title: Motor unit number index examination in dominant and non-dominant hand muscles.
abstract: This study investigated the effect of handedness on motor unit number index (MUNIX). Maximal hand strength, compound muscle action potential (CMAP) and voluntary surface electromyography (EMG) signals were measured bilaterally for the first dorsal interosseous (FDI) and thenar muscles in 24 right-handed and 2 left-handed healthy subjects. Mean (±standard error) grip and pinch forces in the dominant hand were 43.99 ± 2.36 kg and 9.36 ± 0.52 kg respectively, significantly larger than those in the non-dominant hand (grip: 41.37 ± 2.29 kg, p < .001; pinch: 8.79 ± 0.46 kg, p < .01). Examination of myoelectric parameters did not show a significant difference among the CMAP area, the MUNIX or motor unit size index (MUSIX) between the two sides in the FDI and thenar muscles. In addition, there was a lack of correlation between the strength and myoelectric parameters in regression analysis. However, strong correlations were observed between dominant and non-dominant hand muscles in both strength and myoelectric measures. Our results indicate that the population of motor units or spinal motor neurons as estimated from MUNIX may not be associated with handedness. Such findings help understand and interpret the MUNIX during its application for clinical or laboratory investigations.
authors.affiliation: a Department of Physical Medicine and Rehabilitation , University of Texas Health Science Center at Houston, and TIRR Memorial Hermann Research Center , Houston , TX , USA.
authors.forename: Xiaoyan
authors.initials: X
authors.lastname: Li
authors.forename: Wensheng
authors.initials: W
authors.lastname: He
authors.forename: Charles
authors.initials: C
authors.lastname: Li
authors.forename: Ying-Chih
authors.initials: YC
authors.lastname: Wang
authors.forename: Brooke A
authors.initials: BA
authors.lastname: Slavens
authors.forename: Ping
authors.initials: P
authors.lastname: Zhou
mesh_terms: D000328:Adult; D004576:Electromyography / Q000379:methods*; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006225:Hand / Q000502:physiology*; D018737:Hand Strength; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000502:physiology*; D012044:Regression Analysis; D012815:Signal Processing, Computer-Assisted; D055815:Young Adult
keywords: Compound muscle action potential (CMAP); Electromyography (EMG); Hand dominance; Motor unit number index (MUNIX).