Progressive resistance exercise increases strength but does not improve objective measures of mobility in young people with cerebral palsy

Synopsis

Question

Does progressive resistance training (PRT) improve mobility and muscle strength in young people with cerebral palsy (CP)?

Design

Randomised, controlled trial with concealed allocation and blinded outcome assessment.

Setting

Recruitment from a large metropolitan children's hospital and a CP register in Australia.

Participants

Participants had spastic diplegia CP, were aged 14 years to 22 years, had a disability classified as level II or III on the Gross Motor Function Classification System. Exclusion criteria were participation in PRT in the previous six months, single-event multi-level surgery in the previous two years, or contractures more than 20° at the hips and knees. Randomisation of 49 participants allocated 24 to the PRT group and 25 to the control group.

Interventions

The intervention group participated in a twice-weekly, 12-week PRT program performed at community gymnasia. Training was completed alone or in pairs under the supervision of a physiotherapist. Each participant was prescribed four to six individualised exercises, which were targeted to address deficits that had been identified by instrumented gait analysis, supplemented by clinical assessment. Participants completed three sets of 10 to 12 repetitions of each exercise at an intensity of 60% to 80% of one repetition maximum (RM). The control group continued with their usual recreation and physiotherapy provided it did not include PRT.

Outcome measures

The primary outcome was the six-minute walk test at week 13 and at week 24. Secondary outcome measures assessed objective mobility-related function (self-selected walking speed, timed stairs test, Gross Motor Function Measure (GMFM-66) dimensions D and E, Gait Profile Score), participant-rated mobility (Functional Mobility Scale, Functional Assessment Questionnaire) and muscle performance (1-RM) of leg press and reverse leg press).

Results

Forty-eight participants completed the study. After 12 weeks of training, there was no difference between the groups for the six-minute walk (0.1 m, 95% CI -20.6 to 20.9), stairs test (-0.9 s, 95% CI -4.7 to 2.9), GMFM dimension D (-1.3%, 95% CI -4.8 to 2.4) and E (0.9%, 95% CI -3.0 to 4.7), and reverse leg press 1-RM (-0.7 kg, 95% CI -4.3 to 2.8). The intervention group showed significant improvement in the Functional Mobility Scale at 5 m (0.6 units, 95% CI 0.1 to 1.1), the Functional Assessment Questionnaire (0.8 units, 95% CI 0.1 to 1.6) and leg press 1-RM (14.8 kg, 95% CI 4.3 to 25.3), compared with the control group. At week 24, there were no differences between the groups for any outcome. The groups did not significantly differ for the remaining secondary outcomes at either time-point.

Conclusion

Individualised PRT increases strength in young people with CP. The participants thought their mobility had improved, although objectively it had not.

Commentary

Is this study another ‘death knell’ for the use of strengthening to improve mobility in cerebral palsy (CP) (Scianni et al 2009) or are there alternative explanations that we are missing? This randomised, controlled trial (RCT) in young people with CP improved strength in targeted muscles but failed to improve mobility. The investigators are experts on CP, the study design is exemplary, the outcome measures are well chosen and the compliance is excellent. They concluded that the participants gained only what they practised (ie, strengthening exercises, not gait).

These results are nearly identical to Scholtes et al (2012), which was another well-conducted RCT. These studies have notable similarities. Strength gains were modest (11% to 27%) in comparison to other studies (Steele et al 2012, Damiano et al 2010) and were likely to have been insufficient to produce measurable functional change. Both utilised resisted functional exercises involving multiple muscle groups; this approach may not adequately target the desired muscles, especially if selective control is compromised (Verschuren et al 2011) – single-joint exercises might be a better alternative. It may also inadvertently strengthen non-desired muscles, leading to greater muscle imbalance and contracture in some participants (Scholtes et al 2012, Dodd et al 2002, Damiano et al 2010), which could negate the potential benefits. Muscles that tend to develop contractures in CP were among those strengthened here. Perhaps CP warrants a more precise approach to weakness and muscle imbalance, providing justification that physiotherapists have input into these programs.

Whilst strengthening guidelines (6 to 15 repetitions, one to three sets, two to three times/week, for eight to twenty weeks) were clearly met here, strengthening should optimally be lifelong in people with CP. Irrefutable evidence supports the multiple health benefits of strengthening. People with physical disabilities such as CP are more sedentary, weaker and more likely to experience functional deterioration in adulthood than others, unless they remain physically active (Ando and Ueda 2000), so it could be devastating to insinuate that strengthening is not helpful. Instead, we as therapists need to ensure that individuals with CP are strengthening the correct muscles in the right way and that other impairments do not interfere or compete with the functional goals of training.