Effects of aerobic exercise on the torque-velocity relationship in cycling

The kinetics of the torque-velocity (T-ω) relationship after aerobic exercise was studied to assess the effect of fatigue on the contractile properties of muscle. A group of 13 subjects exercised until fatigued on a cycle ergometer, at an intensity which corresponded to 60% of their maximal aerobic power for 50 min (MAP60%); ten subjects exercised until fatigued at 80% of their maximal aerobic power for 15 min (MAP80%). Of the subjects 7 exercised at both intensities with at least a 1-week interval between sessions. Pedalling rate was set at 60?rpm. The T-ω relationship was determined from the velocity data collected during all-out sprints against a 19?N?·?m braking torque on the same ergometer, according to a method proposed previously. Maximal theoretical velocity (ω₀) and maximal theoretical torque (T ₀) were estimated by extrapolation of the linear T-ω relationship. Maximal power (P _max) was calculated from the values of T ₀ and ω₀ (P _max?=?0.25 ω₀?T ₀). The T-ω relationships were determined before, immediately after and 5 and 10?min after the aerobic exercise. The kinetics of ω₀, T ₀ and P _max was assumed to express the effects of fatigue on the muscle contractile properties (maximal shortening velocity, maximal muscle strength and maximal power). Immediately after exercise at MAP60% a 7.8% decrease in T ₀ and 8.8% decrease in P _max was seen while the decrease in ω₀ was nonsignificant, which suggested that P _max decreased in the main because of a loss in maximal muscle strength. In contrast, MAP80% induced a 8.1% decrease in ω₀ and 12.8% decrease in P _max while the decrease in T ₀ was nonsignificant, which suggested that the main cause of the decrease in P _max was probably a slowing of maximal shortening velocity. The short recovery time of the T-ω relationship suggests that the causes of the decrease of torque and velocity are processes which recover rapidly.     

Effect of fatigue on maximal velocity and maximal torque during short exhausting cycling

A group of 24 subjects performed on a cycle ergometer a fatigue test consisting of four successive all-out sprints against the same braking torque. The subjects were not allowed time to recover between sprints and consequently the test duration was shorter than 30 s. The pedal velocity was recorded every 10 ms from a disc fixed to the flywheel with 360 slots passing in front of a photo-electric cell linked to a microcomputer which processed the data. Taking into account the variation of kinetic energy of the ergometer flywheel, it was possible to determine the linear torque-velocity relationship from data obtained during the all-out cycling exercise by computing torque and velocity from zero velocity to peak velocity according to a method proposed previously. The maximal theoretical velocity (₁) and the maximal theoretical torque (T ₁) were estimated by extrapolation of each torque-velocity relationship. Maximal power (P _max) was calculated from the values of T ₀ and ₀ (P _max = 0.25₀ T ₀). The kinetics of ₀, T ₀ and P _max was assumed to express the effects of fatigue on the muscle contractile properties (maximal shortening velocity, maximal muscle strength and maximal power). Fatigue induced a parallel shift to the left of the torque-velocity relationships. The ₀, T ₀ and P _max decreases were equal to 16.3%, 17.3% and 31%, respectively. The magnitude of the decrease was similar for ₀ and T ₀ which suggested that P _max decreased because of a slowing of maximal shortening velocity as well as a loss in maximal muscle strength. However, the interpretation of a decrease in cycling ₀ which has the dimension of a maximal cycling frequency is made difficult by the possible interactions between the agonistic and the antagonistic muscles and could also be explained by a slowing of the muscle relaxation rate.     

Torque-velocity relationship during cycle ergometer sprints with and without toe clips

The torque-velocity relationship in cycling has been studied during all-out sprints (n?=?6 subjects) with and without toe clips on an electronic Lode ergometer with strain gauges, to estimate the importance of the expected decrease in torque, velocity and power output. As previously found with different cycling protocols, the torque-velocity relationship was linear for all-out sprints with toe clips. A similar relationship was observed when cycling without toe clips but the torque-velocity relationship was inflected downwards at low or high velocities in several subjects who were not regular cyclists. The pulling action during the rise of the pedal at low velocities cannot explain why the torque-velocity relationship is not hyperbolic for cycling exercises with toe clips because similar relationships were observed without toe clips. The maximal power output was significantly higher during cycling with toe clips (782?W vs 668?W, P?T ₀ (138 N?·?m vs 122 N?·?m, P<0.05). In contrast, the maximal extrapolated velocity, V ₀ and peak velocity were not significantly improved by the use of toe clips. The comparison of the angle-torque patterns at low and high velocities suggested that the kinetic energy of the legs can be transformed into power output when cycling without toe clips as well as it can when cycling with toe clips.     

The effect of ambient temperature and exercise intensity on post-exercise thermal homeostasis

We have previously demonstrated a prolonged (65?min or longer) elevated plateau of esophageal temperature (T _es ) (0.5–0.6°C above pre-exercise values) in humans following heavy dynamic exercise (70% maximal oxygen consumption, V˙O_2max) at a thermoneutral temperature (T _a) of 29°C. The elevated T _es value was equal to the threshold T _es at which active skin vasodilation was initiated during exercise (Th_dil). A subsequent observation, i.e., that successive exercise/recovery cycles (performed at progressively increasing pre-exercise T _es levels) produced parallel increases of Th_dil and the post-exercise T _es, further supports a physiological relationship between these two variables. However, since all of these tests have been conducted at the same T _a (29°C) and exercise intensity (70% V˙O_2max) it is possible that the relationship is limited to a narrow range of T _a/exercise intensity conditions. Therefore, five male subjects completed 18?min of treadmill exercise followed by 20?min of recovery in the following T _a/exercise intensity conditions: (1) cool with light exercise, T _a?=?20°C, 45% V˙O_2max (CL); (2) temperature with heavy exercise, T _a?=?24°C, 75% O_{2 max} (TH); (3) warm with heavy exercise, T _a?=?29°C, 75% V˙O_2max (WH); and (4) hot with light exercise, T _a?=?40°C, 45% V˙O_2max (HL). An abrupt decrease in the forearm-to-finger temperature gradient (T _fa??T _fi) was used to identify the Th_dil during exercise. Mean pre-exercise T _es values were 36.80, 36.60, 36.72, and 37.20°C for CL, TH, WH, and HL conditions respectively. T _es increased during exercise, and end post-exercise fell to stable values of 37.13, 37.19, 37.29, and 37.55°C for CL, TH, WH, and HL trials respectively. Each plateau value was significantly higher than pre-exercise values (P?dil values (i.e., 37.20, 37.23, 37.37, and 37.48°C for CL, TH, WH, and HL) were comparable to the post-exercise T _es values for each condition. The relationship between Th_dil and post-exercise T _es remained intact in all T _a/exercise intensity conditions, providing further evidence that the relationship between these two variables is physiological and not coincidental.     

Determination of the velocity associated with the longest time to exhaustion at maximal oxygen uptake

The so-called velocity associated with V˙O_2max, defined as the minimal velocity which elicits V˙O_2max in an incremental exercise protocol (v _{V˙ O2max}), is currently used for training to improve V˙O_2max. However, it is well known that it is not the sole velocity which elicits V˙O_2max and it is possible to achieve V˙O_2max at velocities lower and higher than v _{V˙ O2max}. The goal of this study was to determine the velocity which allows exercise to be maintained the longest time at V˙O_2max. Using the relationship between time to exhaustion at V˙O_2max in the all-out runs at 90%, 100%, 120% and 140% of v _{V˙ O2max} and distance run at V˙O_2max, the velocity which elicits the longest time to exhaustion at V˙O_2max (CV′) was determined. For the six subjects tested (physical education students), this velocity was not significantly different from v _{V˙ O2max} (16.96?±?0.92?km?·?h^?1 vs 17.22?± 1.12?km?·?h^?1, P?=?0.2 for CV′ and v _{V˙ O2max}, respectively) and these two velocities were correlated (r?=?0.88, P?=?0.05).     

Effectiveness of low-frequency vibration recovery method on blood lactate removal,muscle contractile properties and on time to exhaustion during cycling at <Emphasis Type="Italic">V</Emphasis>O<Subscript>2max</Subscript> power output

The aim of the study was to determine the effectiveness of low-frequency vibration recovery (LFV-rec) on blood lactate removal, muscle contractile properties, and on time to exhaustion during cycling at maximal oxygen uptake power output (pVO_2max). Twelve active males carried out three experimental sessions. In session 1, participant’s maximal oxygen uptake (VO_2max) and pVO_2max were determined, and in sessions 2 and 3, the participants performed a fatiguing exercise (2 min of cycling at pVO_2max) and then a 15 min recovery period using one of two different methods: LFV-rec which consisted on sitting with feet on the vibratory platform (20 Hz; 4 mm) and passive recovery (P-rec), sitting without vibration stimulus. After that, participants performed an all-out exercise test on cycle ergometer at pVO_2max. In the recovery period, variables such as heart rate (HR), blood lactate concentration [Lac], and tensiomyographic parameters (D _m: maximal radial displacement; T _s: time of contraction maintenance, and T _r: relaxation time) were measured. In an all-out exercise test, mean time to exhaustion (TTE), total distance covered (TD), mean cycling velocity (V _m), and maximal HR (HR_max) were also assessed. The results showed no effect of recovery strategy on any of the assessed variables; nevertheless, higher values, although not significant, were observed in TTE, TD, and V _m after LFV-rec intervention. In conclusion, LFV-rec strategy applied during 15 min after short and intense exercise does not seem to be effective on blood lactate removal, muscle contractile properties, and on time to exhaustion during cycling at pVO_2max.     

Relationship in humans between spontaneously chosen crank rate and power output during upper body exercise at different levels of intensity

The aim of this study was to assess the relationship between spontaneously chosen crank rate (SCCR) and power output during two upper body exercise tests: firstly, an incremental maximal aerobic power test (T₁), with an initial intensity of 50?W followed by 15-W increases at each subsequent 90-s stage and secondly, a test (T₂) with consecutive exercise periods set at 50%, 60%, 70%, 80%, 110% and 120% of maximal power (P _max) separated by passive recovery periods. Eight nationally and internationally ranked kayakers, aged 20 (SD 2) years, performed the tests. During both T₁ and T₂, mean SCCR values were correlated (r?=?1) and increased significantly (P?1 suggests that it may be used to predict the crank rate which will be chosen in upper body exercise, whatever the intensity. Finally, the results of testing at 110% and 120% of P _max would suggest that a high crank rate (>90?rpm) should be used during the test procedure using supramaximal exercises where accumulated oxygen deficit is calculated, and more particularly when exercise is performed using the upper body.     

Impact of three different types of exercise on components of the inflammatory response

It was hypothesized that muscle injury would be greater with eccentric than with all-out or prolonged exercise, and that immune changes might provide an indication that supplements the information provided by traditional markers such as creatine kinase (CK) or delayed-onset muscle soreness. Eight healthy males [mean (SE): age?=?24.9?(2.3) years, maximum oxygen consumption (V˙O_2max)=43.0?(3.1)?ml?·?kg^?1?·?min^?1] were each assigned to four experimental conditions, one at a time, using a randomized-block design: 5?min of cycle ergometer exercise at 90% V˙O_2max (AO), a standard circuit-training routine (CT), 2?h cycle ergometer exercise at 60% V˙O_2max (Long), or remained seated for 5?h. Blood samples were analyzed for CK, natural killer (NK) cell counts (CD3^?/CD16⁺56⁺), cytolytic activity and plasma levels of the cytokines interleukin (IL)-6, IL-10, and tissue necrosis factor α (TNF-α). CK levels were only elevated significantly 72?h following CT. NK cell counts increased significantly during all three types of exercise, but returned to pre-exercise baseline values within 3?h of recovery. Cytolytic activity per NK cell was not significantly modified by any type of exercise. Prolonged exercise induced significant increases in plasma IL-6 and TNF-α. We conclude that the lack of correlation between traditional markers of muscle injury (plasma CK concentrations and muscle soreness rankings) and immune markers of the inflammatory response suggests that, for the types and intensities of exercise examined in this study, the exercise-induced inflammatory response is modified by humoral and cardiovascular correlates of exercise.     

Rectal and esophageal temperatures during upper- and lower-body exercise

This study investigated the question: is core temperature measurement influenced by whether exercise involves predominantly upper- or lower-body musculature? Healthy men were allocated to three groups: treadmill ergometry (T) n=4, cycle ergometry (C) n=6 and arm crank ergometry (AC) n=5. Subjects underwent an incremental exercise test to exhaustion on an exercise-specific ergometer to determine maximum/peak oxygen consumption (V˙O_2max). One week later subjects exercised for 36?min on the same ergometer at approximately 65% V˙O_2max while temperatures at the rectum (T _re) and esophagus (T _es) were simultaneously measured. The V˙O_2max (l?·?min^?1) for groups T [4.76 (0.50)] and C [4.35 (0.30)] was significantly higher than that for the AC group [2.61 (0.24)]. At rest, T _re was significantly higher than T _es in all groups (P<0.05). At the end of submaximal exercise in the C group, T _re [38.32 (0.11)°C] was significantly higher than T _es [38.02 (0.12)°C, P<0.05]. No significant differences between T _re and T _es at the end of exercise were noted for AC and T groups. The temperature difference (T _diff) between T _re and T _es was dissimilar at rest in the three groups; however, by the end of exercise T _diff was approximately 0.2°C for each of the groups, suggesting that at the end of steady-state exercise T _re can validly be used to estimate core temperature.     

The influence of maximal aerobic power on recovery of skeletal muscle following anaerobic exercise

Phosphorus magnetic resonance spectroscopy (³¹P-MRS) was used to investigate the influence of maximal aerobic power (˙VO _2max) on the recovery of human calf muscle from high-intensity exercise. The (˙VOO_2max) of 21 males was measured during treadmill exercise and subjects were assigned to either a low-aerobic-power (LAP) group (n?=?10) or a high-aerobic-power (HAP) group (n?=?11). Mean (SE) ˙VO _2max of the groups were 46.6 (1.1) and 64.4 (1.4) ml?·?kg^?1?·?min^?1, respectively. A calf ergometry work capacity test was used to assign the same relative exercise intensity to each subject for the MRS protocol. At least 48 h later, subjects performed the rest (4 min), exercise (2 min) and recovery (10 min) protocol in a 1.5 T MRS scanner. The relative concentration of phosphocreatine (PCr) was measured throughout the protocol and intracellular pH (pH_i) was determined from the chemical shift between inorganic phospate (P_i) and PCr. End-exercise PCr levels were 27 (3.4) and 25 (3.5)% of resting levels for LAP and HAP respectively. Mean resting pH_i was 7.07 for both groups, and following exercise it fell to 6.45 (0.04) for HAP and 6.38 (0.04) for LAP. Analysis of data using non-linear regression models showed no differences in the rate of either PCr or pH_i recovery. The results suggest that ˙VO_2max is a poor predictor of metabolic recovery rate from high-intensity exercise. Differences in recovery rate observed between individuals with similar ˙VO_2max imply that other factors influence recovery.     

Intense exercise increases the post-exercise threshold for sweating

We demonstrated previously that esophageal temperature (T _es) remains elevated by ≈0.5°C for at least 65?min after intense exercise. Following exercise, average skin temperature (T _avg) and skin blood flow returned rapidly to pre-exercise values even though T _es remained elevated, indicating that the T _es threshold for vasodilation is elevated during this period. The present study evaluates the hypothesis that the threshold for sweating is also increased following intense exercise. Four males and three females were immersed in water (water temperature, T _w?=?42°C) until onset of sweating (Immersion 1), followed by recovery in air (air temperature, T _a?=?24°C). At a T _a of 24°C, 15?min of cycle ergometry (70% VO_2max) (Exercise) was then followed by 30?min of recovery. Subjects were then immersed again (T _w?=?42°C) until onset of sweating (Immersion 2). Baseline T _es and T _skavg were 37.0 (0.1)°C and 32.3 (0.3)°C, respectively. Because the T _skavg at the onset of sweating was different during Exercise [30.9 (0.3)°C] than during Immersion 1 and Immersion 2 [36.8 (0.2)°C and 36.4 (0.2)°C, respectively] a corrected core temperature, T _es (calculated), was calculated at a single designated skin temperature, T _{sk(designated)}, as follows: T _{es(calculated)}?=?T _es?+?[β/(1?β)][T _skavg?T _{sk(designated)}]. The T _{sk(designated)} was set at 36.5°C (mean of Immersion 1 and Immersion 2 conditions) and β represents the fractional contribution of T _skavg to the sweating response (β for sweating?=?0.1). While T _{es(calculated)} at the onset of sweating was significantly lower during exercise [36.7 (0.2)°C] than during Immersion 1 [37.1 (0.1)°C], the threshold of sweating during Immersion 2 [37.3 (0.1)°C] was greater than during both Exercise and Immersion 1 (P?相似文献   

Maximal power and torque-velocity relationship on a cycle ergometer during the acceleration phase of a single all-out exercise

Seven subjects pedalled on a Monark cycle ergometer as fast as possible for approximately 7 s against four different resistances which corresponded to braking torques (T _B) equal to 19, 38, 57 and 76 N · m at the crank level. Exercise periods were separated by 5-min recovery periods. Pedal velocity was recorded every 50 ms by means of a disc with 360 slots fixed on the flywheel, passing in front of a photo-electric cell linked to a microcomputer which processed the data. Every 50 ms, the time necessary to perform half a pedal revolution (t _1/2) was computed by adding the 50-ms periods necessary to reach 669 slots (the number of slots corresponding to half a pedal revolution). To measuret _1/2 to an accuracy better than 50 ms, this time was computed by a linear interpolation of the time-slot number relationship. Power (P) was averaged duringt ₁₂ by adding the power dissipated against braking torque and the power necessary to accelerate the flywheel. The torque-velocity (T-) relationship was studied during the acceleration phase of a sprint against a single TB by computing every 50 ms the relationship between and T (N · m), equal to the sum ofT _B and the torque necessary to accelerate the flywheel at the same time. The T- relationships calculated from the acceleration phase of a single all-out exercise were linear and similar to the previously described relationships between peak velocity and braking force. These relationships can be expressed as follows: = _0,acc (1 –T/T _0,acc) where is pedal velocity,T the torque exerted on the crank andT _0,acc and _0,acc have the dimensions of maximal torque and maximal velocity respectively. Based on this model, maximal power (P _max,acc) is calculated as 0.257_{0, acc} T _{0, acc}. Maximal powerP _max,acc measured with the acceleration method was independent of braking torqueT _B and slightly higher thanP _max calculated from the relationship between peak velocity andT _B.     

Effect of exercise intensity on post-exercise oxygen consumption and heart rate recovery

Purpose

There is some evidence that measures of acute post-exercise recovery are sensitive to the homeostatic stress of the preceding exercise and these measurements warrant further investigation as possible markers of training load. The current study investigated which of four different measures of metabolic and autonomic recovery was most sensitive to changes in exercise intensity.

Methods

Thirty-eight moderately trained runners completed 20-min bouts of treadmill exercise at 60, 70 and 80 % of maximal oxygen uptake (VO_2max) and four different recovery measurements were determined: the magnitude of excess post-exercise oxygen consumption (EPOC_MAG), the time constant of the oxygen consumption recovery curve (EPOCτ), heart rate recovery within 1 min (HRR_60s) and the time constant of the heart rate recovery curve (HRRτ) .

Results

Despite significant differences in exercise parameters at each exercise intensity, only EPOC_MAG showed significantly slower recovery with each increase in exercise intensity at the group level and in the majority of individuals. EPOCτ was significantly slower at 70 and 80 % of VO_2max vs. 60 % VO_2max and HRRτ was only significantly slower when comparing the 80 vs. 60 % VO_2max exercise bouts. In contrast, HRR_60s reflected faster recovery at 70 and 80 % of VO_2max than at 60 % VO_2max.

Conclusion

Of the four recovery measurements investigated, EPOC_MAG was the most sensitive to changes in exercise intensity and shows potential to reflect changes in the homeostatic stress of exercise at the group and individual level. Determining EPOC_MAG may help to interpret the homeostatic stress of laboratory-based research trials or training sessions.     

Serum hormone and myocellular protein recovery after intermittent runs at the velocity associated with V˙O2max

The responses of serum myocellular proteins and hormones to exercise were studied in ten well-trained middle-distance runners [maximal oxygen consumption (V˙O_2max)?=?69.4?(5.1)?ml?·?kg^?1?·?min^?1] during 3 recovery days and compared to various measures of physical performance. The purpose was to establish the duration of recovery from typical intermittent middle-distance running exercises. The subjects performed, in random, order two 28-min treadmill running exercises at a velocity associated with V˙O_2max: 14 bouts of 60-s runs with 60?s of rest between each run (IR₆₀) and 7 bouts of 120-s runs with 120?s of rest between each run (IR₁₂₀). Before the exercises (pre- exercise), 2?h after, and 1, 2 and 3 days after the exercises, the same series of measurements were performed, including those for serum levels of the myocellular proteins creatine kinase, myoglobin and carbonic anhydrase III (S-CK, S-Mb and S-CA III, respectively), serum hormones testosterone, Luteinizing hormone, follicle-stimulating hormone and cortisol (S-testosterone, S-LH, S-FSH and S-cortisol, respectively) and various performance parameters: maximal vertical jump height (CMJ) and stride length, heart rate and ratings of perceived exertion during an 8-min run at 15?km?·?h^?1 (SL_15?km·h?1, HR_15?km?·?h?1 and RPE_15?km?·?h?1, respectively). Two hours after the end of both exercise bouts the concentration of each measured serum protein had increased significantly (P?15?km?·?h?1 or CMJ. During the recovery days only S-CK was significantly raised (P?P?15?km?·?h?1 (P?120 the post-exercise responses returned to their pre-exercise levels within the 3 days of recovery. The present findings suggest that a single 28-min intermittent middle-distance running exercise does not induce changes in serum hormones of well-trained runners during recovery over 3 days, while changes in S-CK, CMJ and RPE_15?km?·?h?1 indicate that 2–3 days of light training may be needed before the recovery at muscle level is complete.     

Effects of heat acclimation on endurance capacity and prolactin response to exercise in the heat

We examined the effect of heat acclimation (HA) on endurance capacity and blood prolactin (PRL) response to moderate intensity exercise in the heat in young male subjects (n?=?21). Three exercise tests (ET) were completed on a treadmill: H1 (walk at 60% VO₂peak until exhaustion at 42°C), N (walk at 22°C; duration equal to H1) and H2 (walk until exhaustion at 42°C after a 10-day HA program). Heart rate (HR), skin (T _sk) and core (T _c) temperatures and body heat storage (HS) were measured. Blood samples were taken immediately before, during and immediately after each ET. HA resulted in lower HR, T _sk, T _c and HS rate (P?<?0.05) during ET, whereas endurance capacity increased from 88.6?±?27.5?min in H1 to 162.0?±?47.8?min in H2 (P?<?0.001). Blood PRL concentration was lower (P?<?0.05) during exercise in H2 compared to H1 but the peak PRL level observed at the time of exhaustion did not differ in the two trials. Blood PRL concentration at 60?min of exercise in H1 correlated with time to exhaustion in H1 (r?=?–0.497, P?=?0.020) and H2 (r?=?–0.528, P?=?0.014). In conclusion, HA slows down the increase in blood PRL concentration but does not reduce the peak PRL level occurring at the end of exhausting endurance exercise in the heat. Blood PRL response to exercise in the heat in non-heat-acclimated subjects is associated with their endurance capacity in the heat in a heat-acclimated state.     

Relevance of individual characteristics for human heat stress response is dependent on exercise intensity and climate type

Multiple heterogeneous groups of subjects (both sexes and a wide range of maximal oxygen uptake V˙O_{2 max} , body mass, body surface area (A _D),% body fat, and A _D/mass coefficient) exercised on a cycle ergometer at a relative (%V˙O_2max, REL) or an absolute (60?W) exercise intensity in a cool (CO 21°C, 50% relative humidity), warm humid (WH 35°C, 80%) and a hot dry (HD 45°C, 20%) environment. Rectal temperature (T _re) responses were analysed for the influence of the individual's characteristics, environment and exercise intensity. Exposures consisted of 30-min rest, followed by 60-min exercise. The T _re was negatively correlated with mass in all conditions. Body mass acted as a passive heat sink in all the conditions tested. While negatively correlated with V˙O_{2 max} and V˙O_{2 max} per kilogram body mass in most climates, T _re was positively correlated with V˙O_{2 max} and V˙O_{2 max} per kilogram body mass in the WH/REL condition. Thus, when evaporative heat loss was limited as in WH, the higher heat production of the fitter subjects in the REL trials determined T _re and not the greater efficiency for heat loss associated with high V˙O_{2 max} . Body fatness significantly affected T _re only in the CO condition, where, with low skin blood flows (measured as increases in forearm blood flow), the insulative effect of fat was pronounced. In the warmer environments, high skin blood flows offset the resistance offered by peripheral adipose tissue. Contrary to other studies, T _re was positively correlated with A _D/mass coefficient for all conditions tested. For both exercise types used, being big (a high heat loss area and heat capacity) was apparently more beneficial from a heat strain standpoint than having a favourable A _D/mass coefficient (high in small subjects). The total amount of variance in T _re responses which could be attributed to individual characteristics was dependent on the climate and the type of exercise. Though substantial for absolute exercise intensities (52%–58%) the variance explained in T _re differed markedly for relative intensities: 72% for the WH climate with its limited evaporative capacity, and only 10%–26% for the HD and CO climates. The results showed that individual characteristics play a significant role in determining the responses of body core temperature in all conditions tested, but their contribution was low for relative exercise intensities when evaporative heat loss was not restricted. This study demonstrated that effects of individual characteristics on human responses to heat stress cannot be interpreted without taking into consideration both the heat transfer properties of the environment and the metabolic heat production resulting from the exercise type and intensity chosen. Their impact varies substantially among conditions.     

Effect of ambient temperature on endurance performance while wearing cross-country skiing clothing

This study assessed the effects of exposure to cold (?14 and ?9?°C), cool (?4 and 1?°C) and moderate warm (10 and 20?°C) environments on aerobic endurance performance-related variables: maximal oxygen consumption (VO_2max), running time to exhaustion (TTE), running economy and running speed at lactate threshold (LT). Nine male endurance athletes wearing cross-country ski racing suit performed a standard running test at six ambient temperatures in a climatic chamber with a wind speed of 5?m?s^?1. The exercise protocol consisted of a 10-min warm-up period followed by four submaximal periods of 5?min at increasing intensities between 67 and 91?% of VO_2max and finally a maximal test to exhaustion. During the time course mean skin temperature decreased significantly with reduced ambient temperatures whereas T _re increased during all conditions. T _re was lower at ?14?°C than at ?9 and 20?°C. Running economy was significantly reduced in warm compared to cool environments and was also reduced at 20?°C compared to ?9?°C. Running speed at LT was significantly higher at ?4?°C than at ?9, 10 and 20?°C. TTE was significantly longer at ?4 and 1?°C than at ?14, 10 and 20?°C. No significant differences in VO_2max were found between the various ambient conditions. The optimal aerobic endurance performance wearing a cross-country ski racing suit was found to be ?4 and 1?°C, while performance was reduced under moderate warm (10 and 20?°C) and cold (?14 and ?9?°C) ambient conditions.     

Influence of short-term aerobic training and hydration status on tolerance during uncompensable heat stress

The purpose of the present study was to determine the separate and combined effects of a short-term aerobic training program and hypohydration on tolerance during light exercise while wearing nuclear, biological, and chemical protective clothing in the heat (40°C, 30% relative humidity). Males of moderate fitness [<50?ml?·?kg^?1?·?min^?1 maximal O₂ consumption (V˙O_{2 max} )] were tested while euhydrated or hypohydrated by ≈2% of body weight through exercise and fluid restriction the day preceding the trials. Tests were conducted before and after either a 2-week program of daily aerobic training (1?h treadmill exercise at 65% V˙O_{2 max} for 12 days; n?=?8) or a control period (n?=?7), which had no effect on any measured variable. The training increased V˙O_{2 max} by 6.5%, while heart rate (f _c) and the rectal temperature (T _re) rise decreased during exercise in a thermoneutral environment. In the heat, training resulted in a decreased skin temperature and increased sweat rate, but did not affect f _c, T _re or tolerance time (TT). In both training and control groups, hypohydration significantly increased T _re and f _c and decreased the TT. It was concluded that the short-term aerobic training program had no benefit on exercise-heat tolerance in this uncompensable heat stress environment.     

Effect of immobilization and retraining on torque-velocity relationship of human knee flexor and extensor muscles

The effect of 2 weeks immobilization of the uninjured right knee and 10 weeks of retraining on muscle torque-velocity characteristics was investigated in nine young subjects. Left and right knee extension and flexion maximal voluntary isometric torque (T_max) and dynamic torque at 60°·s^–1 (T₆₀) and 180°·s^–1 (T₁₈₀) were measured before (PRE) and after immobilization (POST) and after 3 (R3) and 10 (R10) weeks of dynamic retraining. The torque-velocity relationship was quantified by expressing T₆₀ and T₁₈₀ relative to T_max (NT₆₀ and NT₁₈₀, respectively). For the right extensor muscles, percutaneous biopsy samples were obtained from the vastus lateralis muscle and fibre type distribution was measured. POST extension and flexion torque (mean of T_max, T₆₀ and T₁₈₀) decreased by 27% and 11%, respectively. During the course of the experiment, the changes in NT₆₀ and NT₁₈₀ were similar. POST extensor muscle NTV (mean of NT₆₀ and NT₁₈₀) was decreased significantly (12%, P<0.05), but no significant change was found for flexor muscle NTV (+3%). At R3 T_max, dynamic torque and NTV were restored to normal. Unlike isometric torque, NTV did not change from R3 to R10. No changes in fibre type distribution were found. The adaptation of muscle length is suggested as the mechanism to explain the change in NTV. Electronic Publication