Despite the lack of consensus of the role of spasticity in the observed motor disability in cerebral palsy (CP), alleviation of spasticity remains a primary focus in the clinical management of these patients. The purposes of this study were to: (1) quantify voluntary torque and passive resistance across speeds in the hamstrings and quadriceps muscle groups with respect to the presence of stretch responses and/or passive muscle stiffness in patients with CP compared to age-related children without disability, and (2) relate these parameters to each other and to functional performance, as measured by the Gross Motor Function Measure (GMFM), in CP. Included were 23 subjects with CP, sub-grouped by the presence or absence of stretch responses as determined by electromyography, and 9 subjects without CP. Results indicated that peak torque was considerably greater in the comparison group than for each of the CP groups and resistance was greater in the CP group with spasticity compared to the nonspastic CP group in both muscles at all speeds. Stiffness differed between the spastic CP group and the comparison group only for the quadriceps at the fastest speed. Higher passive resistance torque and stiffness were correlated with decreased voluntary torque, particularly for the antagonists, and with lower GMFM scores. In conclusion, strength and motor function are related to the magnitude of resistance torque and stiffness in CP, although the small amount of variance explained reinforces the multidimensional nature of this disorder, and the challenges inherent in managing it.

This study aimed to explore the limitations of the Ashworth scale for measuring spasticity. An isokinetic dynamometer to quantify resistance to passive stretch and surface EMG was used to verify if a stretch response occurred and, if so, at what joint angle. The authors sought to determine which components of passive resistance (magnitude, rate of change, onset angle of stretch, or velocity dependence) were most related to Ashworth scores and which were related to motor function in cerebral palsy (CP). Twenty-two individuals with spastic CP (11 males, 11 females; mean age 11.9 years, SD 4.3) and a comparison group of nine children without CP (four males, five females; mean age 11.3 years, SD 2.5) participated in the study. The group with CP included those with a diagnosis of spastic diplegia, hemiplegia, or quadriplegia, distributed across Gross Motor Functional Classification Levels. Procedures included: (1) clinical assessment at the knee joint, (2) functional assessments, and (3) isokinetic assessment of passive resistance torque in hamstrings and quadriceps at three velocities. EMG data were recorded simultaneously to identify stretch responses. Detecting stretch responses using the Ashworth scale compared with instrumented measures showed near complete agreement at extremes of the scale, with marked inconsistencies in mid-range values. Ashworth scores were correlated with instrumented measures, particularly for the quadriceps, with higher correlations to the rate of change in resistance (stiffness) and onset angle of stretch than to peak resistance torque. Those with greater resistance tended to have poorer function with isokinetic relations typically stronger.

This study aimed to explore the limitations of the Ashworth scale for measuring spasticity. An isokinetic dynamometer to quantify resistance to passive stretch and surface EMG was used to verify if a stretch response occurred and, if so, at what joint angle. The authors sought to determine which components of passive resistance (magnitude, rate of change, onset angle of stretch, or velocity dependence) were most related to Ashworth scores and which were related to motor function in cerebral palsy (CP). Twenty‐two individuals with spastic CP (11 males, 11 females; mean age 11.9 years, SD 4.3) and a comparison group of nine children without CP (four males, five females; mean age 11.3 years, SD 2.5) participated in the study. The group with CP included those with a diagnosis of spastic diplegia, hemiplegia, or quadriplegia, distributed across Gross Motor Functional Classification Levels. Procedures included: (1) clinical assessment at the knee joint, (2) functional assessments, and (3) isokinetic assessment of passive resistance torque in hamstrings and quadriceps at three velocities. EMG data were recorded simultaneously to identify stretch responses. Detecting stretch responses using the Ashworth scale compared with instrumented measures showed near complete agreement at extremes of the scale, with marked inconsistencies in mid‐range values. Ashworth scores were correlated with instrumented measures, particularly for the quadriceps, with higher correlations to the rate of change in resistance (stiffness) and onset angle of stretch than to peak resistance torque. Those with greater resistance tended to have poorer function with isokinetic relations typically stronger.

Children with CP have diminished eccentric as well as concentric peak torques at the knee and ankle. The influence of spasticity on voluntary force production can be inferred from the bias toward greater eccentric torque and the greater decrement in concentric torque across speeds in children with spastic CP.