Acute Effects Of Plantar Sensory Stimulation On Postural Control In Individuals With Chronic Ankle Instability

Objective: Chronic ankle instability(CAI)is common after lateral ankle sprain,which is characterized by recurrent ankle sprains,“giving away”,self-perceived ankle instability and decreased functional performance.Individuals with CAI complain of sensorimotor dysfunctions,and abnormal somatosensory have been noted to be impaired.Diminished plantar sensory is among the most easily neglected sensory problems.The method that plantar sensory stimulation aimed to activate cutaneous receptors could increase sensitivity of receptors and improve postural stability.However,researches about the effects of plantar sensory stimulation on postural control in individuals with CAI are limited,and lack of consistent conclusion.Our study is consisted of two trails.The purpose of the first trail is to explore the acute effects of plantar sensory stimulation on plantar light touch and ankle proprioception in individuals with chronic ankle instability.The purpose of the second trail is to differentiate the influences of distinct intensities of plantar sensory stimulation on postural control and plantar light touch.Methods: In the first trail,each participant was invited to laboratory in two separated days.For the first time,they performed an intervention(Plantar sensory stimulation)and two kind of tests including light touch thresholds and ankle kinesthesis.These two tests were measured at baseline,0 minutes,30 minutes,and 60 minutes after plantar sensory stimulation).For the second time,they performed an intervention(Plantar sensory stimulation)and two tests,including inversion position sense and eversion force sense in the ankle joint.Friedman test was applied to identify difference of light touch threshold.Repeated-measures analyses of variance was applied to identify difference of ankle kinesthesia,and the paired t-test was applied to identify difference of inversion position sense and eversion force sense in the ankle.In the second trail,all participants completed 3 test sessions during a 3-week period of time.A 7-day wash-out period was required between interventions(different intensities of plantar sensory stimulation).For the first session,participants needed to complete a pretest,an intervention and a posttest.For the last two sessions,participants only needed to complete an intervention and a posttest.these tests consisted of the detection of plantar light touch threshold and the evaluation of postural control.Additionally,visual analogue scaling was employed to identify the self-perceived intensity of plantar sensory at the time of 0min,5min,10 min when performing plantar sensory stimulation.Repeated-measures analyses of variance was applied to identify difference of postural control and self-perceived intensity of plantar sensory.Friedman test was applied to identify difference of light touch threshold.The significant difference was p ≤ 0.05.Results:In the first trail:(1)Friedman tests demonstrated a significant main effect of Time in all 4 regions(Big Toe: p = 0.002;1MT: p = 0.002;5MT: p(27)0.001;Heel: p(27)0.001).Post hoc comparisons revealed different outcomes in four regions.In the big toe,SWM thresholds at the time when immediately(p = 0.014)and 30 minutes(p = 0.010)after plantar sensory stimulation were higher than that of baseline.In the heel,SWM thresholds at the time when 60minutes(p = 0.022)after plantar sensory stimulation was lower than that of immediately after stimulation.(2)The results found no significant differences in plantarflexion,dorsiflexion and eversion motion threshold in ankle joint.However,there was a main effect of Time in inversion motion threshold,and results showed that inversion motion threshold(p =0.019)was significantly lower after plantar sensory stimulation than that of baseline.Post hoc comparisons found no differences between the pairwise time points.(3)The paired t-test results revealed significant differences in standard value of absolute error(p = 0.019)between before and after plantar sensory stimulation.However,no significant differences were found in relative and variable errors.In the second trail:Friedman tests demonstrated no significant main effect of intensity in three regions,including the big toe,1MT,and 5MT.The heel(p = 0.045)was the only region that revealed the significant main effect of intensity.Repeated-measures analyses of variance demonstrated no significant main effect of intensity in self-perceived intensity of plantar sensoryRepeated-measures analyses of variance demonstrated a significant main effect of intensity in SOT,LOS,MCT and ADT.In SOT,there was a significant difference for equilibrium score(p(27)0.001)and strategy score(p(27)0.001)in the condition 5.There was a significant difference for equilibrium score(p = 0.002)and strategy score(p(27)0.001)in the condition 6.Post-hoc analysis showed the equilibrium scores after three intensities of plantar sensory stimulation(BW-Baseline: p(27)0.001,110%BW-Baseline: p(27)0.001,120%BW-Baseline: p(27)0.001)were all significantly higher than that of no plantar sensory stimulation when performing condition 5.The equilibrium scores after two intensities of plantar sensory stimulation(BW-Baseline: p = 0.009,120%BW-Baseline: p = 0.027)were all significantly higher than that of no plantar sensory stimulation when performing condition 6.The strategy scores after three intensities of plantar sensory [BW-Baseline:(p = 0.001),110%BW-Baseline:(p(27)0.001),120%BW-Baseline:(p = 0.004)] were all significantly higher than that of no plantar sensory stimulation when performing condition 5.The strategy scores after three intensities of plantar sensory [BW-Baseline:(p = 0.008),110%BW-Baseline:(p= 0.013),120%BW-Baseline:(p = 0.022)] were all significantly higher than that of no plantar sensory stimulation when performing condition 6.There was a significant difference for vestibular-sensory score(p(27)0.001)and composite score(p(27)0.001).Post-hoc analysis showed the vestibular-sensory scores after three intensities of plantar sensory stimulation(BW-Baseline: p(27)0.001,110%BW-Baseline: p(27)0.001,120%BW-Baseline: p(27)0.001)were all significantly higher than that of no plantar sensory stimulation.The composite scores after three intensities of plantar sensory stimulation(BW-Baseline: p(27)0.001,110%BW-Baseline: p(27)0.001,120%BW-Baseline: p(27)0.001)were all significantly higher than that of no plantar sensory stimulation.No significant difference was observed in all data of postural control between three intensities of plantar sensory stimulation.Conclusion: 10-minute plantar sensory stimulation decreased the sensitivity of plantar light touch,but increase the sensitivity of eversion force sense in the ankle joint.Furthermore,plantar sensory stimulation improved the dynamic postural control in individuals with CAI,and the vestibular-sensory system compensated for the deficit the somatosensory system in individuals with CAI to maintain postural balance.