(3) EFFECTS OF LAW ENFORCEMENT LOAD CARRIAGE ON INTERMUSCULAR COORDINATION DURING STANDING AND WALKING

Introduction:  Law enforcement officers (LEO) experience high rates of injuries, specifically to the lower extremity and back regions. LEO commonly wear a duty belt or tactical vest while on duty. Prior literature has reported on the biomechanical effects of load carriage on center of pressure measures related to postural stability and gait kinematics. Given these reported effects, it is plausible load carriage alters muscular coordination and subsequently increases injury risk. However, the effects of LEO style load carriage on intermuscular coordination is scarce in the current literature.

Purpose: The purpose of this study was to examine the effects of law enforcement load carriage on intermuscular coordination.   

Methods: 24 non-LEO volunteers participated (male=13, age=24.5, yrs±6.0, hheight=1.7m±9.8, mass=73.0kg±11.1). Surface electromyography (sEMG) electrodes were placed bilaterally on the vastus lateralis, biceps femoris, multifidus, and lower rectus abdominus. Participants completed 2 load carriage conditions (leather duty BELT and tactical VEST; both 7.2kg) and a CONTROL condition in a randomized order. For each condition, participants stood quietly and walked on a treadmill at 3mph for 30s. sEMG data were sampled at 2000Hz, bandpass filtered (20-490Hz) then lowpass filtered (5Hz cutoff) with a 4^th order Butterworth filter. Pearson correlation coefficients were computed for each muscle pair during the trials. The correlations were z-transformed prior to descriptive and inferential statistical analyses. Appropriate repeated measures inferential statistical testing was conducted based on whether data had a normal (i.e. repeated measures ANOVA) or non-normal distribution (i.e. Friedman’s Test).

Results: Consistent across conditions, the largest correlations during quiet standing were observed between the right and left abdominals; whereas, for walking, the largest correlations were observed between the left and right multifidus. During quiet standing a main effect of condition on the correlation between right vastus lateralis with right biceps femoris (χ²(2)=9.333, p=0.009, W=0.19; no significant post-hoc comparisons) and right vastus lateralis with left abdominal (χ²(2)=8.083, p=0.018, W=0.17; post-hoc: CONTROL >BELT, p=0.021) was found. During walking, a main effect of condition on the correlation between left vastus lateralis with left abdominal (F(2,46)=5.487, p=0.007, h_g²=0.076; post-hoc: VEST >CONTROL, p=0.021), left biceps femoris with right abdominal (χ²(2)=6.083, p=0.048, W=0.13; post-hoc: CONTROL >VEST, p=0.009), right biceps femoris with left abdominal (F(2,46)=3.582, p=0.036, h_g²=0.038; no significant post-hoc comparisons), right biceps femoris with right abdominal (χ²(2)=8.333, p=0.016, W=0.17; post-hoc: VEST >CONTROL, p=0.002), and right biceps femoris with left multifidus (F(2,46)=3.226, p=0.049, h_g²=0.031; no significant post-hoc comparisons) was found.

Conclusion: LEO load carriage results in small differences in intermuscular coordination during walking and has less of an effect during quiet standing. Future research should address limitations of the present study by examining the effects of heavier loads, more dynamic movements and longer durations on intermuscular coordination.

 
PRACTICAL APPLICATIONS: Practitioners working with LEO required to wear tactical vests should be aware that altered muscular coordination between core muscles and primary movers in the lower extremity may occur.

Acknowledgements: None