Potential participants were identified from the medical records of habilitation centres around Göteborg. Inclusion criteria were bilateral spastic CP, age 10 to 15 years, and GMFCS levels I and II (walking without aids). Children had to be able to follow instructions and participate in a group. Exclusion criteria were orthopaedic surgery or botulinum toxin injections in the past 12 months. The Ethics Committee at the Medical Faculty at the University of Göteborg approved this study. Written informed consent was obtained from parents of each participant.
Examination before and after a period of muscle strength training consisted of: muscle strength measurement, GMFM, 3D gait analysis, joint range of motion (ROM) measurement, and grading of spasticity. In terms of the International Classification of Functioning, Disability and Health,22 these methods measure ‘body function’ (muscle strength, 3D gait analysis, ROM, and spasticity) and ‘activity’ (GMFM).
Muscle strength was measured with a handheld device: a myometer (adapted Chatillon dynamometer; Axel Ericson Medical AB, Göteborg, Sweden) using the ‘make’ technique, where the child gradually builds up force against the myometer for about 5 seconds. Three attempts were made for each muscle group and the maximum-recorded force value was used for data analysis. Lever arm was measured with a tape measure, and torque (Nm) was calculated by multiplying force by the length of each lever arm. Data were also compared to a normative predicted value based on an equation with parameters for age, body weight, and sex.21 Measurements were divided by the predicted value giving a percentage for every muscle group in each child. This made it possible to compare muscle groups and to compare children with different ages and weights. Eight muscle groups were tested (hip extensors, flexors, abductors and adductors; knee extensors and flexors; and ankle dorsiflexors and plantarflexors) with the same testing positions as in the normative study.21 For ankle plantarflexors no normative predicted value was available for children over the age of 9 years.
Gross motor function was tested with GMFM domains D: standing, and E: walking, running, and jumping. The Gross Motor Ability Estimator software which was included in the GMFM-66 version23 was used to calculate a score.
3D gait analysis was carried out with a motion capture system consisting of six infrared cameras (ProReflex Qualisys AB, Göteborg, Sweden) and two Kistler force plates (Kistler 9281C, Kistler Instruments AG, Winterthur, Switzerland) working synchronically at 240Hz. Recordings of motion and calculations were made with the software QtracC version 2.51, QtracV version 2.60, and QGait 2.0 (Qualisys Medical AB, Göteborg, Sweden).24 At least three acceptable trials for each child were collected. Parents confirmed that the performance was representative of their children’s regular gait pattern. 3D gait data were compared with the laboratory reference database for children between 10 and 15 years of age (27 children, mean age 12y 11mo). Gait velocity, stride length, and cadence were compared with age norms.25
ROM was measured in the lower extremities using a regular plastic goniometer (hip extension, hip abduction, knee flexion, popliteal angle, and ankle dorsiflexion). Deviations outside 2 standard deviations from normal values were noted.26,27
Spasticity was tested in four muscle groups with the Ashworth scale:28 0=hypotonus; 1=normal; 2=resistance through less than half ROM; 3=resistance through most of ROM; and 4=difficult to move passively. Examination was done with children lying in a relaxed supine position for hip adductors, hamstrings, and plantarflexors, and in a prone position for rectus femoris. Scores for each child were totalled and divided by number of muscles tested, a method described by Ostensjø et al.29 The summary index was then categorized: no increase (≤1), mild (>1 to ≤2), or moderate (>2).
Muscle strength measurements, GMFM, ROM, and spasticity were tested by two of the authors (MNE, KA who are physiotherapists and gait analysis was carried out by the gait laboratory staff). Testing was performed the week before training started and a week after training. Muscle strength was also tested 2 weeks before training and 2 weeks after training. Mean muscle strength measurements in Nm before, were compared with mean measurements after training.
Before training started there was an individual analysis of each child based on muscle strength measurements and 3D gait analysis, identifying muscles with the most pronounced muscle weakness and most important gait pattern abnormalities (like a small abducting moment in the hip, too much knee flexion during stance, or no power generation in the ankle at push off). This resulted in an individual training programme for each child, containing specific training instructions for four different muscle groups.
The training period lasted for 8 weeks, three times a week: twice a week at home with parental assistance and once a week in a small group with a physiotherapist at the physiotherapy department after school. Children were divided into small training groups based on age. At home they carried out the individual programme with three sets of 10 repetitions for each muscle group: first set easy, second medium, and third with a heavy load – 10 Repetition Maximum (10RM). Resistance was provided by adjustable weight cuffs for the medium and heavy sets. Rubber bands and body weight were used for the easy set and when it was not possible to use weight cuffs. Weight resistance was increased during the training period when the children could do more than 10 repetitions with the 10RM weight.
The group session consisted of a low intensity short warm-up session with a cycle ergometer, rowing machine, or step-up. After initial warm-up, children carried out their individual programmes with strength training exercises. Stretching of hamstrings, rectus femoris, and plantarflexor muscles followed the training session. All meetings ended with a group activity chosen by the children (different games). The sessions lasted for one hour and a half in total. Each child had a training diary, indicating dates and resistance. Group training sessions and decisions on increasing resistance were carried out by two physiotherapists.
Non parametric tests were used as the group was small and data could not be proved to be normally distributed. Gait data for the CP group and laboratory reference database were analyzed with the Mann–Whitney U test. All differences before and after training were analyzed with the Wilcoxon signed rank test except for spasticity grading where the paired sign test was used. Significance level was set at p<0.05. Statistical tests were performed using StatView software (SAS Institute Inc).