Análise sigmoidal da curva da lactatemia em teste incremental: novos horizontes

Abstract

CHAPTER II: The aim of the present study was to compare five methods of lactate thre-shold (LT) identification in resistance exercise (RE). Eight healthy males, non se-dentary (25.6 ± 6.61 years old, 78.6 ± 3.48 kg of body weight) performed an in-cremental test in leg press resistance exercise until the voluntary exhaustion. The initial workload was 10% of one maximal repetition (1RM), with 5% of increment each stage. The stages were consisted of 1 min with 1 min of rest between them. Blood samples of 25 ml, were collected for blood lactate concentration ([Lac]) anal-ysis. Five methods for LT intensity identification in RE were compared with each other: Lactate quotient (LQ); fixed point of 4 mM (OBLA); visual inspection (VI); 1mM of [Lac] above the baseline (OPLA); and the novel method, proposed by our study, consisted in 20% of the maximum [Lac] during the incremental test (X20). It was possible to identify the LT using all the five methods. However, the ANOVA showed significant difference between the OBLA and all the methods, and this suggest that this method overestimates the exercise intensity at the LT. Based in our results, we concluded that the X20 was not statistically different from the QL, IV and OPLA. Morever the incremental protocol with 1 minute of exercise bout, 1 minute of rest between the bouts and increment of 5% of the 1RM, was valid for LT identification using all the methods. CHAPTER III: This study was designed to analyse the curve of lactate in response to in-cremental exercise as a sigmoid.To this end, 25 male volunteers, aged 23.2 ± 2.1 years old, 71.6 ± 6 1 kg body mass, 180 ± 10 cm tall, underwent an incremental test to determine the X50; they also underwent submaximal constant load tests to determine maximal lactate steady state (MLSS). The exercise intensity in Watts at X50 (W-X50) was determined based on the dependence between the concentra-tion of lactate and exercise intensity, which were analyzed in a sigmoid function (Boltzmann function). The results showed that the intensities of W-X50 (162.16 ± 33.59 Watts) and W-MLSS (157.80 ± 31.55 Watts) were not significantly different at p <0.05. In addition, W-X50 has a higher correlation with the W-MLSS (r = 0.8, p<0.05) and the W-peak (r = 0.92, p <0.05) than does the OBLA (r = 0, 77, p <0.05 for W-MLSS; r = 0.79, p <0, 05, W-peak). Based on these results, one can con-clude that (1) lactate kinetics can be analyzed in the form of a sigmoid; (2) X50 intensity can be used to determine the W-MLSS. CHAPTER IV: The aim of this study was to analyse the curve of lactate in response to incre-mental exercise as a sigmoid and verify if this response is sensible in hot environ-ment to determine the maximal lactate steady state in a single day test in this envi-ronment. Eight volunteers (age: 24.2 ± 2.5, Weight: 74.99 ± 7.4, height: 178.7 ± 4.0; and VO2 Max: 48.07 ± 4.63) performed two incremental tests (initial load of 60 W with 15 W increase every three minutes) until voluntary exhaustion, at two dif-ferent temperatures: warm environment (40 °C) and temperate environment (22 °C), as well as several submaximal tests to determine the MLSS at both tempera-tures. The exercise intensity was analyzed in a sigmoid function (Boltzmann func-tion) to determine the watts based on the dependence between exercise intensity and the lactate concentration to find the half point of its concentration (X-50). The results showed that the intensities of W-X50 and W-MLSS were not significantly different (p>0.05) at 22°C (181.4±30,1W and 180.0±32.1W, respectively) and at 40 °C (155.8±27.0W and 148.1±32.5W, respectively), however they were different (p<0.05) when analysing between different environments. Therefore, the W-X50 can be used to valid and sensible method to predict the W-MLSS and assessment of submaximal aerobic performance in thermoneutral and hyperthermic environ-ments.