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.     

Day-to-day changes in oxygen uptake kinetics at the onset of exercise during strenuous endurance training

Summary The aim of this study was to assess the effect of strenuous endurance training on day-to-day changes in oxygen uptake (VO₂) on-kinetics (time constant) at the onset.of exercise. Four healthy men participated in strenuous training, for 30 min·day^–1, 6 days·week^–1 for 3 weeks. The VO₂ was measured breath-by-breath every day except Sunday at exercise intensities corresponding to the lactate threshold (LT) and the onset of blood lactate accumulation (OBLA) which were obtained before training. Furthermore, an incremental exercise test was performed to determine LT, OBLA and maximal oxygen uptake (VO_2max) before and after the training period and every weekend. The 30-min heavy endurance training was performed on a cycle ergometer 5 days·week^–1 for 3 weeks. Another six men served as the control group. After training, significant reductions of the VO₂ time constant for exercise at the pretraining LT exercise intensity (P<0.05) and at OBLA exercise intensity (P<0.01) were observed, whereas the VO₂ time constants in the control group did not change significantly. A high correlation between the decrease in the VO₂ time constant and training day was observed in exercise at the pretraining LT exercise intensity (r=–0.76; P<0.001) as well as in the OBLA exercise intensity (r= –0.91; P<0.001). A significant reduction in the blood lactate concentration during submaximal exercise and in the heart rate on-kinetics was observed in the training group. Furthermore, VO₂ at LT, VO₂ at OBLA and VO_2max increased significantly after training (P<0.05) but such was not the case in the control group. These findings indicated that within a few weeks of training a rapidly improved VO₂ on-kinetics may be observed. This may be explained. by some effect of blood lactate during exercise on VO₂ on-kinetics, together with significantly improved cardiovascular kinetics at the onset of exercise.     

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.     

Effect of exercise duration during incremental exercise on the determination of anaerobic threshold and the onset of blood lactate accumulation

Summary To determine the effect of the duration of incremental exercise on the point at which arterial blood lactate concentration (HLa) increases above the resting value (anaerobic threshold: AT) and on the point at which HLa reaches a constant value of 4 mM (onset of blood lactate accumulation: OBLA), eight male students performed two different kinds of incremental exercise. A comparison of arterial HLa and venous HLa was made under both conditions of incremental exercise. The incremental bicycle exercise tests consisted of 25 W increase every minute (1-min test) and every 4 min (4-min test). At maximal exercise, there were no significant differences in either gas exchange parameters or HLa values for the two kinds of incremental exercise. However, the peak workloads attained during the two exercises were significantly different (P<0.01). At OBLA and AT, there were no significant differences in gas exchange parameters during the 1-min and 4-min tests except for the workload (at OBLAP<0.01; at ATP<0.05). When venous blood HLa was used instead of arterial HLa for a 4-min test, AT was not significantly different from that obtained by arterial HLa, but OBLA was significantly different from that obtained by arterial HLa (P<0.05). On the other hand, for the 1-min test, venous HLa values yielded significantly higher AT and OBLA compared with those obtained using arterial HLa (P<0.01).It was concluded that when arterial blood was used, there was no effect of duration of workload increase in an incremental exercise test on the determination of the AT and OBLA expressed in . On the other hand, when venous HLa was used instead of arterial blood, these points might be overestimated when a fast increase in workload, such as the 1-min test, is used.     

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.     

The ventilatory threshold gives maximal lactate steady state

Summary The purpose of this study was to examine whether the ventilatory threshold (Th _v) would give the maximal lactate steady state ([1a]_{ss, max}), which was defined as the highest work rate (W) attained by a subject without a progressive increase in blood lactate concentration [1a]_b at constant intensity exercise. Firstly, 8 healthy men repeated ramp-work tests (20 W·min^–1) on an electrically braked cycle ergometer on different days. During the tests, alveolar gas exchange was measured breath-by-breath, and theW atTh _v (W _{Th v}) was determined. The results of two-way ANOVA showed that the coefficient of variation of a singleW _{Th v} determination was 2.6%. Secondly, 13 men performed 30-min exercise atW _{Th v} (Th _v trial) and at 4.9% aboveW _{Th v} (Th _v + trial), which corresponded to the 95% confidence interval of the single determination. The [1a]_b was measured at 15 and 30 min from the onset of exercise. The [1a]_b at 15 min (3.15 mmol·1^–1, SEM 0.14) and at 30 min (2.95 mmol·1^–1, SEM 0.18) were not significantly different inTh _v trial. However, the [1a]_b ofTh _v+ trial significantly increased (P<0.05) from 15 min (3.62 mmol·1^–1, SEM 0.36) to 30 min (3.91 mmol·1^–1, SEM 0.40). These results indicate thatTh _v gives the [1a]_ss,max, at which one can perform sustained exercise without continuous [1a]_b accumulation.     

Changes in the concentrations of Na+, K+ and Cl− in secretion from the skin during progressive increase in exercise intensity

Summary A simple method for sampling skin secretion in 1-min periods was developed for investigating the effects of progressive increases in exercise intensity on Na⁺, K⁺ and CI^– secretions from the skin of the forearm. Ten healthy male subjects performed exercise consisting of eight stepwise increases in intensity from 50 to 225 W, with a 25-W increase at each step. Exercise at each step was for 3 min followed by a 1-min recovery period. Samples of blood and skin secretion were taken during the recovery period. Significant positive correlations were found between the mean concentrations of Na⁺ and Cl^– and between those of K⁺ and Cl^– in the skin secretion. The concentrations of electrolytes in the skin secretion also showed significant correlations with the blood lactate concentrations. The inflection points for secretions of Na⁺, K⁺ and Cl^– were 4.04, 3.61 and 3.83 mmol · l^– of blood lactate; 64.42, 61.96 and 62.14% of maximal oxygen consumption ( ); and exercise intensities of 123.01, 117.65 and 125.07 W, respectively. No significant differences were observed between the value of 67.27% of or 134.00W at the onset of blood lactate accumulation (OBLA) and the inflection points. From these results we concluded that changes in electrolyte concentrations in skin secretion during incremental exercise according to this protocol were closely related with the change in the blood lactate concentration, and that the inflection points for electrolytes may have been near the exercise intensity at OBLA.     

Blood lactate in trained cyclists during cycle ergometry at critical power

Summary The purposes of this investigation were to determine the validity of critical power (CP) as a measure of the work rate that can be maintained for a very long time without fatigue and to determine whether this corresponded with the maximal lactate steady-state (la_ss,max). Eight highly trained endurance cyclists (maximal oxygen uptake 74.1 ml · kg^–1 · min^–1, SD 5.3) completed four cycle ergometer tests to exhaustion at predetermined work rates (360, 425, 480 and 520 W). From these four co-ordinates of work and time to fatigue the regression of work limit on time limit was calculated for each individual (CP). The cyclists were then asked to exercise at their CP for 30 min. If CP could not be maintained, the resistance was reduced minimally to allow the subject to complete the test and maintain a blood lactate plateau. Capillary blood was sampled at 0, 5, 10, 20 and 30 min into exercise for the analysis of lactate. Six of the eight cyclists were unable to maintain CP for 30 min without fatigue. In these subjects, the mean power attained was 6.4% below that estimated by CP. Mean blood lactates (n = 8) reached a steady-state (8.9 mmol · l^–1, SD 1.6) during the last 20 min of exercise indicating that CP slightly overestimated la_{ss, max}. Individual blood lactates during the last 20 min of exercise were more closely related to the y-intercept of the CP curve (r=0.78, P<0.05) than either CP (0.34, NS) or mean power output (r=0.42, NS). The present investigation has shown that highly trained endurance cyclists can tolerate previously unreported levels of blood lactate during 30 min of exercise at or near their CP. Blood lactates during continuous exercise are higher than at the same work rate during an incremental test. The CP provides a simple and inexpensive means of assessing the exercise intensity which can be maintained continuously, while avoiding the methodological difficulties associated with ventilatory and lactate thresholds.     

The relationship between anaerobic threshold and electromyographic fatigue threshold in college women

Summary The purpose of this study was to investigate the relationship between anaerobic threshold (Th_an) and muscle fatigue threshold (EMG_FT) as estimated from electromyographic (EMG) data taken from the quadriceps muscles (vastus lateralis) during exercise on a cycle ergometer. The subjects in this study were 20 female college students, including highly trained endurance athletes and untrained sedentary individuals, whose fitness levels derived from their maximal oxygen consumption ranged from 24.9 to 62.2 ml · kg^–1·min^–1. The rate of increase in integrated EMG (iEMG) activity as a function of time (iEMG slope) was calculated at each of four constant power outputs (350, 300, 250, 200 W), sufficiently high to bring about muscle fatigue. The iEMG slopes so obtained were plotted against the exercise intensities imposed, resulting in linear plots which were extrapolated to zero slope to give an intercept on the power axis which was in turn interpreted as the highest exercise intensity sustainable without electromyographic evidence of neuromuscular fatigue (EMGF_FT). The Th_an was estimated from gas exchange parameters during an incremental exercise test on the same cycle ergometer. The mean results indicated that oxygen uptake (VO₂) at Th_an was 1.391·min^–1, SD 0.44 andVO₂ at EMG_FT was 1.33 1·min^–1, SD 0.57. There was no significant difference between these mean values (P>0.05) and there was a highly significant correlation betweenVO₂ at Th_an andVO₂ at EMG_FT (r=0.823,P<0.01). These data supported the concept of Th_an on the basis that Than was associated with the highest exercise intensity that could be sustained without evidence of neuromuscular fatigue and thus suggested that EMG_FT may provide an attractive alternative to the measurement of Th_an.     

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     

Lactate after exercise in man: IV. Physiological observations and model predictions

Summary Following earlier papers that established the mathematical form of the time dependence of lactate concentrations during recovery from several types of exercise, and that set up a two-compartment model predicting the same time dependences, the present work applies the model to obtain parameters of specific physiological processes. Satisfactory agreement between predictions of the model and our experiment and literature data is obtained in the cases where comparisons can be made, as in the muscular lactate time evolution measured from biopsy samples, in blood flows through the active muscle at the end of exercise or at rest and their evolution during recovery, as well as in the volume of the active muscle compartment. The model prediction that lactate efflux from the muscles to the blood can reduce to zero during recovery is verified experimentally.List of Abbreviations and Symbols A ₁, A ₂ Amplitudes of the two exponential terms fitted to arterial lactate concentrations (mol·1^–1) - ₁₂, ₂₁ Transfer coefficients from (M) to (S) and (S) to (M) respectively (min^–1) - A _D Area of the body according to Dubois (m²) - BM Body mass (kg) - C ₁, C ₂ Amplitudes of the exponential terms of L _m (t) (mol·1^–1) - c ₁, d ₁ Rates of lactate production in (M) and (S), respectively (mol·min^–1) - c ₂, d ₂ Coefficients of lactate disappearance in (M) and (S) respectively (min^–1) - F ₁ Field of validity of the model (see [32]) - ₁, ₂ Velocity constants of the exponential terms fitted to arterial lactate concentrations (min^–1) - L _a (t) Arterial lactate concentration at time t (mmol·1^–1 or mol·1^–1) - L _a max Maximum arterial lactate concentration of the recovery (mmol·1^–1) - L _fv (t) Femoral venous blood lactate concentration at time t (mmol·^–1) - L _M (t), L _S (t) Lactate concentrations in (M) and (S), respectively at time t (mmol·1^–1 or mol·1^–1) - (M) Working or active muscle space - q(t) Blood flow through (M) at time t (ml·100 ml^–1·min^–1) - _MS (t) Rate of net lactate release from (M) to (S) at time t (mmol·min^–1) - Rate of net lactate release from (M) to (S) at t(mol·min^–1) - (S) Remaining lactate space - t Time after the end of exercise (min) - , Moments at which the net lactate release from (M) to (S) becomes zero (min) - ₂ Moment of the intersection of the arterial and brachial venous blood lactate curves (min) - _fa1, _fa2 Moments of the intersection of the arterial and femoral venous blood lactate curves (min) - V _M , V _s , V _TLS Volume of (M), (S), and (TLS), respectively, [1] - (TLS) Total lactate space - Difference between L _M () and L _s ()     

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.     

Saliva electrolytes as a useful tool for anaerobic threshold determination

The purpose of the present study was to determine the anaerobic threshold by analysis of changes in saliva composition during an incremental exercise test on a cycle ergometer. Thirteen healthy males underwent a submaximal test with an initial load of 50 W and load increases of 50 W per 3 min, until capillary blood lactate exceeded 4 mmol · l^–1. A maximal test for maximum O₂ uptake (VO_2max) determination (initial load of 100 W and load increases of 50 W per 2 min) was also performed. Saliva and blood samples were obtained only in the submaximal test. Saliva threshold (Th_sa) was defined as the point at which the first increase in either Cl^– or Na⁺ occurred. Catecholamine threshold (Th_ca) was defined as the point at which a nonlinear increase occurred in either adrenaline or noradrenaline. The lactate (Th_la) and ventilatory (Th_ve) thresholds were determined according to published criteria. No significant differences were found between Th_sa values and the other methods of threshold determination. A high correlation was found between Th_sa and Th_la (r = 0.82, P < 0.01), and Th_sa and Th_ca (r = 0.75, P < 0.05). These results support the validity of Th_sa as a new method for noninvasive determination of the anaerobic threshold.     

The effect of different blood sampling sites and analyses on the relationship~ between exercise intensity and 4.0 mmol ·1− blood lactate concentration

Summary The aim of the study was to examine whether the difference in lactate concentration in different blood fractions is of practical importance when using blood lactate as a test variable of aerobic endurance capacity. Ten male firefighters performed submaximally graded exercise on a cycle ergometer for 20–25 min. Venous and capillary blood samples were taken every 5 min for determination of haematocrit and lactate concentrations in plasma, venous and capillary blood. At the same time, expired air was collected in Douglas bags for determination of the oxygen consumption. A lactate concentration of 4.0 mmol·1^–1 was used as the reference value toi compare the oxygen consumption and exercise intensity when different types of blood specimen and sampling sites were used for lactate analysis. At this concentration the exercise intensity was 17% lower (P<0.01) when plasma lactate was compared toi venous blood lactate, and 12% lower (P<0.05) when capillary blood lactate was used. Similar discrepancies were seen in oxygen consumption. The results illustrated the importance of standardizing sampling and handling of blood specimens for lactate determination to enable direct comparisons to be made among results obtained in different studies.The study was performed at the Department of Clinical Physiology University Hospital, S-75185 Uppsala, Sweden     

Circadian rhythms in blood lactate concentration during incremental ergometer rowing

This study examined whether circadian rhythms affect lactate threshold (Th_lac) during rowing exercise. Eleven male, endurance-trained athletes [mean (SD) age 29.5 (6.1) years] rowed at 0200, 0600, 1000, 1400, 1800 and 2200 hours under the same experimental conditions. Capillary blood (25 l) was obtained from the tip of the toe during the last 30 s of a continuous, multi-stage, 3-min, incremental protocol on the Concept II ergometer. To determine Th_lac, a curve-fitting procedure (the D_max method), a visual method (Th_lac-vis) and the fixed blood lactate concentration of 4.0 mmol l^–1 (Th_{lac-4 mM}) were used. Circadian rhythms were apparent for oxygen consumption and heart rate at Th_lac using the D_max method (P=0.02 and P=0.04 respectively), with the acrophases at 2139 hours and 2032 hours respectively coinciding in phase with that of core body temperature. The conclusion is that tests should be completed at the same time of day at which the athlete usually trains, to ensure precision of Th_lac determination, especially when the D_max method is used to determine Th_lac.     

Lactate after exercise in man: III. Properties of the compartment model

Summary Lactate movements during recovery following muscular exercise in man were studied by means of a two-compartment model. Mathematical discussion of the literal expressions obtained allows one to represent parameters concerning lactate exchange, utilization, and production in the previously working muscles and in the remaining lactate distribution space. It also shows that bi-exponential time courses predicted for muscular and blood lactate concentrations as well as for rates of lactate uptake, release, and utilization can denote several morphologies. All of the time evolutions for muscular and blood lactate concentrations found in the literature are consistent with these theoretical possibilities in the model. A numerical application confirms this concordance. Thus, this simple model, for which the basic assumptions were previously justified, appears to be qualitatively able to describe lactate exchanges and disappearance after exercise. A practical algorithm is put forward to display its possibilities and to test further its quantitative validity.List of Abbreviations and Symbols ₁₂, ₂₁ Coefficients of efficiency in lactate transfer from (M) to (S) and (S) to (M), respectively (min^–1) - A ₁, A ₂ Amplitudes of the exponential terms of fits to L _a (t) (mmol·l^–1) - (AS1), (AS2), (AS3), (AS4) Assumptions on which the model is based - A-curves Graphs of monotonic time functions - B-curves Graphs of time functions showing an extremum and an inflexion point - C ₁, d ₁ Lactate production rates in (M) and (S), respectively (mmol·min^–1) - c ₂, d₂ Coefficients of efficiency in lactate utilization by (M) and (S), respectively (min^–1) - C ₁, C ₂ Amplitudes of the exponential terms of L _M (t) (mmol·l^–1) - D ₁, D ₂ Amplitudes of the exponential terms of L _S (t) (mmol·l^–1) - (D ₁), (D ₂), (D ₃) Separating lines for definitions (+) and (–) of the parameters (Fig. 4) - (F ₁), (F ₂) Areas of validity of the model - L _a (t) Lactate concentration in arterial blood at time t obtained by fits to experimental data (mmol·l^–1) - L _M (t), L _S (t) Lactate concentrations in (M) and (S), respectively, at time t (mmol·l^–1) - L _v (t) Lactate concentration in blood leaving (M) at time t (mmol·l^–1) - L ₁, L ₂, L ₃ Maximum allowable values for d ₂ (Fig. 4) (min^–1) - (M), (S) Worked muscle space and remaining lactate space - ₁, ₂ Invariant points of () - (P ₁), (P ₂), (P ₃) Properties of the function y(t) - q(t) Blood flow perfusing (M) at time t (l·min^–1) - t Time after the end of exercise (min) - t ₁, t ₂ Instants at which y _t (t) and y' _t (t) reduce to zero (min) - V _M , V _S Volumes of (M) and (S), respectively (l) - V _MS V _M to V _S ratio - V _SM V _S to V _M ratio - y _t General form of time functions generated by the model (mmol·l^–1 or mmol·min^–1) - ₁, ₂ Amplitudes of the transient terms of y(t) (mmol·l^–1 or mmol·min^–1) - () Conics describing the relation between c ₂ and d ₂ - ₁, ₂ Velocity constants of the exponential fits to L _a (t) (min^–1) - ₁, ₂ Theoretical velocity constants of the time functions (min^–1) - , Instants at which _MS (t) reduces to zero (min) - Net muscular release rate of lactate at t (mmol·min^–1) - ₁, ₁ Instants at which L _M (t) crosses L _S (t) (min) - _mM (t), _mS (t) Lactate utilization rates in (M) and (S), respectively (mmol·min^–1) - _MS (t) Net muscular release rate of lactate (mmol·min^–1)     

Anaerobic threshold and maximal steady-state blood lactate in prepubertal boys

Summary To elucidate further the special nature of anaerobic threshold in children, 11 boys, mean age 12.1 years (range 11.4–12.5 years), were investigated during treadmill running. Oxygen uptake, including maximal oxygen uptake (VO_2max), ventilation and the ventilatory anaerobic threshold were determined during incremental exercise, with determination of maximal blood lactate following exercise. Within 2 weeks following this test four runs of 16-min duration were performed at a constant speed, starting with a speed corresponding to about 75% ofVO_2max and increasing it during the next run by 0.5 or 1.0 km·h^–1 according to the blood lactate concentrations in the previous run, in order to determine maximal steady-state blood lactate concentration. Blood lactate was determined at the end of every 4-min period. Anaerobic threshold was calculated from the increase in concentration of blood lactate obtained at the end of the runs at constant speed. The mean maximal steady-state blood lactate concentration was 5.0 mmol · 1^–1 corresponding to 88% of the aerobic power, whereas the mean value of the conventional anaerobic threshold was only 2.6 mmol · 1^–1, which corresponded to 78% of theVO_2max. The correlations between the parameters of anaerobic threshold, ventilatory anaerobic threshold and maximal steady-state blood lactate were only poor. Our results demonstrated that, in the children tested, the point at which a steeper increase in lactate concentrations during progressive work occurred did not correspond to the true anaerobic threshold, i.e. the exercise intensity above which a continuous increase in lactate concentration occurs at a constant exercise intensity.     

Influence of moderate cold exposure on blood lactate during incremental exercise

Summary This study examined the effect of exposure of the whole body to moderate cold on blood lactate produced during incremental exercise. Nine subjects were tested in a climatic chamber, the room temperature being controlled either at 30°C or at 10°C. The protocol consisted of exercise increasing in intensity in 35 W increments every 3 min until exhaustion. Oxygen consumption (VO₂) was measured during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for the measurement of blood glucose, free fatty acid (FFA), noradrenaline (NA) and adrenaline (A) concentrations and, during the last 15 s of each exercise intensity, for the determination of blood lactate concentration [la^–]_b. TheVO₂ was identical under both environments. At 10°C, as compared to 30°C, the lactate anaerobic threshold (Th_{an, la} ^–) occurred at an exercise intensity 15 W higher and [Th_{an, la} ^–]_b was lower for submaximal intensities above the Th_{an, la} ^– Regardless of ambient temperature, glycaemia, A and NA concentrations were higher at exhaustion while FFA was unchanged. At exhaustion the NA concentration was greater at 10°C [15.60 (SEM 3.15) nmol·l^–1] than at 30°C [8.64 (SEM 2.37) nmol·l^–1]. We concluded that exposure to moderate cold influences the blood lactate produced during incremental exercise. These results suggested that vasoconstriction was partly responsible for the lower [la^–]_b observed for submaximal high intensities during severe cold exposure.     

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

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

Changes in onset of blood lactate accumulation (OBLA) and muscle enzymes after training at OBLA

Summary Eight well-trained middle and long distance male runners added to their regular training program a weekly 20-min treadmill run at a velocity calculated to elicit a blood lactate concentration of 4 mmol×1^–1. O₂ max, the running velocity eliciting 4 mmol×1^–1 blood lactate (V _OBLA), and the activities of citrate synthase (CS), phosphofructokinase (PFK), lactate dehydrogenase (LDH) and LDH isozymes in the M. vastus lateralis were determined before and after 14 weeks of this training. Significant increases were observed in V _OBLA and the relative fraction of heart-specific LDH, while the activity of PFK and the ratio of PFK/CS decreased after training. The change in V _OBLA was negatively correlated to the mean rate of blood lactate accumulation during the last 15 min of the treadmill training runs, and positively correlated to the percentage of slow twitch fibers in the M. vastus lateralis. The data support the hypothesis that a steady state training intensity which approximates V _OBLA will increase V _OBLA, and will result in measureable local metabolic adaptations in the active skeletal muscles of well-trained runners without a significant change in maximal aerobic power. Muscle fiber type composition may be an indicator of the trainability of the musculature.Supported in part by grants from the Research Council of the Swedish Sports Federation and the Swedish Armed Forces Enrolment Board