Polar h10 chest strap hr monitor

Participants were positioned supine on a treatment bed for 15 min with a Polar H10 chest strap HR monitor (Polar Electro Oy, Kempele, Finland). The participants relaxed for 10 min before the data were taken and 5 min after the data were taken [31 (link)].
The variables measured were resting HR, the average time between RR intervals (mean RR), which is inversely proportional to HR, and four HRV variables. Linear methods in time were applied to analyse HRV. In the time domain indexes, the variables analysed were the square root of the average of the square of the differences between normal adjacent RR intervals (RMSSD) and standard deviation of the average of all normal RR intervals (SDNN). The Poincaré plot indexes were of the standard deviation of the instantaneous rate variability. The rhythm (SD1) and standard deviation of long-term continuous RR interval variability (SD2) were also analysed [32 (link)].
Kubios HRV Premium analysis software version 4.1.0 (Kubios, Biosignal Analysis and Medical Image Group Department of Physics, University of Kuopio, Finland) [31 (link)] was used to analyse all the variables.

A Polar H10 chest strap HR monitor (H10 Polar; Polar Electro. Oy, Kempele, Finland) was used in this study to record the HR at a sampling rate of 1 Hz. Three accelerometers (Naxsen 9, SIPPLink Co., Ltd., Hsinchu City, Taiwan) were used to record acceleration at a sampling rate of 200 Hz. The participant simultaneously wore three accelerometers at standardized body sites (non-dominant [left] wrist, trunk, and right shank), as shown in Figure 1. The trunk accelerometer was fixed to the heart rate belt and located on the left erector spinae muscle (T9~10) to avoid shaking. The shank accelerometer was fixed to the lateral of the tibial tuberosity. The shank accelerometer was placed on the right leg (racket-side) because the lunge with the racket-side leg is often performed in badminton [24 (link)]. This study did not place an accelerometer on the racket-wrist because the PL at this position was unable to estimate the internal load well alone due to the specificity of the racket motion to the racket hand [8 (link)].