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Biomechanics/Neuromuscular

(04) Seasonal Lower Body Musculoskeletal and Neuromuscular Adaptations in NCAA Division I Cross-Country Athletes

Thursday, July 11, 2024
9:15 AM – 9:30 AM East Coast USA Time
Location: Room 337-338
Abstract Details: Cross-country (XC) athletes undergo high frequency arduous training throughout a competitive season. While these specific demands are essential for performance improvement, chronic repetitive loading may induce neuromuscular fatigue and influence regional muscle morphological and bone health adaptations. However, these avenues have rarely been investigated concurrently. PURPOSE: To determine lower body musculoskeletal and neuromuscular adaptations across a competitive season in collegiate XC athletes. METHODS: Twenty-three NCAA Division I XC athletes (female n=18, male=5) were tested pre and post-XC season. Athletes provided voluntary informed consent, completed training and injury logs, and underwent total body and dual-hip Dual-energy X-ray Absorptiometry (DXA) scans, assessing regional bone and body composition measures. Real-time brightness mode ultrasonography assessed bilateral vastus lateralis (VL) quadriceps muscle thickness, pennation angle, and subcutaneous fat-corrected muscle echo-intensity (mEI). Maximal voluntary isometric contractions were conducted, determining bilateral knee extensor peak force production and spectral rate of force development (RFD) encompassing 50ms increments from 0-250ms. Surface electromyographic amplitude (EMGRMS) was recorded from the VL with bipolar sensors. Paired t-tests assessed pre/post season differences, Cohen’s d effect sizes were calculated, and α=0.050. RESULTS: Athletes’ weekly mileage was consistent pre- (58±27mi) and post-season (54±23mi) (p=0.100; d=0.16). Additionally, body mass and all DXA lean and fat mass measures remained unchanged (all p≥0.050; d≤0.11). Athletes’ non-dominant total hip bone mineral density increased (p=0.014; d=0.09), however their dominant femoral neck density decreased (p=0.024; d=0.11) pre-to-post season. This coincided with an increase in bilateral VL mEI (both p≤0.009; d≥0.25), indicating increased intramuscular adiposity. Athletes’ also demonstrated reduced bilateral peak force and slower RFD normalized to peak force across all time-domains (all p< 0.001; d=0.45-1.21) post-season. Furthermore, peak EMGRMS and EMGRMS at peak force normalized to peak EMGRMS were lower at post-season (all p≤0.018; d=0.35-0.69). CONCLUSIONS: Athletes demonstrated reduced force and electromyographic profiles, indicating neuromuscular fatigue coinciding with hip-specific skeletal adaptations throughout the XC season. Additionally, indication of increased intramuscular fat, traditionally thought to be detrimental, may serve a sport-specific physiological benefit given their metabolic demands. PRACTICAL APPLICATIONS: While high-mileage is a common occurrence for XC athletes, this unwavering demand elicits a reduction in muscle quality, coinciding with a drastic decrease in neuromuscular performance and disjointed bone adaptations. This may warrant alteration of training loads to potentially stave off fatigue, preserve muscle morphological characteristics, and amplify positive bone changes.

Acknowledgements: None