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.     

Diurnal variation in the salivary melatonin responses to exercise: relation to exercise-mediated tachycardia

Salivary melatonin concentration is an established marker of human circadian rhythmicity. It is thought that melatonin is relatively robust to the masking effects of exercise. Nevertheless, the extent and even the direction of exercise-related change is unclear, possibly due to between-study differences in the time of day exercise is completed. Therefore, we aimed to compare melatonin responses between morning and afternoon exercise, and explore the relationships between exercise-related changes in melatonin and heart rate. At 08:00 and 17:00 hours, seven male subjects (mean ± SD age, 27 ± 5 years) completed 30 min of cycling at 70% peak oxygen uptake followed by 30 min of rest. Light intensity was maintained at ~150 lx. Salivary melatonin (ELISA) and heart rate were measured at baseline, 15 min during exercise, immediately post-exercise and following 30 min recovery. Melatonin was ≈15 pg ml⁻¹ higher in the morning trials compared with the afternoon (P = 0.030). The exercise-related increase in melatonin was more pronounced (P = 0.024) in the morning (11.1 ± 8.7 pg ml⁻¹) than in the afternoon (5.1 ± 5.7 pg ml⁻¹). The slope of the heart rate–melatonin relationship was significantly (P = 0.020) steeper in the morning (0.12 pg ml⁻¹ beats⁻¹ min⁻¹) than in the afternoon (0.03 pg ml⁻¹ beats⁻¹ min⁻¹). In conclusion, we report for the first time that the masking effect of moderate-intensity exercise on melatonin is approximately twice as high in the morning than the afternoon. The much steeper relationship between heart rate and melatonin changes in the morning raises the possibility that time of day alters the relationships between exercise-mediated sympathetic nervous activity and melatonin secretion.     

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.     

Fluid balance, thermal stress, and post exercise response in women's Islamic athletic clothing

This study examined heat stress, heart rate (HR), fluid balance, micro-environment temperature and humidity with Islamic athletic clothing (IC) compared to traditional soccer uniform (SC). Ratings of perceived exertion (RPE), session RPE (S-RPE), comfort, and cooling response were also examined. Female volunteers (N = 8) completed a treadmill [(V)\dot]\textO_2\textpeak \dot{V}{\text{O}}_{{2{\text{peak}}}} test and then, in a randomized, counter-balanced order, two intermittent running bouts (45 min total) in a hot environment (30.0°C WBGT) in IC and SC. Thereafter, participants sat for 40 min in the hot ambient environment. Repeated measures ANOVA revealed significantly greater micro-environment temperature (p = 0.02) (IC 33.3 ± 3.2°C, SC 32.0 ± 2.8°C) and humidity (p = 0.04) (IC 48.4 ± 8.1%, SC 42.9 ± 7.9%) in IC during the exercise trial but no difference in the 40-min recovery period for micro-environment temperature (p = 0.25) or humidity (p = 0.18). No significant difference (p > 0.05) was shown for core temperature (T _rec) (IC 38.3 ± 0.4°C, SC 38.2 ± 0.4°C), HR (IC l54 ± 28 beats min⁻¹, SC 151 ± 26 beats min⁻¹) or RPE (IC 4.7 ± 2.1, SC 3.8 ± 1.7) during the exercise trial or recovery period. Results from a paired t test revealed a significantly greater (p < 0.05) S-RPE (IC 5.8 ± 1.2, SC 4.3 ± 1.9), sweat loss (IC 1.4 ± 0.4 L h⁻¹, SC 1.2 ± 0.4 L h⁻¹) and greater discomfort during the exercise and recovery period for the IC. IC clothing appears to have no detrimental effects on heat storage or heat strain during exercise or recovery.     

The contribution of haemoglobin mass to increases in cycling performance induced by simulated LHTL

We sought to determine whether improved cycling performance following ‘Live High-Train Low’ (LHTL) occurs if increases in haemoglobin mass (Hb_mass) are prevented via periodic phlebotomy during hypoxic exposure. Eleven, highly trained, female cyclists completed 26 nights of simulated LHTL (16 h day⁻¹, 3000 m). Hb_mass was determined in quadruplicate before LHTL and in duplicate weekly thereafter. After 14 nights, cyclists were pair-matched, based on their Hb_mass response (ΔHb_mass) from baseline, to form a response group (Response, n = 5) in which Hb_mass was free to adapt, and a Clamp group (Clamp, n = 6) in which ΔHb_mass was negated via weekly phlebotomy. All cyclists were blinded to the blood volume removed. Cycling performance was assessed in duplicate before and after LHTL using a maximal 4-min effort (MMP_4min) followed by a ride time to exhaustion test at peak power output (T _lim). VO_2peak was established during the MMP_4min. Following LHTL, Hb_mass increased in Response (mean ± SD, 5.5 ± 2.9%). Due to repeated phlebotomy, there was no ΔHb_mass in Clamp (−0.4 ± 0.6%). VO_2peak increased in Response (3.5 ± 2.3%) but not in Clamp (0.3 ± 2.6%). MMP_4min improved in both the groups (Response 4.5 ± 1.1%, Clamp 3.6 ± 1.4%) and was not different between groups (p = 0.58). T _lim increased only in Response, with Clamp substantially worse than Response (−37.6%; 90% CL −58.9 to −5.0, p = 0.07). Our novel findings, showing an ~4% increase in MMP_4min despite blocking an ~5% increase in Hb_mass, suggest that accelerated erythropoiesis is not the sole mechanism by which LHTL improves performance. However, increases in Hb_mass appear to influence the aerobic contribution to high-intensity exercise which may be important for subsequent high-intensity efforts.     

Oxidative stress, inflammation and recovery of muscle function after damaging exercise: effect of 6-week mixed antioxidant supplementation

There is no consensus regarding the effects of mixed antioxidant vitamin C and/or vitamin E supplementation on oxidative stress responses to exercise and restoration of muscle function. Thirty-eight men were randomly assigned to receive either placebo group (n = 18) or mixed antioxidant (primarily vitamin C & E) supplements (n = 20) in a double-blind manner. After 6 weeks, participants performed 90 min of intermittent shuttle-running. Peak isometric torque of the knee flexors/extensors and range of motion at this joint were determined before and after exercise, with recovery of these variables tracked for up to 168 h post-exercise. Antioxidant supplementation elevated pre-exercise plasma vitamin C (93 ± 8 μmol l⁻¹) and vitamin E (11 ± 3 μmol l⁻¹) concentrations relative to baseline (P < 0.001) and the placebo group (P ≤ 0.02). Exercise reduced peak isometric torque (i.e. 9–19% relative to baseline; P ≤ 0.001), which persisted for the first 48 h of recovery with no difference between treatment groups. In contrast, changes in the urine concentration of F₂-isoprostanes responded differently to each treatment (P = 0.04), with a tendency for higher concentrations after 48 h of recovery in the supplemented group (6.2 ± 6.1 vs. 3.7 ± 3.4 ng ml⁻¹). Vitamin C & E supplementation also affected serum cortisol concentrations, with an attenuated increase from baseline to the peak values reached after 1 h of recovery compared with the placebo group (P = 0.02) and serum interleukin-6 concentrations were higher after 1 h of recovery in the antioxidant group (11.3 ± 3.4 pg ml⁻¹) than the placebo group (6.2 ± 3.8 pg ml⁻¹; P = 0.05). Combined vitamin C & E supplementation neither reduced markers of oxidative stress or inflammation nor did it facilitate recovery of muscle function after exercise-induced muscle damage.     

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.     

Effect of ambient temperature on caffeine ergogenicity during endurance exercise

It is well established that caffeine ingestion during exercise enhances endurance performance. Conversely, the physiological and psychological strain that accompanies increased ambient temperature decreases endurance performance. Little is known about the interaction between environmental temperature and the effects of caffeine on performance. The purpose of this study was to compare the effects of ambient temperature (12 and 33°C) on caffeine ergogenicity during endurance cycling exercise. Eleven male cyclists (mean ± SD; age, 25 ± 6 years; [(V)\dot] \textO_2max , {\dot V \text{O}}_{2\max } , 58.7 ± 2.9 ml kg⁻¹ min⁻¹) completed four exercise trials in a randomized, double blind experimental design. After cycling continuously for 90 min (average 65 ± 7% [(V)\dot] \textO_2max {\dot V \text{O}}_{2\max } ) in either a warm (33 ± 1°C, 41 ± 5%rh) or cool (12 ± 1°C, 60 ± 7%rh) environment, subjects completed a 15-min performance trial (PT; based on total work accumulated). Subjects ingested 3 mg kg⁻¹ of encapsulated caffeine (CAF) or placebo (PLA) 60 min prior to and after 45 min of exercise. Throughout exercise, subjects ingested water so that at the end of exercise, independent of ambient temperature, their body mass was reduced 0.55 ± 0.67%. Two-way (temperature × treatment) repeated-measures ANOVA were conducted with alpha set at 0.05. Total work (kJ) during the PT was greater in 12°C than 33°C [P < 0.001, η² = 0.804, confidence interval (CI): 30.51–62.30]. When pooled, CAF increased performance versus PLA independent of temperature (P = 0.006, η² = 0.542 CI: 3.60–16.86). However, performance differences with CAF were not dependent on ambient temperature (i.e., non-significant interaction; P = 0.662). CAF versus PLA in 12 and 33°C resulted in few differences in other physiological variables. However, during exercise, rectal temperature (T _re) increased in the warm environment (peak T _re; 33°C, 39.40 ± 0.45; 12°C, 38.79 ± 0.42°C; P < 0.05) but was not different in CAF versus PLA (P > 0.05). Increased ambient temperature had a detrimental effect on cycling performance in both the CAF and PLA conditions. CAF improved performance independent of environmental temperature. These findings suggest that caffeine at the dosage utilized (6 mg/kg body mass) is a, legal drug that provides an ergogenic benefit in 12 and 33°C.     

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.     

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.     

Effects of whole-body heat acclimation on cell injury and cytokine responses in peripheral blood mononuclear cells

To test the hypothesis that whole-body heat acclimation (HA) would increase peripheral blood mononuclear cells’ (PBMC) tolerance to heat shock (HS) and/or alter the release of cytokines (IL-1β, IL-6, IL-10 and TNF-α) to bacterial lipopolysaccharide (LPS), we heat acclimated nine subjects by exercising them for 100 min in a hot environment for 10 days. The subjects’ PBMC were separated and cultured on days 1 and 10 of HA pre- and post-exercise. Pre-exercise PBMC were allocated to three treatments: control (PRE, 37°C), HS (42.5°C for 2 h), or LPS (1 ng mL⁻¹ for 24 h). Post-exercise samples were incubated at 37°C. PBMC lactate dehydrogenase release increased (p < 0.05) after HS but it was not different (p > 0.05) between days 1 and 10 (0.100 ± 0.012 and 0.102 ± 0.16 abs., respectively). LPS treatment induced an increased (p < 0.05) release of cytokines but HA did not alter this response (p > 0.05). Pre-exercise intracellular heat shock protein 72 (Hsp72) was higher (p < 0.05) on day 10 compared to day 1 of HA (13 ± 5 and 8 ± 5 ng mL⁻¹, respectively). HS treatment caused a greater increase (p < 0.05) in Hsp72 than the exercise sessions on HA days 1 and 10. In addition, after HA, the Hsp72 response to HS was reduced (day 1, 129 ± 46; day 10, 80 ± 32 ng mL⁻¹, p < 0.05). In conclusion, HA increases PBMC Hsp72 but it does not reduce cellular damage to HS or alter cytokine response to LPS. We speculate that the stress applied during HA is not sufficient to modify the PBMC response.     

Indirect measures of human vagal withdrawal during head-up tilt with and without a respiratory acidosis

Human ECG records were analyzed during supine (SUP) rest and whole body 80° head-up tilt (HUT), with a respiratory acidosis (5%CO₂) and breathing room air (RA). HUT increased heart rate in both conditions (RA_SUP 60 ± 13 vs. RA_HUT 79 ± 16; 5%CO_2SUP 63 ± 12 vs. 5%CO_2HUT 79 ± 14 beats min⁻¹) and decreased mean R–R interval, with no changes in the R–R interval standard deviation. When corrected for changes in frequency spectrum total power (NU), the high frequency (0.15–0.4 Hz) component (HF_NU) of heart rate variability decreased (RA_SUP 44.01 ± 21.57 vs. RA_HUT 24.05 ± 13.09; 5%CO_2SUP 69.23 ± 15.37 vs. 5%CO_2HUT 47.64 ± 21.11) without accompanying changes in the low frequency (0.04–0.15 Hz) component (LF_NU) (RA_SUP 52.36 ± 21.93 vs. RA_HUT 66.58 ± 19.49; 5%CO_2SUP 22.97 ± 11.54 vs. 5%CO_2HUT 40.45 ± 21.41). Positive linear relations between the tilt-induced changes (Δ) in HF_NU and R–R interval were recorded for RA (ΔHF_NU = 0.0787(ΔR−R) − 11.3, R ² = 0.79, P < 0.05), and for 5%CO₂ (ΔHF_NU = 0.0334(ΔR−R) + 1.1, R ² = 0.82, P < 0.05). The decreased HF component suggested withdrawal of vagal activity during HUT. For both RA and 5%CO₂, the positive linear relations between ΔHF_NU and ΔR−R suggested that the greater the increase in heart rate with HUT, the greater the vagal withdrawal. However, a reduced range of ΔHF during HUT with respiratory acidosis suggested vagal withdrawal was lower with a respiratory acidosis.     

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.     

Pressure and coverage effects of sporting compression garments on cardiovascular function,thermoregulatory function,and exercise performance

Sporting compression garments (CG) are used widely during exercise despite little evidence of benefits. The purpose of this study was to investigate coverage and pressure effects of full-body CG on cardiovascular and thermoregulatory function at rest and during prolonged exercise, and on exercise performance. Twelve recreationally trained male cyclists [mean (SD) age, 26 (7) years; [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } , 53 (8) mL kg⁻¹ min⁻¹] completed three sessions (counterbalanced order), wearing either correctly-sized CG (CSG; 11–15 mmHg), over-sized CG (OSG; 8–13 mmHg), or gym shorts (CONT). Test sessions were conducted in temperate conditions [24 (1)°C, 60 (4)% relative humidity; ~2 m s⁻¹ air velocity during exercise], consisting of resting on a chair then on a cycle ergometer, before 60-min fixed-load cycling at ~65% [(V)\dot]\textO_2max \dot{V}{\text{O}}_{2\max } and a 6-km time trial. Wearing CG (CSG or OSG) did not mitigate cardiovascular strain during mild orthostatic stress at rest (p = 0.20–0.93 for garment effects). During exercise, cardiac output was ~5% higher in the CG conditions (p < 0.05), which appears to be accounted for via non-significant higher end-exercise heart rate (~4–7%, p = 0.30; p = 0.06 for greater heart rate drift in CSG); other cardiovascular variables, including stroke volume, were similar among conditions (p = 0.23–0.91). Covered-skin temperature was higher in CG conditions (p < 0.001) but core (oesophageal) temperature was not (p = 0.79). Time-trial performance (mean power, time taken) was similar with or without CG (p = 0.24–0.44). In conclusion, any demonstrable physiological or psychophysical effects of full-body CG were mild and seemingly reflective more of surface coverage than pressure. No benefit was evident for exercise performance.     

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.     

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

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

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.     

Changes in glucose tolerance and insulin sensitivity following 2 weeks of daily cinnamon ingestion in healthy humans

Cinnamon can improve fasting glucose in humans yet data on insulin sensitivity are limited and controversial. Eight male volunteers (aged 25 ± 1 years, body mass 76.5 ± 3.0 kg, BMI 24.0 ± 0.7 kg m⁻²; mean ± SEM) underwent two 14-day interventions involving cinnamon or placebo supplementation (3 g day⁻¹). Placebo supplementation was continued for 5 days following this 14 day period. Oral glucose tolerance tests (OGTT) were performed on days 0, 1, 14, 16, 18, and 20. Cinnamon ingestion reduced the glucose response to OGTT on day 1 (−13.1 ± 6.3% vs. day 0; P < 0.05) and day 14 (−5.5 ± 8.1% vs. day 0; P = 0.09). Cinnamon ingestion also reduced insulin responses to OGTT on day 14 (−27.1 ± 6.2% vs. day 0; P < 0.05), as well as improving insulin sensitivity on day 14 (vs. day 0; P < 0.05). These effects were lost following cessation of cinnamon feeding. Cinnamon may improve glycaemic control and insulin sensitivity, but the effects are quickly reversed.     

Peripheral markers of central fatigue in trained and untrained during uncompensable heat stress

The development of fatigue is more pronounced in the heat than thermoneutral environments; however, it is unclear whether biomarkers of central fatigue are consistent with the higher core temperature (T _c) tolerated by endurance trained (TR) versus untrained (UT) during exertional heat stress (EHS). The purpose of this study was to examine the indicators of central fatigue during EHS in TR versus UT. Twelve TR and 11 UT males (mean ± SE [(V)\dot]\textO _{2 \textpeak} \dot{V}{\text{O}}_{{ 2 {\text{peak}}}}  = 70 ± 2 and 50 ± 1 mL kg LBM⁻¹ min⁻¹, respectively) walked on a treadmill to exhaustion (EXH) in 40°C (dry) wearing protective clothing. Venous blood was obtained at PRE and 0.5°C T _c increments from 38 to 40°C/EXH. Free tryptophan (f-TRP) decreased dramatically at 39.5°C for the TR. Branch chain amino acids decreased with T _c and were greater for UT than TR at EXH. Tyrosine and phenylalanine remained unchanged. Serum S100β was undetectable (<5 pg mL⁻¹). Albumin was greater for the UT from PRE to 39.0°C and at EXH. Prolactin (PRL) responded to relative thermal strain with similar EXH values despite higher T _c tolerated for TR (39.7 ± 0.09°C) than UT (39.0 ± 0.09°C). The high EXH PRL values for both groups support its use as a biomarker of the serotonin and dopamine interplay within the brain during the development of central fatigue.