Relationships between training load demands measured by surface EMG wearable technology and the military drag

INTRODUCTION: An essential job task for military personnel is a casualty drag, where a fellow soldier must be dragged from a hazardous environment. A simulation that measures the capacity to perform this task involves dragging a 123-kg dummy (equivalent weight to a soldier wearing a combat load) backwards over a 15-m distance. A casualty drag can be demanding, and execution of this task could affect subsequent tasks a soldier may need to perform (e.g. moving under direct fire). Surface electromyography (sEMG), a wearable technology that can measure tactical tasks in a practical environment, was used to measure the training load (TL) demands associated with the casualty drag. PURPOSE: To determine the relationships between muscle TL measured by sEMG wearable technology and casualty drag velocity. METHODS: A convenience sample of 36 college-aged participants (males = 25; females = 11) performed two trials of a 123-kg casualty drag over 15-m. A 91-kg dummy with 32-kg of additional load via a weighted vest was positioned on the ground. Participants grabbed the vest handles and dragged the dummy backwards over the required distance. Time was recorded to calculate drag velocity, with the fastest trial analyzed. Prior to testing, participants were fitted with compression shorts or leggings embedded with sEMG sensors to measure the vastus lateralis and medialis (quadriceps; QUAD), biceps femoris (BF), and gluteus maximus (GM) of both legs. The sEMG signal for each muscle was measured as a percentage of maximal voluntary contraction to calculate TL. The variables included the TL of each muscle and overall TL (sum of all muscles). Pearson’s correlations (p < 0.05) calculated relationships between drag velocity and the sEMG variables; the sexes were analyzed separately. RESULTS: A slower drag velocity correlated with a greater overall TL for both sexes (males: p < 0.01, r = -0.65; females: p = 0.03, r = -0.66). Greater QUAD TL related to a slower drag velocity for both males (p < 0.01, r = -0.68) and females (p = 0.01, r = -0.73). No significant relationships were found for BF or GM. CONCLUSIONS: Performing a casualty drag slower will increase the TL demands, predominantly via greater QUAD stress. This could impact other activities where QUAD activity is also required, such as moving to cover. Training staff should ensure efficient performance of tasks such as the casualty drag to limit impact on other demanding tasks.