Rapid force generation is impaired in cerebral palsy and is related to decreased muscle size and functional mobility

Abstract

Limb movements involving contraction times of 50–200ms occur in many everyday activities, such as gait, which is faster than the time required to generate maximal force. Therefore, the ability to rapidly produce force may be even more important for the performance of functional activities. In this study rate of force development (RFD) and impulse of the knee extensors were examined in 12 ambulatory children with cerebral palsy (CP) (Age:11.9 ± 2.9 yrs) and 11 with typical development (TD) (Age: 11.3 ± 3.0 yrs). The relationship with muscle architecture and functional mobility was also determined. RFD and impulse were calculated during a maximal isometric knee extension contraction. Rectus femoris (RF) cross-sectional area and RF and vastus lateralis (VL) muscle thickness (MT), fascicle length (FL), and fascicle angle (FA) were measured using ultrasound imaging. Gait temporal-spatial parameters, Pediatric Outcomes Data Collection Instrument (PODCI), and Activities Scale for Kids performane version (ASKp) were collected. Although VL MT was the primary determinant of RFD and impulse in CP, FA and FL were also significant predictors in the TD group. RFD and impulse were significantly lower in CP compared to TD (70% decrease) in addition to maximal strength (50% decrease). RFD and impulse were predictive of measures of functional mobility, including gait, transfers, and sports and higher level activities but not temporal-spatial gait measures. Results suggest that the ability to rapidly generate torque may be of greater importance than maximal strength during certain tasks, such as transfers and sports and higher level activities.

Impaired gait function in adults with cerebral palsy is associated with reduced rapid force generation and increased passive stiffness

“…We used two different measures that relate to muscle weakness in the subjects. MVC is a measure of the maximal strength that the subjects may generate when given ample time, whereas RFD is a measure of the ability of the subjects to generate force as quickly as possible within the early part of a muscle contraction (Aagaard et al, 2002, Suetta et al, 2004, Moreau et al, 2011. RFD of either dorsiflexors or plantar flexors correlated better than MVC for all kinematic measures of gait function.…”

“…For all RFD intervals, the average muscle strength of the CP-group was much lower than the controls. For the 0-200 ms time-interval (RFD200 df ), which is often regarded as the maximum time available for many everyday movements to occur (Suetta et al, 2004, Moreau et al, 2011, the adults with CP produced only 21% of the torque produced by the controls (28.3 ± 6.6 Nm/s vs. 137.5 ± 11.2 Nm/s; p < 0.001). For the MVC df , the adults with CP produced 42% of the torque produced by the controls (15.8 ± 3.8 Nm vs. 37.7 ± 2.4 Nm; p < 0.001).…”

“…Many everyday activities allow a limited time to develop muscle force (up to 200 ms) whereas the time required to develop maximal force takes considerably longer (Aagaard et al, 2002). Interestingly, the rate at which force or torque is produced, known as the rate of force development (RFD), have been shown to be a good predictor of functional performance in elderly (Bassey et al, 1992, Skelton et al, 1994 and recently also in children with CP (Downing et al, 2009, Moreau et al, 2011. Nevertheless, the importance of RFD for gait function has been largely overlooked in adults with CP.…”

Lower limb loading during knee up in step aerobics: a pilot study

“…Therefore, they have greater efficiency and are used for activities that need strength [2,33]. A review of the literature has shown that few studies [1,8,17,20,29] go beyond a description of muscle length changing during a crouching gait, and no references were found in sport application and above all in knee up move analysis.…”

Relative fascicle excursion effects on dynamic strength generation during gait in children with cerebral palsy

“…Power training which combines both force and velocity components may be beneficial as it targets both strength development (through increase of sarcomeres in parallel) and velocity development (through increase of sarcomeres in series) which has been greatly associated to functional activities [9]. Moreau et al (2012) observed that the combination of RFD and MVC predicted 77% of variance in overall gait function, which might be due to the fact that each variable accounts for different functions during gait, power and force respectively. Furthermore, muscles with different functions (power and force) should also be combined as together they better predict performance on functional scales than alone [8].…”