PERSPECTIVE OF MUSCLE ACTIVATION AND MUSCLE FIBER CHARACTERISTICS IN AGING LOWER EXTREMITY MUSCLES FOR MOVEMENT MODALITIES PERFORMED AT DIFFERENT CONDITIONS
Chow Khuen Chan1,2, Timothy Guojun Fu1, Cai Lin Chua1, Chen Hua Yeow1
1National University of Singapore, Singapore;
2University of Malaya, Malaysia
The sensorimotor performance in human movement with dissimilar conditions and age has not been established. Deterioration of the sensorimotor causes poor gait performance, peculiarly in muscle strength and muscle reaction timing. This further elicits that older people has lower ability to control their movement and speed, which causes instability and falling cases. Also, the sensorimotor decline affects the muscle activation and peak activation timing. Furthermore, deterioration of muscle properties (slow- and fast-twitching fibers) attribute to gait decline. Thence, forward gait is selected as the movement modality and this study ought to provide the threefold objectives. The main aim is to investigate the speed and age factors in manipulating the muscle recruitment by the realization of maximum muscle activation. The secondary objective is to examine the sensorimotor functionality associations in relation to ageing forward walking with different speed, particularly the time to peak muscle activation. The third aim is to investigate the modulation of muscle fiber type as the speed and age alters. Eighteen participants (9 young and 9 elderly) were recruited; electromyography (EMG) signals were recorded from the lower extremity muscles: rectus femoris (RF), vastus lateralis (VL), vastus medialis (VM), semimembranosus/semitendinosus (STSM), biceps femoris (BF), tibialis anterior (TA), gastrocnemius lateralis (GL), gastrocnemius medialis (GM), soleus (SOL) and gluteus maximus (GMax). Upon filtering and normalizing the EMGs, essential points were selected from stance and swing phases for evaluation. In assessing muscle fiber selection, EMGs were converted to frequency domain by utilizing mean frequency (MNF) variable; thereafter, extracted from both gait phases. As the age increases, there is a peak activation reduction in GM (p<0.05) and slower reaction time in RF, BF and STSM (p<0.05). Additionally, there is reduction in fast-twitching muscles (p<0.05) in RF and TA as age heightens. This study is crucial for rehabilitation program and assistive device designation.