EFFECT OF SCHOOL BACKPACK ON CARDIO-RESPIRATORY ADJUSTMENTS, ENERGY COST OF WALKING, AND LOW BACK PAIN IN CHILDREN

Abstract

Backpack (BP) use has gained a large popularity in children daily life. However, the use of BP to carry heavy weights to and from school has been recently associated to an increasing incidence of back pain in children. An epidemiological evaluation of BP weight, fatigability and back pain occurrence associated to BP use was carried out on a group of 220 Italian children (12.1 ± 0.6 yr). The mean BP weight (1 week school use) was 8.2 ± 1.2 kg in males and 8.7 ± 0.8 kg in females (range 4.5–12.5 kg), corresponding to 18% and 21% of mean body weight, respectively. The occurrence of back pain in the last 15 days was recorded in 11% males and 23% females. In a subgroup of 18 males (47 ± 9 Kg, 152 ± 8 cm) and 18 females (43 ± 10 kg, 150 ± 7 cm), the cardio-respiratory response to BP use and the cost of locomotion with and without BP were measured during treadmill walking at 3 km/h, (simulating the usual self-selected speed during normal walking in children), with no load or carrying an 8 kg commercially available BP (35 cm high, 12.5 cm width and 24.5 cm length). Moreover, the maximal oxygen uptake was also evaluated. Since no differences were observed between males and females, data were pooled and analysed irrespective of gender. Standing VO2 was 215 ± 45 ml/min. Walking at 3 Km/h required a VO2 of 503 ± 101 ml/min, which increased to 541 ± 98 ml/min during BP walking, (p < 0.01 vs unloaded conditions), corresponding to 23.9% of max in males, and 27.7% in females. BP walking was associated to a minimal increase of heart rate (from 111 ± 14 in unloaded conditions to 115 ± 13 beats/min during BP walking, p < 0.001), but did not affect ventilation (from 18.1 ± 6.2 without BP to 17.8 ± 5.8 l/min with BP). The total O2 cost to cover 1 m distance at 3 Km/h was 10.0 ± 2.0 ml without BP, and increased to 10.8 ± 1.9 ml with BP (p < 0.01). The net energy cost of locomotion (actual minus standing) was 0.129 ± 0.032 ml/KgBW m without load and slightly lower, 0.123 ± 0.025 ml/KgBW+backpack m (p < 0.05) during BP walking. The step frequency decreased from 59 ± 5 without BP to 56 ± 6 steps/min in loaded conditions (p < 0.01). When subjects were divided for the occurrence of back pain, children with a the lower level of physical fitness were most likely to experience back pain. In conclusion, the metabolic and cardio-respiratory effort required to walk at a self-selected speed carrying a BP is minimal and can be tolerated without requiring any particular fitness level. However, back pain is more likely to occure in less physically performing subjects, who also report fatigability more frequently. Thus, a better fitness condition in school children may be useful to prevent the occurrence of back pain during locomotion with BP.