Tsang P1, MacDermid J1, Miller T2, Ross D2, Doherty C2, Doherty T2
1University of Western Ontario, Health and Rehabilitation Science, London, Canada, 2University of Western Ontario, Schulich School of Medicine & Dentistry, London, Canada

Background: Decomposition-based quantitative electromyography (DQEMG) is one method of measuring neuromuscular changes in human muscles. This technique has been applied to healthy adults and patient populations (i.e. persons with ALS). DQEMG can measure motor unit number estimations (MUNE) and other motor unit properties, allowing clinicians and investigators to explore neuromuscular changes. Capturing motor unit information may lead to future rehabilitation approaches of maintaining muscle mass, muscle strength, and motor control (specifically to the hand). To date there have been no studies investigating the motor unit properties of the ulnar nerve innervated intrinsic hand muscles using DQEMG in a healthy aging population.

Purpose: To compare the motor unit physiology of healthy younger (20 to 40 year old) and older (40 to 60 year old) adults using DQEMG in the intrinsic hand muscles.

Methods: Seven healthy younger adults were tested (Mean Age = 27.7 ± 2.8; 3 Females) and seven healthy older adults were tested (Mean Age = 68.9 ± 3.9; 3 Females). Measurements of DQEMG were detected with a standard concentric needle and surface EMG for ~30 seconds during a mild-moderate intensity voluntary isometric contraction. DQEMG was obtained from the first dorsal interosseous (FDI) and the abductor digiti minimi (ADM) to measure the MUNE. Neuromuscular measurements of motor unit potential amplitude and near-fiber (NF) jiggle were also obtained from the FDI and ADM. Independent t-test were performed to evaluate group differences between EMG data in younger adults vs. older adults.

Results: MUNE of the FDI were not significantly reduced (p>0.05) in older adults when compared to younger adults (442 units vs 285 units, respectively). Likewise, MUNE of the ADM muscles were not significantly greater in younger adults vs older adults (259 units vs 272 units, respectively). Motor unit potential amplitude and NF jiggle were not significantly different between younger adults and older adults (p>0.05). Although there were no significant differences in neuromuscular measurements between older and younger adults, there is still an observable difference in MUNE within the FDI.

Conclusion(s): Results from this study indicate that there may be changes in motor unit number within the FDI as aging occurs (though not statistically significant). The FDI muscle is a well investigated intrinsic hand muscle which is responsible for the action of abducting the 2nd MCP joint. The FDI is involved with many hand actions such as pinching and grasping. Hand and neuromuscular health are essential for ADLs and other meaningful activities. Although no statistical significance was shown in the current data, further investigations may reveal age-related changes in hand neuromuscular physiology (i.e. NF jiggle and MUP amplitude).

Implications: With aging there are considerable changes that may occur in the intrinsic hand muscles. In order to measure these changes, DQEMG may be a useful future tool for investigating motor unit stability in future aging and patient populations (i.e. those with ulnar nerve injury). Exploring these neuromuscular changes may inform rehabilitation and exercise approaches to mitigate decreases in muscle strength and power that accompany aging.

Keywords: Electromyography, Motor Unit, Aging

Funding acknowledgements: Dr. Joy MacDermid is supported by the Canadian Institute of Health Research as chair of Musculoskeletal Measurement and Knowledge Translation.

Topic: Musculoskeletal: upper limb; Musculoskeletal: upper limb; Older people

Ethics approval required: Yes
Institution: University of Western Ontario
Ethics committee: The Western University Human Research Ethics Board
Ethics number: 107863

All authors, affiliations and abstracts have been published as submitted.

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