Effect of prolonged vibration to synergistic and antagonistic muscles on the rectus femoris activation during multi-joint exercises

Ryoichi Ema,Naokazu Miyamoto,Ryota Akagi,Hirokazu Takayama

doi:10.1007/s00421-017-3702-1

Abstract

PurposeUnique neuromuscular activation of the quadriceps femoris is observed during multi-joint leg extensions: lower activation of the biarticular rectus femoris (RF) than monoarticular vasti muscles. As one of the potential mechanisms for the lower RF activation, Ia afferent-mediated inhibitory connections between synergistic muscles and/or between agonist and antagonist muscles have been proposed. If this is the major factor, it is hypothesized that RF activation during multi-joint leg extensions increases after prolonged vibration to synergistic and/or antagonist muscles. This study tested the hypothesis.MethodsFourteen men exerted maximal voluntary isometric knee extension and flexion and performed submaximal parallel squat before and after one of the following three interventions on different days: prolonged vibration to the vastus lateralis (VL, synergist) or biceps femoris (BF, antagonist), or quiet sitting for 30 min. Muscle activations of the quadriceps femoris and hamstrings were determined using surface electromyography.ResultsAfter prolonged VL or BF vibration, VL (21%) or BF (30%) activation during isometric contractions significantly decreased, which was significantly correlated with the reduction of the maximal isometric knee extension or flexion strength. The magnitude of RF activation during squat was significantly lower than those of VL and the vastus medialis. No significant increase in RF activation during squat was observed after vibrations.ConclusionThe findings suggest that lower biarticular RF activation compared with the monoarticular vasti muscles during multi-joint exercises does not result from the modulation by peripheral inhibitory input from Ia afferents originating from synergist and/or antagonist muscles.

Highlights

A synergistic muscle group is generally composed of monoarticular and biarticular muscles
On the second to fourth days, the participants joined the following three interventions during quiet sitting for 30 min in random order: tonic vibration to the right thigh’s VL muscle belly (VL condition), tonic vibration to the right thigh’s biceps femoris long head (BF) muscle belly (BF condition) and quiet sitting without any vibration (CON condition)
The MVCKE torque significantly decreased after the intervention in VL condition (P = 0.006), whereas it did not change in BF or CON condition (P = 0.125–0.607)

Summary

Introduction

A synergistic muscle group is generally composed of monoarticular and biarticular muscles. Because RF contraction produces hip flexion torque as well as knee extension torque, and because muscle shortening of RF during multi-joint leg extensions can be smaller than those of the vasti and higher force-generating capability (Gregoire et al 1984), it is possible that less excitatory and/or inhibitory mechanisms exist for RF activation during multi-joint leg extensions As one of such mechanisms, Ia afferent-mediated inhibitory connections between synergistic muscles (Gritti and Schieppati 1989) and/or between agonist and antagonist muscles (Crone et al 1987) have been proposed (Ema et al 2016a; Yamashita 1988). Focusing on the underpinning mechanisms for the lower RF activation compared with the vasti during multi-joint leg extensions at high intensity is expected to provide significant information regarding the specificity in training response of the quadriceps femoris induced by multi-joint exercises

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