Effect of strength training on musculotendinous stiffness in elderly individuals

The present study deals with the question whether 24-week strength training alters neuromechanical properties of plantar flexors in elderly people (73-83 years). The first purpose of the present study was to evaluate the effect of strength training on musculotendinous (MT) stiffness of the triceps surae (TS). The training was performed twice per week and mainly consisted of three series of ten repetitions of calf-rise and leg-press exercises at 75% of the three-repetition maximum. Using quick-release movements at different levels of submaximal torques performed measurements of MT stiffness. Surface electromyograms (EMG) of each part of the TS and the tibialis anterior were also recorded. A stiffness index (SI), defined as the slope of the angular stiffness-torque relationship (SI(MT-Torque)), was used to quantify changes in MT stiffness. Results showed a significant decrease in SI(MT-Torque) by 25.2% following training (P < 0.05). The second purpose of the study was to evaluate whether neural mechanism has influences on this decrease. Therefore, an activation SI, defined as the slope of the angular stiffness-EMG relationship (SI(MT-EMG)) was used to overcome the influence of changes in agonist activity, and thus to quantify changes in MT intrinsic elastic properties. SI(MT-EMG) only decreased by 11.2% following training (P < 0.05). The present results underlined that MT stiffness decreases following training in elderly individuals, counterbalancing the effect of ageing. These changes seem not only to be due to peripheral but also to neural adaptations.