Fitness as a determinant of oxygen uptake response to constant-load exercise

Summary Exercise performed above the lactate threshold (Θ _La) produces a slowly-developing phase of oxygen uptake ( ) kinetics which elevates above that predicted from the sub-Θ _La -work rate relationship. This phenomenon has only been demonstrated, to date, in subjects who were relatively homogeneous with respect to fitness. This investigation therefore examined whether this behaviour occurred at a given absolute or whether it was a characteristic of supra-Θ _La exercise in a group of subjects with over a threefold range ofΘ _La (990–3000 ml O₂·min⁻¹) and peak (1600–5260 ml O₂·min⁻¹). Twelve healthy subjects performed: 1) exhausting incremental cycle ergometer exercise for estimation ofΘ _La ( ) and peak , and 11) a series of constant-load tests above and below for determination of the profile and efficiency of work. During all tests expired ventilation, and carbon dioxide production were monitored breath-by-breath. The efficiency of work determined during incremental exercise (28.1±0.7%, ,n=12) did not differ from that determined during sub- constant-load exercise (27.4±0.5%,p>0.05). For constant-load exercise, rose above that predicted, from the sub- -work rate relationship, for all supra- work rates. This was evident above 990 ml O₂·min⁻¹ in the least fit subject but only above 3000 ml O₂·min⁻¹ in the fittest subject. As a consequence the efficiency of work was reduced from 27.4±0.5% for sub- exercise to 22.6±0.4% (p<0.05) at the lowest supra- work rate (i.e. +20 W, on average). The efficiency of work generally decreased further at the higher supra- work rates. We conclude that the response to constant-load exercise includes an additional slow phase of the kinetics for all exercise intensities above irrespective of the fitness of the subject. Consequently, measurements of the aerobic efficiency of work during constant-load exercise must rigorously constrain the exercise intensity to the sub- domain. Supported by grants from the John D. and Catherine T. Mac-Arthur Foundation, USPHS RR 00865-15, and NIH HL 07694-01     

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     

Oxygen consumption and metabolic strain in rowing ergometer exercise

Summary Oxygen consumption ( ) when rowing was determined on a mechanically braked rowing ergometer (RE) with an electronic measuring device. was measured by an open spirometric system. The pneumotachograph valve was fixed to the sliding seat, thus reducing movement artefacts. A multi-stage test was performed, beginning with a work load of 150 W and increasing by 50 W every 2 minutes up to exhaustion. Serum lactate concentrations were determined in a 30 s break between the work stages. 61 examinations of oarsmen performing at maximum power of 5 W · kg⁻¹ or more were analysed. and heart rate (HR) for each working stage were measured and the regression line of on the work load (P) and an estimation error (s_xy) were calculated: (ml · min⁻¹) (S_xy = ± 337 ml,r = 0.98) Good reproducibility was found in repeated examinations. Similar spiroergometry was carried out on a bicycle ergometer (BE) with 10 well trained rowers and 6 trained cyclists. of rowing was about 600 ml · min⁻¹ higher than for bicycling in the submaximal stages for both groups. The of RE exercise was 2.6% higher than for oarsmen on BE, and the cyclists reached a greater on BE than the oarsmen. No differences were found between RE and BE exercise heart rate. The net work efficiency when rowing was 19% for both groups, experienced and inexperienced: when cycling it was 25% for cyclists and 23% for oarsmen.     

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.     

Heart rate changes caused by varying the oxygen supply to isolated hind legs of rats

Summary In a rat with an isolated hind leg circulation perfused with varying tyrode solutions, heart rate (HR) changes were studied in dependence of in the isolated hind leg and of , [K⁺], pH and lactic acid concentration ([Lac]) measured in the venous outflow of the isolated hind leg. In experimental series I the inflow was kept constantly high (either about 65 or 72 kPa). The perfusion pressure alternated between 16 and 24 kPa leading to flow rates in isolated hind legs ( ) from 30 to 50 ml · 100 g⁻¹ · min⁻¹. The depended on the momentary (flow-limited oxygen uptake). The [K⁺] and [Lac], the pH and the remained nearly constant while the was lower at small flow rates. The HR decreases some 4 min after initial enhancement of and . Series II comprised experiments with low flow rates and a medium oxygen supply ( =2.5−17.4 ml · 100 g⁻¹ · min⁻¹), =17.5−62.7 kPa). The ranged between 0.02 and 0.2 ml · 100 g⁻¹ · min⁻¹. The [K⁺] and [Lac], the and the HR increased while the pH decreased. The [Lac] in the outflow showed a strong dependence on oxygen uptake and — at a weak oxygen supply — on the time. Cross-correlation analyses between the parameters confirmed that the HR was best temporally correlated to the [Lac] in the outflow. In series III a 17 min perfusion of normoxic solution ( =65.3 kPa) was followed by perfusion with a hypoxic tyrode solution ( =8.7 kPa). was 30 ml · 100 g⁻¹ · min⁻¹. The [Lac], the and the HR increased accompanied by a decrease in pH. However a HR increase was observed only when the actual values of [Lac], and pH exceeded their normal ranges for a resting muscle. The results support the hypothesis that heart rate is additionally influenced by metabolic muscle receptors measuring lactic acid concentration in working muscle.     

Precision of ventilatory and gas exchange alterations as a predictor of the anaerobic threshold

Summary Anaerobic threshold has been defined as the oxygen uptake ( ) at which blood lactate (La) begins to rise systematically during graded exercise (Davis et al. 1982). It has become common practice in the literature to estimate the anaerobic threshold by using ventilatory and/or gas exchange alterations. However, confusion exists as to the validity of this practice. The purpose of this study was to examine the precision with which ventilatory and gas exchange techniques for determining anaerobic threshold predicted the anaerobic threshold resolved by La criteria. The anaerobic threshold was chosen using three criteria: (1) systematic increase in blood La (AT_La), (2) systematic increase in ventilatory equivalent for O₂ with no change in the ventilatory equivalent for CO₂ ( ), and (3) non-linear increase in expired ventilation graphed as a function of ( ). Thirteen trained male subjects performed an incremental cycle ergometer test to exhaustion in which the load was increased by 30 W every 3 minutes. Ventilation, gas exchange measures, and blood samples for La analysis were obtained every 3rd min throughout the test. In five of the thirteen subjects tested the anaerobic threshold determined by ventilatory and gas exchange alterations did not occur at the same as the AT_La. The highest correlation between a gas exchange anaerobic threshold and AT_La was found for and was r=0.63 (P<0.05). These data provide evidence that the AT_La and do not always occur simultaneously and suggest limitations in using ventilatory or gas exchange measures to estimate the AT_la.     

Intraerythrocyte and plasma lactate concentrations during exercise in humans

Summary The purpose of this study was to examine plasma and intraerythrocyte lactate concentrations during graded exercise in humans. Seven adult volunteers performed a maximum O₂ uptake ( ) test on a cycle ergometer. Plasma and intraerythrocyte lactate concentrations (mmol · L⁻¹ of plasma or cell water) were determined at rest, during exercise, and at 15-min post-exercise. The results show that plasma and intraerythrocyte lactate concentrations were not significantly different from each other at rest or moderate (⩽50% ) exercise. However, the plasma concentrations were significantly increased over the intraerythrocyte levels at 75% and 100% . The plasma to red cell lactate gradient reached a mean (±SE) 1.7±0.4 mmol · L⁻¹ of H₂O at exhaustion, and was linearly (r=0.84) related to the plasma lactate concentration during exercise. Interestingly, at 15-min post-exercise the direction of the lactate gradient was reversed, with the mean intraerythrocyte concentration now being significantly increased over that found in the plasma. These results suggest that the erythrocyte membrane provides a barrier to the flux of lactate between plasma and red cells during rapidly changing blood lactate levels. Furthermore, these data add to the growing body of research that indicates that lactate is not evenly distributed in the various water compartments of the body during non-steady state exercise.     

The effect of citrate loading on exercise performance,acid-base balance and metabolism

Summary Nine subjects ( 65±2 ml·kg⁻¹·min⁻¹, mean±SEM) were studied on two occasions following ingestion of 500 ml solution containing either sodium citrate (C, 0.300 g·kg⁻¹ body mass) or a sodium chloride placebo (P, 0.045 g·kg⁻¹ body mass). Exercise began 60 min later and consisted of cycle ergometer exercise performed continuously for 20 min each at power outputs corresponding to 33% and 66% , followed by exercise to exhaustion at 95% . Pre-exercise arterialized-venous [H⁺] was lower in C (36.2±0.5 nmol·l⁻¹; pH 7.44) than P (39.4±0.4 nmol·l⁻¹; pH 7.40); the plasma [H⁺] remained lower and [HCO ₃ ⁻ ] remained higher in C than P throughout exercise and recovery. Exercise time to exhaustion at 95% was similar in C (310±69 s) and P (313±74 s). Cardiorespiratory variables (ventilation, , , heart rate) measured during exercise were similar in the two conditions. The plasma [citrate] was higher in C at rest (C, 195±19 μmol·l⁻¹; P, 81±7 μmol·l⁻¹) and throughout exercise and recovery. The plasma [lactate] and [free fatty acid] were not affected by citrate loading but the plasma [glycerol] was lower during exercise in C than P. In conclusion, sodium citrate ingestion had an alkalinizing effect in the plasma but did not improve endurance time during exercise at 95% . Furthermore, citrate loading may have prevented the stimulation of lipolysis normally observed with exercise and prevented the stimulation of glycolysis in muscle normally observed in bicarbonate-induced alkalosis.     

Growth hormone regulation in two types of aerobic exercise of equal oxygen uptake

Summary Five normal men, aged 23 to 35 years, participated in two bouts of continuous aerobic cycling separated by five days. The first type of exercise (EI) was cycling at a pedalling frequency of 50 rev · min⁻¹ with a load which produced a steady state O₂ uptake of approximately 40% of the subjects' . The second type of exercise (EII) was cycling at a pedalling frequency of 90 rev · min⁻¹ with a load such that an equal steady state was reached and maintained. Both EI and EII lasted 40 min. GH levels increased in EI and EII, reaching their maximum at 8 min of recovery (245 and 300% of resting values, respectively). No significant differences were observed between EI and EII in GH, lactate, glucagon, insulin, cortisol and glucose levels between the two exercises. While it has been reported earlier that GH levels were frequently related to lactate levels and/or decreased O₂ availability (Sutton 1977; Raynaud et al. 1981; Kozlowski et al. 1983; VanHelder et al. 1984a, b), this study suggests that the opposite is also valid, that is, different types of exercise of equal , duration and lactate production do not produce significantly different GH responses.     

Metabolic and endocrine responses to graded exercise under acute hypoxia

Summary Eight male subjects (24±1 years old) performed graded ergocycle exercises in normoxic (N) and acute hypoxic (H) conditions (14.5% O₂). decreased from 55.5±1.3 to 45.8±1.4 ml · kg⁻¹ · min⁻¹ in H condition. Plasma glucose and free fatty acid concentrations remained unchanged throughout exercise in both conditions. Increase in blood lactate concentration was associated with relative workload in both conditions. At lactate concentrations were similar in the two conditions, plasma insulin, glucagon, and LH concentrations did not significantly change in either. Plasma δ4-androstenedione and testosterone increased in a similar manner in both conditions. Finally plasma norepinephrine concentration reached at was significantly lower in hypoxia. These results suggest that acute moderate hypoxia does not affect metabolic and hormonal responses to short exercise performed at similar relative workloads, i.e. when the reduction of due to hypoxia is taken into consideration. The lower catecholamine response to maximal exercise under acute hypoxia might suggest that the sympathetic response could be related to relative as well as absolute workloads. Supported by grants from FCAC and FRSQ, Québec and NSERC, Canada     

Critical determinants of endurance performance in middle-aged and elderly endurance runners with heterogeneous training habits

Summary The current investigation was designed to determine which factor or what combination of factors would best account for distance running performance in middle-aged and elderly runners (mean age 57.5 years SD±9.7) with heterogeneous training habits. Among 35 independent variables which were arbitrarily selected as possible prerequisites in the distance running performance of these runners, oxygen uptake at lactate threshold (LT) (r=0.781∼0.889), maximal oxygen uptake (r=0.751∼0.886), and chronological age (r=−0.736∼−0.886) were found to be the 3 predictor variables showing the highest correlations with the mean running velocity at 5 km (V _{5 km}), 10 km (V _{10 km}), and marathon (V _M). When all independent variables were used in a multiple regression analysis, any 3 or 4 variables selected from among at LT, chronological age, systolic blood pressure (SBP), atherogenic index (AI), and Katsura index (KI) were found to give the best explanation ofV _{5 km},V _{10 km}, orV _M in a combined linear model. Linear multiple regression equations constructed for predicting the running performances were:V _{5 km}=0.046X ₁−0.026X ₂−0.0056X ₃+5.17,V _{10 km}=0.028X ₁−0.028X ₂−0.190X ₄−1.34X ₅+6.45, andV _M=−0.0400X ₂−0.324X ₄−1.16X ₅+7.36, where at LT (ml·min⁻¹·kg⁻¹),X ₂ = chronological age,X ₃=SBP,X ₄=AI, andX ₅=KI. We suggest that distance running performance of middle-aged and elderly runners could be predicted with a relatively high accuracy by a single predictor of at LT or , or by a combination of either of these predictors with more easily measurable indices such as age, AI, KI, or SBP. The prediction equations which have been developed can be applied to a larger population of middle-aged and elderly runners. Data were collected at the Human Performance Laboratory, Hiroshima University     

Differences in oxygen consumption and external power between male and female speed skaters during supramaximal cycling

Summary Differences in performance levels between elite male and female endurance athletes are often explained by differences found in max even when expressed in max per kilogram lean body mass ( /LBM). Such an explanation is only a matter of course when less or no difference exists in mechanical efficiency, anaerobic power and technical variables like friction constants between males and females, particularly during supramaximal exercises. In this study five elite male speed skaters were compared with five elite female speed skaters with respect to oxygen consumption and external power during a 3 min supramaximal bicycle ergometer test. The training background and training history of both groups were comparable. Although the elite males showed a 20% higher /BW and 8% higher /LBM (71.0 versus 65.0 1·min⁻¹·kg⁻¹) than the females, the female group showed the same mean external power P_c per kilogram bodyweight, and a surprising 12% higher P_C/LBM than the males (6.47 versus 5.79 W·kg⁻¹). Hence the female group delivered 22% more external power per liter of oxygen consumption. With the help of additional data from 14 male and 11 female sub-elite skaters it is shown that the differences between the elite groups are mainly due to sex differences. In the light of differences between men and women reported in other studies, it seems likely that the differences found in this study are due to a difference in mechanical efficiency which particularly occurs in supramaximal tasks. With respect to skating performance, it is concluded that the difference in performance level between elite male and female skaters will mainly be determined by differences in skating technique and in frictional losses, and not by differences in work capacity.     

Ventilatory anaerobic threshold in healthy children

Summary The ventilatory anaerobic threshold (VAT) during graded exercise was defined as the oxygen uptake ( ) immediately below the exercise intensity at which pulmonary ventilation increased disproportionally relative to . Since VAT is considered to be a sensitive and noninvasive measure for evaluating cardiorespiratoy endurance performance, the purpose of the present study was to determine normal values in children. We examined 257 healthy children (140 boys and 117 girls) varying in age from 5.7 to 18.5 years, during treadmill exercise. The data were analyzed in relation to sex and age. In boys the lowest (ml · min⁻¹ · kg⁻¹) was found in the youngest age group (5–6 year). In girls, on the other hand, no significant increase occurred with age. For VAT, expressed as ml O₂ · min⁻¹ · kg⁻¹ or as a percent of a significant decrease was found in boys and girls with age. This suggests an increase in lactacid anaerobic capacity during growth. In contrast to observations in adults, only low correlations were found between and VAT (r=0.28 in boys and r=0.52 in girls), which suggests that the development of the underlying physiological mechanism does not occur at the same rate in growing children. These data provide normal values for VAT that can be used for clinical exercise testing in the pediatric age group.     

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.     

Effects of standing cycling and the use of toe stirrups on maximal oxygen uptake

Summary Twenty-eight subjects (6 normal men, 14 distance runners, and 8 rowers) were tested for maximal oxygen uptake ( ) and associated physiological measures during bicycle ergometer exercise with toe stirrups while standing (BEts) and during treadmill exercise (TM). Correlation between BEts and TM was high (r=0.901, p<0.05). No significant difference existed between the two values (60.3±8.9 vs. 60.5±9.7 ml · kg⁻¹ · min⁻¹; n=28). No differences were found even when three different subgroups were separately compared. It is concluded that the higher elicited during BEts as compared with normal sitting cycling may be attributed to the increased muscle blood flow and/ or involvement of a larger muscle mass, the latter being partly evidenced by the observation of greater electrornyographic activity during BEts.     

Acute altitude exposure and altered acid-base states

Summary This study examined the influence of acute altitude (AL) exposure alone or in combination with metabolic acid-base manipulations on the exercise ventilatory and blood lactate responses. Four subjects performed a 4 min, 30 W incremental test to exhaustion at ground level (GL) and a 4 min, 20 W incremental test during three acute exposures to a simulated altitude of 4200 m; (i) normal (NAL), (ii) following 0.2 g·kg^–1 ingestion of sodium bicarbonate (BAL), and (iii) following 0.5 g·day^–1 ingestion of acetazolamide for 2 days prior to exposure (AAL). increased progressively throughout the incremental tests at AL and the minimum value was not related to a change in the blood lactate response. In contrast, the decreased initially to reach a minimum value at the same power output for each altitude trial and was related to a lactate threshold defined by a log-log transformation (r=0.78). This transformation of the blood lactate data was not influenced by the altered acid-base states. The relative exercise intensity corresponding to both a lactate of 1 mM and an absolute lactate of 4 mM was significantly increased during the AAL (79.9±12.9 and 93.9±13.7% , respectively) compared with NAL (59.1±5.5 and 78.0±5.8% , respectively). These data suggest that strong relationships exist between the ventilatory and blood lactate response during AL exposure and altered acid-base states. Further, it is concluded that, unless the acid-base status is known, the use of an absolute or lactate value to compare submaximal exercise should be interpreted with caution.     

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     

Transfer effects in endurance exercise

Summary The effects of 8 weeks of bicycle endurance training (5 x /week for 30 min) on maximal oxygen uptake capacity ( ) during arm and leg ergometry, and on the ultrastructure of an untrained arm muscle (m. deltoideus), and a trained leg muscle (m. vastus lateralis) were studied. With the training, leg- for bicycling increased by +13%, while the capillary per fiber ratio and the volume density of mitochondria in m. vastus lateralis increased by +15% and +40%, respectively. In contrast, the untrained m. deltoideus showed an unchanged capillary per fiber ratio and a decreased mitochondrial volume density (−17%). Despite this decrease of mitochondrial volume arm- increased by +9%. It seems unlikely that the observed discrepancy can be explained by cardiovascular adaptations, since arm cranking did not fully tax the cardiovascular system (arm- /leg- : 0.74 and 0.71 before and after training, respectively). Thus neither cardiovascular adaptations nor local structural changes in the untrained muscles could explain the increased arm- . However, the enhanced capacity for lactate clearance after endurance training could be sufficient to account for the larger during arm cranking. We propose that an increased net oxidation of lactate might be responsible for the increased arm- found after bicycle endurance training. This work was supported by grant 3.128.81 from the Swiss National Science Foundation, and by Cilo S.A., Bicycles, Romanel/Switzerland     

The energetics of middle-distance running

Summary In order to assess the relative contribution of aerobic processes to running velocity (v), 27 male athletes were selected on the basis of their middle-distance performances over 800, 1500, 3000 or 5000 m, during the 1987 track season. To be selected for study, the average running velocity corresponding to their performances had to be superior to 90% of the best French of the season. Maximum O₂ consumption and energy cost of running (C) had been measured within the 2 months preceding the track season, which, together with oxygen consumption at rest allowed us to calculate the maximalv that could be sustained under aerobic conditions: . The treadmill runningv corresponding to a blood lactate of 4 mmol·^–1 (v _la4), was also calculated. In the whole group, C was significantly related to height (r=–0.43;P<0.03). Neither C nor (with, in this case, the exception of the 3000 m athletes) were correlated to . On the other hand,v _{a max} was significantly correlated to over distances longer than 800 m. These were also correlated tov _la4. Howeverv _la4 occurred at 87.5% SD 3.3% ofv _{a max}, this relationship was interpreted as being an expression of the correlation betweenv _{a max} and . Calculation ofv _{a max} provided a useful means of analysing the performances. At the level of achievement studied, sustained over 3000 m corresponded tov _{a max}. The shape of the relationship ofv/v _{a max} as a function of the duration of the event raised the question of a possible change in C as a function of v during middle-distance running competitions.     

Comparison of incremental and steady state tests of endurance training

Summary To compare the results obtained by incremental or constant work load exercises in the evaluation of endurance conditionning, a 20-week training programme was performed by 9 healthy human subjects on the bicycle ergometer for 1 h a day, 4 days a week, at 70–80% . Before and at the end of the training programme, (1) the blood lactate response to a progressive incremental exercise (18 W increments every 2nd min until exhaustion) was used to determine the aerobic and anaerobic thresholds (AeT and AnT respectively). On a different day, (2) blood lactate concentrations were measured during two sessions of constant work load exercises of 20 min duration corresponding to the relative intensities of AeT (1st session) and AnT (2nd session) levels obtained before training. A muscle biopsy was obtained from vastus lateralis at the end of these sessions to determine muscle lactate. AeT and AnT, when expressed as % , increased with training by 17% (p<0.01) and 9% (p<0.05) respectively. Constant workload exercise performed at AeT intensity was linked before training (60% ) to a blood lactate steady state (4.8±1.4 mmol·l^–1) whereas, after training, AeT intensity (73% ) led to a blood lactate accumulation of up to 6.6±1.7 mmol·l^–1 without significant modification of muscle lactate (7.6±3.1 and 8.2±2.8 mmol·kg^–1 wet weight respectively). It is concluded that increase in AeT with training may reflect transient changes linked to lower early blood lactate accumulation during incremental exercise. Nevertheless, the results obtained at the end of the constant work load exercises were assumed to be independant of these changes, the occurrence of blood lactate accumulation being postulated to reflect a decreased removal from the blood linked to a higher relative work intensity. So, the use of incremental exercise is an incomplete procedure when evaluating endurance training effects.