Targeted Muscle Activation During Strength Training for Children With CP (TACT-CP)

Targeted Muscle Activation During Strength Training for Children With Cerebral Palsy

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.

Study Overview

• Status: Not yet recruiting
• Conditions: Cerebral Palsy (CP)

Detailed Description

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.

• Study Type: Observational
• Enrollment (Estimated): 30

Contacts and Locations

• Study Contact: Name: Jolien Vanloocke; Phone Number: +32 16 34 10 16; Email: jolien.vanloocke@kuleuven.be
• Study Contact Backup: Name: Julie Stegen; Email: julie.stegen@kuleuven.be

Study Locations

• Belgium
  • Vlaams-Brabant
    • Leuven, Vlaams-Brabant, Belgium, 3000
      • UZ Leuven
      • Contact: Kaat Desloovere, prof. dr.; Phone Number: +3216338009; Email: kaat.desloovere@kuleuven.be

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child
• Accepts Healthy Volunteers: No

• Sampling Method: Non-Probability Sample

Study Population

Children with spastic cerebral palsy, who have routine follow-up care at the CP reference center of the university hospitals Leuven

Description

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.

Study Plan

How is the study designed?

Number of groups / cohorts

1

Cohorts and Interventions

Group / Cohort
Children with cerebral palsy; Children with spastic cerebral palsy, aged 5-12 years, GMFCS levels I-III

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Peak EMG amplitude of the target muscles	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).	Assessed across three study visits over approximately 4 weeks.
Integrated EMG of the target muscles	Integrated normalized EMG over the duration of the complete task or phase of interest, used as a measure of total targeted muscle activation.	Assessed across three study visits over approximately 4 weeks.
Co-activation index	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).	Assessed across three study visits over approximately 4 weeks.
Selectivity ratio	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.	Assessed across three study visits over approximately 4 weeks.
Joint angle compensation parameter	A predefined joint angle (expressed in °) selected according to the exercise task, used to quantify compensatory movement strategies.	Assessed across three study visits over approximately 4 weeks.
Joint moment compensation parameter	A predefined joint moment (expressed in Nm/kg) selected according to the exercise task, used to quantify compensatory movement strategies.	Assessed across three study visits over approximately 4 weeks.
Joint power compensation parameter	A predefined joint power (expressed in W/kg) selected according to the exercise task, used to quantify compensatory movement strategies.	Assessed across three study visits over approximately 4 weeks.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Continuous EMG waveforms	Time-normalized EMG waveforms of target, antagonist, and compensatory muscles across the full exercise cycle and relevant task phases.	Assessed across three study visits over approximately 4 weeks.
Continuous joint angle waveforms	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.	Assessed across three study visits over approximately 4 weeks.
Continuous joint moment waveforms	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.	Assessed across three study visits over approximately 4 weeks.
Continuous joint power waveforms	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.	Assessed across three study visits over approximately 4 weeks.
Mean EMG amplitude	Mean normalized EMG amplitude of the target muscle during the exercise, expressed as a percentage (%) relative to the reference signal used for EMG normalization.	Assessed across three study visits over approximately 4 weeks.
Muscle activation timing	Activation onset and offset timing of the target muscle, determined from the normalized EMG signal and expressed in milliseconds (ms).	Assessed across three study visits over approximately 4 weeks.
Additional co-activation measures	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.	Assessed across three study visits over approximately 4 weeks.
Additional selectivity measures	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.	Assessed across three study visits over approximately 4 weeks.
Additional kinematic parameters	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 (°).	Assessed across three study visits over approximately 4 weeks.
Peak joint moments	Exercise-specific peak joint moments. Values are expressed in Nm/kg.	Assessed across three study visits over approximately 4 weeks.
Peak joint powers	Exercise-specific peak joint powers. Values are expressed in W/kg.	Assessed across three study visits over approximately 4 weeks.
Movement variability	Variability of biomechanical parameters across repeated exercise trials, calculated as the standard deviation of the parameter of interest.	Assessed across three study visits over approximately 4 weeks.
Number of repetitions completed	Number of exercise repetitions successfully completed during the exercise task.	Assessed across three study visits over approximately 4 weeks.
Exercise duration parameters	Task execution measures including movement duration and task phase duration during strengthening exercises. Values are expressed in seconds.	Assessed across three study visits over approximately 4 weeks.
Task execution success	Success of task execution during strengthening exercises, expressed as the proportion of successfully completed repetitions to the total number of attempted repetitions.	Assessed across three study visits over approximately 4 weeks.
Ability to perform the exercise under feedback conditions	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.	Assessed across three study visits over approximately 4 weeks.
Maximal isometric strength	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.	Assessed across three study visits over approximately 4 weeks.
Age	Age of the participant at study inclusion (expressed in years).	Collected during screening and/or Visit 1, before the experimental exercise assessments.
Sex	Sex of the participant (male, female, other).	Collected during screening and/or Visit 1, before the experimental exercise assessments.
Gross Motor Function Classification System (GMFCS) level	GMFCS Levels I-III (higher levels indicate greater functional limitation).	Collected during screening and/or Visit 1, before the experimental exercise assessments.
General treatment history	General treatment history relevant to the management of cerebral palsy.	Collected during screening and/or Visit 1, before the experimental exercise assessments.
Previous strength training experience	Previous participation in strength training activities.	Collected during screening and/or Visit 1, before the experimental exercise assessments.
Botulinum neurotoxin history	Previous treatment with botulinum neurotoxin.	Collected during screening and/or Visit 1, before the experimental exercise assessments.
Orthopaedic surgery history	Previous lower-limb orthopaedic surgery.	Collected during screening and/or Visit 1, before the experimental exercise assessments.
Use of orthoses or assistive devices	Current use of orthoses or assistive devices.	Collected during screening and/or Visit 1, before the experimental exercise assessments.

Collaborators and Investigators

• Sponsor: Universitaire Ziekenhuizen KU Leuven
• Investigators: Principal Investigator: Kaat Desloovere, Prof. dr., Department of Rehabilitation Sciences, KU Leuven, Belgium

Study record dates

Study Major Dates

• Study Start (Estimated): September 1, 2026
• Primary Completion (Estimated): February 28, 2029
• Study Completion (Estimated): February 28, 2029

Study Registration Dates

• First Submitted: August 24, 2026
• First Submitted That Met QC Criteria: August 28, 2026
• First Posted (Actual): September 2, 2026

Study Record Updates

• Last Update Posted (Actual): September 2, 2026
• Last Update Submitted That Met QC Criteria: August 28, 2026
• Last Verified: August 1, 2026

More Information

Terms related to this study

• Keywords: Electromyography; Biofeedback; Motion analysis; Spastic Cerebral Palsy; Targeted muscle activation; Lower limb strengthening
• Additional Relevant MeSH Terms: Brain Diseases; Central Nervous System Diseases; Nervous System Diseases; Brain Damage, Chronic; Cerebral Palsy
• Other Study ID Numbers: S72414

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No