Table 1 Characteristics of the study participants and non-participants

Number of participants, n (%)

632

342

272 (44.3)

331

630

223

Sex, female, %

40.7

40.6

40.8

0.96

40.5

78.4

34.1

0.019

Age, years

13.8 ± 1.5

13.7 ± 1.5

14.0 ± 1.6

<0.05

14.7 ± 1.6

14.4 ± 1.6

13.5 ± 1.4

<0.001

Body mass index, kg/m²

19.0 ± 2.4

18.9 ± 2.5

19.1 ± 2.3

0.21

19.9 ± 3.2

19.6 ± 2.8

18.7 ± 2.6

<0.001

Sleep length, h/d

7.8 ± 1.8

7.9 ± 2.1

7.6 ± 0.9

<0.05

7.3 ± 0.9

7.2 ± 1.0

7.8 ± 0.9

<0.001

Screen time, h/wk

20.7 ± 10.9

21.5 ± 11.1

19.6 ± 10.6

0.06

21.5 ± 10.7

20.6 ± 12.5

21.5 ± 10.7

0.185

Sports activity time, h/wk

18.4 ± 6.0

17.7 ± 5.6

19.1 ± 6.3

<0.01

15.7 ± 6.1

-

16.3 ± 10.7

<0.001

Regular player, %

48.4

46.5

51.9

0.19

60.2

-

45.2

0.266

Type of team sport, n (%)^a

 Baseball

176

100

73 (42.2)

-

-

-

 Softball

102

56

42 (42.9)

-

-

-

 Basketball

111

50

57 (53.3)

-

-

-

 Soccer

40

21

17 (44.7)

-

-

-

 Volleyball

200

113

82 (42.1)

-

-

-

 Other

3

2

1 (33.4)

-

-

-

Teammate quantity index^b

1.3 ± 0.6

1.3 ± 0.5

1.4 ± 0.6

0.16

-

-

-