Bone, muscle, tendon, and nerve’s synergistic adaptation to sport and physical training

Objectives: Sport and physical training elicit external forces, induce internal mechanical loads, and provoke adaptations to bones, muscles, tendons, and nerves. However, different athletic and tactical disciplines require various loading demands, which may potentially lead to unique synergistic adaptations to the musculoskeletal, tendinous, and neuromuscular systems. Thus, the purpose of these studies was to investigate bone, muscle, tendon, and neuromuscular characteristics and adaptations within multiple sport disciplines and among pre-service military personnel to identify potential adaptive tissue interplay. Methods: Three projects assessed musculoskeletal, tendinous, and neuromuscular characteristics and adaptations among collegiate track and field and cross-country (TF-XC), softball athletes, and Reserve Officers Training Corps (ROTC) cadets. Project 1 compared musculoskeletal health and density, musculotendinous morphology, and neuromuscular performance characteristics between TF-XC (n=30) and controls (n=30), and in cross-country (XC) athletes across a competitive season (n=20). Project 2 compared musculoskeletal health, density, and asymmetries, and muscle strength and power imbalances in softball athletes (n=25) and controls (n=25). Project 3 compared body composition and musculotendinous structure, quality, and mechanics between ROTC cadets (n=34) and controls (n=34), and in cadets pre-to-post 12-week training block (n=31). Results: In project 1, TF-XC reported 3-fold greater injury rates than controls, despite greater bone health, and muscle mass and quality (all p≤0.008). However, XC athletes’ muscle quality and force production, and Achilles tendon quality decreased from pre- to post-season (all p≤0.001). In project 2, softball athletes demonstrated better bone health and body composition, and larger arm bone density asymmetries, favoring their dominant arm, than controls (all p≤0.037); However, though athletes produced greater muscle power (p≤0.003), they presented hamstrings-to-quadriceps muscles torque ratios indicative of elevated knee injury risk. In project 3, ROTC presented lower muscle volume and force production (all p≤0.039), coinciding with a smaller, stiffer, and poorer quality Achilles tendon (all p≤0.017) than controls. Additionally, cadets demonstrated a longitudinal reduction in muscle volume and force production, and tendon mechanical properties (all p≤0.011). Conclusions: Overall, sport participation, regardless of discipline, presented better musculoskeletal health and density to non-athletes. However, individuals undergoing chronic repetitive sport and occupational training demonstrated suboptimal musculotendinous and neuromuscular characteristics and potentially unfavorable synergistic adaptations.