however , a 
 decrease in core stability is one of the main problems which keeps older adults from easily 
 performing activities of daily living1 . many previous studies 
 have reported that impairments of core stability are mainly caused by core muscle 
 weakness2 , 3 . core muscles are known to consist of the muscles around the 
 abdominal and lumbar regions , such as the rectus abdominis , erector spinae , quadratus 
 lumborum , external oblique and gluteus medius4 . these muscles play a key role in providing individuals with 
 stability during movement of the extremities1 , 5 . many therapists have conducted 
 strengthening exercises such as trunk stabilization exercise in order to improve the core 
 stability . however , there is a lack of scientific evidence showing the validity of trunk 
 stabilization exercise , and the effects of trunk stabilization exercise on muscle 
 activations are still controversial . thus , the purpose of this study was to investigate the 
 effects of trunk stabilization exercise on the muscle activations of the core stability 
 muscles , to provide scientific evidence for the validity of trunk stabilization 
 exercises . the study subjects were 15 elderly people hospitalized in a geriatric hospital ( table 1table 1.general characteristics of the subjectsvariablessubjects ( n=15)gender ( m / f)6/9age ( years)76.510.1height ( cm)158.910.9weight ( kg)51.116.0meansd ) . the inclusion criteria for the subjects were as follows : at least 65  years 
 old , no falls within the last year , and no disease that might have affected the results of 
 this study . those who had visual impairment , hearing damage , nervous system or vestibular 
 organ problems , or who were unable to understand the nature of the experiment were excluded . all subjects understood the purpose of this study and provided their informed consent in 
 writing prior to their participation in the study in accordance with the ethical principles 
 of the declaration of helsinki . the subjects carried out their ordinary activities and performed trunk stabilization 
 exercises with a swiss ball in the geriatric hospital for 20 minutes , five times per week 
 for 8 weeks . trunk stabilization exercises were carried out using the professional exercise 
 ball ( thera - band , usa ) and the diameter of the ball was individually chosen so that the 
 subjects feet confort touched on the ground when sitting on the ball . the subjects trunk muscle activations were measured using a mp150 ( biopac system , usa ) . to 
 focus on specific muscles , electrodes were attached to the skin over the rectus abdominis , 
 erector spinae , lateral low - back ( quadratus lumborum and external oblique ) , and gluteus 
 medius muscles . the paired t - test was used to 
 examine differences between pre- and post - intervention . after the intervention , the muscle activations of the rectus abdominis , erector spinae , 
 lateral low - back ( quadratus lumborum and external oblique ) , and gluteus medius ( p < 
 0.05 ) . especially , the lateral low - back and gluteus medius activities showed greater 
 increases than the other muscles ( table 
 2table 2.comparison of muscle activations between pre- and post - testvariablesprepostra ( % rvc)93.320.8134.039.7*es ( % rvc)78.520.3112.923.8*lateral low - back ( % rvc)91.519.6158.460.9*gm ( % rvc)107.431.6167.962.5*meansd . * p<0.05 . ra , rectus abdominis ; es , erector spinae ; lateral low - back , 
 quadratus lumborum and external oblique ; gm , gluteus medius ) . meansd . * p<0.05 . ra , rectus abdominis ; es , erector spinae ; lateral low - back , 
 quadratus lumborum and external oblique ; gm , gluteus medius this study was conducted to investigate the effects of trunk stabilization exercise on core 
 muscle activities . the results show that there were significant increases in emg activities 
 of the core muscles . that is , core muscles such as rectus abdominis , erector spinae , 
 quadratus lumborum , external oblique and gluteus medius were more activated after performing 
 the trunk stabilization exercise program of this study . we consider this is because the trunk stabilization exercise with a swiss ball increased 
 the muscle activity . many previous studies have reported that strengthening exercises , such 
 as trunk stabilization exercise , are effective at increasing muscle activity6 , 7 . stephen reported that greater motor unit recruitment and a higher rate of motor unit firing , 
 which may be elicited by strengthening exercise , can raise the level of muscle 
 activation8 . furthermore , our results 
 are in agreement with previous studies of core stability exercises . konin reported that the 
 transverse abdominis muscle is the first and main contractor among the core muscles during 
 movements , and it has also been reported that the external oblique muscle is the main factor 
 responsible for maintaining stability , by fixation of the pelvis5 , 9 . paraspinal muscles 
 assist the multifidus muscle to maintain the spine in diverse curvature alignments created 
 by the abdominal muscles4 . in addition , 
 the thoracolumbar fascia which is connected to the arms and legs is believed to activate 
 proprioception10 . through this 
 connection , it is possible that synergic activation would occur . besides , to maintain 
 balance , synergistic muscles have been reported to provide agonist muscle groups with 
 inhibitory and facilitatory inputs11 , 12 . according to these explanations and 
 results , the trunk stabilization exercise with a swiss ball increased the muscle activities 
 of the elderly . generally , the elderly are not powerful enough to perform common resistance exercises . the 
 results of this study not only provide evidence of the validity of trunk stabilization 
 exercise but also suggest an alternative approach to improve the core stability of the 
 elderly . second , a follow - up test was not scheduled or conducted . further study that 
 addresses these limitations
[ purpose ] the purpose of this study was to investigate the effects of trunk stabilization 
 exercise on the muscle emg activations related to core stability . [ subjects and methods ] 
 fifteen elderly people in a geriatric hospital performed trunk stabilization exercises 
 with a swiss ball for 20 minutes five times per week for 8 weeks . 
 trunk muscle activations 
 were measured using electromyography before and after the intervention . [ results ] after 
 the intervention , the muscle activations of the rectus abdominis , erector spinae , lateral 
 low - back ( quadratus lumborum and external oblique ) , and gluteus medius muscles increased 
 significantly . 
 [ conclusion ] the trunk stabilization exercise with a swiss ball 
 significantly increased the muscle activities of the elderly .