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- Gago, Paulo, 1984-, et al.
(författare)
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Effects of post activation potentiation on electromechanical delay
- 2019
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Ingår i: Clinical Biomechanics. - : Elsevier. - 0268-0033 .- 1879-1271. ; 70, s. 115-122
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Tidskriftsartikel (refereegranskat)abstract
- Electromechanical delay (EMD) presumably depends upon both contractile and tensile factors. It has recently been used as an indirect measure of muscle tendon stiffness to study adaptations to stretching and training. The aim of the present study was to investigate whether contractile properties induced by a 6 s maximum voluntary isometric contraction (MVIC) could affect EMD without altering passive muscle tendon stiffness or stiffness index. Plantar flexor twitches were evoked via electrical stimulation of the tibial nerve in eight highly trained male sprinters before and after a 6 s MVIC in passive isometric or passively shortening or lengthening muscles. For each twitch, EMD, twitch contractile properties and SOLM-Wave were measured. Passive muscle tendon stiffness was measured from the slope of the relation between torque and ankle angle during controlled passive dorsal flexion and stiffness index by curve-fitting the torque angle data using a second-order polynomial function. EMD did not differ between isometric, lengthening or shortening movements. EMD was reduced by up to 11.56 ± 5.64% immediately after the MVIC and stayed depressed for up to 60 s after conditioning. Peak twitch torque and rate of torque development were potentiated by up to 119.41 ± 37.15% and 116.06 ± 37.39%, respectively. Rising time was reduced by up to 14.46 ± 7.22%. No significant changes occurred in passive muscle tendon stiffness or stiffness index. Using a conditioning MVIC, it was shown that there was an acute enhancement of contractile muscle properties as well as a significant reduction in EMD with no corresponding changes in stiffness. Therefore, caution should be taken when using and interpreting EMD as a proxy for muscle tendon stiffness.
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| 2. |
- Gago, Paulo, et al.
(författare)
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Passive Muscle Length Changes Affect Twitch Potentiation in Power Athletes.
- 2014
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Ingår i: Medicine & Science in Sports & Exercise. - 0195-9131 .- 1530-0315. ; 46:7, s. 1334-1342
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Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: A conditioning maximal voluntary muscle action (MVC) has been shown to induce post-activation potentiation, i.e. improved contractile muscle properties, when muscles are contracted isometrically. It is still uncertain how the contractile properties are affected during ongoing muscle length changes. The purpose of this study was to investigate the effects of a 6 s conditioning MVC on twitch properties of the plantar flexors during ongoing muscle length changes.METHODS: Peak twitch, rate of torque development (RTD) and relaxation (RTR), rising time and half relaxation time (HRT) were measured from supramaximal twitches evoked in the plantar flexors of 11 highly trained athletes. Twitches were evoked prior to a 6 s MVC and subsequently on 8 different occasions during a 10-minute recovery, for five different modes: fast lengthening, slow lengthening, isometric, fast shortening and slow shortening of the plantar flexors.RESULTS: The magnitude and duration of effects from the conditioning MVC were significantly different between modes. Peak twitch, RTD and RTR significantly increased for all modes but more so for twitches evoked during fast and slow shortening as compared to lengthening. Rising time was reduced in the lengthening modes, but slightly prolonged in the shortening modes. HRT was significantly reduced for all modes except fast lengthening.CONCLUSION: The findings show that the effects of a conditioning MVC on twitch contractile properties are dependent on direction and velocity of ongoing muscle length changes. This may imply that functional enhancements from a conditioning MVC might be expected to be greatest for concentric muscle actions, but are still present in isometric and eccentric parts of a movement.
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