title: Upper-extremity spinal reflex inhibition is reproducible and strongly related to grip force poststroke.
abstract: OBJECTIVE
  Impaired reflex regulation is assumed to contribute to upper-extremity motor impairment poststroke; however, the relationship between reflex inhibition and motor function remains unclear. To address this question, it is first necessary to determine the reproducibility of reflex responses. The objective of this study was to establish the test-retest reliability of flexor carpi radialis H-reflex inhibition in healthy control and stroke participants and investigate the correlation between H-reflex inhibition and grip strength.
  
  
  METHODS
  Eighteen persons poststroke (mean ± SD: age 63 ± 13 years; 6 ± 5 years poststroke; 13 males) and 16 healthy controls (age: 62 ± 12 years) participated. Reflex inhibition was tested on 2 separate days by conditioning the H-reflex with radial nerve stimulation at two different interstimulus intervals: 13 ms (presynaptic Ia inhibition-PSI) and 0 ms (disynaptic inhibition). Pearson's and intraclass correlation coefficients [two-way mixed model-ICC (1, 2)], and standard error of measurement (SEM) were calculated.
  
  
  RESULTS
  Relative reliability (ICCs) ranged from good to excellent (0.61-0.78). SEM was low (range 10-19%, stroke; 15-20%, healthy controls). Paretic grip strength and paretic limb PSI revealed a positive correlation (r = 0.70; p < 0.0125). Disynaptic inhibition and paretic grip strength were not correlated.
  
  
  CONCLUSIONS
  To our knowledge, this is the first study to demonstrate reproducibility of reflex inhibition in individuals poststroke. Furthermore, we quantify smallest real differences, which provide an estimate of the magnitude of effect required to determine a meaningful change, exceeding measurement error. The correlation between PSI and grip strength suggests the potential contribution of PSI to grip force production and upper-extremity motor function.
authors.affiliation: 1Brain Rehabilitation Research Center of Excellence, Malcom Randall VAMC, 1601 SW Archer Road, Gainesville, FL, USA.
authors.forename: Chetan P
authors.initials: CP
authors.lastname: Phadke
authors.forename: Christopher T
authors.initials: CT
authors.lastname: Robertson
authors.forename: Carolynn
authors.initials: C
authors.lastname: Patten
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D016022:Case-Control Studies; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009433:Neural Inhibition / Q000502:physiology*; D020127:Recovery of Function / Q000502:physiology; D015203:Reproducibility of Results; D013223:Statistics as Topic; D020521:Stroke / Q000473:pathology* / Q000503:physiopathology*; D034941:Upper Extremity / Q000503:physiopathology*
keywords: H-reflex; Stroke; disynaptic inhibition; presynaptic inhibition; reliability