doi:10.3850/978-981-08-7615-9_RE01

ABSTRACT

Monitoring cardiac condition by electrocardiograms (ECG) during outdoor activities is beneficial for fitness management. The most commonly- used method to measure heart rates (HR) from ECG is detecting R-peaks to compute 1/R-R intervals. However, R-peaks can be un-detectable during moderate-to-intensive exercise, such as jogging, due to artifacts induced by respiration and movement. Heart instantaneous frequency (HIF), a technique for estimating HR changes by ECG without detecting R-peaks, is applied and evaluated by this study. An activity-adapted method is proposed to acquire HIF during sleeping, free-indoor-activities, outdoor walking, outdoor jogging and post-exercise recovery. The ECG data were recorded from 6 healthy individuals (all males, age = 23.5 ± 1.0 y/o, height = 178.8 ± 3.4 cm, weight = 74.6 ± 12.0 kg) by a portable device at a sampling rate = 200 Hz. Three-axial acceleration of body was also recorded on the chest simultaneously with ECG for identifying activity intensity. The speed of walking and jogging were self-paced in favor and comfortable cadence. Based on the results, the obtained HIF is highly correlated with HR. During outdoor jogging, HIF is 3.0 ± 0.1 Hz related to HR about 180 beats/min. For other activities, HIF and related HR are 1.3 ± 0.2 Hz and 70 beats/min during sleeping, 1.6 ± 0.1 Hz and 90 beats/ min during free-indoor-activities, 1.7 ± 0.1 Hz and 100 beats/min during outdoor walking, and 2.3 ± 0.2 Hz and 135 beats/min in recovery phase. The findings would be useful in developing tools for further applications on cardiac monitoring during outdoor exercise.

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