title: Stretch-reflex mechanical response to varying types of previous muscle activities.
abstract: This study was designed to examine the effects of varying types of background muscle activity on the stretch-reflex mechanical response. A rapid stretch was applied to the calf muscles after an isometric (pre-ISO), shortening (pre-SHO) and lengthening contraction (pre-LEN) with several pre-contraction levels, respectively. The stretch perturbation was applied with the tibio-tarsal joint angle at 90 degrees. The ankle joint torque elicited by the stretch showed a first peak (non-reflex torque: NRT), a transient drop and a second peak (reflex torque: RT). The muscle activities before the stretch clearly influenced the stretch-reflex mechanical response. The NRT reached the largest peak with the longest duration in pre-ISO. The peak NRT increased with the pre-contraction level in pre-ISO and pre-LEN, whereas it remained unchanged in pre-SHO. The RT responded to the stretch-reflex EMG response most quickly and reached the largest peak in pre-ISO. Pre-ISO generated the mechanical response most efficiently against the size of the stretch-reflex EMG response. Pre-SHO showed lower peak RT than pre-ISO in spite of the similar size of stretch-reflex EMG response. The peak RT was closely related to the peak NRT in all conditions. Consequently, the peak RT also increased with the pre-contraction level in pre-ISO and pre-LEN, whereas it remained unchanged in pre-SHO. In conclusion, a stretch after an isometric contraction evoked a larger stretch-reflex mechanical response more efficiently than that after phasic contractions when a given effort was being maintained.
authors.affiliation: Neuromuscular Research Center, Department of Biology of Physical Activity, University of Jyväskylä, FIN-40100, Jyväskylä, Finland. ogiso@kogakkan-u.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Ogiso
authors.forename: J M
authors.initials: JM
authors.lastname: McBride
authors.forename: T
authors.initials: T
authors.lastname: Finni
authors.forename: P V
authors.initials: PV
authors.lastname: Komi
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology*; D004576:Electromyography; D006801:Humans; D016014:Linear Models; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D012026:Reflex, Stretch / Q000502:physiology*; D013997:Time Factors; D019415:Torque