Viscoelastic properties of short calf muscle-tendon units of older women: effects of slow and fast passive dorsiflexion stretches in vivo

Abstract

Changes in connective tissues of the skeletal muscle-tendon unit (MTU) of aging animal muscles have been associated with increased passive viscoelastic properties. This study examined whether similar changes in the viscoelastic properties were present in short calf MTUs of older women in vivo. Fifteen women 68-87 years of age with short calf MTUs, as represented by limited active dorsiflexion (DF) range of motion (ROM) of < or =5 degrees, and 15 women 20-26 years of age without decreased DF ROM participated. A Kin-Com dynamometer stretched the MTU from plantarflexion to maximal DF at the slow velocity of 5 degrees s(-1) (0.087 rad s(-1)) and the fast velocity of 120 degrees s(-1) (2.094 rad s(-1)) with minimal surface electromyogram activity in the soleus, gastrocnemius, and tibialis anterior muscles. Two-way analysis of variance (ANOVA) tests for repeated measures (Velocity x Group) indicated that all women showed greater passive torque, average passive elastic stiffness, and total absorbed passive elastic energy for the fast stretch than for the slow stretch (P < 0.001). The older women had greater percent increases for the average passive torque (30%) and total absorbed passive elastic energy (26%) for the fast stretch than the younger women (P < 0.05), who had 17.5 and 13% increases, respectively. The older women had less maximal and average passive torque (Nm) and total absorbed passive elastic energy (degrees Nm), but greater average passive elastic stiffness (Nm degrees (-1)) at both stretch velocities (P < 0.001). The results indicated that short calf MTUs of older women have increased passive viscoelastic properties that could have implications for balance and ambulatory function.

Adaptational responses of the human Achilles tendon by modulation of the applied cyclic strain magnitude

“…At this ankle joint angle, the passive joint moment can achieve values between 20 and 30·Nm (Riener and Edrich, 1999;Mullaney et al, 2006). Moreover, due to the viscoelastic behaviour of the connective tissues, in a dorsiflexed position the passive ankle joint moments may be higher in a dynamic condition (Gajdosik et al, 2005) such as walking. Studies examining the EMG activity of the triceps surae muscles while walking reported values between 19 and 42% of the maximal isometric EMG value (Ericson et al, 1986).…”

Accuracy of Biodex system 3 pro computerized dynamometer in passive mode

“…Computerized dynamometers have often been used in passive mode to assess passive musculo-articular properties [7][8][9][10][11][12][13][14][15][16][17][18]. However, to our knowledge, the accuracy of the measurements provided by dynamometers under these conditions has not been demonstrated.…”

“…Consequently, our results demonstrated that the Biodex system 3 pro performed reliable and valid torque measurements during passive stretching at different velocities. This tool would be suitable to perform clinical studies, for instance, to assess the effects of ageing [12] or spasticity [13][14][15][16][17][18] on passive musculo-articular properties determined at different angular velocities.…”

“…In this study, the accuracy of torque measurements was demonstrated, but only in a static (isometric) condition at a given angle. However, computerized dynamometers can also be used to assess musculo-articular mechanical properties using the torque-angle relationship obtained under a given range of motion by passively stretching the studied joint [7][8][9][10][11] for various preset velocities [12][13][14][15][16][17][18]. During passive movement, torque levels are lower than during active contractions.…”

“…The reliability of velocity patterns performed under these conditions has not been assessed experimentally. Since resistance offered by the musculo-articular complex is angle [7,22] and velocity [12][13][14][15][16][17][18] dependent, it would be quite prejudicial to the results if the dynamometer did not perform identical patterns during cyclic stretching series or between two experimental sessions. Moreover, Rabita et al [14] have shown that their dynamometer (Cybex) was not effectively able to reach preset velocities higher than 180 • s −1 over a range of motion of 40 • .…”