Biomechanical and metabolic effects of varying backpack loading on simulated marching

Twelve healthy, male Army recruits performed three, 40-min treadmill marche s at 6 km/h, under three load carriage conditions: 0%-body weight (BW) back pack load, 15%-BW load and 30%-BW load. Kinematic and kinetic data were obt ained, immediately before and after each treadmill march, for computing ank le, knee and hip joint rotations and moments. Metabolic data (oxygen uptake ((V) over dot O-2), expired ventilation ((V over dot) E), respiratory exch ange ratio (RER)), heart rate (HR) and ratings of perceived exertion (RPE) were collected continuously during marching. Significant differences (p les s than or equal to 0.05) were observed between each load for (V over dot) O -2, HR and (V) over dot E)throughout the marches. At 40 min, relative energ y costs for 0%-BW, 15%-BW and 30%-BW loads were 30, 36 and 41% ((V over dot ) O(2)max, respectively. RPE responses during marching significantly differ ed for only the 30%-BW load and were greater than responses at 0%-BW and 15 %-BW loads. During load carriage trials prior to treadmill marches (pre-mar ch), peaks in internal, hip extension, knee extension and ankle plantar fle xion moments increased with increasing backpack load. Relative to 0%-BW loa d, percentage increases in knee moments, due to 15%-BW and 30%-BW loads, pr e-march, were substantially larger than the percentage increases for hip ex tension and plantar flexion moments, pre-march. Pre-march and post-march pe aks in hip extension and ankle plantar flexion moments were similar with al l loads, while notable pre-march to post-march declines were observed for k nee extension moment peaks, at 15%-BW and 30%-BW load. Pre-march joint load ing data suggests that the knee may be effecting substantial compensations during backpack loaded marching, perhaps to attenuate shock or reduce load elsewhere. Post-march kinetic data (particularly at 15%-BW and 30%-BW load) , however, indicates that such knee mechanics were not sustained and sugges ts that excessive knee extensor fatigue may occur prior to march end, even though overall metabolic responses, at 15%-BW and 30%-BW load, remained wit hin generally recommended limits to prevent fatigue during prolonged work.