Internal vs. External Frame Backpacks

Abstract

1781 Internal (IF) and external (EF) frames are used in modern load carriage systems. The perceptual and physiological impact of using these different load carriage systems have been investigated, but the biomechanical differences between these frame types have not. PURPOSE: To determine the effect of IF and EF backpacks on gait kinematics during load carriage. METHODS: 11 males (mean ± SD: age 21.6 ± 2.3 yr, height 1.77 ± 0.1 m, body mass 75.8 ± 8.0 kg) walked at 1.35 m/sec on a force sensing treadmill. Direct video data capture at 100Hz was used to collect kinematic data. In separate trials while carrying a loaded (41–43 kg) IF or EF pack, ground reaction forces and gait kinematics were measured from 25 separate strides. Repeated measures ANOVA was used for statistical analysis. RESULTS: There were significant (p<0.05) differences in both ground reaction forces and kinematic gait variables between the IF and EF load carriage systems. Means ± SD and (% differences) for IF and EF respectively, were: stride length (cm) 146 ± 0.10, 148 ± 0.11, (1.2%), stride length normalized to height 0.83 ± 0.05, 0.84 ± 0.05 (1.2%), trunk range of motion (deg) 5.96 ± 1.06, 6.47 ± 1.06 (7.9%), maximum angle of shoulder extension (deg) 4.99 ± 10.68, 6.63 ± 10.53 (24.7%), shoulder range of motion (deg) 6.67 ± 2.11, 7.12 ± 2.56 (6.4%), forward trunk inclination (deg) 12.15 ± 2.21, 12.73 ± 2.77 (4.8 %), maximum heel strike vertical ground reaction force normalized for total load 1.08 ± 0.19, 1.05 ± 0.21 (− 2.6%), and the range of hip flexion/extension (deg) 46.24 ± 5.04, 45.26 ± 5.69 (−2.2%). CONCLUSIONS: There are several small but significant differences in kinematics and kinetics between EF and IF backpacks. These small differences do not indicate a clear advantage of one frame type over the other.