Lower calf raise efficiency in obesity is partially related to higher triceps surae MTU passive stiffness, hysteresis, and reduced relative strength

The objective of this study was to assess the efficiency of calf raise exercise in individuals with obesity, and to what extent this is related to the structural and mechanical properties of the triceps surae muscle-tendon-unit (MTU). In 22 obese (body mass index; BMI, 32.2 ± 1.5 kg/m²) and 22 nonobese (BMI, 23.3 ± 1.5 kg/m²) men we measured anthropometric parameters, gas exchange, heart rate, and rating of perceived exertion in sitting, standing, and during a self-paced 30-s calf raise exercise. Maximal voluntary isometric contraction of the plantar flexor muscles and passive resistive torque of the triceps surae MTUs were measured using an isokinetic dynamometer. B-mode ultrasound imaging of plantar flexor muscles and Achilles tendon was also performed. Individuals with obesity exhibited a greater metabolic energy cost during standing and calf raise exercise, and a lower exercise efficiency and ankle mobility (<i>P</i> < 0.05). Plantar flexor MTUs stiffness and hysteresis were greater, whereas gastrocnemius-medialis tendon strain was lower in subjects with obesity compared with controls (<i>P</i> < 0.05). There was a negative correlation between calf raise exercise net efficiency, plantar flexor MTUs hysteresis (<i>r</i> = 0.38; <i>P</i> < 0.05), and the body mass by maximal voluntary isometric torque ratio (<i>r</i> = 0.41; <i>P</i> < 0.05). These observations indicate that increased musculotendinous stiffness and hysteresis, together with a lower strength to body mass ratio, are among the factors contributing to higher metabolic energy costs, and lower exercise efficiency in individuals with obesity.<b>NEW & NOTEWORTHY</b> Obesity is associated with greater triceps surae muscle-tendon stiffness, hysteresis, and a lower muscle strength to body mass ratio that, reduce calf raise efficiency, contributing to reduced exercise tolerance in individuals with obesity.