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Abstract

  1. Top of page
  2. Abstract
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Aim

The aim of this study was to investigate whether individualized resistance training improves the physical mobility of young people with cerebral palsy (CP).

Method

Forty-eight participants with spastic diplegic CP (26 males, 22 females; mean age 18y 1mo, SD 1y 11mo) classified as level II or III on the Gross Motor Function Classification System were allocated randomly to progressive resistance training or usual-care control. Resistance training was completed twice weekly for 12 weeks at a community gymnasium under the supervision of a physiotherapist. Exercises were based on instrumented gait analysis and targeted muscles contributing to walking difficulties. Outcomes at 12 weeks and 24 weeks included objective measures of mobility (6-min walk test, instrumented gait analysis, and Gross Motor Function Measure dimensions D and E), participant-rated measures of mobility (Functional Mobility Scale and Functional Assessment Questionnaire), and muscle performance.

Results

The strength of targeted muscles increased by 27% (95% CI 8–46%) compared with control group. There were no between-group differences in any objective measure of mobility at 12 weeks (6-min walk test: mean difference 0.1m; 95% CI −21 to 21m) or at 24 weeks. Participant-rated mobility improved (Functional Mobility Scale at 5m: mean 0.6 units; 95% CI 0.1–1.1 units; Functional Assessment Questionnaire: 0.8 units; 95% CI 0.1–1.6 units) compared with control group at 12 weeks.

Interpretation

Individualized progressive resistance training increased strength in adolescents and young adults with spastic diplegic CP. Despite participant-rated benefits, the increased strength did not result in objective improvements in mobility.

What this paper adds
  • Increasing muscle strength does not carry over into objective improvements in mobility in adolescents and young adults with spastic diplegic CP.
  • Resistance training may result in participants perceiving that their mobility has improved.
  • The benefit of resistance training as a therapeutic option to improve mobility in this population remains in doubt.
  • Resistance training may, however, have other psychosocial benefits.

Walking disorders are some of the most frequent and disabling problems associated with spastic diplegic cerebral palsy (CP). Individuals with spastic diplegia typically walk more slowly than their peers without CP[1] and often have difficulty performing activities such as walking up and down a flight of steps, running, or navigating safely over different terrain.[2] Walking ability deteriorates with age in adolescents and young adults with CP.[3] For these reasons, improved walking ability is the primary therapeutic goal for many young people with spastic diplegia and is particularly relevant for adolescents as they prepare to make the transition to adulthood.

Muscle weakness has been identified as one of the primary deficits contributing to motor dysfunction in individuals with CP,[2] and there is a strong relationship between muscle weakness and mobility in people with CP.[4] Some have reported that increased muscle strength through progressive resistance training can carry over into improved mobility.[1, 5] Although these studies have provided important preliminary evidence to suggest that progressive resistance training could improve mobility, the lack of randomization reduces confidence in the findings. Recent randomized controlled trials that have addressed this limitation have not identified changes in mobility after progressive resistance training in young children[6, 7] or in middle-aged adults with CP.[8] However, in these trials, all participants underwent the same exercise programme regardless of their individual presentation. It is also possible that the optimal stage in life to apply an intensive intervention such as progressive resistance training is adolescence and early adulthood. This is a stage when other medical and surgical approaches have been applied but when mobility deteriorates and when participants are mature enough to adhere to this intensive form of exercise.

We aimed to find out if an individualized progressive resistance training programme for the lower limbs can improve mobility-related function of adolescents and young adults with CP who have difficulty walking.

Method

  1. Top of page
  2. Abstract
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

The research design was a single-blind randomized controlled trial of progressive resistance training compared with usual care (control group).

Participants

Participants were recruited through a large metropolitan children's hospital and a CP register. To be included, participants had to have spastic diplegic CP, be aged between 14 years and 22 years, be classified as level II or III on the Gross Motor Function Classification System (GMFCS),[9] and be able to follow simple instructions. Volunteers were excluded if they had participated in a strength training programme in the previous 6 months, had undergone single-event multi-level orthopaedic surgery in the previous 2 years, or if they had contractures of more than 20° at the hip and knees. Relevant ethics committees approved the registered trial (ACTRN12607000553471) and written informed consent was obtained from each participant and/or guardian.

Procedure

A separate randomization procedure was prepared for each stratum (GMFCS levels II and III) using permuted blocks. An independent researcher generated a block allocation sequence for each stratum by drawing pieces of paper from a sealed container and then sealing assignments in sequentially numbered opaque envelopes. The research coordinator allocated participants after enrolment and baseline testing.

Participants allocated to the experimental group completed a twice-weekly, 12-week progressive resistance training programme in a community gymnasium close to home. Participants completed their training on weights machines either singly or in pairs under the supervision of a physiotherapist. Participants completed three sets of 10 to 12 repetitions of each exercise, with a 2-minute break between each set.[10] Participants lifted enough weight such that they could complete only 10 to 12 repetitions before they experienced muscle fatigue. This intensity of training (10–12 repetition maximum) is approximately equal to training at an intensity of 60% to 80% of one-repetition maximum. Participants were instructed that they should feel as though they had worked ‘hard’, scoring at least a 5 on the 0 to 10 category of the Borg Perceived Exertion Scale, which was evaluated at the end of each session.[11] When able to complete three sets of 12 repetitions of an exercise, the weight to be lifted was increased at the next session. Each participant had a logbook detailing each exercise, the weight lifted, the number of repetitions, the number of sets completed, and the details of any injuries. After 12 weeks participants were asked to take a break from resistance training, but to continue with all usual activities until the final testing session at 24 weeks.

Exercises were individualized and targeted to address deficits identified by instrumented gait analysis collected with a 10-camera Vicon system (Oxford Metrics, Oxford, UK) supplemented by the physical examination of joint range of motion and muscle strength. Each participant was prescribed four to six individualized exercises that the panel of at least three members of the research team considered would best address their problems in walking.

Participants allocated to the control group continued with usual care during the intervention period. In that time they could continue with their usual recreation and physiotherapy provided that these did not include progressive resistance training.

Outcome measures

Outcome measures were evaluated at baseline, after the intervention (week 12), and after a further 12 weeks (week 24). Assessments were completed in a hospital gait laboratory by an assessor blinded to group allocation.

The primary outcome measure was the 6-minute walk test. Participants walked as far as they could on a flat standardized course in 6 minutes. The 6-minute walk test has been shown to be highly reliable (intraclass correlation coefficient 0.93–0.98)[12] and responsive in young people with CP with improvements of 86m (31%) in test performance after a 10-week strengthening programme.[5]

The secondary measures of mobility-related function were assessed objectively and comprised self-selected walking speed over 10m, a timed stairs test assessing the ability to go up and down three stairs,[13] and the Gross Motor Function Measure (GMFM-66) dimensions D, which evaluates activities in standing, and dimension E, which assesses walking, running, and jumping activities.[14] The Gait Profile Score provided an overall measure of gait kinematic deviation from normal in degrees, derived from instrumented gait data.[15] We had planned to measure kinematic deviation with the Gillette Gait Index. Although both indices are derived from similar kinematic data, the Gait Profile Score was chosen because it quantifies gait deviation in degrees, whereas the Gillette Gait Index expresses the deviation in a dimensionless unit.

In addition, two participant-rated mobility outcomes were assessed: the Functional Mobility Scale, which describes the level of assistance that children with CP require to cover different distances and environments;[16] and the Functional Assessment Questionnaire, a 10-level report of the level that best describes typical walking ability.[17]

The secondary outcome of muscle performance was assessed using one-repetition maximum of a leg press and a reverse leg press (using the major ‘lift-off’ muscles of hip flexors, knee flexors, and ankle dorsiflexors).[18] A hand-held dynamometer (Nicholas Manual Muscle Tester, Lafayette, LA, USA) was used to assess isometric strength of the targeted muscles for each participant.[19]

Statistical analysis

Sample size calculation was based on an observed effect size of d=0.71 reported for the 6-minute walk distance after resistance training for young adults with CP.[5] To achieve 80% power of detecting a difference with 95% confidence with a two-tailed test, a sample size of 31 participants in each group was required, not allowing for loss to follow-up.

To determine if the progressive resistance training group improved more than the control group, data were analysed with analysis of covariance at 12 weeks and 24 weeks using the baseline measures as covariates, appropriate for longitudinal analysis of parametric and non-parametric data.[20] Ordinal data were also analysed with the appropriate non-parametric test (Mann–Whitney U test) applied to change scores. Dichotomous outcomes were analysed with odds ratios. The intention-to-treat principle was applied, with available data of all participants who were allocated and commenced their programme included in analyses. We had planned to analyse data using the carry-forward method but did not do so because this method may introduce bias.[21] The associations between any significant changes in outcomes were explored using correlation coefficients.

Results

  1. Top of page
  2. Abstract
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Of 49 participants, 24 were allocated to the progressive resistance training intervention and 25 to the control group (Table 1). One participant withdrew from the intervention group after allocation but before the start of training because surgery was scheduled unexpectedly (Fig. 1).

Table 1. Characteristics of participants
CharacteristicExperimental group (n=23)Control group (n=25)
  1. GMFCS, Gross Motor Function Classification System.

Mean age (SD)18y 2mo (1y 11mo)18y 7mo (2y 11mo)
Sex, n males (%)13 (56)13 (52)
Mean height (SD)164.2cm (12.5cm)163.0cm (8.5cm)
Mean weight (SD)55.3kg (13.1kg)62.5kg (15.1kg)
GMFCS level, n (%)
II13 (57)16 (64)
III10 (43)9 (36)
Orthotics, n (%)
Yes8 (35)11 (44)
Gait aid use, n (%)
No gait aid13 (57)15 (60)
Sticks5 (22)5 (20)
Crutches1 (4)3 (12)
Walker4 (17)2 (8)
Previous single-event multi-level surgery, n (%)
Yes11 (48)11 (44)
Mean time since surgery (SD)7y 3mo (3y)7y 6mo (3y 2mo)
Hip morphology, n of hips (%)
Grade I, normal hip1 (2)3 (7)
Grade II, near normal hip23 (52)27 (59)
Grade III, dyplastic hip19 (43)16 (35)
Grade IV, subluxated hip1 (2)0 (0)
image

Figure 1. Flow of participants through the trial. PRST, progressive resistance strength training; GMFCS, Gross Motor Function Classification System.

Download figure to PowerPoint

Participants in the intervention group completed a mean of 21.9 (SD 2.4) of their 24 scheduled training sessions. Participants typically completed four to six exercises during each session. Targeted muscle groups were the knee extensors (n=7), the plantar flexors (n=4), the hip extensors (n=3), the hip abductors (n=2), and generalized extensors, represented by the leg press (n=7). The mean rating of perceived exertion at the end of each session was 6.9 (SD 1.1), equating to a perception that sessions were ‘hard’ to ‘very hard’. Participants increased their training load of exercises for targeted muscles from session 3 to session 24 by a mean of 183% (SD 23%). Baseline data suggest that participants were well matched for factors such as age, sex, height, functional level, previous single-event multi-level surgery, and hip morphology.

Effect of progressive resistance training after 12 weeks

Mobility

After 12 weeks of training, walking performance among participants in the progressive resistance training group had not improved, as measured by the distance they walked in 6 minutes (mean difference 0.1m; 95% CI −20.6 to 20.9m), their self-selected walking speed (mean difference 0.01m/s; 95% CI −0.06 to 0.07m/s), or their stairs test time (mean difference −0.9s; 95% CI −4.7 to 2.9s) compared with the control group (Table 2). There were also no differences between the groups in gait kinematics (gait profile score mean difference 0.2°; 95% CI −0.6 to 0.9°) or in gross motor function (GMFM-D: mean difference −1.3%; 95% CI −4.8 to 2.4%; GMFM-E: mean difference 0.9%, 95% CI –3.0 to 4.7%). A per protocol analysis of the participants who attended at least 21 of their scheduled sessions (n=17) also showed no significant between-group differences in measures of walking performance, gross motor function, or gait kinematics.

Table 2. Mean (SD) of groups, mean (SD) difference within groups, and mean (95% CI) difference between groups for mobility-related function
OutcomeGroupsDifference within groupsDiffererence between groups
wk0wk12wk24wk12–wk0wk24–wk0wk12–wk0wk24 –wk0
Exp (n=23)Con (n=25)Exp (n=23)Con (n=25)Exp (n=23)Con (n=24)ExpConExpConExp–ConExp–Con
  1. Exp, experimental group; Con, control group; GMFM, Gross Motor Function Measure; FAQ, Functional Assessment Questionnaire; FMS, Functional Mobility Scale.

  2. a

    p<0.05.

6-min walk (m)380.7 (117.8)377.4 (114.4)389.3 (120.4)386.0 (110.7)387.7 (121.9)395.1 (123.9)8.6 (40.8)8.6 (30.4)7.0 (36.5)19.3 (38.7)0.1 (–20.6 to 20.9)–12.3 (–34.8 to 10.2)
Self-selected walking speed (m/s1)0.94 (0.34)0.90 (0.30)0.95 (0.34)0.91 (0.29)0.93 (0.33)0.93 (0.30)0.01 (0.13)0.01 (0.09)–0.01 (0.13)0.04 (0.08)0.01 (–0.06 to 0.07)–0.05 (–0.11 to 0.02)
Timed stairs test (s)21.1 (28.9)13.8 (11.7)19.2 (28.5)13.3 (10.1)17.9 (23.2)12.6 (9.1)–1.9 (5.8)–0.5 (6.6)–4.2 (8.9)–1.5 (7.0)–0.9 (–4.7 to 2.9)–0.6 (–4.2 to 3.0)
Gait Profile Score (°)9.9 (2.6)10.6 (3.0)10.2 (3.0)10.7 (3.1)10.0 (2.9)10.5 (3.0)0.3 (1.3)0.1 (1.3)0.1 (1.4)–0.2 (1.3)0.2 (–0.6 to 0.9)0.2 (–0.8 to 1.2)
GMFM-66 Dimension D (%)81.4 (13.0)78.9 (12.5)80.8 (13.1)80.2 (9.7)83.7 (12.6)78.7 (13.7)–0.6 (6.1)1.3 (7.6)2.3 (6.4)0.2 (8.6)–1.3 (–4.9 to 2.4)2.5 (–1.8 to 6.9)
GMFM-66 Dimension E (%)70.2 (22.6)66.6 (20.7)72.1 (21.7)67.9 (20.6)71.9 (23.4)66.3 (20.2)1.9 (6.4)1.3 (6.4)1.7 (6.9)0.8 (4.8)0.9 (–3.0 to 4.7)1.0 (–2.6 to 4.5)
FAQ (0–10)8.0 (1.6)8.3 (1.1)8.6 (1.7)7.9 (1.8)8.0 (2.2)8.1 (1.5)0.5a (0.9)–0.4 (1.3)0.1 (1.4)–0.2 (1.0)0.8a (0.1 to 1.6)0.3 (–0.5 to 1.0)
FMS 5m (1–6)4.6 (1.3)4.7 (1.1)5.1 (1.4)4.6 (1.4)5.0 (1.3)4.6 (1.2)0.5a (0.6)–0.1 (0.1)0.4 (0.8)a–0.1 (0.6)0.6a (0.1 to 1.1)0.4 (= 0.07) (–0.03 to 0.9)
FMS 50m (1–6)4.1 (1.6)4.3 (1.3)4.6 (1.5)4.3 (1.6)4.6 (1.8)4.0 (1.7)0.5 (1.0)–0.05 (0.8)0.4 (1.4)–0.2 (1.1)0.5 (–0.1 to 1.1)0.6 (–0.2 to 1.4)
FMS 500m (1–6)3.9 (1.7)3.4 (2.0)4.0 (2.0)3.5 (2.1)4.1 (2.0)3.4 (2.1)0.1 (0.6)0.1 (1.5)0.1 (1.4)0.2 (1.6)0.04 (–0.7 to 0.8)0.08 (–0.9 to 1.0)

After 12 weeks, the progressive resistance training group showed improvement in participant-rated measures of mobility of the Functional Assessment Questionnaire (mean difference 0.8 units; 95% CI 0.1–1.6 units; Mann–Whitney U test, p=0.02) and the Functional Mobility Scale at 5m (mean difference 0.6 units; 95% CI 0.1–1.1 units; Mann–Whitney U test, p=0.04) (Table 2). More participants in the intervention group (10 of 23) than in the control group (4 of 25) rated that they had improved at least one level on the Functional Assessment Questionnaire (odds ratio 4.03; 95% CI 1.05–15.60). There was a trend for more participants in the intervention group (8 of 23) than in the control group (4 of 25) to improve by at least one unit on the Functional Mobility Scale at 5m (odds ratio 2.80; 95% CI 0.71–11.03). There were no differences in other participant-rated measures of mobility.

Muscle performance

After 12 weeks, muscle strength of targeted muscle groups in the resistance training group had increased by 27% (95% CI 8–46%), and the strength of leg press had increase by a mean of 14.8kg (95% CI 4.3–25.3kg) compared with the control group (Table 3), an average strength increase of 17%. There was no between-group difference in reverse leg press strength (mean difference −0.7kg; 95% CI –4.3kg to 2.8kg). Exploration of the association between change in muscle performance with change in mobility did not demonstrate any significant relationships.

Table 3. Mean (SD) of groups, mean (SD) difference within groups, and mean (95% CI) difference between groups for measures of muscle performance
OutcomeGroupsDifference within groupsDiffererence between groups
wk0wk12wk24wk12–wk0wk24–wk0wk12–wk0wk24–wk0
Exp (n=23)Con (n=25)Exp (n=23)Con (n=25)Exp (n=23)Con (n=24)ExpConExpConExp–ConExp–Con
  1. Exp, experimental group; Con, control group; 1RM, one repetition maximum.

  2. a

    p<0.05.

Increase in strength of targeted muscle groups (%)  27.1 (42.4)0.4 (17.0)27.8 (91.2)6.1 (17.5)    26.7a (7.9 to 45.5)21.7 (–17.3 to 61.7)
1RM leg press (kg)84.7 (34.9)78.4 (31.7)99.5 (37.4)79.1 (31.2)97.7 (41.1)83.0 (29.7)14.8 (20.6)0.7 (14.6)13.1 (28.0)4.2 (16.6)14.8a (4.3 to 25.3)10.0 (–3.6 to 23.6)
1RM reverse leg press (kg)14.8 (10.7)14.2 (10.4)12.8 (10.4)14.2 (11.2)12.4 (11.2)10.3 (10.8)–0.9 (7.1)–0.2 (4.3)–2.3 (6.1)–3.9a (7.1)–0.7 (–4.3 to 2.8)1.6 (–2.3 to 5.6)

Effects of progressive resistance strength training after 24 weeks

Twelve weeks after the end of training, there was no improvement in any objective measures of walking performance, gait kinematics, or muscle performance in participants in the progressive resistance training group compared with the control group. At 24 weeks, participants in the progressive resistance training group showed improvement in the participant-rated Functional Mobility Scale at 5m (mean difference 0.4 units; 95% CI −0.03 to 0.9 units; Mann–Whitney U, p=0.04) compared with the control group.

Safety and adverse events

The most common reasons for missing training sessions were travel or holidays, illness, and difficulty scheduling around other commitments. Short-term muscle soreness was reported by most participants but almost always resolved in a few days without change to training. One participant experienced a minor calf strain and another experienced minor discomfort to the plantar fascia; these injuries resulted in adjustment to their programmes, but did not cause the participants to miss any training sessions.

Discussion

  1. Top of page
  2. Abstract
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

A 12-week programme of individualized progressive resistance training for adolescents and young adults with spastic diplegic CP that led to increased leg muscle strength was not effective in improving objective measures of mobility. Our results complement reports of recent randomized controlled trials investigating resistance training for younger children (aged 6–13y) and middle-aged adults with CP, which also found that strengthening exercise did not improve objective measures of mobility.[6-8] Previous reports not based on randomized controlled designs may have overestimated the effect that resistance training can have on improving mobility.[1, 5]

The progressive resistance training programme that led to strength increases in our trial fulfilled key requirements of resistance training including training intensity, frequency, and duration[10, 22] and was effective in its intended purpose of increasing muscle strength. In addition, participants showed high levels of adherence to the intervention and demonstrated evidence of progression. Therefore, the lack of difference in mobility-related function between the groups was most likely not caused by deficits in the quality of the intervention.

A possible explanation for the lack of objective change in mobility-related function was that resistance training did not provide a sufficient stimulus to change walking or mobility-related function. Walking is a complex task. Although muscle weakness is associated with and can contribute to walking disorders, other impairments, such as impaired motor planning, impaired balance and postural control, spasticity, and limited range, could all affect walking function. Therefore, addressing the single impairment of muscle weakness for a relatively short duration of 12 weeks may not have provided the task-specific practice necessary to improve mobility.[23] Consistent with the principle of specificity of training,[10] our participants appeared to improve what they practised (muscle strength) with little carry-over into skills that they did not practise (walking).

Despite the lack of objective change in mobility, we observed significant improvements in participant-rated measures of mobility. Participants who took part in progressive resistance training perceived that they could walk around the house better, and rated their typical walking ability as improved by almost one unit on the Functional Assessment Questionnaire compared with the control group. Participants who took part in resistance training perceived that their walking had improved, even if, objectively, it had not. Perhaps participants expected to improve because they had enrolled and participated in a programme. It is also possible that resistance training improved the confidence that participants had in their mobility, an interpretation consistent with qualitative analysis.[24] Another possible explanation is that progressive resistance training did improve some aspects of walking that were not detected by the outcomes used in our trial. However, a broad range of measures of mobility were used.

Clinically, our results suggest that prescription of progressive resistance training for adolescents and young adults with spastic diplegic CP may not be effective if the aim is to improve objective measures of mobility. This raises the question of whether resistance training has a role in this population. Even if prescription of progressive resistance training does not improve objective measures of mobility, it could have other important psychosocial benefits such as improved perception of mobility. In addition, the intervention was safe and feasible, so it could be seen as part of a community recreation programme that could help young people with CP get stronger and achieve physical activity guidelines. Guidelines for the maintenance of good health recommend that young adults, including those with disabilities, should perform muscle strengthening activities on two or more days a week.[25]

The main strength of the current study is that it is a single-blinded randomized controlled trial. In addition, the trial has addressed issues thought to be possible explanations as to why previous programmes may not have been optimal by targeting the intervention to adolescents and young adults who are developmentally suited to the intervention of resistance training, and by individualizing the programme to muscles assessed as those most likely to be contributing to walking difficulties. A limitation is that it was a pragmatic trial conducted in community gymnasiums so therefore not as tightly controlled as in a laboratory setting. However, this is how progressive resistance training would be prescribed and implemented in practice. A further limitation is that the amount of other activity conducted by both groups was not documented. However, the fact that the control group did not demonstrate within-group changes suggests that they were not doing extra activities that obscured any true differences between the groups. Another important limitation was that the target sample was not achieved. Despite this, the sample size appeared sufficient to detect significant differences between the groups where they existed. Finally, it should be considered whether the duration of the programme, which was relatively short, was insufficient to result in strength increases large enough to affect mobility in young people with CP. However, there was no association between improved strength and mobility, and observed strength increases were consistent with those typically achieved after resistance training interventions.

In conclusion, progressive resistance training for adolescents and young adults with diplegic CP that is safe and feasible and increases muscle strength did not lead to objective improvements in mobility-related function but did improve participant-rated mobility. The discrepant findings of improved participant-rated mobility in the face of no change in objectively measured mobility require further exploration.

Acknowledgements

  1. Top of page
  2. Abstract
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

This trial was supported financially by a grant from the National Health and Medical Research Council of Australia (ID 487321).

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  2. Abstract
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References
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