heel height
somatosensory alternation around the ankle and foot ( Gefen et al ., 2002 ). However , no adverse effect on postural reaction was found even in 10.1 cm HHS . This finding suggested that the delay of latency was often associated with neurological disorders and anatomical constraints , other than the footwear design ( Redfern et al ., 2001 ). Previous studies demonstrated that HHS can impair human balance during other extrinsic perturbations ( e . g ., sinusoidal oscillations and waist pulling ) ( Choi & Cho , 2006 ; Sun et al ., 2017 ). Sun et al . found that the COP displacement increased , and the COP trajectory transferred to the medial foot significantly during AP and ML perturbations when wearing 6.6 cm compared with 0.8 cm HH . However , the study did not control the shoe design and applied three types of HHS in the experiment ( Sun et al ., 2017 ). Choi and Cho compared human balance control of HHS wearers in barefoot and highheeled posture when experiencing a waist-pull perturbation by quantifying the displacement and velocity of the COP . Results suggested that human balance control was approximately twice worse in HHS than barefoot , and the perturbation amplitude was not attributed to the participants ’ body weight and height ( Choi & Cho , 2006 ). Experienced HHS wearers exhibited no improvement in postural control under dynamic perturbations . They applied different muscle activation patterns compared with inexperienced wearers . Experienced wearers exerted significantly more muscle activities on GM and less muscular effort on VL , TA , and erector spinae than novices in SOT ( Hapsari & Xiong , 2016 ). During HHS walking , substantial increases in muscle fascicle strains and muscle activation were
"... experienced HHS wearers may have increased muscle fascicle strains and lower limb muscle activation than inexperienced wearers during HHS walking ."
found in experienced HHS wearers compared with barefoot walking during the stance phase ( Cronin , Barrett & Carty , 2012 ). Experienced wearers may regulate the flexibility of the neuromuscular system to adapt to possible perturbations ( e . g ., walking and external perturbations ) and can vary according to different HHs ( Alkjær et al ., 2012 ).
Our study investigated that the COG movement velocity and directional control in LOS significantly decreased in 10.1 cm compared with that in 3.9 cm HHS . Consistent with the previous study , when HH increased to 10 cm , slower COG movement velocity was observed in 10 cm than in four cm HH in LOS ( Mika et al ., 2016 ). The increased HH may induce the fear of falling in HHS wearers . The HHS
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