The Effect of Short-term Muscle Vibration on Knee Joint Torque and Muscle Firing Patterns during a Maximal Voluntary Isometric Contraction

Abstract

Objective: To investigate the effect of short-term vibration frequencies on muscle force generation capabilities.Method: Six healthy participants were recruited for this study and only their dominant leg was tested. The subjects were tested under five conditions of vibration frequencies with constant amplitude: 0 Hz (no vibration), 30 Hz, 60 Hz, and 90 Hz, and the vibration amplitude was 10 mm for all frequency conditions. The vibration was applied to the rectus femoris (RF). The subjects were then instructed to maintain a steadystate isometric knee joint torque (100 Nm) for the first 6 s. After the steady-state torque production, the subjects were required to produce isometric knee joint torque by leg extension as hard as possible with a start signal within the next 3 s. The vibration was applied for ~4 s starting from 1 s before initiation of the change in the steady-state knee joint torque. Results:The results showed that the maximum voluntary torque (MVT) of the knee joint increased with the vibration frequencies. On average, the MVTs were 756.47 Nm for 0 Hz (no vibration) and 809.61 Nm for 90 Hz. There was a significant positive correlation (r = 0.71) between the MVTs and integrated electromyograms (iEMGs). Further, the co-contraction indices (CCIs) were computed, which represent the ratio of the iEMGs of the antagonist muscle to the iEMGs of all involved muscles. There was a significant negative correlation (r = 0.62) between the CCIs and MVTs, which was accompanied by a significant positive correlation (r = 0.69) between the iEMGs of the vibrated muscle (RF). There was no significant correlation between the MVTs and iEMGs of the antagonist muscle. Conclusion:The results of this study suggest that the short-term vibration on the muscle increases the level of muscle activation possibly owing to the increased Ia afferent activities, which enhances the muscle force generation capability.

The Effects of External Vibration on Coordination Strategies of Multi-Muscles during Voluntary Isometric Torque Production

“…Several previous studies that have applied vibration stimuli have shown an increase in force generation [31]. The maximal voluntary torque (MVT) capacity in our previous study also increased about 20% when vibration stimulation was applied to the rectus femoris [16]. In addition, similar to the task of this study, vibration stimulation improves the nervous system capacity, such as a specific receptor feedback mechanism, in a task that generates a constant target force while reducing the activity of the agonist without increasing the size and number of muscle fibers, thereby exhibiting positive impacts on the accuracy [32].…”

“…1A). The hip and knee joint angles with respect to the horizontal axis were fixed at 100° and 120° [16,21]. The vibrators were attached along the periphery of the RF (Fig.…”

“…The organization of M-modes is beneficial to some extent in reducing the number of variables governed by the controller. As such, M-mode is an activated muscle group that is individually manipulated by the central nervous system (CNS) and reduces the problem of motor redundancy [15][16][17][18].…”

History-Dependence of Muscle Excitation and Oxygenation During Isometric Knee Extension Force Production

“…1A). The hip and knee joint angles with respect to the horizontal axis were fixed at 100° and 120°, respectively [23,24]. A strap across the waist and trunk prevented excessive movement, and the participants were required to hold the side grips tightly by using both hands (Fig.…”