Anaerobic Power of the Arms and Legs of Young and Older Men

The purpose of this study was to examine differences in the anaerobic exercise performance of young and older men. Eight healthy, active older (68.5 +/- 2.4 years old, mean S.D.) and eight healthy, active young (30.6 +/- 4.5 years old) subjects were assessed for peak and mean power output (PP and MP, respectively) of the legs and arms, during 30 s Wingate tests. PP during leg exercise was significantly (P < 0.05) higher in the young (14.6 +/- 1.6 W kg-1) compared with the older (10.7 +/- 1.0 W kg-1) group. MP of the legs was also greater in the young subjects (10.7 +/- 0.7 vs. 7.4 +/- 0.9 W kg-1). These differences in PP and MP remained significant when expressed relative to lean leg volume. PP during arm cranking was significantly greater in the young subjects (8.9 +/- 0.7 vs. 7.5 +/- 0.6 W kg-1) as was MP (6.4 +/- 0.7 vs. 5.0 +/- 0.7 W kg-1). Post-exercise blood lactate concentration in the older group (7.0 +/- 1.6 mmol l-1) was less (P < 0.05) than in the young group (10.6 +/- 2.0 mmol l-1), for leg work only. The significant loss of anaerobic power in the older group could not be explained by a difference in muscle mass. Power output was also lower in the arms, but to a lesser extent. The results of this study suggest that a reduction in the ability to perform high intensity exercise may be an inevitable consequence of ageing. The extent, however, of this decline varies with different muscle groups.     

Effects of the infusion mode on bicarbonate balance in on-line hemodiafiltration

BACKGROUND: Electrolyte and acid-base balance may be differently affected by the infusion mode in on-line hemodiafiltration (HDF). We studied the effects of the different infusion modes on bicarbonate transport across the dialyzer membrane, and thus on the final bicarbonate balance of the HDF sessions. METHODS: Instantaneous HCO3- transfer across the dialyzer membrane, blood bicarbonate profile and the total balance of the sessions were studied in six dialysis patients under the same operating conditions over 36 HDF sessions, in order to compare the effects of predilution HDF (pre-HDF), postdilution HDF (post-HDF), and mixed HDF on the final bicarbonate balance. RESULTS: The final HCO3- balance was more positive in post-HDF vs pre-HDF (142 +/- 36 vs 99 +/- 41 mmol/session, p<0.05), with a final blood HCO3- concentration of 26.6 +/- 1.0 vs 25.4 +/- 1.1 mmol/L, (p<0.05). Mixed HDF yielded intermediate results (balance: 119 +/- 42 mmol/session, final HCO3- 26.2 (1.2 mmol/L). These differences were seen to result from the increased HCO3- concentration of blood entering the filter in predilution, due to the infused HCO3-, enhancing convective loss and reducing the driving force for diffusive HCO3- gain. CONCLUSIONS: Bicarbonate concentration in dialysate-reinfusate is critical in order to obtain an adequate end of session HCO3- balance in on-line HDF. The predilution method produced the lowest cumulative net HCO3- gain between the three studied infusion modes. Our data suggest that, under the same operating conditions and excluding the effect of ultrafiltration, dialysate HCO3- should be increased by about 2 mmol/L in pre-HDF, and 1 mmol/L in mixed HDF, to yield the same final balance as in post-HDF.     

Role of muscle mass on sprint performance: gender differences?

The aim of this study was to determine if gender differences in muscle mass explain the gender differences in running and cycling sprint performance. Body composition (dual-energy X-ray absorptiometry), and running (30 and 300 m test) and cycling (Wingate test) sprint performance were assessed in 123 men and 32 women. Peak power (PP) output in the Wingate test expressed per kg of lower extremities lean mass (LM) was similar in males and females (50.4 ± 5.6 and 50.5 ± 6.2 W kg⁻¹, P = 0.88). No gender differences were observed in the slope of the linear relation between LM and PP or mean power output (MP). However, when MP was expressed per kg of LM, the males attained a 22% higher value (26.6 ± 3.4 and 21.9 ± 3.2 W kg⁻¹, P < 0.001). The 30 and 300-m running time divided by the relative lean mass of the lower extremities (RLM = LM × 100/body mass) was significantly lower in males than in females. Although, the slope of the linear relationship between RLM and 300-m running time was not significantly different between genders, the males achieved better performance in the 300-m test than the females. The main factor accounting for gender differences in peak and mean power output during cycling is the muscle mass of the lower extremities. Although, the peak power generating capability of the muscle is similar in males and females, muscle mass only partially explains the gender difference in running sprints, even when expressed as a percentage of the whole body mass.     

Acute effects of supramaximal exercise on carotid artery compliance and pulse pressure in young men and women

The purpose of this study was to determine the cumulative effects of repeated cycling sprints (Wingate tests) on carotid compliance and blood pressure (BP). Fourteen young, healthy men and women completed this study. Vascular and hemodynamic measurements were taken at rest, 5 min following a first Wingate test, 25 min following the first Wingate test, 5 min following a second Wingate test, and 25 min following the second Wingate test. At each time point, the measurements taken included brachial and carotid pulse pressure (PP), heart rate, carotid artery maximum and minimum diameters, and carotid compliance. Carotid BP was obtained with applanation tonometry. Carotid diameters were obtained using ultrasonography and compliance was calculated from carotid diameters and BP. Carotid and brachial PP increased significantly (P < 0.05) 5 min after each Wingate test and returned to near baseline 25 min after each Wingate test. No cumulative PP effects were seen. A cumulative effect was seen for carotid compliance: 5 min following the second sprint, carotid arterial compliance decreased significantly more than 5 min following the first sprint (P < 0.05). A single cycling sprint reduces carotid artery compliance immediately after exercise. Performance of a second identical cycling sprint further compounds this vascular change, reducing carotid artery compliance beyond levels seen following a single cycling sprint.     

Elevations in core and muscle temperature impairs repeated sprint performance

AIM: The present study investigated the effects of hyperthermia on intermittent exercise and repeated sprint performance. METHODS: Seven men completed 40 min of intermittent cycling comprising of 15 s exercise (306 +/- 22 W) and 15 s rest periods (0 W) followed by 5 x 15 s maximal sprints on a cycle ergometer in normal (approximately 20 degrees C, control) and hot (40 degrees C, hyperthermia) environments. RESULTS: Completion of the intermittent protocol in the heat elevated core and muscle temperatures (39.5 +/- 0.2 degrees C; 40.2 +/- 0.4 degrees C), heart rate (178 +/- 11 beats min(-1)), rating of perceived exertion (RPE) (18 +/- 1) and noradrenaline (38.9 +/- 13.2 micromol l(-1)) (all P < 0.05). During the first sprint (n = 6), both peak and mean power output were similar across the environmental conditions. However, mean power over the last four sprints declined to a larger extent during hyperthermia compared with the control trial (P < 0.05). Consequently, average mean power output during the five sprints was lower in hyperthermia (558.0 +/- 146.9 W) compared with control (617.5 +/- 122.6 W; P < 0.05). Power output during the repeated sprints was reduced by hyperthermia despite an elevated muscle temperature that should promote sprint performance. Venous plasma potassium concentrations (H; 5.3 +/- 0.8 mmol l(-1) vs. C; 6.3 +/- 1.0 mmol l(-1), P = 0.06) and muscle lactate levels (H; 76.6 +/- 24.3 mmol kg(-1) dry weight vs. C; 108.8 +/- 20.1 mmol kg(-1) dry weight) were lower following the hyperthermic sprints compared to control. CONCLUSION: Although an elevated muscle temperature is expected to promote sprint performance, power output during the repeated sprints was reduced by hyperthermia. The impaired performance does not seem to relate to the accumulation of recognized metabolic fatigue agents and we, therefore, suggest that it may relate to the influence of high core temperature on the function of the central nervous system.     

Attenuated RPE and leg pain in response to short-term high-intensity interval training

This study examined the effect of 6 days of high intensity interval training (HIT) on rating of perceived exertion (RPE) and leg pain. Eleven men (age and VO(2)max=25.3±5.5 year and 45.6± mL/kg/min) and 9 women (age and VO(2)max=25.2±3.1 year and 41.1±6.1 mL/kg/min) with similar activity level and VO(2)max underwent HIT consisting of repeated Wingate tests separated by 5 min recovery over a 2-3 week period. Five men and four women served as controls and did not perform HIT. Four minutes after each bout across all days of training, RPE and leg pain were recorded using categorical scales. Repeated measure ANOVA was used to assess differences in RPE and leg pain in response to acute bouts and days of HIT. Data revealed that RPE and pain increased (p<0.05) after bout 1 to after bout 4. Compared to day 1 (6.3±1.9), RPE after bout 4 (5.0±1.4) decreased (p=0.001) in response to 6d of HIT. Training significantly reduced (p<0.05) leg pain, as pain declined from day 1 (6.20±2.29) of HIT versus day 6 (5.20±2.04). Data show that RPE and leg pain are significantly attenuated by 6 d of HIT, which is likely due to the physiological adaptations accrued in response to this modality of training.     

Effects of centrifuging at 2g on rat long bone metaphyses

Thermal stress is known to impair endurance capacity during moderate prolonged exercise. However, there is relatively little available information concerning the effects of thermal stress on the performance of high-intensity short-duration exercise. The present experiment examined human power output during repeated bouts of short-term maximal exercise. On two separate occasions, seven healthy males performed two 30-s bouts of sprint exercise (sprints I and II), with 4?min of passive recovery in between, on a cycle ergometer. The sprints were performed in both a normal environment [18.7?(1.5)°C, 40 (7)% relative humidity (RH; mean SD)] and a hot environment [30.1?(0.5)°C, 55 (9)% RH]. The order of exercise trials was randomised and separated by a minimum of 4 days. Mean power, peak power and decline in power output were calculated from the flywheel velocity after correction for flywheel acceleration. Peak power output was higher when exercise was performed in the heat compared to the normal environment in both sprint I [910 (172)?W vs 656?(58)?W; P?P?P?P?P?P?相似文献   

Duplication of paternal IGF2 or loss of maternal IGF2 imprinting occurs in half of Wilms tumors with various structural WT1 abnormalities

The WT1 gene essential for the embryonic kidney development is mutated in 15-25% of Wilms tumors (WTs). To clarify whether genetic subtypes of WT1 abnormalities are correlated with IGF2 or CTNNB1 alterations or clinicopathological characteristics, we performed comprehensive WT1, IGF2, and CTNNB1 analyses of 36 WTs with WT1 abnormalities using single nucleotide polymorphism arrays, and methylation analysis of the IGF2-H19 differentially methylated region. The tumors were classified into three subtypes based on WT1 abnormalities: 13 with WT1 deletion, 12 with WT1 mutation, and 11 with both deletion and mutation. IGF2 alterations were found in 50% (18/36), paternal uniparental disomy (UPD) of 11p13-11p15 in 13 tumors, UPD limited to 11p15 in 3, and loss of IGF2 imprinting in 2. Quantitative RT-PCR analysis showed that tumors with IGF2 alteration had higher levels of IGF2 mRNA than tumors without IGF2 alteration (P = 0.02). WT1 mRNA levels were very low in six of eight WTs with WT1 deletion, whereas four of eight WTs with WT1 mutation or both deletion and mutation showed higher levels of WT1 mRNA than fetal kidneys. WTs with WT1 mutations occurred in younger patients (P < 0.01), and WTs with mutations or both deletion and mutation (12/23) were more frequent in syndromic patients than WTs (1/13) with the deletion (P = 0.02). WTs with WT1 mutations or both deletion and mutation had the triphasic histological-type (15/23; P = 0.03) and CTNNB1 mutation (17/23; P = 0.03) more frequently than WTs with the deletion (2/13 and 4/13). Thus, three WT1 subtypes were correlated with certain genetic and clinicopathological characteristics.     

A comparison of bicarbonate kinetics and acid-base status in high flux hemodialysis and on-line post-dilution hemodiafiltration

Objectives: To compare bicarbonate kinetics and acid base status in HD and HDF for the same patient; and to investigate the effect of patient physiologic parameters on these kinetics. Methods: In order to monitor HCO3- kinetics during dialysis, acid-base parameters, pH, blood gases partial pressures, and HCO3- concentrations were recorded during 3 regular dialysis (HD) and 3 on-line post-dilution HDF sessions performed on 12 patients, using same dialysis fluid with a 38 mmol/l HCO3- concentration. HCO3- mass transfers through the hemodialyzers membranes and into the patients were continuously calculated during the sessions from HCO3- concentrations, together with HCO3-dialysance. The"apparent" HCO3-gain was calculated by integrating over time the instantaneous mass transfer from dialyzer and re-infusion fluid to the patient. A second method consisted in calculating the patient apparent bicarbonate space (ABS) and HCO3- mass (ABS times plasma concentration) at beginning and end of session. Results: No significant differences were observed between acid base parameters at the end of HD and HDF sessions. In contrast to urea clearances, HCO3- dialysances decayed with time during sessions from 110 to 140 ml/min to about 40 ml/min after one hour. The net HCO3- gain was taken as the difference between final and initial HCO3-masses. This net gain was in average 63% of apparent gain in HD and 74% in HDF. Conclusions: Uremic acidosis was well corrected without risk of alkalosis. An unexpected result was the continuous decay of bicarbonate dialysance both in HD and HDF during runs.     

Post-exercise diaphragm shielding: a novel approach to exercise-induced diaphragmatic fatigue

Based on the "post-exercise diaphragm shielding" hypothesis this study tested whether both diaphragmatic force-generation (DFG) and diaphragmatic fatigue (DF) remain unchanged during consecutive exercise-trials. Twelve subjects ( [Formula: see text] 58.4+/-6.6mlkg(-1)min(-1)) performed three consecutive exercise-trials (T(alpha)/T(beta)/T(gamma); workload(max) 85% [Formula: see text] ) each followed by recovery (6min). Twitch transdiaphragmatic pressure during supramaximal magnetic phrenic nerve stimulation (TwPdi, every 30s), ratings of perceived exertion (RPE, every 90s) and ergospirometric data (continuously) were assessed throughout the entire protocol (46.5min). DFG and DF did not differ among all trials (TwPdi-baseline: 2.2+/-0.7kPa; TwPdi-peak: T(alpha)/T(beta)/T(gamma) 3.1+/-0.7kPa vs 3.0+/-0.8kPa vs 3.2+/-0.8kPa; TwPdi-bottom: T(alpha)/T(beta)/T(gamma) 1.9+/-0.6kPa vs 2.0+/-0.7kPa vs 1.8+/-0.5kPa, both p>0.4, RM-ANOVA). Furthermore, TwPdi revealed close relationships with RPE (r=0.91, p<0.0001) and oxygen uptake (r=0.94, p<0.0001) during exercise. In conclusion, both DFG (baseline-to-peak) and DF (baseline-to-bottom) achieve similar magnitudes during and after consecutive exercise-trials and are closely linked to RPE and oxygen uptake. This suggests that DF neither reflects impaired diaphragmatic function nor impairs exercise performance; rather it is likely to reflect post-exercise diaphragm shielding.     

Determinants of repeated-sprint ability in females matched for single-sprint performance

This study investigated the relationship between VO2max and repeated-sprint ability (RSA), while controlling for the effects of initial sprint performance on sprint decrement. This was achieved via two methods: (1) matching females of low and moderate aerobic fitness (VO2max: 36.4 +/- 4.7 vs 49.6 +/- 5.5 ml kg(-1) min(-1) ; p < 0.05) for initial sprint performance and then comparing RSA, and (2) semi-partial correlations to adjust for the influence of initial sprint performance on RSA. Tests consisted of a RSA cycle test (5 x 6-s max sprints every 30 s) and a VO2max test. Muscle biopsies were taken before and after the RSA test. There was no significant difference between groups for work (W1, 3.44 +/- 0.57 vs 3.58 +/- 0.49 kJ; p = 0.59) or power (P1, 788.1 +/- 99.2 vs 835.2 +/- 127.2 W; p = 0.66) on the first sprint, or for total work (W(tot), 15.2 +/- 2.2 vs 16.6 +/- 2.2 kJ; p = 0.25). However, the moderate VO2max group recorded a smaller work decrement across the five sprints (W(dec), 11.1 +/- 2.5 vs 7.6 +/- 3.4%; p = 0.045). There were no significant differences between the two groups for muscle buffer capacity, muscle lactate or pH at any time point. When a semi-partial correlation was performed, to control for the contribution of W1 to W(dec), the correlation between VO2max and W(dec) increased from r = -0.41 (p > 0.05) to r = -0.50 (p < 0.05). These results indicate that VO2max does contribute to performance during repeated-sprint efforts. However, the small variance in W(dec) explained by VO2max suggests that other factors also play a role.     

Influence of gender on the EMG signal of the quadriceps femoris muscles and performance in high-intensity short-term exercise

The aim of this study was to investigate the influence of gender on the EMG signal of the muscles of the quadriceps femoris and the physical performance in high-intensity, short-term exercise. Fourteen volunteers (7 men = 29.1 +/- 2.8 years and 7 women = 22.6 +/- 2.9 years) performed a Wingate Test (WT) with a load of 7.5% of body mass. The variables analyzed during the WT were the Relative Peak Power (W.Kg(-1)) (RPP), Relative Mean Power (W.Kg(-1)) (RMP), Fatigue Index (%) (FI) and Peak Power Instant (s) (PPI). EMG signals of the superficial muscles of the quadriceps femoris (QF) from the right leg: rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM) were analyzed through root mean square (RMS) values and the normalized median frequency (MNF) determined using the Fast Fourier Transform (FFT). The RPP and the RMP were significantly higher in men when compared to women (9.99 +/- 0.96 vs. 7.66 +/- 1.00 W.kg(-1); 7.23 +/- 0.49 vs. 5.65 +/- 0.61 W.kg(1), P < 0.05; respectively). No significant difference between genders was found on RMS and NMF during WT (P > 0.05). Although RPP and RMP were influenced by gender, the RMS and the NMF of the superficial muscles of the QF did not show the same behavior, suggesting that other mechanisms, not related to motor unit recruitment and speed of nervous stimuli in the muscle fiber may be associated to the lower performance of women in high-intensity, short-term exercise.     

Effect of potassium depletion on cerebrospinal fluid bicarbonate homeostasis.

We have examined the effect of K depletion on CSF [HCO3-] homeostasis in awake rats. The relationship of CSF [HCO3-] to arterial [HCO3-] in metabolic acid-base disturbances is displaced is an upward direction and has a significantly increased slope in K-depleted vs. control rats (0.51 +/- 0.02 vs. 0.42 +/- 0.02). Results of partial K-repletion experiments, with peripheral acid-base balance held constant, suggest that the effect is K specific. The K-depleted animals also exhibit a wider (CSF-arterial) PCO2 difference than controls (11.1 vs. 8.4 mmHg). When CSF [HCO3-] is shown as a function of CSF PCO2 the data of K-depleted rats are no longer displaced when compared to controls but still have a significantly greater slope (1.21 +/- 0.23 vs. 0.89 +/- 0.08). This increased slope is interpreted to reflect enhanced HCO3- movement from blood to CSF at high arterial [HCO3-]. Analysis of our data and observations from the literature in conditions of mixed acid-base disturbances suggest that CSF [HCO3-] is determined by a) CSF PCO2 and b) the level of arterial [HCO3-] when the latter is greater than the normal CSF [HCO3-].     

Bone marrow ablation demonstrates that excess endogenous parathyroid hormone plays distinct roles in trabecular and cortical bone

Mice null for Cyp27b1, which encodes the 25-hydroxyvitamin D-1α-hydroxylase [1α(OH)ase(-/-) mice], lack 1,25-dihydroxyvitamin D [1,25(OH)(2)D] and have hypocalcemia and high parathyroid hormone (PTH) secretion. Intermittent, exogenous PTH is anabolic for bone. To determine the effect of the chronic excess endogenous PTH on osteogenesis and bone turnover, bone marrow ablations (BMX) were performed in tibiae and femurs of 6-week-old 1α(OH)ase(-/-) mice and in wild-type (WT) controls. Newly formed bone tissue was analyzed at 1, 2, and 3 weeks after BMX. BMX did not alter the higher levels of PTH in 1α(OH)ase(-/-) mice. In the marrow cavity, trabecular volume, osteoblast number, alkaline phosphatase-positive areas, type I collagen-positive areas, bone formation-related genes, and protein expression levels all increased significantly after BMX in 1α(OH)ase(-/-) mice, compared with WT. Osteoclast numbers and surface and ratio of RANKL/OPG-relative mRNA levels decreased significantly after BMX in 1α(OH)ase(-/-) mice, compared with WT. In the cortex, alkaline phosphatase-positive osteoblasts and osteoclast numbers increased significantly after BMX in 1α(OH)ase(-/-) mice, compared with WT. These results demonstrate that chronic excess endogenous PTH exerts an anabolic role in trabecular bone by stimulating osteogenic cells and reducing bone resorption, but plays a catabolic role in cortical bone by enhancing bone turnover with an increase in resorption.     

A perceptually regulated, graded exercise test predicts peak oxygen uptake during treadmill exercise in active and sedentary participants

The validity of predicting peak oxygen uptake ([Formula: see text]) in sedentary participants from a perceptually regulated exercise test (PRET) is limited to two cycle ergometry studies. We assessed the validity of a treadmill-based PRET. Active (n?=?49; 40.7?±?13.8?years) and sedentary (n?=?26; 33.4?±?13.2 y) participants completed two PRETS (PRET 1 and PRET2), requiring a change in speed or incline corresponding to ratings of perceived exertion (RPE) 9, 11, 13 and 15. Extrapolation of RPE: [Formula: see text] data to RPE 19 and 20 from the RPE 9-13 and 9-15 ranges were used to estimate [Formula: see text], and compared to [Formula: see text] from a graded exercise test (GXT). The [Formula: see text] :heart rate (HR) data (≥RPE 15) from the GXT were also extrapolated to age-predicted maximal HR (HRmax(pred)) to provide further estimation of [Formula: see text]. ANOVA revealed no significant differences between [Formula: see text] predictions from the RPE 9-15 range for PRET 1 and PRET 2 when extrapolated to RPE 19 in both active (54.3?±?7.4; 52.9?±?8.1?ml?kg(-1)?min(-1)) and sedentary participants (34.1?±?10.2; 34.2?±?9.6?ml?kg(-1)?min(-1)) and no difference between the HRmax(pred) method and measured [Formula: see text] from the GXT for active (53.3?±?10.0; 53.9?±?7.5?ml?kg(-1)?min(-1), respectively) and sedentary participants (33.6?±?8.4, 34.4?±?7.0?ml?kg(-1)?min(-1), respectively). A single treadmill-based PRET using RPE 9-15 range extrapolated to RPE 19 is a valid means of predicting [Formula: see text] in young and middle to older-aged individuals of varying activity and fitness levels.     

No effect of glutamine ingestion on indices of oxidative metabolism in stable COPD

COPD patients have reduced muscle glutamate which may contribute to an impaired response of oxidative metabolism to exercise. We hypothesised that prior glutamine supplementation would enhance V(O2) peak, V(O2) at lactate threshold and speed pulmonary oxygen uptake kinetics in COPD. 13 patients (9 males, age 66±5 years, mean±SD) with severe COPD (mean FEV(1) 0.88±0.23l, 33±7% predicted) performed on separate days ramp cycle-ergometry (5-10 W min(-1)) to volitional exhaustion and subsequently square-wave transitions to 80% estimated lactate threshold (LT) following consumption of either placebo (CON) or 0.125 g kg bm(-1) of glutamine (GLN) in 5 ml kg bm(-1) placebo. Oral glutamine had no effect on peak or V(O2) at LT, {V(O2) peak: CON=0.70±0.1 l min(-1) vs. GLN=0.73±0.2 l min(-1); LT: CON=0.57±0.1 l min(-1) vs. GLN=0.54±0.1 lmin(-1)} or V(O2) kinetics {tau: CON=68±22 s vs. GLN=68±16 s}. Ingestion of glutamine before exercise did not improve indices of oxidative metabolism in this patient group.     

Caffeine lowers muscle pain during exercise in hot but not cool environments

Caffeine (CAF) ingestion may enhance endurance exercise by lowering perceived exertion (RPE) and muscle pain. However, exercise in the heat may be detrimental to performance by increasing RPE and pain. The purpose of this study was to examine if caffeine affects pain and related perceptual responses differently in cool and hot ambient conditions. Eleven male cyclists (mean ± SD; age, 25 ± 6 years; mass, 72.6 ± 8.1 kg; VO(2max), 58.7 ± 2.9 ml kg(-1) min(-1)) completed four trials in a randomized, double blind design. While remaining euhydrated, subjects cycled for 90 min at 65 ± 7% VO(2max) followed by a 15-min performance trial. Subjects ingested 3 mg kg(-1) of encapsulated caffeine (CAF) or placebo (PLA) 60 min before and 45 after beginning exercise in 12°C and 33°C (i.e., 12-CAF, 33-CAF, 12-PLA, and 33-PLA trials). Central, local, and overall perceived exertion (C-, L-, and O-RPE) and pain were measured throughout exercise. Throughout submaximal exercise C-, L-, and O-RPE were significantly greater in 33°C (P<0.05) but were not affected by CAF (P>0.05). Using area-under-the-curve analysis, pain in 33-PLA was increased by 74% vs 12-PLA (P<0.05). CAF did not reduce pain in 12°C (P=0.542), but in 33°C, CAF reduced pain by 27% (P=0.032). Despite this apparent advantage, CAF improved performance independent of ambient temperature (i.e., non-significant interaction; P=0.662). This study found that, although caffeine improves exercise capacity, its effect on leg muscle pain is dependent on ambient temperature. Although exercise in the heat increases muscle pain compared to a cooler environment, caffeine reduces this pain.     

Effect of menstrual cycle phase on sprinting performance

This study examined the effects of menstrual cycle phase (MCP) upon sprinting and recovery as well as upon metabolic responses to such exercise. Eight females performed a repeated 30-s sprint on a non-motorised treadmill interspersed with a 2-min rest in three phases of the MCP, follicular (low 17β-estradiol and progesterone), just prior to ovulation (midcycle trial, highest 17β-estradiol concentration and low progesterone) and in the luteal phase (high 17β-estradiol and high progesterone). MCP was verified later by radioimmunoassay of 17β-estradiol and progesterone. Peak power output (PPO) and mean power output (MPO) were unaltered (P > 0.05) due to MCP [PPO for sprint 1: 463 (18) W vs. 443 (15) W vs. 449 (18) W; PPO for sprint 2: 395 (17) W vs. 359 (16) W vs. 397 (17) W; MPO for sprint 1: 302 (15) W vs. 298 (13) W vs. 298 (14) W; MPO for sprint 2: 252 (10) W vs. 248 (10) W vs. 259 (12) W for follicular, midcycle and luteal trial, mean (SEM), respectively]. Similarly, percentage recovery of PPO and MPO (the PPO or MPO during sprint 2 expressed as a percentage of the PPO or MPO during sprint 1) was also unchanged (P > 0.05). Blood lactate, blood pH and plasma ammonia after sprinting and estimated plasma volume were also unaltered by MCP (P > 0.05). These findings suggest that hormonal fluctuations due to MCP do not interfere with maximal intensity whole body sprinting and the metabolic responses to such exercise.     

The physiological effects of low-intensity neuromuscular electrical stimulation (NMES) on short-term recovery from supra-maximal exercise bouts in male triathletes

This study investigated the acute effects of NMES on blood lactate (BLa) and performance parameters in trained male triathletes. On three separate days, 13 trained male triathletes performed six 30 s Wingate tests (30 WanT) on a cycle ergometer. Each session consisted of performing 3 × 30 WanT (bouts 1-3) followed by a randomly assigned 30 min recovery intervention of either: (i) passive (seated), (ii) active (cycling at 30% VO(2 max)) or (iii) NMES (1 Hz/500 μs-ON:OFF 2:6 s). The 3 × 30 WanT bouts were then repeated (bouts 4-6) and compared to bouts 1-3 for peak power (PP), mean power (MP) and fatigue index (FI). BLa and heart rate (HR) were recorded at designated time points throughout. Data were analyzed using repeated measures ANOVA with Tukey's honestly significant difference post hoc test. BLa decreased significantly faster during the active recovery intervention (P < 0.001), however, there were no significant differences between interventions for PP (P = 0.217), MP (P = 0.477) and FI (P = 0.234) when the post intervention bouts (4-6) where compared to the pre intervention bouts (1-3). NMES during recovery was not more effective than active or passive recovery for improving subsequent performance. Despite BLa clearing at a significantly faster rate for the active recovery intervention, PP, MP or FI did not improve significantly compared to NMES and passive. In conclusion, NMES does not appear to be more effective than traditional methods for enhancing short-term recovery from supra-maximal exercise bouts in trained male triathletes.     

Switching from three times a week to short daily online hemodiafiltration: effects on acid-base balance

AIMS: This study examines the effect of a change from the standard 4-5 hours 3 times a week of online hemodiafiltration (OL-HDF) to 2-2.5 hours daily (6 times a week) OL-HDF, on acid-base balance, and attempts assess the modifications of acid-base parameters, ionic concentration, and electrical charges of albumin and phosphate available for diffusion and convection mechanisms across the membrane and subsequent infusion. METHODS: In 18 patients on online HDF, blood gas, electrolytes (Na, K, Cl), lactate, phosphate, albumin, apparent strong ion difference (SIDa), effective strong ion difference (SIDe), strong ion gap (SIG), anion gap (AG), and bicarbonate and pH time-averaged concentration (TAC) and time-averaged deviation (TAD) variables were evaluated at baseline, and 1, 3, 6, 9, and 12 months after patients were switched to daily OL-HDF. Additionally, in 12 patients, the same parameters measured simultaneously at dialyzer inlet, outlet, and after reinfusion were studied. RESULTS: Throughout the study, weekly single-pool Kt/V, equilibrated Kt/V, and TAC urea remained constant. However, standard Kt/V increased and TAD urea decreased on daily OL-HDF. There were no statistical differences during the time span of 12 months in pH, cations (Na, K), anions (Cl, HCO3(-) AG, and lactate), or SIDa, SIDe, and SIG pre-HDF; while pH and HCO3(-) TAD decreased from 0.02 and 1.02 +/- 0.74 mEq/L, to 0.01 and 0.64 +/- 0.52 mEq/L, respectively (p<0.01). Net albumin charge and AG increased significantly at dialyzer outlet and decreased after reinfusion. CONCLUSIONS: We did not observe changes in the acid-base balance in patients who switched from 3 times a week to short daily OL-HDF. The main benefit observed was a lower pH and bicarbonate TAD. This shows a better physiology for daily OL-HDF.