Abstract
Muscle activation (activation time) and the beginning of movement (motor reaction time) can be changed depending on the complexity of the task. The objectives of this study were to compare the time for activation of the paraspinal and the vastus lateralis muscles, and the motor reaction time during the execution of the tasks sit-to-stand (STS) and sit-to-walk (STW), which includes the execution of the subsequent task of gait initiation. Twelve healthy young subjects participated in the study. They performed two tasks(STS and STW), five times each, randomly, separated by two minutes of rest. The kinematics of the movement were recorded using a digital electrogoniometer attached to the hip joint and muscle activation using surface electromyographyin both muscles. The average of the five repetitions was calculated for each task. The beginning of the task was signaled by a luminous device, which was also used to identify the initial point for calculating the activation time andmotor reaction time. Both muscles showed a longer latency for the activation time and motor reaction time during the STW task when compared with STS. Basedon these results, it can be concluded that both the postural (paraspinal) and prime mover muscles (vastus lateralis) undergo change in the motor programming during the execution of the STS task when a subsequent task (gait initiation) is included. Motor programming is dependent on task complexity, where a more complex task (STW) will result in delays of movement programming and execution.
Highlights
The physiological and biomechanical mechanisms that allow humans to maintain a bipedal posture, generally called postural control, are frequent topics in the area of biomechanics and motor control[1,2,3,4]
The paraspinal muscle showed lower values of AT for the STS task compared with the STW task [t(11) = -3.132; p=0.010] (Figure 2A)
The vastus lateralis muscle showed significantly lower values of AT for the STS task compared with the STW task [t(11) = -4.776; p=0.001] (Figure 2B)
Summary
The physiological and biomechanical mechanisms that allow humans to maintain a bipedal posture, generally called postural control, are frequent topics in the area of biomechanics and motor control[1,2,3,4]. An efficient control of the muscles by the central nervous system (CNS) is required in order to maintain the position and body orientation in space[3]. It is vital that sensory and motor information are precisely coordinated so that the desired task is performed successfully[1,5]. The sit-to-stand (STS) movement is common in our everyday lives and is essential in maintaining an individual’s independence. This movement requires synergistic actions among the extensor and flexor muscles of the trunk and knees. Studies[1,6,7] that analyzed electromyographic patterns during the STS task in healthy young adults have assigned the role of prime movers to the quadriceps and hamstring muscles, while the paraspinal, tibialis anterior, soleus, abdominal, sternocleidomastoid, and trapezius muscles were considered responsible for fine postural adjustments during the action of the prime movers
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