An Analysis of Muscle Activity During Load Carriage, ACFT Scores, and Back Pain in Army ROTC Cadets

Context: Low back pain (LBP) is a leading musculoskeletal complaint among the military population. Load carriage tasks are a frequently reported mechanism of injury for low back pain (LBP) in the Army. Furthermore, researchers have demonstrated a clear association between physical fitness and injury incidence. Objectives: 1) to analyze changes in muscle activity during load carriage and how LBP relates to changes in muscle activation; and 2) to analyze a possible relationship between performance on the Army Combat Fitness Test (ACFT) and LBP, muscle activity, and kinesiophobia in Army Reserve Officer Training Corps (ROTC) cadets. Methods: 30 Army ROTC cadets (age 21?1.82) completed a 5-kilometer walk with and without a 35-pound load. Electromyography (EMG) data were obtained of the rectus femoris (RF), rectus abdominis (RA), gluteus medius (GM), gluteus maximus (GMx), erector spinae (ES), and biceps femoris (BF), and a questionnaire was used to assess LBP. Twenty-one cadets from the initial sample completed the six-event ACFT, the Tampa Scale of Kinesiophobia (TSK), and visual analog scales (VAS). ANOVA models were estimated for each muscle with time and load as independent factors. Correlations were used to assess relationships between pain and muscle activity. Regression was used to model the ability of muscle activity, MMBQ, TSK, and VAS scores to predict performance on each component of the ACFT. Results: Muscle activation for all muscles declined significantly over time (p<.001). Amplitude of RF (p=.014), GM (p<.001), and GMx (p=.007) significantly increased in the LC condition. Cadets who reported pain had greater average muscle activation; however, only the RF showed a significant association (p=.01). Significant regression equations were found for the Sprint-Drag-Carry (p=.009) and two-mile run (p=.004). Conclusion: Due to the associations between LBP and increased muscle activation with added loads, cadets displaying muscle activity at greater percentages of their MVC should consider adopting a core strengthening program prior to embarking on foot marches with load carriage. Additionally, cadets with poor performance on the SDC and 2MR should require a fitness program focused on improving these measures, as they are significantly associated with LBP