Lactate accumulation in response to supramaximal exercise in rowers

A comparison of historical versus proposed physical employment standards for flight paramedics performing helicopter winch rescue

BACKGROUND

Paramedics working in helicopter teams undertake water and land rescues. Historical assessments of role-related fitness were not developed using physical employment standards methodology.

OBJECTIVE

To compare the historical selection tests with new tests developed via contemporary scientific methodology.

METHODS

Candidates undergoing selection to the role of flight paramedic (n = 14; age 37±5 yrs, body mass index [BMI] 26±4 kg.m2) undertook existing paramedic selection tests on land and in water, measurements of task duration, maximum heart rate (HRmax), rate of perceived exertion (RPE6 - 20) and capillary blood lactate (Lacmax) were recorded. These results were compared to the same variables in experienced paramedics (n = 14; age 44±5 yrs, BMI 25±3 kg.m2) who undertook the new tests.

RESULTS

Land task duration (existing 17±2 min vs. proposed 7±2 min, p <  0.05) HRmax (existing 186±13 b.min-1 vs. proposed 173±11 b.min-1, p <  0.05), and Lacmax (existing 23±3 mmol.L-1 vs. proposed 8±2 mmol.L-1, p <  0.05) were higher in the existing test compared to the proposed tests. Water task duration (existing 12±2 min vs. proposed 10±1 min, p <  0.05) was longer in the existing test, but HRmax (existing 166±18 b.min-1 vs. proposed 167±15 b.min-1, p = 0.90), Lacmax (existing 11±4 mmol.L-1 vs. proposed 11±4 mmol.L-1, p = 0.90) did not differ. RPE6 - 20 did not differ between groups for water or land.

CONCLUSIONS

The historical land-based physical tests for paramedics differed from the proposed tests, however the water-based tests had similar duration and physiological demands. Use of tests not developed via established scientific methodologies risks eliminating candidates suitable to work in the role, or including candidates that are not.

Identifying physiological determinants of 800 m running performance using post-exercise blood lactate kinetics

PURPOSE

The aims of the present study were to investigate blood lactate kinetics following high intensity exercise and identify the physiological determinants of 800 m running performance.

METHODS

Fourteen competitive 800 m runners performed two running tests. First, participants performed a multistage graded exercise test to determine physiological indicators related to endurance performance. Second, participants performed four to six 30-s high intensity running bouts to determine post-exercise blood lactate kinetics. Using a biexponential time function, lactate exchange ability (γ1), lactate removal ability (γ2), and the quantity of lactate accumulated (QLaA) were calculated from individual blood lactate recovery data.

RESULTS

800 m running performance was significantly correlated with peak oxygen consumption (r = -0.794), γ1 and γ2 at 800 m race pace (r = -0.604 and -0.845, respectively), and QLaA at maximal running speed (r = -0.657). V ˙ O2peak and γ2 at 800 m race pace explained 83% of the variance in 800 m running performance.

CONCLUSION

Our results indicate that (1) a high capacity to exchange and remove lactate, (2) a high capacity for short-term lactate accumulation and, (3) peak oxygen consumption, are critical elements of 800 m running performance. Accordingly, while lactate has primarily been utilized as a performance indicator for long-distance running, post-exercise lactate kinetics may also prove valuable as a performance determinant in middle-distance running.

Acute anodal transcranial direct current stimulation improves the performance of professional rowers

Introduction

The aim of the present study was to evaluate the influence of acute transcranial direct current stimulation (tDCS) on physical and subjective responses in professional rowing during the 2,000-m time trial test.

Methods

Seven rowers (age 20.86 ± 4.49 years; weight 71.66 ± 7.97 kg) participated in this randomized triple-blind trial with a crossover experimental design. The protocol consists of 2 days with different conditions (anodal and sham). The tDCS anodic stimulation conducted was 2 mA for 20 min in the left temporal cortex (2.5 cm from the F7 zone and 2.5 cm from the T3 zone), targeting the left insular cortex. In the sham moment, the participants experienced 30 s of stimulation. Afterward, they performed a standardized progressive warm-up for 15 min, following the Brazilian Rowing Confederation's assessment protocols, and rested for 3 min before the test started. All procedures were made on an indoor rowing machine, which allowed the capture of performance variables such as time performed, power in watts (W), pace (m/min), and stroke rate (strokes/min). The ratings of perceived exertion [Borg scale (CR-20)] were recorded in each 2-min during the test.

Results

The results presented differences in power [Z: -2.371; p = 0.018; effect size (ES) = -0.896 (large)] and pace [Z: -2.371; p = 0.018; ES = -0.896 (large)] and time performance [Z: -1.612; p = 0.107; ES = -0.609 (large)] throughout the protocol for the anodal moment.

Discussion

However, no differences for the other variables were found. According to the results, the current tDCS with the present protocol improved the physical performance at the 2,000-m time trial Test providing ergogenic aid.

Is the Energy Cost of Rowing a Determinant Factor of Performance in Elite Oarsmen?

In elite oarsmen, the rowing ergometer is a valuable tool for both training and studying rowing performance determinants. However, the energy cost of rowing, often reported as a determinant of performance, has never been described for ergometer rowing. Therefore, this study aimed to characterize the energy cost of ergometer rowing (ECR) in elite oarsmen, its contribution to 2,000 m performance, and its determinants. This study was conducted on 21 elite oarsmen from the French national team. It included an incremental exercise test up to exhaustion and an all-out performance test over 2,000 m, both conducted on a rowing ergometer. Gas exchange analysis was performed to calculate oxygen uptake and substrate utilization rate. Whole blood lactate concentrations during the incremental test were obtained from the earlobe. During the incremental test, ECR displayed a significant linear increase up to a plateau that reached a mean rowing speed of 5.23 ± 0.02 m⋅s^–1. The ECR values at 300, 350, and 400 W were positively correlated with performance expressed as the time required to perform the 2,000 m distance on the rowing ergometer. The same ECR values were found to be significantly related to fat oxidation (expressed in percentage of total energy supply) and blood lactate concentrations. This study provides the first description of ECR and of its relationship to exercise intensity on the rowing ergometer in elite oarsmen. ECR appeared to be a factor of performance and interestingly was related to energy supply from fat and blood lactate concentrations.

Modelling of Blood Lactate Time-Courses During Exercise and/or the Subsequent Recovery: Limitations and Few Perspectives

Because lactate is an important metabolic intermediate and a signalling molecule between/within cells/organs, it appears essential to be able to describe the kinetics of this central molecule, during and/or after physical exercise. The present study aimed to confront three models and their approaches [Freund and co-workers (F&co), Beneke and co-workers (B&co), and Quittmann and co-workers (Q&co)] to investigate the lactate exchange (γ₁) and removal (γ₂) abilities (min⁻¹) during and/or after exercise. Nine healthy male subjects performed 3- and 6-min easy, moderate, and heavy exercise. Blood lactate concentration (BLC) was measured every 5 s over the entire period of exercise and recovery. Approaches differ depending on the domain in which the model is applied: considering exercise and part of the recovery (B&co and Q&co) or the entire period of recovery (F&co). The different approaches result in differing γ₁ and γ₂ values. Model fitting is closer to the experimental values following the method (model and approach) of F&co. Complementary analyses show that consideration of (i) exercise drastically impairs the quality of model fitting and therefore the γ₁ and γ₂ values and (ii) the entire period of recovery considerably improves the quality of fits and therefore of the γ₁ and γ₂ values. We conclude that (i) it is neither realistic nor reliable to take into account exercise and recovery in the same model and (ii) the longer the period of recovery studied, the better the quality of the γ₁ and γ₂ values.

Sex-related differences in accumulated O2 deficit incurred by high-intensity rowing exercise during childhood and adolescence

PURPOSE

The aims of the present study were to determine during childhood and adolescence (i) the effect of sex on non-oxidative energy production, quantified by the accumulated oxygen deficit (AOD), and (ii) the influence of AOD on high-intensity performance.

METHODS

Thirty-nine boys and 35 girls aged 10-17 years performed a 60 s all-out test on a rowing ergometer to determine AOD and mean power output (MPO). Multiplicative allometric modelling was used to assess the concurrent effects of lean body mass (LBM) and age on AOD.

RESULTS

AOD significantly increased with age in both sexes (p < 0.001) with boys exhibiting significantly higher AOD than girls from the age of 14 years (10-11.9 yr: 1.9 vs 1.9 L, 12-13.9 yr: 2.4 vs 2.7 L, 14-15.9 yr: 2.8 vs 4.6 L and 16-17.9 yr: 2.9 vs 5.2 L, in girls and boys respectively, p < 0.001). However, a sex difference was no longer significant when AOD was analysed using an allometric model including age and LBM (p = 0.885). Finally, significant correlations were found between AOD and MPO in boys and girls but with lower evidence in girls (r² = 0.41 vs. 0.89).

CONCLUSION

Non-oxidative energy production increased more extensively in boys than girls from the age of 14 years. Age and LBM accounted for the sexual differentiation of AOD during childhood and adolescence. In addition, AOD was found to be a determinant factor of high-intensity performance, more particularly in boys.

Importance of dimensional changes on glycolytic metabolism during growth

PURPOSE

The aim of the present study was to investigate (i) how glycolytic metabolism assessed by accumulated oxygen deficit (AOD_gly) and blood metabolic responses (lactate and pH) resulting from high-intensity exercise change during growth, and (ii) how lean body mass (LBM) influences AOD_gly and its relationship with blood markers.

METHODS

Thirty-six 11- to 17-year olds performed a 60-s all-out test on a rowing ergometer. Allometric modelling was used to investigate the influence of LBM and LBM + maturity offset (MO) on AOD_gly and its relationship with the extreme post-exercise blood values of lactate ([La]_max) and pH (pH_min) obtained during the recovery period.

RESULTS

AOD_gly and [La]_max increased while pH_min decreased linearly with LBM and MO (r² = 0.46 to 0.72, p < 0.001). Moreover, AOD_gly was positively correlated with [La]_max (r² = 0.75, p < 0.001) and negatively correlated with pH_min (r² = 0.77, p < 0.001). When AOD_gly was scaled for LBM, the coefficients of the relationships with blood markers drastically decreased by three to four times ([La]_max: r² = 0.24, p = 0.002; pH_min: r² = 0.30, p < 0.001). Furthermore, by scaling AOD_gly for LBM + MO, the correlation coefficients with blood markers became even lower ([La]_max: r² = 0.12, p = 0.037; pH_min: r² = 0.18, p = 0.009). However, MO-related additional changes accounted much less than LBM for the relationships between AOD_gly and blood markers.

CONCLUSION

The results challenge previous reports of maturation-related differences in glycolytic energy turnover and suggest that changes in lean body mass are a more powerful influence than maturity status on glycolytic metabolism during growth.

Non-oxidative Energy Supply Correlates with Lactate Transport and Removal in Trained Rowers

This study aimed to test if the non-oxidative energy supply (estimated by the accumulated oxygen deficit) is associated with an index of muscle lactate accumulation during exercise, muscle monocarboxylate transporter content and the lactate removal ability during recovery in well-trained rowers. Seventeen rowers completed a 3-min all-out exercise on rowing ergometer to estimate the accumulated oxygen deficit. Blood lactate samples were collected during the subsequent passive recovery to assess individual blood lactate curves, which were fitted to the bi-exponential time function: La(t)= [La](0)+A₁·(1-e^-γ ₁ ^t)+A₂·(1-e^-γ ₂ ^t), where the velocity constants γ₁ and γ₂ (min^-1) denote the lactate exchange and removal abilities during recovery, respectively. The accumulated oxygen deficit was correlated with the net amount of lactate released from the previously active muscles (r =0.58, P<0.05), the monocarboxylate transporters MCT1 and MCT4 (r=0.63, P<0.05) and γ₂ (r=0.55, P<0.05). γ₂ and the lactate release rate at exercise completion were negatively correlated with citrate synthase activity. These findings suggest that the capacity to supply non-oxidative energy during supramaximal rowing exercise is associated with muscle lactate accumulation and transport, as well as lactate removal ability.

Lactate recovery kinetics in response to high-intensity exercises

PURPOSE

The aim of this study was to investigate lactate recovery kinetics after high-intensity exercises.

METHODS

Six competitive middle-distance runners performed 500-, 1000-, and 1500-m trials at 90 % of their current maximal speed over 1500 m. Each event was followed by a passive recovery to obtain blood lactate recovery curves (BLRC). BLRC were fitted by the bi-exponential time function: La(t) = La(0) + A 1(1-e (-γ1t) ) + A 2(1-e (-γ2t) ), where La(0) is the blood lactate concentration at exercise completion, and γ 1 and γ 2 enlighten the lactate exchange ability between the previously active muscles and the blood and the overall lactate removal ability, respectively. Applications of the model provided parameters related to lactate release, removal and accumulation rates at exercise completion, and net amount of lactate released during recovery.

RESULTS

The increase of running distance was accompanied by (1) a continuous decrease in γ 1 (p < 0.05), (2) a primary decrease (p < 0.05) and then a stabilization of γ 2, and (3) a constant increase in blood concentrations (p < 0.05) and whole body accumulation of lactate (p < 0.05). Estimated net lactate release, removal and accumulation rates at exercise completion, as well as the net amount of lactate released during recovery were not significantly altered by distance.

CONCLUSION

Alterations of lactate exchange and removal abilities have presumably been compensated by an increase in muscle-to-blood lactate gradient and blood lactate concentrations, respectively, so that estimated lactate release, removal and accumulation rates remained almost stable as distance increased.

Muscle MCT4 Content Is Correlated with the Lactate Removal Ability during Recovery Following All-Out Supramaximal Exercise in Highly-Trained Rowers

The purpose of this study was to test if the lactate exchange (γ₁) and removal (γ₂) abilities during recovery following short all-out supramaximal exercise correlate with the muscle content of MCT1 and MCT4, the two isoforms of the monocarboxylate transporters family involved in lactate and H⁺ co-transport in skeletal muscle. Eighteen lightweight rowers completed a 3-min all-out exercise on rowing ergometer. Blood lactate samples were collected during the subsequent passive recovery to assess an individual blood lactate curve (IBLC). IBLC were fitted to the bi-exponential time function: La(t) = [La](0) + A₁(1 − e-γ1t) + A₂(1 − e-γ2t) where [La](0) is the blood lactate concentration at exercise completion and the velocity constants γ₁ and γ₂ denote the lactate exchange and removal abilities, respectively. An application of the bi-compartmental model of lactate distribution space allowed estimation of the lactate removal rate at exercise completion [LRR(0)]. Biopsy of the right vastus lateralis was taken at rest to measure muscle MCT1 and MCT4 content. Fiber type distribution, activity of key enzymes and capillary density (CD) were also assessed. γ₁ was correlated with [La](0) (r = −0.54, P < 0.05) but not with MCT1, MCT4 or CD. γ₂ and LRR(0) were correlated with MCT4 (r = 0.63, P < 0.01 and r = 0.73, P < 0.001, respectively) but not with MCT1 or cytochrome c oxidase activity. These findings suggest that the lactate exchange ability is highly dependent on the milieu so that the importance of the muscle MCT1 and MCT4 content in γ₁ was hidden in the present study. Our results also suggest that during recovery following all-out supramaximal exercise in well-trained rowers, MCT4 might play a significant role in the distribution and delivery of lactate for its subsequent removal.

Peak torque and rate of torque development influence on repeated maximal exercise performance: contractile and neural contributions

Rapid force production is critical to improve performance and prevent injuries. However, changes in rate of force/torque development caused by the repetition of maximal contractions have received little attention. The aim of this study was to determine the relative influence of rate of torque development (RTD) and peak torque (T_peak) on the overall performance (i.e. mean torque, T_mean) decrease during repeated maximal contractions and to investigate the contribution of contractile and neural mechanisms to the alteration of the various mechanical variables. Eleven well-trained men performed 20 sets of 6-s isokinetic maximal knee extensions at 240°·s^-1, beginning every 30 seconds. RTD, T_peak and T_mean as well as the Rate of EMG Rise (RER), peak EMG (EMG_peak) and mean EMG (EMG_mean) of the vastus lateralis were monitored for each contraction. A wavelet transform was also performed on raw EMG signal for instant mean frequency (if_mean) calculation. A neuromuscular testing procedure was carried out before and immediately after the fatiguing protocol including evoked RTD (eRTD) and maximal evoked torque (eT_peak) induced by high frequency doublet (100 Hz). T_mean decrease was correlated to RTD and T_peak decrease (R²=0.62; p<0.001; respectively β=0.62 and β=0.19). RER, eRTD and initial if_mean (0-225 ms) decreased after 20 sets (respectively -21.1±14.1, -25±13%, and ~20%). RTD decrease was correlated to RER decrease (R²=0.36; p<0.05). The eT_peak decreased significantly after 20 sets (24±5%; p<0.05) contrary to EMG_peak (-3.2±19.5 %; p=0.71). Our results show that reductions of RTD explained part of the alterations of the overall performance during repeated moderate velocity maximal exercise. The reductions of RTD were associated to an impairment of the ability of the central nervous system to maximally activate the muscle in the first milliseconds of the contraction.

Relationships between V̇O2 and blood lactate responses after all-out running exercise

To verify the effects of training status and blood lactate concentration (BLC) responses on the early excess postexercise oxygen consumption (EPOC), 8 sprinters, 7 endurance runners, and 7 untrained subjects performed an incremental test to determine maximal oxygen uptake and a 1-min all-out test to determine BLC and oxygen uptake recovery curves. BLC kinetics was evaluated to assess the quantity of lactate accumulated during exercise (QlaA), lactate removal ability (k2), and quantity of lactate removed from 0 to 10 min postexercise (QlaR). Oxygen uptake off-kinetics was evaluated to assess the decay time constants (τ1 and τ2); moreover, EPOC was measured during the first 10 min after exercise. While sprinters had 98%-100% and 94%-100% likelihood of having the highest EPOC and decay time constants, endurance runners had 98%-100% and 95%-100% likelihood of having the lowest EPOC and decay time constants. EPOC was correlated with QlaA (r = 0.74) and QlaR (r = 0.61). τ1 and τ2 were correlated with maximal oxygen uptake (r > -0.57), k2 (r > -0.48), and QlaR relative to QlaA (r > -0.60). Our findings indicate that oxygen uptake recovery is associated with fast lactate removal and aerobic training. Furthermore, the metabolites derived from anaerobic energy production seem to induce a greater EPOC after all-out exercise.

Differences in lactate exchange and removal abilities between high-level African and Caucasian 400-m track runners

The present study aimed to investigate (1) whether high-level 400-m track runners of different ethnic origin displayed divergent post-run blood lactate concentrations (p400m[La]) and (2) if this discrepancy was based on differences in lactate exchange and removal abilities. Twenty male African (n = 12) and Caucasian (n = 8) runners, paired in terms of personal record, performed (1) an all-out 400-m run to measure p400m[La] at 3, 5 and 7 min into recovery and (2) a 1-min 25.2 km h(-1) running (not maximal but standardized) exercise followed by 90-min passive recovery to determine individual blood lactate recovery curves (IBLRC). IBLRCs were fitted to a bi-exponential time function: [Formula: see text] where γ 1 and γ 2 denote lactate exchange ability between the previously worked muscles and blood, and overall ability for lactate removal, respectively. The quantity of lactate accumulated at the end of the 1-min exercise (Q LaA) was also estimated. Our study showed that after the all-out 400-m run, p400m[La] was lower in African than in Caucasian runners at 3 and 5 min but not at 7 min into recovery. After the standardized exercise, γ 1 and γ 2 were lower (p < 0.01) and Q LaA was higher (p < 0.05) in African than in Caucasian runners. These data suggest that for similar performance levels, ethnicity involves differences in lactate accumulation, exchange and removal.