Differences in properties of the triceps surea muscle tendon unit in professional dancers and active controls: a cross-sectional s[t]udy with emphasis on stretching exercise

Abstract

Purpose: The purpose of this thesis is to compare structural- and mechanical properties in the triceps surae muscle-tendon unit system (MTU) of professional dancers with >15 years of systematic stretching to a control group consisting of physically active subjects. Method: 20 healthy subjects (dancers n=10, controls n=10) participated and one leg was tested. Ultrasound images (US) of muscle architecture was assessed, including muscle thickness, fascicle pennation angle and fascicle length. US images of tendon (CSA) area and tendon length were analyzed. The elongations of the Free Achilles tendon (free AT) and gastrocnemius medialis tendon (GM tendon) in ramped isometric plantarflexions up to the voluntary maximum were directly measured with ultrasound. Maximal dorsiflexion range of motion (ROM) and passive torque was measured in an isokinetic dynamometer. Young’s modulus and stiffness was assessed. Results: ROM was larger in dancers compared to controls (P < 0.01). Dancers displayed longer GM muscle fascicles (12.8 ± 0.6 mm) than controls (9.5 ± 0.3mm), and thicker GM than controls (Thickness: controls 17.7 ± 2 mm, dancers 21.7 ± 2 mm) with P < 0.01. Both free AT and GM tendons were longer in dancers (GM tendon: 220 ± 32 mm. free AT: 81.7 ± 33) compared to controls (GM tendon: 175 ± 19. Free AT: 55 ± 25) with P < 0.01. No difference was found in free AT CSA, Young’s modulus or mechanical properties. Conclusions: Dancers displayed different structural and morphological properties in the triceps surea MTU compared to controls. It is likely that the differences found in the present study results from substantial differences in stretching exercise volume, frequency and intensity. There were no differences in mechanical properties of the MTU.