Effects of prolonged running performed at the intensity corresponding to the onset of blood lactate accumulation, on maximum isokinetic strength in active non-athletic individuals

OBJECTIVE: The objective of this study was to analyze the effects of prolonged continuous running performed at the intensity corresponding to the onset of blood lactate accumulation (OBLA), on the peak torque of the knee extensors, analyzed in relation to different types of contraction and movement velocities in active individuals. METHOD: Eight men (23.4 ± 2.1 years; 75.8 ± 8.7 kg; 171.1 ± 4.5 cm) participated in this study. First, the subjects performed an incremental test until volitional exhaustion to determine the velocity corresponding to OBLA. Then, the subjects returned to the laboratory on two occasions, separated by at least seven days, to perform five maximal isokinetic contractions of the knee extensors at two angular velocities (60 and 180º.s-1) under eccentric and concentric conditions. Eccentric peak torque (EPT) and Concentric peak torque (CPT) were measured at each velocity. One session was performed after a standardized warm-up period (5 min at 50 percent VO2max). The other session was performed after continuous running at OBLA until volitional exhaustion. These sessions were conducted in random order. RESULTS: There was a significant reduction in CPT only at 60º.s-1 (259.0 ± 46.4 and 244.0 ± 41.4 N.m). However, the reduction in EPT was significant at 60º.s-1 (337.3 ± 43.2 and 321.7 ± 60.0 N.m) and 180º.s-1 (346.1 ± 38.0 and 319.7 ± 43.6 N.m). The relative strength losses after the running exercise were significant different between contraction types only at 180º.s-1. CONCLUSION: We can conclude that, in active individuals, the reduction in peak torque after prolonged continuous running at OBLA may be dependent on the type of contraction and angular velocity.

OBJETIVO: O objetivo deste estudo foi analisar os efeitos da corrida contínua prolongada realizada na intensidade correspondente ao início do acúmulo do lactato no sangue (OBLA) sobre o torque máximo dos extensores do joelho analisado em diferentes tipos de contração e velocidade de movimento em indivíduos ativos. MÉTODO: Oito indivíduos do gênero masculino (23,4 ± 2,1 anos; 75,8 ± 8,7 kg; 171,1 ± 4,5 cm) participaram deste estudo. Primeiramente, os sujeitos realizaram um teste incremental até a exaustão voluntária para determinar a velocidade correspondente ao OBLA. Posteriormente, os sujeitos retornaram ao laboratório em duas ocasiões, separadas por pelo menos sete dias, para realizar 5 contrações isocinéticas máximas para os extensores do joelho em duas velocidades angulares (60 e 180º.s-1) sob as condições excêntrica (PTE) e concêntrica (PTC). Uma sessão foi realizada após um período de aquecimento padronizado (5 min a 50 por centoVO2max). A outra sessão foi realizada após uma corrida contínua no OBLA até a exaustão voluntária. Essas sessões foram executadas em ordem randômica. RESULTADOS: Houve redução significante do PTC somente a 60º.s-1 (259,0 ± 46,4 e 244,0 ± 41,4 N.m). Entretanto, a redução do PTE foi significante a 60º.s-1 (337,3 ± 43,2 e 321,7 ± 60,0 N.m) e 180º.s-1 (346,1 ± 38,0 e 319,7 ± 43,6 N.m). As reduções relativas da força após o exercício de corrida foram significantemente diferentes entre os tipos de contração somente a 180º.s-1. CONCLUSÃO: Podemos concluir que, em indivíduos ativos, a redução no torque máximo após uma corrida contínua prolongada no OBLA pode ser dependente do tipo de contração e da velocidade angular.

Effect of the aerobic capacity on the validity of the anaerobic threshold for determination of the maximal lactate steady state in cycling

The maximal lactate steady state (MLSS) is the highest blood lactate concentration that can be identified as maintaining a steady state during a prolonged submaximal constant workload. The objective of the present study was to analyze the influence of the aerobic capacity on the validity of anaerobic threshold (AT) to estimate the exercise intensity at MLSS (MLSS intensity) during cycling. Ten untrained males (UC) and 9 male endurance cyclists (EC) matched for age, weight and height performed one incremental maximal load test to determine AT and two to four 30-min constant submaximal load tests on a mechanically braked cycle ergometer to determine MLSS and MLSS intensity. AT was determined as the intensity corresponding to 3.5 mM blood lactate. MLSS intensity was defined as the highest workload at which blood lactate concentration did not increase by more than 1 mM between minutes 10 and 30 of the constant workload. MLSS intensity (EC = 282.1 ± 23.8 W; UC = 180.2 ± 24.5 W) and AT (EC = 274.8 ± 24.9 W; UC = 187.2 ± 28.0 W) were significantly higher in trained group. However, there was no significant difference in MLSS between EC (5.0 ± 1.2 mM) and UC (4.9 ± 1.7 mM). The MLSS intensity and AT were not different and significantly correlated in both groups (EC: r = 0.77; UC: r = 0.81). We conclude that MLSS and the validity of AT to estimate MLSS intensity during cycling, analyzed in a cross-sectional design (trained x sedentary), do not depend on the aerobic capacity.

Effects of caffeine on time to exhaustion in exercise performed below and above the anaerobic threshold

Controversy still exists concerning the potential ergogenic benefit of caffeine (CAF) for exercise performance. The purpose of this study was to compare the effects of CAF ingestion on endurance performance during exercise on a bicycle ergometer at two different intensities, i.e., approximately 10 percent below and 10 percent above the anaerobic threshold (AT). Eight untrained males, non-regular consumers of CAF, participated in this study. AT, defined as the intensity (watts) corresponding to a lactate concentration of 4mM, was determined during an incremental exercise test from rest to exhaustion on an electrically braked cycle ergometer. On the basis of these measurements, the subjects were asked to cycle until exhaustion at two different intensities, i.e., approximately 10 percent below and 10 percent above AT. Each intensity was performed twice in a double-blind randomized order by ingesting either CAF (5 mg/kg) or a placebo (PLA) 60 min prior to the test. Venous blood was analyzed for free fatty acid, glucose, and lactate, before, during, and immediately after exercise. Rating of perceived exertion and time to exhaustion were also measured during each trial. There were no differences in free fatty acids or lactate levels between CAF and PLA during and immediately after exercise for either intensity. Immediately after exercise glucose increased in the CAF trial at both intensities. Rating of perceived exertion was singificantly lower (CAF = 14.1 + 2.5 vs PLA = 16.6 + 2.4) and time to exhaustion was significantly higher (CAF = 46.54 + 8.05 min vs PLA = 32.42 + 14.81 min) during exercise below AT with CAF. However, there was no effect of CAF treatment on rating of perceived exertion (CAF = 18.0 + 2.7 vs PLA = 17.6 + 2.3) and time to exhaustion (CAF = 18.45 + 7.28 min vs PLA = 19.17 + 4.37 min) during exercise above AT. We conclude that in untrained subjects caffeine can improve endurance performance during prolonged exercise performed below AT and that decrease of perceived exertion can be involved in this process.

Effect of caffeine on the metabolism of rats exercising by swimming

Several studies have demonstrated that caffeine improves endurance exercise performance but the mechanisms are not fully understood. Possibilities include increased free fatty acid (FFA) oxidation with consequent sparing of muscle glycogen as well as enhancement of neuromuscular function during exercise. The present study was designed to investigate the effects of caffeine on liver and muscle glycogen of 3-month old, male Wistar rats (250-300 g) exercising by swimming. Caffeine (5 mg/kg) dissolved in saline (CAF) or 0.9 percent sodium chloride (SAL) was administered by oral intubation (1 µl/g) to fed rats 60 min before exercise. The rats (N = 8-10 per group) swam bearing a load corresponding to 5 percent body weight for 30 or 60 min. FFA levels were significantly elevated to 0.475 + or - 0.10 mEq/l in CAF compared to 0.369 + or - 0.06 mEq/l in SAL rats at the beginning of exercise. During exercse, a significant difference in FFA levels between CAF and SAL rats was observed at 30 min (0.325 + or - 0.06 vs 0.274 + or - 0.05 mEq/l) but not at 60 min (0.424 + or - 0.13 vs 0.385 + or - 0.10 mEq/l). Blood glucose showed an increase due to caffeine only at the end of exercise (CAF = 142.1 + or - 27.4 and SAL = 120.2 + or - 12.9 mg/100 ml). No significant difference in liver or muscle glycogen was observed in CAF as compared to SAL rats, at rest or during exercise. Caffeine increased blood lactate only at the beginning of exercise (CAF = 2.13 + or - 0.2 and SAL = 1.78 + or - 0.2 mmol/l). These data indicate that caffeine (5 mg/kg) has no glycogen-sparing effect on rats exercising by swimming even though the FFA levels of CAF rats were significantly higher at the beginning of exercise