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.     

Maximal voluntary hyperpnoea increases blood lactate concentration during exercise

Ventilatory work during heavy endurance exercise has not been thought to influence systemic lactate concentration. We evaluated the effect of maximal isocapnic volitional hyperpnoea upon arterialised venous blood lactate concentration ([lac⁻]_B) during leg cycling exercise at maximum lactate steady state (MLSS). Seven healthy males performed a lactate minimum test to estimate MLSS, which was then resolved using separate 30 min constant power tests (MLSS=207±8 W, mean ± SEM). Thereafter, a 30 min control trial at MLSS was performed. In a further experimental trial, the control trial was mimicked except that from 20 to 28 min maximal isocapnic volitional hyperpnoea was superimposed on exercise. Over 20–28 min minute ventilation, oxygen uptake, and heart rate during the control and experimental trials were 87.3±2.4 and 168.3±7.0 l min⁻¹ (P<0.01), the latter being comparable to that achieved in the maximal phase of the lactate minimum test (171.9±6.8 l min⁻¹), 3.46±0.20 and 3.83 ± 0.20 l min⁻¹ (P<0.01), and 158.5±2.7 and 166.8±2.7 beats min⁻¹ (P<0.05), respectively. From 20 to 30 min of the experimental trial [lac⁻]_B increased from 3.7±0.2 to 4.7±0.3 mmol l⁻¹ (P<0.05). The partial pressure of carbon dioxide in arterialised venous blood increased approximately 3 mmHg during volitional hyperpnoea, which may have attenuated the [lac⁻]_B increase. These results show that, during heavy exercise, respiratory muscle work may affect [lac⁻]_B. We speculate that the changes observed were related to the altered lactate turnover in respiratory muscles, locomotor muscles, or both.     

Effect of performance level on pacing strategy during a 10-km running race

The aim of this study was to examine the influence of the performance level of athletes on pacing strategy during a simulated 10-km running race, and the relationship between physiological variables and pacing strategy. Twenty-four male runners performed an incremental exercise test on a treadmill, three 6-min bouts of running at 9, 12 and 15 km h⁻¹, and a self-paced, 10-km running performance trial; at least 48 h separated each test. Based on 10-km running performance, subjects were divided into terziles, with the lower terzile designated the low-performing (LP) and the upper terzile designated the high-performing (HP) group. For the HP group, the velocity peaked at 18.8 ± 1.4 km h⁻¹ in the first 400 m and was higher than the average race velocity (P < 0.05). The velocity then decreased gradually until 2,000 m (P < 0.05), remaining constant until 9,600 m, when it increased again (P < 0.05). The LP group ran the first 400 m at a significantly lower velocity than the HP group (15.6 ± 1.6 km h⁻¹; P > 0.05) and this initial velocity was not different from LP average racing velocity (14.5 ± 0.7 km h⁻¹). The velocity then decreased non-significantly until 9,600 m (P > 0.05), followed by an increase at the end (P < 0.05). The peak treadmill running velocity (PV), running economy (RE), lactate threshold (LT) and net blood lactate accumulation at 15 km h⁻¹ were significantly correlated with the start, middle, last and average velocities during the 10-km race. These results demonstrate that high and low performance runners adopt different pacing strategies during a 10-km race. Furthermore, it appears that important determinants of the chosen pacing strategy include PV, LT and RE.     

Carbohydrate ingestion and pre-cooling improves exercise capacity following soccer-specific intermittent exercise performed in the heat

Ingestion of carbohydrate and reducing core body temperature pre-exercise, either separately or combined, may have ergogenic effects during prolonged intermittent exercise in hot conditions. The aim of this investigation was to examine the effect of carbohydrate ingestion and pre-cooling on the physiological responses to soccer-specific intermittent exercise and the impact on subsequent high-intensity exercise performance in the heat. Twelve male soccer players performed a soccer-specific intermittent protocol for 90 min in the heat (30.5°C and 42.2% r.h.) on four occasions. On two occasions, the participants underwent a pre-cooling manoeuvre. During these sessions either a carbohydrate–electrolyte solution (CHOc) or a placebo was consumed at (PLAc). During the remaining sessions either the carbohydrate–electrolyte solution (CHO) or placebo (PLA) was consumed. At 15-min intervals throughout the protocol participants performed a mental concentration test. Following the soccer-specific protocol participants performed a self-chosen pace test and a test of high-intensity exercise capacity. The period of pre-cooling significantly reduced core temperature, muscle temperature and thermal sensation (P < 0.05). Self-chosen pace was greater with CHOc (12.5 ± 0.5 km h⁻¹) compared with CHO (11.3 ± 0.4 km h⁻¹), PLA (11.3 ± 0.4 km h⁻¹) and PLAc (11.6 ± 0.5 km h⁻¹) (P < 0.05). High-intensity exercise capacity was improved with CHOc and CHO when compared with PLA (CHOc; 79.8 ± 7 s, CHO; 72.1 ± 5 s, PLAc; 70.1 ± 8 s, PLA; 57.1 ± 5 s; P < 0.05). Mental concentration during the protocol was also enhanced during CHOc compared with PLA (P < 0.05). These results suggest pre-cooling in conjunction with the ingestion of carbohydrate during exercise enhances exercise capacity and helps maintain mental performance during intermittent exercise in hot conditions.     

Near infrared spectroscopy-derived interstitial hydrogen ion concentration and tissue oxygen saturation during ambulation

The objective of this study was to determine whether walking and running at different treadmill speeds resulted in different metabolic and cardiovascular responses in the vastus lateralis (VL) and lateral gastrocnemius (LG) by examining metabolite accumulation and tissue oxygen saturation. Ten healthy subjects (6 males, 4 females) completed a submaximal treadmill exercise test, beginning at 3.2 km h⁻¹ and increasing by 1.6 km h⁻¹ increments every 3 min until reaching 85% of age-predicted maximal heart rate. Muscle tissue oxygenation (SO₂), total hemoglobin (HbT) and interstitial hydrogen ion concentration ([H⁺]) were calculated from near infrared spectra collected from VL and LG. The [H⁺] threshold for each muscle was determined using a simultaneous bilinear regression. Muscle and treadmill speed effects were analyzed using a linear mixed model analysis. Paired t-tests were used to test for differences between muscles in the [H⁺] threshold. SO₂ decreased (P = 0.001) during running in the VL and LG, but the SO₂ response across treadmill speeds was different between muscles (P = 0.047). In both muscles, HbT and [H⁺] increased as treadmill speed increased (P < 0.001), but the response to exercise was not different between muscles. The [H⁺] threshold occurred at a lower whole-body VO₂ in the LG (1.22 ± 0.63 L min⁻¹) than in the VL (1.46 ± 0.58 L min⁻¹, P = 0.01). In conclusion, interstitial [H⁺] and SO₂ are aggregate measures of local metabolite production and the cardiovascular response. Inferred from simultaneous SO₂ and [H⁺] measures in the VL and LG muscles, muscle perfusion is well matched to VL and LG work during walking, but not running.     

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.     

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.     

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.     

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

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

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.     

Computationally Managed Bradycardia Improved Cardiac Energetics While Restoring Normal Hemodynamics in Heart Failure

In acute heart failure, systemic arterial pressure (AP), cardiac output (CO), and left atrial pressure (P _LA) have to be controlled within acceptable ranges. Under this condition, cardiac energetic efficiency should also be improved. Theoretically, if heart rate (HR) is reduced while AP, CO, and P _LA are maintained by preserving the functional slope of left ventricular (LV) Starling’s curve (S _L) with precisely increased LV end-systolic elastance (E _es), it is possible to improve cardiac energetic efficiency and reduce LV oxygen consumption per minute (MVO ₂). We investigated whether this hemodynamics can be accomplished in acute heart failure using an automated hemodynamic regulator that we developed previously. In seven anesthetized dogs with acute heart failure (CO < 70 mL min⁻¹ kg⁻¹, P _LA > 15 mmHg), the regulator simultaneously controlled S _L with dobutamine, systemic vascular resistance with nitroprusside and stressed blood volume with dextran or furosemide, thereby controlling AP, CO, and P _LA. Normal hemodynamics were restored and maintained (CO; 88 ± 3 mL min⁻¹ kg⁻¹, P _LA; 10.9 ± 0.4 mmHg), even when zatebradine significantly reduced HR (−27 ± 3%). Following HR reduction, E _es increased (+34 ± 14%), LV mechanical efficiency (stroke work/oxygen consumption) increased (+22 ± 6%), and MVO ₂ decreased (−17 ± 4%) significantly. In conclusion, in a canine acute heart failure model, computationally managed bradycardia improved cardiac energetic efficiency while restoring normal hemodynamic conditions.     

The effect of 48?weeks of aerobic exercise training on cutaneous vasodilator function in post-menopausal females

Skin blood flow (SkBF) and endothelial-dependent vasodilatation decline with ageing and can be reversed with exercise training. We tested whether 48 weeks of training could improve SkBF and endothelial function in post-menopausal females; 20 post-menopausal subjects completed the study. SkBF was measured by laser-Doppler flowmetry (LDF). Cutaneous vascular conductance (CVC) was calculated as LDF/blood pressure. Resting CVC was measured at 32°C and peak CVC at 42°C. Cutaneous endothelial-dependent and -independent vasodilatations were determined by the iontophoresis of acetylcholine (ACh) and sodium nitroprusside (SNP), respectively. All assessments described were performed at entry (week 0), and after 6, 12, 24, 36, and 48 weeks of training. Resting CVC measures did not change (P > 0.05) throughout the study. Peak CVC increased (P < 0.05) after 24 weeks (7.2 ± 1.2 vs. 11.6 ± 1.4 AU mmHg⁻¹) and at the 36- and 48-week assessments (13.0 ± 1.7 and 14.9 ± 2.1 AU mmHg⁻¹, respectively). Responses to ACh also increased (P < 0.05) at the 24-week assessment (5.1 ± 2.1 vs. 8.55 ± 2.3 AU mmHg⁻¹) and increased further at the 36 and 48-week assessments (11.6 ± 3.7 and 13.2 ± 3.9 AU mmHg⁻¹, respectively). Cutaneous responses to SNP increased (P < 0.05) after 36 weeks (8.7 ± 2.1 vs. 13.02 ± 2.23 AU mmHg⁻¹ at 36 weeks). VO_2max increased after 12 weeks (23.5 ± 0.7 vs. 25.4 ± 0.9 ml kg⁻¹ min⁻¹) and improved (P < 0.05) further throughout the study (31.6 ± 1.8 ml kg⁻¹ min⁻¹ at week 48). Aerobic exercise produces positive adaptations in the cutaneous vasodilator function to local heating as well as in cutaneous endothelial and endothelial-independent vasodilator mechanisms. Aerobic capacity was also significantly improved. These adaptations were further enhanced with progressive increases in exercise intensity.     

The validity of two Omron pedometers during treadmill walking is speed dependent

The purpose of this study was to examine the effects of walking speed on the accuracy of measurement of steps, distance, and energy expenditure of two commercially available Omron pedometers [HJ-720IT-E2 (HJ-720) and HJ-113-E (HJ-113)]. Twenty-four untrained males (age, 22.7 ± 2.8 years; BMI, 24.38 ± 2.19 kg m⁻²; body fat (%), 16 ± 2.2; VO_2max, 40.2 ± 6.5 ml kg⁻¹ min⁻¹) and 18 females (age, 22.4 ± 2.9 years; BMI, 21.68 ± 2.43 kg m⁻²; body fat (%), 23% ± 1.8; VO_2max, 35.9 ± 2.8 ml kg⁻¹ min⁻¹) walked at five different velocities (54, 67, 80, 94 and 107 m min⁻¹) on a treadmill in 5-min stages while wearing three types of pedometers: (a) HJ-720, (b) HJ-113, and (c) Yamax Digi-Walker SW-200 (YAM). Step-count for each pedometer was recorded at the end of each stage and compared with the value of a hand counter. Additionally, Omron pedometers were evaluated on their distance and energy expenditure (against VO₂ measurement with a gas-exchange analyzer) accuracy during each stage. HJ-720 and HJ-113 demonstrated high accuracy (r = 0.80–0.99) at all speeds. YAM underestimated step-count only at 54 m min⁻¹ (r = 0.46). HJ-720 and HJ-113 overestimated distance at slower speeds and underestimated distance at faster speeds, providing mean distance values that where to within 1.5–4% at 80 m min⁻¹. HJ-720 and HJ-113 underestimated energy expenditure (gross kilocalories) by 28%, when compared to indirect calorimetry. These results suggest that although the Omron HJ-720 and HJ-113 pedometers are accurate in the measurement of step-count, they demonstrate limited accuracy in the assessment of traveled distance and energy expenditure in a speed-dependent manner.     

Complete correction of anemia by erythropoiesis-stimulating agents is associated with insulin resistance in hemodialysis patients

Insulin resistance and anemia secondary to erythropoietin deficiency characterize patients with end-stage kidney disease. In a cross-sectional analysis, we examined the relationship between erythropoietin-mediated correction of anemia and insulin sensitivity in nondiabetic hemodialysis patients. Insulin sensitivity (euglycemic-hyperinsulinemic clamp) and endogenous glucose production (primed-continuous infusion of [6,6-²H₂]glucose) were determined in two groups of patients with normal hemoglobin (n:8; mean hemoglobin: 14.0 ± 0.3 g/dl) or with mild anemia (n:10; mean hemoglobin: 12.1 ± 0.9 g/dl). The patients with normal hemoglobin were receiving higher (P < 0.05) erythropoietin doses than those with mild anemia (171 ± 73 and 91 ± 39 U kg⁻¹ wk⁻¹, respectively). The two groups were matched for all other potential determinants of insulin resistance. Endogenous glucose production was similar in the two groups of patients in the postabsorptive state and was completely suppressed by insulin infusion. During the hyperinsulinemic clamp, the rate of glucose infusion to maintain euglycemia was significantly lower (P < 0.01) in the patients with normal hemoglobin levels [166 ± 31 mg (m²)⁻¹ min⁻¹] than in those with mild anemia [251 ± 49 mg (m²)⁻¹ min⁻¹] and in a group of matched controls [275 ± 68 mg (m²)⁻¹ min⁻¹]. In pooled patients, individual values of hemoglobin concentrations inversely correlated with the rates of insulin-mediated glucose infusion, both as absolute values (r = −0.58; P < 0.05) and as values normalized by steady-state plasma insulin concentration (r = −0.74; P < 0.001). In conclusion, this exploratory study indicates that complete correction of anemia by erythropoietin treatment in patients with end-stage kidney disease on hemodialysis is associated with impaired insulin sensitivity.     

Maximal lactate steady state concentration independent of pedal cadence in active individuals

The maximal lactate steady state (MLSS) is defined as the highest blood lactate concentration that can be maintained over time without a continual blood lactate accumulation. The objective of the present study was to analyze the effects of pedal cadence (50 vs. 100 rev min⁻¹) on MLSS and the exercise workload at MLSS (MLSS_workload) during cycling. Nine recreationally active males (20.9±2.9 years, 73.9±6.5 kg, 1.79±0.09 m) performed an incremental maximal load test (50 and 100 rev min⁻¹) to determine anaerobic threshold (AT) and peak workload (PW), and between two and four constant submaximal load tests (50 and 100 rev min⁻¹) on a mechanically braked cycle ergometer to determine MLSS_workload and MLSS. MLSS_workload was defined as the highest workload at which blood lactate concentration did not increase by more than 1 mM between minutes 10 and 30 of the constant workload. The maximal lactate steady state intensity (MLSS_intensity) was defined as the ratio between MLSS_workload and PW. MLSS_workload (186.1±21.2 W vs. 148.2±15.5 W) and MLSS_intensity (70.5±5.7% vs. 61.4±5.1%) were significantly higher during cycling at 50 rev min⁻¹ than at 100 rev min⁻¹, respectively. However, there was no significant difference in MLSS between 50 rev min⁻¹ (4.8±1.6 mM) and 100 rev min⁻¹ (4.7±0.8 mM). We conclude that MLSS_workload and MLSS_intensity are dependent on pedal cadence (50 vs. 100 rev min⁻¹) in recreationally active individuals. However, this study showed that MLSS is not influenced by the different pedal cadences analyzed.     

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.     

In a hot–dry environment racewalking increases the risk of hyperthermia in comparison to when running at a similar velocity

The purpose of this study was to determine if in a hot–dry environment, racewalking increases intestinal temperature (T_int) above the levels observed when running either at the same velocity or at a similar rate of heat production. Nine trained racewalkers exercised for 60 min in a hot–dry environment (30.0 ± 1.4°C; 33 ± 8% relative humidity; 2.4 m s⁻¹ air speed) on three separate occasions: (1) racewalking at 10.9 ± 1.0 km h⁻¹ (Walk), (2) running at the same velocity (RunVel) and (3) running at 13 ± 1.8 km h⁻¹ to obtain a similar [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} than during Walk (Run [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} ). As designed, energy expenditure rate was similar during Walk and Run [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} , but lower during RunVel (842 ± 78 and 827 ± 75 vs. 713 ± 55 W; p < 0.01). Final T_int was lower during RunVel than during both Walk and Run [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} (38.4 ± 0.3 vs. 39.2 ± 0.4 and 39.0 ± 0.4°C; p < 0.01). Heart rate and sweat rate were also lower during RunVel than during Walk and Run [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} (i.e. heart rate 159 ± 13 vs. 179 ± 11 and 181 ± 11 beats min⁻¹ and sweat rate 0.8 ± 0.3 vs. 1.1 ± 0.3 and 1.1 ± 0.3 L h⁻¹; p < 0.01). However, we could not detect differences in skin temperature among trials. In conclusion, our data indicate that in a hot–dry environment racewalking increases the risk of hyperthermia in comparison with when running at a similar velocity. However, exercise mode (walking vs. running) had no measurable impact on T_INT or heat dissipation when matched for energy expenditure.     

Mechanically versus electro-magnetically braked cycle ergometer: performance and energy cost of the Wingate Anaerobic Test

Performance and metabolic profiles of the Wingate Anaerobic Test (WAnT) were compared between a mechanically resisted (ME) and an electro-magnetically braked (EE) cycle ergometer. Fifteen healthy subjects (24.0±3.5 years, 180.5±6.1 cm, 75.4±11.9 kg) performed a WAnT on ME, and EE 3 days apart. Performance was measured as peak power (PP), minimum power (MP), mean power (AP), time to PP (TTPP), fatigue rate (FR), and maximum cadence (RPM_MAX). Lactic (W _LAC) and alactic (W _PCR) anaerobic energy were calculated from net lactate appearance and the fast component of post-exercise oxygen uptake. Aerobic metabolism (W _AER) was calculated from oxygen uptake during the WAnT. Total energy cost (W _TOT) was calculated as the sum of W _LAC, W _PCR, and W _AER. There was no difference between ME and EE in PP (873±159 vs. 931±193 W) or AP (633±89 vs. 630±89 W). In the EE condition TTPP (2.3±0.7 vs. 4.3±0.7 s) was longer (P<0.001), MP (464±78 vs. 388±57 W) was lower (P<0.001), FR (15.2±5.2 vs. 20.5±6.8%) was higher (P<0.005), and RPM_MAX (168±18 vs. 128±15 rpm) was slower (P<0.001). There was no difference in W _TOT (1,331±182 vs. 1,373±120 J kg⁻¹), W _AER (292±76 vs. 309±72 J kg⁻¹), W _PCR (495±153 vs. 515±111 J kg⁻¹) or W _LAC (545±132 vs. 549±141 J kg⁻¹) between ME and EE devices. The EE produces distinctly different performance measures but valid metabolic WAnT results that may be used to evaluate anaerobic fitness.     

A low carbohydrate diet affects autonomic modulation during heavy but not moderate exercise

The aim of this study was to examine the effects of low carbohydrate (CHO) availability on heart rate variability (HRV) responses during moderate and severe exercise intensities until exhaustion. Six healthy males (age, 26.5 ± 6.7 years; body mass, 78.4 ± 7.7 kg; body fat %, 11.3 ± 4.5%; [(V)\dot] \textO_{2 max} , \dot{V} {\text{O}}_{{2{ \max }}} , 39.5 ± 6.6 mL kg⁻¹ min⁻¹) volunteered for this study. All tests were performed in the morning, after 8–12 h overnight fasting, at a moderate intensity corresponding to 50% of the difference between the first (LT₁) and second (LT₂) lactate breakpoints and at a severe intensity corresponding to 25% of the difference between the maximal power output and LT₂. Forty-eight hours before each experimental session, the subjects performed a 90-min cycling exercise followed by 5-min rest periods and subsequent 1-min cycling bouts at 125% [(V)\dot] \textO_{2 max} \dot{V} {\text{O}}_{{2{ \max }}} (with 1-min rest periods) until exhaustion, in order to deplete muscle glycogen. A diet providing 10% (CHO_low) or 65% (CHO_control) of energy as carbohydrates was consumed for the following 2 days until the experimental test. The Poicaré plots (standard deviations 1 and 2: SD1 and SD2, respectively) and spectral autoregressive model (low frequency LF, and high frequency HF) were applied to obtain HRV parameters. The CHO availability had no effect on the HRV parameters or ventilation during moderate-intensity exercise. However, the SD1 and SD2 parameters were significantly higher in CHO_low than in CHO_control, as taken at exhaustion during the severe-intensity exercise (P < 0.05). The HF and LF frequencies (ms²) were also significantly higher in CHO_low than in CHO_control (P < 0.05). In addition, ventilation measured at the 5 and 10-min was higher in CHO_low (62.5 ± 4.4 and 74.8 ± 6.5 L min⁻¹, respectively, P < 0.05) than in CHO_control (70.0 ± 3.6 and 79.6 ± 5.1 L min⁻¹, respectively; P < 0.05) during the severe-intensity exercise. These results suggest that the CHO availability alters the HRV parameters during severe-, but not moderate-, intensity exercise, and this was associated with an increase in ventilation volume.