Time to exhaustion at the onset of blood lactate accumulation in runners with different athletic ability

Abstracts

OBJECTIVE: To characterize the physiological responses of runners with different velocity abilities at the onset of blood lactate accumulation (OBLA) and to determine if 4 mmol•L-1 represent the same relative exercise intensity for each runner. METHODS: Eleven trained and twelve well-trained runners completed two running tests on treadmill: first, a maximal incremental lactate test to calculate OBLA (Test 1), and then another one at the corresponding OBLA until exhaustion (Test 2). Gas exchange and heart rate (HR) were continuously measured and plotted as a percentage of time to exhaustion in Test 2 (TET2). The individual lactate threshold velocity (VLT) and lactate concentration ([La-1]LT) were calculated according to the D-max method. RESULTS: VOBLA and VLT were higher in well-trained runners (P<0.001). [La-1]LT was <4 mmol•L-1 in the well-trained runners (P<0.001), but not in the trained ones. Well-trained runners were faster at VOBLA than at VLT (P<0.001). Well-trained runners ran a shorter TET2 than the trained runners (P<0.05). Moreover, well-trained runners presented a higher respiratory rate at 50, 80 and 90% of TET2 and VO2 at 20-100% of TET2 (P<0.05). TET2 was inversely correlated (P<0.01) with VOBLA and positively with personal best 10-km performance (P<0.01). VOBLA was positively correlated with the %VO2max in Test 2 (P<0.01). The standard value (4 mmol•L-1) for the concentration of blood lactate seems to represent a different exercise intensity for runners of different athletic ability. CONCLUSION: VOBLA may not be accurate for the design of running training sessions or for evaluation of aerobic capacity.

athletes; OBLA; fatigue; exercise intensity; performance

OBJETIVO: Caracterizar as respostas fisiológicas de corredores com diferentes habilidades de velocidade durante o lactato sanguíneo (OBLA) e determinar se 4 mmol•L-1 representam a mesma intensidade de exercício relativa para cada corredor. MÉTODOS: Onze corredores treinados e doze bem treinados completaram dois testes de corrida em esteira: primeiramente, um teste máximo de lactato com incremento para calcular o OBLA (Teste 1) e a seguir um outro no OBLA correspondente até exaustão (Teste 2). As trocas de gases e frequência cardíaca (FC) foram continuamente medidas e plotadas em porcentagem de tempo referente à exaustão no Teste 2 (TET 2). A velocidade de limite de lactato individual (VLL) e concentração de lactato ([La-1]LL) foram calculadas de acordo com o método de D-max. RESULTADOS: OBLA e VLL foram maiores em corredores bem treinados (P<0.001).[La-1]LL foi<4 mmol•L-1 nos corredores bem treinados (P<0.001), mas não nos treinados. Os corredores bem treinados foram mais rápidos em OBLA do que em VLL (P<0.001). Os corredores bem treinados correram um TET2 mais curto do que os corredores treinados (P<0.05). Além disso, os corredores bem treinados apresentaram taxa respiratória mais alta em 50, 80 e 90% de TET2 e VO2 em 20-100% de TET2 (P<0.05). TET2 se relacionou inversamente (P<0.01) com OBLA e positivamente com melhor rendimento individual em 10km (P<0.01).OBLA se relacionou positivamente com a %VO2max no Teste 2 (P<0.01). O valor padrão (4 mmol•L-1) para a concentração de lactato sanguíneo parece representar uma intensidade de exercício diferente para corredores com habilidades atléticas diferentes. CONCLUSÃO: OBLA pode não ser preciso para desenvolver sessões de treinamento de corrida ou para a avaliação da capacidade aeróbica.

atletas; OBLA; fadiga; intensidade de exercício; rendimento

ORIGINAL ARTICLE

EXERCISE AND SPORTS SCIENCES

Time to exhaustion at the onset of blood lactate accumulation in runners with different athletic ability

Jordan Santos-Concejero^I,II; Cristina Granados^II; Jon Irazusta^II; Iraia Bidaurrazaga-Letona^II; Jon Zabala-Lili^II; Susana Gil^II

^IUniversity of Cape Town, UCT/MRC ESSM, South Africa

^IIUniversity of the Basque Country UPV/EHU, Spain.

Correspondence

ABSTRACT

OBJECTIVE: To characterize the physiological responses of runners of different athletic ability at the velocity at onset of blood lactate (V_OBLA) and to determine if 4 mmol·L^-1 represents the same relative exercise intensity for every runner.

METHODS: Eleven trained and twelve well-trained runners completed two running tests on a treadmill: first, a maximal incremental lactate test to calculate the V_OBLA (Test 1), and then another one at the corresponding V_OBLA until exhaustion (Test 2). Gas exchange and heart rate (HR) were continuously measured and plotted as a percentage of time to exhaustion in Test 2 (TE_T2). The individual lactate threshold velocity (V_LT) and lactate concentration ([La^-1]_LT) were calculated according to the D-max method.

RESULTS: V_OBLA and V_LT were higher in well-trained runners (P<0.001). [La^-1]_LT was <4 mmol·L^-1 in the well-trained runners (P<0.001), but not in trained runners. Well-trained runners were faster at V_OBLA than at V_LT (P<0.001). Well-trained runners ran a shorter TE_T2 than the trained runners (P<0.05). Moreover, well-trained runners presented a higher respiratory rate at 50, 80 and 90% of TE_T2 and VO₂ at 20-100% of TE_T2 (P<0.05). TE_T2 was inversely correlated (P<0.01) with V_OBLA and positively with personal best 10-kmperformance (P<0.01). V_OBLA was positively correlated with the %VO_2max in Test 2 (P<0.01). The standard value (4 mmol·L^-1) for the concentration of blood lactate appears to represent a different exercise intensity for runners of different athletic ability.

CONCLUSION: V_OBLA may not be accurated for programming running training sessions or for performing an evaluation of aerobic capacity.

Keywords: Athletes, OBLA, fatigue, exercise intensity, performance.

INTRODUCTION

The determination of blood lactate concentration ([La^-]) during exercise has been traditionally used as an important factor for the estimation of workload intensity in training exercise¹. The maximal exercise intensity which elicits a constant [La^-] over time, more specifically a rise lower than 1 mmol·L^-1 in the last 20 minutes of a constant work rate test of 30 minutes, has been defined as the maximal lactate steady-state (MLSS)². MLSS represents the highest intensity of exercise at which a balance exists between the rate of lactate production and lactate clearance^3,4.

The MLSS has been proposed as a useful tool for the evaluation of aerobic capacity, training intensity prescription and the prediction of exercise performance¹. However, the technique required for the accurate determination of the MLSS is complex and time-consuming, as 3 to 5 constant work-rate tests have to be performed on different days⁵. As a result, several authors have recommended the use of single day tests for the indirect determination of MLSS^3,6.

During running exercise, a lactate concentration of 4 mmol·L^-1 was reported to be associated with the MLSS⁷ and consequently, different researchers have proposed the use of the 4 mmol·L^-1 value as a reference value for the MLSS^8,9. This value of 4 mmol·L^-1, first proposed by Mader et al in 1976¹⁰, was later termed as the onset of blood lactate accumulation (OBLA)¹¹. Some studies have reported that the exercise intensity which induces an optimum qualitative stimulus should elicit a steady-state [La^-] of approximately 4 mmol·L^-112, and therefore OBLA exercise intensity has been adopted by coaches all over the world as a useful index of training status and fitness3).

However, several researchers are against the utilization of OBLA as an indirect marker for the MLSS^13,14, because [La^-] corresponding to MLSS may be reduced as a result of aerobic training¹⁵. In addition, it is acknowledged that the 4 mmol·L^-1 value does not take into account inter-individual variability in the MLSS¹⁶. Thus, use of the OBLA as universal index for accurately estimating aerobic capacity, prescribing training intensity or a predicting performance, may have important limitations.

Currently, it is unclear if relative exercise intensity corresponding to OBLA is similar in athletes of different levels or training status. Thus, the main purpose of this study was to investigate the physiological responses at OBLA exercise intensity and consequently, to ascertain if the 4 mmol·L^-1 value for lactate concentration represents the same relative exercise intensity in runners of different athletic ability. These results will assist us in determining if the OBLA index could be used to design and program running training sessions independently of the runner’s athletic level.

METHODS

Subjects

Twenty-three long distance Caucasian male runners participated in this study: eleven trained (39.9 ± 5.8 years) and twelve well-trained (28.4 ± 6.8 years). Before participation, subjects were medically examined to ensure that they had no signs of cardiovascular, musculoskeletal and metabolic diseases. The Ethics Committee for research on Human subjects at the University of Basque Country (CEISH/GIEB) approved this study. All athletes were informed about all the tests and the possible risks involved and signed a written informed consent prior to testing. For the purpose of this study, athletes were selected according to their recent 10-km personal best time. Inclusion criteria for the trained runners group included a minimum of three days per week of running sessions, current participation in competitions and a 10-km race time between 35-45 minutes. Inclusion criteria in the well-trained athletes group included current participation in international or national level competitions and a 10-km race time below 33.5 minutes.

Procedures

Anthropometry - Height (cm) and body mass (kg) were measured with the use of a precision stadiometer and balance (Seca, Bonn, Germany), and body mass index (BMI) was calculated. Eight skinfold sites (biceps, triceps, subscapular, supraspinale, abdominal, suprailiac, mid-thigh, and medial calf) were determined in duplicate with a skinfold caliper (Holtain, Crymych, UK) by the same researcher and the sum of skinfolds was determined. The body fat percentage was calculated for each athlete, as described elsewhere¹⁷.

All subjects performed two maximal running tests: a peak treadmill lactate test (Test 1) and a constant treadmill V_OBLA test (Test 2) with a break of one week between them. 24 hours prior to testing, athletes were encouraged to be well rested and to abstain from a hard training session and competition. All athletes were familiarized with running on the treadmill.

Peak treadmill lactate test (Test 1) - All subjects completed a maximal effort incremental running test on a treadmill with a 1% gradient (ERGelek EG2, Vitoria-Gasteiz, Spain), starting at 9 km·h^-1 without previous warm up. The velocity was increased by 1.5 km·h^-1 every 4 minutes until volitional exhaustion, with 1 minute of recovery between each stage. Verbal encouragement was provided to ensure that a maximal effort was reached. During the test, respiratory rate (RR), ventilatory output (VE), oxygen uptake (VO₂) and respiratory exchange ratio (RER) were continuously measured using the same calibrated gas analyzer system (Ergocard, Medisoft, Sorinnes, Belgium), which was calibrated before each session according to the instructions of the manufacturers.

Athletes were considered to have attained their maximal ability, and therefore, reached their VO_2max, when three of the following criteria were fulfilled: 1) a plateau in VO₂;2) RER > 1.15; 3) HR within 5 beats·min^-1 of theoretical maximal HR (220-age); 4) lactate concentration > 8 mmol·L^-1; 5) RPE= 10.

Peak treadmill velocity in km·h^-1 (PTV) was calculated as follows taking every second into account¹⁸:

PTV= Completed full intensity in km·h^-1 + [(seconds at final velocity · 240 seg^-1)·1.5 km·h^-1]

Immediately after each exercise stage, a 25 µl sample of capillary blood was drawn from the earlobe and analyzed in order to determine the blood lactate concentration (Lactate Pro, Arkray, KDK Corporation, Kyoto, Japan). This system has been validated as an effective analyzer for lactate measurements¹⁹. The individual lactate threshold (LT) was calculated by the D-max method²⁰. The reliability of this method has previously been reported²¹. A third order polynomial regression equation was established on the plasma lactate concentrations versus workloads. The D-max was identified as the point on the polynomial regression curve that yielded the maximal distance to the straight line formed by the two end data points²¹.

Constant treadmill V_OBLA test (Test 2) - This test involved running on a treadmill at the individual’s velocity corresponding to a lactate concentration of 4 mmol·L^-1 (V_OBLA) until volitional exhaustion with a 1% gradient. V_OBLA was calculated by interpolation, expressing the collected blood lactate data of each subject in Test 1 as a function of running velocity. A quadratic equation was used to perform the regression of the [La^-] and velocity. During the test, HR and gas exchange were continuously measured and plotted as 10-100% of time to exhaustion (TE_T2) as suggested by Pires et al.²². Lactate concentration was sampled immediately ([La^-]_finalT2) and 3 minutes ([La^-]_3minT2) after the test.

Statistics

All values are expressed as mean ± standard deviation (SD) and the statistical analyses of data were performed using the Statistical Package for the Social Sciences 15.0 software package (StatSoft, USA). Data were screened for normality of distribution and homogeneity of variances using a Shapiro-Wilk normality test and a Levene test respectively. An independent Student t-test for the comparison of the means of both groups was utilized. In cases in which variables were not normal, a Mann-Whitney U-test was utilized. Relationships between variables were evaluated by using linear regressions and Pearson and Spearman correlation analyses. Significance for all analyses was set at P<0.05.

RESULTS

Anthropometric characteristics and maximal treadmill test results in trained and well-trained runners are listed in Table 1. Well-trained runners were younger and faster according to their best 10-km time than trained runners (P<0.001). There were no differences in height between the two groups. However, well-trained runners were lighter, and presented lower values of BMI, sum of skinfolds and %BF than trained runners (P<0.01-0.05). Well-trained runners achieved a higher PTV during Test 1 (table 1, P<0.001). Nevertheless, there were no significant differences in any maximum physiological parameter, such as VO₂ (absolute and relative to body mass), HR, RER or [La^-] between both groups.

V_OBLA and the velocity at the lactate threshold (V_LT) were faster in the well-trained runners when compared to the trained runners (P<0.001) (table 2). Further, the blood lactate concentration at the lactate threshold ([La^-]_LT) was lower in the well-trained runners (P<0.001). V_OBLA was faster than V_LT in the well-trained runners (P<0.001), but not in the trained runners. Similarly, [La^-]_LT was <4mmol·L^-1 in the well-trained runners (P<0.001), but not in the trained runners.

TE_T2 was 46.8% shorter (P<0.05) in the well-trained runners than in the trained runners (table 3). However, there were no significant differences in %VO_2max, %PTV, [La^-]_finalT2, [La^-]_3minT2 between both groups (although the values were higher in well-trained runners), neither in distance covered in Test 2.

During Test 2, well-trained runners showed a statistically higher VO₂ (ml·kg^-1·min^-1) at 20 to 100% of the TE_T2, and a higher respiratory rate (RR) at 50, 80 and 90% of the TE_T2 than trained runners (P<0.05, figure 1). There were no statistically significant differences in the physiological responses of volume ventilation (VE), carbon dioxide production (VCO₂), percentage of maximum heart rate (%HR_max) or RER during the V_OBLA. The overall trend was a physiological steady state in the last half of the Test 2.

The individual values of the TE_T2 correlated negatively with the individual V_OBLA values (r=0.719, P<0.001, n=23) (figure 2A), as well as positively with the individual best 10-km race time values (r=0.536, P<0.01, n=23) (figure 2B). Further, V_OBLA correlated positively with %VO_2max in Test 2 (r=0.604, P<0.001, n=23) (figure 3).

DISCUSSION

This is the first study to compare the physiological responses (measured as a function of % time to exhaustion) at V_OBLA, in order to ascertain if a 4 mmol·L^-1 lactate concentrationrepresents the same relative exercise intensity for runners of different athletic ability.

Time to exhaustion is considered a good indicator of the relative exercise intensity²². An important finding of this study is that the time to exhaustion at the velocity corresponding to 4 mmol·L^-1 lactate concentration (TE_T2) was shorter in well-trained runners compared to trained runners. This result, together with the negative correlation between TE_T2 and the V_OBLA, and the positive correlation between TE_T2 and the 10-km race time, suggests that the athletic level of the runners is a determinant factor for the exercise duration at the velocity corresponding to a lactate concentration of 4 mmol·L^-1. This idea is corroborated by the finding that VO₂ (ml·kg^-1·min^-1) and respiratory rate (RR) values during the V_OBLA test were higher for well-trained runners at certain points. Respiratory responses are related to the exercise intensity²³, so these results suggest that, although at a consistent V_OBLA, the intensity of workload was greater in the well-trained runners.

The key to understanding why the higher level athletes experienced a shorter TE_T2 during Test 2 may be explained by differences in the V_LT and [La^-]_LT between the trained and the well-trained runners. V_OBLA was close to the V_LT in trained runners, whereas V_LT was faster in the well-trained runners. Similarly, the [La^-]_LT was not different to OBLA in trained runners and was lower than OBLA in the well-trained runners. These results indicate that V_OBLA does not represent the same relative exercise intensity in runners of different athletic ability and that the time to exhaustion at a running velocity corresponding to a lactate concentration of 4 mmol·L^-1 appears to be influenced by the athletic conditioning of the runners.

This statement is further supported by the positive correlation between %VO_2max in Test 2 and V_OBLA. These results suggest that athletes of a higher athletic level (athletes with a higher V_OBLA) ran at a higher %VO_2max during Test 2. This finding may imply that the athletic level of the runners is a factor that influences the relative intensity corresponding to 4 mmol·L^-1 lactate concentration. Although, the athletes were exercising at a speed set to maintain 4 mmol·L^-1 blood lactate concentration, %VO_2max differed between athletes. Thus, suggesting the athletes exercised at different relative intensities during Test 2.

Currently, it is known that during prolonged exercise at intensities eliciting the MLSS, glycolytic muscle fibers are producing and releasing lactate²⁴ into the blood for oxidation by distant tissues as well as conversion to glucose and glycogen, while some lactate may diffuse to adjacent oxidative muscle fibers to be oxidized²⁵. Lactate exchange is a dynamic process with simultaneous muscle uptake and release at rest and during exercise²⁶. Consequently, lactate values measured in blood are not necessarily indicative of the levels of lactate produced in active muscles. In fact, well-trained runners are likely to have an enhanced lactate clearance capacity²⁷. Thus, the 4 mmol·L^-1 blood lactate concentration may be associated with higher relative exercise intensity in this group of athletes.

During exercise performed at V_OBLA volitional exhaustion occurred whilst there was evidence for physiological reserve capacity. Thus, exercise termination at V_OBLA may be induced by an integrative homoeostatic control of the central and peripheral physiological system. This is to specifically ensure the maintenance of homeostasis and not a result of the failure of the body to perform work, as proposed by the Central Governor Model²⁸.

In summary, the present study suggests that V_OBLA does not represent the same relative exercise intensity in runners of different competitive level, possibly due to differences in lactate kinetics. Our results demonstrate that the time to exhaustion_, which is a good indicator of the relative exercise intensity, is closely related to the level of the athletes when running at V_OBLA. Thus, we conclude that this index should not be recommended for programming training sessions, performing an aerobic capacity evaluation or comparing runners of different athletic ability and conditioning.

ACKNOWLEDGEMENTS

This study has been partially supported by the Department of Physical Education and Sport, of the Faculty of Physical Activity and Sport, University of the Basque Country (UPV/EHU). J.S.C. is supported by a predoctoral fellowship from the Basque Government (ref. BFI08.51).

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Publication Dates

• Publication in this collection
  18 Sept 2013
• Date of issue
  Aug 2013