Data analysis

The inclusion criterion for the data analysis was that the wearable device was worn for at least 10 h per day for at least four days in a week. Valid data were categorized into days when performing or not performing tennis lessons. The structure of an 80 min tennis lesson conducted at the target tennis school consists of a 10 min warm-up, a 20 min stroke rally, a 40 min rotation drill, and a 10 min match practice. This study has been conducted in the structure of the regular tennis school lesson regardless of the study. The data measured every 10 s with a high temporal resolution were used to analyze the 80 min tennis lessons. METs were categorized into sedentary behavior (SB, < 1.5 METs), light physical activity (LPA, 1.5–2.9 METs), moderate physical activity (MPA, 3–5.9 METs), and vigorous physical activity (VPA, > 6 METs), following a previously reported definition^29,30. The mean intensity of physical activity during daily tennis lessons (METs), physical activity intensity (METs/day), number of steps (steps/day), and duration of physical activity per day (min/day) for each physical activity intensity were obtained.

To evaluate rest periods during the tennis lessons, 90 and 120 s short-bout rests were obtained, which are the same rest periods as between the court changes and sets during a tennis match. Data processing followed previous studies³¹, and one short-bout rest was counted when all physical activity intensities for each 10-s frame were less than 2.9 METs per unit time for 90 and 120 consecutive seconds. The total number of short rests per tennis lesson was counted, and the percentage of short rests per tennis lesson was calculated by dividing the total number of short rests by the duration of the lesson. The mean percentage of short rests per lesson was then determined for 90 and 120 s, respectively.

To investigate the effect of the tennis lesson on the mean daily physical activity intensity, the following data were used: (1) physical activity intensity on the day of the tennis lesson (TL) (incl TL); (2) daily physical activity intensity excluding the time during the tennis lesson (excluding TL); and (3) daily physical activity intensity excluding the time during the tennis lesson and the travel time (TT) from the day of the performed tennis lesson (excluding TL + TT). The travel time was assumed to be 1 h each day, and the data for the day of the performed tennis lesson were analyzed after removing the activities 1 h before and after the tennis lesson.

Repeated measures analysis of variance were conducted to examine differences in physical activity intensity during daily tennis lessons and between conditions on the day of the tennis lessons. When differences between conditions were found, multiple comparisons were made using the Tukey–Kramer method. In addition, a paired t-test was used to identify differences in mean physical activity intensity and the number of steps taken on the days of performed and non-performed tennis lessons. Statistical analysis was performed using Python (Python version 3.10.1, PythonTM, Python Software Foundation, Wilmington, DE), and p < 0.05 were considered statistically significant.