| Purpose:Based on data from the World Health Organization,the population aged at 65 or above will reach by 1.4 billion,and the elderly population will account for 16.5% of the world’s total population by 2030.At the same time,aging would influence the functions in different systems of human.In particular,the somatosensory system will fluctuate significantly with age,which in turn affects postural stability during standing and walking.Foot-ankle complex is the unique part of body to interaction with the ground,which is one of the important sensory pathways to provide sensory input to the central nervous system(CNS),then CNS control the center of gravity(Co G)to achieve postural stability.Previous studies have shown that older adults rely more on sensory input from their feet than younger adults in postural control.In addition,sensory input from the soles of the feet plays an even more important role in maintaining postural stability when other sensory systems such as vestibular sense or vision are defective or disturbed.However,the trends in plantar sensory sensitivity at different age groups and the effect of artificially altered sensory input of feet on postural control in young and old are quite unclear.Based on this,this study was divided into three parts(1)Are there any differences in the sensory input characteristics of foot-ankle complex among people of different age groups,and what kind of differences appear?(2)Immediate effects of foot sensory input stimulation on postural control in young and old.(3)To explore the effect of multimodal foot mechanical sensory input-increasing intervention methods on postural control in the elderly Research Methods:In the first part,we explored the characteristics of foot-ankle complex in different age groups,including 202 subjects,according to criteria of WHO,which are divided into four age groups: teenagers(n = 46),adults(n = 55),middle-aged adults(n = 47)and elderly(n = 54).Semmes Weinstein monofilaments(SWM)was used to test the tactile perception threshold of the plantar surface.The distance between the two points on the plantar was determined by the two-point discriminator.The vibration threshold was measured by VPT-I.The testing sites including the great toe,the first metatarsal region,the center of the forefoot,the fifth metatarsal region,the foot center and the heel.128 Hz tuning fork was used to measure the vibration sensation at the distal interphalangeal joint and lateral malleolus.Proprioception of ankle joint is divided into kinesthesia,position sense and muscle force sense,which are completed by motion threshold tester and CONTREX isokinetic respectively.Ankle position perception is expressed by the absolute error from the target value,and force perception test is expressed by the relative value of the absolute error.SPSS20.0 was used to statistically analyze the data,Shapiro Wilk is used to test whether the data is normally distributed,and Kruskal Wallis h test is used to judge whether there is a significant difference in the light touch of the foot in different age groups;One way ANOVA will be used to judge whether there are differences between the test indicators,and Tukey correction will be used for multiple comparisons.The significance level is set at p ≤ 0.05.In the second part,we mainly explore the immediate influence of different intensities of plantar pressure perception training on the posture control of young and elderly.A total of 61 subjects participated,including 30 elderly and 31 young adults.All the participants need to complete three tests,with a washout period of 7 days between each test.In the initial test,the foot and ankle sensory characteristics of young people and old people were tested,and the test method was the same as that in study 1.After the initial test,the subjects randomly selected three different hardness of rubber pads,namely Shore 45HA(5mm thick),Shore 30HA(15mm thick),and Shore 15HA(25mm thick),to stand with the whole foot touching the rubber pad for10 minutes.The participants perceived the pressure stimulus applied to the plantar.In order to ensure the existence of the intervention effect,SWM tests were immediately conducted on the great toe,the first metatarsal area and the fifth metatarsal area of the plantar.The Novel Pedar X system was used to collect the contact time,peak pressure,peak pressure and contact area parameters of nine areas of the plantar during3 M walking(M01 lateral heel;M02 medial heel;M03 lateral arch;M04 medial arch;M05 first metatarsal,M06 second-third metatarsal;M07 fourth-fifth metatarsal;M09great toe and M08 other four toes),At the same time,the dynamic posture control parameters(Center of pressue,Co P)of the subjects were collected during 3M walking;K-force plate was used to collect static posture control parameters after standing on rubber mat for ten minutes.The posture control parameters specifically include the sway displacement / velocity / velocity variation / amplitude of the human body pressure center(Co P)in the anterior/posterior,medial/lateral direction and the 95%confidence ellipse area(disturbance area).After the test,all participants returned to the laboratory for the second test,after a seven-day washout period,and then returned to the laboratory for the third test.SPSS 20.0 was used to statistically analyze the data;Mann Whitney U test was used to compare the inter group differences of SWM test between young adults and elderly,and Wilcoxon rank sum test was used to compare the intra group differences of SWM test between young people and old people before and after different intensity pressure stimulation.One-way ANOVA was used to compare the TPD,VPT and ankle kinesthetic threshold between the young and the old.The correlation between SWM plantar light tactile threshold test and posture stability parameters was assessed by Spearman correlation analysis.Pearson correlation analysis was used to judge whether there was a correlation between two-point discrimination test,vibration threshold test,ankle proprioception(kinesthetic and positional sensation)Whether there is correlation between muscle force perception and posture stability parameters;Two factor repeated measures ANOVA is used to pretest whether there is a difference between the posture control test indicators of young and old people after different hardness of rubber pad pressure stimulation.Tukey correction will be used for multiple comparisons,and the significance level is set at p≤ 0.05.In the third part,we conducted an 8-week randomized controlled experiment to explore the effect of multimodal plantar mechanoreceptor stimulation training on the posture stability of the elderly.96 elderly subjects(49 in the intervention group and47 in the control group)were included.The intervention group received multimodal plantar mechanoreceptor stimulation training three times a week for eight weeks.Specifically,it used a vibrator with a vibration frequency of 30 Hz to vibrate the great toe,the first metatarsal area,the fifth metatarsal area,the center of the forefoot,the foot center and the heel,and used rubber pads with different hardness used in the second part to stimulate plantar surface.Besides,participants also wearing customized textured insoles for 30 minutes of light tactile stimulation training.The control group received 30 minutes of walking training with ordinary insoles,three times a week for eight weeks.The test was conducted before and after the intervention,and the specific indicators were: foot sensation and ankle proprioception(the same as the first part);The contact time,peak pressure,peak pressure,contact area parameters and dynamic posture control parameters of the subjects in 9 zones of the plantar during 3M walking before and after the intervention were collected by the Novel Pedar X system(the specific parameters are the same as those in Study 2);Neurocom balance manager was used to collect the posture control parameters of subjects in sensory organization test,stability limit test,motor control test and adaption test of single leg standing tester.Shapiro-Wilk is used to analyze whether the data is normally distributed.Chi square test and the differences in demographic data between the two groups were assessed by One way ANOVA;The repeated measures ANOVA will be used to judge whether there are difference between the two groups before and after the intervention and between the test groups.Bonferroni correction will be used for multiple comparisons,and the significance level is set at p ≤ 0.05.Results:In Study 1,we found that there were significant differences in SWM test,TPD test,VPT test and the 128 HZ tuning fork test among teenagers,adults,middle-aged people and the elderly(p<0.001);There was a significant difference between the kinesthesia of ankle joint(p<0.001)in four age groups at the plantarflexion,dorsiflexion,inversion,eversion of the ankle joint;and the JPT in the plantarflexion(p=0.03)and dorsiflexion(p=0.03)of the ankle joint,but there was no significant difference between the ankle force sense tests in the plantarflexion and dorsiflexion.In Study 2,results showed that there were significant differences between young and old people in the SWM test in the great toe,the first metatarsal area and the fifth metatarsal area after different intensity of pressure stimulation,but there was no significant intra group difference in the SWM test;After the young and old people received different intensity of pressure stimulation,there were significant differences in the Co P-AP displacement/amplitude(p<0.001)Co P-ML displacement(p<0.001)and Co P-95% CI area(p<0.001)under EC-SLS.There were no significant differences in dynamic posture control parameters and plantar pressure parameters of young and old people during 3m walking after plantar pressure stimulation of different intensity.Spearman correlation analysis found that in EC-SLS,the plantar sensation of the elderly group was moderately correlated with Co P-AP displacement(r=0.580,p<0.001,95%CI:0.17～0.76),Co P-95% CI area(r=0.515,p<0.001,95%CI:0.18～0.74);Pearson correlation analysis results showed that in EC-SLS,there was no correlation between the young group and the elderly in ankle kinesthesia threshold posture stability parameters;In EO-SLS,the kinesthesia of ankle plantarflexion was moderately correlated with Co P-AP displacement(r=0.517,p<0.001,95% CI: 0.19 ～0.74),and moderately correlated with Co P-ML displacement(r=0.370,p=0.04,95%CI: 0.01 ～ 0.64)and moderate correlation Co P-95% CI area(r=0.565,p=0.01,95%CI: 0.26 ～ 0.77).The correlation of ankle position perception,muscle force perception and static posture control parameters between young and old people showed that in EC-SLS,significant difference was found on correlation between ankle plantar flexion position perception and Co P-AP direction displacement(r=0.695,p=0.04,95% CI: 0.03～0.65);In EO-SLS,ankle plantar flexion position perception was moderately correlated with Co P-AP displacement(r=0.656,p<0.001,95% CI: 0.65～0.91)in young people.The results of study 3 showed that after 8 weeks of multi-model stimulation on plantar mechanoreceptors,there was a significant difference between the intervention group and the control group in the SWM and VPT test at the great toe,the first metatarsal region,the fifth metatarsal region,the center of the forefoot,the foot center,and the heel(p<0.001);However,there was no significant difference in TPD test,and 128 Hz tuning fork test;Significant difference were found between the intervention group and the control group in the kinesthesia sense of ankle plantar flexion(p=0.01),dorsiflexion(p=0.03),inversion(p=0.02)and eversion(p=0.01);However,there was no significant difference between ankle JPT test and muscle force sense test.In the Neurocom Balance Manager postural stability test,in the SOT test,there was a significant difference between the intervention group and the control group in the test of condition 3,i.e.visual instability,stable supporting surface(p=0.04)and eye closure,unstable supporting surface(p=0.05),visual instability,unstable supporting surface(i.e.condition 6)(p=0.03);In addition,there was a significant difference in the swing speed of the Co G between the intervention group and the control group in EC-SLS(p=0.04)and EO-SLS(p=0.03);However,there was no significant difference between the intervention and the control group in the parameters of dynamic posture stability during 3m walking;In the plantar pressure parameter peak pressure(PP)during 3m walking,there was a significant difference between the intervention group and the control group in the first metatarsal of M05(p=0.01),the second to third metatarsal of M06(p=0.01),and the fourth to fifth metatarsal region of M07(p=0.02).Conclusion:(1)Significant differences were found on plantar sensation,ankle kinesthesia and muscle force sense of different age groups.Therefore,this study found that foot sensation and ankle proprioception decline in midlife,which will provide a theoretical basis for the timing of interventions for plantar sensation and ankle proprioception.(2)Applying pressure stimulation with different hardness on plantar surface had no significant effect on the SWM test and dynamic posture control parameters;plantar pressure parameters in young and elderly,there had limited effect on static posture control in young and old people.This will guide the intervention of plantar mechanoreceptors and the intensity of stimulation training of plantar sensation and postural control.(3)This study found that 8-week multimodal plantar mechanoreceptor stimulation training had a significant effect on the plantar sensory sensitivity and peak pressure in the plantar pressure parameters of the elderly,as well as the postural stability when other sensory systems were disturbed.Which will provide a rationale for the role of enhanced plantar mechanoreceptor function in fall prevention strategies in the elderly. |
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