Post activation potentiation can be induced without impairing tendon stiffness
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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.
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.
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.
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.
KeywordsPotentiation Twitch Tendon Stiffness Isometric
Analysis of variance
Achilles tendon stiffness
Achilles tendon stiffness at 30 % of maximal voluntary isometric contraction
Achilles tendon stiffness at 50 % of maximal voluntary isometric contraction
Half relaxation time
Intra-class correlation coefficients
Maximal voluntary isometric contraction
Compound muscle action potential
Newton meter per millimeter
Post activation potentiation
Root mean square
Rate of torque development
Time to peak
This project was financially supported by the Swedish National Centre for Research in Sports (CIF) and Fundação para a Ciência e Tecnologia (FCT). Paulo Gago wishes to thank the Fundação para a Ciência e Tecnologia (FCT), Portugal for the Ph.D. grant SFRH/BD/79184/2011. We acknowledge Paul Sandamas´ contribution in developing the algorithm used for calculating Achilles tendon length.
Conflicts of interest
No conflicts of interests, financial or otherwise, are declared by the authors.
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