Head-borne Load Effects on Soldier Completion Times of a Shuffle-Kettlebell Carry-Sprint Task

In addition to ballistic protection, a Soldier’s helmet serves as a platform for mounting technology (e.g. night vision devices, communications etc.) that aids in successful mission completion. The cumulative effect of adding components to the helmet is increased mass and a change in weight distribution of the total head-borne load being supported by the wearer’s neck. Wearing head-supported mass (HSM) can increase risk of injury, cause fatigue and reduce performance. However, limited research exists on understanding the impacts that wearing head-borne loads have on a dismounted Soldier’s performance and mobility. PURPOSE: To quantify the effects of wearing head-borne load for an extended period on Soldier speed. METHOD: Sixteen male Soldiers with 10 ± 3 years of military service performed dismounted Soldiering tasks while wearing five load conditions: 1) LMRO, low-mass (1.5 kg) rear-offset (-2 cm), 2) MMFO, mid-mass (2.5 kg) forward-offset (3.5 cm), 3) MMM, mid-mass (2.5 kg) midline (0 cm), 4) HMM, high-mass (3 kg) midline (0 cm), and 5) HMFO, high-mass (3 kg) forward-offset (3 cm). Offsets were relative to the subject’s tragion notch and one load condition per session was worn. Test sessions began with a marksmanship task followed by a 25 m lateral shuffle, kettle bell carry and sprint (LSCS). The LSCS was derived from the Army Combat Fitness Test sprint-drag-carry. The first LSCS was immediately followed by a 60 min walk on a treadmill at 60% of the Soldier’s Froude velocity and then a second LSCS was performed. Completion times of the LSCS were recorded and average and max heart rate (HR) were measured. Effects of load condition and time were compared using a repeated measures ANOVA. RESULTS: There was a significant effect of load on LSCS completion times. The MMFO and HMFO both significantly increased completion times relative to the smallest load LMRO by 1.06 sec (p = .016) and 1.19 sec (p = .013) respectively. No differences in the pre- vs post-walk completion times were found. A significant increase of 7 bpm (p = .002) in the average HR was measured post- vs pre-walk. No differences in max HR were found. CONCLUSION: Of the five load conditions, the MMFO and HMFO loads create the greatest torque on the neck. An increase in completion times of the LSCS task with these loads indicates that HSM configuration can degrade Soldier mobility.