Can strength training predictably improve gait kinematics? A pilot study on the effects of hip and knee extensor strengthening on lower-extremity alignment in cerebral palsy

Abstract

Background: Computer simulations have demonstrated that excessive hip and knee flexion during gait, as frequently seen in ambulatory children with cerebral palsy (CP), can reduce the ability of muscles to provide antigravity support and increase the tendency of hip muscles to internally rotate the thigh. These findings suggest that therapies for improving upright posture during gait also may reduce excessive internal rotation.

Objective: The goal of this study was to determine whether strength training can diminish the degree of crouched, internally rotated gait in children with spastic diplegic CP.

Design: This was a pilot prospective clinical trial.

Methods: Eight children with CP participated in an 8-week progressive resistance exercise program, with 3-dimensional gait analysis and isokinetic testing performed before and after the program. Secondary measures included passive range of motion, the Ashworth Scale, and the PedsQL CP Module. To identify factors that may have influenced outcome, individual and subgroup data were examined for patterns of change within and across variables.

Results: Strength (force-generating capacity) increased significantly in the left hip extensors, with smaller, nonsignificant mean increases in the other 3 extensor muscle groups, yet kinematic and functional outcomes were inconsistent. The first reported subject-specific computer simulations of crouch gait were created for one child who showed substantial benefit to examine the factors that may have contributed to this outcome.

Limitations: The sample was small, with wide variability in outcomes.

Conclusions: Strength training may improve walking function and alignment in some patients for whom weakness is a major contributor to their gait deficits. However, in other patients, it may produce no change or even undesired outcomes. Given the variability of outcomes in this and other strengthening studies in CP, analytical approaches to determine the sources of variability are needed to better identify those individuals who are most likely to benefit from strengthening.

Figure 1.

Two examples of hip extensor strengthening exercises performed during training using weight machines. Other exercises also were performed (see text).

Figure 2.

Change in isokinetic peak torque divided by body weight and multiplied by 100 for each participant for the (A) right and left hip extensors and (B) right and left knee extensors. A positive change indicates an increase in strength. (C) Change in minimum knee flexion angle during stance. A positive change indicates an increase in knee flexion (ie, greater crouch).

Figure 3.

Scatterplot of change in minimum knee flexion angle (average for right and left legs) against (A) Ashworth Scale score and (B) change in knee extensor strength. Positive correlation between change in minimum knee flexion angle during stance and Ashworth Scale score of the hamstring muscles. Note that the Ashworth Scale score was not collected for one participant.

Figure 4.

Joint angles (with standard deviation bands), obtained from gait analysis, from the left side of one participant who responded well to the strengthening program (one for whom computer simulation was created). Note that the participant's excessive knee flexion, hip flexion, and internal hip rotation were diminished after strengthening. Pre=before strengthening, Post=after strengthening, Flex=flexion, Ext=extension, Dorsi=dorsiflexion, Plantar=plantar flexion.

Figure 5.

(Left) The 3-dimensional musculoskeletal model in poses corresponding to key events in the gait cycle. The musculoskeletal model used to create a simulation of one of the participants has 10 body segments and 92 muscle compartments. (Right) Capacity of the gluteus maximus and vastus muscles to accelerate the hip and knee into extension before (Pre) and after (Post) strengthening for the participant on whom the simulation was performed.