Noriyoshi Yamashita

EMG activities in mono- and bi-articular thigh muscles in combined hip and knee extension.

Summary8 male subjects were tested to elucidate the organization of EMG activities in mono- and bi- articular thigh muscles when hip and knee extension are combined. 2 types of isometric movement, single and dual joint movements, were studied: 1) 20% of maximal voluntary contraction (MVC) in separate hip extension (HE20) and knee extension (KE20), 2) simultaneous HE20 and KE20, combined voluntarily (HE20 · KE20). In HE20 · KE20, the value of the integrated EMG (IEMG) from the muscles tested was normalized as a percentage (%IEMG) of the IEMG of each muscle in HE20 for gluteus maximus (GM) and semimembranosus (SM), and in KE20 for vastus medialis (VM) and rectus femoris (RF). The average %IEMG was 50.5±16.9% for GM, 42.1±6.1% for SM, 153.4±22.8% for VM and 66.6±18.7% for RF. These data suggest that the EMG activities of GM, SM and RF are inhibited and the EMG activity of VM is facilitated by combining hip extension with knee extension.

Anticipatory changes of soleus H-reflex amplitude during execution process for heel raise from standing position

Soleus (SOL) H-reflex amplitude changes before the EMG onset of that muscle were compared between simple plantar flexion (SPF) and heel raise from standing position (STM). Results indicated that (1) the SOL H-reflex amplitude decreased during the STM but not the SPF, (2) in the STM, anticipatory EMG activity in the antagonist tibialis anterior (TA) appeared before the EMG onset of the agonist (SOL) and the onset corresponded to the initiation of the decreasing SOL H-reflex, and (3) EMG reaction time of the SOL in the STM was significantly longer than in the SPF. These results suggest that the decreasing SOL H-reflex amplitude is caused by the reciprocal inhibition originating from the postural synergy, the TA. The functional significance of the decreased SOL H-reflex amplitude might lead to a delay in the activation of focal musculature.

Inter-relationships among anticipatory EMG activity, Hoffmann reflex amplitude and EMG reaction time during voluntary standing movement

SummaryIn order to understand the process of executing a voluntary standing movement, the parameters latency (AEA-LT), duration (AEA-DUR) and amplitude (AEA-AMP) of the anticipatory electromyographic (EMG) activity (AEA) in the tibialis anterior muscle, Hoffmann (H) reflex amplitude in the soleus muscle (Sol) prior to the onset of EMG activity in that muscle, and EMG reaction time (EMG-RT) were measured during heel raising from the standing position. The following results were obtained: the three parameters of AEA correlated with EMG-RT in each subject; the average values for all nine normal subjects werer=0.856 for AEA-DUR,r=0.448 for AEA-LT andr= −0.215 for AEA-AMP; for the group the mean value of AEA-DUR correlated significantly with that of EMG-RT (r=0.983,P<0.01), while no such significant correlation was observed for AEA-LT; the average value of the AEA-DUR in three slower EMG-RT performers (SLOW-PFM) was significantly longer (P<0.05) than that in three faster ones (FAST-PFM), while no significant difference in the AEA-LT was observed; and lastly the total area of the anticipatory suppression of the Sol H reflex amplitude in the SLOW-PFM was greater than that in the FAST-PFM. These results suggest that AEA-DUR, representing postural responses, rather than AEA-LT, reflecting cognitive processes, may have had a close link with EMG-RT, and that the increased suppression in Sol H reflex amplitude originated from the increased anticipatory postural requirement, thus bringing about the EMG-RT delay.