Influence of sodium bicarbonate ingestion on plasma ammonia accumulation during incremental exercise in man

This investigation evaluated the influence of metabolic alkalosis on plasma ammonia (NH₃) accumulation during incremental exercise. On two occasions separated by at least 6 days, six healthy men cycled at 70, 80, and 90%g of maximum oxygen consumption ( ) for 5 min; each exercise period was followed by 5 min of seated recovery. Exercise was then performed at 100% until exhaustion. Beginning 3 h prior to exercise, subjects ingested 3.6 mmol · kg body mass^– NaHCO₃ (test, T) or 3.0 mmol · kg body mass^–1 CaCO₃ (placebo, P) (both equivalent to 0.3 g · kg^–1) over a 2-h period. Trials were performed after an overnight fast and the order of treatments was randomized. Arterialized venous blood samples for the determination of acid-base status, blood lactate and plasma NH₃ concentrations were obtained at rest before treatment, 15 s prior to each exercise bout (Pre 70%, Pre 80%, Pre 90%, and Pre 100%), and at 0, 5 (5Post), and 10 (10'Post) min after exhaustion. Additional samples for blood lactate and plasma NH₃ determination were obtained immediately after each exercise bout (Post 70%, Post 80%, Post 90%) and at 15 min after exercise (15Post). Time to exhaustion at 100% of was not significantly different between treatments [mean (SE): 173 (42) s and 184 (44) s for T and P respectively]. A significant treatment effect was observed for plasma pH with values being significantly higher on T than on P Pre 70% [7.461 (0.007) vs 7.398 (0.008)], Pre 90% [7.410 (0.010) vs 7.340 (0.016)], and 10'Post [7.317 (0.032) vs 7.242 (0.036)]. The change in plasma pH was significantly greater following the 90%g bout (Pre 100% Pre 90%) for T [–0.09 (0.02)] than for P [–0.06 (0.01)]. Blood base excess and plasma bicarbonate concentrations were significantly higher for T than P before each exercise bout but not at the point of exhaustion. During recovery, base excess was higher for T than P at 5Post and 10Post while the bicarbonate concentration was higher for T than P at 10Post. A significant treatment effect was observed for the blood lactate concentration with T on the average being higher than P [7.0 (1.0) and 6.3 (1.1) mmol · l^–1 for T and P averaged across the 12 sampling times]. Plasma NH₃ accumulation was not different between treatments at any point in time. In addition, no differences were observed between treatments in blood alanine accumulation. The results suggest that under the conditions of the present investigation metabolic alkalosis does not influence plasma NH₃ accumulation or endurance capacity during intense incremental exercise.     

Relationship between cardiac output and oxygen uptake at the onset of exercise

The purpose of the present study was to assess the relationship between the rapidity of increased gas exchange (i.e. oxygen uptake ) and increased cardiac output ( ) during the transient phase following the onset of exercise. Five healthy male subjects performed multiple rest-exercise or light exercise (25 W)-exercise transitions on an electrically braked ergometer at exercise intensities of 50, 75, or 100 W for 6 min, respectively. Each transition was performed at least eight times for each load in random order. The was obtained by a breath-by-breath method, and was measured by an impedance method during normal breathing, using an ensemble average. On transitions from rest to exercise, rapidly increased during phase I with time constants of 6.8–7.3 s. The also showed a similar rapid increment with time constants of 6.0–6.8 s with an apparent increase in stroke volume (SV). In this phase I, increased to about 29.7%–34.1% of the steady-state value and increased to about 58.3%–87.0%. Thereafter, some 20 s after the onset of exercise a mono-exponential increase to steady-state occurred both in and with time constants of 26.7–32.3 and 23.7–34.4 s, respectively. The insignificant difference between and time constants in phase I and the abrupt increase in both and SV at the onset of exercise from rest provided further evidence for a cardiodynamic contribution to following the onset of exercise from rest.     

The effects of acute phosphate supplementation in subjects of different aerobic fitness levels

Six trained cyclists (high-fitness group) and six untrained individuals (low-fitness group), performed a 20-min cycle ergometer exercise test at 70% of maximum oxygen consumption ( followed by a 30-min rest period and then an incremental ride to exhaustion on two occasions, 1 week apart. Ninety minutes prior to exercise subjects consumed a drink containing either 22.2 g dibasic calcium phosphate (DCP; treatment) or calcium carbonate (placebo). Blood was drawn prior to drink ingestion, during submaximal exercise, during recovery and at exhaustion for determination of blood 2,3-DPG, blood ATP, plasma lactate, plasma phosphate, haemoglobin and haematocrit. Throughout exercise, cardiorespiratory variables [oxygen uptake ( minute ventilation, ( ), respiratory exchange ratio, heart rate and oxygen pulse] were monitored, and ratings of perceived exertion obtained. Although there was a trend for the low-fitness group to have a higher plasma phosphate concentration prior to treatment ingestion, no treatment effects on plasma phosphate were noted at any sample time in either group. 2,3-DPG, oxygen pulse, time to exhaustion and were significantly higher in the high-fitness group; however, no differences in these variables were observed as a result of phosphate ingestion. Plasma lactate was significantly lower in the high-fitness group during the submaximal exercise and the recovery period, but again phosphate ingestion had no effect. These results suggest that acute DCP supplementation is not effective as an ergogenic aid and that aerobic fitness level does not affect the response to phosphate supplementation.     

Perception of effort during high-intensity exercise at low, moderate and high wet bulb globe temperatures

The purpose of this study was to determine the effect of low, moderate and high wet bulb globe temperatures (T _wbg) on cardiovascular variables and ratings of perceived exertion (RPE) during moderately prolonged, high-intensity exercise. Six subjects [four men and two women; mean (SD) age, 22.0 (1.2) years; maximum oxygen consumption ({ie519-1}), 51.0 (8.4) ml · kg^–1 · min^–1] completed 30 min of exercise (80% {ie519-2}) on a cycle ergometer at low [14.7 (2.1)°C], moderate [21.0 (1.5)° C], and high [27.4 (2.3)° C]T _wbg. Two additional subjects completed 20 min of exercise in the high temperature condition, but completed 30 min in the moderate and lowT _wbg. Heart rate (f _c), blood pressure, blood lactate (La), mean skin temperature ( _sk), , and RPE were measured at 10, 20 and 30 min. Results showed thatf _c, rate pressure product, RPE, pulmonary ventilation and ventilatory equivalent for oxygen increased (P < 0.05) across time for all conditions, while decreased across time. _sk andf _c were significantly greater across time in the high condition [35.9 (0.65)° C; 176 (12.6) beats · min^–1] compared to the moderate [34.6 (1.5)° C; 170 (17.2) beats · min^–1] and the low condition [31.7 (1.5)° C; 164 (17.1) beats-min^–1]. However, there were no differences throughout exercise in RPE [high,.16.2 (2.0); moderate, 16.4 (2.2); low, 16.3 (1.9)] and across the conditions. These data suggest that RPE is closely related to metabolic intensity but is not a valid indicator of cardiovascular strain during exercise in highT _wbg conditions.     

Respiratory responses of elite oarsmen, former oarsmen, and highly trained non-rowers during rowing, cycling and running

The position of the body and use of the respiratory muscles in the act of rowing may limit ventilation and thereby reduce maximal aerobic power relative to that achieved in cycling or running, in spite of the greater muscle mass involved in rowing. This hypothesis was investigated for three groups of male subjects: nine elite senior oarsmen, eight former senior oarsmen and eight highly trained athletes unskilled in rowing. The subjects performed graded exercise to maximal effort on a rowing ergometer, cycle ergometer and treadmill while respiratory minute volume and oxygen consumption were monitored continuously. The VE at a given during intense submaximal exercise (greater than 75% of maximal ) was not significantly lower in rowing compared with that in cycling and treadmill running for any group, which would suggest that submaximal rowing does not restrict ventilation. At maximal effort, and for rowing were less than those for the other types of exercise in all the groups, although the differences were not statistically significant in the elite oarsmen. These data are consistent with a ventilatory limitation to maximal performance in rowing that may have been partly overcome by training in the elite oarsmen. Alternatively, a lower maximal VE in rowing might have been an effect rather than a cause of a lower maximal if maximal was limited by the lower rate of muscle activation in rowing.     

Evaluation of physical fitness from field tests at high altitude in circumpubertal boys: comparison with laboratory data

Field tests of running and laboratory tests were performed in La Paz [high altitude (HA), 3700 m] and in Clermont-Ferrand [low altitude (LA), 300 m] to investigate their validity at HA. Prepubertal boys of mean ages 10.6 years (HA1,n = 16; LA1,n = 28) and pubertal boys of 13.7 years (HA2,n = 12; LA2,n = 41) took part in the study. All the boys performed a 30-m sprint (v _30m), a 30-s shuttle run (v _3os) and a progressive shuttle run test until their maximal aerobic velocity (v _maxsRT). Maximal oxygen consumption was extrapolated from the last test. . In the laboratory, the boys performed a force-velocity test (P _max), a Wingate test (P _Wing) and a graded test to measure maximal oxygen consumption ; direct method) on a cycle ergometer. At similar ages, there was no significant difference between HA and LA boys forv _30m andP _max. Thev _30s of HA boys was 3%–4% lower than those of LA boys (P<0.05); there was no significant difference forP _Wing. Significant relationships were observed at both altitudes betweenP _max (watts per kilogram) andv _30m (HA:r=0.76; LA:r=0.84) and betweenP _Wing andv _30s (HA:r=0.67; LA:r = 0.77); the slopes and the origins were the same at HA and LA. The ,v _maxSRT and were lower by 9%, 12% and 20%, respectively, at HA than at LA (P<0.05). However, the relationships between and (litres per minute) at HA (r=0.88) and at LA (r=0.93) were identical. In conclusion, chronic hypoxia did not modify performance in very short dash exercises. The influence of HA appeared when the exercise duration increased and, during a maximal shuttle run test, performance was reduced by 10% at HA. Moreover, it was possible to assessP _max,P _Wing and at HA as well as at LA from field tests.     

Metabolic, endocrine, haemodynamic and pulmonary responses to different types of exercise in individuals with normal or reduced liver function

The liver is central to the metabolic response to exercise but measurements of effects of reduced liver function on the physiological adaptation to exercise are scarce. We investigated metabolic, endocrine, pulmonary and haemodynamic responses to exercise in 15 healthy untrained controls (Co) and in 30 subjects with reduced liver function (i.e. liver cirrhosis, Ci). The following protocols were used: protocol 1 maximal oxygen uptake and anaerobic threshold (AT), protocol 2 stepwise increases in exercise intensity from 0 to 40% giving steady-stage conditions, protocol 3 1 h exercise at 20% . Muscle glycogen content was determined in 15 Ci. Spirometry was essentially normal in Ci. Result: protocol 1 Ci had impaired and reduced AT (P < 0.05). Basal plasma concentrations of insulin, glucagon, growth hormone and adrenaline were increased in Ci (P < 0.05); cortisol was normal. During exercise, only glucagon remained different between groups. In protocol 2 Ci had decreased resting respiratory exchange ratio (RQ: p < 0.05) associated with increased plasma concentrations of free fatty acids and glycerol. They had disproportionately enhanced lipolysis and RQ. heart rate (+ 24%), ventilation (+ 28%), thermal effects of exercise (+ 31%) and intrapulmonary shunt volume (+ 76%), which accounted for 11.7 (SD 3.0) or 7.4 (SD 0.9%) of cardiac output during exercise in Ci and Co, respectively (P < 0.05 for all the differences reported). The metabolic effects of Ci were independent of the clinical and nutritional state of the patients. In protocol 3 muscle glycogen content was highly variable in Ci, but mean values were normal [16.9 (SD 8.9) mol·g^–1 wet mass]. Glycogen content positively correlated with resting and exercise-induced RQ, but negatively correlated with the exercise-induced alterations in plasma glucose concentration. From these results we concluded that with reduced liver function , and AT are reduced, but metabolic, pulmonary and haemodynamic reponses per unit power output are enhanced. Muscle glycogen content would seem to contribute to the metabolic response, but its mobilization to be limited in individuals with reduced liver function.Dedicated to Professor D.F.W. Schmidt on the occasion of his 70th birthday     

Ventilatory responses to exercise and carbon dioxide in elderly and younger humans

The present investigation examined the relationship between CO₂ sensitivity [at rest (S _R) and during exercise (S _E)] and the ventilatory response to exercise in ten elderly (61–79 years) and ten younger (17–26 years) subjects. The gradient of the relationship between minute ventilation and CO₂ production ( _E/ CO₂) of the elderly subjects was greater than that of the younger subjects [mean (SEM); 32.8 (1.6) vs 27.3 (0.4); P<0.01]. At rest, S _R was lower for the elderly than for the younger group [10.77 (1.72) vs 16.95 (2.13) 1 · min^–1 · kPa^–1; 1.44 (0.23) vs 2.26 (0.28) 1 · min^–1 · mmHg^–1; P<0.05], but S _E was not significantly different between the two groups [17.85 (2.49) vs 19.17 (1.62) l · min^–1 · kPa^–1; 2.38 (0.33) vs 2.56 (0.21) 1 · min^–1 · mmHg^–1]. There were significant correlations between both S _R and S _E, and _E/ CO₂ (P<0.05; P<0.001) for the younger group, bot none for the elderly. The absence of a correlation for the elderly supports the suggestion that _E/ CO₂ is not an appropriate index of the ventilatory response to exercise for elderly humans.     

Effect of anthropometric characteristics and socio-economic status on physical performances of pre-pubertal children living in Bolivia at low altitude

We have previously observed that 11-year-old children of low socio-economic status (LSES) showed a delayed physical growth of approximately 2 years and developed lower normalized short-term power output than children of high socio-economic status (HSES) of the same age. In contrast, maximal oxygen uptake per unit of fat free mass was no different in either group. The aim of this study was to evaluate the effect of anthropometric characteristics between HSES and LSES prepubertal children in aerobic and anaerobic performance. To compare children of the same body dimensions, 11-year-old boys (n = 30) and girls (n = 31) of LSES and 9-year-old boys (n = 21) and girls (n = 27) of HSES were studied. Anthropometric measurements, (direct test), maximal anaerobic power (P _max, force-velocity test) and mean anaerobic power ( , Wingate test) were determined. In these children having the same body dimensions: mean were the same in LSES and HSES children [1.2 (SD 0.2)1-min^–1];P _max and were lower in LSES subjects [154.0 (SD 33.2) vs 174.6 (SD 38.4) W and 116.3 (SD 23.3) vs 128.2 (SD 28.0) W, respectively]; the linear relationships between and fat free mass were the same in LSES and HSES boys but, in the girls, the LSES group had lower values. For anaerobic performance, the relationships were significantly different: the slopes were the same but LSES values for the both sexes were lower. These results would suggest that factors other than differences in body dimensions alone were responsible for the lower performance of LSES girls and boys. Cultural factors and motor learning, structural and functional alterations of muscle induced by marginal malnutrition have been discussed.     

Severe hypoxia decreases oxygen uptake relative to intensity during submaximal graded exercise

The effect of severe acute hypoxia (fractional concentration of inspired oxygen equalled 0.104) was studied in nine male subjects performing an incremental exercise test. For power outputs over 125 W, all the subjects in a state of hypoxia showed a decrease in oxygen consumption ( O₂) relative to exercise intensity compared with normoxia (P < 0.05). This would suggest an increased anaerobic metabolism as an energy source during hypoxic exercise. During submaximal exercise, for a given O₂, higher blood lactate concentrations were found in hypoxia than in normoxia (P < 0.05). In consequence, the onset of blood lactate accumulation (OBLA) was shifted to a lower O₂ ( O₂ 1.77 l·min^–1 in hypoxia vs 3.10 l·min^–1 in normoxia). Lactate concentration increases relative to minute ventilation ( _E) responses were significantly higher during hypoxia than in normoxia (P < 0.05). At OBLA, _E during hypoxia was 25% lower than in the normoxic test. This study would suggest that in hypoxia subjects are able to use an increased anaerobic metabolism to maintain exercise performance.     

A method for estimating bicarbonate buffering of lactic acid during constant work rate exercise

A method to estimate the CO₂ derived from buffering lactic acid by HCO₃ ^– during constant work rate exercise is described. It utilizes the simultaneous continuous measurement of O₂ uptake ( O₂) and CO₂ output ( CO₂), and the muscle respiratory quotient (RQ_m). The CO₂ generated from aerobic metabolism of the contracting skeletal muscles was estimated from the product of the exercise-induced increase in O₂ and RQ_m calculated from gas exchange. By starting exercise from unloaded cycling, the increase in CO₂ stores, not accompanied by a simultaneous decrease in O₂ stores, was minimized. The total CO₂ and aerobic CO₂ outputs and, by difference, the millimoles (mmol) of lactate buffered by HCO₃ ^– (corrected for hyperventilation) were estimated. To test this method, ten normal subjects performed cycling exercise at each of two work rates for 6 min, one below the lactic acidosis threshold (LAT) (50 W for all subjects), and the other above the LAT, midway between LAT and peak O₂ [mean (SD), 144 (48) W]. Hyperventilation had a small effect on the calculation of mmol lactate buffered by HCO₃ ^– [6.5 (2.3)% at 6 min in four subjects who hyperventilated]. The mmol of buffer CO₂ at 6 min of exercise was highly correlated (r = 0.925, P < 0.001) with the increase in venous blood lactate sampled 2 min into recovery (coefficient of variation = ±0.9 mmol·l^–1). The reproducibility between tests done on different days was good. We conclude that the rate of release of CO₂2 from HCO₃ ^– can be estimated from the continuous analysis of simultaneously measured CO₂, O₂, and an estimate of muscle substrate.     

Differential cardiorespiratory response to combined exercise with different combinations of forearm and calf exercise

The purpose of this study was to examine whether cardiorespiratory responses to combined rhythmic exercise (60 contractions · min^–1) was affected by different combinations of upper and lower limb exercise in seven healthy women. Six different rhythmic exercises were compared: 6-min rhythmic handgrip at 10% of isometric maximal voluntary contraction (MVC) (H10); 6-min rhythmic plantar flexion at 10% MVC (P10); exhausting rhythmic handgrip at 50% MVC (H50); exhausting rhythmic plantar flexion at 50% MVC (P50); H50 was added to P10 (P1OH50); and P50 was added to H10 (H10P50). Exercise duration, after handgrip was combined with plantar flexion (P10H50), was shorter than that of H50, although the exercise duration of HIOP50 was not significantly different from P50. No significant difference was found between the difference from rest in oxygen uptake ( O₂) during H10P50 and the sum of O₂ during H10 and P50. Also, the differences from rest in forearm blood flow ( FBF) and calf blood flow ( CBF) during H10P50 were not significantly different from FBF in H10 and from CBF in P50. In contrast, O₂ in P10H50 was lower than the sum of O₂ in P10 and H50 (P < 0.05), and J FBF in P10H50 was lower than that in H50 (P < 0.05) , while CBF was not significantly different between P1OH50 and P10. The changes in heart rate from rest (d HR) during the combined exercises were lower than the sums of HR in the corresponding single exercises (P < 0.05). These results demonstrated an inhibitory summation of several cardiorespiratory responses to combined exercise resulting in a reduction in exercise performance which would seem to occur easily when upperlimb exercise is added to lower limb exercise.     

Cardiovascular responses to sustained maximal isometric contractions of the finger flexors

This study investigated cardiovascular responses to 2 min sustained submaximal (20% MVC) and maximal (100% MVC) voluntary isometric contractions of the finger flexors in healthy young women. Cardiovascular variables investigated were: heart rate (f _c), mean arterial pressure ( _a), and stroke volume (SV). Doppler echocardiography was used to estimate SV from measures of aortic diameter (AD) and time-velocity integrals. Preliminary studies indicated that AD did not change significantly after 2 min sustained 100% MVC. Therefore, pre-exercise AD values were used to calculate SV before, during and after exercise. During the 2-min 100% MVC period, f _c and _aincreased significantly during the first 30 s of contraction. f _c then remained constant during the remainder of the 2-min contraction period, while _acontinued to rise. SV did not change significantly during the 100% MVC task but increased significantly during recovery from sustained 100% MVC. The data suggest that the magnitude of cardiovascular responses to isometric exercise is dependent on the specific task performed, and that there is a different pattern of response for f _c, _a, and SV during 20% and 100% MVC tasks. Unlike f _c and _a, SV did not change significantly during isometric exercise, but increased significantly after sustained 100% MVC.     

Enhanced endurance in trained cyclists during moderate intensity exercise following 2 weeks adaptation to a high fat diet

These studies investigated the effects of 2 weeks of either a high-fat (HIGH-FAT: 70% fat, 7% CHO) or a high-carbohydrate (HIGH-CHO: 74% CHO, 12% fat) diet on exercise performance in trained cyclists (n = 5) during consecutive periods of cycle exercise including a Wingate test of muscle power, cycle exercise to exhaustion at 85% of peak power output [90% maximal oxygen uptake ( O_2max), high-intensity exercise (HIE)] and 50% of peak power output [60% O_2max, moderate intensity exercise (MIE)]. Exercise time to exhaustion during HIE was not significantly different between trials: nor were the rates of muscle glycogen utilization during HIE different between trials, although starting muscle glycogen content was lower [68.1 (SEM 3.9) vs 120.6 (SEM 3.8) mmol · kg ^–1 wet mass, P < 0.01] after the HIGH-FAT diet. Despite a lower muscle glycogen content at the onset of MIE [32 (SEM 7) vs 73 (SEM 6) mmol · kg ^–1 wet mass, HIGH-FAT vs HIGH-CHO, P < 0.01], exercise time to exhaustion during subsequent MIE was significantly longer after the HIGH-FAT diet [79.7 (SEM 7.6) vs 42.5 (SEM 6.8) min, HIGH-FAT vs HIGH-CHO, P<0.01]. Enhanced endurance during MIE after the HIGH-FAT diet was associated with a lower respiratory exchange ratio [0.87 (SEM 0.03) vs 0.92 (SEM 0.02), P<0.05], and a decreased rate of carbohydrate oxidation [1.41 (SEM 0.70) vs 2.23 (SEM 0.40) g CHO · min^–1, P<0.05]. These results would suggest that 2 weeks of adaptation to a high-fat diet would result in an enhanced resistance to fatigue and a significant sparing of endogenous carbohydrate during low to moderate intensity exercise in a relatively glycogen-depleted state and unimpaired performance during high intensity exercise.     

Effects of selective cooling of the facial area on physiological and metabolic output during graded maximal or prolonged submaximal exercise

Physiological and metabolic output responses to facial cooling during a graded maximal exercise and a prolonged submaximal exercise lasting 30 min at 65% max were investigated in five male subjects. Pedalling on a cycle ergometer was performed both with and without facial cooling (10°C, 4.6 m s^–1). Facial cooling at the end of graded maximal exercise apparently had no effect on plasma lactate (LA), maximal oxygen consumption ( max), maximal heart rate (HR max), rectal temperature (T _re), work-load, lactate threshold (LT), ventilatory threshold (VT) and onset of blood lactate accumulation (OBLA). However, the response to facial cooling after prolonged submaximal exercise is significantly different for heart rate and work-load. The results suggest that facial wind stimulation during maximal exercise does not produce a stress high enough to alter the metabolic and physiological responses.     

The influence of exercise/rest schedule on the physiological and psychophysical response to isometric shoulder-neck exercise

Six female subjects, aged 24-34 years, performed shoulder-neck exercise for 1 h or until they were exhausted by holding out their arms horizontally at 60° to the sagittal plane. One continuous and six intermittent protocols were applied, all with a mean load corresponding to the torque of the arms, i.e. about 15% maximal voluntary contraction (MVC). The intermittent protocols varied according to cycle time (10 s, 60 s, 360 s) and duty cycle (0.33, 0.50, 0.67, 0.83). Electromyogram (EMG), mean arterial blood pressure ( _a), heart rate (f _c) and perceived fatigue were monitored at regular intervals during exercise. Blood concentrations of potassium, lactate and ammonia were determined in pre- and postexercise samples of venous blood. Before and up to 4 h after exercise, measurements were made of MVC, pressure pain threshold, proprioceptive performance, and of EMG, _a and f _c during 1-min arm-holding at 25% MVC. Endurance times ranged from about 10 min to more than 1 h, significantly relating to both cycle time and duty cycle. The _a, f _c EMG amplitude and perceived fatigue increased early during all protocols and continued to increase throughout the exercise period. Duty cycle influenced all of these variables, while only _a and fatigue perception were related to cycle time. Cardiovascular and neuromuscular recovery was incomplete for hours after several of the protocols, as indicated for example by a sensitizised response to the 1-min armholding. The protocols differed substantially as regards the relationship between different responses. Thus, ranking of the protocols in terms of physiological strain was different, depending on the criterion variable. The result stresses the relevance of applying a comprehensive selection of variables when evaluating the responses to intermittent shoulder-neck exercise.     

Are oxygen uptake kinetics at the onset of exercise speeded up by local metabolic status in active muscles?

To assess the rate-limiting factor of oxygen uptake ( ) kinetics at the onset of exercise, six healthy male sedentary subjects performed repeated one-legged constant-load cycle exercise. The one-legged constant-load exercise test consisted of two 5-min periods of pedalling at an exercise intensity of 50 W, with a 5-min rest between periods (these exercise periods, i.e. first and second exercises, were performed by the same leg). The exercise was then repeated using the other leg. In addition, two-legged incremental exercise was investigated to establish whether kinetics were affected by slower heart rate kinetics. The incremental exercise test consisted of two-legged pedalling first with the cycle unloaded as a warm-up for 5 min followed by 50-W exercise for 5 min. The exercise intensity was then increased to 100 W for 5 min. During exercise, gas exchange parameters were determined by the breath-by-breath method and cardiac output ( ) was determined continuously by an impedance technique with a computer-based automated system. To determine the kinetics of heart rate (HR), and , a best fit procedure was employed using least-squares criteria with a time delay, except during the initial increase. During the one-legged constant-load exercise test, kinetics were significantly accelerated by repeated exercise using the same leg. On the other hand, when the exercise was changed to the other leg, kinetics were significantly slower, although kinetics continued to be faster. During the incremental exercise test, although the HR response was slower at the transition from 50-W to 100-W exercise than at the transition from warm-up to 50-W exercise, there were no significant changes in kinetics. These findings suggest that kinetics may be affected by metabolic conditions in the muscle, but not by blood flow ( and/or HR) kinetics.     

Times to exhaustion at 100% of velocity at [(V)\dot]\textO\text2 \dot V{\text{O}}_{\text{2}} max and modelling of the time-limit / velocity relationship in elite long-distance runners

The aim of this study was to measure running times to exhaustion (Tlim) on a treadmill at 100% of the minimum velocity which elicits _{max max} in 38 elite male long - distance runners _max = 71.4 ± 5.5 ml.kg^–1.min^–1 and _max = 21.8 ± 1.2 km.h^–1). The lactate threshold (LT) was defined as a starting point of accelerated lactate accumulation around 4 mM and was expressed in _max. Tlim value was negatively correlated with _max (r = -0.362, p< 0.05) and _max (r = –0.347, p< 0.05) but positively with LT (%v _max) (r = 0.378, p < 0.05). These data demonstrate that running time to exhaustion at _max in a homogeneous group of elite male long-distance runners was inversely related to _max and experimentally illustrates the model of Monod and Scherrer regarding the time limit-velocity relationship adapted from local exercise for running by Hughson et al. (1984) .     

Influence of the menstrual cycle and oral contraceptives on thermoregulatory responses to exercise in young women

Thermoregulatory responses to exercise in relation to the phase of the menstrual cycle were studied in ten women taking oral contraceptives (P) and in ten women not taking oral contraceptives (NP). Each subject was tested for maximal aerobic capacity ( ) and for 50% exercise in the follicular (F) and luteal (L) phases of the menstrual cycle. Since the oral contraceptives would have prevented ovulation a quasi-follicular phase (q-F) and a quasi-luteal phase (q-L) of the menstrual cycle were assumed for P subjects. Exercise was performed on a cycle ergometer at an ambient temperature of 24° C and relative air humidity of 50%. Rectal (T _re), mean skin ( ), mean body ( ) temperatures and heart rate (f _c) were measured. Sweat rate was estimated by the continuous measurement of relative humidity of air in a ventilated capsule placed on the chest, converted to absolute pressure (PH₂O_chest). Gain for sweating was calculated as a ratio of increase inPH₂O_chest to the appropriate increase inT _re for the whole period of sweating (G) and for unsteady-state (G_u) separately. The did not differ either between the groups of subjects or between the phases of the menstrual cycle. In P, rectal temperature threshold for sweating (T _{re, td}) was 37.85° C in q-L and 37.60° C in q-F (P < 0.01) and corresponded to a significant difference fromT _re at rest. TheT _re, andf _c increased similarly during exercise in q-F and q-L. No menstrual phase-related differences were observed either in the dynamics of sweating or in G. In NP,T _{re, td} was shorter in L than in F (37.70 vs 37.47° C,P<0.02) with a significantly greater value fromT _re at rest. The dynamics and G for sweating were also greater in L than in F. The G_u was 36.8 versus 16.6 kPa · ° C^–1 (P<0.01) while G was 6.4 versus 3.8 kPa · ° C^–1 (P<0.05), respectively. TheT _re, andf _c increased significantly more in phase F than in phase L. It was concluded that in these women performing moderate exercise, there was a greater temperature threshold and larger gains for sweating in phase L than in phase F. Intake of oral contraceptives reduced the differences in the gains for sweating making the thermoregulatory responses to exercise more uniform.     

Physical performance and metabolic changes induced by combined prolonged exercise and different energy intakes in humans

The purpose of this study was to evaluate the effects on physical performance of three levels of energy intake during a 5-day period of prolonged physical exercise and relative sleep deprivation. A group of 27 male soldiers were randomly assigned to three groups receiving either 1800 kcal · 24 h^–1 (7560 kJ, LC), 3200 kcal · 24h^–1 (13440 kJ, MC) or 4200 kcal-24h^–1 (17640 kJ, HC). They took part in a 5-day combat course (CC) of heavy and continuous physical activities, with less than 4 h sleep per day. Performance capacity was tested just before and at the end of CC. Maximal oxygen uptake ( O_2max) was determined during an exhausting incremental exercise test on a cycle ergometer. Anaerobic performance was measured from the time during which exercise could be maintained at supra maximal loads on a cycle ergometer. After CC, the subjects receiving LC exhibited a 14% decrease in power output at exhaustion in the incremental exercise test [from 325 (SEM 8) to 278 (SEM 9) W,P < 0.001] and a significant decrease in O_2max of 8% [from 3.74 (SEM 0.06) to 3.45 (SEM 0.05) l · min^–1,P<0.05]. The remaining two experimental groups demonstrated the same mechanical and metabolic performances on days 1 and 5. Anaerobic performance was not influenced by energy intake and the field course. Blood samples were obtained at rest on days 1 and 5. At the end of CC, the data demonstrated a significant decrease in blood glucose concentrated ion (P<0.01) for LC diet only. Plasma free fatty acid, blood glycerol and -OH butyrate were significantly increased in all groups, from day 1, but the values observed for LC were higher than those for the MC and HC diets. The concentrations of the anabolic hormones, insulin and testosterone, decreased in the three groups, the lowest values being observed in the LG group (P < 0.05). In conclusion, we found that only a severe energy deficit decreased physical performance during submaximal exercise. A moderate deficit between energy intake and expenditure did not affect performance. Supramaximal exercise did not appear to be influenced by energy intake and CC.