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Event-related Potentials During Target-response Tasks to Study Cognitive Processes of Upper Limb Use in Children with Unilateral Cerebral Palsy
Published on: January 11, 2016
Involuntary and voluntary muscle activation in children with unilateral cerebral palsy--relationship to upper limb
Siri Merete Brændvik1, Ann-Kristin G Elvrum, Beatrix Vereijken
1Clinical Services, St. Olavs University Hospital, Trondheim, Norway. siri.brendvik@stolav.no
Insights
In children with cerebral palsy (CP), reduced muscle strength, not spasticity, most strongly impacts upper limb activity. Both factors likely combine to limit daily tasks, with voluntary muscle activation showing the key relationship.
Area of Science:
- Neuromuscular Rehabilitation
- Pediatric Physical Therapy
- Cerebral Palsy Research
Background:
- Cerebral palsy (CP) is characterized by spasticity and reduced strength, impacting motor function.
- The relative contribution of spasticity versus weakness to activity limitations in CP remains unclear.
Purpose of the Study:
- To investigate if involuntary muscle activation (spasticity) and reduced strength independently or jointly affect upper limb activity in children with CP.
- To determine the relationship between muscle activation, strength, and functional performance in the context of CP.
Main Methods:
- Assessed involuntary biceps brachii activation during passive elbow extension at various speeds in 15 children with unilateral CP.
- Measured elbow flexion peak torque (strength) and voluntary biceps brachii activation during maximal voluntary contraction.
- Evaluated bimanual upper limb activity using the Assisting Hand Assessment (AHA).
Main Results:
- Both involuntary (spasticity) and voluntary muscle activation correlated with activity limitations.
- Voluntary muscle activation demonstrated the strongest relationship with activity performance (Spearman's rho = .84).
- Involuntary muscle activation was negatively associated with muscle strength at multiple velocities.
Conclusions:
- Spasticity does not appear to independently limit upper limb activity beyond the effects of reduced strength.
- Muscle weakness and spasticity likely interact to cause activity limitations in children with CP.
- The capacity for voluntary muscle activation is a strong predictor of functional activity performance.
Background:
Spasticity and reduced strength are both primary neuromuscular impairments associated with cerebral palsy (CP). However, it is unclear whether spasticity or reduced strength is the strongest contributor to activity limitations.
Aim:
To study whether involuntary activation of the biceps brachii muscle, in addition to reduced strength, contributes to limitations in upper limb activity in children with CP.
Method:
Fifteen children with unilateral CP (9 males and 6 females, age range 8-17 years) participated in this study. Involuntary activation, reflecting spasticity, was studied as biceps brachii activity during passive elbow extension at four isokinetic velocities (10, 90, 180 and 300°/s). Elbow flexion peak torque, reflecting strength, was measured during maximal voluntary isometric contraction, and concurrent biceps brachii activity was registered reflecting voluntary muscle activation. Bimanual upper limb activity was assessed in the performance domain using the Assisting Hand Assessment (AHA).
Results:
Both involuntary and voluntary muscle activation were related to activity, the former negatively, but voluntary activation showed the strongest relationship (Spearmans rho = .84). Involuntary muscle activation at 10, 90 and 180°/s was negatively related to muscle strength (Spearmans rho = -.63, -.58 and -.62, respectively).
Conclusions:
Our results do not indicate that spasticity affects upper limb activity in addition to strength. Most likely, muscle weakness and spasticity jointly contribute to activity limitations, reflected by the strong relationship between the ability to voluntarily activate a muscle and activity performance.
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