# Muscle fascicle length adaptations to high-velocity training in young adults with cerebral palsy

## TL;DR

High-velocity training increases muscle fascicle length in young adults with cerebral palsy, potentially improving muscle power.

## Contribution

Demonstrates that high-velocity training can increase fascicle length in individuals with CP, a novel approach to enhance muscle function.

## Key findings

- HVT significantly increased fascicle length in CP participants compared to no training.
- HVT showed large effect sizes for improving maximal shortening velocity and peak power output in CP participants.
- Healthy adults had significantly greater muscle power and fascicle lengths compared to CP participants.

## Abstract

In individuals with Cerebral Palsy (CP), both muscle cross-sectional area and fascicle length are reduced, contributing to decreased muscle strength, muscle shortening velocity and muscle mechanical power output, particularly in the plantarflexor muscles. A proposed mechanism to target increased muscle mechanical power output is to incorporate high velocity training (HVT) in these individuals, to increase fascicle length via sarcomerogenesis. To determine the effects of HVT on changes in MG muscle fascicle length and that impact on changes to MG muscle force-length-velocity-power characteristics in young adults with CP.

12 young adults with CP (GMFCS I or II, 22.8 ± 6.0 years) were randomly allocated (some crossover) to no training (CP-NT, n = 8), or training (CP-T, n = 8). 10 recreationally trained healthy adults (HA, 22.5 ± 2.8 years) served as controls. CP-T performed 10-week training of biweekly sessions consisting of progressive intensity 10 m sprints, plyometrics and agility tasks. Triceps surae muscle force-power-velocity relationships were quantified with isokinetic dynamometry and ultrasound imaging. Data are expressed relative to pre-intervention values.

HVT resulted in a significant increase in fascicle length in CP-T (+1.92 ± 3.21 mm, p < 0.005) compared to a significant decrease in CP-NT (−1.63 ± 3.00 mm, p < 0.013). While HVT did not result in significant changes in maximal shortening velocity (Vmax) or maximal peak power output (Pmax), a large effect size for vmax following training in CP-T was seen (+45.2 ± 76.4%, d = 0.909, p = 0.452), in contrast to CP-NT (+2.9 ± 70.5%, d = 0.059, p = 1.00). HVT also resulted in a very large effect for Pmax in CP-T (+35.0 ± 49.1%, d = 1.093, p = 0.232), but only a small effect was observed in CP-NT (+7.8 ± 49.1%, d = 0.245, p = 1.00). HA had significantly greater Pmax (p < 0.001), longer resting and active fascicle lengths (p < 0.001) and greater muscle force (p < 0.001), compared to CP-T.

HVT is a feasible training intervention to increase triceps surae muscle fascicle length in individuals with CP. HVT can partially mitigate losses in Pmax in CP compared to healthy adults. Longer HVT programs may be required to increase muscle mechanical power output in CP to levels observed in HA.