Abstract
Different adaptive responses to mechanical loading between muscle and tendon can lead to non-uniform biomechanical properties within the muscle-tendon unit. The current study aimed to analyze the mechanical properties of the triceps surae muscle-tendon unit in healthy male and female elite track and field jumpers in order to detect possible inter-limb differences and intra-limb non-uniformities in muscle and tendon adaptation. The triceps surae muscle strength and tendon stiffness were analyzed in both limbs during maximal voluntary isometric plantar flexion contractions using synchronous dynamometry and ultrasonography in sixty-seven healthy young male (n = 35) and female (n = 32) elite international level track and field jumpers (high jump, long jump, triple jump, pole vault). Triceps surae muscle-tendon unit intra-limb uniformity was assessed using between limb symmetry indexes in the muscle strength and tendon stiffness. Independent from sex and jumping discipline the take-off leg showed a significantly higher (p < 0.05) triceps surae muscle strength and tendon stiffness, suggesting different habitual mechanical loading between legs. However, despite these inter-limb discrepancies no differences were detected in the symmetry indexes of muscle strength (5.9 ± 9.4%) and tendon stiffness (8.1 ± 11.5%). This was accompanied by a significant correlation between the symmetry indexes of muscle strength and tendon stiffness (r = 0.44; p < 0.01; n = 67). Thus, the current findings give evidence for a uniform muscle-tendon unit adaptation in healthy elite track and field jumpers, which can be reflected as a protective mechanism to maintain its integrity to meet the functional demand.
Highlights
The ability to sprint and jump maximally requires high mechanical power outputs and energy generation capabilities at the joints of the lower extremity (Bobbert et al, 1986; Stefanyshyn and Nigg, 1998)
Male jumpers showed significantly (p = 0.002) higher triceps surae (TS) muscle strength compared to female jumpers (Figure 1)
In order to identify possible differences in age, body mass, and body height a two-way analysis of variance (ANOVA) was implemented with sex and jumping discipline as factors
Summary
The ability to sprint and jump maximally requires high mechanical power outputs and energy generation capabilities at the joints of the lower extremity (Bobbert et al, 1986; Stefanyshyn and Nigg, 1998). Plyometric training is, by its nature, a form of high magnitude mechanical loading (likely higher than in any resistance exercise), the time durations under which the forces cause tendon strain are rather short with ground contact times mostly under 200 ms during jumping This could possibly explain why different plyometric loading regimens have not always demonstrated that rapid muscle strength adaptations (Saez de Villarreal et al, 2010) are accompanied by similar adaptive responses in tendons (Burgess et al, 2007; Kubo et al, 2007; Fouré et al, 2009, 2010; Houghton et al, 2013; Bohm et al, 2014; Hirayama et al, 2017). From a practical viewpoint this supports the suggestion that the total jumping volume is a risk factor for tendon overload injuries in elite athletes (Bahr and Bahr, 2014)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
