Abstract
Introduction: During running and jumping activities, elastic energy is utilized to enhance muscle mechanical output and efficiency. However, training-induced variations in tendon spring-like properties remain under-investigated. The present work extends earlier findings on sport-specific profiles of tendon stiffness and cross-sectional area to examine whether years of distinct loading patterns are reflected by tendons' ability to store and return energy.Methods:Ultrasound scans were performed to examine the morphological features of knee extensor and plantar flexor muscle-tendon units in elite ski jumpers, distance runners, water polo players, and sedentary controls. Tendon strain energy and hysteresis were measured with combined motion capture, ultrasonography, and dynamometry.Results: Apart from the fractional muscle-to-tendon cross-sectional area ratio being lower in the knee extensors of ski jumpers (−31%) and runners (−33%) than in water polo players, no difference in the considered muscle-tendon unit morphological features was observed between groups. Similarly, no significant difference in tendon energy storage or energy return was detected between groups. In contrast, hysteresis was lower in the patellar tendon of ski jumpers (−33%) and runners (−30%) compared to controls, with a similar trend for the Achilles tendon (significant interaction effect and large effect sizes η2 = 0.2). Normalized to body mass, the recovered strain energy of the patellar tendon was ~50% higher in ski jumpers than in water polo players and controls. For the Achilles tendon, recovered strain energy was ~40% higher in ski jumpers and runners than in controls.Discussion: Advantageous mechanical properties related to tendon spring-like function are observed in elite athletes whose sport require effective utilization of elastic energy. However, the mechanisms underpinning the better tendon capacity of some athletes to retain elastic energy could not be ascribed to intrinsic or morphological features of the lower limb muscle-tendon unit.
Highlights
During running and jumping activities, elastic energy is utilized to enhance muscle mechanical output and efficiency
The different tendon cross-sectional areas (CSA) found between athletes (Rosager et al, 2002; Kongsgaard et al, 2005) or the different tendon stiffness measured in athletes specialized in different types of running (Arampatzis et al, 2007) seem to support the hypothesis of functionally driven tendon adaptations
Muscle fascicles of the vastus lateralis were significantly longer in water polo athletes than in runners [+27%, Q(4;35) = 2.71, P = 0.048, η2 = 0.02] but differences between other groups did not reach significance [main effect: F(3;35) = 2.66, P = 0.064, η2 = 0.19]
Summary
During running and jumping activities, elastic energy is utilized to enhance muscle mechanical output and efficiency. The different tendon cross-sectional areas (CSA) found between athletes (Rosager et al, 2002; Kongsgaard et al, 2005) or the different tendon stiffness measured in athletes specialized in different types of running (Arampatzis et al, 2007) seem to support the hypothesis of functionally driven tendon adaptations Such studies have far focused on certain variables (e.g., tendon morphology) or certain activities (e.g., running), preventing a broader interpretation of training-induced tendon adaptations. Decreases in hysteresis measured following plyometric or resistance training indicate that these forms of exercise are effective in reducing the energy lost during the recoil of the patellar (PT) (Reeves et al, 2003b) and Achilles tendons (AT) (Kubo et al, 2002, 2012; Fouré et al, 2010) Beyond these interesting findings and the increase in stiffness typically observed after such interventions, the long-term optimization of tendon properties to store and return energy remains underinvestigated
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