title: Depression of Hoffmann reflexes following voluntary contraction and implications for proprioceptive neuromuscular facilitation therapy.
abstract: Postcontraction depression of Hoffmann-reflex (H-reflex) amplitudes was examined to study the rationale underlying proprioceptive neuromuscular facilitation relaxation techniques. The time course of H-reflex amplitude depression was used to assess postcontraction changes in motoneuron reflex excitability. Sixteen healthy female subjects performed voluntary isometric plantar-flexion contractions (65%-75% of maximal voluntary contraction) in a prone position. H-reflex stimulation began at a postcontraction delay of 0.05, 0.1, 0.5, 1, or 5 seconds and continued every 10 seconds for 1 minute. Reflexes were depressed (mean = 67% decrease) by 0.05 second postcontraction, reached maximal depression (mean = 83.3% decrease) from 0.1 to 1 second postcontraction, recovered to 70% of control amplitudes (mean = 30% decrease) by 5 seconds postcontraction, and reached 90% control amplitudes (mean = 10% decrease) by 10.05 seconds postcontraction. The results indicate that proprioceptive neuromuscular facilitation techniques (eg, hold-relax) purported to produce a phase of relaxation following voluntary contraction do appear to produce a strong, but brief, neuromuscular inhibition that may be clinically useful for applying stretch.
authors.affiliation: Physical Therapy Program, University of Rhode Island, Kingston 02881.
authors.forename: M A
authors.initials: MA
authors.lastname: Moore
authors.forename: C G
authors.initials: CG
authors.lastname: Kukulka
mesh_terms: D000328:Adult; D004558:Electric Stimulation / Q000379:methods; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction / Q000502:physiology*; D026741:Physical Therapy Modalities / Q000379:methods; D011403:Pronation; D011434:Proprioception / Q000502:physiology*; D013979:Tibial Nerve / Q000502:physiology*