Efeitos do incremento do número de passos diários sobre a função autonômica cardíaca e o desempenho físico no limiar anaeróbico, em indivíduos normais sedentários

AUTOR(ES)
DATA DE PUBLICAÇÃO

2007

RESUMO

Introduction: Promoting an active life style has become a central concern in the Public Health sector. Evidences of the positive association between physical activity and health are abundant. Nevertheless, there are gaps on the effects of interventions based on the amount of daily steps, as well as in what concerns the physiological mechanisms involved. Objectives: To verify the effects of the increase of 3500 daily steps, during a three week period on the cardiac autonomic function (CAF) and the physical performance at the anaerobic threshold (AT), in normal and inactive subjects. To evaluate the effectiveness of increasing the number of daily steps and to corrolate this increase to the heart rate variability (HRV) and to the variables of physical performance at the AT. Subjects and Methods: Nineteen men, with median age of 30 years old (19-46 years), clinically normal, sedentary and with BMI between 18.5 and 29.9 Kg/m2 were studied. The participants were submitted to CAF assessment test through temporal and spectral analysis of HRV in 5 minute temporal series of R-R intervals of ECG, obtained from the Polar S810 heart rate monitor, in supine rest and in orthostatic posture. Following that, the usual pattern of daily steps was recorded for 18 days, using SW710 Yamax Pedometer (control stage). Right after, they were submitted to a new CAF assessment and to a cardiopulmonary exercise test (CET) in order to assess physical performance at the AT. Intervention stage was then started with a minimum increase of 3500 daily steps, during 23 days, increase which was calculated on the mean number of daily steps accumulated during week days in the control stage. At the end, a new CAF assessment was performed as well as a new cardiopulmonary exercise test. Results: The median and the extremes of number of steps/day during the intervention stage (11772, 8998 18620) were higher than those recorded in the control stage (7295, 4700 14752). Functional variables (HR, SBP and DBP) and anthropometric variables of rest (weight and BMI) were not altered by the intervention (p>0.05). Most temporal indexes of HRV remained stable (p>0.05), except for the mean of R-R intervals (supine and orthostatic) and of rMSSD on orthostatism (p=0.07 0.05 e 0.07). Among the spectral indexes, only the spectral area of low frequency on supine showed a statistic tendency to reduction (p=0.076). The intervention caused an increase in physical performance at the AT, with an average increase of 8% in the covered distance (p=0.02) and of 6% in time until AT, not modifying, however, the oxygen consumption and the heart rate (HR) at the AT (p=0.12). A tendency of positive correlation between the percental increase of steps and pNN50 and the absolute spectral area of low frequency on supine in the last evaluation (rs = 0.39 - p = 0.09) and the pNN50 and the rMSSD in orthostatic posture was observed. There was a negative correlation between the HR at rest and the percentual variation of HR at rest until AT, in two effort tests (rs = -0.67 and -0.69 respectively, p<0.002). Conclusions: The increase in number of daily steps led to a slight increase in parasympathetic modulation, especially in orthostatic posture, though with no change to the sympathovagal balance. Physical training proved efficient in improving sub maximum physical performance at the anaerobic threshold. The subtle changes observed become important, when bearing in mind the age scope of the sample and the type of intervention used, which was based only on the increase of daily steps.

ASSUNTO(S)

limiar anaeróbico variabilidade da freqüência cardiáca atividade física pedômetro tolerância do esforço caminhada ciencias da saude

ACESSO AO ARTIGO

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