Author(s): AMIEZ, N., MARTIN, A., PAIZIS, C., Institution: UNIVERSITÉ BOURGOGNE FRANCHE-COMTÉ, Country: FRANCE, Abstract-ID: 1748

INTRODUCTION:
The acute application of local vibration (LV) leads to the projection of Ia afferents to the alpha motor neurons pool and sensorimotor areas of the cortex. Depending on the conditions under which the LV is applied, two phenomena may occur: the tonic vibratory reflex (TVR) and the illusion of movement (1, 2). This study aimed to understand the role of these two phenomena, whose presence is rarely controlled in studies, on the ability to produce maximum voluntary isometric contraction (MVIC).
METHODS:
The LV was applied to the flexor carpi radialis muscle (FCR) of 16 participants (6 minutes, continuous, 80 Hz, 2mm amplitude) in two separate sessions to test both conditions: one favoring the presence of TVR (visual attention focused on the vibrating wrist, no electromyographic muscle feedback), the other favoring ILLUSION (hand hidden, focus on kinesthetic feedback, electromyographic feedback from the FCR muscle). Illusion perception was measured subjectively, and electromyographic activity (EMGa) of the FCR muscle and the extensor carpi radialis (ECR) antagonist muscle recorded during LV was compared with EMGa recorded at rest. MVIC with superimposed and potentiated doublet electrical stimulations at 100Hz were performed in isometric flexion and extension. Assessments were performed 10 minutes before (PR1), and just before (PR2) the LV protocol, and then 0 (P0) and 30 minutes (P30) after the end of the protocol. In addition, voluntary activation level (VAL) and maximal EMGa of the FCR and ECR muscles during MVIC were studied.
RESULTS:
Compared to rest, EMGa increased during LV for vibrated muscle only in TVR condition (P < 0.001). The illusion of movement was greater in the ILLUSION condition than in the TVR condition (P < 0.001). The repeated measures ANOVA showed an interaction only for MVIC performed in flexion. While the ILLUSION condition showed no change (P > 0.472), MVIC in the TVR condition was lower at P0 (P < 0.027) and P30 (P < 0.034) compared with PR1 and PR2. In addition, the MVIC at P0 was lower than that observed in the ILLUSION condition (P = 0.001). Moreover, the amount of TVR was negatively correlated with the decrease in MVIC. Other variables remained unchanged.
CONCLUSION:
The ability to produce maximal force is reduced only when the six minutes of LV induces TVR, and the amount of TVR recorded on the vibrated muscle is negatively correlated with force loss. Consequently, the conditions under which LV is applied (i.e., EMGa of the vibrated and antagonist muscle and the presence of illusion) should be better controlled to ensure reproducibility of results accros studies.

References:
1. Burke D, et al., J Physiol, 1976. doi: 10.1113/jphysiol.1976.sp011580.
2. Taylor MW, et al., Multisens Res, 2017. doi: 10.1163/22134808-00002544.