Comparison of the Polar S810i monitor and the ECG for the analysis of heart rate variability in the time and frequency domains

The aim of the present study was to compare heart rate variability (HRV) at rest and during exercise using a temporal series obtained with the Polar S810i monitor and a signal from a LYNX® signal conditioner (BIO EMG 1000 model) with a channel configured for the acquisition of ECG signals. Fifteen healthy subjects aged 20.9 ± 1.4 years were analyzed. The subjects remained at rest for 20 min and performed exercise for another 20 min with the workload selected to achieve 60 percent of submaximal heart rate. RR series were obtained for each individual with a Polar S810i instrument and with an ECG analyzed with a biological signal conditioner. The HRV indices (rMSSD, pNN50, LFnu, HFnu, and LF/HF) were calculated after signal processing and analysis. The unpaired Student t-test and intraclass correlation coefficient were used for data analysis. No statistically significant differences were observed when comparing the values analyzed by means of the two devices for HRV at rest and during exercise. The intraclass correlation coefficient demonstrated satisfactory correlation between the values obtained by the devices at rest (pNN50 = 0.994; rMSSD = 0.995; LFnu = 0.978; HFnu = 0.978; LF/HF = 0.982) and during exercise (pNN50 = 0.869; rMSSD = 0.929; LFnu = 0.973; HFnu = 0.973; LF/HF = 0.942). The calculation of HRV values by means of temporal series obtained from the Polar S810i instrument appears to be as reliable as those obtained by processing the ECG signal captured with a signal conditioner.

Relação entre a tensão aplicada e a sensação de desconforto nos músculos isquiotibiais durante o alongamento / Relationship between tension applied and sensations of discomfort in the hamstring muscle during stretching

CONTEXTUALIZAÇÃO: O alongamento muscular é amplamente empregado no tratamento e na prevenção de doenças musculoesqueléticas. Estudos utilizam informações subjetivas do paciente como "desconforto" e "tensão sem dor" para limitar intensidade de alongamento, sem estabelecer uma tensão adequada de estiramento. OBJETIVO: Estudar a relação entre tensão aplicada e informações subjetivas, durante alongamento estático passivo para analise da reprodutibilidade e variações nas informações sensoriais. MÉTODOS: Participaram 20 jovens com idade média de 20 anos (±2,25), sem experiência prévia com programa de alongamento, divididos em dois grupos: G1 - participou de programa de alongamento dos músculos isquiotibiais, G2 sem programa de alongamento. Os grupos foram submetidos a três avaliações para mensurar o torque e a atividade eletromiográfica (EMG), nas posições de sensação de desconforto (SD) sem dor e sensação de desconforto com dor (SDD), por meio de um sistema de aquisição de sinais, constituído de condicionador de sinais, eletrodo bipolar ativo de superfície, célula de carga, eletrogoniômetro, sensor de pressão e modelo biomecânico. RESULTADO: As análises do torque nas posições SD e SDD revelaram comportamento semelhante nos dois grupos, sem diferenças significantes entre as três avaliações (P > 0.05), demonstrando reprodutibilidade das informações subjetivas dos grupos nas duas posições. A EMG nas posições de SD e SDD não mostrou diferença significante com a EMG obtida em repouso. CONCLUSÃO: Este trabalho revelou que a informação da sensação subjetiva de alongamento é confiável, segura e possível de ser reproduzida clinicamente.

BACKGROUND: Muscle stretching is widely used in the prevention and treatment of musculoskeletal diseases. Previous studies have used subjective information like "discomfort" and "tension without pain" for limiting the intensity of stretching, but without establishing appropriate tensions for stretching. OBJECTIVE: To study the relationship between applied tension and subjective information during static passive stretching, in order to analyze the reproducibility and variability of sensorial information. METHOD: Twenty subjects (mean age: 20 ± 2.25 years) without previous experience of stretching programs were recruited and divided into two groups. G1 participated in a hamstring muscle stretching program, while G2 did not follow a stretching program. Both groups underwent three evaluations to quantify torque and electromyographic activity, in positions that produced a sensation of discomfort without pain (SD) and a sensation of discomfort with pain (SDP), using a signal acquisition system consisting of a signal conditioner, active bipolar surface electrode, load cell, electrogoniometer, pressure sensor and biomechanical model. RESULTS: The torque analyses in the SD and SDP positions showed similar behavior in the two groups, without significant differences between the three evaluations (p > 0.05), thereby demonstrating the reproducibility of the subjective information from the groups in the two positions. Electromyography in the SD and SDP positions did not show significant differences in relation to the findings at rest. CONCLUSION: This study demonstrated that the subjective information on stretching sensations is reliable and secure, and can be reproduced clinically.