Acute effect of tendon vibration applied during isometric contraction at two knee angles on maximal knee extension force production

Abstract

The aim of the current study was to investigate the effect of a single session of prolonged tendon vibration combined with low submaximal isometric contraction on maximal motor performance. Thirty-two young sedentary adults were assigned into two groups that differed based on the knee angle tested: 90° or 150° (180° = full knee extension). Participants performed two fatigue-inducing exercise protocols: one with three 10 min submaximal (10% of maximal voluntary contraction) knee extensor contractions and patellar tendon vibration (80 Hz) another with submaximal knee extensor contractions only. Before and after each fatigue protocol, maximal voluntary isometric contractions (MVC), voluntary activation level (assessed by the twitch interpolation technique), peak-to-peak amplitude of maximum compound action potentials of vastus medialis and vastus lateralis (assessed by electromyography with the use of electrical nerve stimulation), peak twitch amplitude and peak doublet force were measured. The knee extensor fatigue was significantly (P<0.05) greater in the 90° knee angle group (-20.6% MVC force, P<0.05) than the 150° knee angle group (-8.3% MVC force, P = 0.062). Both peripheral and central alterations could explain the reduction in MVC force at 90° knee angle. However, tendon vibration added to isometric contraction did not exacerbate the reduction in MVC force. These results clearly demonstrate that acute infrapatellar tendon vibration using a commercial apparatus operating at optimal conditions (i.e. contracted and stretched muscle) does not appear to induce knee extensor neuromuscular fatigue in young sedentary subjects.

Fig 1. Illustration of the experimental protocol.

MVC: maximal voluntary contraction; 1 arrow: single electrical stimulus; 2 arrows: doublet stimulation (10 ms between 2 electrical stimuli); condition: with vibration or without vibration; dotted line: rest period.

Fig 2. Illustration of experimental setup used during neuromuscular assessment and fatiguing exercise for the experimental session in which the individuals were tested at 150° knee angle.

VL: Vastus Lateralis; VM: Vastus Medialis.

Fig 3. Effect of knee angle and fatiguing exercise on neuromuscular characteristics.

A represents the effect of knee angle and fatiguing exercise on MVC force. B represents the effect of knee angle and fatiguing exercise on voluntary activation level, C represents the effect of knee angle and fatiguing exercise on potentiated doublet force. Note that this figure represents the significant interaction between angle and time, i.e. the conditions with vibration and without vibration are pooled. MVC: Maximal voluntary contraction; VAL: Voluntary activation level. * P <0.05, **P<0.01, ***P<0.001.