Limitation of muscle deoxygenation in the triceps during incremental arm cranking in women

The present study investigated the difference in oxygen kinetics in the exercising muscle between arm cranking and leg cycling in women. Twenty-seven females completed incremental arm cranking and leg cycling tests on separate days. During each exercise, spatially resolved near-infrared spectroscopy was used to measure changes in the tissue oxygen saturation (SO₂), oxygenated (oxy-) hemoglobin and/or myoglobin (Hb/Mb), deoxygenated (deoxy-) Hb/Mb, and total Hb/Mb in the triceps during arm cranking and in the vastus lateralis during leg cycling. During arm cranking, there was a rapid increase in the respiratory exchange ratio and a lower ventilatory threshold compared to leg cycling, which confirmed accelerated anaerobic glycolysis in this mode of exercise. During leg cycling, SO₂ remained decreased near to or until approaching peak oxygen uptake (O_2peak). During arm cranking, however, the decrease in oxy-Hb/Mb and increase in deoxy-Hb/Mb stopped at the middle of O_2peak (mean 51.4%), consequently resulting in a leveling off in the SO₂ decrease, although total Hb/Mb continued to increase. These results might suggest that the oxygen demand in the triceps attained the maximum at that intensity, despite an adequate oxygen supply during arm cranking.     

Oxygen uptake and heart rate kinetics during heavy exercise: a comparison between arm cranking and leg cycling

This study examined the oxygen uptake (V˙O₂) and heart rate (HR) kinetics during arm cranking and leg cycling at work rates above the anaerobic threshold (AT). Ten untrained male subjects [21.6 (1.3) years] completed two 7 min 15 s constant-load arm cranking and two leg cycling tests at a power output halfway between the mode-specific AT and peak V˙O₂. The time constants for phase II V˙O₂ (τ) and HR (τ) kinetics were determined by fitting a monoexponential curve from the end of phase I until 3 min of exercise. V˙O₂ τ and HR τ values were significantly (P<0.001) slower in arm cranking [V˙O₂ τ = 66.4 (3.0) s; HR τ = 74.7 (4.4) s] than in leg cycling [V˙O₂ τ = 42.0 (1.9) s; HR τ = 55.6 (3.5) s]. The V˙O₂ slow component (V˙O_2SC) accounted for a significantly (P<0.001) greater percentage of the total exercise response during arm cranking [23.8 (1.6)%] than during leg cycling [14.2 (1.5)%]. The greater relative V˙O_2SC and the slower V˙O₂ τ with arm exercise are consistent with a greater recruitment of metabolically inefficient type II muscle fibres during arm cranking than during leg cycling. Electronic Publication     

Ventilatory efficiency and exercise tolerance in 101 healthy volunteers

The ventilatory equivalent for CO₂ defines ventilatory efficiency largely independent of metabolism. An impairment of ventilatory efficiency may be caused by an increase in either anatomical or physiological dead space, the latter being the most important mechanism in the hyperpnoea of heart failure, pulmonary embolism, pulmonary hypertension and the former in restrictive lung disease. However, normal values for ventilatory efficiency have not yet been established. We investigated 101 (56 men) healthy volunteers, aged 16–75 years, measuring ventilation and gas exchange at rest (n?=?64) and on exercise (modified Naughton protocol, n?=?101). Age and sex dependent normal values for ventilatory efficiency at rest defined as the ratio ventilation:carbon dioxide output (V˙ _E:V˙CO₂), exercise ventilatory efficiency during exercise, defined as the slope of the linear relationship between ventilation and carbon dioxide output (V˙ _E vs V˙CO₂ slope), oxygen uptake at the anaerobic threshold and at maximum (V˙O_2AT,V˙O_2max, respectively) and breathing reserve were established. Ventilatory efficiency at rest was largely independent of age, but was smaller in the men than in the women [V˙ _E:V˙CO₂ 50.5 (SD 8.8) vs 57.6 (SD 12.6) P<0.05]. Ventilatory efficiency during exercise declined significantly with age and was smaller in the men than in the women (men: (V˙ _E vs V˙CO₂ slope?= 0.13?×?age?+?19.9; women: V˙ _E vs V˙CO₂ slope?= 0.12?×?age?+?24.4). The V˙O_2AT and V˙O_2max were 23 (SD 5) and 39 (SD 7) ml O₂?·?kg?·?min^?1 in the men and 18 (SD 4) and 32 (SD 7) in the women, respectively, and declined significantly with age. The V˙O_2AT was reached at 58 (SD 9)% V˙O_2max. Breathing reserve at the end of exercise was 41% and was independent of sex and age. It was concluded from this study that ventilatory efficiency as well as peak oxygen uptake are age and sex dependent in adults.     

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.     

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.     

Effect of arm-cranking on leg blood flow and noradrenaline spillover during leg exercise in man

Controversy exists whether recruitment of a large muscle mass in dynamic exercise may outstrip the pumping capacity of the heart and require neurogenic vasoconstriction in exercising muscle to prevent a fall in arterial blood pressure. To elucidate this question, seven healthy young men cycled for 70 minutes at a work load of 5540%VO_2max. At 30 to 50 minutes, arm cranking was added and total work load increased to (mean ± SE) 82 ± 4% of Vo_2max. During leg exercise, leg blood flow average 6.15 4.511 minutes^-1, mean arterial blood pressure 137 ± 4 mmHg and leg conductance 42.3 ± 2.2 ml minutes^-1 mmHg^-1. When arm cranking was added to leg cycling, leg blood flow did not change significantly, mean arterial blood pressure increased transiently to 147 ± 5 mmHg and leg vascular conductance decreased transiently to 33.5 ± 3.1 ml minutes^-1 mmHg^-1. Furthermore, arm cranking doubled leg noradrenaline spillover. When arm cranking was discontinued and leg cycling continued, leg blood flow was unchanged but mean arterial blood pressure decreased to values significantly below those measured in the first leg exercise period. Furthermore, leg vascular conductance increased transiently, and noradrenaline spillover decreased towards values measured during the first leg exercise period. It is concluded that addition of arm cranking to leg cycling increases leg noradrenaline spillover and decreases leg vascular conductance but leg blood flow remains unchanged because of a simultaneous increase in mean arterial blood pressure. The decrease in leg vascular conductance observed when arm cranking increased mean arterial blood pressure could be regarded more as a measure to prevent overperfusion than a measure to maintain arterial blood pressure.     

Physiological effects of variations in spontaneously chosen crank rate during incremental upper-body exercise

The aims of the present study were: first, to assess the interindividual variations of a spontaneously chosen crank rate (SCCR) in relation to the power developed during an incremental upper body exercise on an arm ergometer set at a constant power regime, and second, to compare heart rate (HR) responses, expired minute ventilation (V˙ _E) and oxygen consumption (V˙O₂) when the pedal rates were chosen spontaneously (T_SCCR) or set at ±10% of the freely chosen rates (T_+10% and T_?10%, respectively). The mean pedal rate values were linearly related (P?r?=?0.96), although large variations of pedalling rate strategies were observed between subjects. Maximal power (MP) and time to exhaustion values were significantly higher (P?SCCR than during T_+10% and T_?10%. Peak V˙O₂ values were significantly higher (P?+10% than in T_SCCR and T_?10%. The increase in HR, V˙ _E, and V˙O₂ mean values, in relation to the increase in the power developed, was significantly higher (P?±10%) than in the two other conditions. The findings of the present study suggest that the use of an electromagnetically braked ergometer, which automatically adjusts the resistance component to maintain a constant work rate, should be used in order to achieve the highest MP values during an incremental upper body exercise. A 10% increase of the SCCR should be used in order to provide the highest peak V˙O₂ value.     

Relative exercise intensity of long-distance marching (120 km in 4 days) in 153 subjects aged 69–87 years

The aim of this study was to determine the relative exercise intensity (oxygen uptake during the march/maximal oxygen uptake, V˙O_{2 march}/V˙O_{2 max} ) during a long-distance march in subjects or over 70 years of age. Secondly, the effect of hypertension, cardiovascular and pulmonary diseases on the relative exercise intensity was evaluated. One hundred and fifty-three subjects, 97 men aged 76.7 (4.6) years and 56 women aged 72.8 (3.6) years who completed the 1993 Nijmegen–day long-distance march (30?km?·?day^?1 on 4 consecutive days) participated in the study. Oxygen uptake (V˙O₂) during walking at different velocities () was measured in a subgroup of nine men and nine women, selected randomly from the population under study. With these data, regression equations describing the relationship between V˙O₂ and were made. V˙O_{2 march} was estimated with the obtained regression equations from an average of the _march measured in all participants. V˙O_{2 max} was determined using incremental cycle ergometry in all subjects. V˙O_{2 march} was 13.7 (1.8) ml?·?kg^?1?·?min^?1 in men and 15.2 (1.3) ml?·?kg?·?min^?1 in women at a mean of 5?km?·?h^?1 in both sexes. This corresponded to 52% of V˙O_{2 max} in men and 63% in women. In both sexes subjects with cardiovascular and/or pulmonary diseases walked at a slower and thus lower V˙O_{2 march} compared to subjects without these diseases. Due to the lower V˙O_{2 max} in subjects with these diseases there was no difference in the relative exercise intensity between the groups. A multiple linear regression analysis showed that and not age on the prevalence of hypertension, cardiovascular and/or pulmonary that V˙O_{2 max} was the most important predictor of the variance in self-selected _march. This study demonstrates that these active people aged over 70 years could maintain a high relative exercise intensity during endurance walking on 4 subsequent days. Furthermore, it shows that the relative exercise intensity of marching is within the range recommended for improving fitness and reducing the risk of cardiovascular diseases. Finally, these results demonstrate that V˙O_{2 max} has a more important influence on performance than does age or chronic diseases in active elderly people.     

Effect of exercise modality on oxygen uptake kinetics during heavy exercise

The mechanisms responsible for the oxygen uptake (V˙O₂) slow component during high-intensity exercise have yet to be established. In order to explore the possibility that the V˙O₂ slow component is related to the muscle contraction regimen used, we examined the pulmonary V˙O₂ kinetics during constant-load treadmill and cycle exercise at an exercise intensity that produced the same level of lactacidaemia for both exercise modes. Eight healthy subjects, aged 22–37 years, completed incremental exercise tests to exhaustion on both a cycle ergometer and a treadmill for the determination of the ventilatory threshold (defined as the lactate threshold, Th_la) and maximum V˙O₂ (V˙O_{2 max}). Subsequently, the subjects completed two “square-wave” transitions from rest to a running speed or power output that required a V˙O₂ that was halfway between the mode-specific Th_la and V˙O_{2 max}. Arterialised blood lactate concentration was determined immediately before and after each transition. The V˙O₂ responses to the two transitions for each exercise mode were time-aligned and averaged. The increase in blood lactate concentration produced by the transitions was not significantly different between cycling [mean (SD) 5.9 (1.5) mM] and running [5.5 (1.6) mM]. The increase in V˙O₂ between 3 and 6?min of exercise; (i.e. the slow component) was significantly greater in cycling than in running, both in absolute terms [290 (102) vs 200 (45) ml?·?min^?1; P<0.05] and as a proportion of the total V˙O₂ response above baseline [10 (3)% vs 6 (1)%; P<0.05]. These data indicate that: (a) a V˙O₂ slow component does exist for high-intensity treadmill running, and (b) the magnitude of the slow component is less for running than for cycling at equivalent levels of lactacidaemia. The greater slow component observed in cycling compared to running may be related to differences in the muscle contraction regimen that is required for the two exercise modes.     

Cycling efficiency and pedalling frequency in road cyclists

The purpose of this study was to determine the influence of pedalling rate on cycling efficiency in road cyclists. Seven competitive road cyclists participated in the study. Four separate experimental sessions were used to determine oxygen uptake (V˙O₂) and carbon dioxide output (V˙CO₂) at six exercise intensities that elicited a V˙O₂ equivalent to 54, 63, 73, 80, 87 and 93% of maximum V˙O₂ (V˙O_2max). Exercise intensities were administered in random order, separated by rest periods of 3–5?min; four pedalling frequencies (60, 80, 100 and 120?rpm) were randomly tested per intensity. The oxygen cost of cycling was always lower when the exercise was performed at 60?rpm. At each exercise intensity, V˙O₂ showed a parabolic dependence on pedalling rate (r = 0.99–1, all P?r = 0.94–1, all P?P?P?r = 0.98, n = 6, P?r = 0.98, P?P?V˙O₂ (P?V˙O₂. These results may help us to understand why competitive cyclists often pedal at cadences of 90–105?rpm to sustain a high power output during prolonged exercise.     

V˙O2peak and the gas-exchange anaerobic threshold during incremental arm cranking in able-bodied and paraplegic men

Resting energy expenditure, peak oxygen uptake (V˙O_2peak) and the gas-exchange anaerobic threshold (Th_an) were measured during incremental arm cranking (15?W?·?min^?1) in six able-bodied (AB) and six paraplegic (P) subjects. Only male subjects with traumatic spinal cord injuries in the area of the 10–12th thoracic segment were included in the P group. All AB and P subjects were physically active. Mean (SE) values for age and body mass were 28 (2)?years and 78.9 (3.9)?kg for the AB group and 32 (4)?years and 70.8 (7.9)?kg for the P group (P?>?0.05). Resting energy expenditure values were not found to be significantly different between AB [5.8 (0.2)?kJ?·?min^?1] and P [5.1 (0.3)?kJ?·?min^?1] subjects. Mean V˙O_2peak values were 29.3 (2.4)?ml?· kg^?1?· min^?1 and 29.6 (2.2)?ml?·?kg^?1?·?min^?1 for the AB and P groups, respectively (P?>?0.05). Absolute oxygen uptake values measured at two gas-exchange anaerobic threshold (Th_an) were not significantly different between the two groups. However, the Th_an occurred at a significantly higher percentage of V˙O_2peak in the P [58.9 (1.7)%] group than in the AB [50.0 (2.8)%] group (P?R) values obtained at the Th_an and at 15, 45, 60, 75 and 90?W of incremental exercise were significantly lower in the P group than in the AB group. Heart rates were significantly elevated at every submaximal work stage (15–120?W) in the P group compared to the AB group (P?R) during arm exercise. These local adaptations may be in part responsible for the significantly higher Th_an observed for arm exercise in P subjects, even though V˙O_2peak values were essentially the same for both groups.     

Comparison of cardiopulmonary responses to two types of dry-land upper-body exercise testing modes in competitive swimmers

In this study we compared cardiopulmonary responses to upper-body exercise in 12 swimmers, using simulation of the front-crawl arm-pulling action on a computer-interfaced isokinetic swim bench and arm cranking on a modified cycle ergometer. Subjects adopted a prone posture; exercise was initially set at 20?W and subsequently increased by 10?W?·?min^?1. The tests were performed in a randomised order at the same time of day, within 72?h. The highest (peak) oxygen consumption (V˙O_2peak), heart rate (HR_peak), blood lactate ([la^?]_peak) and exercise intensity (EI_peak) were recorded at exhaustion. Mean (SEM) peak responses to simulated swimming were higher than those to arm cranking for V˙O_2peak [2.9 (0.2) vs 2.4 (0.1) l?·?min^?1; P?=?0.01], HR_peak [174 (2) vs 161 (2) beats?·?min^?1; P?=?0.03], and EI_peak [122 (6) vs 102 (5) W; P?=?0.02]. However, there were no significant differences in [la^?]_peak [9.6 (0.6) vs 8.2 (0.6) mmol?·?l^?1; P?=?0.08]. Thus simulated swimming is the preferred form of dry-land ergometry for the assessment of swimmers.     

Diurnal variations in ventilatory and cardiorespiratory responses to submaximal treadmill exercise in females

Diurnal variations in ventilatory and cardiorespiratory responses to submaximal treadmill exercise were analysed in 11 eumenorrhoeic women and in 10 women using monophasic oral contraceptives. Subjects performed submaximal treadmill exercise at three intensities averaging 7, 8, and 9?km?·?h^?1, each for 4?min at 0800, 1300 and 1700 hours, assigned randomly on 3 separate days. Rectal temperature was measured before (T _recb) and after (T _reca) exercise. Cardiac frequency (f _c), ventilation (V˙ _E), oxygen uptake (V˙O₂), carbon dioxide output (V˙CO₂), and respiratory exchange ratio (R) were assessed in the last minute of each stage of the exercise. Both T _recb and T _reca increased from 0800 to 1700 hours (P?V˙O₂ and V˙CO₂ were higher in the afternoon compared to the morning. Similarly, R was increased at 1700 hours compared to 0800 hours during the recovery period following exercise (P?V˙ _E did not vary significantly during the day at any of the running intensities. No significant interactions (group?×?time of day) were observed in any of the studied parameters. In contrast to ventilation, the V˙O₂ and V˙CO₂ of the females during submaximal exercise were both affected by the time of day, without any differences between eumenorrhoeic women and users of oral contraceptives.     

Effects of artificially-induced anaemia on sudomotor and cutaneous blood flow responses to heat stress

The influence of artificially induced anaemia on thermal strain was evaluated in trained males. Heat stress trials (38.6°C, water vapour pressure 2.74?kPa) performed at the same absolute work rates [20?min of seated rest, 20?min of cycling at 30% peak aerobic power (V˙O_2peak), and 20?min cycling at 45% V˙O_2peak] were completed before (HST1) and 3–5?days after 3 units of whole blood were withdrawn (HST2). Mild anaemia did not elevate thermal strain between trials, with auditory canal temperatures terminating at 38.5°C [(0.16), HST1] and 38.6°C [(0.13), HST2; P?>?0.05]. Given that blood withdrawal reduced aerobic power by 16%, this observation deviates from the close association often observed between core temperature and relative exercise intensity. During HST2, the absolute and integrated forearm sweat rate (m˙ _sw) exceeded control levels during exercise (P?m˙ _sw occurred (P?相似文献   

Sensation of breathlessness and respiratory oxygen cost during cycle exercise with and without conscious entrainment of the breathing rhythm

The conscious entrainment of respiratory rhythm to exercise rhythm (ENT) has been hypothesized to alleviate breathing discomfort and reduce the oxygen (O₂) cost of ventilation with a resulting decrease in total O₂ uptake (V˙O₂) during rhythmic exercise. This hypothesis has been tested in the study reported here. Eight female subjects performed cycle exercise at 50 rpm under two work load conditions of 40% and 60% of maximal V˙O₂. During a 30-min exercise period at each work load, each subject was asked to breathe under two conditions for 15 min each: (1) spontaneously (non-ENT run), and (2) deliberately entraining the breathing rhythm to the cycling rhythm at preferred coupling ratios of the two rhythms (ENT run). In the ENT run, most subjects chose a ratio of 1:2. In each run, pulmonary ventilation (V˙ _E), total V˙O₂ and the breathlessness sensation (BS) were measured at 4–5 min. BS was assessed according to a Borg category scale. The remaining 10 min of each 15-min run were allotted for measurement of the O₂ cost of ventilation (ΔV˙O₂/ΔV˙ _E), assessed by a hypercapnia-induced hyperventilation method in which the V˙O₂ of the respiratory muscles (V˙O_2RM) was calculated by multiplying ΔV˙O₂/ΔV˙ _E by the prevailing V˙ _E. On average, there were no significant differences in any of the variables, V˙O₂,ΔV˙O₂/ΔV˙ _E,V˙O_2RM and BS, between the non-ENT and ENT runs performed at any work load. However, there were wide variations among the subjects in the differences (Δ) between the two runs, and significant correlations were found between ΔV˙O₂ vs ΔV˙ _E, ΔV˙O₂ vs ΔV˙O_2RM, and Δ BS vs ΔO_2RM of individual subjects. These results indicate that reductions of the total V˙O₂ and BS with ENT could occur in subjects in whom the V˙O_2RM decreased during ENT.     

Heart rate variability in exercising humans: effect of water immersion

Power spectrum analysis of heart-rate variability was made in seven men [mean age 22 (SEM 1) years] in head-out water immersion (W) and in air (A, control) at rest and during steady-state cycling to maximal intensity (maximum oxygen uptake, V˙O_2max). At rest W resulted in a trebled increase in the total power (P?V˙O_2max, thereafter decreasing towards nil in both conditions. The HF% decreased in similar ways in W and A to about half at 55%–60% V˙O_2max and then increased to reach 1.5 times the resting values at V˙O_2max. The central frequency of HF increased linearly with oxygen uptake, showing a tendency to be higher in W than in A at medium to high intensities. The VLF% remained unchanged. The lack of differences in the LF peak between W and A during exercise would suggest that blood distribution had no effect on the readjustments in control mechanisms of arterial pressure. On the other hand, the findings of similar HF powers and the very similar values for ventilation in W and A confirmed the direct effect of the respiratory activity in heart rate modulation during exercise.     

A comparison of skeletal muscle oxygenation and fuel use in sustained continuous and intermittent exercise

In this study we compared substrate oxidation and muscle oxygen availability during sustained intermittent intense and continuous submaximal exercise with similar overall (i.e. work and recovery) oxygen consumption (V˙O₂). Physically active subjects (n?=?7) completed 90?min of an intermittent intense (12?s work:18?s recovery) and a continuous submaximal treadmill running protocol on separate days. In another experiment (n?=?5) we compared oxygen availability in the vastus lateralis muscle between these two exercise protocols using near-infrared spectroscopy. Initially, overall V˙O₂ (i.e. work and recovery) was matched, and from 37.5?min to 67.5?min of exercise was similar, although slightly higher during continuous exercise (8%; P??1?·?kg^?1] and continuous submaximal [0.85 (0.01)?kJ?·?min^?1?·?kg^?1] exercise. Overall exercise intensity, represented as a proportion of peak aerobic power (V˙O_2peak), was 68.1 (2.5)% V˙O_2peak and 71.8 (1.8)% V˙O_2peak for intermittent and continuous exercise protocols, respectively. Fat oxidation was almost 3 times lower (P?P?P?P?P?r?=?0.72; P?V˙O₂ and identical energy expenditure.     

The influence of cold stress and a 36- h fast on the physiological responses to prolonged intermittent walking in man

In a previous study, rectal temperature (T _re) was found to be lower, and oxygen consumption (V˙O₂) and the respiratory exchange ratio (R) were higher in a cold (+5°C), wet and windy environment (COLD), compared with a thermoneutral environment during intermittent walking at ≈30% of peak V˙O₂ (Weller AS, Millard CE, Stroud MA et al. Am J Physiol 272:R226–R233, 1997). The aim of the present study was to establish whether these cold-induced responses are influenced by prior fasting, as impaired thermoregulation has been demonstrated in cold-exposed, resting men following a 48-h fast. To address this question, eight men attempted a 360-min intermittent (15?min rest, 45?min exercise) walking protocol under COLD conditions on two occasions. In one condition, the subjects started the exercise protocol ≈120?min after a standard meal (FED/COLD), whereas in the other the subjects had fasted for 36?h (FASTED/COLD). The first two exercise periods were conducted at a higher intensity (HIGHER, 6?km?·?h^?1 and 10% incline), than the four subsequent exercise periods (LOW, 5 km?·?h^?1 and 0% incline). There was no difference in the time endured in FED/COLD and FASTED/COLD. In FASTED/COLD com pared with FED/COLD, R was lower during HIGHER and LOW, and T _re was lower during LOW, whereas there was no difference in V˙O₂, mean skin temperature and heart rate. Therefore, although the 36-h fast impaired temperature regulation during intermittent low-intensity exercise in the cold, wet and windy environment, it was unlikely to have been the principal factor limiting exercise performance under these experimental conditions.