Load-Speed Interaction Effects on the Biomechanics of Backpack Load Carriage
Abstract
We biomechanically examined how backpack load and walking speed interact in their effects. 16 males walked under all 12 combinations of 6, 20 , 33 and 47 kg backpack loads and 117,133 and 1.50 m/s walking speeds. Generally, the effects of load were consistent over the speeds, and the effects of speed were consistent over the loads. Ground reaction forces and impulses, joint forces, muscle torques, muscle electrical activity and backpack acceleration increased when speed and,'or load increased, likely increasing the probability of fatigue and injury. As load increased percentage of stride in double-support and time of toe-off increased, and maximum hip angle decreased, likely improving stability and reducing stress on the musculoskeletal system. However increases in walking speed tended to cancel these adaptations. At the lower speeds but not the highest one, stride frequency increased and stride time decreased when the load increased from 33 to 47 kg. Downward impulses for the major lower body joints increased with load carried, but decreased as walking speed increased. At the 1.33 m/s speed, but not at 1.50 m/s, a gait adaptation resulted in a less-than-expected impulse increase when the load increased from 33 kg to 47 kg. At the fastest walking speed, the volunteers could not further increase stride frequency to reduce stride length increase stability and reduce potential lower body stresses. Thus it appears that soldiers should avoid, if possible, walking faster than 1.33 m/s (4.8 km/hr; 3.0 mi/hr) when carrying backpack loads approaching 47 kg (100 lb).
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 2001
- Accession Number
- ADP010991
Entities
People
- Evertt Harman
- Ki-hoon Han
- Peter Frykman
Organizations
- United States Army Research Institute of Environmental Medicine