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NCT Number: NCT07800221

Targeted Muscle Activation During Strength Training for Children With CP

Cerebral palsy (CP) is the most common cause of physical disability in children and is associated with muscle weakness, spasticity, and impaired motor control. These impairments often lead to compensatory movement strategies, in which other muscles are recruited or movements are adapted to offload weaker target muscles. Although lower limb strengthening is widely used to improve motor function in children with CP, outcomes remain inconsistent. One potentially important but rarely examined factor is whether the intended muscles are actually activated during training. This study aims to develop and apply an activation-driven assessment protocol that combines individualized exercise selection, real-time electromyography (EMG) biofeedback, and compensation monitoring to identify conditions that promote target-muscle activation while limiting compensatory mechanisms. The focus is on three key muscle groups: hip extensors (HE), knee extensors (KE), and plantar flexors (PF). In this prospective[JV2.1], within-subject repeated-measures study, 30 ambulant children aged 5-12 years with spastic CP and Gross Motor Function Classification System levels I-III will complete three assessment visits in which exercise conditions and feedback strategies are compared using surface EMG and three-dimensional movement analysis.

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Key information

Conditions

Cerebral Palsy (CP) Brain Damage, Chronic Brain Diseases Central Nervous System Diseases Cerebral Palsy Nervous System Diseases

Age range

5 year–12 year

Sex eligibility

All sexes

Study type

Observational

Primary location

About this study

CP causes primary neurological impairments such as spasticity, muscle weakness, and reduced selective motor control. Over time, these impairments contribute to secondary musculoskeletal changes, including muscle contractures and skeletal deformities, which further limit mobility and affect gait. Muscle weakness in CP is multifactorial and results not only from reduced force-generating capacity but also from impaired muscle activation, altered muscle morphology, and biomechanical disadvantages. Consequently, children may compensate through alternative muscle recruitment and altered movement strategies that offload weaker muscles.

Lower limb strength training is a common intervention and has shown benefits for muscle strength, gait, and gross motor function. However, findings across studies are highly variable. One potentially important but rarely examined factor is whether strengthening exercises activate the intended target muscles. Due to impaired selective motor control, children with CP may unintentionally train compensatory muscles rather than the weaker muscles that require strengthening.

To address this limitation, the present study proposes an activation-driven approach to lower limb strengthening. The protocol combines individualized exercise selection, EMG-biofeedback, and explicit management of compensatory mechanisms to promote more selective muscle activation. The ultimate goal is to improve training specificity and support the development of more effective strengthening interventions for children with spastic CP. The study specifically focuses on the gluteus maximus, vastus lateralis, and soleus, as these muscles play a crucial role in gait, are commonly weakened in CP, and may be offloaded through compensatory muscle recruitment.

In this prospective, [JV3.1]within-subject repeated-measures study, 30 ambulant children aged 5-12 years with spastic CP and Gross Motor Function Classification System levels I-III will complete three assessment visits. Visit 1 will evaluate 3-5 bodyweight exercise conditions per muscle group and select up to three individualized conditions based on target-muscle activation and compensatory mechanisms. Visit 2 will compare standardized instruction, patient-tailored verbal feedback, and visual single-target EMG feedback. Visit 3 will compare single-target EMG feedback with dual-target EMG feedback and combined EMG and biomechanical feedback. Surface EMG, three-dimensional motion capture, and force platforms will be used to assess the immediate effects of these conditions on target-muscle activation, compensatory muscle activity, and compensatory movement patterns.

Who can participate

Healthy volunteers accepted: No

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Confirmed diagnosis of spastic cerebral palsy
  • Aged 5 - 12 years at the time of inclusion
  • GMFCS level I - III
  • At least 3 months post-injection with Botulinum neurotoxin in muscles relevant to the target or compensatory activation patterns (rationale: there is no expected residual neuromuscular effect of Botulinum neurotoxin injections on muscle activation patterns ≥3 months post Botulinum neurotoxin injection)
  • ≥12 months post lower-limb orthopaedic surgery

Exclusion criteria

  • Dyskinetic or ataxic cerebral palsy
  • Severe spasticity (Modified Ashworth ≥3)
  • Severe bony deformities or comorbidities precluding valid assessments
  • Insufficient ability to understand instructions or cooperate with the assessment procedures.

Treatment and study plan

Primary outcomes

  1. Peak EMG amplitude of the target muscles

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Peak normalized EMG amplitude during the exercise, used as a measure of maximal targeted activation of the hip extensors (HE), knee extensors (KE), and plantar flexors (PF).

  2. Integrated EMG of the target muscles

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Integrated normalized EMG over the duration of the complete task or phase of interest, used as a measure of total targeted muscle activation.

  3. Co-activation index

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Quantification of simultaneous activation of the target muscle and relevant antagonist or compensatory muscle, used to assess co-activation during strengthening exercises.

    It is calculated as: Co-activation index (%) = 2 × (Common Area of A and B / (Area of A + Area of B)) × 100 where A and B represent the two muscles being compared. Values range from 0% to 100%, with higher values indicating greater simultaneous muscle activation (co-activation).

  4. Selectivity ratio

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Integrated EMG of the point-by-point ratio between the time-normalized activation waveform of the target muscle and the corresponding activation waveform of a relevant synergistic or compensatory muscle, used as a measure of target muscle selectivity during the exercise.

  5. Joint angle compensation parameter

    Time frame: Assessed across three study visits over approximately 4 weeks.

    A predefined joint angle (expressed in °) selected according to the exercise task, used to quantify compensatory movement strategies.

  6. Joint moment compensation parameter

    Time frame: Assessed across three study visits over approximately 4 weeks.

    A predefined joint moment (expressed in Nm/kg) selected according to the exercise task, used to quantify compensatory movement strategies.

  7. Joint power compensation parameter

    Time frame: Assessed across three study visits over approximately 4 weeks.

    A predefined joint power (expressed in W/kg) selected according to the exercise task, used to quantify compensatory movement strategies.

Secondary outcomes

  1. Continuous EMG waveforms

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Time-normalized EMG waveforms of target, antagonist, and compensatory muscles across the full exercise cycle and relevant task phases.

  2. Continuous joint angle waveforms

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Time-normalized joint angle waveforms across the full exercise cycle and task-specific phases. Values are expressed in degrees (°) and reported over 0-100% of the exercise cycle.

  3. Continuous joint moment waveforms

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Time-normalized joint moment waveforms across the full exercise cycle and task-specific phases. Values are expressed in Nm/kg and reported over 0-100% of the exercise cycle.

  4. Continuous joint power waveforms

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Time-normalized joint power waveforms across the full exercise cycle and task-specific phases. Values are expressed in W/kg and reported over 0-100% of the exercise cycle.

  5. Mean EMG amplitude

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Mean normalized EMG amplitude of the target muscle during the exercise, expressed as a percentage (%) relative to the reference signal used for EMG normalization.

  6. Muscle activation timing

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Activation onset and offset timing of the target muscle, determined from the normalized EMG signal and expressed in milliseconds (ms).

  7. Additional co-activation measures

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Co-activation indices (expressed in %) for other relevant muscle pairs, including agonist-antagonist and proximal-distal muscle combinations. Co-activation is calculated as:

    Co-activation Index (%) = 2 × (Common Area of A and B / (Area of A + Area of B)) × 100 where A and B represent the two muscles being compared. Values range from 0% to 100%, with higher values indicating greater simultaneous muscle activation.

  8. Additional selectivity measures

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Selectivity ratios involving other target, synergistic, antagonist, or compensatory muscles to further describe the specificity of muscle recruitment. The selectivity ratio is calculated as the integrated EMG of the point-by-point ratio between the time-normalized activation waveform of the target muscle and the corresponding activation waveform of the comparison muscle. Values are expressed as a %, with higher values indicating greater selective activation of the target muscle relative to the comparison muscle.

  9. Additional kinematic parameters

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Exercise-specific kinematic variables, including joint range of motion, peak joint angles, trunk inclination, pelvic movement, knee position, ankle strategy. Values are expressed in degrees (°).

  10. Peak joint moments

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Exercise-specific peak joint moments. Values are expressed in Nm/kg.

  11. Peak joint powers

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Exercise-specific peak joint powers. Values are expressed in W/kg.

  12. Movement variability

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Variability of biomechanical parameters across repeated exercise trials, calculated as the standard deviation of the parameter of interest.

  13. Number of repetitions completed

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Number of exercise repetitions successfully completed during the exercise task.

  14. Exercise duration parameters

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Task execution measures including movement duration and task phase duration during strengthening exercises. Values are expressed in seconds.

  15. Task execution success

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Success of task execution during strengthening exercises, expressed as the proportion of successfully completed repetitions to the total number of attempted repetitions.

  16. Ability to perform the exercise under feedback conditions

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Ability to perform the exercise across the different feedback conditions, expressed as the proportion of feedback conditions in which the participant is able to complete the exercise.

  17. Maximal isometric strength

    Time frame: Assessed across three study visits over approximately 4 weeks.

    Maximal voluntary isometric strength of the hip extensors (HE), knee extensors (KE), and plantar flexors (PF), measured with a hand-held dynamometer during the maximal voluntary isometric contraction (MVIC) procedures to characterize participant-specific strength capacity.

  18. Age

    Time frame: Collected during screening and/or Visit 1, before the experimental exercise assessments.

    Age of the participant at study inclusion (expressed in years).

  19. Sex

    Time frame: Collected during screening and/or Visit 1, before the experimental exercise assessments.

    Sex of the participant (male, female, other).

  20. Gross Motor Function Classification System (GMFCS) level

    Time frame: Collected during screening and/or Visit 1, before the experimental exercise assessments.

    GMFCS Levels I-III (higher levels indicate greater functional limitation).

  21. General treatment history

    Time frame: Collected during screening and/or Visit 1, before the experimental exercise assessments.

    General treatment history relevant to the management of cerebral palsy.

  22. Previous strength training experience

    Time frame: Collected during screening and/or Visit 1, before the experimental exercise assessments.

    Previous participation in strength training activities.

  23. Botulinum neurotoxin history

    Time frame: Collected during screening and/or Visit 1, before the experimental exercise assessments.

    Previous treatment with botulinum neurotoxin.

  24. Orthopaedic surgery history

    Time frame: Collected during screening and/or Visit 1, before the experimental exercise assessments.

    Previous lower-limb orthopaedic surgery.

  25. Use of orthoses or assistive devices

    Time frame: Collected during screening and/or Visit 1, before the experimental exercise assessments.

    Current use of orthoses or assistive devices.

Study contacts

Contact information is provided by the study sponsor or research team.

Jolien Vanloocke

CONTACT

[email protected]

+32 16 34 10 16

Julie Stegen

CONTACT

[email protected]

Sponsors and collaborators

Lead sponsor

Universitaire Ziekenhuizen KU Leuven

Other

Registry information

Official study title

Targeted Muscle Activation During Strength Training for Children With Cerebral Palsy

Acronym: TACT-CP

Important dates

Study start
2026
Primary completion
2029
Study completion
2029
First posted
Sep 2, 2026
Registry last updated
Sep 2, 2026

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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