Effects of carrying a load on foot strike and stride length in AFROTC cadets
Carrying a backpack load has been proven to cause postural changes. However, the effect of carrying a load on the anterior and posterior sides of the body simultaneously and the effect on the kinematics of gait have not been clearly defined.
PURPOSE: To determine if there is a difference in stride length (SL), foot strike (FS), and joint angles (JA) when carrying a load as opposed to not carrying a load.
METHODS: Ten collegiate Air Force/Reserve Officer Training Corps (AFROTC) cadets (age 19.8± 0.91 yrs; ht 180.24±6.37 cm; wt 70.92± 6.08 kg) completed two trials of light jogging (LJ); once without a load (NL) and once with a load (L) that consisted of a 12.81 kg backpack and 3.86 kg rifle. Subjects were videotaped with a high-definition video camera from the side and analyzed with motion analysis software to determine FS (heel strike (HS), mid foot (MF) or Toe strike (TS)), SL, and JA. A two-sample t-test determined significance between SL when carrying L versus NL. Knee, arm (A), and trunk (T) joint angles were compared carrying L versus NL.
RESULTS: SL- NL versus SL-L (3.02± 0.470m vs. 2.88±0.539m, p=0.553) was not significant. FS NL-T versus L-T (160.07±6.56 vs. 143.94±10.56, p=0.001) were significant. FS-Mid Support (MS) NL-T versus FS MS L-T (153.57±4.33 vs. 144.47±4.76, p=0.000) were significant. FS-Toe off (TO) NL-A versus FS TO L-A (94.06±9.65 vs. 115.18±10.10, p=0.000) were significant. FS NL occurred at HS 80% of the time, MF and TS 10% each. FS L occurred at HS 70%, MF 30%, and TS 0%.
CONCLUSION: SL and T decreased when carrying L suggesting an adjusted center of gravity forward to counteract the weight being carried on the back.