), muscle deoxygenation (sprint ΔTOI = −27%) and [La]_b (15.3 ± 0.7 mmol l⁻¹) levels. Muscle deoxygenation and Reoxy rate increased throughout sprint repetitions (P < 0.001 for both). Except for t > 90% [(V)\dot]\textO _{2 \textp} max \dot{V}{\text{O}}_{{ 2 {\text{p}}}} { \max } versus [(V)\dot]\textO _{2 \textp} t_\textoff \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \tau_{\text{off}} [r = 0.68 (90% CL, 0.20; 0.90); P = 0.03], there were no significant correlations between any index of aerobic function and either SIT performance or physiological responses [e.g., %Dec vs. [(V)\dot]\textO _{2 \textp} t_\textoff \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \tau_{\text{off}} : r = −0.41 (−0.78; 0.18); P = 0.24]. Present results show that SIT elicits a greater muscle O₂ extraction with successive sprint repetitions, despite the decrease in external power production (%Dec = 21%). Further, our findings obtained in a small and homogenous group indicate that performance and physiological responses to SIT are only slightly influenced by aerobic fitness level in this population.     

Prediction of maximal oxygen uptake from submaximal ratings of perceived exertion and heart rate during a continuous exercise test: the efficacy of RPE 13

This study assessed the utility of a single, continuous exercise protocol in facilitating accurate estimates of maximal oxygen uptake ( [(V)\dot] \textO ₂ \dot{V} {\text{O}}_{ 2} max) from submaximal heart rate (HR) and the ratings of perceived exertion (RPE) in healthy, low-fit women, during cycle ergometry. Eleven women estimated their RPE during a continuous test (1 W 4 s⁻¹) to volitional exhaustion (measured [(V)\dot] \textO ₂ \dot{V} {\text{O}}_{ 2} max). Individual gaseous exchange thresholds (GETs) were determined retrospectively. The RPE and HR values prior to and including an RPE 13 and GET were extrapolated against corresponding oxygen uptake to a theoretical maximal RPE (20) and peak RPE (19), and age-predicted HRmax, respectively, to predict [(V)\dot] \textO ₂ \dot{V} {\text{O}}_{ 2} max. There were no significant differences (P > 0.05) between measured (30.9 ± 6.5 ml kg⁻¹ min⁻¹) and predicted [(V)\dot] \textO ₂ \dot{V} {\text{O}}_{ 2} max from all six methods. Limits of agreement were narrowest and intraclass correlations were highest for predictions of [(V)\dot] \textO ₂ \dot{V} {\text{O}}_{ 2} max from an RPE 13 to peak RPE (19). Prediction of [(V)\dot] \textO ₂ \dot{V} {\text{O}}_{ 2} max from a regression equation using submaximal HR and work rate at an RPE 13 was also not significantly different to actual [(V)\dot] \textO ₂ \dot{V} {\text{O}}_{ 2} max (R ²  = 0.78, SEE = 3.42 ml kg⁻¹ min⁻¹, P > 0.05). Accurate predictions of [(V)\dot] \textO ₂ \dot{V} {\text{O}}_{ 2} max may be obtained from a single, continuous, estimation exercise test to a moderate intensity (RPE 13) in low-fit women, particularly when extrapolated to peak terminal RPE (RPE₁₉). The RPE is a valuable tool that can be easily employed as an adjunct to HR, and provides supplementary clinical information that is superior to using HR alone.     

Influence of training status and exercise modality on pulmonary O2 uptake kinetics in pre-pubertal girls

The limited available evidence suggests that endurance training does not influence the pulmonary oxygen uptake ( [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} ) kinetics of pre-pubertal children. We hypothesised that, in young trained swimmers, training status-related adaptations in the [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and heart rate (HR) kinetics would be more evident during upper body (arm cranking) than during leg cycling exercise. Eight swim-trained (T; 11.4 ± 0.7 years) and eight untrained (UT; 11.5 ± 0.6 years) girls completed repeated bouts of constant work rate cycling and upper body exercise at 40% of the difference between the gas exchange threshold and peak [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} . The phase II [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} time constant was significantly shorter in the trained girls during upper body exercise (T: 25 ± 3 vs. UT: 37 ± 6 s; P < 0.01), but no training status effect was evident in the cycle response (T: 25 ± 5 vs. UT: 25 ± 7 s). The [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} slow component amplitude was not affected by training status or exercise modality. The time constant of the HR response was significantly faster in trained girls during both cycle (T: 31 ± 11 vs. UT: 47 ± 9 s; P < 0.01) and upper body (T: 33 ± 8 vs. UT: 43 ± 4 s; P < 0.01) exercise. The time constants of the phase II [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and HR response were not correlated regardless of training status or exercise modality. This study demonstrates for the first time that swim-training status influences upper body [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics in pre-pubertal children, but that cycle ergometry responses are insensitive to such differences.     

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.     

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.     

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.     

Inter-individual variability in adaptation of the leg muscles following a standardised endurance training programme in young women

There is considerable inter-individual variability in adaptations to endurance training. We hypothesised that those individuals with a low local leg-muscle peak aerobic capacity ([(V)\dot] \textO_2\textpeak) (\dot{V} {\text{O}}_{{2{\text{peak}}}}) relative to their whole-body maximal aerobic capacity ( [(V)\dot] \textO_2max) ( \dot{V} {\text{O}}_{2\max}) would experience greater muscle training adaptations compared to those with a relatively high [(V)\dot] \textO_2\textpeak \dot{V} {\text{O}}_{{2{\text{peak}}}} . 53 untrained young women completed one-leg cycling to measure [(V)\dot] \textO_2\textpeak \dot{V} {\text{O}}_{{2{\text{peak}}}} and two-leg cycling to measure [(V)\dot] \textO_2max \dot{V} {\text{O}}_{2\max} . The one-leg [(V)\dot] \textO_2\textpeak \dot{V} {\text{O}}_{{2{\text{peak}}}} was expressed as a ratio of the two-leg [(V)\dot] \textO_2max \dot{V} {\text{O}}_{2\max} (Ratio _1:2). Magnetic resonance imaging was used to indicate quadriceps muscle volume. Measurements were taken before and after completion of 6 weeks of supervised endurance training. There was large inter-individual variability in the pre-training Ratio _1:2 and large variability in the magnitude of training adaptations. The pre-training Ratio _1:2 was not related to training-induced changes in [(V)\dot] \textO_2max \dot{V} {\text{O}}_{2\max} (P = 0.441) but was inversely correlated with changes in one-leg [(V)\dot] \textO_2\textpeak \dot{V} {\text{O}}_{{2{\text{peak}}}} and muscle volume (P < 0.05). No relationship was found between the training-induced changes in two-leg [(V)\dot] \textO_2max \dot{V} {\text{O}}_{2\max} and one-leg [(V)\dot] \textO_2\textpeak \dot{V} {\text{O}}_{{2{\text{peak}}}} (r = 0.21; P = 0.129). It is concluded that the local leg-muscle aerobic capacity and Ratio _1:2 vary from person to person and this influences the extent of muscle adaptations following standardised endurance training. These results help to explain why muscle adaptations vary between people and suggest that setting the training stimulus at a fixed percentage of [(V)\dot] \textO_2max \dot{V} {\text{O}}_{2\max} might not be a good way to standardise the training stimulus to the leg muscles of different people.     

Short-term exercise-heat acclimation enhances skin vasodilation but not hyperthermic hyperpnea in humans exercising in a hot environment

We tested the hypothesis that short-term exercise-heat acclimation (EHA) attenuates hyperthermia-induced hyperventilation in humans exercising in a hot environment. Twenty-one male subjects were divided into the two groups: control (C, n = 11) and EHA (n = 10). Subjects in C performed exercise-heat tests [cycle exercise for ~75 min at 58% [(V)\dot]_{\textO 2 \textpeak} \dot{V}_{{{\text{O}}_{{ 2 {\text{peak}}}} }} (37°C, 50% relative humidity)] before and after a 6-day interval with no training, while subjects in EHA performed the tests before and after exercise training in a hot environment (37°C). The training entailed four 20-min bouts of exercise at 50% [(V)\dot]_{\textO 2 \textpeak} \dot{V}_{{{\text{O}}_{{ 2 {\text{peak}}}} }} separated by 10 min of rest daily for 6 days. In C, comparison of the variables recorded before and after the no-training period revealed no changes. In EHA, the training increased resting plasma volume, while it reduced esophageal temperature (T _es), heart rate at rest and during exercise, and arterial blood pressure and oxygen uptake ( [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} ) during exercise. The training lowered the T _es threshold for increasing forearm vascular conductance (FVC), while it increased the slope relating FVC to T _es and the peak FVC during exercise. It also lowered minute ventilation ( [(V)\dot]_\textE \dot{V}_{\text{E}} ) during exercise, but this effect disappeared after removing the influence of [(V)\dot]_\textO2 \dot{V}_{{{\text{O}}_{2} }} on [(V)\dot]_\textE \dot{V}_{\text{E}} . The training did not change the slope relating ventilatory variables to T _es. We conclude that short-term EHA lowers ventilation largely by reducing metabolism, but it does not affect the sensitivity of hyperthermia-induced hyperventilation during submaximal, moderate-intensity exercise in humans.     

Effect of hyperventilation and prior heavy exercise on O2 uptake and muscle deoxygenation kinetics during transitions to moderate exercise

The effect of hyperventilation-induced hypocapnic alkalosis (HYPO) and prior heavy-intensity exercise (HVY) on pulmonary O₂ uptake ([(V)\dot]\textO _{2 \textp}) (\dot{V}{\text{O}}_{{ 2 {\text{p}}}}) kinetics were examined in young adults (n = 7) during moderate-intensity exercise (MOD). Subjects completed leg cycling exercise during (1) normal breathing (CON, P_ETCO₂ ~ 40 mmHg) and (2) controlled hyperventilation (HYPO, P_ETCO₂ ~ 20 mmHg) throughout the protocol, with each condition repeated on four occasions. The protocol consisted of two MOD transitions (MOD1, MOD2) to 80% estimated lactate threshold with MOD2 preceded by HVY (Δ50%); each transition lasted 6 min and was preceded by 20 W cycling. [(V)\dot]\textO _{2 \textp} \dot{V}{\text{O}}_{{ 2 {\text{p}}}} was measured breath-by-breath and concentration changes in oxy- and deoxy-hemoglobin/myoglobin (Δ[HHb]) of the vastus lateralis muscle were measured by near-infrared spectroscopy. Adjustment of [(V)\dot]\textO _{2 \textp} \dot{V}{\text{O}}_{{ 2 {\text{p}}}} and Δ[HHb] were modeled using a mono-exponential equation by non-linear regression. During MOD1, the phase 2 time constant (τ) for [(V)\dot]\textO _{2 \textp}  (t[(V)\dot]\textO _{2 \textp} ) \dot{V}{\text{O}}_{{ 2 {\text{p}}}} \,(\tau \dot{V}{\text{O}}_{{ 2 {\text{p}}}} ) was greater (P < 0.05) in HYPO (45 ± 24 s) than CON (28 ± 17 s). During MOD2, t[(V)\dot]\textO _{2 \textp} \tau \dot{V}{\text{O}}_{{ 2 {\text{p}}}} was reduced (P < 0.05) in both conditions (HYPO: 24 ± 7 s, CON: 20 ± 8 s). The Δ[Hb_TOT] and Δ[O₂Hb] were greater (P < 0.05) prior to and throughout MOD2. The Δ[HHb] mean response time was similar in MOD1 and MOD2, and between conditions, however, the MOD1 Δ[HHb] amplitude was greater (P < 0.05) in HYPO compared to CON, with no differences between conditions in MOD2. These findings suggest that the speeding of [(V)\dot]\textO _{2 \textp} \dot{V}{\text{O}}_{{ 2 {\text{p}}}} kinetics after prior HVY in HYPO was related, in part, to an increase in microvascular perfusion.     

Effect of ramp bicycle exercise on exhaled carbon monoxide in humans

The effect of exercise on the increase of exhaled CO in smokers compared to non-smokers has not been clarified yet. In this study we compared the dynamics of exhaled CO before, during and after exercise between smokers and non-smokers. A group of 8 smokers and a group of 8 non-smokers underwent a bicycle exercise in a ramp fashion to near maximum intensity. Ventilation and gas exchange, and CO exhalation were continuously measured every 30-s before, during and after the exercise. The fraction of CO (F _CO) in the exhaled air decreased gradually, but the total amount of exhaled CO ([(V)\dot]_\textCO ) (\dot{V}_{{{\text{CO}}}} ) increased in a linear manner during the ramp exercise, and F _CO and [(V)\dot]_\textCO \dot{V}_{\text{CO}} returned to the pre-exercise level within several minutes after exercise in all subjects. A linear relationship was observed between [(V)\dot]_{\textO 2} \dot{V}_{{{\text{O}}_{ 2} }} and [(V)\dot]_\textCO , \dot{V}_{\text{CO}} , and between [(V)\dot]_\textE \dot{V}_{\text{E}} and [(V)\dot]_\textCO \dot{V}_{\text{CO}} in both the whole period of measurement and during the ramp exercise period in all subjects. However, the [(V)\dot]_\textCO \dot{V}_{\text{CO}} at 0 W, the peak [(V)\dot]_\textCO \dot{V}_{\text{CO}} and the slope coefficients in the regression equation between [(V)\dot]_\textCO \dot{V}_{\text{CO}} and [(V)\dot]_{\textO 2} , \dot{V}_{{{\text{O}}_{ 2} }} , and between [(V)\dot]_\textCO \dot{V}_{\text{CO}} and [(V)\dot]_\textE \dot{V}_{\text{E}} in the ramp exercise as well as the entire periods of measurement were significantly higher in smokers compared with those in non-smokers, and these were correlated with the number of cigarettes smoked per day. It was concluded that CO exhalation increases linearly with the increase of [(V)\dot]_{\textO 2} \dot{V}_{{{\text{O}}_{ 2} }} and [(V)\dot]_\textE \dot{V}_{\text{E}} during exercise, and habitual smoking shifts these relationships upward depending on the number of cigarettes smoked daily.     

Effect of sprint interval training on circulatory function during exercise in sedentary, overweight/obese women

Very high-intensity, low-volume, sprint interval training (SIT) increases muscle oxidative capacity and may increase maximal oxygen uptake ( [(V)\dot]\textO _{2 \textmax} {\dot{V}\text{O}}_{{ 2 {\text{max}}}} ), but whether circulatory function is improved, and whether SIT is feasible in overweight/obese women is unknown. To examine the effects of SIT on [(V)\dot]\textO _{2 \textmax} {\dot{V}\text{O}}_{{ 2 {\text{max}}}} and circulatory function in sedentary, overweight/obese women. Twenty-eight women with BMI > 25 were randomly assigned to SIT or control (CON) groups. One week before pre-testing, subjects were familarized to [(V)\dot]\textO _{2 \textmax} {\dot{V}\text{O}}_{{ 2 {\text{max}}}} testing and the workload that elicited 50% [(V)\dot]\textO _{2 \textmax} {\dot{V}\text{O}}_{{ 2 {\text{max}}}} was calculated. Pre- and post-intervention, circulatory function was measured at 50% of the pre-intervention [(V)\dot]\textO _{2 \textmax} {\dot{V}\text{O}}_{{ 2 {\text{max}}}} , and a GXT was performed to determine [(V)\dot]\textO _{2 \textmax} {\dot{V}\text{O}}_{{ 2 {\text{max}}}} . During the intervention, SIT training was given for 3 days/week for 4 weeks. Training consisted of 4–7, 30-s sprints on a stationary cycle (5% body mass as resistance) with 4 min active recovery between sprints. CON maintained baseline physical activity. Post-intervention, heart rate (HR) was significantly lower and stroke volume (SV) significantly higher in SIT (−8.1 and 11.4%, respectively; P < 0.05) during cycling at 50% [(V)\dot]\textO _{2 \textmax} {\dot{V}\text{O}}_{{ 2 {\text{max}}}} ; changes in CON were not significant (3 and −4%, respectively). Changes in cardiac output ( [(\textQ)\dot] {\dot{\text{Q}}} ) and arteriovenous oxygen content difference [(a − v)O₂ diff] were not significantly different for SIT or CON. The increase in [(V)\dot]\textO _{2 \textmax} {\dot{V}\text{O}}_{{ 2 {\text{max}}}} by SIT was significantly greater than by CON (12 vs. −1%). Changes by SIT and CON in HR_max (−1 vs. −1%) were not significantly different. Four weeks of SIT improve circulatory function during submaximal exercise and increases [(V)\dot]\textO _{2 \textmax} {\dot{V}\text{O}}_{{ 2 {\text{max}}}} in sedentary, overweight/obese women.     

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.     

Influence of training status and exercise modality on pulmonary O<Subscript>2</Subscript> uptake kinetics in pubertal girls

The influence of training status on the oxygen uptake ( [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} ) response to heavy intensity exercise in pubertal girls has not previously been investigated. We hypothesised that whilst training status-related adaptations would be evident in the [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} , heart rate (HR) and deoxyhaemoglobin ([HHb]) kinetics of pubertal swimmers during both lower and upper body exercise, they would be more pronounced during upper body exercise. Eight swim-trained (T; 14.2 ± 0.7 years) and eight untrained (UT; 14.5 ± 1.3 years) girls completed a number of constant-work-rate transitions on cycle and upper body ergometers at 40% of the difference between the gas exchange threshold and peak [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} . The phase II [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} time constant (τ) was significantly shorter in the trained girls during both cycle (T: 21 ± 6 vs. UT: 35 ± 11 s; P < 0.01) and upper body exercise (T: 29 ± 8 vs. UT: 44 ± 8 s; P < 0.01). The [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} slow component was not influenced by training status. The [HHb] τ was significantly shorter in the trained girls during both cycle (T: 12 ± 2 vs. UT: 20 ± 6 s; P < 0.01) and upper body exercise (T: 13 ± 3 vs. UT: 21 ± 7 s; P < 0.01), as was the HR τ (cycle, T: 36 ± 5 vs. UT: 53 ± 9 s; upper body, T: 32 ± 3 vs. UT: 43 ± 2; P < 0.01). This study suggests that both central and peripheral factors contribute to the faster [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} kinetics in the trained girls and that differences are evident in both lower and upper body exercise.     

Determination of critical power in trained rowers using a three-minute all-out rowing test

The purpose of this study was to determine whether the hyperbolic relationship between power output and time to exhaustion (work − time and power − [1/time] models) could be estimated from a modified version of a three-minute all-out rowing test (3-min RT), and to investigate the test–retest reliability of the 3-min RT. Eighteen male rowers volunteered to participate in this study and underwent an incremental exercise test (IRT), three constant-work rate tests to establish the critical power (CP) and the curvature constant (W′), and two 3-min RTs against a fixed resistance to estimate the end-test power (EP) and work-done-above-EP (WEP) on a rowing ergometer. Peak ( [(V)\dot]\textO _{2 \textpeak} ) \left( {\dot{V}{\text{O}}_{{ 2 {\text{peak}}}} } \right) and maximal ( [(V)\dot]\textO_2max ) \left( {\dot{V}{\text{O}}_{2\max } } \right) oxygen uptakes were calculated as the highest 30 s average achieved during the 3-min RT and IRT tests. The results showed that EP and WEP determinations, based on the 3-min RT, have moderate reproducibility (P = 0.002). EP (269 ± 39 W) was significantly correlated with CP (work − time, 272 ± 30 W; power − [1/time], 276 ± 32 W) (P = 0.000), with no significant differences observed between the EP and CP values (P = 0.474). However, WEP did not significantly correlate with W′ (P = 0.254), and was significantly higher than the W′ values. There was a significant correlation between the [(V)\dot]\textO _{2 \textpeak} \dot{V}{\text{O}}_{{ 2 {\text{peak}}}} (60 ± 3 ml kg⁻¹ min⁻¹) and [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } (61 ± 4 ml kg⁻¹ min⁻¹) (P = 0.003). These results indicate that the 3-min RT has moderate reliability, and is able to appropriately estimate the aerobic capacity in rowers, particularly for the CP and [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } parameters.     

Critical power in adolescents: physiological bases and assessment using all-out exercise

This study examined whether critical power (CP) in adolescents: (1) provides a landmark for maximal steady-state exercise; and (2) can be determined using ‘all-out’ exercise. Nine active 14–15 year olds (6 females, 3 males) performed five cycling tests: (1) a ramp test to determine [(V)\dot]\textO_2 \textpeak \dot{V}{\text{O}}_{{2\,{\text{peak}}}} ; (2) up to four constant power output tests to determine CP; (3–4) constant power output exercise 10% above and 10% below CP; and (5) a 3 min all-out cycle test to establish the end power (EP) at 90 and 180 s of exercise. All participants completed 30 min of exercise below CP and were characterized by steady-state blood lactate and [(V)\dot]\textO₂ {\dot{V}\text{O}}_{2} profiles. In contrast, time to exhaustion during exercise above CP was 15.0 ± 7.0 min and characterized by an inexorable rise in blood lactate and a rise, stabilization (~91% [(V)\dot]\textO_2 \textpeak {\dot{V}\text{O}}_{{2\,{\text{peak}}}} ) and fall in [(V)\dot]\textO₂ {\dot{V}\text{O}}_{2} (~82% [(V)\dot]\textO_2 \textpeak {\dot{V}\text{O}}_{{2\,{\text{peak}}}} ) prior to exhaustion. Eight out of nine participants completed the 3 min test and their EPs at 90 s (148 ± 29 W) and 180 s (146 ± 30 W) were not different from CP (146 ± 27 W) (P = 0.98). The typical error of estimates for establishing CP using EP at 90 s or 180 s of the 3 min test were 25 W (19.7% CV) and 25 W (19.6% CV), respectively. CP in active adolescence provides a valid landmark for maximal steady-state exercise, although its estimation on an individual level using the 3 min all-out test may be of limited value.     

Assessment of the effects of physical training in patients with chronic heart failure: the utility of effort-independent exercise variables

Traditionally, the effects of physical training in patients with chronic heart failure (CHF) are evaluated by changes in peak oxygen uptake (peak [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} ). The assessment of peak [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , however, is highly dependent on the patients’ motivation. The aim of the present study was to evaluate the clinical utility of effort-independent exercise variables for detecting training effects in CHF patients. In a prospective controlled trial, patients with stable CHF were allocated to an intervention group (N = 30), performing a 12-week combined cycle interval and muscle resistance training program, or a control group (N = 18) that was matched for age, gender, body composition and left ventricular ejection fraction. The following effort-independent exercise variables were evaluated: the ventilatory anaerobic threshold (VAT), oxygen uptake efficiency slope (OUES), the [(V)\dot]_\textE /[(V)\dot]\textCO ₂ \dot{V}_{\text{E}} /\dot{V}{\text{CO}}_{ 2} slope and the time constant of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics during recovery from submaximal constant-load exercise (τ-rec). In addition to post-training increases in peak [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and peak [(V)\dot]_\textE , \dot{V}_{\text{E}} , , the intervention group showed significant within and between-group improvements in VAT, OUES and τ-rec. There were no significant differences between relative improvements of the effort-independent exercise variables in the intervention group. In contrast with VAT, which could not be determined in 9% of the patients, OUES and τ-rec were determined successfully in all patients. Therefore, we conclude that OUES and τ-rec are useful in clinical practice for the assessment of training effects in CHF patients, especially in cases of poor subject effort during symptom-limited exercise testing or when patients are unable to reach a maximal exercise level.     

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.     

Evaluation of the Oxycon Mobile metabolic system against the Douglas bag method

The aim of this study was to evaluate two versions of the Oxycon Mobile portable metabolic system (OMPS1 and OMPS2) in a wide range of oxygen uptake, using the Douglas bag method (DBM) as criterion method. The metabolic variables [(V)\dot]\textO₂ , [(V)\dot]\textCO₂ , \dot{V}{\text{O}}_{2} , \dot{V}{\text{CO}}_{2} , respiratory exchange ratio and [(V)\dot]_\textE \dot{V}_{\text{E}} were measured during submaximal and maximal cycle ergometer exercise with sedentary, moderately trained individuals and athletes as participants. Test–retest reliability was investigated using the OMPS1. The coefficients of variation varied between 2 and 7% for the metabolic parameters measured at different work rates and resembled those obtained with the DBM. With the OMPS1, systematic errors were found in the determination of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and [(V)\dot]\textCO₂ . \dot{V}{\text{CO}}_{2} . At submaximal work rates [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} was 6–14% and [(V)\dot]\textCO₂ \dot{V}{\text{CO}}_{2} 5–9% higher than with the DBM. At [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } both [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} and [(V)\dot]\textCO₂ \dot{V}{\text{CO}}_{2} were slightly lower as compared to DBM (−4.1 and −2.8% respectively). With OMPS2, [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} was determined accurately within a wide measurement range (about 1–5.5 L min⁻¹), while [(V)\dot]\textCO₂ \dot{V}{\text{CO}}_{2} was overestimated (3–7%). [(V)\dot]_\textE \dot{V}_{\text{E}} was accurate at submaximal work rates with both OMPS1 and OMPS2, whereas underestimations (4–8%) were noted at [(V)\dot]\textO_2max . \dot{V}{\text{O}}_{2\max } . The present study is the first to demonstrate that a wide range of [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} can be measured accurately with the Oxycon Mobile portable metabolic system (second generation). Future investigations are suggested to clarify reasons for the small errors noted for [(V)\dot]_\textE \dot{V}_{\text{E}} and [(V)\dot]\textCO₂ \dot{V}{\text{CO}}_{2} versus the Douglas bag measurements, and also to gain knowledge of the performance of the device under applied and non-laboratory conditions.