Reliability, Validity and Minimal Detectable Change of a Power Leg Press Test in Individuals with Cerebral Palsy

Abstract

Background

Lower extremity muscle power influences walking ability in individuals with Cerebral Palsy (CP).

Aim

Determine the reliability, validity, and minimal detectable change (MDC) of a novel power leg press (PLP) test to measure muscle power in individuals with CP.

Methods

Individuals with spastic CP (n = 26 (10 adults, 16 children); mean (SD) age = 19.3 (7.8) years(all); 27.9 (4.89) years (adults); 13.85(2.68) years (children)) performed 2 sessions of the PLP test, 2–10 days apart. A linear position transducer and custom computer code were used to calculate mean and peak power in watts (W). Intraclass correlation coefficients (ICC), standard error of measurement, MDC, and percent change of MDC (MDC%) were calculated for 4 power measures (average and maximum of mean and peak powers) for all participants (AP) and separately for adults (A) and children (C). Validity was evaluated against isokinetic knee extensor power.

Results

Test-retest reliability was excellent for all measures of power (ICC = 0.94–0.99). Ranges for MDC/MDC% by the group for power measures were between 33.7–80.7W/15.5–29.4% (AP), 41.1–65.3W/10.7–22.3% (A), and 27.6–79.8W/19–34.3% (C). Correlations were good to excellent between PLP and isokinetic power at all speeds (r = 0.75–0.88, p < .001).

Conclusions

The PLP test demonstrates excellent validity, reliability, and precision for measuring muscle power in those with CP.

Keywords:

• Cerebral palsy
• evidence-based practice
• knowledge translation
• psychometric testing

Acknowledgements

The authors would like to acknowledge Max Kurz, Ph.D., for the LabView and Matlab codes used in this study.

Disclosure Statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was supported by the (NIH) National Institutes of Health and Human Development [R01HD091089] titled “Power Training Combined with Interval Treadmill Training (PT³) to Improve Walking Activity in Cerebral Palsy” and the Academy of Pediatric Physical Therapy (APPT) of the American Physical Therapy Association.

Notes on contributors

Mattie Pontiff

Dr. Mattie Pontiff completed this work as part of her doctoral training at LSUHSC. She is currently a postdoctoral research fellow at Rocky Mountain Regional VAMC and the University of Colorado Anschutz Medical Center.

Li Li

Dr. Li Li is a Professor of Kinesiology at Georgia Southern University and his research focuses on the neuromuscular coordination of human postural control, especially stability during standing and walking.

Noelle G. Moreau

Dr. Noelle G. Moreau is a Professor of Physical Therapy at LSUHSC – New Orleans and served as Dr. Pontiff's doctoral advisor. Her research focuses on investigating the neuromuscular mechanisms underlying abnormal muscle function and movement impairments in children with CP.