A robotic exoskeleton that provides resistance while walking could be used to strengthen leg muscles, allowing for greater ease of walking in people with cerebral palsy (CP), a small study suggests.
The study, “Adaptive Ankle Resistance from a Wearable Robotic Device to Improve Muscle Recruitment in Cerebral Palsy,” was published in the Annals of Biomedical Engineering.
People with CP often have weak and poorly coordinated plantar flexors — the muscles in the calf that allow the foot to move up and down (pointing or flexing your toes). These muscles contribute as much as half of the force that is generated while walking; as such, people with CP often experience gait dysfunction.
This can be treated to some extent with surgery, though current surgical techniques can only fix secondary problems with bones, not the underlying muscle weakness itself. Some physical therapy and strength training regimens have been tried, but data on the effectiveness of these interventions are limited.
This may be due, in part, to the fact that many exercises designed to strengthen muscle rely on fairly controlled, repetitive motions.
“While this serves to increase strength, it does not train the motor control that would allow an individual to effectively utilize this strength during gait,” the researchers wrote.
“Research suggests that improving neuromuscular function requires repetitive volitional engagement during functional tasks.”
In other words, it may not be enough to simply strengthen the muscles — effective therapy may require methods to strengthen the muscles as they are being used (that is, while walking).
To accomplish this, the researchers designed a robotic exoskeleton that can be worn around the legs. Through a combination of sensors, the exoskeleton can track the gait of the person wearing it, and provide a modest amount of resistance while the person is stepping forward. The muscles of the leg then have to work harder to overcome this resistance, which is the basic principle behind most muscle-strengthening exercises.
The exoskeleton was first calibrated on two volunteers with spastic CP (both male, ages 9 and 13) who had the ability to walk continuously for at least six minutes with or without support.
The researchers confirmed that the device worked as intended, providing the anticipated amount of resistance at the correct time.
Then, six other volunteers with spastic CP (1 female, 5 male, ages 12–17) and the same ability to walk with or without support underwent four to five sessions of walking while using the exoskeleton, with each session lasting 20 minutes. Participants’ self-reported soreness following sessions ranged from “none” to “moderate.”
Muscle activity was measured in the legs before and after these sessions.
In the leg that was more affected by CP, activity in the soleus (the muscle in the back of the calf) increased significantly, by an average of 45%. This is the muscle responsible for moving the foot down, providing a pushing force during ambulation.
Interestingly, a significant decrease in activity (by 26%) was seen in another muscle — the tibialis anterior, which is on the front of the calf and helps move the foot in the opposite direction.
“Combined with the significant increase in soleus activity of the more-affected limb, this resulted in a substantial decrease in co-contraction,” the investigators wrote.
Co-contraction is a phenomenon wherein two muscles exert force in opposite directions in order to stabilize a joint. Although it’s not fully understood why, children with CP often exhibit higher-than-normal co-contraction in the ankle, which is believed to cause walking problems.
“Our significant finding of decreased cocontraction of the more-affected limb may be the most compelling feature of this proposed intervention,” the investigators wrote.
The above findings were only significant in participants’ more affected legs. While some modest changes in the less-affected limbs were observed, these did not reach statistical significance.
Broadly, this study supports the idea that more functional exercise regimes could allow for better gait-improving outcomes, and it specifically recommends further exploring “the use of this wearable adaptive resistance device” in a larger and longer-term intervention.
This was a very small feasibility study, and more research is needed to validate these findings.