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.     

Mountaineering experience decreases the net oxygen cost of climbing Mont Blanc (4,808 m)

The purpose of this study was to test the hypothesis that mountaineering experience decreases the net oxygen cost of uphill walking (OCw) on steep mountain trails and in ice and snow conditions. OCw was measured during an ascent of Mont Blanc in eight experienced alpinists and eight non-alpinists who were matched for sex (4 + 4) and low-altitude aerobic power ( [(V)\dot]\textO_{2 max} \dot{V}{\text{O}}_{{2{ \max }}} 50–55 ml kg⁻¹ min⁻¹). Subjects carried a breath-by-breath gas exchange analyzer and a GPS. [(V)\dot]\textO_{2 max} \dot{V}{\text{O}}_{{2{ \max }}} at altitude was estimated from measured low-altitude [(V)\dot]\textO_2max \dot{V}{\text{O}}_{{2{\max}}} using Bassett’s equation to calculate fractional use of [(V)\dot]\textO_{2 max} \dot{V}{\text{O}}_{{2{ \max }}} during the ascent (F [(V)\dot]\textO_{2 max} \dot{V}{\text{O}}_{{2{ \max }}} ). OCw was calculated as the difference between [(V)\dot]\textO₂ \dot{V}{\text{O}}_{{2}} while climbing minus resting [(V)\dot]\textO₂ \dot{V}{\text{O}}_{{2}} . At all elevations, Alpinists exhibited a lower OCw (P < 0.01). In all subjects, OCw increased when encountering ice and snow conditions. \textF[(V)\dot]\textO_{2 max} {\text{F}}\dot{V}{\text{O}}_{{2{ \max }}} remained stable around 75% at all elevations independent of experience or sex. In conclusion, the OCw is lower in experienced mountaineers compared to non-experienced subjects, and increases when going from steep rocky mountain terrain to ice and snow conditions, independent of mountaineering experience or sex.     

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.     

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.     

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 peak oxygen uptake from age and power output at RPE 15 in obese women

The purpose of this study was to develop a simple, convenient and indirect method for predicting peak oxygen uptake ( [(V)\dot]\textO_2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}} ) from a sub-maximal graded exercise test (GXT), in obese women. Thirty obese women performed GXT to volitional exhaustion. During GXT, oxygen uptake and the power at RPE 15 ( P_{\textRPE  15} P_{{{\text{RPE}}\;15}} ) were measured, and [(V)\dot]\textO_2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}} was determined. Following assessment of the relationships between [(V)\dot]\textO_2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}} and P_{\textRPE  15} P_{{{\text{RPE}}\;15}} , age, height and mass were made available in a stepwise multiple regression analysis with [(V)\dot]\textO_2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}} as the dependent variable. The equation to predict [(V)\dot]\textO_2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}} was:

Predicting {\dot{V}}{\text{O}}_{2{\text{max}}} with an objectively measured physical activity in Japanese men

The present study investigated the use of the accelerometer-determined physical activity (PA) variables as the objective PA variables for estimating [(V)\dot]\textO _{2 \textmax} \dot{V}{\text{O}}_{{ 2 {\text{max}}}} in Japanese adult men. One hundred and twenty-seven Japanese adult men aged from 20 to 69 years were recruited as subjects of the present study. Maximal oxygen uptake ( [(V)\dot]\textO _{2 \textmax} \dot{V}{\text{O}}_{{ 2 {\text{max}}}} ) was measured with a maximal incremental test on a bicycle ergometer. Daily step counts (SC) and the amount spent in moderate to vigorous PA (MVPA) and vigorous PA (VPA) were measured using accelerometer-based activity monitors worn at the waist for seven consecutive days. The non-exercise models were derived using hierarchical linear regression analysis, and cross-validated using two separate cross-validation procedures. SC, MVPA, and VPA were significantly related to [(V)\dot]\textO _{2 \textmax} \dot{V}{\text{O}}_{{ 2 {\text{max}}}} (partial correlation coefficient r = 0.58, r = 0.42, and r = 0.51, respectively) after adjusting for age. Two models were developed by multiple regression to estimate [(V)\dot]\textO _{2 \textmax} \dot{V}{\text{O}}_{{ 2 {\text{max}}}} using data of age, SC, VPA, and either BMI (the coefficient of determination (R ²) = 0.71, standard error of estimate (SEE) = 4.2 ml kg⁻¹ min⁻¹), or waist circumference (R ² = 0.74, SEE = 3.9 ml kg⁻¹ min⁻¹). All regression models demonstrated a high level of cross-validity supported by the minor shrinkage of R ² and increment of SEE in the PRESS procedure, and by small constant errors for subgroups of age, SC, and [(V)\dot]\textO _{2 \textmax} . \dot{V}{\text{O}}_{{ 2 {\text{max}}}} . This study demonstrated that combining SC with VPA, but not with MVPA, was useful in predicting [(V)\dot]\textO _{2 \textmax} \dot{V}{\text{O}}_{{ 2 {\text{max}}}} variance and improved the ability of the regression models to accurately predict [(V)\dot]\textO _{2 \textmax} \dot{V}{\text{O}}_{{ 2 {\text{max}}}} .     

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.     

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.     

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.     

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.     

Does cerebral oxygenation affect cognitive function during exercise?

This study tested whether cerebral oxygenation affects cognitive function during exercise. We measured reaction times (RT) of 12 participants while they performed a modified version of the Eriksen flanker task, at rest and while cycling. In the exercise condition, participants performed the cognitive task at rest and while cycling at three workloads [40, 60, and 80% of peak oxygen uptake ( [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} )]. In the control condition, the workload was fixed at 20 W. RT was divided into premotor and motor components based on surface electromyographic recordings. The premotor component of RT (premotor time) was used to evaluate the effects of acute exercise on cognitive function. Cerebral oxygenation was monitored during the cognitive task over the right frontal cortex using near-infrared spectroscopy. In the exercise condition, we found that premotor time significantly decreased during exercise at 60% peak [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} relative to rest. However, this improvement was not observed during exercise at 80% peak [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} . In the control condition, premotor time did not change during exercise. Cerebral oxygenation during exercise at 60% peak [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} was not significantly different from that at rest, while cerebral oxygenation substantially decreased during exercise at 80% peak [(V)\dot]\textO ₂ \dot{V}{\text{O}}_{ 2} . The present results suggest that an improvement in cognitive function occurs during moderate exercise, independent of cerebral oxygenation.     

Correspondences between continuous and intermittent exercises intensities in healthy prepubescent children

The aim of this article is to determine correspondences between three levels of continuous and intermittent exercise (CE and IE, respectively) in terms of steady-state oxygen uptake ([(V)\dot]\textO _2 \textSS ) (\dot{V}{\text{O}}_{{ 2\,{\text{SS}}}} ) and heart rate (HR) in children. Fourteen healthy children performed seven exercises on a treadmill: one graded test for the determination of maximal aerobic speed (MAS), three CE at 60, 70 and 80% of MAS (CE60, CE70 and CE80) and three IE (alternating 15 s of exercise intercepted with 15 s of passive recovery) at 90, 100 and 110% of MAS (IE90, IE100 and IE110). Mean [(V)\dot]\textO _2 \textSS \dot{V}{\text{O}}_{{ 2\,{\text{SS}}}} and mean HR were determined for both continuous and intermittent exercises. For comparison, three associations were designed: CE60 versus IE90, CE70 versus IE100 and CE80 versus IE110. No [(V)\dot]\textO _2 \textSS \dot{V}{\text{O}}_{{ 2\,{\text{SS}}}} difference was observed for CE60 versus IE90 and CE70 versus IE100 whereas a significant difference (P < 0.01) was found for CE80 versus IE110 (1.36 ± 0.45 vs. 1.19 ± 0.38 L min⁻¹, respectively). Significant linear regressions were found for the three CE versus IE associations for [(V)\dot]\textO _2 \textSS \dot{V}{\text{O}}_{{ 2\,{\text{SS}}}} (0.60 < r ² < 0.99, P < 0.05). For the three associations, mean HR presented no significant difference. Only one significant relation was found for CE80 versus IE110 association (r2 = 0.49, P < 0.05). Correspondences between CE and IE intensities are possible in terms of [(V)\dot]\textO _2 \textSS \dot{V}{\text{O}}_{{ 2\,{\text{SS}}}} whatever the level of exercise; even if for high intensities, [(V)\dot]\textO _2 \textSS \dot{V}{\text{O}}_{{ 2\,{\text{SS}}}} was higher during CE. These results demonstrated that it is possible to diversify the exercise modality while conserving exercise individualization.     

Slow $$ \dot{V}{\text{O}}_{2} $$ kinetics during moderate-intensity exercise as markers of lower metabolic stability and lower exercise tolerance

An analysis of previously published data obtained by our group on patients characterized by markedly slower pulmonary [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics (heart transplant recipients, patients with mitochondrial myopathies, patients with McArdle disease) was carried out in order to suggest that slow [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics should not be considered the direct cause, but rather a marker, of impaired exercise tolerance. For a given ATP turnover rate, faster (or slower) [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics are associated with smaller (or greater) muscle [PCr] decreases. The latter, however, should not be taken per se responsible for the higher (or lower) exercise tolerance, but should be considered within the general concept of “metabolic stability”. Good muscle metabolic stability at a given ATP turnover rate (~power output) is associated with relatively smaller decreases, compared to rest, in [PCr] and in the Gibbs free energy of ATP hydrolysis, as well as with relatively smaller increases in [Pi], [ADP_free], [AMP_free], and [IMP_free], metabolites directly related to fatigue. Disturbances in muscle metabolic stability can affect muscle function in various ways, whereas good metabolic stability is associated with less fatigue and higher exercise tolerance. Smaller [PCr] decreases, however, are strictly associated with a faster [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics. Thus, faster [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} kinetics may simply be an “epiphenomenon” of a relatively higher metabolic stability, which would then represent the relevant variable in terms of fatigue and exercise tolerance.     

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.     

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.     

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.     

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.     

Age-related changes in cardio-respiratory responses and muscular performance following an Olympic triathlon in well-trained triathletes

The aim of the present study was to compare the maximal isometric torque and cardio-respiratory parameters in well-trained young and master triathletes prior to and following an Olympic distance triathlon. One day before and 24 h following the event, participants performed three maximum voluntary isometric knee extensions and flexions and an incremental running test on a treadmill to determine the maximal isometric torque, maximal oxygen uptake ( [(V)\dot]\textO_2max ) \left( {\dot{V}{\text{O}}_{2\max } } \right) , speed at [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } (vVO₂max), speed at ventilatory thresholds (VT1 and VT2) and submaximal running economy. Prior to the event [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } , vVO₂max, speed at ventilatory thresholds and running economy were significantly lower in master athletes, but maximal voluntary torque was similar between the groups. 24 h following the race, a similar significant decrease in [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } (−3.1% in masters, and −6.2% in young, p < 0.05), and vVO₂max (−9.5% in masters, and −5.6% in young, p < 0.05) was observed in both the groups. The speed at VT2 significantly decreased only in master athletes (−8.3%, p < 0.05), while no change was recorded in maximal voluntary torque or submaximal running economy following the event. The results indicate that for well-trained subjects, the overall relative exercise intensity during an Olympic distance triathlon and the fatigue 24 h following the event seem to be independent of age.