This randomized, within-participant, contralateral-limb-controlled clinical trial will compare individually optimized compliant and rigid stiffness settings of a portable isokinetic knee training robot in children with spinal muscular atrophy. At least 13 children aged 6 to 12 years will be enrolled. For each participant, one leg will be randomly assigned to the compliant setting and the contralateral leg to the rigid setting using sequentially numbered, opaque, sealed envelopes. Both legs will receive the same training volume, number of repetitions, and angular velocity for up to 8 weeks. The primary outcome is the between-setting difference in the change from baseline in peak isokinetic knee-extension torque. Secondary outcomes include knee-extension range of motion, quadriceps cross-sectional area on magnetic resonance imaging, femoral nerve conduction measures, and sit-to-stand performance. Knee pain, suprapatellar skin temperature, fatigue, and other adverse events will be monitored throughout the study.
Age 6 to 12 years.
Diagnosis of spinal muscular atrophy.
Able to maintain an independent seated position.
If receiving disease-modifying treatment, including nusinersen or risdiplam, the participant must have received a stable dose for at least 6 months before enrollment and must not change the treatment regimen during the study.
Any other major disease or medical condition that, in the investigator's judgment, would interfere with safe participation or interpretation of the study results.
The legal guardian declines to provide written informed consent, or the participant is unable to complete the study procedures.
Unable to undergo magnetic resonance imaging or electromyography and nerve conduction testing.
Blood pressure above the 95th percentile for age, sex, and height, as assessed by a clinician.
Parallel
Portable Isokinetic Knee Training Robot With an Individually Optimized Compliant Setting
DeviceThe compliant setting will be individualized within the device's predefined safe stiffness range. At each candidate stiffness, the participant will perform five knee-extension repetitions. The stiffness producing the highest mean peak knee-extension torque while the movement remains painless, without obvious fatigue, and with a stable trajectory will be selected. The assigned limb will then train at this setting for up to 8 weeks, no more than five sessions per week. Each session will use a target angular velocity of 45 degrees per second, an individualized maximum voluntary pain-free range of motion, at least six sets of 10 extension-flexion repetitions per leg, and approximately 1 minute of rest between sets. Training volume will be matched to the contralateral limb.
Portable Isokinetic Knee Training Robot With a Rigid Setting
DeviceThe assigned limb will train with the device's predefined rigid stiffness setting for up to 8 weeks, no more than five sessions per week. Each session will use a target angular velocity of 45 degrees per second, an individualized maximum voluntary pain-free range of motion, at least six sets of 10 extension-flexion repetitions per leg, and approximately 1 minute of rest between sets. Training volume will be matched to the contralateral limb.
Between-setting difference in the change from baseline in peak knee-extension torque
Peak isokinetic knee-extension torque will be measured separately for each limb using the portable isokinetic knee training robot and reported in newton-meters. For each participant, the change from baseline will be calculated for the compliant-setting limb and the rigid-setting limb. The primary outcome is the within-participant difference between these two changes: (post-intervention minus baseline change for the compliant setting) minus (post-intervention minus baseline change for the rigid setting).
Between-setting difference in the change from baseline in active knee-extension range of motion
Active knee-extension range of motion will be measured separately for each limb by the robot and reported in degrees. The outcome is the within-participant difference between the compliant-setting and rigid-setting limbs in change from baseline.
Between-setting difference in the change from baseline in quadriceps cross-sectional area
Quadriceps cross-sectional area will be quantified separately for each thigh using magnetic resonance imaging and reported in square centimeters. The outcome is the within-participant difference between the compliant-setting and rigid-setting limbs in change from baseline.
Between-setting difference in the change from baseline in femoral nerve compound muscle action potential amplitude
Femoral nerve conduction testing will be performed separately for each limb. Compound muscle action potential amplitude will be reported in millivolts. The outcome is the within-participant difference between the compliant-setting and rigid-setting limbs in change from baseline.
Change from baseline in the minimum initial knee angle for successful sit-to-stand performance
The minimum initial knee flexion angle from which the participant can successfully complete an unassisted sit-to-stand task will be measured in degrees. The post-intervention value will be compared with baseline at the participant level.
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