Effects Of A Loaded Roach March On Isometric Muscle Strength Measured With A Novel HHD Fixation System

Abstract

PURPOSE: Understanding the effect that field exercises have on soldier muscular strength is an area of interest for the US Army. Reliably quantifying muscle strength in this context has been limited by availability of portable assessment equipment. The widely used hand-held dynamometer (HHD) presents a challenge when assessing strong muscle groups of healthy soldiers accurately. We devised a portable, field-ready HHD fixation solution to assist researchers in the evaluation of lower body and core isometric maximal muscle contractions. Reliability of the fixation system (patent pending) was assessed prior to implementation at a large-scale data collection during a military field exercise. The purpose of the current investigation was to identify strength changes in select muscle groups prior to and immediately following a loaded road march. METHODS: 39 soldiers (36M, 3F) performed 4 maximal isometric contraction types, including lumbar extension, lumbar flexion, hip flexion, and knee extension. 3 trials of each contraction type were recorded during a pre-mission baseline, and 2 trials were recorded immediately following a 6-mi road march executed with an average load of 50% body weight. Measurements were recorded using the system developed, which provided repeatable subject stabilization, muscle group isolation, and HHD fixation. The maximum force recorded from each muscle group during a session was used for analysis. A paired sample t-test was conducted to compare pre and post road march strength measures. RESULTS: No significant change in lumbar extension strength was identified between the pre and post conditions. Significant decreases in strength performance were observed in the hip flexion (8.3%; p=.003), knee extension (7.8%; p=.032), and lumbar flexion (9.9%; p=.009) measurements between the pre and post conditions. CONCLUSION: While lumbar extension strength did not change following the road march, the decreases identified for hip flexion, knee extension, and lumbar flexion followed the hypothesized trend. This study provides novel insight into the effects of field activities on soldier muscle strength that were not quantifiable prior to the portable HDD fixation system, and presents a range of new opportunities to understand the impact of military exercises on strength.