Pain inhibition-the unintended benefit of electrically elicited muscle strengthening contractions.

BACKGROUND: Neuromuscular electrical stimulation (NMES) is effective in muscle strengthening after orthopedic injury particularly when muscle activation failure is present, but the associated pain can be a barrier. Pain itself can produce a pain inhibitory response called Conditioned Pain Modulation (CPM). CPM is often used in research studies to assess the state of the pain processing system. However, the inhibitory response of CPM could make NMES more tolerable to patients and could improve functional outcomes in people with pain. This study compares the pain-inhibitory effect of NMES compared to volitional contractions and noxious electrical stimulation (NxES). METHODS: Healthy participants, 18-30 years of age experienced 3 conditions: 10 NMES contractions, 10 bursts of NxES on the patella, and 10 volitional contractions on the right knee. Pressure pain thresholds (PPT) were measured before and after each condition in both knees and the middle finger. Pain was reported on an 11-point VAS. Repeated measures ANOVAs with 2 factors: site and time were performed for each condition followed by post-hoc paired t-tests, with Bonferroni correction. RESULTS: Pain ratings were higher in the NxES condition compared to NMES (p = .000). No differences in PPTs prior to each condition were observed but PPTs were significantly higher in the right and left knees after the NMES contractions (p = .000, p = .013, respectively) and after the NxES (p = .006, P-.006, respectively). Pain during NMES and NxES did not correlate with pain inhibition (p > .05). Self-reported pain sensitivity correlated with pain during NxES. CONCLUSION: NxES and NMES produced higher PPTs in both knees but not in the finger, suggesting that the mechanisms responsible for the reduction in pain are located in the spinal cord and local tissues. Pain reduction was elicited during the NxES and NMES conditions regardless of the self-reported pain ratings. When NMES is used for muscle strengthening significant pain reduction can also occur, which is an unintended benefit of the intervention that could improve functional outcomes in patients.

Combined effects of fast treadmill walking and functional electrical stimulation on post-stroke gait.

Gait dysfunctions are highly prevalent in individuals post-stroke and affect multiple lower extremity joints. Recent evidence suggests that treadmill walking at faster than self-selected speeds can help improve post-stroke gait impairments. Also, the combination of functional electrical stimulation (FES) and treadmill training has emerged as a promising post-stroke gait rehabilitation intervention. However, the differential effects of combining FES with treadmill walking at the fast versus a slower, self-selected speed have not been compared previously. In this study, we compared the immediate effects on gait while post-stroke individuals walked on a treadmill at their self-selected speed without FES (SS), at the SS speed with FES (SS-FES), at the fastest speed they are capable of attaining (FAST), and at the FAST speed with FES (FAST-FES). During SS-FES and FAST-FES, FES was delivered to paretic ankle plantarflexors during terminal stance and to paretic dorsiflexors during swing phase. Our results showed improvements in peak anterior ground reaction force (AGRF) and trailing limb angle during walking at FAST versus SS. FAST-FES versus SS-FES resulted in greater peak AGRF, trailing limb angle, and swing phase knee flexion. FAST-FES resulted in further increase in peak AGRF compared to FAST. We posit that the enhancement of multiple aspects of post-stroke gait during FAST-FES suggest that FAST-FES may have potential as a post-stroke gait rehabilitation intervention.

Novel patterns of functional electrical stimulation have an immediate effect on dorsiflexor muscle function during gait for people poststroke.

BACKGROUND: Foot drop is a common gait impairment after stroke. Functional electrical stimulation (FES) of the ankle dorsiflexor muscles during the swing phase of gait can help correct foot drop. Compared with constant-frequency trains (CFTs), which typically are used during FES, novel stimulation patterns called variable-frequency trains (VFTs) have been shown to enhance isometric and nonisometric muscle performance. However, VFTs have never been used for FES during gait. OBJECTIVE: The purpose of this study was to compare knee and ankle kinematics during the swing phase of gait when FES was delivered to the ankle dorsiflexor muscles using VFTs versus CFTs. DESIGN: A repeated-measures design was used in this study. PARTICIPANTS: Thirteen individuals with hemiparesis following stroke (9 men, 4 women; age=46-72 years) participated in the study. METHODS: Participants completed 20- to 40-second bouts of walking at their self-selected walking speeds. Three walking conditions were compared: walking without FES, walking with dorsiflexor muscle FES using CFTs, and walking with dorsiflexor FES using VFTs. RESULTS: Functional electrical stimulation using both CFTs and VFTs improved ankle dorsiflexion angles during the swing phase of gait compared with walking without FES (X+/-SE=-2.9 degrees +/- 1.2 degrees). Greater ankle dorsiflexion in the swing phase was generated during walking with FES using VFTs (X+/-SE=2.1 degrees +/- 1.5 degrees) versus CFTs (X+/-SE=0.3+/-1.3 degrees). Surprisingly, dorsiflexor FES resulted in reduced knee flexion during the swing phase and reduced ankle plantar flexion at toe-off. CONCLUSIONS: The findings suggest that novel FES systems capable of delivering VFTs during gait can produce enhanced correction of foot drop compared with traditional FES systems that deliver CFTs. The results also suggest that the timing of delivery of FES during gait is critical and merits further investigation.

Functional electrical stimulation of ankle plantarflexor and dorsiflexor muscles: effects on poststroke gait.

BACKGROUND AND PURPOSE: Functional electrical stimulation (FES) is a popular poststroke gait rehabilitation intervention. Although stroke causes multijoint gait deficits, FES is commonly used only for the correction of swing-phase foot drop. Ankle plantarflexor muscles play an important role during gait. The aim of the current study was to test the immediate effects of delivering FES to both ankle plantarflexors and dorsiflexors on poststroke gait. METHODS: Gait analysis was performed as subjects (N=13) with chronic poststroke hemiparesis walked at their self-selected walking speeds during walking with and without FES. RESULTS: Compared with delivering FES to only the ankle dorsiflexor muscles during the swing phase, delivering FES to both the paretic ankle plantarflexors during terminal stance and dorsiflexors during the swing phase provided the advantage of greater swing-phase knee flexion, greater ankle plantarflexion angle at toe-off, and greater forward propulsion. Although FES of both the dorsiflexor and plantarflexor muscles improved swing-phase ankle dorsiflexion compared with noFES, the improvement was less than that observed by stimulating the dorsiflexors alone, suggesting the need to further optimize stimulation parameters and timing for the dorsiflexor muscles during gait. CONCLUSIONS: In contrast to the typical FES approach of stimulating ankle dorsiflexor muscles only during the swing phase, delivering FES to both the plantarflexor and dorsiflexor muscles can help to correct poststroke gait deficits at multiple joints (ankle and knee) during both the swing and stance phases of gait. Our study shows the feasibility and advantages of stimulating the ankle plantarflexors during FES for poststroke gait.

Management of a patient with a forearm fracture and median nerve injury.

STUDY DESIGN: Case report. OBJECTIVES: Patients with peripheral nerve injury may demonstrate long-lasting impairments and functional limitations. In this case report, we describe the diagnosis of a patient with a peripheral nerve injury and a conventional plan of care, along with the novel intervention of neuromuscular electrical stimulation (NMES). We feel that the additional NMES intervention was instrumental in achieving more rapid functional improvements than the more traditional interventions that are reported in the literature. BACKGROUND: The patient was a 21-year-old male who sustained a forearm fracture that was complicated by injury to the anterior interosseous branch of the median nerve. He was unable to flex the interphalangeal (IP) joint of his thumb, had decreased strength of thenar eminence musculature, and was unable to perform fine motor activities with his hand. METHODS AND MEASURES: Electrophysiological tests revealed partial denervation of the flexor pollicis longus and pronator quadratus muscles. In the fifth physical therapy session, NMES to the flexor pollicis longus and thenar muscles was added to the patient's conventional plan of care. RESULTS: With a conventional ROM and strengthening plan of care, no improvement was seen in thumb IP joint flexion over a period of 2 weeks. After 3 sessions of NMES and conventional interventions, gains in active ROM were made in thumb IP joint flexion. After 9 sessions of NMES and conventional interventions, force of thumb IP flexion was registered on a pinch dynamometer. Twenty weeks after initial examination, strength and ROM measures had improved and the patient reported no functional deficits. CONCLUSIONS: The patient showed gains in strength of the thumb IP joint after a few NMES sessions, which suggests that NMES was a helpful adjunct to the plan of care, even though the precise mechanism underlying the functional gains are not known.