Assessing Anterior Crural Muscle Function

In vivo maximal isometric torque of the anterior crural muscles was assessed as previously described (13 (link), 18 (link), 27 (link), 29 (link)). The anaesthetized mouse (see above) was placed on a temperature-controlled platform to maintain rectal body temperature at 37°C, and the left knee was clamped and the left foot was secured to an aluminum footplate that is attached to the shaft of the servomotor system (Model 300B-LR; Aurora Scientific, Aurora, Ontario, Canada). Contractile function of the anterior crural muscles was assessed by measuring isometric torque as a function of stimulation frequency (20–300 Hz; 150-ms train with 0.1-ms pulses). The anterior crural muscles were then injured by performing 50 electrically stimulated maximal ECC contractions. During each ECC contraction the foot was passively moved from 0 deg (positioned perpendicular to tibia) to 19° of dorsiflexion where the anterior crural muscles performed a pre-lengthening 100 ms isometric contraction followed by an additional 20 ms of stimulation while the foot was moved from 19° of dorsiflexion to 19° of plantarflexion at 2000 deg s⁻¹. A 5-min rest following the ECC contraction protocol was given prior to reassessing contractile function via the aforementioned torque-frequency protocol.