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