Co‐activity during maximum voluntary contraction: a study of four lower‐extremity muscles in children with and without cerebral palsy

Abstract

This study was designed to determine whether children with cerebral palsy (CP) showed more co-activity than comparison children in non-prime mover muscles with regard to the prime mover during maximum voluntary isometric contraction (MVIC) of four lower-extremity muscles. Fourteen children with spastic diplegic CP (10 males, four females; age range 4-10y), seven children with spastic hemiplegic CP (five males, two females; age range 5-10y), and 14 comparison children (eight males, six females; age range 4-11y) participated in the study. Gross Motor Function Classification System levels of the children with CP were as follows: eight children at Level I, seven children at Level II, five children at Level III, and one child at Level IV. Surface electromyographic recordings were made simultaneously from the vastus lateralis (VL), medial hamstrings (MH), tibialis anterior, and lateral gastrocnemius (LG) muscles during maximal voluntary contraction. Children with CP showed higher co-activity than the comparison children in both antagonist and adjacent muscles. This was particularly true when VL, MH, or LG muscles were engaged in MVIC. These findings may contribute to the weakness and abnormal movement patterns seen in CP, and they have implications for treatment.Cerebral palsy (CP) is a multisymptomatic, non-progressive disorder caused by an early insult to the developing brain. The motor dysfunction includes features such as retained developmental reactions, spasticity, dyskinesias, secondary musculoskeletal conditions, excessive muscle co-contraction, central dyscoordination, and paresis. 1 Recently, the impact of multiple neurological symptoms and deficits has been acknowledged and a new definition and classification has been presented. 2 The focus of rehabilitation has changed considerably over the past century; in the first half of the century, treatment entailed muscle stretching and strengthening, application of orthoses, and functional skill training. This was abandoned when concern arose that strength training caused undesirable spasticity. Subsequently, assumptions about the relationships between strength and spasticity were refuted. 3 Current renewed attention to strengthening is supported by evidence for positive functional benefits of strength training. [4][5][6] Although several studies point to the presence of weakness in children with CP, 7-9 the mechanism behind this weakness is not fully understood and probably results from multiple factors. 10 Weakness could be caused by an inability to activate agonist muscles voluntarily, 8,11,12 changes in contractile and non-contractile muscle morphology, 13,14 or excessive antagonist muscle co-contraction or co-activation, effectively reducing force or torque-generating capacity. 7,8,11 Analysis of agonist/ antagonist pairs in lower-extremity muscles shows increased co-contraction or co-activity to varying extents in selected muscles in participants with CP compared with those in healthy participants. 7,8,11 A reduced ability to activate intended muscles and in...

Changes in Muscle Activation Following Ankle Strength Training in Children with Spastic Cerebral Palsy: An Electromyography Feasibility Case Report

“…The participant could essentially turn "off' the muscle when it was not required. These results support the idea that the methods of the present study could be used to test the hypothesis that decreasing excessive activation in antagonist muscles could positively impact functional performance (Damiano et al, 2000;Tedroff, Knutson, & Soderberg, 2008). Co-activation data were collected and investigated; however, the outcomes did not contribute in any way to the elucidation of the results (e.g., participant 2 did not yield any coactiva tion numbers for items 53,54,56, and 76 during both the initial and final session).…”

The role of co-activation in strength and force modulation in the elbow of children with unilateral cerebral palsy

“…Our results are in line with studies reporting decreased strength and increased coactivation in patients with CP (Ikeda et al, 1998;Elder et al, 2003;Tedroff et al, 2008). Moreover, our participants were weaker in elbow flexion than extension, combined with higher coactivation in TB than in BB, but there was no difference between the affected and the contralateral arm according to this.…”

“…Coactivation is the concurrent activation of agonist and antagonist muscles around a joint and excessive presence of this phenomenon could imply an inherent reciprocal action by the neuromuscular system and can be seen as a form of muscle overactivity (Sheean and Mcguire, 2009). Indeed, reduced strength and increased coactivation are reported in CP compared to typically developing peers (Damiano et al, 2000;Tedroff et al, 2008). Besides its possible strength-limiting effect, coactivation may also represent a motor control strategy in situations with a need of increased joint stability or improved movement accuracy (Gribble et al, 2003).…”

Method and strain rate dependence of Achilles tendon stiffness

“…For example, in clinical populations where patients with neuromuscular or musculoskeletal disorders may be unable to perform a maximal voluntary contraction (MVC) reliably (Tedroff et al, 2008), it may be more appropriate to use the passive method. The primary advantage of this method is that it allows for both tendon stiffness and muscle stiffness to be estimated (Morse et al, 2008).…”