wearers manifested slow COG movement velocity , declined COG excursions , and worst directional control , particularly in the forward and backward directions ( Hapsari & Xiong , 2016 ). The experienced HHS wearers showed higher percentage of directional control in 10.1 cm HHS . It may be due to the motor learning effects in the experienced wearer , resulting in superior ankle strategy in maintaining postural stability ( Schaefer & Lindenberger , 2013 ). Nonetheless , another study suggested that the increased muscular coactivation around the ankle joint could enhance joint stiffness during HHS walking . The walking balance may be improved through altered muscle activation patterns ( Alkjær et al ., 2012 ; Nielsen & Kagamihara , 1993 ). The effects of muscle activation patterns on the postural control process in LOS among HHS wearers remain unclear .
The functional mobility was impaired when HH reached 3.9 cm . A number of studies have shown that walking in HHS may affect neuromechanics and kinematics of the lower limbs when HH increased to four cm HH ( Naik et al ., 2017 ). When walking in 4 and 10 cm HHS compared with flat shoes , the postural stability may be decreased on the account of high joint stiffness evaluated by muscle pair synchronization around the knee joint ( Pratihast et al ., 2018 ). Accordingly , the TUGT completion time was longer for impaired postural stability and reduced perceived stability , consistent with previous findings ( Arnadottir & Mercer , 2000 ). Our study found that the experienced HHS wearers had significantly shorter TUGT completion time and FRT distance than the novices . Long-time use of HHS has been suggested to shorten the gastrocnemius muscle fascicles and increase the Achilles tendon stiffness , thereby contributing to a restricted ankle ROM and reduced functional reach mobility ( Csapo et al ., 2010 ). Cronin et al . suggested that experienced HHS wearers may have increased muscle fascicle strains and lower limb muscle activation than inexperienced wearers during HHS walking . This finding indicates chronic adaptations in muscle – tendon structure related to HHS ( Cronin , Barrett & Carty , 2012 ). The experienced wearers could apply altered movement strategies to increase effort on muscular control around the knee and ankle joints , so as to obtain postural stability during HHS walking . However , high muscle activities may contribute to muscle inefficiency and raised energy cost during walking , thereby leading to muscle strains , muscle fatigue , and pain ( Cronin , 2014 ; Csapo et al ., 2010 ; Ebbeling , Hamill & Crussemeyer , 1994 ).
Although we found better functional mobility and higher perceived stability in experienced HHS wearer , no significant increase in overall postural control was detected in longtime HHS users in SOT . In functional tests , important resources , such as biomechanical constraints ( e . g ., strength and limits of stability ), cognitive processing ( e . g ., learning and attention ), movement strategies ( e . g ., anticipatory and voluntary ), and sensory strategies ( e . g ., sensory integration and reweighting ), are required for postural control . Thus , the loss of somatosensory in the foot and higher sensory weighting in vision cannot completely predict the deficiencies in functional mobility because the function
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