Influence of recovery manipulation after hyperlactemia induction on the lactate minimum intensity

This study analyzed the influence of recovery phase manipulation after hyperlactemia induction on the lactate minimum intensity during treadmill running. Twelve male runners (24.6 ± 6.3 years; 172 ± 8.0 cm and 62.6 ± 6.1 kg) performed three lactate minimum tests involving passive (LMT_P) and active recoveries at 30%vVO_2max (LMT_A30) and 50%vVO_2max (LMT_A50) in the 8-min period following initial sprints. During subsequent graded exercise, lactate minimum speed and VO₂ in LMT_A50 (12.8 ± 1.5 km h⁻¹ and 40.3 ± 5.1 ml kg⁻¹ min⁻¹) were significantly lower (P < 0.05) than those in LMT_A30 (13.3 ± 1.6 km h⁻¹ and 42.9 ± 5.3 ml kg⁻¹ min⁻¹) and LMT_P (13.8 ± 1.6 km h⁻¹ and 43.6 ± 6.1 ml kg⁻¹ min⁻¹). In addition, lactate minimum speed in LMT_A30 was significantly lower (P < 0.05) than that in LMT_P. These results suggest that lactate minimum intensity is lowered by active recovery after hyperlactemia induction in an intensity-dependent manner compared to passive recovery.     

Carbohydrate intake reduces fat oxidation during exercise in obese boys

The recent surge in childhood obesity has renewed interest in studying exercise as a therapeutic means of metabolizing fat. However, carbohydrate (CHO) intake attenuates whole body fat oxidation during exercise in healthy children and may suppress fat metabolism in obese youth. To determine the impact of CHO intake on substrate utilization during submaximal exercise in obese boys, seven obese boys (mean age: 11.4 ± 1.0 year; % body fat: 35.8 ± 3.9%) performed 60 min of exercise at an intensity that approximated maximal fat oxidation. A CHO drink (CARB) or a placebo drink (CONT) was consumed in a double-blinded, counterbalanced manner. Rates of total fat, total CHO, and exogenous CHO (CHO_exo) oxidation were calculated for the last 20 min of exercise. During CONT, fat oxidation rate was 3.9 ± 2.4 mg × kg fat-free mass (FFM)⁻¹ × min⁻¹, representing 43.1 ± 22.9% of total energy expenditure (EE). During CARB, fat oxidation was lowered (p = 0.02) to 1.7 ± 0.6 mg × kg FFM⁻¹ × min⁻¹, contributing to 19.8 ± 4.9% EE. Total CHO oxidation rate was 17.2 ± 3.1 mg × kg FFM⁻¹ × min⁻¹ and 13.2 ± 6.1 mg × kg FFM⁻¹ × min⁻¹ during CARB and CONT, respectively (p = 0.06). In CARB, CHO_exo oxidation contributed to 23.3 ± 4.2% of total EE. CHO intake markedly suppresses fat oxidation during exercise in obese boys.     

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.     

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.     

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

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

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.     

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.     

Muscle sympathetic nerve activity at rest compared to exercise tolerance

Cardiovascular autonomic function is associated with physical performance and exercise training adaptation. The association between physical performance and sympathetic regulation is not well known. We hypothesized that sympathetic nervous system activity is associated with physical performance among male runners. The study population included 26 healthy male club runners [age 33 ± 5 years, body mass index (BMI) 24 ± 1 kg/m², VO_2max 58 ± 5 ml kg⁻¹ min⁻¹; mean ± SD]. Muscle sympathetic nerve activity (MSNA) was assessed from the peroneal nerve by the microneurography technique during 5 min of supine rest. Physical performance was assessed by time to exhaustion during treadmill running. The mean resting MSNA was 20 ± 6 bursts min⁻¹ (range 6–34). The mean time to exhaustion was 1,005 ± 136 s (range 720–1260). When the study group was divided into tertiles according to their running performance (866 ± 69, 994 ± 30 and 1154 ± 71 s in time to exhaustion, P < 0.0001 between the groups), MSNA was lower (P = 0.032) in the group with the best running performance (16 ± 5 bursts min⁻¹) compared to those with the worst running performance (23 ± 7 bursts min⁻¹). In conclusion, baseline sympathetic activity, measured by a microneurography at rest, may be associated with the maximal running performance of healthy subjects.     

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.     

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.     

Comparison of two waist-mounted and two ankle-mounted electronic pedometers

This study compared two ankle-mounted pedometers [StepWatch 3 (SW-3_Ankle) and Activity Monitoring Pod 331 (AMP_Ankle)] and two waist-mounted pedometers [New Lifestyles NL-2000 (NL_Waist) and Digiwalker SW-701 (SW-701_Waist)] under controlled and free-living conditions. In part I, 20 participants walked on a treadmill at speeds of 27–107 m min⁻¹. Actual steps were counted with a hand counter. In part II, participants performed leg swinging, heel tapping, stationary cycling, and car driving. In part III, 15 participants wore all pedometers for a 24 h period. The SW-3_Ankle displayed values that were within 1% of actual steps during treadmill walking at all speeds. The other devices underestimated steps at slow speeds but all gave mean values that were within ±3% of actual steps at 80 m min⁻¹ and above. The SW-3_Ankle registered some steps during heel tapping, leg swinging, and cycling, while the AMP_Ankle was only responsive to leg swinging. During car driving no devices recorded more than eight steps, on average. Over 24 h, the AMP_Ankle recorded 18% fewer steps than the SW-3_Ankle (P<0.05), while the SW-701_Waist and the NL_Waist recorded 15 and 11% less than the SW-3_Ankle, respectively (NSD). The SW-3_Ankle has superior accuracy at slow treadmill walking speeds (although it was also more likely to detect “fidgeting” activities). Over 24 h, the SW-3_Ankle tended to give higher estimates of steps per day than the other ankle- and waist-mounted pedometers.     

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.     

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.     

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.     

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.     

Thermoregulation, pacing and fluid balance during mass participation distance running in a warm and humid environment

Deep body temperature (T _c), pacing strategy and fluid balance were investigated during a 21-km road race in a warm and humid environment. Thirty-one males (age 25.3 ± 3.2 years; maximal oxygen uptake 59.1 ± 4.2 ml kg⁻¹ min⁻¹) volunteered for this study. Continuous T _c responses were obtained in 25 runners. Research stations at approximately 3-km intervals permitted accurate assessment of split times and fluid intake. Environmental conditions averaged 26.4°C dry bulb temperature and 81% relative humidity. Peak T _c was 39.8 ± 0.5 (38.5–40.7) °C with 24 runners achieving T _c > 39.0°C, 17 runners ≥39.5°C, and 10 runners ≥40.0°C. In 12 runners attaining peak T _c ≥ 39.8°C, running speed did not differ significantly when T _c was below or above this threshold (208 ± 15 cf. 205 ± 24 m min⁻¹; P = 0.532). Running velocity was the main significant predictor variable of ∆T _c at 21 km (R ² = 0.42, P < 0.001) and was the main discriminating variable between hyperthermic (T _c ≥ 39.8°C) and normothermic runners (T _c < 39.8°C) up to 11.8 km. A reverse J-shaped pacing profile characterised by a marked reduction in running speed after 6.9 km and evidence of an end-spurt in 16 runners was observed. Variables relating to fluid balance were not associated with any T _c parameters or pacing. We conclude that hyperthermia, defined by a deep body temperature greater than 39.5°C, is common in trained individuals undertaking outdoor distance running in environmental heat, without evidence of fatigue or heat illness.     

Light-intensity activities are important for estimating physical activity energy expenditure using uniaxial and triaxial accelerometers

This study evaluated the validity of the total energy expenditure (TEE) estimated using uniaxial (ACCuni) and triaxial (ACCtri) accelerometers in the elderly. Thirty-two healthy elderly (64–87 years) participated in this study. TEE was measured using the doubly labeled water (DLW) method (TEE_DLW). TEE_ACCuni (6.79 ± 1.08 MJ day⁻¹) was significantly lower than TEE_DLW (7.85 ± 1.54 MJ day⁻¹) and showed wider limits of agreement (−3.15 to 1.12 MJ day⁻¹) with a smaller correlation coefficient (r = 0.703). TEE_ACCtri (7.88 ± 1.27 MJ day⁻¹) did not differ from TEE_DLW and showed narrower limits of agreement (−1.64 to 1.72 MJ day⁻¹) with a larger correlation coefficient (r = 0.835, P < 0.001). The estimated intensities of light activities were significantly lower with ACCuni. Greater mediolateral acceleration was observed during 6-min walk tests. The results suggest that ACCtri is a better choice than ACCuni for assessing TEE in the elderly.     

Effects of low and high cadence interval training on power output in flat and uphill cycling time-trials

This study tested the effects of low-cadence (60 rev min⁻¹) uphill (Int₆₀) or high-cadence (100 rev min⁻¹) level-ground (Int₁₀₀) interval training on power output (PO) during 20-min uphill (TT_up) and flat (TT_flat) time-trials. Eighteen male cyclists ( [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } : 58.6 ± 5.4 mL min⁻¹ kg⁻¹) were randomly assigned to Int₆₀, Int₁₀₀ or a control group (Con). The interval training comprised two training sessions per week over 4 weeks, which consisted of six bouts of 5 min at the PO corresponding to the respiratory compensation point (RCP). For the control group, no interval training was conducted. A two-factor ANOVA revealed significant increases on performance measures obtained from a laboratory-graded exercise test (GXT) (P _max: 2.8 ± 3.0%; p < 0.01; PO and [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} at RCP: 3.6 ± 6.3% and 4.7 ± 8.2%, respectively; p < 0.05; and [(V)\dot]\textO₂ \dot{V}{\text{O}}_{2} at ventilatory threshold: 4.9 ± 5.6%; p < 0.01), with no significant group effects. Significant interactions between group and uphill and flat time-trial, pre- versus post-training on PO were observed (p < 0.05). Int₆₀ increased PO during both TT_up (4.4 ± 5.3%) and TT_flat (1.5 ± 4.5%). The changes were −1.3 ± 3.6, 2.6 ± 6.0% for Int₁₀₀ and 4.0 ± 4.6%, −3.5 ± 5.4% for Con during TT_up and TT_flat, respectively. PO was significantly higher during TT_up than TT_flat (4.4 ± 6.0; 6.3 ± 5.6%; pre and post-training, respectively; p < 0.001). These findings suggest that higher forces during the low-cadence intervals are potentially beneficial to improve performance. In contrast to the GXT, the time-trials are ecologically valid to detect specific performance adaptations.     

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.