Triceps Brachii in Incomplete Tetraplegia: EMG and Dynamometer Evaluation of Residual Motor Resources and Capacity for Strengthening

Abstract

cortical4-6 and spinal excitability 7 and to improve upper limb function. [4][5][6][7] However, it is not clear that all individuals with incomplete tetraplegia are necessarily good candidates for these types of programs. If the motoneuron pool of a particular muscle remains largely intact, then an activity-based therapy program that targets the re-establishment of neural connections to activate those motoneurons may increase strength and contribute to improved function. On the other hand, if there has been a major loss of lower motoneurons (gray matter), then the remaining ones may not be able to support an intense schedule of exercise. For these individuals, activitybased therapy might result in overuse weakness and fatigue, as it does in post-polio syndrome. 8,9The conventional clinical measures for assessing motor impairment after cSCI may not be adequate Background: Candidates for activity-based therapy after spinal cord injury (SCI) are often selected on the basis of manual muscle test scores and the classification of the injury as complete or incomplete. However, these scores may not adequately predict which individuals have sufficient residual motor resources for the therapy to be beneficial. Objective: We performed a preliminary study to see whether dynamometry and quantitative electromyography (EMG) can provide a more detailed assessment of residual motor resources. Methods: We measured elbow extension strength using a hand-held dynamometer and recorded fine-wire EMG from the triceps brachii muscles of 4 individuals with C5, C6, or C7 level SCI and 2 able-bodied controls. We used EMG decomposition to measure motor unit action potential (MUAP) amplitudes and motor unit (MU) recruitment and firing-rate profiles during constant and ramp contractions. Results: All 4 subjects with cervical SCI (cSCI) had increased MUAP amplitudes indicative of denervation. Two of the subjects with cSCI had very weak elbow extension strength (<4 kg), dramatically reduced recruitment, and excessive firing rates (>40 pps), suggesting profound loss of motoneurons. The other 2 subjects with cSCI had stronger elbow extension (>6 kg), more normal recruitment, and more normal firing rates, suggesting a substantial remaining motoneuron population. Conclusions: Dynamometry and quantitative EMG may provide information about the extent of gray matter loss in cSCI to help guide rehabilitation strategies.

Quantitative electrodiagnostic patterns of damage and recovery after spinal cord injury: a pilot study

“…In the C5-6 myotome, MU amplitudes were generally higher at the 1-year time point, which could represent maturation of collateral sprouting following AHC loss at the time of initial injury. This finding of increased MU amplitudes was also seen in our prior work [10]. The nearly ubiquitous finding of ASA at 3 months that resolved by 1 year is also consistent with initial denervation at these levels.…”

“…We previously published our EMG decomposition findings in the triceps brachii of four patients with chronic cervical SCI [10]. In that report, we showed both variable denervation patterns between individuals and within different muscle heads of the triceps of the same person.…”

Upper limb muscle activation during sports video gaming of persons with spinal cord injury

“…The activation level may be due to higher firing rates of fewer motor units. 19 A weaker muscle may be subject to fatigue from highly repetitive actions which could lead to potential overuse and emergent compensatory movements to complete the video sport tasks.…”

Distinct Corticospinal and Reticulospinal Contributions to Voluntary Control of Elbow Flexor and Extensor Muscles in Humans with Tetraplegia

“…This is interesting considering that the location of corticospinal projections (Penfield and Boldrey, 1937) and motoneurons (Schirmer et al, 2011) that innervate these muscles largely overlap, and that most injuries to the cervical spinal cord affect more than one spinal segment (Schaefer et al, 1989;Benavides et al, 2020). Loss of motoneurons near the injury site (Grumbles and Thomas, 2017), alterations in motor unit recruitment patterns and muscle atrophy (Thomas et al, 1997a(Thomas et al, ,b, 1998Johanson et al, 2013) might contribute to the poor recovery in triceps brachii. However, it is likely that other factors are involved in the asymmetrical recovery between elbow flexor and extensor muscles after SCI.…”