Table 1.
Baseline characteristics by back pain status at baseline a
| Baseline Characteristics | Back Pain at Baseline (n = 56), Mean (SD) | No Back Pain at Baseline (Risk Cohort) (n = 215), Mean (SD) | P | All (n = 271), Mean (SD) |
|---|---|---|---|---|
| Age, y | 14.8 (1.7) | 14.5 (2.0) | 0.30 | 14.6 (2.0) |
| Sex, male, % (n) | 52 (29) | 59 (127) | 0.35 | 58 (156) |
| Height, cm | 171.7 (11.7) | 169.4 (10.7) | 0.30 | 169.9 (10.9) |
| Mass, kg | 61.3 (13.2) | 57.8 (12.3) | 0.06 | 58.5 (12.5) |
| BMI, kg/m2 | 20.5 (2.5) | 19.9 (2.5) | 0.11 | 20.0 (2.5) |
| Passion for sport (AIMS) b | 29.4 (3.1) | 29.1 (3.6) | 0.57 | 29.2 (3.5) |
| Quality of sleep c | 7.8 (1.5) | 8.1 (1.7) | 0.23 | 8.0 (1.7) |
| No. of hours of sleep per night | 7.8 (1.3) | 8.2 (1.5) | 0.07 | 8.2 (1.5) |
| General health c | 8.3 (1.9) | 8.4 (1.6) | 0.69 | 8.4 (1.7) |
| No. of matches in year 2017 | 66.4 (28.7) | 65.2 (37.7) | 0.82 | 65.4 (36.0) |
| Hours per week of tennis training in year 2017 | 9.8 (3.4) | 9.5 (3.8) | 0.59 | 9.5 (3.7) |
| Hours per week of fitness training in year 2017 | 4.0 (2.1) | 3.7 (2.4) | 0.39 | 3.8 (2.4) |
| Normal racket tension | 23.4 (1.1) | 23.4 (1.3) | 0.99 | 23.4 (1.3) |
| One responsible tennis coach, % (n) | 57 (32) | 70 (151) | 0.07 | 68 (184) |
| One responsible fitness coach, % (n) | 64 (36) | 62 (133) | 0.78 | 63 (171) |
AIMS, Athletic Identity Measurement Scale; BMI, body mass index.
a
Numbers may differ due to internal missing.
b
Sum of total score of 7 items of the AIMS questionnaire (minimum 7, maximum 35) where high scores correspond to a high passion for sport.
c
Rated on a numerical rating scale of 1 to 10 where 1 = very bad and 10 = very good.