Plantar flexor voluntary activation capacity, strength and function in cerebral palsy

Area of Science:

• Neurology
• Rehabilitation Medicine
• Movement Science

Background:

• Distal lower limb motor impairment in cerebral palsy (CP) affects gait mechanics.
• The specific contribution of muscle activation deficits to reduced gross motor function (GMF) in CP remains unclear.

Purpose of the Study:

• To investigate deficits in plantar flexion voluntary activation capacity in individuals with CP compared to typically developed (TD) peers.
• To evaluate the relationships between voluntary activation capacity, muscle strength, and GMF in CP.

Main Methods:

• Plantar- and dorsiflexion strength assessed via dynamometry.
• Voluntary activation capacity measured using the interpolated twitch technique with tibial nerve stimulation.
• GMF evaluated using standardized tests including the timed upstairs, 10m walk, muscle power sprint, and six-minute walk tests.

Main Results:

• Individuals with CP exhibited significantly lower plantar flexion (55.6%) and dorsiflexion (60.7%) strength compared to TD peers.
• Plantar flexion voluntary activation capacity was 17.9% lower in CP, but nearly half achieved activation within the TD range.
• Plantar flexion voluntary activation capacity did not correlate with strength or GMF in high-functioning individuals with CP (GMFCS I-II).

Conclusions:

• Plantar flexion activation capacity is not a strong predictor of weakness or reduced GMF in high-functioning individuals with CP.
• Muscle size may be a more significant factor in weakness than voluntary activation capacity in this population.
• The relationship between muscle activation and functional capacity in CP is complex, influenced by multi-joint effects.