The effects of progressive dehydration on strength and power: is there a dose response?

This study examined the effect of exercise- and heat-induced dehydration on strength, jump capacity and neuromuscular function. Twelve recreationally active males completed six resistance exercise bouts (baseline and after each 5 exposure sessions) in an increasing state of hypohydration obtained by repeated heat exposure and exercise sessions (5 periods of 20 min jogging at up to ~80% age predicted heart rate maximum at 48.5 ± 0.48°C, relative humidity 50 ± 4%). Relative to starting values, body mass decreased 1.0 ± 0.5, 1.9 ± 0.7, 2.6 ± 0.8, 3.3 ± 0.9 and 3.9 ± 1.0% after exposure 1, 2, 3, 4 and 5, respectively. However, plasma volume remained constant. No significant differences existed amongst trials in vertical jump height, electromyography data or isokinetic leg extension at a rate of 120° s⁻¹. Isometric leg extensions were significantly reduced (P < 0.05) after the first (1% body mass loss) and subsequent exposures in comparison to baseline. Isokinetic leg extensions at a rate of 30° s⁻¹ were significantly reduced after the third (2.6% body mass loss) and subsequent exposures compared with baseline. No dose response was identified in any of the tested variables yet a threshold was observed in isometric and isokinetic strength at 30° s⁻¹. In conclusion, dehydration caused by jogging in the heat had no effect on vertical jumping or isokinetic leg extensions at a rate of 120° s⁻¹. Alternatively, exercise-induced dehydration was detrimental to isometric and isokinetic leg extensions at a rate of 30° s⁻¹, suggesting the force–velocity relationship in hypohydration merits further research.     

Effectiveness of short-term heat acclimation for highly trained athletes

Effectiveness of short-term acclimation has generally been undertaken using untrained and moderately-trained participants. The purpose of this study was to determine the impact of short-term (5-day) heat acclimation on highly trained athletes. Eight males (mean ± SD age 21.8 ± 2.1 years, mass 75.2 ± 4.6 kg, [(V)\dot] \dot{V}O_2peak 4.9 ± 0.2 L min⁻¹ and power output 400 ± 27 W) were heat acclimated under controlled hyperthermia (rectal temperature 38.5°C), for 90-min on five consecutive days (T _a = 39.5°C, 60% relative humidity). Acclimation was undertaken with dehydration (no fluid-intake) during daily bouts. Participants completed a rowing-specific, heat stress test (HST) 1 day before and after acclimation (T _a = 35°C, 60% relative humidity). HST consisted 10-min rowing at 30% peak power output (PPO), 10 min at 60% PPO and 5-min rest before a 2-km performance test, without feedback cues. Participants received 250 mL fluid (4% carbohydrate; osmolality 240–270 mmol kg⁻¹) before the HST. Body mass loss during acclimation bouts was 1.6 ± 0.3 kg (2.1%) on day 1 and 2.3 ± 0.4 kg (3.0%) on day 5. In contrast, resting plasma volume increased by 4.5 ± 4.5% from day 1 to 5 (estimated from [Hb] & Hct). Plasma aldosterone increased at rest (52.6 pg mL⁻¹; p = 0.03) and end-exercise (162.4 pg mL⁻¹; p = 0.00) from day 1 to 5 acclimation. During the HST T _re and f _c were lowered 0.3°C (p = 0.00) and 14 b min⁻¹ (p = 0.00) after 20-min exercise. The 2-km performance time (6.52.7 min) improved by 4 s (p = 0.00). Meaningful physiological and performance improvements occurred for highly trained athletes using a short-term (5-day) heat acclimation under hyperthermia control, with dehydration.     

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.     

Effect of moderate intensity resistance training during weight loss on body composition and physical performance in overweight older adults

The impact of resistance training has not been thoroughly examined in overweight older adults undergoing weight loss. Subjects (n = 27) were overweight and obese (BMI 31.7 ± 3.6 kg/m²) older (age 67 ± 4 years) adults and were randomized into either a 10-week Dietary Approaches to Stop Hypertension for weight loss diet (DASH, n = 12) or DASH plus moderate intensity resistance training (DASH-RT, n = 15). Outcomes included weight loss, total body and mid-thigh composition, muscle and physical function. There were no significant weight loss differences between the DASH-RT and DASH groups (−3.6 ± 0.8 vs. −2.0 ± 0.9%, p = 0.137). The DASH-RT group had a greater reduction in body fat than the DASH group (−4.1 ± 0.9 vs. −0.2 ± 1.0 kg, p = 0.005). The DASH-RT group had greater changes in lean mass (+0.8 ± 0.4 vs. −1.4 ± 0.4 kg, p = 0.002) and strength (+60 ± 18 vs. −5 ± 9 N, p = 0.008) than the DASH group. There were favorable changes in mid-thigh composition variables in the DASH-RT group that were different than the lack of changes observed in the DASH group, except for intermuscular adipose tissue. Both groups experienced decreases in 400-m walk times showed (DASH −36 ± 11 s, DASH-RT −40 ± 7 s) with no differences between groups. Moderate intensity resistance training during weight loss appears to improve fat mass and thigh composition, but weight loss only does not. However, global measures of physical functioning may improve with a weight loss-only program.     

Impact of dehydration on a full body resistance exercise protocol

This study examined effects of dehydration on a full body resistance exercise workout. Ten males completed two trials: heat exposed (with 100% fluid replacement) (HE) and dehydration (~3% body mass loss with no fluid replacement) (DEHY) achieved via hot water bath (~39°C). Following HE and DEHY, participants performed three sets to failure (using predetermined 12 repetition maximum) of bench press, lat pull down, overhead press, barbell curl, triceps press, and leg press with a 2-min recovery between each set and 2 min between exercises. A paired t test showed total repetitions (all sets combined) were significantly lower for DEHY: (144.1 ± 26.6 repetitions) versus HE: (169.4 ± 29.1 repetitions). ANOVAs showed significantly lower repetitions (~1–2 repetitions on average) per exercise for DEHY versus HE (all exercises). Pre-set rate of perceived exertion (RPE) and pre-set heart rate (HR) were significantly higher [~0.6–1.1 units on average in triceps press, leg press, and approached significance in lat pull down (P = 0.14) and ~6–13 b min⁻¹ on average in bench press, lat pull down, triceps press, and approached significance for overhead press (P = 0.10)] in DEHY versus HE. Session RPE difference approached significance (DEHY: 8.6 ± 1.9, HE: 7.4 ± 2.3) (P = 0.12). Recovery HR was significantly higher for DEHY (116 ± 15 b min⁻¹) versus HE (105 ± 13 b min⁻¹). Dehydration (~3%) impaired resistance exercise performance, decreased repetitions, increased perceived exertion, and hindered HR recovery. Results highlight the importance of adequate hydration during full body resistance exercise sessions.     

Heat balance and cumulative heat storage during exercise performed in the heat in physically active younger and middle-aged men

On separate days, eight physically active younger (22 ± 2 years) and eight highly trained middle-aged (45 ± 4 years) men matched for physical fitness and body composition performed 90 min of semi-recumbent cycling at a constant rate of heat production (290 W) followed by 60 min of seated recovery in either a temperate (T, 30°C), warm (W, 35°C) or hot (H, 40°C) ambient condition. Rectal temperature (T _re) was measured continuously, while the rate of whole-body heat loss (H _L), as well as changes in body heat content (∆H _b) was measured simultaneously using direct whole-body and indirect calorimetry. No difference in H _L was observed between age groups for all ambient conditions. Accordingly, the average ∆H _b during the 90-min exercise was similar for the younger (+193 ± 52, 212 ± 82 and +211 ± 44 kJ for T, W and H, respectively) and middle-aged men (+192 ± 119, +225 ± 76 and +217 ± 130 kJ for T, W and H, respectively). This was paralleled by a similar increase in T _re of 0.40 ± 0.20, 0.36 ± 0.14 and 0.34 ± 0.23°C for T, W and H, respectively in the younger men and 0.37 ± 0.23, 0.32 ± 0.19 and 0.28 ± 0.14°C for T, W and H, respectively in the middle-aged men. After 60 min of recovery, ∆H _b was similar for the younger and the middle-aged men, respectively (−45 ± 52 and −38 ± 31 kJ for T; −57 ± 78 and −40 ± 25 kJ for W; and −32 ± 71 and 11 ± 96 kJ for H). End recovery T _re remained elevated to similar levels in both the younger and middle-aged men, respectively, for each of the ambient conditions (0.24 ± 019 and 0.18 ± 0.18°C for T; 0.25 ± 0.11 and 0.24 ± 0.14°C for W and 0.33 ± 0.21 and 0.33 ± 0.13°C for H). We conclude that highly trained middle-aged men demonstrate a similar capacity for heat dissipation when compared with physically active younger men.     

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.     

Relevance of individual characteristics for thermoregulation during exercise in a hot-dry environment

The aim of this study was to investigate the relevance of individual characteristics for thermoregulation during prolonged cycling in the heat. For this purpose, 28 subjects cycled for 60 min at 60% VO_2peak in a hot-dry environment (36 ± 1°C; 25 ± 2% relative humidity, airflow 2.5 m/s). Subjects had a wide range of body mass (99–43 kg), body surface area (2.2–1.4 m²), body fatness (28–5%) and aerobic fitness level (VO_2peak = 5.0–2.1 L/min). At rest and during exercise, rectal and mean skin temperatures were measured to calculate the increase in body temperature (ΔT _body) during the trial. Net metabolic heat production (M _NET) and potential heat loss (by means of evaporation, radiation and convection) were calculated. Although subjects exercised at the same relative intensity, ΔT _body presented high between-subjects variability (range from 0.44 to 1.65°C). ΔT _body correlated negatively with body mass (r = −0.49; P < 0.01), body surface area (r = −0.47; P < 0.01) and T_body at rest (r = −0.37; P < 0.05), but it did not significantly correlate with body fatness (r = 0.12; P > 0.05). ΔT _body positively correlated with the body surface area/mass ratio (r = 0.46; P < 0.01) and the difference between M _NET and potential heat loss (r = 0.56; P < 0.01). In conclusion, a large body size (mass and body surface area) is beneficial to reduce ΔT _body during cycling exercise in the heat. However, subjects with higher absolute heat production (more aerobically fit) accumulate more heat because heat production may exceed potential heat loss (uncompensability).     

Intermittent versus constant aerobic exercise: effects on arterial stiffness

Aerobic exercises (of sufficient duration and intensity) decreases arterial stiffness. However, the direct relationship between the type of aerobic exercise (i.e. constant versus interval) and the alteration in arterial stiffness has been poorly explored. We evaluated the hemodynamic responses of 11 healthy males (22.5 ± 0.7 years, height 177.7 ± 1.1 cm, body mass 70.5 ± 2.4 kg) following acute constant (CE) and intermittent cycling exercise (IE). Exercise duration and intensity (mean heart rate) were matched during both exercises (142.9 ± 2.4 bpm for CE and 144.2 ± 2.4 bpm for IE). Heart rate (HR) and cardiac output (CO) were measured throughout the whole session, while blood pressure and pulse wave velocity (PWV) were measured during pre exercise and 30 min recovery. Arterial stiffness and cardiac autonomic control were assessed through PWV and heart rate variability, respectively. After IE, lower limb arterial stiffness was significantly and steadily decreased compared to pre exercise value (from 8.6 ± 0.1 to m s⁻¹ to 7.6 ± 0.3 to m s⁻¹ at 30 min) and was lower than after CE (8.2 ± 0.3 m s⁻¹ at 30 min, which did not significantly change compared to pre exercise: 8.7 ± 0.2 m s⁻¹). We hypothesized that the higher HR and lower arterial stiffness after IE were likely due to variations in peripheral vascular changes during the exercise which may trigger the release of endothelial or metabolic vasoactive factors. These data appear to show that IE may result in a greater stimulus for vascular adaptations when compared to CE.     

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.     

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.     

The effects of whole body vibration and exercise on fibrinolysis in men

Whole body vibration (WBV) is a novel modality that has been demonstrated to enhance muscular and cardiovascular functions reported to increase fibrinolytic activity. The purpose of this study was to examine the fibrinolytic response to WBV and exercise in men. Twenty healthy males (23.8 ± 0.9 years, 25.6 ± 0.2 kg m⁻²) participated in the study. Each subject performed three trials in randomized order separated by 1 week: exercise (X), vibration (V) and vibration + exercise (VX). Exercise sessions consisted of 15 min of unloaded squatting at a rate of 20 per minute. Vibration sessions were conducted on a WBV platform vibrating for 15 min. Tissue plasminogen activator (tPA) and plasminogen activator inhibitor (PAI-1) were assessed at baseline and immediately after each condition. The increase in tPA activity was significantly greater in VX (0.87 ± 0.35 to 3.21 ± 1.06 IU ml⁻¹) compared to X (0.71 ± 0.36 to 2.4 ± 1.13 IU ml⁻¹) or V (0.83 ± 0.25 to 1.00 ± 0.37 IU ml⁻¹) conditions, and greater in the X condition compared to the V condition. PAI-1 activity decreased significantly more in the VX (6.54 ± 5.53 to 4.89 ± 4.13 IU ml⁻¹) and X (9.76 ± 8.19 to 7.48 ± 7.11 IU ml⁻¹) conditions compared to the V (5.68 ± 3.53 to 5.84 ± 3.52 IU ml⁻¹) condition. WBV does not augment fibrinolytic activity in healthy men. However, WBV combined with squatting exercise increases fibrinolytic activity more than exercise alone.     

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.     

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.     

Intensity-dependent effect of body tilt angle on calf muscle fatigue in humans

Body tilt angle affects the fatigue of human calf muscle at a high contractile force (i.e. 70 %MVC); but the range of forces across which this effect occurs is not known and we sought to determine this in the present study. Fourteen men performed intermittent calf muscle contractions at either 30, 40, 50 and 60 %MVC (Group 1 n = 7) or at 80 and 90 %MVC (Group 2 n = 7). Two tests were performed at each intensity in the supine (tilt angle = 0°) and inclined head-up position (tilt angle = 67°). MVC was measured prior to and during each calf exercise test, and the linear rate of decline in MVC during each test was used to estimate muscle fatigue. MVC prior to each test was unaffected by body tilt angle in Groups 1 and 2. In Group 1 muscle fatigue was significantly lower in the inclined than supine position at 50 %MVC (0.10 ± 0.05 vs. 0.19 ± 0.10 N s⁻¹) and 60 %MVC (0.22 ± 0.20 vs. 0.36 ± 0.33 N s⁻¹); but there was no significant difference in fatigue at 30 %MVC (0.07 ± 0.06 vs. 0.07 ± 0.07 N s⁻¹) and 40 %MVC (0.12 ± 0.07 vs. 0.18 ± 0.08 N s⁻¹). In Group 2, muscle fatigue was significantly lower in the inclined compared with the supine position at 80 %MVC (0.90 ± 0.50 vs. 1.49 ± 0.87 N s⁻¹) and 90 %MVC (1.19 ± 0.47 vs. 1.79 ± 0.78 N s⁻¹). These data demonstrate that the postural effect on calf muscle fatigue during intermittent contractions is manifest at moderate to very high forces, but that it does not occur at low forces.     

Vascular and baroreceptor abnormalities in young males with a family history of hypertension

Vascular and baroreceptor abnormalities in 44 young males, mean age 21 years, comprising of offspring with (FH⁺; n = 22) and without (FH⁻; n = 22) hypertensive parents, were investigated. Peak forearm blood flow (FBF), which was defined as the highest blood flow obtained following reactive hyperaemia, was assessed using strain gauge plethysmography following 5 min of ischemia. Cardiopulmonary baroreceptor sensitivity was assessed using lower body negative pressure for 5 min at −20 mmHg and was determined by calculating change of stroke volume and forearm vascular resistance (FVR) to lower body negative pressure. Carotid baroreceptor sensitivity was assessed using neck suction at −20, −40, −60, and −80 mmHg and was calculated by dividing RR interval by systolic blood pressure. Augmentation index, a measure of wave reflection, was assessed using applanation tonometry and was calculated as the ratio of augmented pressure and pulse pressure. Peak FBF of FH⁺ was 19% lower than the FH⁻ (p = 0.02). Also FH⁺ had 17% higher peak FVR compared to FH⁻ (p = 0.04). However, there were no significant differences between groups for cardiopulmonary, carotid baroreceptor sensitivity, and augmentation index. These results suggest that peripheral vascular dysfunction appears earlier than abnormal baroreceptor sensitivity in young males with a family history of hypertension.     

Syncope is unrelated to supine and postural hypotension following prolonged exercise

Syncope is widely reported following prolonged exercise. It is often assumed that the magnitude of exercise-induced hypotension (post-exercise hypotension; PEH), and the hypotensive response to postural change (initial orthostatic hypotension; IOH) are predictors of syncope post-exercise. The aim of this study was to determine the relationship between PEH, IOH, the residual IOH and syncope following prolonged exercise. Blood pressure (BP; Finometer) was measured continuously in 19 athletes (47 ± 20 years; BMI: 23.2 ± 2.2 kg m²; [(V)\dot] \dot{V} O₂ max: 51.3 ± 10.8 mL kg⁻¹ min⁻¹) whilst supine and during head-up tilt (HUT) to 60° for 15 min (or to syncope), prior to and following 4 h of running at 70–80% maximal heart rate. Syncope developed in 15 of 19 athletes post-exercise [HUT-time completed, Pre: 14:39 (min:s) ± 0:55; Post: 5:59 ± 4:53; P < 0.01]. PEH was apparent (−7 ± 7 mmHg; −8 ± 8%), but was unrelated to HUT-time completed (r ² = 0.09; P > 0.05). Although the magnitude of IOH was similar to post-exercise [−28 ± 12 vs. −20 ± 14% (pre-exercise); P > 0.05], the BP recovery following IOH was incomplete [−9 ± 9 vs. −1 ± 11 (pre-exercise); P < 0.05]; however, neither showed a relation to HUT-time completed (r ² = 0.18, r ² = 0.01; P > 0.05, respectively). Although an inability to maintain BP is a common feature of syncope post-exercise, the magnitude of PEH, IOH and residual IOH do not predict time to syncope. Practically, endurance athletes who present with greater hypotension are not necessarily at a greater risk of syncope than those who present with lesser reductions in BP.     

Influences of a dietary supplement in combination with an exercise and diet regimen on adipocytokines and adiposity in women who are overweight

The influence of a proprietary blend of modified cellulose and cetylated fatty acids (Trisynex™, Imagenetix, Inc., San Diego, CA 92127, USA) on adipocytokine and regional body composition responses to a weight loss program was examined. Twenty-two women (Supplement group (S) (n = 11): age = 36.8 ± 7.2 years; weight = 87.1 ± 6.2 kg; % body fat = 43.4 ± 4.1; Placebo group (P) (n = 11): age = 38.3 ± 6.8 years; weight = 86.9 ± 4.7 kg; % body fat = 44.3 ± 2.0) completed an 8-week placebo-controlled, double-blind study consisting of a caloric restricted diet and cardiovascular exercise. Body composition and serum insulin, leptin, and adiponectin were assessed at pre-, mid-, and post-intervention. From pre- to post-intervention, significant decreases (P < 0.05) were observed for body weight (S: 87.1 ± 6.2–77.9 ± 5.1 kg; P: 86.9 ± 4.7–82.7 ± 3.8 kg) (P < 0.05 S vs. P), % body fat (S: 43.4 ± 4.1–36.1 ± 3.6; P: 44.3 ± 2.0–40.6 ± 1.2) (P < 0.05 S vs. P), leptin (S: 28.3 ± 3.5–16.2 ± 2.6 ng ml⁻¹; P: 29.4 ± 3.2–19.9 ± 1.1 ng ml⁻¹) (P < 0.05 S vs. P), and insulin (S: 7.3 ± 0.8–5.1 ± 0.2 mU l⁻¹; P: 7.7 ± 0.9–5.1 ± 0.3 mU l⁻¹). Serum adiponectin increased (P < 0.05) (S: 12.2 ± 2.4–26.3 ± 3.0 μg ml⁻¹: 12.6 ± 2.0–21.8 ± 3.1 μg ml⁻¹) (P < 0.05 for S vs. P). Supplementation with a proprietary blend of modified cellulose and cetylated fatty acids during an 8-week weight loss program exhibited favorable effects on adipocytokines and regional body composition.     

Potential impact of a 500-mL water bolus and body mass on plasma osmolality dilution

A methodological discrepancy exists in the hydration assessment literature regarding the establishment of euhydration, as some investigations utilize a pre-hydration technique, while others do not (overnight fluid/food fast). However, the degree that plasma osmolality (P _osm) dilutes when using the pre-hydration method and how body mass/composition might influence the results is not known. Thirty subjects (22 M, 8 F; 20 ± 2 years (mean ± SD); 1.8 ± 0.1 m; 75.8 ± 13.5 kg) had P _osm measured after an 8-h food and fluid fast (overnight fast) and 90 min after a 500-mL (4–9 mL/kg) water bolus (pre-hydration). From pre- to post-bolus, participants’ P _osm declined from 297 ± 3.5 to 295 ± 3.8 mmol/kg (p < 0.05; ∆ −1.7 ± 3.5 mmol/kg). One-third of the sample diluted to more than −3 mmol/kg. The effect of body mass on P _osm dilution was investigated by comparing dilution in the ten lightest (62.8 ± 3.4 kg) and heaviest (92.0 ± 9.8 kg) participants; however, the change between the light (∆ −1.9 ± 3.8 mmol/kg) versus heavy groups (∆ −1.1 ± 3.0 mmol/kg) was not different (p > 0.05). The correlation between body mass or total body water and change in P _osm was weak (p > 0.05), as was the correlation between relative fluid intake based on mass and change in P _osm (p > 0.05). The two methodologies appear to produce similar P _osm values when measured in most individuals. However, the potential for significant dilution (>3 mmol/kg) should be considered when choosing the pre-hydration methodology.