title: Faster Movement Speed Results in Greater Tendon Strain during the Loaded Squat Exercise.
abstract: BACKGROUND
  Tendon dynamics influence movement performance and provide the stimulus for long-term tendon adaptation. As tendon strain increases with load magnitude and decreases with loading rate, changes in movement speed during exercise should influence tendon strain.
  
  
  METHODS
  Ten resistance-trained men [squat one repetition maximum (1RM) to body mass ratio: 1.65 ± 0.12] performed parallel-depth back squat lifts with 60% of 1RM load at three different speeds: slow fixed-tempo (TS: 2-s eccentric, 1-s pause, 2-s concentric), volitional-speed without a pause (VS) and maximum-speed jump (JS). In each condition joint kinetics, quadriceps tendon length (LT), patellar tendon force (FT), and rate of force development (RFDT) were estimated using integrated ultrasonography, motion-capture, and force platform recordings.
  
  
  RESULTS
  Peak LT, FT, and RFDT were greater in JS than TS (p < 0.05), however no differences were observed between VS and TS. Thus, moving at faster speeds resulted in both greater tendon stress and strain despite an increased RFDT, as would be predicted of an elastic, but not a viscous, structure. Temporal comparisons showed that LT was greater in TS than JS during the early eccentric phase (10-14% movement duration) where peak RFDT occurred, demonstrating that the tendon's viscous properties predominated during initial eccentric loading. However, during the concentric phase (61-70 and 76-83% movement duration) differing FT and similar RFDT between conditions allowed for the tendon's elastic properties to predominate such that peak tendon strain was greater in JS than TS.
  
  
  CONCLUSIONS
  Based on our current understanding, there may be an additional mechanical stimulus for tendon adaptation when performing large range-of-motion isoinertial exercises at faster movement speeds.
authors.affiliation: Human Performance Laboratory, Department of Kinesiology, University of Rhode IslandKingston, RI, USA; Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan UniversityJoondalup, WA, Australia.
authors.forename: Jacob E
authors.initials: JE
authors.lastname: Earp
authors.affiliation: Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan University Joondalup, WA, Australia.
authors.forename: Robert U
authors.initials: RU
authors.lastname: Newton
authors.affiliation: Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan UniversityJoondalup, WA, Australia; Institute for Health and Ageing, Australian Catholic UniversityMelbourne, VIC, Australia.
authors.forename: Prue
authors.initials: P
authors.lastname: Cormie
authors.affiliation: Centre for Exercise and Sports Science Research, School of Medical and Health Sciences, Edith Cowan University Joondalup, WA, Australia.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Blazevich
keywords: Young's modulus; fascicle; patellar; quadriceps; rate of force development; tendon; viscoelastic