Tempo para exaustão no acúmulo de lactato sanguíneo em corredores com diferentes habilidades atléticas / Time to exhaustion at the onset of blood lactate accumulation in runners with different athletic ability

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.

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.

Effects of experimental acid-base disturbance on blood lactate kinetics during incremental exercise / 体力科学

The present study was conducted to investigate the effect of acid-base disturbance on blood lactate concentration (bLA) and OBLA (Onset of Blood Lactate Accumulation) during an incremental bicycle test.<BR>Nine healthy male subjects underwent the incremental test at 60 min after the oral administration of NH<SUB>4</SUB>Cl (acidotic-treatment ; Acid), NaHCO<SUB>3</SUB> (alkalotic-treatment ; Alk) and NaCI (control ; Cont) at 1.87 mM⋅kg<SUP>-1</SUP>body weight. Exercise was started at a load of 80W, which was subsequently increased by 10W every minute until exhaustion. During exercise, O<SUP>2</SUP>intake (VO<SUP>2</SUP>), ventilatory volume (VE) and heart rate (HR) were monitored continuously. Venous blood samples were obtained before administration and every 2 min during exercise.<BR>No change could be detected in resting VO<SUB>2</SUB>, VE and HR following oral administration of NH<SUB>4</SUB>Cl, NaHCO<SUB>3</SUB>and/or NaCl. At 60 min after oral administration venous blood pH (<SUB>v</SUB>pH) and bicarbonate ion concentration (<SUB>v</SUB> [HCO<SUB>3</SUB><SUP>-</SUP>] ) were significantly lower in Acid (7.265±0.033; p <0.001, 23.6±1.8 mM⋅1<SUP>-1</SUP>; p<0.01) ; and significantly higher in Alk (7.370±0.045 ; p<0.01, 29.7±1.6 mM⋅1<SUP>-1</SUP>; p<0.01) compared to Cont (7.318±0.041, 26.6±2.1 mM⋅1<SUP>-1</SUP>) . Changes in VO<SUB>2</SUB>, VE and HR during exercise were essentially the same in all cases. No differences were observed in exercise time. During exercise, vpH and<SUB>v</SUB> [HCO<SUB>3</SUB><SUP>-</SUP>] gradually decreased, but remained significantly lower in Acid and higher in Alk compared to Cont. Blood lactate concentration (bLA) increased during exercise. Peak values were observed at exhaustion, but it was lower in Acid (8.03±1.18mM⋅1<SUP>-1</SUP>) and higher in Alk (10.73±1.48) compared to Cont (9.49±1.79) in all subjects. The Onset of Blood Lactate Accumulation (OBLA) was determined for each subject. OBLA was significantly higher in Acid (71.9±9.1%VO<SUB>2</SUB>max) than Cont (62.5±9.9%VO<SUB>2</SUB>max) and Alk (62.2±8.0%VO<SUB>2</SUB>max) .<BR>Changes in acid-base balance were found to cause differences in bLA responses to the same exercise load and possibly change OBLA. Care must be taken when using OBLA or LT as an index of aerobic capacity in some patients with acid-bace disorders; hemodialitic, obese or diabetic patient.