title: Do practical durations of stretching alter muscle strength? A dose-response study.
abstract: OBJECTIVE
  To examine the time course (immediate, 10, 20, and 30 min) for the acute effects of 2, 4, and 8 min of passive stretching (PS) on isometric peak torque (PT), percent voluntary activation (%VA), EMG amplitude, peak twitch torque (PTT), rate of twitch torque development (RTD), and range of motion (ROM) of the plantarflexors.
  
  
  METHODS
  Thirteen volunteers (mean +/- SD age, 22 +/- 3 yr) participated in four randomly ordered experimental trials: control (CON) with no stretching, 2 min (PS2), 4 min (PS4), and 8 min (PS8) of PS. Testing was conducted before (pre), immediately after (post), and at 10, 20, and 30 min poststretching. The PS trials involved varied repetitions of 30-s passive stretches, whereas the CON trial included 15 min of resting. PT, %VA, EMG amplitude, PTT, and RTD were assessed during the twitch interpolation technique, whereas ROM was quantified as the maximum tolerable angle of passive dorsiflexion.
  
  
  RESULTS
  PT decreased (P < or = 0.05) immediately after all conditions [CON (4%), PS2 (2%), PS4 (4%), and PS8 (6%)] but returned to baseline at 10, 20, and 30 min poststretching. %VA and EMG amplitude were unaltered (P > 0.05) after all conditions. PTT and RTD decreased (P < or = 0.05) immediately after the PS4 (7%) and the PS8 (6%) conditions only; however, these changes were not sufficient to alter voluntary force production. There were also increases (P < or = 0.05) in ROM after the PS2 (8%), the PS4 (14%), and the PS8 (13%) conditions that returned to baseline after 10 min.
  
  
  CONCLUSIONS
  Practical durations of stretching (2, 4, or 8 min) of the plantarflexors did not decrease isometric PT compared with the CON but caused temporary improvements in the ROM, thereby questioning the overall detrimental influence of PS on performance.
authors.affiliation: Biophysics Laboratory, Department of Health and Exercise Science, University of Oklahoma, Norman, OK 73019-6081, USA.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Ryan
authors.forename: Travis W
authors.initials: TW
authors.lastname: Beck
authors.forename: Trent J
authors.initials: TJ
authors.lastname: Herda
authors.forename: Holly R
authors.initials: HR
authors.lastname: Hull
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Hartman
authors.forename: Jeffery R
authors.initials: JR
authors.lastname: Stout
authors.forename: Joel T
authors.initials: JT
authors.lastname: Cramer
mesh_terms: D000328:Adult; D004576:Electromyography; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic / Q000379:methods; D053580:Muscle Strength / Q000502:physiology*; D052580:Muscle Stretching Exercises / Q000379:methods*; D016059:Range of Motion, Articular; D013997:Time Factors; D019415:Torque