(53) CONTRIBUTIONS FROM CRITICAL SPEED, BODY COMPOSITION, AND LOWER BODY STRENGTH TO LOAD CARRIAGE PERFORMANCE

Load carriage is inherent in the tactical population, and the mass required can depend on the occupation. Critical speed (CS) has been associated with technical and combat-specific performance measures (e.g., loaded running). The 3-min all-out exercise test (3MT) provides estimates of CS and the maximal capacity to displace the body (D’) at speeds above CS. Loaded time trials can be used in tactical populations for an aerobic and load carriage performance assessment, along with body composition and lower body strength to measure physical performance.

Purpose: The purpose of this study was to examine the contributions of CS, D’, body composition, local lean mass, and lower body isokinetic strength and endurance parameters as they relate to load carriage time trials.

Methods: Twenty-two young adults (16 = males, 6 = females, age = 20.82 ± 1.59 yrs.) underwent various assessments that included a running 3MT to determine CS and D’, isokinetic knee extension (KE) muscle strength and endurance on a Biodex System, body composition assessed by dual-energy X-ray absorption (DXA), and two load carriage (21 kg) time trials (LCTT) of 400 m and 3200 m, respectively. Researchers completed a secondary region of interest analysis in the DXA to estimate local mineral-free thigh lean mass (TLM). Pearson’s Product-Moment Correlations investigated relationships between CS, D’, body composition, local lean mass, and lower-body strength parameters. The scale for interpretation was as follows: 0.1-0.3 = small, 0.3-0.5 = medium, and 0.5-1= large. Stepwise multiple linear regression analyses were used to determine the relationship between selected predictor variables (lean body mass (LBM), % body fat, CS, D’, KE peak torque, KE endurance work, and TLM) and which variables predicted load carriage performance using SPSS (v.28). Significance was set at p< 0.05.

Results: Descriptive data (M ± SD) for the sample includes height: 175.1 ± 8.9cm, body mass = 76.70 ± 11.73 kg, LBM = 56.39 ± 11.22 kg, % body fat = 21.73 ± 7.14 %, TLM = 7.95 ± 1.61 kg, CS = 3.54 ± 0.55 m∙s^-1, D’ = 154.1 ± 40.69 m, KE peak torque = 216.1 ± 57.04 Nm, KE endurance work = 2404 ± 539.6 J, 400m LCTT = 1.62 ± 0.32 mins, and 3200m LCTT = 20.83 ± 3.88 mins. Significant correlations, in descending order, were as follows: LBM and CS (r= 0.651, p< 0.001), KE endurance work and CS (r= 0.645, p< 0.001), TLM and CS (r=0.593, p< 0.05), and KE peak torque and CS (r= 0.529, p< 0.05). The stepwise regression analyses indicated that CS and LBM contributed significantly to predicting 3200m LCTT (F [2,19] = 81.85, R² = 0.90, p< 0.001) with β coefficients (-0.723 and -0.301, respectively) and TLM contributed significantly to predicting the 400m LCTT (F [1,20] = 46.586, R² = 0.70, p< 0.001).

Conclusion: The results of this study highlight that CS and LBM were the best predictors of the 3200 LCTT, and TLM was the best predictor of the 400m LCTT. CS and D’ also correlated to 400m LCTT times. LBM, KE endurance work, peak torque, and TLM correlate to higher CS. TLM was associated with higher KE peak torque and KE endurance work. PRACTICAL APPLICATION: The findings of this study support that CS and LBM, including TLM, are important in predicting load carriage task completion in the time trial tasks. However, in addition to LBM, muscle strength and endurance contribute to CS and should be considered when training for load carriage tasks.

Acknowledgements:

The authors would like to thank the Northland American College of Sports Medicine Innovative Student Research Grant, the Department of Health, Nutrition, and Exercise Sciences, and the College of Human Science and Education at North Dakota State University for funding support for this study.