AIM To evaluate the effectiveness of functional progressive resistance exercise (PRE) strength training on muscle strength and mobility in children with cerebral palsy (CP).METHOD Fifty-one children with spastic uni-and bilateral CP; (29 males, 22 females; mean age 10y 5mo, SD 1y 10mo, range 6y 0mo-13y 10mo; Gross Motor Function Classification System levels I-III) were randomized to the intervention group (n=26) or the control group (n=25, receiving usual care). The intervention group trained for 12 weeks, three times a week, on a five-exercise circuit, which included a leg-press and functional exercises. The training load progressively increased based on the child's maximum level of strength, determined by the eight-repetition maximum. Muscle strength (measured with hand-held dynamometry and a six-repetition maximum leg-press test), mobility (measured with the Gross Motor Function Measure, two functional tests, and a mobility questionnaire), and spasticity (measured by the appearance of a catch) were evaluated before, during, directly after, and 6 weeks after the end of training by two blinded research assistants.RESULTS Directly after training, there was a statistically significant effect (p<0.05) on muscle strength (knee extensors +12% [0.56N ⁄ kg; 95% confidence interval {CI} 0.13-0.99]; hip abductors +11% [0.27N ⁄ kg; 95% CI 0.00-0.54]; total +8% [1.30N ⁄ kg; 95% CI 0.56-2.54]; six-repetition maximum +14% [14%; 95% CI 1.99-26.35]), but not on mobility or spasticity. A detraining effect was seen after 6 weeks.INTERPRETATION Twelve weeks of functional PRE strength training increases muscle strength up to 14%. This strength gain did not lead to improved mobility.Cerebral palsy (CP) describes a group of disorders in the development of movement and posture, causing activity limitation, that are attributed to non-progressive disturbances that occurred in the developing brain. 1 It is the most common cause of movement disability in childhood. Children with CP may experience a variety of impaired muscle functions, such as spasticity, muscle weakness, and loss of selective motor control. Although all impaired muscle functions limit the performance of daily life activities and participation in a child with CP, a recent study has shown that muscle weakness showed a stronger association with mobility limitations in children with CP than spasticity. 2 Strength training for these children is, therefore, expected to improve or maintain their mobility.Until recently, strength training in children with CP was discouraged as it was assumed that it would increase spasticity. However, this was not supported by the results of earlier uncontrolled studies which showed that strength training can improve lower-limb muscle strength in children with CP without increasing spasticity. 3,4 Although studies have shown there to be sufficient evidence for its effectiveness on muscle strength, these effects are probably overestimated because of the low methodological quality of the studies. 5,6 The few uncontrolled studies that have evalua...