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Article Title

THE EFFECTS OF PASSIVE STRETCHING PLUS VIBRATION ON VOLUNTARY INACTIVATION AND PEAK TORQUE OF THE PLANTAR FLEXORS AT A SHORT AND LONG MUSCLE LENGTH

Abstract

Omar M. Rehman1, Jonathan D. Miller1, Lauren M. Marquess1, Jeremy D. Lippman1, Eric M. Mosier1, Michael A. Trevino1, Trent J. Herda1 1University of Kansas, Lawrence, Kansas; e-mail: o800r545@ku.edu

PURPOSE: Passive stretching (PS) has been reported to reduce peak torque (PT) due to increases in percent voluntary inactivation (%VI) and mechanical mechanisms. Conversely, prolonged vibration (VIB) solely reduces PT as a result of %VI. It remains unclear the influence PS may have on PT and %VI at short and long muscle lengths. Therefore, this study examined the effects of PS, in conjunction with VIB, on PT and %VI of the plantar flexors (PF) at a short and long muscle length. METHODS: 14 healthy men (Age = 21.9 ± 3.5 yrs) volunteered for this study. Subjects completed 1 familiarization and 2 randomized visits (control [CON] and VIB). The CON visit consisted of 8, 30-s PS of the PF, whereas the VIB visit consisted of PS with VIB during the post-testing. VIB was applied to the Achilles tendon and 55 Hz 2-m before post-testing and continued during the remainder of testing. Subjects completed maximal voluntary contractions (MVC) of the right PF at an ankle joint of 70° plantarflexion (short muscle length [PF]) and 105° dorsiflexion (long muscle length, [DF]) in random order pre- and post-PS. During MVCs, an evoked doublet stimulus was applied to the tibial nerve to calculate %VI. PT was determined from a 0.25-s epoch during the MVC (Nm) prior to stimulation. Two separate 3-way ANOVAs (treatment [CON vs. VIB] x time [Pre vs. Post] x muscle length [PF vs. DF]) were used to examine differences in PT and %VI. RESULTS: For %VI, there were no significant 3- or 2-way interactions (p > 0.05). There were significant main effects for time (p = 0.003) and length (p = 0.007). %VI was greater post- (10.2 ± 9.7%) than pre-PS (5.5 ± 5.5%) and at the DF (10.9 ± 8.7%) than PF (4.8 ± 7.7%). For PT, there was no 3-way interaction. There was a significant 2-way interaction (time x treatment; p = 0.008). PT decreased pre- to post-CON (p = 0.016, pre = 109.8 ± 27.9 Nm, post = 101.7 ± 28.0 Nm) and -VIB (p < 0.001, pre = 113.3 ± 33.8 Nm, post = 92.8 ± 31.9 Nm). In addition, PT was greater at the DF (122.4 ± 37.8 Nm) than PF (86.4 ± 20.9 Nm). CONCLUSION: No further decreases in PT or increases %VI occurred with VIB following PS and, therefore, suggested that strength losses following PS is primarily neural. In addition, muscle activation deficiencies were present at the longer muscle length despite greater PT in comparison to the shorter muscle length.

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