Eleven studies (10 empirical with 130 participants, and 1 review) were included. Of the 10 empirical studies, one was a randomised controlled trial (RCT) and 9 were observational studies that used a repeated-measures, single-group design. Six of the observational studied had no control data with which to evaluate the effects of strengthening exercise on participants with CP.
The median PEDro score for empirical studies was 4 (interquartile range 3 to 5).
Changes in strength (10 empirical studies, 15 comparisons): 8 studies (11 comparisons) reported strength increases as a result of the strength-training programme, with effect sizes ranging from 1.16 (95% CI: 0.11, 2.21) to 5.27 (95% CI: 4.69, 5.85).
Activity (4 studies, 7 comparisons): 2 studies (2 comparisons) reported improvements in activity, with effect sizes ranging from 1.0 (95% CI: 0.33, 1.67) to 1.22 (95% CI: 0.18, 2.26).
Participation: none of the 10 studies measured the effect of a strengthening programme on participation limitation.
Other outcome measures: one study reported an improvement in self-perception.
No negative effects, such as reduced range of motion (4 studies) or spasticity (2 studies), were reported. There was insufficient evidence from which to draw conclusions about the effects of environmental and personal contextual factors.
Results of the included review: one RCT and 6 case series (without concurrent or historical controls) were included, all of which reported positive results on strength increases; none reported negative effects. The authors concluded that the relationship between strength gains and improvement in function remained unclear.