Cardio-respiratory adjustments and cost of locomotion in schoolchildren during backpack walking (the Italian Backpack Study)

Abstract.

The use of a school backpack is one of the possible causes of back pain in children. Oxygen consumption ($\dot V{\rm O}_{\rm 2}$ ), pulmonary ventilation, and heart rate (f _c) were measured in 35 pre-pubertal subjects [17 girls and 18 boys, mean (SD) age 11.3 (0.6) years]. They took part in a four-step experiment: (1) standing for 5 min, (2) walking at 3 km·h^–1 for 7 min, (3) walking at 3 km·h^–1 for 7 min carrying a school backpack weighing 8 kg, and (4) walking at 7 km·h^–1 for 5 min with no load. The occurrence of back pain in the last 2–3 years and during the last 15 days was assessed for the subjects by means of a questionnaire. Mean (SD) standing $\dot V{\rm O}_{\rm 2}$ was 215 (45) ml^.min^–1 during walking at 3 km·h^–1, 503 (101) ml^.min^–1 during walking without a load, and increased to 541 (98) ml^.min^–1 during walking with a load (P<0.01). Carrying a backpack increased f _c only minimally. The energy cost of walking at 3 km^.h^–1 without the backpack was 10.0 (2.0) ml O₂ ^.m^–1, and with the backpack was 10.8 (1.9) ml O₂ ^.m^–1 (P<0.01). The net energy cost of locomotion was 0.129 (0.032) ml^.kg body mass^–1.m^–1 for the unloaded condition and slightly lower, at 0.123 (0.025) ml^.kg body mass^–1.m^–1 during loaded walking (P<0.05). Ventilation did not change significantly between unloaded and loaded conditions. When the data were assessed according to the occurrence of back pain, the f _c/$\dot V{\rm O}_{\rm 2}$ slope was significantly lower in children without back pain, even though the net energy cost of locomotion was similar. Overall, these data suggest that the cardiovascular effortrequired for locomotion while carrying a backpack is minimal. However, fatigability and back pain are more likely to take place in less physical performing subjects. Thus, the occurrence of back pain in schoolchildren during locomotion while carrying a backpack may improve with an improvement in their level of fitness.