Prediction of <Emphasis Type="Italic">V</Emphasis>O<Subscript>2max</Subscript> with daily step counts for Japanese adult women

The purpose of the study was to develop a new non-exercise VO_2max prediction model using a physical activity (PA) variable determined by pedometer-determined step counts (SC, steps day⁻¹) in Japanese women aged 20–69 years old. Eighty-seven and 102 subjects were used to develop the prediction model, and to validate the new model, respectively. VO_2max was measured using a maximal incremental test on a bicycle ergometer. SC was significantly related to VO_2max (partial correlation coefficient r = 0.40, P < 0.001) after adjusting for BMI (kg m⁻²) and age (years). When the new prediction equation developed by multiple regression to estimate VO_2max from age, BMI, and SC (R = 0.71, SEE = 5.3 ml kg⁻¹ min⁻¹, P < 0.001) was applied to the Validation group, predicted VO_2max correlated well with measured VO_2max (r = 0.81, P < 0.001), suggesting that SC is a useful PA variable for non-exercise prediction of VO_2max in Japanese women.     

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.     

Fibrinolytic markers and vasodilatory capacity following acute exercise among men of differing training status

We evaluated the effect of differing physical activity patterns on fibrinolysis and vasodilatory capacity using a cross-sectional design with 16 endurance-trained (ET) (mean ± SE) (28 ± 6 years), 14 resistance-trained (RT) (28 ± 7 years), and 10 untrained (UT) (26 ± 7 years) men. t-PA and PAI-1 activity and t-PA antigen were measured before and after a maximal treadmill test (VO_2peak). Vasodilatory capacity was assessed using strain-gauge plethysmography on the forearm following reactive hyperemia (RH) before and after the treadmill test. The ET group had a smaller body mass index (BMI) (22.8 ± 0.5 ET, 26.4 ± 0.4 RT, 25.1 ± 0.8 UT kg m⁻²) (P < 0.05) and a greater VO_2peak (57 ± 1 ET, 42 ± 2 RT, 45 ± 2 UT mL min⁻¹ kg⁻¹) (P < 0.05). Peak vasodilatory capacity (29.7 ± 2 ET, 32.0 ± 2 RT, 27.4 ± 2 UT mL min⁻¹ 100 mL of tissue) was similar between groups before and after exercise. Area under the curve for forearm blood flow was greater following acute exercise (212 vs. 122, P < 0.05), again with no differences between groups. t-PA activity and antigen increased following maximal exercise in all groups (P < 0.0001), with no group differences. PAI-1 activity decreased the least in RT after exercise (70% decrease vs. 86% ET and 82% UT; P < 0.05). The change in t-PA activity with exercise was not related to exercise-induced change in overall vasodilatory capacity. These findings demonstrate that in healthy young men different physical activity patterns do not appear to impact the exercise-induced changes in fibrinolysis or vasodilatory capacity.     

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.     

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.     

Exercise intensity and oxygen uptake kinetics in African-American and Caucasian women

The effect of exercise intensity on the on- and off-transient kinetics of oxygen uptake (VO₂) was investigated in African American (AA) and Caucasian (C) women. African American (n = 7) and Caucasian (n = 6) women of similar age, body mass index and weight, performed an incremental test and bouts of square-wave exercise at moderate, heavy and very heavy intensities on a cycle ergometer. Gas exchange threshold (LT_GE) was lower in AA (13.6 ± 2.3 mL kg⁻¹ min⁻¹) than C (18.6 ± 5.6 mL kg⁻¹ min⁻¹). The dynamic exercise and recovery VO₂ responses were characterized by mathematical models. There were no significant differences in (1) peak oxygen uptake (VO_2peak) between AA (28.5 ± 5 mL kg⁻¹ min⁻¹) and C (31.1 ± 6.6 mL kg⁻¹ min⁻¹) and (2) VO₂ kinetics at any exercise intensity. At moderate exercise, the on- and off- VO₂ kinetics was described by a monoexponential function with similar time constants τ _1,on (39.4 ± 12.5; 38.8 ± 15 s) and τ _1,off (52.7 ± 10.1; 40.7 ± 4.4 s) for AA and C, respectively. At heavy and very heavy exercise, the VO₂ kinetics was described by a double-exponential function. The parameter values for heavy and very heavy exercise in the AA group were, respectively: τ _1,on (47.0 ± 10.8; 44.3 ± 10 s), τ _2,on (289 ± 63; 219 ± 90 s), τ _1,off (45.9 ± 6.2; 50.7 ± 10 s), τ _2,off (259 ± 120; 243 ± 93 s) while in the C group were, respectively: τ _1,on (41 ± 12; 43.2 ± 15 s); τ _{2, on} (277 ± 81; 215 ± 36 s), τ _1,off (40.2 ± 3.4; 42.3 ± 7.2 s), τ _2,off (215 ± 133; 228 ± 64 s). The on- and off-transients were symmetrical with respect to model order and dependent on exercise intensity regardless of race. Despite similar VO₂ kinetics, LT_GE and gain of the VO₂ on-kinetics at moderate intensity were lower in AA than C. However, generalization to the African American and Caucasian populations is constrained by the small subject numbers.     

Cardiac function and arteriovenous oxygen difference during exercise in obese adults

The purpose of this study was to assess cardiac function and arteriovenous oxygen difference (a-vO₂ difference) at rest and during exercise in young, normal-weight (n = 20), and obese (n = 12) men and women who were matched for age and fitness level. Participants were assessed for body composition, peak oxygen consumption (VO_2peak), and cardiac variables (thoracic bioimpedance)—cardiac index (CI), cardiac output (Q), stroke volume (SV), heart rate (HR), and ejection fraction (EF)—at rest and during cycling exercise at 65% of VO_2peak. Differences between groups were assessed with multivariate ANOVA and mixed-model ANOVA with repeated measures controlling for sex. Absolute VO_2peak and VO_2peak relative to fat-free mass (FFM) were similar between normal-weight and obese groups (Mean ± SEE 2.7 ± 0.2 vs. 3.3 ± 0.3 l min⁻¹, p = 0.084 and 52.4 ± 1.5 vs. 50.9 ± 2.3 ml kg FFM⁻¹ min⁻¹, p = 0.583, respectively). In the obese group, resting Q and SV were higher (6.7 ± 0.4 vs. 4.9 ± 0.1 l min⁻¹, p < 0.001 and 86.8 ± 4.3 vs. 65.8 ± 1.9 ml min⁻¹, p < 0.001, respectively) and EF lower (56.4 ± 2.2 vs. 65.5 ± 2.2%, p = 0.003, respectively) when compared with the normal-weight group. During submaximal exercise, the obese group demonstrated higher mean CI (8.8 ± 0.3 vs. 7.7 ± 0.2 l min⁻¹ m⁻², p = 0.007, respectively), Q (19.2 ± 0.9 vs. 13.1 ± 0.3 l min⁻¹, p < 0.001, respectively), and SV (123.0 ± 5.6 vs. 88.9 ± 4.1 ml min⁻¹, p < 0.001, respectively) and a lower a-vO₂ difference (10.4 ± 1.0 vs. 14.0 ± 0.7 ml l00 ml⁻¹, p = 0.002, respectively) compared with controls. Our study suggests that the ability to extract oxygen during exercise may be impaired in obese individuals.     

Longitudinal changes in haemoglobin mass and <Emphasis Type="Italic">V</Emphasis>O<Subscript>2max</Subscript> in adolescents

This study assessed the relationship between haemoglobin mass (Hb_mass) and maximum oxygen consumption (VO_2max) in adolescents over 1 year. Twenty-three subjects (11–15 years) participated; 12 undertook ~12 months of cycle training (cyclists) and 11 were sedentary (controls). Hb_mass and VO_2max were measured approximately every 3 months. At baseline there was a high correlation (r = 0.82, P < 0.0001) between relative VO_2max (ml kg⁻¹ min⁻¹) and relative Hb_mass (g kg⁻¹). During 12 months there was a significant increase in relative VO_2max of the cyclists but not the controls; however, there was no corresponding increase in relative Hb_mass of either group. The correlation between percent changes in relative VO_2max and relative Hb_mass was not significant for cyclists (r = 0.31, P = 0.33) or controls (r = 0.42, P = 0.19). Training does not increase relative Hb_mass in adolescents consistent with a strong hereditary role for Hb_mass and VO_2max. Hb_mass may be used to identify adolescents who have a high VO_2max.     

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.     

Non-invasive haemodynamic assessments using Innocor™ during standard graded exercise tests

Cardiac output (Q) and stroke volume (V _S) represent primary determinants of cardiovascular performance and should therefore be determined for performance diagnostics purposes. Since it is unknown, whether measurements of Q and V _S can be performed by means of Innocor™ during standard graded exercise tests (GXTs), and whether current GXT stages are sufficiently long for the measurements to take place, we determined Q and V _S at an early and late point in time on submaximal 2 min GXT stages. 16 male cyclists (age 25.4 ± 2.9 years, body mass 71.2 ± 5.0 kg) performed three GXTs and we determined Q and V _S after 46 and 103 s at 69, 77, and 85% peak power. We found that the rebreathings could easily be incorporated into the GXTs and that Q and V _S remained unchanged between the two points in time on the same GXT stage (69% peak power, Q: 18.1 ± 2.1 vs. 18.2 ± 2.3 l min⁻¹, V _S: 126 ± 18 vs. 123 ± 21 ml; 77% peak power, Q: 20.7 ± 2.6 vs. 21.0 ± 2.3 l min⁻¹, V _S: 132 ± 18 vs. 131 ± 18 ml; 85% peak power, Q: 21.6 ± 2.4 vs. 21.8 ± 2.7 l min⁻¹, V _S: 131 ± 17 vs. 131 ± 22 ml). We conclude that Innocor™ may be a useful device for assessing Q and V _S during GXTs, and that the adaptation of Q and V _S to exercise-to-exercise transitions at moderate to high submaximal power outputs is fast enough for 1 and 2 min GXT stage durations.     

The effects of short recovery duration on <Emphasis Type="Italic">V</Emphasis>O<Subscript>2</Subscript> and muscle deoxygenation during intermittent exercise

This study compared the oxygen uptake (VO₂) and muscle deoxygenation (∆HHb) of two intermittent protocols to responses during continuous constant load cycle exercise in males (24 year ± 2, n = 7). Subjects performed three protocols: (1) 10 s work/5 s active recovery (R), R at 20 W (INT1): (2) 10 s work/5 s R, R at moderate intensity (INT2); and (3) continuous exercise (CONT), all for 10 min, on separate days. The work rate of CONT and the 10 s work of INT1 and INT2 were set within the heavy intensity domain. VO₂ and ∆HHb data were filtered and averaged to 5 s bins. Average VO₂ (80–420 s) was highest during CONT (3.77 L/min), lower in INT2 (3.04 L/min), and lowest during INT1 (2.81 L/min), all (p < 0.05). Average ∆HHb (80–420 s) was higher during CONT (p < 0.05) than both INT exercise protocols (CONT; 25.7 ± 0.9 a.u. INT1; 16.4 ± 0.8 a.u., and INT2; 15.8 ± 0.8 a.u.). The repeated changes in metabolic rate elicited oscillations in ΔHHb in both intermittent protocols, whereas oscillations in VO₂ were only observed during INT1. The greater ΔHHb during CONT suggests a reduction in oxygen delivery compared to oxygen consumption relative to INT. The higher VO₂ for INT 2 versus INT 1 and similar ΔHHb during INT suggests an increase in oxygen delivery during INT 2. Thus the different demands of INT1, INT2, and CONT protocols elicited differing physiological responses to a similar heavy intensity power output. These intermittent exercise models seem to elicit an elevated O₂ delivery condition compared to CONT.     

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.     

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.     

Lung-to-lung circulation times during exercise in heart failure

Circulation time (the transit time for a bolus of blood through the circulatory system) is a potential index of cardiac dysfunction in chronic heart failure (HF). In healthy subjects, circulation time falls as cardiac output (Q) rises during exercise, however little is known about this index in HF. In this study we examined the relationship between lung-to-lung circulation time (LLCT) during exercise in ten HF (53 ± 14 year, resting ejection fraction = 23 ± 8%) and control subjects (51 ± 18 year). We hypothesized that HF patients would have slower LLCT times during exercise when compared to control subjects. Each subject completed two identical incremental exercise tests during which LLCT was measured in one test and Q measured in the other. Q was measured using the open circuit C₂H₂ washin technique and circulation time measured using an inert gas technique. In HF patients and control subjects, LLCT decreased and Q increased from rest (HF:LLCT = 53.6 ± 8.2 s, Q = 4.3 ± 1.1 l min⁻¹; control: LLCT = 55.3 ± 10.9 s, Q = 4.5 ± 0.5 l min⁻¹) to peak exercise (HF:LLCT = 20.6 ± 3.9* s, Q = 8.8 ± 2.5* l min⁻¹; control:LLCT = 14.9 ± 2.4 s, Q = 16.5 ± 1.2 l min⁻¹; *P < 0.05 vs control). LLCT was significantly (P < 0.05) slower for the HF group when compared to the control group during submaximal exercise and at peak exercise. However, at a fixed Q the HF subjects had a faster LLCT. We hypothesize that the faster LLCT at a fixed Q for HF patients, may be the result of a more intensive peripheral vasoconstriction of non-active beds and a better redistribution of blood flow.     

Evidence of break-points in breathing pattern at the gas-exchange thresholds during incremental cycling in young, healthy subjects

The present study investigated whether ‘break-points’ in breathing pattern correspond to the first ( G_\textEX1 G_{{{\text{EX}}_{1} }} ) and second gas-exchange thresholds ( G_{\textEX 2} G_{{{\text{EX}}_{ 2} }} ) during incremental cycling. We used polynomial spline smoothing to detect accelerations and decelerations in pulmonary gas-exchange data, which provided an objective means of ‘break-point’ detection without assumption of the number and shape of said ‘break-points’. Twenty-eight recreational cyclists completed the study, with five individuals excluded from analyses due to low signal-to-noise ratios and/or high risk of ‘pseudo-threshold’ detection. In the remaining participants (n = 23), two separate and distinct accelerations in respiratory frequency (f _R) during incremental work were observed, both of which demonstrated trivial biases and reasonably small ±95% limits of agreement (LOA) for the G_\textEX1 G_{{{\text{EX}}_{1} }} (0.2 ± 3.0 ml O₂ kg⁻¹ min⁻¹) and G_{\textEX 2} G_{{{\text{EX}}_{ 2} }} (0.0 ± 2.4 ml O₂ kg⁻¹ min⁻¹), respectively. A plateau in tidal volume (V _T) data near the G_\textEX1 G_{{{\text{EX}}_{1} }} was identified in only 14 individuals, and yielded the most unsatisfactory mean bias ±LOA of all comparisons made (−0.4 ± 5.3 ml O₂ kg⁻¹ min⁻¹). Conversely, 18 individuals displayed V _T-plateau in close proximity to the G_{\textEX 2} G_{{{\text{EX}}_{ 2} }} evidenced by a mean bias ± LOA of 0.1 ± 3.1 ml O₂ kg⁻¹ min⁻¹. Our findings suggest that both accelerations in f _R correspond to the gas-exchange thresholds, and a plateau (or decline) in V _T at the G_{\textEX 2} G_{{{\text{EX}}_{ 2} }} is a common (but not universal) feature of the breathing pattern response to incremental cycling.     

Induction and decay of short-term heat acclimation

The purpose of this work was to investigate adaptation and decay from short-term (5-day) heat acclimation (STHA). Ten moderately trained males (mean ± SD age 28 ± 7 years; body mass 74.6 ± 4.4 kg; [(V)\dot]_{\textO 2\textpeak} \dot{V}_{{{\text{O}}_{ 2{\text{peak}}} }} 4.26 ± 0.37 l min⁻¹) underwent heat acclimation (Acc) for 90-min on 5-days consecutively (T _a = 39.5°C, 60% RH), under controlled hyperthermia (rectal temperature 38.5°C). Participants completed a heat stress test (HST) 1 week before acclimation (Acc), then on the 2nd and 8th day (1 week) following Acc (T _a = 35°C, 60% RH). Seven participants completed HSTs 2 and 3 weeks after Acc. HST consisted of 90-min cycling at 40% peak power output before an incremental performance test. Rectal temperature at rest (37.1 ± 0.4°C) was not lowered by Acc (95% CI −0.3 to 0.2°C), after 90-min exercise (38.6 ± 0.5°C) it reduced 0.3°C (−0.5 to −0.1°C) and remained at this level 1 week later (−0.5 to −0.1°C), but not two (0.1°C −0.4 to 0.5°C; n = 7) or 3 weeks. Similarly, heart rate after 90-min exercise (146 ± 21 b min⁻¹) was reduced (−13: −6 to −20 b min⁻¹) and remained at this level after 1 week (−13: −6 to −20 b min⁻¹) but not two (−9: 6 to −23 b min⁻¹; n = 7) or 3 weeks. Performance (746 s) increased 106 s: 59 to 152 s after Acc and remained higher after one (76 s: 31 to 122) but not two (15 s: −88 to 142 s; n = 7) or 3 weeks. Therefore, STHA (5-day) induced adaptations permitting increased heat loss and this persisted 1 week but not 2 weeks following Acc.     

The effects of 6-week-decoupled bi-pedal cycling on submaximal and high intensity performance in competitive cyclists and triathletes

Aim of this work was to examine the effects of decoupled two-legged cycling on (1) submaximal and maximal oxygen uptake, (2) power output at 4 mmol L⁻¹ blood lactate concentration, (3) mean and peak power output during high intensity cycling (30 s sprint) and (4) isometric and dynamic force production of the knee extensor and flexor muscles. 18 highly trained male competitive male cyclists and triathletes (age 24 ± 3 years; body height 179 ± 11 cm; body mass 78 ± 8 kg; peak oxygen uptake 5,070 ± 680 mL min⁻¹) were equally randomized to exercise on a stationary cycle equipped either with decoupled or with traditional crank system. The intervention involved 1 h training sessions, 5 times per week for 6 weeks at a heart rate corresponding to 70% of VO_2peak. VO₂ at 100, 140, 180, 220 and 260 and power output at 4 mmol L⁻¹ blood lactate were determined during an incremental test. VO_2peak was recorded during a ramp protocol. Mean and peak power output were assessed during a 30 s cycle sprint. The maximal voluntary isometric strength of the quadriceps and biceps femoris muscles was obtained using a training machine equipped with a force sensor. No differences were observed between the groups for changes in any variable (P = 0.15–0.90; effect size = 0.00–0.30). Our results demonstrate that a 6 week (30 sessions) training block using decoupled crank systems does not result in changes in any physiological or performance variables in highly trained competitive cyclists.     

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.