Interação da variabilidade da freqüência cardíaca e do lactato sanguíneo durante o exercício resistido em idosos saudáveis

Abstract

The anaerobic threshold (AT) is an important parameter for prescription of physical exercise in various clinical conditions, because represent the intensity of effort at which the aerobic metabolism begins to be supplemented by anaerobic metabolism for the production of energy. In this context, different methods to identify AT have been described, for example by analysis of blood lactate and the respiratory gas exchanges, yet such methods require expensive equipment and materials. Low cost non-invasive techniques such as heart rate variability (HRV) have been proposed to determine the AT; however, they are most commonly applied in discontinuous protocols on a cycle ergometer or treadmill. Therefore, the objectives of this study were to evaluate the behavior of HRV and blood lactate during resistance exercise (RE) with increasing resistances at a percentage of one repetition maximum (1RM), and investigate the existence of an aerobic-anaerobic transition point in the metabolism during lower leg exercise in healthy older adults. Secondarily, our objective was to evaluate the relationship between different methods, as well as the degree of concordance between the same. Ten healthy men ranging in age from 60 to 70 years old (mean and SD: 64 ± 4 years, 166 ± 3 cm, 70 ± 7 kg), underwent medical examination, ergonomic testing and laboratory exams (hemogram, triglycerides, total and fractional cholesterols, glycemia and uric acid. The protocol for RE was administered on Leg Press 45° (Pró-Fitness) equipment. The protocol resistance loads used were determined by 1RM test; the volunteer complete one full cycle on the equipment at the maximum resistance load that the volunteer could achieve, and the resistance load increases were calculated from this test value at rates of 10% of 1RM until a 30% increase and then at increments of 5% until exhaustion. At each percentage increase of effort, the volunteer performed 4 minutes of exercise followed a rest interval of 15 minutes. Heart rate was captured throughout the protocol by a Polar Vantage Heart rate monitor connected to a Polar Advantage Interface that transmitted the data in real time to a Soyo Notebook computer. The blood samples were collected before the initial effort and immediately after the end of each resistance load. Blood lactate and HRV were analyzed at rest conditions with the volunteer positioned on the equipment and at each percentage of effort. The indexes utilized for HRV analysis were RMSSD, RMSM, SD1, SD2 and SD1/SD2 ratio. To identify the aerobic-anaerobic transition point, blood lactate concentrations were used (gold standard) as well as SD1 and RMSSD indexes; and these points were denominated as lactate threshold (LT), SD1 threshold (SD1T) and RMSSD threshold (RMSSDT). The level of significance for all statistical tests was set at 5%. The principal result showed that the mean of the RMSSD, RMSM and SD1 indexes reduced significantly at 30% 1RM in relation to the rest condition, and blood lactate presented an exponential increase at 30% 1RM, that was significantly greater in relation to the rest condition at 35%. There was no significant difference in relation to absolute and relative values for resistance loads at which the aerobic-anaerobic transition point was identified (absolute values: LT = 101 ± 32 kg, SD1T = 96 ± 28 kg, RMSSDT = 97 ± 21 kg; Relative values: LT = 30 ± 6%, SD1T = 29 ± 6%, RMSSDT = 29 ± 5%). Additionally, good concordance and good correlation were found between LT and RMSSDT (r = 0.78) and between LT and SD1T (0.81). It can be concluded that the behavior of HRV and blood lactate change markedly at 30% 1RM during resistance exercise on the Leg Press 45°. It was possible at this percentage to identify the aerobic-anaerobic metabolism transition point by blood lactate as well as by HRV in healthy older men.