An Acute Exposure to Muscle Vibration Decreases Knee Extensors Force Production and Modulates Associated Central Nervous System Excitability

Abstract

Local vibration (LV) has been recently validated as an efficient training method to improve muscle strength. Understanding the acute effects may help elucidate the mechanism(s). This study aimed to investigate the effects of a single bout of prolonged LV on knee extensor force production and corticospinal responsiveness of vastus lateralis (VL) and rectus femoris (RF) muscles in healthy young and old adults. Across two visits, 23 adult subjects (20–75 years old) performed pre- and post-test measurements, separated by 30-min of either rest (control; CON) or LV. Maximal voluntary contraction (MVC) force was assessed and transcranial magnetic stimulation (TMS) was used to evaluate cortical voluntary activation (VATMS) as well as the motor evoked potential (MEP) and silent period (SP). In 11 young adults, thoracic electrical stimulation was used to assess the thoracic motor evoked potential (TMEP). Although MVC decreased after both CON (−6.3 ± 4.4%, p = 0.01) and LV (−12.9 ± 7.7%, p < 0.001), the MVC loss was greater after LV (p = 0.001). Normalized maximal electromyographic (EMG) activity decreased after LV for both VL (−25.1 ± 10.7%) and RF (−20.9 ± 16.5%; p < 0.001), while it was unchanged after CON (p = 0.32). For RF, the TMEP and MEP/TMEP ratio decreased (p = 0.01) and increased (p = 0.01) after LV, respectively. Both measures were unchanged for VL (p = 0.27 and p = 0.15, respectively). No changes were reported for TMS-related parameters. These results confirm our hypothesis that modulations within the central nervous system would accompany the significant reduction of maximal voluntary force. A reduced motoneuron excitability seems to explain the decreased MVC after prolonged LV, as suggested by reductions in maximal EMG (all subjects) and TMEP area (data from 11 young subjects). A concomitant increased cortical excitability seems to compensate for lower excitability at the spinal level.

Vibration‐induced depression in spinal loop excitability revisited

“…), this confirms our recent findings of a decrease in rectus femoris TMEPs after LV (Souron et al . a ). We acknowledge that the magnitude of LV‐induced depressed motoneuron excitability reported here is largely lower than the global spinal loop excitability.…”

“…LV was applied while the subjects were relaxed in a seated position, with knee and ankle angles of 120 and 90°, respectively. According to previous studies reporting that Ia afferents discharge synchronously with vibration frequencies up to 80-120 Hz (Roll & Vedel, 1982;Roll et al 1989) and are sensitive to small vibration amplitude (Roll et al 1989), a 100 Hz frequency and a 1 mm amplitude were used in this study, in line with our previous studies investigating the acute effects of prolonged LV (Farabet et al 2016;Souron et al 2017a).…”

Intermediate Muscle Length and Tendon Vibration Optimize Corticospinal Excitability During Knee Extensors Local Vibration

“…Therefore, in line with our recent works that investigated the acute ( Souron et al, 2017b ) and chronic effects ( Souron et al, 2017a ) of LV on neuromuscular function of the KE, the present study aimed to investigate the effects of muscle length and vibration site (i.e., muscle vs. tendon) on LV-induced changes in corticospinal excitability of the KE. We hypothesized that the increase in MEPs amplitude during LV would be higher at a knee angle corresponding to a lengthened quadriceps muscle because of the increased responses of Ia afferents at long muscle length ( Burke et al, 1976b ).…”

“…The vibrating device (VB 115, Techno Concept, Mane, France) was locally applied and strapped directly on (i) the right RF muscle (40% of the muscle length from the upper edge of the patella to the anterior superior iliac spine) ( Souron et al, 2017a , b ) and (ii) the mid-portion of the infrapatellar tendon ( Konishi et al, 2002 ; Fry and Folland, 2014 ) ( Figure 1B ). As Ia afferents are sensitive to a small vibration amplitude ( Roll et al, 1989 ) and fire synchronously with vibration frequencies up to 120 Hz ( Roll and Vedel, 1982 ; Roll et al, 1989 ), vibration was set in the present study with a 100-Hz frequency and 1-mm amplitude, as in our previous works on KE ( Souron et al, 2017a , b ). During the control condition (see the Experimental protocol section for further details), the vibrators were turned off but remained strapped to the RF and the infrapatellar tendon.…”

“…When local vibration (LV) is acutely applied for 20–30 min to a muscle or a tendon, fatigue, i.e., a decrease in maximal-force generating capacity, is commonly reported ( Kouzaki et al, 2000 ; Konishi et al, 2002 ; Jackson and Turner, 2003 ; Yoshitake et al, 2004 ; Shinohara et al, 2005 ; Ushiyama et al, 2005 ; Richardson et al, 2006 ; Herda et al, 2009 ; Saito et al, 2016a ; Souron et al, 2017b ). It is suggested to be principally due to a reduction of maximal central drive ( Jackson and Turner, 2003 ; Ushiyama et al, 2005 ; Souron et al, 2017b ) related to the strong activation of muscle spindles Ia afferents during LV ( Burke et al, 1976a ). Since LV stimuli is a significant neuromuscular workload that induces fatigue, it is not surprising that when repeated, it could trigger long-term adaptations leading to improved neuromuscular function ( Souron et al, 2017c ), as already reported for traditional training that involved a variety of voluntary dynamic exercises, e.g., resistance training or cycling ( Burtin et al, 2012 ; Gathercole et al, 2015 ).…”