The effect of a low-carbohydrate diet on performance, hormonal and metabolic responses to a 30-s bout of supramaximal exercise

The aim of this study was to find out whether a low-carbohydrate diet (L-CHO) affects: (1) the capacity for all-out anaerobic exercise, and (2) hormonal and metabolic responses to this type of exercise. To this purpose, eight healthy subjects underwent a 30-s bicycle Wingate test preceded by either 3 days of a controlled mixed diet (130?kJ/kg of body mass daily, 50% carbohydrate, 30% fat, 20% protein) or 3 days of an isoenergetic L-CHO diet (up to 5% carbohydrate, 50% fat, 45% protein) in a randomized order. Before and during 1?h after the exercise venous blood samples were taken for measurement of blood lactate (LA), β-hydroxybutyrate (β-HB), glucose, adrenaline (A), noradrenaline (NA) and insulin levels. Oxygen consumption (V˙O₂) was also determined. It was found that the L-CHO diet diminished the mean power output during the 30-s exercise bout [533 (7)?W vs 581 (7)?W, P??1, P??1, P??1, P??1] were lower. The 1-h post-exercise excess of V˙O₂ [9.1 (0.25)?vs 10.6 (0.25)?l, P??1, P??1 and 14.30 (1.41)?vs 8.20 (1.31)?nmol?·?l^?1, P?相似文献   

The Impact of heat exposure and repeated exercise on circulating stress hormones

To determine if heat exposure alters the hormonal responses to moderate, repeated exercise, 11 healthy male subjects [age?=?27.1 (3.0) years; maximal oxygen consumption, V˙O_2max?=?47.6 (6.2) ml?·?kg?· min^?1; mean (SD)] were assigned to four different experimental conditions according to a randomized-block design. While in a thermoneutral (23°C) or heated (40°C, 30% relative humidity) climatic chamber, subjects performed either cycle ergometer exercise (two 30-min bouts at ≈50% V˙O_2max, separated by a 45-min recovery interval, CEx and HEx conditions), or remained seated for 3?h (CS and HS conditions). Blood samples were analyzed for various exercise stress hormones [epinephrine (E), norepinephrine (NE), dopamine, cortisol and human growth hormone (hGH)]. Passive heating did not alter the concentrations of any of these hormones significantly. During both environmental conditions, exercise induced significant (P < 0.001) elevations in plasma E, NE and hGH levels. At 23°C during bout 1: E?=?393 (199) pmol?·?l^?1 (CEx) vs 174 (85) pmol?·?l^?1 (CS), NE?=?4593 (2640) pmol?·?l^?1 (CEx) vs 1548 (505) pmol?·?l^?1 (CS), and hGH?=?274 (340) pmol?·?l^?1 (CEx)vs 64 (112) pmol?·?l^?1 (CS). At 40°C, bout 1: E?=?596 (346) pmol?·?l^?1 (HEx) vs 323 (181) pmol?·?l^?1 (HS), NE?=?7789 (5129) pmol?·?l^?1 (HEx) vs 1527 (605) pmol?·?l^?1 (HS), and hGH?=?453 (494) pmol?·?l^?1 (HEx) vs 172 (355) pmol?·?l^?1 (HS). However, concentrations of plasma cortisol were increased only in response to exercise in the heat [HEx?=?364 (168) nmol?·?l^?1 vs HS?=?295 (114) nmol?·?l^?1). Compared to exercise at room temperature, plasma levels of E, NE and cortisol were all higher during exercise in the heat (P < 0.001 in all cases). The repetition of exercise did not significantly alter the pattern of change in cortisol or hGH levels in either environmental condition. However, repetition of exercise in the heat increased circulatory and psychological stress, with significantly (P < 0.001) higher plasma concentrations of E and NE. These results indicate a differential response of the various stress hormones to heat exposure and repeated moderate exercise.     

Effect of repeated bouts of short-term exercise on plasma free and sulphoconjugated catecholamines in humans

We tested the hypothesis that measurement of plasma catecholamine sulphate concentration after exercise reflects the overall activation of the sympathoadrenergic system during the whole period of repeated bouts of short-term exercise. A group of 11 male athletes performed two exercise tests at similar average power outputs consisting of three sets each. The tests either started with one set of three very intense sprints (95% of maximal running speed) followed by two sets of three less intense sprints (85% of maximal running speed; HLX) or vice versa (LHX). Similar mean areas under the curve of free noradrenaline (NA) during HLX and LHX [622 (SEM 13) vs 611 (SEM 14) nmol?·?l^?1?·?min) as well as similar mean heart rates [143 (SEM 9) vs 143 (SEM 8) beats?·?min^?1] indicated comparable sympathetic activation during both exercise tests. Even so, plasma concentration of free NA was still significantly higher at the end of LHX than of HLX [35.7 (SEM 3.5) vs 22.5 (SEM 2.1) nmol?·?l^?1, respectively], i.e. when exercise ended with the more intense set of sprints. Plasma noradrenaline sulphate (NA-S) increased with exercise intensity showing higher mean increments after the first set of HLX compared to LHX [1.83 (SEM 0.42) vs 1.18 (SEM 0.29) nmol?·?l^?1; P?0.05]. However, after the end of HLX and LHX, increments in plasma NA-S were similar [4.52 (SEM 0.76) vs 4.06 (SEM 0.79) nmol?·?l^?1], suggesting that NA-S response changed in parallel with the overall activation of the sympathetic nervous system during repeated bouts of short-term exercise. The results supported the hypothesis that measurement of plasma NA-S immediately after repeated bouts of short-term exercise reflects overall activation of the sympathetic nervous system during prolonged periods of this type of exercise.     

Plasma catecholamine and serum testosterone responses to four units of resistance exercise in young and adult male athletes

The plasma noradrenaline (NA) and adrenaline (A) concentration responses of seven young male athletes [15 (SD 1) years] and seven adult male athletes [25 (SD 6) years] were investigated together with the serum testosterone (Tes) concentration responses in four different half-squatting exercises. The loads, number of repetitions, exercise intensity and recovery between the sets were manipulated such that different types of metabolic demand could be expected. However, the amount of work done was kept equal in each kind of exercise. After the most exhausting unit of exercise (E3; two sets of 30 repetitions with 50% of 1 repetition maximum and with 2-min recovery between the sets) the plasma NA concentration was significantly lower in the younger than in the adult subjects [15.7 (SD 7.8) vs 32.7 (SD 13.2) nmol · l^?1, P < 0.05], while the A concentrations were similar. In the other three exercises no differences in the plasma catecholamine concentration responses among the groups were observed. The postexercise Tes concentrations, however, were significantly lower in the younger than in the adult subjects in every exercise unit. No correlations between the plasma catecholamine and serum Tes concentration responses were observed in any of the exercise units in either group. The results of the present study may suggest reduced sympathetic nervous activity in the younger subjects compared to the adults in response to exhausting resistance exercise. The results may also suggest that the catecholamines were less involved in eliciting an increase in Tes secretion in these resistance exercises.     

Detection of the change point in oxygen uptake during an incremental exercise test using recursive residuals: relationship to the plasma lactate accumulation and blood acid base balance

The purpose of this study was to develop a method to determine the power output at which oxygen uptake (V˙O₂) during an incremental exercise test begins to rise non-linearly. A group of 26 healthy non-smoking men [mean age 22.1?(SD 1.4)?years, body mass 73.6?(SD 7.4)?kg, height 179.4?(SD 7.5)?cm, maximal oxygen uptake (V˙O_2max) 3.726?(SD 0.363)?l?·?min^?1], experienced in laboratory tests, were the subjects in this study. They performed an incremental exercise test on a cycle ergometer at a pedalling rate of 70?rev?·?min^?1. The test started at a power output of 30?W, followed by increases amounting to 30?W every 3?min. At 5?min prior to the first exercise intensity, at the end of each stage of exercise protocol, blood samples (1?ml each) were taken from an antecubital vein. The samples were analysed for plasma lactate concentration [La]_pl, partial pressure of O₂ and CO₂ and hydrogen ion concentration [H⁺]_b. The lactate threshold (LT) in this study was defined as the highest power output above which [La^?]_pl showed a sustained increase of more than 0.5?mmol?·?l^?1?·?step^?1. The V˙O₂ was measured breath-by-breath. In the analysis of the change point (CP) of V˙O₂ during the incremental exercise test, a two-phase model was assumed for the 3rd-min-data of each step of the test: X _i =at _i +b+? _i for i=1,2,…,T, and E(X _i )>at _i +b for i =T+1,…,n, where X ₁, … , X _n are independent and ? _i ～N(0,σ²). In the first phase, a linear relationship between V˙O₂ and power output was assumed, whereas in the second phase an additional increase in V˙O₂ above the values expected from the linear model was allowed. The power output at which the first phase ended was called the change point in oxygen uptake (CP-V˙O₂). The identification of the model consisted of two steps: testing for the existence of CP and estimating its location. Both procedures were based on suitably normalised recursive residuals. We showed that in 25 out of 26 subjects it was possible to determine the CP- O₂ as described in our model. The power output at CP-V˙O₂ amounted to 136.8?(SD 31.3)?W. It was only 11?W – non significantly – higher than the power output corresponding to LT. The V˙O₂ at CP-V˙O₂ amounted to 1.828?(SD 0.356)?l?·?min^?1 was [48.9?(SD 7.9)% V˙O_{2 max} ]. The [La^?]_pl at CP-V˙O₂, amounting to 2.57?(SD 0.69)?mmol?·?l^?1 was significantly elevated (P<0.01) above the resting level [1.85?(SD 0.46)?mmol?·?l^?1], however the [H⁺]_b at CP-V˙O₂ amounting to 45.1 (SD 3.0)?nmol?·?l^?1, was not significantly different from the values at rest which amounted to 44.14?(SD 2.79)?nmol?·?l^?1. An increase of power output of 30?W above CP-V˙O₂ was accompanied by a significant increase in [H⁺]_b above the resting level (P=0.03).     

Gender comparison of peak oxygen uptake: repetitive box lifting versus treadmill running

The gender differences in peak oxygen uptake (V˙O_2peak) for various modes of exercise have been examined previously; however, no direct gender comparisons have been made during repetitive lifting (RL). In the present study the V˙O_2peak between RL and treadmill running (TR) was compared between 20 men [mean (SD) age, height, body mass and body fat: 21 (3) years, 1.79 (0.06)?m, 81 (9)?kg, 19 (6)%, respectively] and 20 women [mean (SD) age, height, body mass and body fat: 21 (3) years, 1.63 (0.05)?m, 60 (7)?kg, 27 (6)%, respectively]. V˙O_2peak (l?·?min^?1), defined as the highest value obtained during exercise to volitional fatigue, was determined using discontinuous protocols with treadmill grade or box mass incremented to increase exercise intensity. For RL V˙O_2peak, a pneumatically driven shelf was used to lower a loaded box to the floor, and subjects then lifted the box, at a rate of 15 lifts?·?min^?1. V˙O_2peak (l?·?min^?1 and ml?·?kg^?1?·?min^?1) and minute ventilation (V˙ _E, l?·?min^?1) were determined using an on-line gas analysis system. A two-way repeated measures analysis of variance revealed significant gender effects, with men having higher values for V˙O_2peak (l?·?min^?1 and ml?·?kg^?1?·?min^?1) and V˙ _E, but women having higher values of the ventilatory equivalent for oxygen (V˙ _E/V˙O₂). There were also mode of exercise effects, with TR values being higher for V˙O_2peak (l?·?min^?1 and ml?·?kg^?1?·?min^?1) and V˙ _E and an interaction effect for V˙O_2peak {1?·?min^?1 and ml?·?kg^?1?·?min^?1) and V˙ _E/V˙O₂. The women obtained a greater percentage (≈84%) of their TR V˙O_2peak during RL than did the men (≈79%). There was a marginal tendency for women to decrease and men to increase their V˙ _E/V˙O₂ when comparing TR with RL. The magnitude of the gender differences between the two exercise modalities appeared to be similar for heart rate, V˙ _E and R, but differed for V˙O_2peak (1?·?min^?1 and ml?·?kg^?1?·?min^?1). Lifting to an absolute height (1.32?m for the RL protocol) may present a different physical challenge to men and women with respect to the degree of involvement of the muscle groups used during lifting and ventilation.     

Decreased exercise blood lactate concentrations after respiratory endurance training in humans

For many years, it was believed that ventilation does not limit performance in healthy humans. Recently, however, it has been shown that inspiratory muscles can become fatigued during intense endurance exercise and decrease their exercise performance. Therefore, it is not surprising that respiratory endurance training can prolong intense constant-intensity cycling exercise. To investigate the effects of respiratory endurance training on blood lactate concentration and oxygen consumption (V˙O₂) during exercise and their relationship to performance, 20?healthy, active subjects underwent 30?min of voluntary, isocapnic hyperpnoea 5 days a week, for 4 weeks. Respiratory endurance tests, as well as incremental and constant-intensity exercise tests on a cycle ergometer, were performed before and after the 4-week period. Respiratory endurance increased from 4.6 (SD 2.5) to 29.1?(SD 4.0)?min (P?P?V˙O₂ did not change at any exercise intensity whereas blood lactate concentration was lower at the end of the incremental [10.4 (SD 2.1) vs 8.8?(SD 1.9)?mmol?·?l^?1, P??1, P?相似文献   

Failure to obtain a unique threshold on the blood lactate concentration curve during exercise

The purpose of this study was to compare various methods and criteria used to identify the anaerobic threshold (AT), and to correlate the AT obtained with each other and with running performance. Furthermore, a number of additional points throughout the entire range of lactate concentrations [La^?] were obtained and correlated with performance. A group of 19 runners [mean age 33.7 (SD 9.6) years, height 173 (SD 6.3) cm, body mass 68.3 (SD 5.4)?kg, maximal O₂ uptake (V˙O_{2 max} ) 55.2 (SD 5.9)?ml?·?kg^?1?·?min^?1] performed a maximal multistage treadmill test (1?km?·?h^?1 every 3.5?min) with blood sampling at the end of each stage while running. All AT points selected (visual [La^?], 4?mmol?·?l^?1 [La^?], 1?mmol?·?l^?1 above baseline, log-log breakpoint, and 45° tangent to the exponential regression) were highly correlated one with another and with performance (r?>?0.90) even when there were many differences among the AT (P??1 [La^?], 1 to 6?mmol?·?l^?1 [La^?] above the baseline, and 30 to 70° tangent to the exponential curve of [La^?]) were also highly correlated with performance (r?>?0.90). These results failed to demonstrate a distinct AT because many points of the curve provided similar information. Intercorrelations and correlations between AT and performance were, however, reduced when AT were expressed as the percentage of maximal treadmill speed obtained at AT or percentage of V˙O_{2 max} . This would indicate that different attributes of aerobic performance (i.e. maximal aerobic power, running economy and endurance) are measured when manipulating units. Thus, coaches should be aware of these results when they prescribe an intensity for training and concentrate more on the physiological consequences of a chosen [La^?] rather than on a “threshold”.     

Insulin and glucagon immunoreactivity during high-intensity exercise under opiate blockade

Eight fit men [maximum oxygen consumption ( O_2max) 64.6 (1.9) ml?·?kg^?1?·?min^?1, aged 28.3 (1.7) years (SE in parentheses) were studied during two treadmill exercise trials to determine the effect of endogenous opioids on insulin and glucagon immunoreactivity during intense exercise (80% O_2max). A double-blind experimental design was used with subjects undertaking the two exercise trials in counterbalanced order. Exercise trials were 20 min in duration and were conducted 7 days apart. One exercise trial was undertaken following administration of naloxone (N; 1.2 mg; 3?ml) and the other after receiving a placebo (P; 0.9% NaCl saline; 3?ml). Prior to each experimental trial a flexible catheter was placed into an antecubital vein and baseline blood samples were collected. Immediately after, each subject received either a N or P bolus injection. Blood samples were also collected after 20?min of continuous exercise (running). Glucagon was higher (P?P?P??1 vs 127.2 (7.6) ng?·?l^?1]. There were no differences in insulin during exercise between the P and N trials [50.2 (4.3) pmol?·?l^?1 vs 43.8 (5) pmol?·?l^?1]. These data suggest that endogenous opioids may augment the glucagon response during intense exercise.     

Blood glucose responses in humans mirror lactate responses for individual anaerobic threshold and for lactate minimum in track tests

The equilibrium point between blood lactate production and removal (La^? _min) and the individual anaerobic threshold (IAT) protocols have been used to evaluate exercise. During progressive exercise, blood lactate [La^?]_b, catecholamine and cortisol concentrations, show exponential increases at upper anaerobic threshold intensities. Since these hormones enhance blood glucose concentrations [Glc]_b, this study investigated the [Glc] and [La^?]_b responses during incremental tests and the possibility of considering the individual glucose threshold (IGT) and glucose minimum (Glc_min) in addition to IAT and La^? _min in evaluating exercise. A group of 15 male endurance runners ran in four tests on the track 3000?m run (v _3km); IAT and IGT – 8?×?800?m runs at velocities between 84% and 102% of v _3km; La^? _min and Glc_min– after lactic acidosis induced by a 500-m sprint, the subjects ran 6?×?800?m at intensities between 87% and 97% of v _3km; endurance test (ET) – 30?min at the velocity of IAT. Capillary blood (25?μl) was collected for [La^?]_b and [Glc]_b measurements. The IAT and IGT were determined by [La^?]_b and [Glc]_b kinetics during the second test. The La^? _min and Glc_min were determined considering the lowest [La^?] and [Glc]_b during the third test. No differences were observed (P??1; r?=?0.096; P?? _min [285 (SD 21)] and Glc_min [287 (SD 20) m.?·?min^?1 r?=?0.77; P??]_b reached 5.0? (SD 1.1) and 5.3 (SD 1.0) mmol?·?l^?1 at 20 and 30?min, respectively (P?>?0.05). We concluded that for these subjects it was possible to evaluate the aerobic capacity by IGT and Glc_min as well as by IAT and La^? _min.     

Significant changes in VLDL-Triacylglycerol and glucose tolerance in obese subjects following ten days of training

We characterized the effect of ten days of training on lipid metabolism in 6 [age 37.2 (2.3) years] sedentary, obese [BMI 34.4?(3.0)?kg?·?m^?2] males with normal glucose tolerance. An oral glucose tolerance test was performed prior to and at the end of the 10?d of training period. The duration of each daily exercise session was 40?min at an intensity equivalent to ?75% of the age predicted maximum heart rate. Blood measurements were performed after an overnight fast, before and at the end of the 10?d period. Plasma triacylglycerol was significantly (p??1). Very low density lipoprotein-triacylglycerol was also significantly?(p??1). No significant changes in high density lipoprotein-cholesterol were observed as a result of training. Following training fasting plasma glucose and fasting plasma insulin were significantly reduced [Glucose: 5.9 (0.2)?mmol?·?l^?1 vs.?5.3 (0.22)?mmol?·?l^?1 (p??1 vs. 200.9 (30.1) ρ?·?mol?·?l^?1, p?=?0.05]. The total area under the glucose curve during the OGTT decreased significantly (p?相似文献   

Oxygen uptake does not increase linearly at high power outputs during incremental exercise test in humans

A group of 12 healthy non-smoking men [mean age 22.3 (SD 1.1)?years], performed an incremental exercise test. The test started at 30?W, followed by increases in power output (P) of 30?W every 3 min, until exhaustion. Blood samples were taken from an antecubital vein for determination of plasma concentration lactate [La^?]_pl and acid-base balance variables. Below the lactate threshold (LT) defined in this study as the highest P above which a sustained increase in [La^?]_pl was observed (at least 0.5 mmol?·?l^?1 within 3 min), the pulmonary oxygen uptake (V˙O₂) measured breath-by-breath, showed a linear relationship with P. However, at P above LT [in this study 135 (SD 30)?W] there was an additional accumulating increase in V˙O₂ above that expected from the increase in P alone. The magnitude of this effect was illustrated by the difference in the final P observed at maximal oxygen uptake (V˙O_2max) during the incremental exercise test (P _max,obs at V˙O_2max) and the expected power output at V˙O_2max(P _max,exp at V˙O_2max) predicted from the linear V˙O₂-P relationship derived from the data collected below LT. The P _max,obs at V˙O_2max amounting to 270 (SD 19)?W was 65.1 (SD 35)?W (19%) lower (P<0.01) than the P _max,exp at V˙O_{2max .} The mean value of V˙O_2max reached at P _max,obs amounted to 3555 (SD 226)?ml?·?min^?1 which was 572 (SD 269)?ml?·?min^?1 higher (P<0.01) than the V˙O₂ expected at this P, calculated from the linear relationship between V˙O₂ and P derived from the data collected below LT. This fall in locomotory efficiency expressed by the additional increase in V˙O₂, amounting to 572 (SD 269) ml O₂?·?min^?1, was accompanied by a significant increase in [La^?]_pl amounting to 7.04 (SD 2.2)?mmol?·?l^?1, a significant increase in blood hydrogen ion concentration ([H⁺]_b) to 7.4 (SD 3)?nmol?·?l^?1 and a significant fall in blood bicarbonate concentration to 5.78 (SD 1.7)?mmol?·?l^?1, in relation to the values measured at the P of the LT. We also correlated the individual values of the additional V˙O₂ with the increases (Δ) in variables [La^?]_pl and Δ[H⁺]_b. The Δ values for [La^?]_pl and Δ[H⁺]_b were expressed as the differences between values reached at the P _max,obs at V˙O_2max and the values at LT. No significant correlations between the additional V˙O₂ and Δ[La^?]_pl on [H⁺]_b were found. In conclusion, when performing an incremental exercise test, exceeding P corresponding to LT was accompanied by a significant additional increase in V˙O₂ above that expected from the linear relationship between V˙O₂ and P occurring at lower P. However, the magnitude of the additional increase in V˙O₂ did not correlate with the magnitude of the increases in [La^?]_pl and [H⁺]_b reached in the final stages of the incremental test.     

Increased concentrations of interleukin 1-β in whole blood cultures supernatants after 12 weeks of moderate endurance exercise

The aim of the study was to investigate whether a regular moderate endurance exercise programme influenced the in vitro cytokine synthesis by stimulated whole blood cultures. To this end, eight healthy subjects exercised moderately by running for 3–5?h a week over a period of 12 weeks, whilst seven other healthy subjects served as the control group. The intensity of the exercise was determined by lactic acid concentrations in the blood which were maintained between 1.8 and 2.5?mmol?·?l^?1. Over the period of training the running velocity producing the 4?mmol?·?l^?1 lactic acid threshold increased from 2.86 (SD?0.83)?m?·?s^?1 to 3.06?±?0.79?m?·?s^?1 (P?≤?0.008). Blood samples were taken at rest before and after the training programme. The following blood parameters were determined: leucocyte count, differential leucocyte count, lymphocyte subpopulations [CD14 positive (+)/CD45+, CD4+/CD25+, CD8+, CD16+/CD122+]. Whole blood cultures were stimulated with lipopolysaccarides [interleukin (IL)-1 β and IL-6] and staphylococcal enterotoxin B [IL-2, soluble interleukin 2 receptor (sIL2-R) and interferon (IFN)-γ]. Cytokine concentrations in the supernatants were measured using an enzyme-linked immunosorbent assay. The white blood cell count, differential leucocyte count, lymphocyte subset distribution and the expression of the CD25 and CD122 antigen on lymphocytes were unchanged by training. After the training programme the IL-1 β production changed significantly [1496 (SD?264) pg?·?ml^?1 before, compared to 2127 (SD?672) pg?·?ml^?1 after training, P?≤?0.008]. In the control group these parameters remained unchanged. With respect to changes in the values in both groups the syntheses of IL-1 β (P?≤?0.023) and IL-6 (P?≤?0.021) were significantly higher after regular training. The syntheses of IL-2, sIL-2 and INF-γ were not significantly influenced. Regular endurance exercise influenced the in vitro production of monocyte derived cytokines, while the effect of exercise on the cytokines synthesized by T-cells appeared to be of lesser importance.     

Effect of sodium citrate on performance and metabolism of human skeletal muscle during supramaximal cycling exercise

The aim of this study was to examine whether the alkalosis-induced improvement in supramaximal performance could be explained by a less-altered muscle metabolic status. Eight subjects first performed exhausting exercise at 120% peak oxygen uptake after ingesting either a placebo (PLC) or sodium citrate (CIT) at a dose of 0.5 g · kg^?1 body mass to determine exhaustion time (t _exh). They then, performed exercise (Lim-EX) at the same relative intensity lasting PLCt _exh minus 20 s in both treatments. Samples were taken from vastus lateralis muscle at rest (90-min after the ingestion) and at the end of Lim-EX. Arterial blood samples were obtained at rest (immediately prior to and 90 min after ingesting the drug) and during the 20-min post-exercise recovery. The t _exh was significantly increased by CIT [PLC 258 (SD 29) s, CIT 297 (SD 45) s]. The CIT raised the rest [citrate] in blood [PLC 0.11 (SD 0.01) mmol · l^?1, CIT 0.34 (SD 0.07) mmol · l^?1] and in muscle [PLC 0.78 (SD 0.23) mmol · kg^?1 dry mass, CIT 1.00 (SD 0.21) mmol · kg^?1 dry mass]. Resting muscle pH and buffering capacity were unchanged by CIT. The same fall in muscle pH was observed during Lim-EX in the two conditions. This was associated with similar variations in both the cardio-respiratory response and muscle energy and metabolism status in spite of a better blood acid-base status after CIT. Thus, CIT would not seem to allow the alkalinization of the muscle cytosolic compartment. Though sodium citrate works in a similar way to NaHCO₃ on plasma alkalinization and exercise performance, the exact nature of the mechanisms involved in the delay of exhaustion could be different and remains to be elucidated.     

Sex-related differences in thermoregulatory responses while wearing protective clothing

This study examined the thermoregulatory responses of men (group M) and women (group F) to uncompensable heat stress. In total, 13?M [mean (SD) age 31.8 (4.7) years, mass 82.7 (12.5)?kg, height?1.79?(0.06)?m, surface area to mass ratio 2.46?(0.18)?m²?·?kg^?1?·?10^?2, Dubois surface area 2.01 (0.16)?m², %body fatness 14.6 (3.9)%, V˙O_2peak 49.0?(4.8)?ml?·?kg^?1?·?min^?1] and 17 F [23.2 (4.2) years, 62.4 (7.7)?kg, 1.65 (0.07)?m, 2.71 (0.14)?m²?·?kg^?1?·?10^?2, 1.68 (0.13)?m², 20.2 (4.8)%, 43.2 (6.6)?ml?·?kg^?1?·?min^?1, respectively] performed light intermittent exercise (repeated intervals of 15?min of walking at 4.0?km?·?h^?1 followed by 15?min of seated rest) in the heat (40°C, 30% relative humidity) while wearing nuclear, biological, and chemical protective clothing (0.29?m²?·°C · W^?1 or 1.88 clo, Woodcock vapour permeability coefficient 0.33?i _m). Group F consisted of eight non-users and nine users of oral contraceptives tested during the early follicular phase of their menstrual cycle. Heart rates were higher for F throughout the session reaching 166.7 (15.9) beats?·?min^?1 at 105?min (n?=?13) compared with 145.1 (14.4)?beats?·?min^?1 for M. Sweat rates and evaporation rates from the clothing were lower and average skin temperature ( ) was higher for F. The increase in rectal temperature (T _re) was significantly faster for the F, increasing 1.52 (0.29)°C after 105?min compared with an increase of 1.37?(0.29)°C for M. Tolerance times were significantly longer for M [142.9?(24.5)?min] than for F [119.3?(17.3)?min]. Partitional calorimetric estimates of heat storage (S) revealed that although the rate of S was similar between genders [42.1?(6.6) and 46.1?(9.7) W?·?m^?2 for F and M, respectively], S expressed per unit of total mass was significantly lower for F [7.76?(1.44)?kJ?·?kg^?1] compared with M [9.45?(1.26) kJ?·?kg^?1]. When subjects were matched for body fatness (n?=?8?F and 8?M), tolerance times [124.5?(14.7) and 140.3?(27.4)?min for F and M, respectively] and S [8.67?(1.44) and 9.39?(1.05)?kJ?·?kg^?1 for F and M, respectively] were not different between the genders. It was concluded that females are at a thermoregulatory disadvantage compared with males when wearing protective clothing and exercising in a hot environment. This disadvantage can be attributed to the lower specific heat of adipose versus non-adipose tissue and a higher percentage body fatness.     

Water immersion delays the oxygen uptake response to sitting arm-cranking in humans

We investigated the effect of central hypervolaemia during water immersion up to the xiphoid process on the oxygen uptake (V˙O₂) and heart rate (HR) response to arm cranking. Seven men performed a 6-min arm-cranking exercise at an intensity requiring a V˙O₂ at 80% ventilatory threshold both in air [C trial, 29 (SD 9)?W] and immersed in water [WI trial, 29 (SD 11)?W] after 6 min of sitting. The V˙O₂ (phase 2) and HR responses to exercise were obtained from a mono-exponential fit [f(t)=baseline+gain·(1?e^{?( t ? TD )/})]. The response was evaluated by the mean response time [MRT; sum of time constant () and time delay (TD)]. No significant difference in V˙O₂ and HR gains between the C and WI trials was observed [V˙O₂ 0.78 (SD 0.1) vs 0.80 (SD 0.2) l?·?min^?1, HR 36 (SD 7) vs 37 (SD 8) beats?·?min^?1, respectively]. Although the HR MRT was not significantly different between the C and WI trials [17 (SD 3), 19 (SD 8)?s, respectively), V˙O₂ MRT was greater in the WI trial than in the C trial [40 (SD 6), 45 (SD 6)?s, respectively; P<0.05]. Assuming no difference in V˙O₂ in active muscle between the two trials, these results would indicate that an increased oxygen store and/or an altered response in muscle blood distribution delayed the V˙O₂ response to exercise.     

Does erythrocyte infusion improve 3.2-km run performance at high altitude?

The purpose of this study was to determine whether there are differences in the effects of exercise training between those with a parental history of hypertension and those without such a history. A group of 39 middle-aged hypertensive women were submitted to a 4-month exercise training programme. On the basis of their family histories, 18 individuals were classified as those having a positive parental history of hypertension (group P) and 21 individuals as those without such a history (group N). Both groups participated in a supervised training programme with the intensity set at the level producing the threshold lactate concentration for 90–120?min twice a week, together with self-determined aerobic exercise three times a week. Vital age was estimated to determine the health-fitness status. At the end of the training, group N exhibited reductions in the systolic and diastolic blood pressures at rest (12.6/8.0?mmHg) and increases in the peak oxygen uptake [V˙O_2peak 21.1 (SD 5.2) vs 25.2 (SD 5.7) ml · kg^?1· min^?1] and oxygen uptake corresponding to lactate threshold [13.7 (SD 2.4) vs 17.0 (SD 2.0) ml?·?kg^?1?·?min^?1; P?P?V˙O_2peak (P?>?0.05). There were no changes in the blood lipid and haematocrit variables in either group. The vital age decreased by approximately 4 and 7?years (P?相似文献   

Walking performance and economy in chronic heart failure patients pre and post exercise training

The effect of a 3-week exercise programme on performance and economy of walking was analysed in 16 male patients with chronic heart failure [mean age 51.8 (SD 6.9) years, height 174.9 (SD 6.3) cm, body mass 75.3 (SD 11.5) kg, ejection fraction 20.8 (SD 5.0)%]. They were submitted to a cardiopulmonary exercise test on a cycle ergometer and a 6-min walking test on a treadmill before and after the period of exercise training. The training programme consisted of interval cycle (five times a week for 15 min), and treadmill ergometer training (three times a week for 10 min) at approximately 70% cycling peak oxygen uptake ( O_2peak) and supplementary exercises (three times a week for 20 min). Compared to the pre values cycling O_2peak [11.9 (SD 2.9) vs 14.0 (SD 2.3) ml?·? kg^–1?·?min^–1], maximal self paced walking speed [0.68 (SD 0.33) vs 1.16 (SD 0.30) m?·?s^–1], and net walking power [2.16 (SD 0.89) vs 2.73 (SD 0.91) W?·?kg^–1] had increased (P?–1?·? m^–1] had decreased (P?相似文献   

Effect of circulatory occlusion on human muscle metabolism during exercise and recovery

To assess muscle metabolism and inorganic phosphate (P_i) peak splitting during exercise, 31-phosphorus nuclear magnetic resonance spectroscopy was performed during ramp incremental and submaximal step exercise with and without circulatory occlusion. Seven healthy men performed calf flexion in a superconducting magnet. There was no P_i splitting during ramp incremental exercise with the circulation present and phosphocreatine (PCr) decreased linearly by 0.07 (SEM 0.01) mmol?·?l^?1?·?s^?1, while exercise with the circulation occluded caused the P_i peak to split into a high and a low pH peak. The rate of PCr decrease during exercise with the circulation occluded was 0.15 (SEM 0.03) mmol?·?l^?1?·?s^?1 which with the efficiency of the adenosine 5′-triphosphate (ATP) hydrolysis reaction corresponded well to the mechanical energy. Both with and without occlusion of the circulation PCr decreased with some time lag which may reflect the consumption of residual oxygen. In submaximal step exercise PCr decreased exponentially at the onset of exercise with the circulation open whereas it decreased linearly by 0.15?mmol?·?l^?1?·?s^?1 when the circulation was occluded. After exercise, occlusion of the circulation was maintained for 1 min more and there was no PCr resynthesis. It is suggested that ATP synthesis was limited by the availability of oxygen.