Fig. 1

Experimental timeline. Young (n = 10) and old (n = 11) rats underwent 2 weeks of unilateral casting in full plantar flexion followed by 4 weeks of ambulatory recovery in a “double-cage” setup. Ultrasound measurements (A) were performed weekly. Mechanical testing (B) (construction of a passive and active torque-angle relationship) of the plantar flexors was performed pre-cast, after the 2-week casting intervention, and at 4 weeks of recovery. Post-cast, 5 young and 5 older adult rats were sacrificed for serial sarcomere number (SSN) measurements (C). The remaining 5 young and 6 older adult rats were sacrificed after 4 weeks of recovery for SSN measurements