title: Post activation potentiation can be induced without impairing tendon stiffness.
abstract: OBJECTIVE
  This study aimed to investigate conditioning effects from a single 6-s plantar flexion maximal voluntary isometric contraction (MVIC) on Achilles tendon stiffness (ATS) and twitch properties of the triceps surae in athletes.
  
  
  METHODS
  Peak twitch (PT), rate of torque development (RTD), rising time (RT₁₀₋₉₀%) and half relaxation time (HRT) were measured from supramaximal twitches evoked in the plantar flexors of 10 highly trained athletes. Twitches were evoked before and at seven occasions during 10 min of recovery after a 6-s MVIC. In a second session, but at identical post-conditioning time points, ATS was measured at 30 and 50% of MVIC (ATS₃₀% and ATS₅₀%) using an ultrasonography-based method.
  
  
  RESULTS
  The magnitude and duration of the conditioning MVIC on muscle contractile properties were in accordance with previous literature on post activation potentiation (PAP), i.e., high potentiation immediately after MVIC, with significant PAP for up to 3 min after the MVIC. While PT and RTD were significantly enhanced (by 60.6 ± 19.3 and 90.1 ± 22.5%, respectively) and RT₁₀₋₉₀% and HRT were reduced (by 10.1 ± 7.7 and 18.7 ± 5.6%, respectively) after conditioning, ATS remained unaffected.
  
  
  CONCLUSIONS
  Previous studies have suggested that changes in stiffness after conditioning may interfere with the enhancements in twitch contractile properties. The present study, however, provided some evidence that twitch enhancements after a standard PAP can be induced without changes in ATS. This result may suggest that athletes can use this protocol to enhance muscle contractile properties without performance deficits due to changes in ATS.
authors.affiliation: Research Center for Sport, Health and Human Development, University of Beira Interior (UBI/CIDESD), Covilhã, Portugal.
authors.forename: Paulo
authors.initials: P
authors.lastname: Gago
authors.forename: Anton
authors.initials: A
authors.lastname: Arndt
authors.forename: Olga
authors.initials: O
authors.lastname: Tarassova
authors.forename: Maria M
authors.initials: MM
authors.lastname: Ekblom
mesh_terms: D000125:Achilles Tendon / Q000502:physiology*; D000328:Adult; D006801:Humans; D007537:Isometric Contraction; D008297:Male; D018763:Muscle Fatigue; D018482:Muscle, Skeletal / Q000502:physiology*