Table 3 Characteristics of control and intervention groups in the third grade of compulsory secondary education (CSE3)

From: Backpack weight and back pain reduction: effect of an intervention in adolescents

  Control Intervention p-value
  n % n %
Sex
 Boys 439 48.4 251 46.9 0.623
 Girls 468 51.6 284 53.1  
Age
 14-years old 443 48.8 300 56.1 0.024
 15-years old 330 36.4 173 32.3  
 16-years old 134 14.8 62 11.6  
Overweight or obesity
 No 602 66.4 342 63.9 0.345
 Yes 305 33.6 193 36.1  
School bag
 Two shoulder straps 819 90.3 514 96.1  < 0.001
 Other type 88 9.7 21 3.9  
Backpack weight > 10% of the body weight
 No 414 45.6 243 45.5 1.000
 Yes 493 54.4 291 54.5  
Time per day with the backpack on
 Less than half an hour 476 52.5 314 58.7 0.022
 More than half an hour 431 47.5 221 41.3  
Walking to school
 No 605 66.7 387 72.3 0.029
 Yes 302 33.3 148 27.7  
Performs sports regularly
 No 455 50.2 265 49.5 0.828
 Yes 452 49.8 270 50.5  
Time per day watching TV
 Less than 1 h 322 35.5 229 42.8 0.018
 Between 1 and 2 h 392 43.2 212 39.6  
 More than 2 h 193 21.3 94 17.6  
Time per day on the laptop or video games
 None 413 45.5 186 34.8  < 0.001
 Less than 1 h 276 30.4 177 33.1  
 More than 1 h 218 24.0 172 32.2  
Time per day studying
 Less than 1 h 233 25.7 124 23.2 0.318
 Between 1 and 2 h 312 34.4 204 38.1  
 More than 2 h 362 39.9 207 38.7  
Back lesion
 No 802 88.4 483 90.3 0.274
 Yes 105 11.4 52 9.7