Characteristics And Mechanism Of Neuromuscular Adaptation To Weight Whole-body Vibration Training

Purpose:One purpose of this research was to examine if the addition ofwhole-body vibration and30%1RM external load would enhance increasesin muscle activity during dynamic squatting in8leg muscles and find thevibration frequency which activated maximal muscle activity. The otherpurpose was to study whether whole body vibration (WBV) combined withconventional resistance training (CRT) induce a higher increase inneuromuscular measures compared with CRT. The results enrich anddevelop the training’s theory system and provide reference for WBVtraining program.Methods:Ten healthy male performed a series of dynamic squats (unloaded withno WBV, unloaded with WBV, loaded with no WBV, and loaded withWBV). The load was set to30%of maximum force and WBV included30-,40-,50-Hz frequencies with2-mm amplitude. Muscle activity was recordedwith surface electromyography (EMG) on the rectus femoris (RF), vastusmedialis (VM), vastus lateralis (VL), biceps femoris (BF), tibialis anterior(TA), semitendinosus (SEM), and gastrocnemius (GC) and is reported asEMGrms (root mean square) normalized to%maximal voluntary contraction(MVC).Sixteen male college students who major in track and field wererandomized in two groups; squat only (S) and combination of WBV andsquat (S+V). They were participated in training programs three times aweek. S+V performed eight sets with ten repetitions with corresponding30%1RM loads on the vibrating platform (ZenPro TVR-5930, Taiwan,China), whereas S performed the same protocol without vibration. Thefrequency (50Hz) was chosen after the first studies. Squat jump (SJ),counter movement jump (CMJ), presynpatic inhibition (PSI), the T-reflexand H-reflex were measured before and after training. We analyzed thedifferences of neural adaptation and strength adaptation, applyingindependent-Samples t-test between groups and a paired t-test within eachgroup. Results:A two-factor ANOVA analysis of variance showed that vibrationstimulation had significant effect on EMGrms of all the muscles (P<0.05),and loads had significant effect on EMGrms of RF,VM,VL and GC (P<0.05).There was no significant interaction between vibration and load. Aftermultiple comparisons, it was found that exposure to WBV only50Hzsignificantly increased baseline muscle activity in all muscles.Applying t test within each group revealed that relative maximumstretch force of SJ, CMJ height, relative speed strength index, thecontribution of the stretch-shortening cycle (SSC) to jumpingperformance increased in WBV and CRT after training (P<0.05). H latency,Hmax/Mmax and T latency were significantly reduced, and PSI and Tamplitude were significantly increased only in S+V after training. T testshowed significant changes between groups after training in value-added ofCMJ height, relative speed strength index, the contribution of the SSC tojumping performance and H latency, Hmax/Mmax and PSI.Conclusions:It is suggested that WBV can increase the neuromuscular activity ofthe squat exercise in lower-extremity muscles. During dynamic squats,loads can increase the neuromuscular activity of agonistic muscle but cannot increase the neuromuscular activity of antagonist.During30%1RM loaded dynamic squats, exposure to WBV (50Hz,2mm) increased the neuromuscular activity of agonist and antagonist inlower limbs. The results demonstrate that the WBV can improve thesynchronization of motor unit and coordinating development betweenagonist and antagonist in the loaded condition.During30%1RM loaded dynamic squats, exposure to WBV is betterthan without WBV for increases in speed strength.Neuromuscular adaptation induced by weight whole-body vibrationtraining confirms the occurrence of changes in mechanical properties andthe excitability of the motoneurons and muscle spindle. This proposalwould indicate that neuromuscular adaptation is not only limited to themotor pathway to the muscle, but also concerns its sensory part.