Endurance training regimen based upon arterial blood lactate: Effects on anaerobic threshold

Summary The purpose of this investigation was to assess the effect of endurance training based upon the intensity as determined by the arterial blood lactate concentration (LA). Seven healthy male college students performed endurance training on a Monark bicycle ergometer for 15 min on 3 days/week for 8 weeks, at an intensity corresponding to 4 mmol·l⁻¹ arterial blood LA determined during an incremental exercise test (25 watts increment every minute on a bicycle at 50 rpm). Another six male students served as the control group. To assess the training effect, both an incremental exercise test and a submaximal exercise test were performed before and after the endurance training. In the incremental exercise test, at , anaerobic threshold (AT), and the onset of respiratory compensation for metabolic acidosis (RCMA) were measured. AT was determined as the point at which arterial LA rose above the resting value, and RCMA was determined as the point at which Paco₂ decreased during the incremental exercise test. After training, AT increased significantly (37% increment expressed in ,p<0.05). There was a significant increase (p<0.05) in RCMA (17%) and (14%). This training decreased (4%), (15%), heart rate (10%), respiratory exchange ratio (5%), and LA (23%) significantly (p<0.05) during the submaximal exercise test after training. On the other hand, there were no significant changes in the control group through the period when the training group performed their training. These results showed that the endurance training intensity corresponding to 4 mmol·l₋₁ arterial blood LA was effective for the improvement in AT as well as . It is suggested that the present training regimen could delay the onset of anaerobic glycolysis, thus shifting AT to the higher workload and decreasing LA at a given submaximal exercise after training.     

Comparison of oxygen kinetics in young and old subjects

Summary Five older men (aged 60–69 yr) and five young men (aged 21–29 yr) with approximately equal levels of age-corrected max were compared with respect to oxygen kinetics at equal absolute workloads (100 watts) and at equal relative workloads (45% max) on a cycle ergometer. At 45% max, half times for response to instantaneous transition from unloaded pedalling were 30.0 s and 27.4 s for old and young respectively (t=0.260,p<0.80). No significant differences were found in the response and by inference none existed in O₂ extraction. Mean half times for heart rate responses at a workload of 100 W were 24.2 s and 20.6 s for old and young groups respectively (t=0.722,p<0.49). Mechanical efficiency estimated from steady state data at 100 W was 19.8% and 20.5% for old and young groups respectively (t=0.574). The close similarity in responses to submaximal work in old and young subjects of equivalent fitness suggests caution in the interpretation of agewise decrements observed in physiological variables which may be sensitive to physical fitness status.     

Relationship between record time and maximal oxygen consumption in middle-distance running

Summary The relationship between record time (t _r) and maximal oxygen uptake ( ) has been examined in 69 male physical education students who had taken part in 800-m and 1500-m footraces. It was found thatt _r and were inversely related. The relationshipst _r=f( ) have been fitted by two exponential equations:t _r(1500 m)=698e –0.0145 t _r(800 m) = 272e^–0.01 P<0.001. A mathematical formulation of the energy conservation principle in supramaximal running, based on the exponential increase of the oxygen uptake as a function of time with a rate constant of 0.025 s^–1 has been applied to thet _r calculation from . As calculatedt _r were highly correlated to measuredt _r (P<0.001), it was concluded that the relationshipst _r=f( ) can be interpreted on the basis of the model described in this study.     

Peak oxygen consumption and lactate threshold in full mask versus mouth mask conditions during incremental exercise

Respirator masks vary in inhalation and exhalation resistance, and in dead volume. It is believed that these factors may contribute significantly to an early anaerobic threshold in mask wearers during maximal exercise. Very little is known concerning the effect of respirator masks on maximal oxygen consumption and the lactate threshold (LT). The purpose of the present study was to assess peak LT and the ventilatory threshold (VT) of 14 experienced cyclists performing two maximal cycle exercise protocols while wearing a full respirator mask (FM) (M17 type) and a mouth mask (MM). was 10% lower under FM conditions. Peak values for ventilation , respiratory rate (f _bpeak) and tidal volume (V _Tpeak) were all significantly lower under with FM versus MM conditions. Performance time and maximal heart rate (f _cpeak) were not different between mask conditions. The LT and VT when expressed in % and the lactate concentration (mmol · l⁻¹ at LT and VT were not significantly different across mask conditions. Bland-Altman plots demonstrated longer inhalation times, decreasedf _r values and greater oxygen extraction under FM conditions. Thus, perhaps due to the increased inhalation resistance of the FM condition, subjects were unable to attain their “normal” despite similar performance times and maximalf _c. Furthermore, despite a diminished with FM, LT and VT appeared to be the same as with a MM.     

Adaptations to training at the individual anaerobic threshold

Summary The individual anaerobic threshold (Th_an) is the highest metabolic rate at which blood lactate concentrations can be maintained at a steady-state during prolonged exercise. The purpose of this study was to test the hypothesis that training at the Th_an would cause a greater change in indicators of training adaptation than would training around the Th_an. Three groups of subjects were evaluated before, and again after 4 and 8 weeks of training: a control group, a group which trained continuously for 30 min at the Th_an intensity (SS), and a group (NSS) which divided the 30 min of training into 7.5-min blocks at intensities which alternated between being below the Th_an [Th_an–30% of the difference between Th_an and maximal oxygen consumption ( )] and above the Than (Th_an + 30% of the difference between Th_an and ). The increased significantly from 4.06 to 4.271 · min^–1 in SS and from 3.89 to 4.061-min^–1 in NSS. The power output (W) at Th_an increased from 70.5 to 79.8% in SS and from 71.1 to 80.7% in NSS. The magnitude of change in ,W at Th_an, % at Th_an and in exercise time to exhaustion at the pretraining Th_an was similar in both trained groups. Vastus lateralis citrate synthase and 3-hydroxyacyl-CoA-dehydrogenase activities increased to the same extent in both trained groups. While all of these training-induced adaptations were statistically significant (P<0.05), there were no significant changes in any of these variables for the control subjects. These results suggest that the relative stimulus for physiological adaptation to training was similar in SS and NSS. These results also demonstrate that, when training intensity is set relative to the Th_an, it is the mean intensity during training that determines the extent of adaptation regardless of whether the exercise is performed intermittently or continuously.     

Longitudinal associations between anaerobic threshold and distance running performance

Summary Longitudinal alterations in anaerobic threshold (AT) and distance running performance were assessed three times within a 4-month period of intensive training, using 20 male, trained middle-distance runners (19–23 yr). A major effect of the high intensity regular intensive training together with 60- to 90-min AT level running training (2d ·wk ⁻¹) was a significant increase in the amount of O₂ uptake corresponding to AT ( AT; ml O₂ · min⁻¹ · kg⁻¹) and in maximal oxygen uptake ( ; ml O₂ · min⁻¹ · kg⁻¹). Both AT and showed significant correlations (r=−0.69 to −0.92 andr=−0.60 to −0.85, respectively) with the 10,000 m run time in every test. However, further analyses of the data indicate that increasing AT (r=−0.63,P<0.05) rather than (r=−0.15) could result in improving the 10,000 m race performance to a larger extent, and that the absolute amount of change (δ) in the 10,000 m run time is best accounted for by a combination of δ AT and δ5,000 m run time. Our data suggest that, among runners not previously trained over long distances, training-induced alterations in AT in response to regular intensive training together with AT level running training may contribute significantly to the enhancement of AT and endurance running performance, probably together with an increase in muscle respiratory capacity. This study was supported by Grant 59780141 from the Scientific Research Fund of the Ministry of Education, Science, and Culture, Japan     

Energy consumption of paraplegic locomotion using reciprocating gait orthosis

The energy cost of walking using a reciprocating gait orthosis (RGOII) with functional electrical stimulation (FES) was assessed in 14 patients with spastic complete paraplegia from six rehabilitation centres. Before and after training asing RGOII with FES, the subjects performed a progressive maximal test on an arm-crank ergometer to obtain their laboratory peak oxygen uptake heart rate (HR) and blood lactate concentration changes. At the end of the training session, oxygen uptake was measured during a walking test with orthosis at different speeds (6 min steady state at 0.1 m · s⁻¹, followed by 2-min stages at progressively increasing speeds up to exhaustion). Of the subjects 4 repeated this test using orthosis without FES. At a speed of 0.1 m · s⁻¹, represented 47 (SD 23)% of , mean HR was 137 (SD 21) beats · min⁻¹ and mean blood lactate concentration 2.4 (SD 1.4) mmol · l⁻¹. Maximal speed ranged from 0.23 to 0.5 m · s⁻¹. At maximal speed, was 91 (SD 18) % of mean HR reached 96 (SD 7)% and mean blood lactate concentration only 52 (SD 19)% of the maximal values measured during the laboratory test. Walking without electrical stimulation induced an increase in HR but there was no difference in and blood lactate compared to walking with stimulation. The training period did not result in any improvement in maximal physiological data. We concluded that the free cadence walking speed with orthosis remains much lower than that of able-bodied people or wheelchair users. The metabolic cost at a given speed is much higher even if, using a stimulation device, the cardiovascular stress is reduced.     

The effects of specificity of training on rating of perceived exertion at the lactate threshold

Summary To determine the effects of cycle and run training on rating of perceived exertion at the lactate threshold (LT), college men completed a 40-session training program in 10 weeks (n=6 run training,n=5 cycle training,n=5 controls). Pre-and post-training variables were measured during graded exercise tests on both the bicycle ergometer and treadmill. ANOVA on the pre- and post-training difference scores resulted in similar improvements in for both testing protocols, regardless of training mode. The run training group increased at the LT by 58.5% on the treadmill protocol and by 20.3% on the cycle ergometer. Cycle trainers increased LT only during cycle ergometry (+38.7%). No changes were observed in the control group. No differences for RPE at the LT were found before or after training, or between testing protocols for any group. Perception of exercise intensity at the LT ranged from “very light” to “light”. The relationship between RPE and was altered by the specific mode of training, with trained subjects having a lower RPE at a given (no change in RPE at max.). It was concluded that RPE at the LT was not affected by training, despite the fact that after training the LT occurs at a higher work rate and was associated with higher absolute and relative metabolic and cardiorespiratory demands.     

Adaptive changes in hypercapnic ventilatory response during training and detraining

Summary To confirm the effects of physical training and detraining on CO2 chemosensitivity, we followed hypercapnic ventilatory response at rest in the same five subjects during pre-, post- and detraining for 6 years. They joined our university badminton teams as freshmen and participated regularly in their team's training for about 3 h a day, three times a week, for 4 years. After that they retired from their teams and stopped training in order to study in the graduate school for 2 years. Maximum pulmonary ventilation and maximal oxygen uptake for each subject were determined during maximal treadmill exercise. The slope (S) of ventilatory response to carbon dioxide at rest was measured by Read's rebreathing method. Mean values of increased statistically during training and decreased statistically during detraining. A similar tendency was observed in . The average value ofS before training was 1.91 l·min^–1·mmHg^–1, (+) SD 0.52 and it decreased gradually with increasing training periods; the difference between theS values before (1980) and after training (1982, 1983 and 1984) were all significant. Furthermore, the mean values ofS increased significantly during detraining as compared with those obtained at the end of training (April 1984). We concluded that in normal subjects, long-term physical training increases aerobic work capacity and decreases CO₂ventilatory responsiveness, and that the ventilatory adaptations with training observed here are reversible through detraining.     

Cardiorespiratory adaptation with short term training in older men

Summary The purpose of this study was to assess the rate of training-induced cardiorespiratory adaptations in older men [mean (SD), 66.5 (1.2) years]. The eight subjects trained an average of 4.3 (0.3) times each week. The walk/jog training was in two phases with 4 weeks (phase 1) at a speed to elicit 70% of pre-training maximal oxygen consumption ( ), and 5 weeks (phase 2) at 80%. Maximal exercise treadmill tests and a standardized submaximal protocol were performed prior to training, at weekly intervals during the training programme, and after training. (ml·kg^–1·min^–1) increased significantly over both phases: 6.6% after the first 4 weeks, and an additional 5.2% after the final 5 weeks. The weekly changes in over phase 1 were well fitted by an exponential association curve (r=0.75). The half-time for the rate of adaptation was 13.8 days, or 8.3 training sessions. Over phase 2, the change in did not plateau and a time course could not be determined. Submaximal exercise heart rate (f _c ) was reduced a significant 10 beats · min^–1 after the first 4 weeks, and a further 6 beats · min^–1 over the final 5 weeks. Thef _c reductions showed half-times of 9.1 days (phase 1) and 9.8 days (phase 2) (or 5-6 training sessions). The anaerobic ventilation threshold was increased 13.9% over the 9 weeks of training and the respiratory exchange ratio during constant load heavy exercise was significantly reduced; however, these changes could not be described by an exponential time course. Thus, short-term exercise training of older men resulted in significant and rapid cardiorespiratory improvements.     

Association between heart rate variability and training response in sedentary middle-aged men

The effect of exercise training on heart rate variability (HRV) and improvements in peak oxygen consumption ( _peak) was examined in sedentary middle-aged men. The HRV and absolute and relative _peak of training (n = 19) and control (n = 15) subjects were assessed before and after a 24-session moderate intensity exercise training programme. Results indicated that with exercise training there was a significantly increased absolute and relative _peak (P < 0.005) for the training group (12% and 11% respectively) with no increase for the control group. The training group also displayed a significant reduction in resting heart rate; however, HRV remained unchanged. The trained subjects were further categorized into high (n = 5) and low (n = 5) HRV groups and changes in _peak were compared. Improvements in both absolute and relative _peak were significantly greater (P > 0.005) in the high HRV group (17% and 20% respectively) compared to the low HRV group (6% and 1% respectively). The groups did not differ in mean age, pretraining oxygen consumption, or resting heart rate. These results would seem to suggest that a short aerobic training programme does not alter HRV in middle-aged men. Individual differences in HRV, however, may be associated with _peak response to aerobic training.     

Hypoxic ventilatory response during rest and exercise after a Himalayan expedition

Hypoxic ventilatory response (HVR) was examined before and after acclimatization to high altitude. Transient hyperoxic switches according to Dejours's technique were used to examine the contribution of HVR to the hyperpnoea of increasing exercise intensities. Ten mountaineers were exposed to hypoxia (oxygen fraction in inspired gas,F ₁O₂ = 0.11, 79 mmHg) before the expedition and after return from altitude (56 days, 30 days at 4900 m or higher). After 25-min breathing hypoxic gas, the subjects performed a maximal cycle ergometer test (increments 50 W per 5 min). Respired gases and ventilation were analysed breath-by-breath, partial pressure of oxygen (PO₂) and oxygen saturation (SO₂) were measured in capillary blood. The HVR was tested by switching two breaths to anF ₁O₂ of 1.0. The nadir of after the switch was measured (decrease in ventilation, D ). The HVR was expressed as the D at a PO₂ of 40 mmHg (D ) and the D versus decrease ofSO₂ (D /[100 −SO₂]). The HVR estimated by D increased from 19.9 to 28.01 · min⁻¹ (median,P = 0.013). The HVR expressed as D /(100 −SO₂) at rest was no different before and after acclimatization (0.89 and 0.86 l · min⁻¹ · %⁻¹, respectively) and during exercise it did not change before the expedition (0.831 · min⁻¹ %⁻¹). However, D /(100 −SO₂) increased significantly with exercise intensity after the expedition (1.61 l · min⁻¹ · %⁻¹ at 200 W). The changes of D versusSO₂ as well as of D versus were steeper after the expedition than before. In summary, after return from 30 day at high altitude, an increased HVR was observed. The augmentation of HVR was evident at higher exercise intensities and we suggest that this reflects a change in sensitivity of the peripheral chemoreflex loop.     

Effects of endurance training on hyperammonaemia during a 45-min constant exercise intensity

Summary Eleven laboratory-pretrained subjects (initial =54 ml·kg⁻¹·min⁻¹) took part in a study to evaluate the effect of a short endurance training programme [8–12 sessions, 1 h per session, with an intensity varying from 60% to 90% maximal oxygen consumption ] on the responses of blood ammonia (b[NH ₄ ⁺ ]) and lactate (b[la]) concentrations during progressive and constant exercise intensities. After training, during which did not increase, significant decreases in b[NH ₄ ⁺ ], b[la] and muscle proton concentration were observed at the end of the 80% constant exercise intensity, although b[NH ₄ ⁺ ] and b[la] during progressive exercise were unchanged. On the other hand, no correlations were found between muscle fibre composition and b[NH ₄ ⁺ ] in any of the exercise procedures. This study demonstrated that a constant exercise intensity was necessary to reveal the effect of training on muscle metabolic changes inducing the decrease in b[NH ₄ ⁺ ] and b[la]. At a relative power of exercise of 80% , there was no effect of muscle fibre composition on b[NH ₄ ⁺ ] accumulation.     

The effects of training on the metabolic and respiratory profile of high-intensity cycle ergometer exercise

Summary The tolerable work duration (t) for high-intensity cycling is well described as a hyperbolic function of power (W):W=(W'·t ⁻¹)+W _a , whereW _a is the upper limit for sustainable power (lying between maximumW and the threshold for sustained blood [lactate] increase,Θ _lac), andW' is a constant which defines the amount of work which can be performed >W _a . As training increases the tolerable duration of high-intensity cycling, we explored whether this reflected an alteration ofW _a ,W' or both. Before and after a 7-week regimen of intense interval cycle-training by healthy males, we estimated (^)Θ _lac and determined maximum O₂ uptake ;W _a ;W'; and the temporal profiles of pulmonary gas exchange, blood gas, acid-base and metabolic response to constant-load cycling at and aboveW _a . Although training increased (24%), (15%) andW _a (15%),W' was unaffected. For exercise atW _a , a steady state was attained for , [lactate] and pH both pre- and post-training, despite blood [norepinephrine] and [epinephrine] ([NE], [E]) and rectal temperature continuing to rise. For exercise >W _a , there was a progressive increase in (resulting in at fatigue), [lactate], [NE], [E] and rectal temperature, and a progressive decrease for pH. We conclude that the increased endurance capacity for high-intensity exercise following training reflects an increasedW asymptote of theW−t relationship with no effect on its curvature; consequently, there is no appreciable change in the amount of work which can be performed aboveW _a . Furthermore, regardless of training status,W _a represents the upper power limit at which , blood [lactate] and blood pH can eventually be stabilized. Exercise >W _a , in contrast, is characterized by a steadily increasing and blood [lactate], a falling blood pH and consequently, imminent fatigue. Supported in part by a UCLA Graduate Division Doctoral Research Award     

Age and training effects on the lactate kinetics of master athletes during maximal exercise

Summary To study the effects of age and training on lactate production in older trained subjects, the lactate kinetics of highly trained cyclists [HT,n = 7; 65 (SEM 1.2) years] and control subjects with low training (LT,n = 7) and of similar age were compared to those of young athletes [YA,n = 7; 26 (SEM 0.7) years], during an incremental exercise test to maximum power. The results showed that the lactacidaemia at maximal oxygen uptake ( ) was lower for HT than for LT (P<0.05) and, in both cases, lower than that of YA (P<0.001). The respective values were HT: 3.9 (SEM 0.51), LT: 5.36 (SEM 1.12), and YA: 10.3 (SEM 0.63) mmol·1^–1. At submaximal powers, however, the difference in lactacidaemia was not significant between HT and YA, although the values for lactacidaemia at calculated per watt and per watt normalized by body mass were significantly lower for HT (P<0.001) and LT (P< 0.02). These results would indicate that the decline in power with age induced a decline in lactacidaemia. Yet this loss in power was not the only causative factor; indeed, our results indicated a complementary metabolic influence. In the older subjects training decreased significantly the lactacidaemia for the same submaximal power (P<0.01) and from 60% of onwards (P<0.05); as for YA it postponed the increase and accumulation of lactates. The lactate increase threshold (Th_1a–,1) was found at 46% for LT and at 56% for HT. The lactate accumulation threshold (Th_1a–,₂) was observed at approximately 80% for all three groups but at a value significantly different in each group. At Th_1a–,2 the lactate value of HT was 2 (SEM 0.19) mmol · 1^–1 thus closer to the value normally associated with the increase threshold instead of the accumulation threshold. In conclusion, the reduction in lactacidaemia was enhanced by training. Furthermore, the modification in the lactate kinetics with aging indicated that training at an intensity corresponding to a lactacidaemia of 2 and 4 mmol·1^–1 was inadequate for master endurance athletes.     

Increased ventilation in runners during running as compared to walking at similar metabolic rates

At similar levels of carbon dioxide production ( ) and oxygen consumption ( ), runners have been shown to have a greater minute ventilation ( ) during running as compared to walking. The mechanism responsible for these differences has yet to be identified. To determine if these differences are a result of differences in acid-base status, potassium (K⁺), norepinephrine and/or epinephrine levels, seven well-trained runners completed walk and run tests at similar and levels. The occurrence of entrainment of the breathing and stride frequencies during both walking and running was also determined. was significantly greater during the run as compared to the walk, 73.7 (2.2) versus 68.6 (2.0)l·min⁻¹, respectively, despite the similarity in and levels. Alveolar ventilation was not significantly different between the run and the walk, 60.4 (4.7) versus 59.6 (4.4)l·min⁻¹, respectively. Dead space ventilation was found to be significantly greater during running as compared to walking, 13.3 (3.2) versus 9.0 (4.7)l·min⁻¹, respectively. The increases in were due to increases in breathing frequency and decreases in tidal volume during the run as compared to the walk. Arterial partial pressures of C0₂ (P _aCO₂) were not significantly different when comparing walking and running to rest values nor when comparing walking and running. Arterial pH was significantly lower during walking as compared to rest and running. Bicarbonate levels were significantly lower during walking as compared to rest. Lactate was significantly greater during walking as compared to rest and to running. K⁺ levels were significantly higher during walking and running as compared to rest. Epinephrine and norepinephrine levels were not significantly different between running and walking. During the walk, six of the seven subjects entrained their breathing frequency to the stride frequency, and during the run three of the seven subjects demonstrated entrainment. Results from this investigation do not support mediation of under the present experimental conditions by changes in arterial levels of humoral factors previously shown to influence .     

Cardiovascular and respiratory responses to submaximal exercise training in the thoroughbred horse

Cardiovascular and respiratory responses to submaximal exercise training were investigated in 6 thoroughbred racehorses. Oxygen uptake, heart rate (HR) and arteriovenous oxygen content difference were measured during incremental treadmill exercise tests, before and after 7 weeks of treadmill training. Cardiac output during exercise was calculated by the direct Fick technique. Maximal oxygen uptake ( ) was increased by 23% after training, from 129.7 ml/kg/min to 160.0 ml/kg/min. The treadmill speed at which was attained increased by 19%. The increased aerobic power after training was associated with an increase in maximal cardiac output and stroke volume, a decrease in arteriovenous oxygen difference and no change in HR. There was no change in pulmonary ventilation during exercise at . Mean mixed venous oxygen content ( ) at before training was 2.8±1.0 ml/100 ml blood (mean ±SE). After training the value was 8.6±1.4 ml/100 ml blood. It is concluded that the increase in after training in the horse is dependant on augmented blood flow, and is not dependent on either increased arterial oxygen content or arteriovenous oxygen content difference. Cardiac capacity to pump blood is therefore of primary importance as a determinant of increases in due to training in the horse.     

Use of the force-velocity test to determine the optimal braking force for a sprint exercise on a friction-loaded cycle ergometer

A group of 15 untrained male subjects pedalled on a friction-loaded cycle ergometer as fast as possible for 5–7 s to reach the maximal velocity (V{immax}) against different braking forces (F _B). Power was averaged during a complete crank rotation by adding the power dissipated againstF _B to the power necessary to accelerate the flywheel. For each sprint, determinations were made of peak power output ( ) power output attained atV _max ( ) calculated as the product ofV _max andF _B and the work performed to reachV _max expressed in mean power output ( ). The relationships between these parameters andF _B were examined. A biopsy taken from the vastus lateralis muscle and tomodensitometric radiographs of both thighs were taken at rest to identify muscle metabolic and morphometric properties. The value was similar for allF _B. Therefore, the average of values was defined as corrected maximal power ( ). This value was 11 higher than the maximal power output uncorrected for the acceleration. Whereas the determination did not require high loads, the highest value ( ) was produced when loading was heavy, as evidenced by the -F _B parabolic relationship. For each subject, the braking force ( ) giving was defined as optimal. The , equal to 0.844 (SD 0.108) N · kg⁻¹ bodymass, was related to thigh muscle area (r = 0.78,P < 0.05). The maximal velocity ( ) reached against this force seemed to be related more to intrinsic fibre properties (% fast twitch b fibre area and adenylate kinase activity). Thus, from the determination, it is suggested that it should be possible to predict the conditions for optimal exercise on a cycle ergometer.     

Effect of exercise to rest ratio on plasma lactate concentration at work rates above and below maximum oxygen uptake

Summary The metabolic and physiological responses to different exercise to rest ratios (E: R) (2:1, 1: l, 1:2) of eight subjects exercising at work rates approximately 10% above and below maximum oxygen uptake ( ) were assessed. Each of the six protocols consisted of 15 1-min-long E : R intervals. Total work (kJ), oxygen uptake ( ), heart rate (f _c and plasma lactate concentrations were monitored. With increases in either E : R or work rate, andf _c increased (P <0.05). The average (15 min) andf _c ranged from 40 to 81 %, and from 62 to 91% of maximum, respectively. Plasma lactate concentrations nearly doubled at each E : R when work rate was increased from 90 to 110% of and ranged from a low of 1.8 mmol -I^–1 (1: 2–90) to a high of 10.7 mmol·1^–1 (2:1–110). The 2:1–110 protocol elicited plasma lactate concentrations which were approximately 15 times greater than that of rest. These data suggest that plasma lactate concentrations during intermittent exercise are very sensitive to both work rate and exercise duration.     

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.