Characteristics of Lower Limb Extension Torque in Repetitive Movements of Individuals with Cerebral Palsy in Classified as GMFCS III – IV

This study aimed to compare the maximum lower limb extension torque and muscle activation patterns between individuals with CP and healthy controls. 

Seven individuals with spastic diplegic CP (mean age: 29.4 ± 12.9 years) in classified as Gross Motor Function Classification System level III–IV and eight healthy controls (mean age: 22.9 ± 1.4 years) were included. For the assessment, CP participants used the lower limb they found most comfortable moving, while healthy controls used their dominant leg. The primary evaluation metric, maximum torque (MT) of the lower limb, was measured using Strength Ergo 240 during 20 repetitions of isokinetic movements at 20 rpm. Torque values from the first and last rotations were excluded, and the MT ratio for each rotation was calculated and divided into three phases (Phase I: 2^nd–7^th rotation, II: 8^th–13^th rotation, III: 14^th–19^throtation) to determine the mean.

Electromyographic activity of the rectus femoris was recorded as the secondary outcome. This signals were sampled at 2000 Hz and corrected using maximum voluntary contraction during isokinetic movement to calculate the root mean square (%RMS) for the extension phase and the time from start of extension to maximum RMS (RT), which was used to investigate muscle activity characteristics during repeated rotation movements. Within-group and between-group comparisons for each phase were tested for normality, followed by two-way repeated measures ANOVA and post-hoc Holm tests. Correlation between MT and RT was confirmed by Pearson's correlation coefficient. Statistical significance was considered as a p-value 0.05.

MT ratios for control group in each phase were 91.91%, 84.35%, and 79.58%, while for the CP group they were 67.78%, 76.68%, and 78.82%. A significant interaction between group and phase was observed (F_2,26=25.0282, p0.001). Post-hoc tests revealed significant differences across all phases in the control group and between phases I and III and phases II and III in the CP group. Additionally, the %RMS values at the extension phase were not significantly lower in the CP group than in the control group. A correlation was observed between MT and RT in the CP group (r=0.567, p=0.007).

Healthy controls exhibited a gradual decline in torque generation, whereas individuals with CP who have limited opportunities to walk demonstrated distinctly different torque generation patterns, especially at the start of movement, suggesting that muscle recruitment at the start of extension was more difficult in the CP group.

This study highlights the need to address challenges in torque generation at the onset of movement in individuals with CP. Additionally, the present protocol proved to be useful for evaluating decrease in torque generation during repeated movements.