title: EMG-force relation in the first dorsal interosseous muscle of patients with amyotrophic lateral sclerosis.
abstract: OBJECTIVE
  The relationship between surface electromyography (EMG) and muscle force is essential to assess muscle function and its deficits. However, few studies have explored the EMG-force relation in patients with amyotrophic lateral sclerosis (ALS). The purpose of this study was to examine the EMG-force relation in ALS subjects and its alteration in comparison with healthy control subjects.
  
  
  METHODS
  Surface EMG and force signals were recorded while 10 ALS and 10 age-matched healthy control subjects produced isometric voluntary contractions in the first dorsal interosseous (FDI) muscle over the full range of activation. A linear fit of the EMG-force relation was evaluated through the normalized root mean square error (RMSE) between the experimental and predicted EMG amplitudes. The EMG-force relation was compared between the ALS and the healthy control subjects.
  
  
  RESULTS
  With a linear fit, the normalized RMSE between the experimental and predicted EMG amplitudes was 9.6 ± 3.6% for the healthy control subjects and 12.3 ± 8.0% for the ALS subjects. The slope of the linear fit was 2.9 ± 2.2 μVN-1 for the ALS subjects and was significantly shallower (p < 0.05) than the control subjects (5.1 ± 1.8 μVN-1). However, after excluding the four ALS subjects who had very weak maximum force, the slope for the remaining ALS subjects was 3.5 ± 2.2 μVN-1 and was not significantly different from the control subjects (p > 0.05).
  
  
  CONCLUSIONS
  A linear fit can be used to well describe the EMG-force relation for the FDI muscle of both ALS and healthy control subjects. A variety of processes may work together in ALS that can adversely affect the EMG-force relation.
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA Department of Bioengineering, University of Illinois at Chicago, Chicago, IL, USA.
authors.forename: Faezeh
authors.initials: F
authors.lastname: Jahanmiri-Nezhad
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA.
authors.forename: Xiaogang
authors.initials: X
authors.lastname: Hu
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA.
authors.forename: Nina L
authors.initials: NL
authors.lastname: Suresh
authors.affiliation: Sensory Motor Performance Program, Rehabilitation Institute of Chicago, Chicago, IL, USA Department of Physical Medicine and Rehabilitation, Northwestern University, Chicago, IL, USA.
authors.forename: William Z
authors.initials: WZ
authors.lastname: Rymer
authors.affiliation: Department of Physical Medicine and Rehabilitation, University of Texas Health Science Center at Houston and TIRR Memorial Hermann Research Center, Houston, TX, USA Biomedical Engineering Program, University of Science and Technology of China, Hefei, Anhui, China.
authors.forename: Ping
authors.initials: P
authors.lastname: Zhou
mesh_terms: D000328:Adult; D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000503:physiopathology*; D004576:Electromyography; D005260:Female; D005385:Fingers / Q000503:physiopathology; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D008875:Middle Aged; D009068:Movement; D018482:Muscle, Skeletal / Q000503:physiopathology*; D014584:User-Computer Interface
keywords: ALS; EMG-force relation; FDI; isometric contraction