Fixed Blood Lactate Concentrations Research Articles

Stability of Heart Rate at Physiological Thresholds Between Temperate and Heat Stress Environments in Endurance-Trained Males.

Many endurance athletes perform specific blocks of training in hot environments in "heat stress training camps." It is not known if physiological threshold heart rates measured in temperate conditions are reflective of those under moderate environmental heat stress. A total of 16 endurance-trained cyclists and triathletes performed incremental exercise assessments in 18°C and 35°C (both 60% relative humidity) to determine heart rates at absolute blood lactate and ventilatory thresholds. Heart rate at fixed blood lactate concentrations of 2, 3, and 4mmol·L-1 and ventilatory thresholds were not significantly different between environments (P > .05), despite significant heat stress-induced reductions in power output of approximately 10% to 17% (P < .05, effect size = 0.65-1.15). The coefficient of variation for heart rate at these blood lactate concentrations (1.4%-2.9%) and ventilatory thresholds (2.3%-2.7%) between conditions was low, with significant strong positive correlations between measurements in the 2 environments (r = .92-.95, P < .05). These data indicate heart rates measured at physiological thresholds in temperate environments are reflective of measurements taken under moderate environmental heat stress. Therefore, endurance athletes embarking on heat stress training camps can use heart rate-based thresholds ascertained in temperate environments to prescribe training under moderate environmental heat stress.

Functional Threshold Power as an Alternative to Lactate Thresholds in Road Cycling.

Sitko, S, Cirer-Sastre, R, Corbi, F, and López-Laval, I. Functional threshold power as an alternative to lactate thresholds in road cycling. J Strength Cond Res 36(11): 3179-3183, 2022-This study assessed the relationship between functional threshold power (FTP) and 7 lactate landmarks (Dmax, modified Dmax, fixed blood lactate concentrations of 2 and 4 mmol·L -1 , lactate increases of 1 and 2 mmol·L -1 above baseline, and lactate increases of 1.5 mmol·L-1 above the point of minimum ratio between lactate and work rate) in a sample of 46 road cyclists with a wide range of fitness levels (age 38 ± 9 years, height 177 ± 9 cm, body mass 71.4 ± 8.6 kg, body mass index 22.7 ± 2.2 kg·m -1 , fat mass 7.8 ± 4%, and V̇ o2 max = 61.1 ± 9.1 ml·min -1 ·kg -1 ). The cyclists performed a graded exercise test in which power outputs (POs) at the lactate landmarks were identified. Functional threshold power was established as 95% of the PO during a 20-minute test. Significance was set as p < 0.05. Statistical analyses revealed large to very large correlations between PO, relative PO (RPO), and cadence at FTP and lactate thresholds (LTs) established through Dmax, modified Dmax, and fixed lactate concentrations of 4 mmol·L -1 ( r = 0.68-0.93). Significant differences ( p < 0.001) were also observed for PO and RPO at FTP, fixed blood lactate concentrations of 2 mmol·L -1 , and lactate increases of 1 mmol·L -1 above baseline. Therefore, although FTP estimated from a 20-minute test is strongly related to several lactate landmarks, caution is required when substituting this concept for LTs. This information will allow coaches, cyclists, and scientists to better choose assessments when attempting to estimate LT through power-based field testing.

Effects of Strength Training on Postpubertal Adolescent Distance Runners.

Strength training activities have consistently been shown to improve running economy (RE) and neuromuscular characteristics, such as force-producing ability and maximal speed, in adult distance runners. However, the effects on adolescent (<18 yr) runners remains elusive. This randomized control trial aimed to examine the effect of strength training on several important physiological and neuromuscular qualities associated with distance running performance. Participants (n = 25, 13 female, 17.2 ± 1.2 yr) were paired according to their sex and RE and randomly assigned to a 10-wk strength training group (STG) or a control group who continued their regular training. The STG performed twice weekly sessions of plyometric, sprint, and resistance training in addition to their normal running. Outcome measures included body mass, maximal oxygen uptake (V˙O2max), speed at V˙O2max, RE (quantified as energy cost), speed at fixed blood lactate concentrations, 20-m sprint, and maximal voluntary contraction during an isometric quarter-squat. Eighteen participants (STG: n = 9, 16.1 ± 1.1 yr; control group: n = 9, 17.6 ± 1.2 yr) completed the study. The STG displayed small improvements (3.2%-3.7%; effect size (ES), 0.31-0.51) in RE that were inferred as "possibly beneficial" for an average of three submaximal speeds. Trivial or small changes were observed for body composition variables, V˙O2max and speed at V˙O2max; however, the training period provided likely benefits to speed at fixed blood lactate concentrations in both groups. Strength training elicited a very likely benefit and a possible benefit to sprint time (ES, 0.32) and maximal voluntary contraction (ES, 0.86), respectively. Ten weeks of strength training added to the program of a postpubertal distance runner was highly likely to improve maximal speed and enhances RE by a small extent, without deleterious effects on body composition or other aerobic parameters.

The prediction of endurance performance from work rates at fixed blood lactate concentrations is a mathematical not a physiological phenomenon - a novel hypothesis

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Test–retest reliability of physiological parameters in elite junior distance runners following allometric scaling

This study aimed to quantify the intra-individual reliability of a number of physiological variables in a group of national and international young distance runners. Sixteen (8 male, 8 female) participants (16.7 ± 1.4 years) performed a submaximal incremental running assessment followed by a maximal running test, on two occasions separated by no more than seven days. Maximal oxygen uptake (V̇O2max), speed at V̇O2max (km h−1), running economy and speed and heart rate (HR) at fixed blood lactate concentrations were determined. V̇O2max and running economy were scaled for differences in body mass using a power exponent derived from a larger cohort of young runners (n = 42). Running economy was expressed as oxygen cost and energy cost at the speed associated with lactate turnpoint (LTP) and the two speeds prior to LTP. Results of analysis of variance revealed an absence of systematic bias between trials. Reliability indices showed a high level of reproducibility across all parameters (typical error [TE] ≤2%; intra-class correlation coefficient >0.8; effect size <0.6). Expressing running economy as energy cost appears to provide superior reliability than using oxygen cost (TE ∼1.5% vs. ∼2%). Blood lactate and HR were liable to daily fluctuations of 0.14–0.22 mmol L−1 and 4–5 beats min−1 respectively. The minimum detectable change values (95% confidence) for each parameter are also reported. Exercise physiologists can be confident that measurement of important physiological determinants of distance running performance are highly reproducible in elite junior runners.

Perceived Exertion is Lower in Running than Walking at the Same Heart Rate and Lactate Level

The purpose of this study was to examine perceived effort at various intensities in human walking and running. Fifteen male subjects participated in this study. Two progressive protocols were randomized, starting at a treadmill speed of 3 Metabolic Equivalents (METs) to Measure Ratings of Perceived Exertion (RPE), Heart Rate (HR) and blood lactate concentration. From these data, RPE was estimated at an intensity corresponding to Fixed Heart Rate (FHR; 120, 130, 140, 150 bpm) and Fixed Blood Lactate Concentrations (FBLCs; 2 and 3 mM) from the individual regression line.

Effects of sodium bicarbonate ingestion on lactate steady state responses in female futsal players

This purpose of this study was to investigate the effects of sodium bicarbonate ingestion on lactate steady state responses (blood lactate and heart rate) in female futsal players. 30 female futsal players volunteered to participate in this investigation. Participants were randomly assigned to either experimental group or placebo group. While the experimental group was ingested sodium bicarbonate supplementation (NaHCO3), the placebo group was ingested sodium chloride (NaCl). Participants were first tested using a standard incremental treadmill test to define the blood lactate profile. Running speeds corresponding to fixed blood lactate concentrations of 4.0 mmol.l-1 were calculated using linear interpolation. The maximal lactate steady state was determined from 30-min constant-speed treadmill runs. The maximal lactate steady state was defined as fastest running speed that produced no more than a 1.0 mmol.l-1 increase in blood lactate concentration between 10 and 30 min of exercise. Paired Samples T test was used to determine whether there are significant blood lactate and heart rate differences in before and after sodium bicarbonate ingestion. Test results showed a significant decrease in the post-supplement heart rate responses given by the sodium bicarbonate group at the 10th, 20th and 30th min of the lactate steady state exercise (p 0.05). Key words: Lactate steady state, sodium bicarbonate, heart rate, blood lactate.

Heart Rate-Based Prediction of Fixed Blood Lactate Thresholds in Professional Team-Sport Players.

The aim of this study was to investigate whether the speed associated with 90% of maximal heart rate (S90%HRmax) could predict speeds at fixed blood lactate concentrations of 3 mmol·L(-1) (S3mM) and 4 mmol·L(-1) (S4mM). Professional team-sport players of futsal (n = 10), handball (n = 16), and basketball (n = 10) performed a 4-stage discontinuous progressive running test followed, if exhaustion was not previously achieved, by an additional maximal continuous incremental running test to attain maximal heart rate (HRmax). The individual S3mM, S4mM, and S90%HRmax were determined by linear interpolation. S3mM (11.6 ± 1.5 km·h(-1)) and S4mM (12.5 ± 1.4 km·h(-1)) did not differ (p > 0.05) from S90%HRmax (12.0 ± 1.2 km·h(-1)). Very large significant (p < 0.001) relationships were found between S90%HRmax and S3mM (r = 0.82; standard error of the estimates [SEE] = 0.87 km·h(-1)), as well as between S90%HRmax and S4mM (r = 0.82; SEE = 0.87 km·h(-1)). S3mM and S4mM inversely correlated with %HRmax associated with running speeds of 10 and 12 km·h(-1) (r = 0.78-0.81; p < 0.001; SEE = 0.94-0.87 km·h(-1)). In conclusion, S3mM and S4mM can be accurately predicted by S90%HRmax in professional team-sport players.

Precision in Estimating Maximal Lactate Steady State Performance in Running Using a Fixed Blood Lactate Concentration or a Delta Value from an Incremental Lactate Profile Test

Six definitions of blood lactate threshold were used on an incremental lactate profile test (LPT) to ascertain which of them best estimated the Maximal Lactate Steady State (MLSS) velocity when using the Lactate Pro LT-1710 analyser. These definitions included three fixed blood lactate concentrations of 4.0, 3.0 and 2.0 mmol ·L-1, and three dynamic definitions, in which a value of 1.0, 1.5 and 2.0 mmol ·L-1 were added to the resting blood lactate concentration. Fourteen trained men (age 49±12 yrs, mass 74.5±5.7 kg) performed an incremental LPT and a VO2max test on a treadmill. A few days later they performed several MLSS runs of 30 min. duration to find the highest velocity with a stable blood lactate concentration. Threshold definitions that had resting blood lactate concentrations between 3.0 and 4.0 mmol ·L-1 gave threshold velocities not statistically different from the velocity at MLSS when using the LT-1710 blood lactate analyser. The only definition to overestimate the MLSS running velocity was the fixed blood lactate concentrations of 4.0 mmol ·L-1. The closest match was found when adding a delta value of 2.1 (1.1) mmol ·L-1 to the resting blood lactate concentration. When using the LT-1710 analyser for MLSS estimation from incremental LPTs, lactate threshold definitions that gives blood lactate concentrations of 3.0 to 4.0 mmol ·L-1 can be used

Power–cadence relationship in endurance cycling

In maximal sprint cycling, the power-cadence relationship to assess the maximal power output (P (max)) and the corresponding optimal cadence (C (opt)) has been widely investigated in experimental studies. These studies have generally reported a quadratic power-cadence relationship passing through the origin. The aim of the present study was to evaluate an equivalent method to assess P (max) and C (opt) for endurance cycling. The two main hypotheses were: (1) in the range of cadences normally used by cyclists, the power-cadence relationship can be well fitted with a quadratic regression constrained to pass through the origin; (2) P (max) and C (opt) can be well estimated using this quadratic fit. We tested our hypothesis using a theoretical and an experimental approach. The power-cadence relationship simulated with the theoretical model was well fitted with a quadratic regression and the bias of the estimated P (max) and C (opt) was negligible (1.0 W and 0.6 rpm). In the experimental part, eight cyclists performed an incremental cycling test at 70, 80, 90, 100, and 110 rpm to yield power-cadence relationships at fixed blood lactate concentrations of 3, 3.5, and 4 mmol L(-1). The determined power outputs were well fitted with quadratic regressions (R (2) = 0.94-0.96, residual standard deviation = 1.7%). The 95% confidence interval for assessing individual P (max) and C (opt) was ±4.4 W and ±2.9 rpm. These theoretical and experimental results suggest that P (max), C (opt), and the power-cadence relationship around C (opt) could be well estimated with the proposed method.

Physiological Responses To Simulated Anti-gravity During Treadmill Running

A novel 'anti-gravity' treadmill design (G-Trainer, Alter-G, Freemont, U.S.A) enables athletes to run with a simulated reduced bodyweight (BW). The physiological effect of this technique has not been characterised. PURPOSE: To compare the physiological responses to running in simulated anti-gravity with normal gravity conditions. METHODS: Using a randomised, crossover design, nine male runners of mixed ability (VO2max range: 55.1-78.6 ml.kg-1.min-1) performed a discontinuous incremental treadmill test in three conditions (85% BW, 100% BW, control). The test protocol included 1) a 'step' test (3 min stages, increasing by 1 km.h-1 until a blood lactate concentration (BLC) > 4 mMol.L-1) to measure treadmill speed and heart rate (HR) at a BLC of 2, 4 and at the first rise of 1 mMol.L-1 and 2) a constant speed 'ramp' test to exhaustion (1%.min-1 gradient increase) to measure VO2max. RESULTS: There was a significant effect of treadmill condition on speed at all blood lactate concentrations (P = 0.001). Post hoc tests revealed significant differences between conditions (table). There was no effect of treadmill condition on HR at 4 mMol.L-1 (P = 0.156) and the first rise of 1 mMol.L-1 (P = 0.472). However, there was a significant effect of treadmill on HR at 2 mMol.L-1 (P = 0.034), although post hoc tests were unable to identify where the differences lay. There was also no effect of treadmill on VO2max (P = 0.564). CONCLUSIONS: Simulated anti-gravity increases the speed required to illicit significant rises in BLC during sub-maximal incremental treadmill running. However, it has no significant impact on sub-maximal HR or VO2max.Table: Speed and heart rate data at fixed blood lactate concentrations (BLC)

Submaximal Relative Mechanical Power Output Is A Requirement To Be A Professional Road Cyclist

Numerous studies in the scientific literature show the determinant performance factors in professional road cyclists. Nevertheless, there are some submaximal variables, probably related to endurance cycling performance, that remain to be studied. PURPOSE: To assess new physiological and mechanical factors that could be considered a requirement to become a professional cyclist. METHODS: 161 cyclists of different levels of performance (13 professional and 148 amateurs, age 20.9 ± 3.9 yr) performed a laboratory test on a cyclergometer. Warm-up: 100W·10 min-1, initial workload: 200 W followed by 30 W increments every 4 min until exhaustion. All the tests were performed throughout a 10 year-period during the competitive phase of a cycling season (February to May). Dietary intake and resting period were controlled two days before the tests in order to maximize the test results. Subsequently, relative (W·kg-1) and absolute (W) mechanical power output at different fixed blood lactate concentrations (2, 3, 4, and 5 mmol·l-1), maximal absolute and relative mechanical power output (Wmax·kg-1, Wmax), and VO2max, expressed as L·min-1, mL·kg-1·min-1, and mL·kg-3/4·min-1, were measured and further analyzed using a backward stepwise multivariate logistic regression analysis to evaluate the aforementioned physiological parameters as potential predictors to be a professional cyclist. The level of significance was set at P < 0.05. RESULTS: The logistic regression analysis showed that VO2max expressed as mL·kg-1·min-1 and L·min-1 as well as mechanical power output expressed in absolute or relative terms were not good predictors to become a professional cyclist. Nevertheless, VO2max expressed as mL·kg-3/4·min-1 (P<0,01), W·kg-1(3mM) (P<0,01), W·kg-1(4mM) (P<0,01), and W·kg-1(5mM) (P<0,05) were significant predictors for becoming a professional road cyclist. CONCLUSION: To become a professional cyclist it is important to have a high relative VO2max (mL·kg-3/4·min-1), W·kg-1(2mM), W·kg-1(4mM), W·kg-1(5mM). It is important to emphasize that W·kg-1 at different submaximal intensities is also an important requirement to become a professional road cyclist, although these variables have not been well studied in the past. This study opens a new perspective to evaluate the performance of professional road cyclists.

Determination of Force Corresponding to Maximal Lactate Steady State in Tethered Swimming

The main aim of the present investigation was to verify if the aerobic capacity (AC) measured in tethered swimming corresponds to the maximal lactate steady state (MLSS) and its correlation with 30 min and 400m free style swimming. Twenty-five swimmers were submitted to an incremental tethered swimming test (ITS) with an initial load of 20N and increments of 10N each 3min. After each stage of 3min, the athletes had 30s of interval to blood sample collections that were used to measure blood lactate concentrations ([La-]). The ACBI was determined by the abrupt increase in [La-] versus force (F). The points obtained between [La-] versus force (N) were adjusted by an exponential curve model to determine AC corresponding to 3.5mmol.l-1 (AC3.5) and 4.0mmol.l-1 (AC4.0). After these procedures, the swimmers performed maximal efforts of 30min and 400m in free style swimming. We used the distance performed in 30min and the time performed in 400m to calculate the median velocities (i.e. V30 and V400) of these protocols. After one week, in order to measure the MLSS, nine athletes performed three 30-min tethered swimming efforts with intensities of 90, 100, and 110% of ACBI. The ANOVA one-way was used to compare the ACBI, AC3.5 and AC4.0. Correlations between ACs, and between ACs and V30 and V400 (p&lt;0.05) were determined using the Pearson’s correlation coefficient. The intensity corresponding to 100% of ACBI was similar to the MLSS. It was observed significant correlations of the aerobic capacities (i.e. ACBI, AC3.5 and AC4.0) with V30 (r&gt;0.91) and V400 (r&gt;0.63). According to our results, it is possible to conclude that the ACBI corresponds to the MLSS, and both the AC - individually determined - and the AC - determined using fixed blood lactate concentrations of 3.5 and 4.0mmol.l-1 - can be used to predict the mean velocity of 30min and 400m in free style swimming. In addition to that, the tethered swimming system can be used for aerobic development in places where official sized swimming pools are not available, such as rehabilitation clinics and health clubs.

Running velocities and heart rates at fixed blood lactate concentrations in young soccer players

The purpose of this study was to examine the running velocities and heart rates at fixed lactate concentrations of young soccer players according to playing position and age. A total of 223 young male soccer players participated in this study. Each player performed incremental exercise tests on a treadmill. Running velocities and heart rates at 2 mmol/L-1, 2.5 mmol/L-1, 3 mmol/L-1, and 4 mmol/L-1 blood lactate concentrations were calculated with use of the spline function. Data were analyzed through analysis of variance to examine differences among various playing positions (ie, defenders, midfielders, and forwards) and 3 age groups (U17, under 17 y; U19, under 19 y; and U21, under 21 y). No significant differences were discerned between defenders, midfielders, and forwards in terms of running velocities and heart rates in accordance with specified lactate concentrations. Running velocities corresponding to all lactate concentrations showed no significant differences at all age groups, but heart rates in soccer players in the U21 and U19 age groups were significantly lower than in the U17 age group. Following a 3-y trial of 20 players, running velocities increased and heart rates decreased at all corresponding lactate concentrations. Results of this study suggest that (1) the endurance performance level of young soccer players is similar for all positions, and (2) heart rates are lowered with age and with training.

Running velocities and heart rates at fixed blood lactate concentrations in elite soccer players

This study was undertaken to examine the endurance performance of elite soccer players, according to age and playing position. A total of 197 male soccer players participated in this study. Each player performed exercise tests on the treadmill that included 3-minute runs and 30-second blood sampling intervals. During these tests, running speeds at the first and second stages were 10 km/hr -1 and 12 km/hr -1, respectively. When these tests were completed, running speed was increased by 1 km/hr every 3 minutes until the runner reached exhaustion. Blood samples were analyzed immediately by means of an automated lactate analyzer. Heart rate was monitored continuously at 5-second intervals. Running velocities and heart rates at 2-mmol/L -1, 2.5-mmol/L -1, 3-mmol/L -1, and 4-mmol/L -1 blood lactate concentrations were calculated with use of the spline function. Analysis of variance was used to analyze data to determine the differences between playing positions (goalkeepers, defenders, midfielders, and forwards) and age groups (older than 30 years of age, between 25 and 29 years old, between 20 and 24 years old, and 19 years old and younger). Statistical significance was set at P<.01. No significant differences were revealed between defenders, midfielders, and forwards regarding running velocities and heart rates and their correlation with specified lactate concentrations. Goalkeepers demonstrated lower endurance performance than players in the other playing positions (P<.001). Running velocities corresponding to all lactate concentrations showed no significant differences in all age groups, but heart rates in soccer players older than 30 years of age were significantly lower than those of players in other age groups (P<.01). Results of this study suggest that the endurance performance level of professional players is similar for players in all positions, except for goalkeepers, and that endurance performance is not adversely affected when a person's age increases beyond 30 years of age.

Identification of Blood Lactate Parameters Using the Lactate Pro Portable Analyzer

0823 PURPOSE: Firstly, to determine the agreement between the Lactate Pro and a laboratory analyzer for the measurement of blood lactate, and secondly, to examine the efficacy of the Lactate Pro for the identification of lactate parameters routinely used in the physiological assessment of athletes. METHODS: Twenty well-trained male cyclists performed an incremental cycle ergometry test (starting at 175 W, with 25 W increments every 4 min) to determine the lactate response to exercise. Duplicate earlobe capillary blood samples were taken simultaneously at the end of each 4 min stage and analyzed using the Lactate Pro (LP) and the Analox GM7 (GM7) laboratory analyzer. Linear regression and the Bland and Altman method were used to determine the relationship and agreement between the analyzers. Power-lactate plots, derived from each of the two analyzers, were used to identify power outputs at LT (the work rate preceding an increase of ≥ 0.4 mmol× l−1), LT1 (the work rate preceding an increase of ≥ 1.0 mmol× l−1), and fixed blood lactate concentrations of 2 mmol× l−1 and 4 mmol× l−1. RESULTS: Linear regression demonstrated a strong relationship between the two analyzers in the range 0.5 – 16.2 mmol× l−1 (LP = 1.4309 × GM7; R2 = 0.969, p < 0.001). LP however overestimated blood lactate when compared to GM7 with a mean difference of +1.43 mmol× l-1, a relationship (r = 0.915, p < 0.001) between measurement differences and mean lactate values indicated heteroscedastic errors. Consequently, the data were log-transformed providing 95% ratio limits of agreement (LP/GM7) of 1.40 ×/÷ 1.35, indicating that 95% of the ratios lay between 1.04 (+4%) and 1.89 (+89%), with a mean of 1.40 (+40%). Differences (p < 0.01) were found between analyzers for power output at LT1, 2 mmol× l−1 and 4 mmol× l−1 (270.7 ± 37.7 W vs. 283.8 ± 39.1 W; 225.7 ± 44.0 W vs. 255.7 ± 41.8 W; and 287.8 ± 40.3 W vs. 308.6 ± 37.0 W, for LP and GM7, respectively). No significant difference was found between analyzers for power output at LT (222.5 ± 34.3 W and 228.8 ± 40.8 W, for LP and GM7, respectively). CONCLUSIONS: Agreement between the Lactate Pro and Analox GM7 is poor; on average the Lactate Pro overestimates blood lactate by 40% with 95% of measures overestimated by between 4% and 89%. As a consequence, the Lactate Pro significantly underestimates power output at the lactate parameters LT1, 2 mmol× l−1 and 4 mmol× l−1.

Maximal lactate steady state in trained adolescent runners

The aims of this study were: (1) to identify the exercise intensity that corresponds to the maximal lactate steady state in adolescent endurance-trained runners; (2) to identify any differences between the sexes; and (3) to compare the maximal lactate steady state with commonly cited fixed blood lactate reference parameters. Sixteen boys and nine girls volunteered to participate in the study. They were first tested using a stepwise incremental treadmill protocol to establish the blood lactate profile and peak oxygen uptake ([Vdot]O2). Running speeds corresponding to fixed whole blood lactate concentrations of 2.0, 2.5 and 4.0 mmol · l−1 were calculated using linear interpolation. The maximal lactate steady state was determined from four separate 20-min constant-speed treadmill runs. The maximal lactate steady state was defined as the fastest running speed, to the nearest 0.5 km · h−1, where the change in blood lactate concentration between 10 and 20 min was <0.5 mmol · l−1. Although the boys had to run faster than the girls to elicit the maximal lactate steady state (15.7 vs 14.3 km · h−1, P <0.01), once the data were expressed relative to percent peak [Vdot]O2 (85 and 85%, respectively) and percent peak heart rate (92 and 94%, respectively), there were no differences between the sexes (P >0.05). The running speed and percent peak [Vdot]O2 at the maximal lactate steady state were not different to those corresponding to the fixed blood lactate concentrations of 2.0 and 2.5 mmol · l−1 (P >0.05), but were both lower than those at the 4.0 mmol · l−1 concentration (P <0.05). In conclusion, the maximal lactate steady state corresponded to a similar relative exercise intensity as that reported in adult athletes. The running speed, percent peak [Vdot]O2 and percent peak heart rate at the maximal lactate steady state are approximated by the fixed blood lactate concentration of 2.5 mmol · l−1 measured during an incremental treadmill test in boys and girls.

Substantial influence of level of endurance capacity on the association of perceived exertion with blood lactate accumulation.

Capillary blood lactate assessment is increasingly used by well-trained runners to monitor the intensity of endurance exercise. In order to examine the known association of exercise intensity with blood lactate accumulation also in less trained subjects, we analysed data from a standardized incremental maximal test on the treadmill of 319 men (age 22.9 +/- 5.5 years, [means +/- S.D.]) and 145 women (22.7 +/- 4.5 years) characterized by a wide variation in endurance capacity. Results showed that the running velocity eliciting a blood lactate concentration of 4 mmol/l did not correspond to the same exercise intensity in well endurance-trained vs poorly endurance-trained subjects. At 4 mmol/l blood lactate, the slowest decile of men (i.e. 32 out of 319) ran at 71 +/- 4.7% (corresponding to 2.9 +/- 0.3 m/s) of their maximal treadmill velocity attained during the test (4.1 +/- 0.4 m/s), indicating a rating of perceived exertion (RPE) of 12.3 +/- 1.8 points (Borg scale, range 6-20 points), while the fastest decile of men (n = 32) ran at 91 +/- 3.1% (corresponding to 5.4 +/- 0.2 m/s) of their maximal treadmill speed (5.9 +/- 0.2 m/s), indicating a RPE of 16.6 +/- 1.1 points. Very similar results were observed in women. There was a highly significant, positive correlation between running speed eliciting a blood lactate concentration of 4 mmol/l and RPE when running at this speed, with r = 0.64 in men and r = 0.55 in women. At the same proportional level of maximal running velocity, poorly endurance-trained athletes showed a 2-3 mmol/l higher capillary lactate concentration than well endurance-trained athletes, with both groups indicating the same RPE. These results suggest that fixed blood lactate concentrations not at all mean the same exercise intensity for well vs poorly endurance-trained subjects; this systemic trend should be considered when using blood lactate assessment for individual exercise counselling.

THE EFFECT OF HEAT ON DIFFERENTIATED RPE AT VARIOUS LACTATE CONCENTRATIONS1235

The effect of ambient temperature on differentiated ratings of perceived exertion (RPE) at the lactate threshold (LT) and fixed blood lactate concentrations (FBLC) of 2.0 mM, 2.5 mM, 4.0 mM and at maximal levels was studied during cycle ergometry in eleven untrained (˙VO2max 45.8 ml·kg·min-1), unacclimatized college males. Subjects completed two counterbalanced maximal cycle ergometer tests in thermoneutral(TN) (22-25° C) and hot (HT) (37°C) conditions. Heart rate,˙VO2, RPE, Tre, and Tsk were determined at power outputs corresponding to LT, FBLC and maximal exercise. Repeated measures ANOVA indicated no significant differences in overall RPE between TN and HT at the LT, and FBLC of 2.5 mM, 4.0 mM, and maximal levels. Temperature did not affect heart rate or Tre at any lactate level, or ˙VO2 or%˙VO2max at the LT, 4.0 mM or maximal lactate level. Tsk was significantly higher in the heat at each lactate level. Differentiated RPE was not significantly different between TN and HT despite the trend for RPE-P> RPE-O > RPE-C. It was concluded that moderate exercise-heat stress does not affect the RPE at the LT, most FBLC's, or at maximal exercise, nor does it change the relationship between local, central, and overall RPE.

The Effect of Training Intensity on Ratings of Perceived Exertion

We examined the effects of intensity of training on ratings of perceived exertion (RPE) at the lactate threshold (LT), fixed blood lactate concentrations (FBLC) of 2.0, 2.5 and 4.0 mM and peak in 25 untrained eumenorrheic women (mean +/- SD: age = 30.9 +/- 4.1 yrs; height = 165.7 +/- 5.9 cm; weight = 65.5 +/- 7.6 kg) who completed one year of run training. Subjects were recruited as sedentary controls or were randomly assigned to one of two training groups: 1) at the lactate threshold (at LT) or 2) above the lactate threshold (greater than LT). The at LT group trained at velocity LT and the greater than LT group trained at the velocity midway between velocity LT and peak velocity. Training subjects were reevaluated every fourth menstrual cycle and training intensity was adjusted. The control group was reassessed at menstrual cycle 12. Before training no among group differences were observed for VO2 or velocity at LT, FBLC and peak. Both training groups increased VO2 at LT, FBLC and peak as a result of training (p less than 0.05), with the greater than LT group exhibiting greater improvement than the at LT group (VO2 at LT, FBLC of 2.0, 2.5 and 4.0 mM and peak increased by 6.4, 5.3, 5.1, 4.0 and 4.7 ml/kg.min-1 for at LT and by 10.4, 9.2, 8.6, 5.1 and 5.9 ml/kg.min-1 for greater than LT; p less than 0.05). Similar findings were observed for the velocity associated with these lactate concentrations. No pre/post differences were observed in VO2 or velocity for the control group.(ABSTRACT TRUNCATED AT 250 WORDS)