Passive stiffness of the gastrocnemius muscle in athletes with spastic hemiplegic cerebral palsy.

The passive properties of the muscle-tendon unit are regularly assessed in individuals with cerebral palsy (CP). However, no information is available on the passive properties of adult muscle, and whether any differences exist between the paretic and control muscles. Eleven ambulant male athletes with spastic hemiplegic CP (21.2 ± 3.0 years) and controls without neurological impairment (age = 21.8 ± 2.2 years) completed two and one passive stretch session, respectively. During each session, the ankle was passively dorsiflexed until end range of motion (ROM), whilst recording passive ankle angle, torque and gastrocnemius medialis (GM) myotendinous junction (MTJ) displacement. In addition, GM cross-sectional area (CSA) and length were measured. Subsequently, in vivo stress and strain were determined to calculate elastic modulus. Passive stiffness, MTJ displacement and ROM of the paretic GM were not different from the control muscles. However, the elastic modulus of the paretic GM was two times stiffer than the control GM muscles. In conclusion, athletes with CP exhibit absolute passive muscle stiffness similar to the controls; however, the elastic modulus of the CP muscle was significantly greater. Therefore, throughout the same ROM a smaller GM CSA in CP athletes has to dissipate larger relative torque compared to the control muscles, consequently causing the muscle to elongate to the same extent as the non-paretic muscle under stretch.

The effect of the oral contraceptive pill on the passive stiffness of the human gastrocnemius muscle in vivo.

The aim of this investigation was to determine the effect of sustained monophasic oral contraceptive pill (MOCP) use on the in vivo passive stiffness of the gastrocnemius medialis (GM) muscle-tendon unit. Twenty four females volunteered for this study (age range 20-25 yrs); twelve participants had been taking the combined MOCP for a minimum of 12 months, and twelve participants, who had never taken the MOCP, formed a control group. Distal displacement of the GM myotendinous junction (MTJ) was measured during passive dorsiflexion at 2 Nm increments to 20 Nm, and at end range of motion using ultrasonography. In addition, GM MTJ displacement was measured at passive torques equivalent to 5, 10 and 15% of plantarflexion maximal voluntary contraction (MVC) torque, and relative to GM length. MOCP users had significantly greater GM MTJ displacement at all passive torques (P<0.01), reaching 40% more at 20 Nm; these displacements remained significantly different when MVC and GM length were accounted for (P<0.01). Passive muscle stiffness from 0-20 Nm was 31% less in MOCP users compared to non-users (P<0.01). In conclusion, based on the in vivo assessment of GM MTJ displacement, passive muscle stiffness is less in MOCP using females, compared to non-pill users.