The use of critical power as a determinant for establishing the onset of blood lactate accumulation

Eight highly trained male kayakers were studied to determine the relationship between critical power (CP) and the onset of blood lactate accumulation (OBLA). Four exercise sessions of 90 s, 240 s, 600 s, and 1200 s were used to identify the CP of each kayaker. Each individual CP was obtained from the line of best fit (LBF_CP) obtained from the progressive work output/time relationships. The OBLA was identified by the 4 mmol·l^–1 blood lactate concentration and the work output at this level was determined using a lactate curve test. This consisted of paddling at 50 W for 5 min after which a 1-min rest was taken during which a 25-l blood sample was taken to analyse for lactate. Exercise was increased by 50 W every 5 min until exhaustion, with the blood sample being taken in the 1-min rest period. The exercise intensity at the OBLA for each subject was then calculated and this was compared to the exercise intensity at the LBF_CP. The intensity at LBF_CP was found to be significantly higher (t=2.115, P<0.05) than that at the OBLA of 4 mmol·1^–1. These results were further confirmed by significant differences being obtained in blood lactate concentration (t=8.063, P<0.05) and heart rate values (t=2.90, P<0.05) obtained from the exercise intensity at LBF_CP over a 20-min period and that of the anaerobic threshold (Th_an) parameters obtained from the lactate/heart rate curve. These differences suggest that CP and Th_an are different physiological events and that athletes have utilised either one or the other methods for monitoring training and its effects.     

Blood lactate during submaximal exercises

Summary Values of oxygen consumption, carbon dioxide production, ventilation and blood lactate concentration were determined in eight active male subjects during the minute following submaximal square-wave exercise on a treadmill under two sets of conditions. Square-wave exercise was (1) integrated in a series of intermittent incremental exercises of 4-min duration separated by 1-min rest periods; (2) isolated, of 4- and 12-min duration, and of intensity corresponding to each of the intermittent incremental periods of exercise. For square-wave exercise of the same duration (4 min) and intensity, no significant differences in the above-mentioned parameters were noted between intermittent incremental exercise and isolated exercise. Only at high work rate (>92% maximal oxygen uptake), were blood lactate levels in three subjects slightly higher after 12-min of isolated exercise than after the 4-min periods of isolated exercise. Examination of these results suggests that (1) 80–90% of the blood lactate concentration observed under our experimental conditions results from the accumulation of lactate in the blood during the period of oxygen deficit; (2) therefore the blood lactate concentration/exercise intensity relationship, for the most part, appears to represent the lactate accumulated early in the periods of intermittent incremental exercise.     

Physiological responses during exercise to exhaustion at critical power

Critical power (CP) is a theoretical construct derived from a series of constant load tests to failure. Many studies have examined the methodological limitations of deriving CP, but few studies have examined the responses to exercise at CP in well-trained individuals. The purpose of the present study was to examine the physiological responses to exercise at CP. Seven male subjects [mean (SD) body mass 75.6 (6.4) kg, maximum oxygen uptake 4.6 (0.7) l min^–1] performed three constant load tests to derive CP. Subjects then exercised at CP until volitional exhaustion. Heart rate, oxygen consumption and blood lactate concentration were measured throughout. Repeated measures analysis of variance revealed significant differences over time in heart rate 118 (24) to 177(5) beats min^–1, oxygen consumption 3.7 (0.6) to 4.1 (0.5) l min^–1 and blood lactate concentration 4.3 (1.8) to 6.5 (2.0) mM. All seven subjects completed 20 min of exercise with the range of time to failure at CP from 20 min 1 s to 40 min 37 s. Time to failure and maximum oxygen consumption were significantly correlated (r=0.779, P<0.05). We conclude, therefore, that CP does not represent a sustainable steady-state intensity of exercise. Electronic Publication     

Blood lactate production and recovery from anaerobic exercise in trained and untrained boys

Summary Blood lactate production and recovery from anaerobic exercise were investigated in 19 trained (AG) and 6 untrained (CG) prepubescent boys. The exercises comprised 3 maximal test performances; 2 bicycle ergometer tests of different durations (15 s and 60 s), and running on a treadmill for 23.20±2.61 min to measure maximal oxygen uptake. Blood samples were taken from the fingertip to determine lactate concentrations and from the antecubital vein to determine serum testosterone. Muscle biopsies were obtained from vastus lateralis. Recovery was passive (seated) following the 60 s test but that following the treadmill run was initially active (10 min), and then passive. Peak blood lactate was highest following the 60 s test (AG, 13.1±2.6 mmol·l^–1 and CG, 12.8±2.3 mmol·l^–1). Following the 15 s test and the treadmill run, peak lactate values were 68.7 and 60.6% of the 60 s value respectively. Blood lactate production was greater (p<0.001) during the 15s test (0.470±0.128 mmol·l^–1·s^–1) than during the 60s test (0.184±0.042 mmol·l^–1·s^–1). Although blood lactate production was only nonsignificantly greater in AG, the amount of anaerobic work in the short tests was markedly greater (p<0.05-0.01) in AG than CG. Muscle fibre area (type II%) and serum testosterone were positively correlated (p<0.05) with blood lactate production in both short tests. Blood lactate elimination was greater (p<0.001) at the end of the active recovery phase than in the next (passive) phase. It is concluded that blood lactate production in prepubescent boys is related to serum testosterone level and muscle type II fibre area, indicating the role of maturation and training. Submaximal exercise is likely to increase blood lactate removal during recovery.     

Maximal lactate steady state,critical power and EMG during cycling

We hypothesised that: (1) the maximal lactate steady state (MLSS), critical power (CP) and electromyographic fatigue threshold (EMG_FT) occur at the same power output in cycling exercise, and (2) exercise above the power output at MLSS (P-MLSS) results in continued increases in oxygen uptake (V˙O₂), blood lactate concentration ([La]) and integrated electromyogram (iEMG) with time. Eight healthy subjects [mean (SD) age 25 (3) years, body mass 72.1 (8.2) kg] performed a series of laboratory tests for the determination of MLSS, CP and EMG_FT. The CP was determined from four exhaustive trials of between 2 and 15 min duration. The MLSS was determined as the highest power output at which the increase in blood [La] was less than 1.0 mM across the last 20 min of a series of 30-min trials. The EMG_FT was determined from four trials of 2 min duration at different power outputs. The surface electromyogram was recorded continuously from the vastus lateralis muscle. The CP was significantly higher than the P-MLSS [242 (25) vs. 222 (23) W; P<0.05], although the two variables were strongly correlated (r=0.95; P<0.01). The EMG_FT could not be determined in 50% of the subjects. Blood [La], V˙O₂ and minute ventilation all increased significantly with time for exercise at power outputs above the P-MLSS. In conclusion, the P-MLSS, and not the CP, represents the upper limit of the heavy exercise domain in cycling. During exercise above the P-MLSS, there is no association between changes in iEMG and increases in V˙O₂ and blood [La] with time. Electronic Publication     

Prolonged stage duration during incremental cycle exercise: effects on the lactate threshold and onset of blood lactate accumulation

The aim of this study was to investigate whether increasing the duration of workloads from 3 min to 8 min during incremental exercise would influence workload (W), oxygen consumption ( ) and heart rate (HR) at the lactate threshold (LT) and the onset of blood lactate accumulation(OBLA). Two groups of six male cyclists were assigned to a well-trained (WT) and recreational (REC) group on the basis of their performance in a maximal incremental ramp test. Each subject then performed two incremental lactate tests (EXT) consisting of six workloads of either 3 min (EXT_3-min) or 8 min (EXT_8-min) duration. At the completion of each workload whole capillary blood samples were obtained for the determination of blood lactate (BLa) concentration (mM). Power output (Watts, W), HR and were averaged in the final minute of each workload as well as in the third minute of the EXT_8-min. The workload, HR and at the LT and OBLA were subsequently determined from the data of EXT_3-min and EXT_8-min. The results demonstrate that workload and , but not HR, at the LT and OBLA were higher in the WT cyclists. At the same time, the workload at the LT obtained from the results of the EXT_3-min was significantly (P<0.05) higher then the value obtained in the EXT_8-min in the WT subjects but not the REC subjects. However, the workload, and HR at the OBLA, together with the and HR at the LT were not significantly different when calculated from data obtained from EXT_3-min or EXT_8-min. The data obtained in this study suggest that incremental exercise protocols using workloads of duration longer than 3 min have the effect of increasing the workload at the LT in well-trained cyclists. However, the OBLA determined in exercise tests using stage increments of either 3 min or 8 min is similar in cyclists of different training status. Electronic Publication     

Blood lactate during constant-load exercise at aerobic and anaerobic thresholds

Summary Venous blood lactate concentrations [la_b] were measured every 30 s in five athletes performing prolonged exercise at three constant intensities: the aerobic threshold (Th_aer), the anaerobic threshold (Th_an) and at a work rate (IWR) intermediate between (Th_aer and Th_an. Measurements of oxygen consumption and heart rate (HR) were made every min. Most of the subjects maintained constant intensity exercise for 45 min at Th_aer and IWR, but at Th_an none could exercise for more than 30 min. Relationships between variations in [la_b] and concomitant changes in or HR were not statistically significant. Depending on the exercise intensity (Th_aer, IWR, or Th_an) several different patterns of change in [la_b] have been identified. Subjects did not necessarily show the same pattern at comparable exercise intensities. Averaging [la_b] as a function of relative exercise intensity masked spatial and temporal characteristics of individual curves so that a common pattern could not be discerned at any of the three exercise levels studied. The differences among the subjects are better described on individual [la_b] curves when sampling has been made at time intervals sufficiently small to resolve individual characteristics.     

No difference in net uptake or disposal of lactate by trained and untrained forearms during incremental sodium lactate infusion

A number of training adaptations in skeletal muscle might be expected to enhance lactate extraction during hyperlactataemia. The aim of the present study was to determine whether resting endurance-trained forearms exhibit an increased net lactate removal during hyperlactataemia. Six racquet-sport players attended the laboratory for two experiments, separated by 2 weeks. In the first experiment incremental handgrip exercise to fatigue was performed to identify trained (TRFA, n=6) and untrained (UTFA, n=5) forearms. In the second experiment net forearm lactate exchange was compared between TRFA and UTFA during an incremental infusion of sodium lactate. TRFA performed more work than UTFA during handgrip exercise [mean (SE) TRFA, 66.1 (9.5) J·100 ml^–1; UTFA, 35.1 (2.3) J·100 ml^–1; P=0.02] and UTFA exhibited a greater increase in net lactate output relative to work load (P=0.003). During lactate infusion net lactate uptake across the resting forearms increased linearly with the arterial lactate concentration in both groups (TRFA, r=–0.95 (0.03); UTFA, r=–0.92 (0.04); P<0.02], with no difference in the regression slopes [TRFA, –1.06 (0.13); UTFA, –1.07 (0.27); P=0.97] or y-intercepts [TRFA, 0.67 (0.20); UTFA, 1.36 (0.67); P=0.37] between groups. Almost all of the lactate taken up was disposed of by both groups of forearms [TRFA, 99.6 (0.2)%; UTFA, 98.5 (1.0)%; P=0.37]. It was concluded that the net uptake and removal of lactate by resting skeletal muscle is a function of the concentration of lactate in the blood perfusing the muscle rather than the muscle training status. Electronic Publication     

Blood lactate response to overtraining in male endurance athletes

Many physiological markers vary similarly during training and overtraining. This is the case for the blood lactate concentration ([La⁻]_b), since a right shift of the lactate curve is to be expected in both conditions. We examined the possibility of separating the changes in training from those of overtraining by dividing [La⁻]_b by the rating of perceived exertion ([La⁻]_b/RPE) or by converting [La⁻]_b into a percentage of the peak blood lactate concentration ([La⁻]_b,peak). Ten experienced endurance athletes increased their usual amount of training by 100% within 4 weeks. An incremental test and a time trial were performed before (baseline) and after this period of overtraining, and after 2 weeks of recovery (REC). The [La⁻]_b and RPE were measured during the recovery of each stage of the incremental test. We diagnosed overtraining in seven athletes, using both physiological and psychological criteria. We found a decrease in mean [La⁻]_b,peak from baseline to REC [9.64 (SD 1.17), 8.16 (SD 1.31) and 7.69 (SD 1.84) mmol · l⁻¹, for the three tests, respectively; P < 0.05] and a right shift of the lactate curve. Above 90% of maximal aerobic speed (MAS) there was a decrease of mean [La⁻]_b/RPE from baseline to REC [at 100% of MAS of 105.41 (SD 17.48), 84.61 (SD 12.56) and 81.03 (SD 22.64) arbitrary units, in the three tests, respectively; P < 0.05), but no difference in RPE, its variability accounting for less than 25% of the variability of [La⁻]_b/RPE (r=0.49). Consequently, [La⁻]_b/RPE provides little additional information compared to [La⁻]_b alone. Expressing [La⁻]_b as a %[La⁻]_b,peak resulted in a suppression of the right shift of the lactate curve, suggesting it was primarily the consequence of a decreased production of lactate by the muscle. Since the right shift of the curve induced by optimal training is a result of improved lactate utilization, the main difference between the two conditions is the decrease of [La⁻]_b,peak during overtraining. We propose retaining it as a marker of overtraining for long duration events, and repeating its measurement after a sufficient period of rest to make the distinction with overreaching. Accepted: 26 September 2000     

Blood lactate accumulation in intermittent supramaximal exercise

Summary Blood lactate accumulation rate and oxygen consumption have been studied in six trained male runners, aged 20 to 30 years. Subjects ran on a treadmill at a rate representing 172±5% for four 45 s sessions, separated by 9 min rest periods. Oxygen consumption was measured throughout. Blood lactate was determined in samples taken from the ear and was measured at the end of each exercise session, and two, five and nine minutes later. After the fourth exercise session, the same measurements were made every five min for 30 min. 4 subjects repeated a single exercise of the same type, duration and intensity and the same measurements were taken. With repetitive intermittent exercise, gradual increases in blood lactate concentration ([LA]b) occurred, whereas its rate of accumulation ([LA]b) decreased. The amount of oxygen consumed during each 45 s exercise session remained unchanged for a given subject. After cessation of intermittent exercise, the half-time of blood lactate was 26 min, whereas it was only 15 min after a single exercise session. values, on the other hand, returned to normal after 15 to 20 min. All other conditions being equal, the gradual decrease in [LA]b during intermittent exercise could be explained if the lactate produced during the first exercise session is used during the second period, and/or if the diffusion space of lactate increases. The diffusion space seems to be multicompartmental on the basis of half-time values noted for [LA]b after intermittent exercise, compared with those noted after a single exercise session. The distinction between the rapid return to normal values and the more gradual return to normal blood lactate levels confirms that there is no simple and direct relationship between oxygen debt and the accumulation of blood lactate after muscular exercise. In practical terms, these results show that the calorific equivalent of lactic acid defined by Margaria et al. (1963) cannot be used in the case of intermittent exercise of supramaximal intensity.     

Peak power output predicts maximal oxygen uptake and performance time in trained cyclists

Summary The purposes of this study were firstly to determine the relationship between the peak power output (W _peak) and maximal oxygen uptake (VO_2max) attained during a laboratory cycling test to exhaustion, and secondly to assess the relationship betweenW _peak and times in a 20-km cycling trial. One hundred trained cyclists (54 men, 46 women) participated in the first part of this investigation. Each cyclist performed a minimum of one maximal test during whichW _max andVO_2max were determined. For the second part of the study 19 cyclists completed a maximal test for the determination ofW _peak, and also a 20-km cycling time trial. Highly significant relationships were obtained betweenW _peak andVO_2max (r=0.97,P<0.0001) and betweenW _peak and 20-km cycle time (r= –0.91,P<0.001). Thus,W _peak explained 94% of the variance in measuredVO_2max and 82% of the variability in cycle time over 20 km. We concluded that for trained cyclists, theVO_2max can be accurately predicted fromW _peak, and thatW _peak is a valid predictor of 20-km cycle time.     

Blood ammonia and lactate concentrations during endurance exercise of differing intensities

Summary The purpose of this study was to examine the changes of blood ammonia concentration ([NH₃]_b) during endurance exercise of differing intensities on the cycle ergometer and to compare [NH₃]_b to the changes observed in the simultaneously monitored blood lactate acid concentrations ([la^–]_b) measurements. A group of 16 endurance-trained athletes participated in the first part of the study and performed exercise of 30 min duration in a randomized order at intensities of 85%, 95%, 100% and 105% of their individual anaerobic threshold (Th_an,ind; E85–E105) which had been determined beforehand by a cycle exercise test with stepwise increments in intensity. In the second part, 18 average endurance-trained sports students underwent exhausting intensive endurance exercise (IEE) with an intensity of 95% of Th_an,ind. An extensive endurance exercise (EEE) of the same duration at 85% of the Than,ind was carried out 2 days later. The [NH₃]_b increased constantly with increasing duration of all exercise. However, [la^–]_b only increased during exercise with intensities above the Th_an,ind (E105). The increase of [NH₃]_b was higher with higher exercise intensities. At IEE, [NH₃]_b was significantly higher from the 30th min than at EEE, whereas [la^–]_b increased from the 5th min. In conclusion, [la^–]_b responded more sensitively to the intensity of exercise than [NH₃]_b, but it is conceivable that in the future measurements of [NH₃]_b could be used to advise on the duration of endurance training. At present, however, the lack of experience and lack of appropriate values still hinders the systematic use of [NH₃]_b measurements in the physiological monitoring of sports training.     

Independence of ventilation and blood lactate responses during graded exercise

The effect of power output increment, based on an increase in pedal rate, on blood lactate accumulation during graded exercise is unknown. Therefore, in the present study, we examined the effect of two different rates of power output increments employing two pedal rates on pulmonary ventilation and blood lactate responses during graded cycle ergometry in young men. Males (n=8) with an mean (SD) peak oxygen uptake of 4.2 (0.1) 1·min^–1 served as subjects. Each subject performed two graded cycle ergometer tests. The first test, conducted at 60 rev· min^–1, employed 4 min of unloaded pedaling followed by a standard power output step increment (SI) of 60 W every 3rd min. The second test, conducted at 90 rev·min^–1, employed 4 min of unloaded pedaling followed by a high power output step increment (HI) of 90 W every 3rd min. Venous blood was sampled from a forearm vein after 5 min of seated rest, 4 min of unloaded pedaling, and every 3rd min of graded exercise. Peak exercise values for heart rate, oxygen uptake ( O₂), and ventilation ( _E) were similar (P > 0.05) for SI and HI exercise, as was the relationship between _E and O₂, and between _E and carbon dioxide production ( CO₂). However, the relationship between blood lactate concentration and O₂ was dissimilar between SI and HI exercise with blood lactate accumulation beyond the lowest ventilatory equivalent of oxygen, and peak exercise blood lactate concentration values significantly higher (P < 0.05) for SI [12.8 (2.6) mmol·l^–1] compared to HI [8.0(1.9) mmol·l^–1] exercise. Our findings demonstrate that blood lactate accumulation and _E during graded exercise are dissociated. Blood lactate accumulation is influenced by the rate of external power output increment, while _E is related to O₂ and CO₂.     

The influence of blood sampling site on lactate concentration during submaximal exercise at 4 mmol · 1−1 lactate level

This study examined lactate concentration during incremental and submaximal treadmill exercise at work rates corresponding to 4 mmol· 1^–1 lactate concentration, determined by fingertip (OBLAI) and venous blood (OBLA2). Initially, eight subjects performed a 4-min incremental exercise test until exhaustion. On two other occasions, seven of the subjects undertook submaximal exercise tests (30 min) at work rates corresponding to OBLA1 and OBLA2. Blood was simultaneously obtained from both sites at rest and at the end of each exercise stage during the incremental exercise, and at 5, 10, 20 and 30 min during the submaximal exercise and 5 min into recovery. Fingertip blood lactate concentrations were significantly higher (P<0.05) than venous blood at rest, throughout the incremental exercise, consistently during exercise at OBLA1 and OBLA2, and into recovery. Data also revealed an exercise intensity-dependent lactate difference between the two sampling sites during both exercise protocols. Exercise at OBLA1 did not result in a progressive increase in lactate level nor exhaustion, and the lactate value at the end of 30 min corresponded to the predetermined value. However, exercise at OBLA2 resulted in a significantly higher (P<0.05) lactate level than OBLA1, the lactate concentration at the end of 30 min was substantially higher than the predetermined value (P<0.05) and exhaustion was evident. It is concluded that the lactate concentration value during incremental and submaximal exercise (at 4 mmol·l^–1 OBLA) is dependent on the blood sampling site. This finding should be considered in studies concerned with the determination of OBLA.     

Median power frequency of the surface electromyogram and blood lactate concentration in incremental cycle ergometry

The electromyogram (EMG) median power frequency of the vastus lateralis and flexor digitorum superficialis muscles was measured in 12 subjects during cycle ergometry with step-wise increasing exercise intensities up to 100% of O_2max. Blood lactate concentration was measured to investigate the relationship between changes in lactate concentration and shifts in the EMG median power frequency of exercising vastus lateralis and non-exercising flexor digitorum superficialis muscles. The results indicated that lactate concentration did not systematically affect median frequency: in spite of a considerable increase in blood lactate concentration, no systematic decrease of the median frequency during exercise was found, either for the vastus lateralis or for the flexor digitorum superficialis muscles. Instead of a decrease of the median frequency during exercise, as seen in isometrical protocols, an increase was seen in most subjects. An interesting finding was a decrease of the median frequency of vastus lateralis muscle during recovery in 8 subjects. The present findings showed that the relationship between EMG frequency decrease, lactate accumulation and fatigue, as observed in isometric protocols, cannot be simply applied to dynamic exercise.     

Physiological responses during cycling with noncircular "Harmonic" and circular chainrings

The aim of the present study was to compare physiological data obtained during cycling using a noncircular "Harmonic" chainring versus a standard circular chainring over a range of speeds and slopes in endurance-trained cyclists. Thirteen male subnational cyclists (16–45 years) performed two maximal graded exercises on their own bicycle: one with a circular chainring, the other with a Harmonic chainring with the same gearwheel (52 teeth). The two chainrings were randomly assigned to avoid learning effects. The tests were carried out on a simulator. Speeds and/or slopes were increased every 2 min 30 s until exhaustion of the subject. Ventilation, oxygen uptake, carbon dioxide output, respiratory exchange ratio, and heart rate were continuously measured during the tests. Blood lactate concentration was measured during the last 30 s of each level. No significant difference was observed in any of the submaximal parameters measured during the tests (P>0.05). Similarly, maximal values were not statistically different (P>0.05). In conclusion, although the design of the Harmonic chainring was based on optimization analysis, comparison of the physiological response in this study did not translate into an advantage of the Harmonic over circular chainring during submaximal and maximal pedaling in trained cyclists.     

Influence of cold exposure on blood lactate response during incremental exercise

Summary This study examined the effect of acute exposure of the whole body to cold on blood lactate response during incremental exercise. Eight subjects were tested with a cycle ergometer in a climatic chamber, room temperature being controlled either at 24° C (MT) or at –2° C (CT). The protocol consisted of a step increment in exercise intensity of 30 W every 2 min until exhaustion. Oxygen consumption ( ) was measured at rest and during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for estimations of plasma norepinephrine (NE), epinephrine (E), free fatty acid (FFA) and glucose concentrations, during the last 15 s of each exercise step and also during the 1^st, 4^th, 7^th, and the 10^th min following exercise for the determination of blood lactate (LA) concentration. The , was higher during CT than during MT at rest and during nearly every exercise intensity. At CT, lactate anaerobic threshold (LAT), determined from a marked increase of LA above resting level, increased significantly by 49% expressed as absolute , and 27% expressed as exercise intensity as compared with MT. The LA tended to be higher for light exercise intensities and lower for heavy exercise intensities during CT than during MT. The E and NE concentrations increased during exercise, regardless of ambient temperature. Furthermore, at rest and at exhaustion E concentrations did not differ between both conditions, while NE concentrations were greater during CT than during MT. Moreover, an increase of FFA was found only during CT. The difference in FFA level suggests that alterations in fat metabolism, possibly initiated by an enhanced secretion of NE, may have contributed to a decrease in lactate production.     

Muscle metabolism,blood lactate and oxygen uptake in steady state exercise at aerobic and anaerobic thresholds

Summary Muscle metabolites and blood lactate concentration were studied in five male subjects during five constant-load cycling exercises. The power outputs were below, equal to and above aerobic (AerT) and anaerobic (AnT) threshold as determined during an incremental leg cycling test. At AerT, muscle lactate had increased significantly (p<0.05) from the rest value of 2.31 to 5.56 mmol · kg^–1 wet wt. This was accompanied by a significant reduction in CP by 28% (p<0.05), whereas only a minor change (9%) was observed for ATP. At AnT muscle lactate had further increased and CP decreased although not significantly as compared with values at AerT. At the highest power outputs (> AnT) muscle lactate had increased (p<0.01) and CP decreased (p<0.01) significantly from the values observed at AnT. Furthermore, a significant reduction (p<0.05) in ATP over resting values was recorded. Blood lactate decreased significantly (p<0.01) during the last half of the lowest 5 min exercise, remained unchanged at AerT and increased significantly (p<0.05–0.01) at power outputs AnT. It is concluded that anaerobic muscle metabolism is increased above resting values at AerT: at low power outputs (AerT) this could be related to the transient oxygen deficit during the onset of exercise or the increase in power output. At high power outputs (> AnT) anaerobic energy production is accelerated and it is suggested that AnT represents the upper limit of power output where lactate production and removal may attain equilibrium during constant load exercise.     

Critical power of knee extension exercises does not depend upon maximal strength

A possible dependence of critical power (CP) and the Y-intercept of the work/exhaustion time relationship (Y _intercept) on maximal muscular strength of the same muscle group has been studied in nine endurance-trained subjects, seven gymnasts, and seven weight-lifters. CP was calculated as being equal to the slope of the linear relationship between exhaustion time and the work performed at exhaustion on a knee extension ergometer. Y _intercept was equal to the intercept between this relationship and the work axis. The muscular strength of the knee was evaluated by measuring the torques exerted on a Biodex knee isokinetic dynamometer at four angular velocities: 0° · s⁻¹ (T₀), 90° · s⁻¹ (T₉₀), 180° · s⁻¹ (T₁₈₀) and 240° · s⁻¹ (T₂₄₀). The results of the present study do not support the hypothesis that CP depends upon maximal strength. Indeed, CP was not correlated with T₀, T₉₀, T₁₈₀ or T₂₄₀ (|r| < 0.01). Y _intercept was significantly and positively correlated only with T₉₀. Accepted: 1 November 1999