June 2016

Stroke rehab: Strategies to improve gait velocity

6stroke-iStock_37230558-copyMultiple techniques can help improve gait speed after stroke, from therapeutic exercise to task-specific training to orthotic devices. Despite a growing body of research in this area, however, it is still not clear which intervention is most appropriate for which patients.

By Hank Black

When driving a car, speed can kill. But gait speed, in many patient populations, is an indicator of survival. It’s been called “the sixth vital sign.”1 Famously, Stanaway et al, in studying a large group of community-walking older men, determined a speed (1.36 m/s) at which an individual might “outwalk the Grim Reaper.”2

Walking velocity can also track progression through rehabilitation for individuals who have experienced a hemiplegic stroke. Walking speed, or changes in it, can help predict hospital discharge location and the need for rehabilitation.3 In people with stroke, gait speed also has been found to be significantly correlated with function and level of disability.4,5

In the first week after experiencing a stroke, 63% of patients are unable to walk without assistance, and 50% cannot walk even with help,6 so it’s no surprise that a return to walking is a primary goal of rehabilitation.7

Once patients are medically stable, the goal of the acute care team is to get them up and taking steps if the insult to the central nervous system will allow it. Most patients ambulate more slowly poststroke than they did prior to the stroke due to reduced strength,8 balance,9 and cardiovascular fitness;10 impaired cogni­tion,11 as well as prestroke function, also contribute to ambulatory status.

Ankle foot orthoses and other orthotic devices for poststroke patients need to provide stability even as they allow for increasing mobility and gait speed.

If ambulation is a plausible goal for an individual poststroke, a multitude of techniques are on the table, from therapeutic exercise to task-specific training to orthotic devices, or a combination of some or all of these.12 Despite a growing body of research in this area, however, it is not clear which intervention is best and when it’s best to apply it—at least in part because stroke is highly individualized.

“Truly, if you’ve seen one stroke, you’ve seen only one stroke, so an initial evaluation that can define the specific deficits from stroke is critical to developing the rehab plan,” said Steven R. Flanagan, MD, chair of the Department of Rehabilitation Medicine at New York University Langone Medical Center in New York City. “The amount of time a patient spends in the acute rehabilitation facility has decreased over the past several years, so our primary focus is to tailor a program to get folks to where they can at least negotiate within the home environment and realize that most near-term and long-term goals will mostly be attained in the home or outpatient setting.”   

Regardless of the rehab approach used, gait speed is an important outcome measure. Perry et al4 developed three categories of gait speed that correlate with increasing levels of function. Someone who walks slower than .4 m/s is classified as a household ambulator, one whose gait speed is between .4 m/s and .8 m/s is a limited community ambulator, and one who walks faster than .8 m/s is considered able to walk in the community without substantial limitation. The minimum speed for unlimited community ambulation allows someone to cross a street before the traffic light changes. Those people who recover walking velocity and progress from one category to another experience increasingly better function and quality of life.5

The window of opportunity for increased function after stroke has widened over the years, Flanagan noted, but the most consistent and dramatic return of function occurs in the first few months following a stroke when the brain is most capable of remodeling, or neuroplasticity.

Although it can be a useful outcome measure, gait speed itself may not be the first concern of a clinical stroke rehabilitation team, experts say.

“We initially try to improve the manner with which patients walk, making sure their mechanics are right, and as that improves we may want to pick up their speed,” said Flanagan, a member of the Board of Governors of the American Academy of Physical Medicine and Rehabilitation.

Other therapists may emphasize intensity of training, and the number of repetitions of steps, over biomechanics. Trisha Kesar, PhD, PT, assistant professor of rehabilitation medicine at Emory University School of Medicine in Atlanta, GA, said each method has pros and cons, and using only one global outcome measure such as walking speed for all interventions would be unfair.

Although her background is in biomechanics, in which quality of gait is paramount, Kesar said she sees an advantage of increasing speed and number of steps in the limited period of time available in a therapy session. A conventional outpatient rehabilitation session, she said, might be divided between several types of training, including balance, strength, walking over ground with assistance, and a few minutes on the treadmill.

“The problem is that, in forty-five minutes of therapy, which is what insurance pays for, you can’t focus on any one aspect long enough to effect long-lasting changes in function and take advantage of the brain’s neuroplasticity. That’s the disadvantage of circuit training,” she said. “Spending more time on treadmill training, in contrast, provides the ability to practice thousands of steps in a relatively short period of time, even if every step is not biomechanically beautiful. Intensity and repetition should be good for changing brain function after stroke.”

Because stroke patients’ walking ability can vary even among those with anatomically similar brain lesions, Kesar would like to see more research focusing on tailoring rehabilitation to a patient’s baseline impairments and goals.

“This would help provide the basis for guidelines and criteria for decision-making about the best approach. But in general, gait speed and long-distance walking are the focus for function and return to work after stroke,” she said.

Most interventions will improve speed, Kesar said, though the literature offers little help in determining which is best for a given patient. Task-specific training includes both circuit training, functional task practice, and treadmill training (with or without body weight support). Therapeutic exercise includes strength and resistance training, along with balance and cardiovascular/aerobic training. Orthoses, either conventional devices or those that provide nerve stimulation, are a third type of intervention frequently used early in the rehabilitation process to complement other therapies.12

AFOs and gait speed

Conventional ankle foot orthoses (AFOs) and sometimes knee ankle foot orthoses (KAFOs) are by far the most common devices used in poststroke rehabilitation, though training with neural stimulation devices is receiving increasing attention. Orthotic devices can help combat foot drop,13 which is common to individuals poststroke, and allow gait training to start early on in the process. They are not, however, a substitute for functional exercise if the prognosis for motor recovery is good, experts say.14

Keith M. Smith, CO, LO, FAAOP, of Webster Groves, MO, past president of the American Academy of Orthotists and Prosthetists, described a bracing program for a poststroke patient as like a ladder.

“The particular deficits to be addressed determine which rung the patient is on in the climb back to independent ambulation,” said Smith, who is in private practice at Orthotic and Prosthetic Lab in St. Louis. “The orthosis must be set up to be able to adapt to increasing strengths and ranges of motion, such as having the device’s joints vacuumed in a solid design so it can later be converted to an articulating device as strength increases.”

Orthotic devices for this population need to provide stability even as they allow for increasing mobility and gait speed, said Hilary Englehardt, LCPO, MBA, area clinic manager at Hanger Clinic in Seattle, WA.

“We like to allow as much range of motion as possible while maintaining proper alignment and ensuring that the patient is stable,” Englehardt said. “Patients must be stable while standing before they can progress to working on their gait. If an evaluation of muscle strength reveals flaccidity and little muscle strength below the knee, we will increase the patient’s stability by providing a more rigid orthosis.”

The stability an AFO provides on the affected side allows a hemiplegic patient to advance the unaffected leg more quickly, she said.

“We look at how the design of the orthosis helps the patient progress through stance phase while the affected foot is on the ground. We observe what happens at heel contact, how the tibia progresses through stance, and then how the patient rolls up on their toes, because that whole motion should be smooth and controlled,” Englehardt said. “In the case of weak dorsiflexors or drop foot, providing assistance in picking up the foot increases ground clearance and allows them to swing that limb faster and clear the ground without lifting from the hip.”

Timing of orthotic therapy is crucial for maximizing ambulation, Smith said, with early intervention most likely to prevent compensatory pathological gait patterns from developing and persisting. For example, he said, a patient with increased gastrocsoleus spasticity tends to quickly develop secondary knee hyperextension; if left untreated, this could cause a full loss of passive range of motion in the muscle, potentially leading to a strong pattern of knee hyper­extension that in some cases may require trading a simple AFO for a device that extends more proximally.

“The goal is always to do the least amount of bracing necessary to provide most function,” Smith said. “Typically the issue poststroke is what limits, assistance, or resistance do we need when choosing the AFO design. For example, will we need a dorsiflexion assist or plantar flexion or dorsiflexion stops? What motions can we allow? And should we rocker the shoes that will be used with the AFO?”

AFOs can induce an increase in gait speed by overcoming excessive plantar flexion and allowing the heel of the affected limb to contact the ground first. Karen J. Nolan, PhD, senior research scientist at Kessler Foundation in West Orange, NJ, found that AFO preservation of the first rocker provided the rollover effect that preserves momentum and increases gait speed.15 Her research group also looked at changes in propulsion force at third rocker, or toe-off, but the results were inconsistent, Nolan said.

The AFOs used in that study were of a rigid design. As for energy-returning AFO designs, she said, “We’ve seen some very positive outcomes with those devices in the movement at the hip and at the ankle,16 but we did not investigate the propulsive act.”

Researchers have yet to examine whether newer joint technology systems that provide controlled or resisted motion will further impact gait velocity.

“These systems provide a controlled resistance into plantar flexion ensuring a heel strike at initial contact but also a true first rocker to accept weight in early stance,” Smith said. “The determining factor is the extent of knee hyperextension and whether a plantar flexion stop would be necessary to ensure that the tibia would advance over the foot rather than into knee hyperextension as the patient progresses into the second rocker.”

Rocker shoes, which also help propel patients through the gait cycle, are another option for stroke rehab, especially for those who need the additional stability a solid AFO provides. In a recent study, Farmani et al concluded that, when patients using AFOs also wore rocker shoes, their functional mobility improved and oxygen cost diminished.17

“If we lock down the patient’s ankle with a solid orthosis, we need to consider putting a rocker type sole on the shoe so they have a smooth progression through stance,” Englehardt said. “The degree of rocker depends on the patient’s stability. Those who have better balance, proprioception, and strength can maintain control with a greater rocker, and a minimal rocker is better for those not quite ready for that much motion.”

Rocker shoes may not be right for all patients, however.

“The advantages of a rockered shoe to replace the rockers lost with a solid AFO are great, but getting the patient to wear shoes with extra sole height can be challenging as they can be heavy, expensive, and cosmetically unappealing,” Smith said.

Functional electrical stimulation

A recent review of six randomized controlled trials found functional electrical stimulation (FES) of the peroneal nerve for foot drop after stroke was as effective as conventional AFO use for increasing gait speed.18

“FES actually does more than mechanically reduce foot drop,” Nolan said. “We looked more in depth at use of the device in community ambulation over a one-month period and found it can retrain the activation of the tibialis anterior muscle so when it’s removed the effect continued.19,20 So the FES resulted in a therapeutic effect.”

Kesar said recent studies21,22 from the University of Delaware in Newark showed a combination of fast treadmill walking and FES increased energy efficiency, as well as performance in distance tests. Her lab is studying whether the improvements in endurance after such a program are due to cardiovascular benefits of the faster exercise or to a neuroplastic effect strengthening brain-muscle connections.

“We are using transcranial magnetic stimulation and peripheral electrical stimulation to study if there are changes in spinal or brain circuity with gait rehabilitation,” she said. “But, in parallel with that, we are monitoring biomechanics of the gait in an attempt to tease apart when the quality of walking function changes and when speed or endurance changes. That will tell us whether the time course of change in gait quality, neuroplasticity, and speed or endurance are similar. We also want to know whether we’re improving both legs simultaneously or preferentially changing function in the leg affected by the stroke versus the other.”

The neuroplastic abilities of the brain are also the focus of still other areas of stroke rehabilitation, including constraint-induced therapy.23 More widely used for upper limb impairment because of the obvious difficulty of constraining the unaffected lower limb poststroke, the therapy forces the affected limb to be used repetitively over several weeks, theoretically inducing the development of appropriate neural connections.

Kesar said a similar effect can be seen by preferentially training the stroke-impaired leg instead of constraining the unaffected leg.

“FES can achieve a similar preferential activation of the muscles of the affected leg. We are also looking at split-treadmill walking, differentially speeding up the affected leg’s treadmill belt, but haven’t yet defined the biomechanical effects of this treatment,” she said. “It’s tricky, because preferentially speeding up the affected leg may help with some mechanics, but slowing it down may help with others, such as the asymmetry of a limp. Again, the intervention has to be customized according to an individual’s impairment instead of a one-size-fits-all strategy.”

Asymmetries after stroke are related to slow gait speed.24 Reisman et al found step-length asymmetry could be improved poststroke with repeated split-belt treadmill training.25 She also led a group that reported the effect of step-length symmetry continues after the training, when walking on same-speed belts.26,27 The compelled body-weight shift approach28 proposed by Aruin et al (see “Inserts improve symmetry, velocity in stroke patients,” June 2013, page 23) also calls on the brain’s neuroplasticity in forcing increased weightbearing on the weaker leg to improve symmetry and gait speed, Kesar noted.

“You place a lift under the unaffected foot, so in a way it’s similar to using the split-belt treadmill,” she said. “If you put in a little elevation preferentially on one leg, you bias the system to force the other leg to bear more weight.”

Measuring gait speed

Measuring gait speed is easy, cost effective, and takes very little time. A stopwatch is the only equipment required. Setting up the test is as simple as marking off a straight line 20 meters long and subtly marking the middle 10 meters, which is the only distance timed. The patient walks at a self-selected (safe and comfortable) speed. In confined spaces, an even shorter distance may be measured.1

Defining clinically meaningful improvement in gait speed is more difficult. In a 2006 study of a diverse group of older adults with varying diagnoses, .05 m/s was cited as the necessary change for a meaningful improvement in walking speed.29 But, for patients with subacute stroke, Tilson et al used data from the LEAPS (locomotor experience applied poststroke) multisite randomized clinical trial to develop a reference value of .16 m/s as a minimal clinically important difference that can be used to develop target goals and interpret progress.30

Experts interviewed for this article agreed that gait speed is an important sign of progress in stroke rehabilitation while acknowledging that no research has defined the best intervention to target it. But NYU Langone’s Flanagan is optimistic.

“One of the problems in doing research in rehabilitation medicine is the tremendous heterogeneity of stroke; the phenotype is so variable. And you can’t do a placebo trial because that means you don’t provide rehab to some patients,” he said. “But we recognize these challenges, and I believe the increasing volume and quality of research in stroke rehabilitation will be able to provide the answers we need.” 

Hank Black is a freelance writer in Birmingham, AL.

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