The effect of an arch supporting insole on postural sway and lower limb muscle activity

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1 International Journal of Sport Studies. Vol., 4 (8), , 2014 Available online at http: ISSN ; Science Research Publications The effect of an arch supporting insole on postural sway and lower limb muscle activity Farhad Samimi 1*, Mehrdad Anbarian 2, Uwe G. Kersting 3, Amir Sarshin 4 1- Department of Sports Biomechanics, School of Physical Education and Sport Sciences, Bu Ali Sina University, Hamadan, Iran 2- Associate Professor, Physical Education Department, Bu Ali Sina University, Hamedan, Iran 3- Center for Sensory-Motor Interaction, Dept. of Health Science and Technology, Aalborg University, Denmark and Hammel Neurorehabilitation Centre and University Research Clinic, Aarhus University, Denmark 4- Department of Sport Biomechanics, Faculty of Physical Education and Sport Sciences, Islamic Azad University, Karaj Branch, Karaj, Iran *Corresponding Author, Hemin.Samimi@yahoo.com Abstract Background: The interest in the effects of foot orthoses (FO) on postural stability in elderly adults has recently increased. Arch supporting insoles placed inside the shoe to position the foot near its neutral position may affect the plantar surfaces of the feet, thereby influencing neuromuscular function. Limited reports exist on the effects on postural sway and lower limb muscle activity of arch supporting insoles. The aim of this study was to investigate whether arch supporting insoles alter postural control and lower limb muscle activity during quiet bipedal standing balance. Methods: A Footscan balance system was used synchronously with an electromyography unit (MEGA ME 6000, Mega Electronics) to determine postural sway variables (Anterior-Posterior and Medial-Lateral ranges of centre of pressure (CoP) displacements) and amplitudes of electromyographic (EMG) activity in eight dominant lower limb muscles in 15 healthy males (63±7.8 years) under three randomised conditions: barefoot (BF), shoe only (SO) and shoe with foot orthoses (SFO). Results: In the shoe with foot orthoses (SFO) condition centre of pressure (CoP) ranges are larger than for the two other conditions (p<0.05). However in the shoe with foot orthoses (SFO) condition, no significant differences were observed in lower limb muscle activity. Conclusion: This study points at effects of inserts on balance parameters which warrant future work in the field. In particular, the effect of long-term use of such inserts needs to be clinically evaluated. Keywords: Arch supporting insole; muscle; neuromuscular function; postural stability; EMG activity Introduction The foot is the first point of contact between the body and the external environment, providing important information for stability and locomotion. Postural stability and balance are dependent on the position of the centre of mass of the body and its displacement within the base of support (Gatev et al., 1999). As a part of somatosensory system, probably both the tactile and the proprioceptive system play an important role in balance control. The tactile system provides the central nervous system (CNS) with information concerning the sense of touch, detected by Messner's corpuscles, Pacinian corpuscles, Merkel's disks and Ruffini endings (Bray et al., 1994). The proprioceptive system provides the CNS with information concerning joint angles and changes in 959

2 these angles, detected by muscle spindles, Golgi tendon organs and joint afferents (Bray et al., 1994). Aging has been characterized by a loss of cutaneous touch and pressure sensation (Verrillo, 1993). The loss of cutaneous sensation in the plantar surface of the feet has been correlated with impaired balance control and increased risk of falling (Lord et al., 2003; Lord et al., 1994). Footwear may influence the quality of sensory feedback from the feet and may act as a sensory filter between the feet and the external environment (Arnadottir and Mercer, 2000). Footwear is a modifiable environmental factor that may play an important role in fall prevention while both tactile and proprioceptive mechanisms can be influenced by therapeutic shoes or shoe modifications, which may result in improvement of balance and a reduced risk for falling (Maki et al., 1999; Meyer et al., 2004). The application of circumferential ankle pressure (CAP) using braces, taping, and adaptive shoes or military boots is widely used to address chronic ankle instability (CAI). An underlying assumption for using the circumferential ankle pressure (CAP) is that greater compression at the ankle may improve balance due to increased feedback from cutaneous receptors in the foot and ankle, improving the joint positioning sense (Feuerbach et al., 1994). Foot orthoses can have both positive and negative effects on the detection of tactile input from the bottom of the foot. Soft shoe soles can distribute pressure under the foot, which may have a positive effect on pain, but it also may result in a deterioration of the detection of pressure changes under the foot, which may have a negative effect on balance (Robbins et al., 1978). For many years, arch supporting orthotics has been prescribed for individuals with discomfort and or abnormal skeletal alignments in the structures of the lower extremity. Recently, there has been an increased interest in promoting semi-rigid orthotics as an aid in stimulating the plantar afferents and with that postural control in older adults (Robbins et al., 1978). Arch supporting insoles placed in between the foot and shoe to position the foot near its neutral position may affect the plantar surfaces of the feet, thereby influencing neuromuscular function (James et al., 1978). Limited reports exist on the effects of arch supporting insoles on postural sway and lower limb muscle activity. The aim of this study was to investigate whether arch supporting insoles alter postural sway and lower limb muscle activity during quiet bipedal standing balance with eyes open and eyes closed in older asymptomatic adults. It was hypothesised that in SFO condition there will be less medial-lateral and anterior-posterior range of the centre of pressure (CoP) displacement of and also there will be reduced average muscle activity. Materials and Methods Design The study used a within-subject experimental design with participants taking part in testing in each of three conditions: barefoot (BF), shoe only (SO) and shoe with FO (SFO). The dependent variables were Anterior- Posterior (AP) range of centre of pressure (CoP) displacement, Medial-Lateral (ML) range of center of pressure (CoP) displacement and intensity of electromyographic (EMG) activity in eight dominant lower limb muscles. Participants A total of 15 healthy elderly males (age: 63±7.8 years; height: ±6.22cm, weight: 72.8± 7.78 kg) (mean+/- SD) participated in this study. Exclusion criteria were a self reported history of neuromuscular disease, stroke, peripheral sensory neuropathy, type 2 diabetes, inner ear disorders, dizziness, musculoskeletal injury or pain in the lower limbs or back, surgery of any kind in the 12 months prior to testing, inability to walk 10 m unassistedly, and/or inability to stand up and sit down from a chair without using their hands. Ethical approval was granted by Research Council of the Bu Ali Sina University. Written informed consent was obtained from all participants meeting the inclusion criteria. Foot orthoses and footwear Each participant was fitted with sport shoes and prefabricated arch supporting insoles (Fig. 1). Fig 1: Foot orthotics used in this study 960

3 Intl. j. Sport Std. Vol., 4 (8), , 2014 Postural sway Postural sway was assessed by a Footscan balance system, sampled at 300 Hz. By recording the difference between the maximum and minimum range of center of pressure (CoP) displacements in the Medial-Lateral and Anterior-Posterior directions (Le Clair and Riach, 1996; Raymakers et al., 2005; Robbins and Waked, 1997). Subjects stood on the Footscan mat in the three conditions: BF, SO and SFO. They were tested under two visual conditions, with eyes open and eyes closed. Electromyography The skin overlying the eight muscles of the dominant lower limb of the participants, determined by asking participants which leg they would kick a football with, was shaven, if necessary, and cleaned with surgical spirit before electrode placement. The eight muscles were: biceps femoris (BF), semitendinous (SEM), vastus medialis (VM), vastus lateralis (VL), tibialis anterior (TA), peroneus longus (PL), medial gastrocnemius (MG) and soleus (SOL). Pre-gelled disposable bipolar Ag-AgCl surface electrodes that were placed parallel to the muscle fibers with a centre-to-centre spacing of 3 cm as described by Basmajian and Deluca (Basmajian and De-Luca, 1985). For electrode placement, the SENIAM (surface EMG for non-invasive assessment of muscles) (Hermens et al., 1999) recommendations were followed (Fig.2). After placing the electrodes the subject was asked to perform different movements to ensure the precise placement of the electrodes and to test the EMG signal quality. The ground electrode was placed on the patella bone. To prevent changes in lower limb EMG the temperature of the laboratory remained constant throughout all testing procedures (Bell, 1993). The raw surface EMG signal was recorded at the sampling rate of 1000 Hz using a MEGA ME 6000 system (Mega Electronics Ltd., Kuopio, Finland). This is a sixteen-channel portable microcomputer with a 16-channel A/D conversion (14 bit resolution), a common-mode rejection ratio of 110 db and a band-pass filter of Hz. The EMG signals were transferred via an optical cable to a compatible computer where they were monitored by Megawin 3.0 program and stored for their later analysis. Data analysis: A digital band-pass filtered (15 Hz 450 Hz) was firstly applied to the raw data to remove any possible movement artefacts. Average EMG amplitudes of the rectified data (ARV) was used to quantify muscle activity over time. The averaged EMG values for each muscle were then averaged (mean) over the three trials for each condition. In this study, EMG normalisation was not required because the participants acted as their own control and all procedures were performed in the same session, without the electrode positions being altered (Soderberg and Knutson, 1995). Fig 2: EMG electrode placement 961

4 Procedures Participants conducted practice trials of quiet standing balance test in BF condition and eyes open to ensure familiarity with the testing procedures, prior to data collection. During testing in eyes open condition, participants were instructed to stand with their arms by their side, looking straight forward and to focus on a 2- cm diameter white spot positioned on a screen 2 meters in front of them at their eyes level. This was to standardise the data collection and minimise any variations in postural sway brought about by changing the visual field (Wilson et al., 2008). Foot position was self-selected in a stance which was most comfortable for the subject on the Footscan mat. The sequence of test conditions was randomised. In SO condition, all participants received shoes that were not fitted with prefabricated FO, and stood on the Footscan mat. But in FO condition all participants received shoes that were fitted with prefabricated, arch supporting insoles (FO). Each test repetition lasted for 30 s duration. There were three trials for each condition and the participants completed all three trials of one condition before testing took place under the next condition. Following each condition (test), participants were asked to sit down and take their feet out of the shoe and rest for two minutes. This rest period served to prevent habituation to the sensory stimulus of shoe or FO. In the first trial of each condition when the participant was ready and his center of mass (COM) was placed on the centre of the Footscan mat the location of foot on the Footscan mat were marked by tape so that foot position would be consistent from trial to trial. This was done because foot placement and alteration of foot width are believed to influence postural stability (Chiari et al., 2002). When the participant was ready the tester pressed the start buttons simultaneously on the EMG system and Footscan. Statistical analysis Data was checked for normality using Shapiro-Wilk test A two-way analysis of variance (ANOVA) was carried out for analysis of interaction of visual conditions and footwear conditions for each dependent variable. Also, if the main effects of the two independent variables were significant, the Tukey post hoc test was employed. The significant level was set at p=0.05. Results Medial-lateral postural sway The main effect of visual conditions (F1, 84 = 9.552, P = 0.003) and footwear conditions (F 2.84 = , P = 0.001) for ranges of centre of pressure (CoP) displacements were significant. Also, there was no significant interaction of visual condition and footwear condition (F2, 84 = 0.938, P = 0.395) (Fig 3). eyes open barefoot * shoe only Axis Title shoe with FO Fig 3: Medial-lateral ranges of centre of pressure (CoP) displacements under different conditions Midial-lateral cop displacment (mm) 962

5 *significant difference between eyes open and eyes close in the SO condition (P<0.05). significant difference between BF condition to FO condition in the same visual conditions (P<0.05). significant difference between SO condition to FO condition under the same visual conditions (P<0.05). Anterior-posterior postural sway The main effect of visual conditions (F1,84 = 9.552, P = 0.003) and footwear conditions (F 2.84 =24.264, P = 0.001) for ranges of centre of pressure (CoP) displacements were significant. Also, there was no significant difference in the interaction of visual conditions and footwear conditions (F 2.84 = 2.551, P = 0.084) (Fig 4). eyes open eyes closed * Anterior-posterior cop displacement (mm) barefoot shoe only shoe with FO 0 Fig 4: Anterior-Posterior ranges of centre of pressure (CoP) displacements under different conditions * significant difference between eyes open and eyes closed in FO condition (P< 0.05). Significant difference between BF condition to FO condition in the same visual conditions (P< 0.05). Significant difference between SO condition to FO condition in the same visual conditions (P< 0.05). Significant difference between BFcondition to SO condition in the same visual conditions (P<0.05). EMG There was no significant difference for any of the eight muscle EMG variables by the main effect of footwear conditions and by the main effect of visual conditions too. Also, there was no significant difference in the interaction of visual conditions and footwear conditions for any of the eight muscle EMG variables (Table 1). 963

6 Table 1: Mean(SD) of lower limb EMG average (µv) during quit standing balance on three different surfaces; BF, SO and FO and on two visual conditions; eyes open and eyes closed (P<0.05) Muscle Interaction of visual conditions and footwear conditions mean (SD) Main effect of footwear conditions mean (SD) Main effect of visual conditions mean (SD) BF (0.682) (0.697) 0.011(0.916) SEM 0.127(0.881) 2.542(0.085) 1.002(0.320) VM 0.737(0.307) 0.012(0.988) 0.585(0.447) VL 0.359(0.699) 0.041(0.960) 0.333(0.565) TA 1.191(0.309) 2.416(0.096) 0.501(0.481) PL 0.858(0.154) 1.688(0.192) 0.063(0.802) MG 0.634(0.457) 1.141(0.324) 0.447(0.506) SOL 1.033(0.360) 0.234(1.477) 1.827(0.180) Discussion and Conclusion The purpose of this study was to determine the immediate effects of an arch supporting insole on static postural sway and lower limb muscle activity in older adults. In this study, we found that in the FO condition the range of centre of pressure (CoP) displacement was larger than two other conditions (P<0.05). This finding was contrary to our hypothesis that for the FO condition there would be less Medial-Lateral and Anterior-Posterior movements of the centre of pressure (CoP). We found that there was no significant interaction between visual conditions and footwear conditions for AP or ML postural sway. These data are in agreement with those of Wilson who reported that textured insoles within standardised footwear did not significantly affect postural sway variables over four weeks in middle-aged females (Wilson et al., 2008). We found that postural sway increased when the eyes were closed. These data are in agreement with of Hytonen who reported that the visual system was most important for balance control in elderly persons (Hytonen et al., 1993). This study demonstrated that in the BF condition, ranges of the center of pressure are less then for the two other conditions. When the feet interface directly with the ground, cutaneous cues provide highly detailed spatial and temporal information about the support surface, and about the variations of pressure under the feet that directly results from a shift of center of foot pressure (CoP) displacements (Meyer et al., 2004; Perry, 2006). It seems that this information enables the subjects to compensate effects of the visual system on balance control, therefore, the difference between BF condition with eyes open to BF condition with eyes closed were not significant. But in the SO condition or FO condition the sensory filter induced by the midsole of the shoe reduced the ability of the foot receptors. In this study we controlled shoe type and foot position, and determined the effect of FO on postural sway and lower limb muscle activity. The results of this study illustrate that the constructional properties of footwear and FO are very important for postural control in the older adults. Previous FO studies have demonstrated that footwear type and FO materials can influence postural stability in young adult males ( Maurer et al., 2001; Teasdale and Simoneau, 2001). However, this study only considered normal footwear worn when taking part in an exercise activity and not the main and standardised shoe worn by the individual for prolonged time periods. There is a possibility that older individuals use different postural control strategies in order to maintain centre of gravity over the base of support (Teasdale and Simoneau, 2001; Mackey and Robinovitch, 2005; Morasso and Sanguineti, 2002)This may explain why the expected reduction in excursions of center of pressure in the FO condition was not observed. We also hypothesized that in FO condition the average muscle activity would be reduced, but our findings showed in FO condition no significant differences were observed in lower limb muscle activity. These results are in agreement with those of Hatton et al. (Hatton et al., 2009), who reported the textured insoles did not significantly affect lower limb muscle activity in healthy young participants. In the present study, the static balance test and absence of any external perturbation may have caused the minimal responses in the lower limbs. Thus, it is possible that the averaging EMG amplitude might not be sensitive enough to detect those small adaptations. Had there been changes in EMG would have allowed us to explore relationships between postural sway and corrective postural muscle activity that helped us to find which groups had a stabilizing effect on postural sway. By assessing each lower limb activation pattern separately, we have explored the possibility that the wearing of FO could have decreasing effect on calf muscles activity. As noted above, significantly greater amounts of postural sway and no significantly smaller amounts of calf muscles activity were present in the FO condition compared with the BF condition. It is unknown, however, whether decreased calf muscles activity is a contributing factor to increased postural sway or whether decreased muscle activation is a compensation for increased postural sway. According to our knowledge and reviewing the literature, we were not aware of any 964

7 studies which have investigated the effect of FO on lower limb muscle activity in quiet bipedal standing balance in elderly people. Nurse et al., found under dynamic conditions, as opposed to static, that a different kind of FO caused a significant reduction in both soleus and tibialis anterior intensity during periods of gait when these muscles are most active (Nurse et al., 2005). Eslami et al., found the semi-rigid foot orthoses causing a significantly reduced rearfoot eversion of about 40% (4.1 ; p= 0.001) and peak active ground reaction force 6% (0.96 N/kg; p= 0.008) ( Eslami et al., 2009). It is possible that the neuromuscular mechanisms involved in maintaining and controlling stable quiet standing are different to those mechanisms we use to react appropriately to disturbances of balance (Mackey and Robinovitch, 2005; Morasso and Sanguineti, 2002). This work has some limitations and thus, caution must be exercised in the interpretation of the findings of this research. Agerelated loss of plantar pressure sensation can lead to impaired control of balance. However, the underlying principle of the use of FO is indentation of the skin that enables us to enhance stimulation mechanoreceptors and reducing cutaneous sensory thresholds and for reaching to this aim we had to isolate the potential effect of FO from any effects brought by the construction of footwear. This raises the possibility that any effects are dependent on the nature and/or degree of sensory input, but no foot-sole sensitivity screening of subjects was carried out in this study. Such screening may reveal more information on the relationship between foot-sole sensitivity and footwear/insoles. Also, this study only considered the immediate effects of the FO, but it was better considered the effects when individuals had worn FO over a familiarization period of several days or weeks. In conclusion, these results showed that in the FO condition CoP ranges are larger than for the two other conditions (p<0.05). However, in the FO condition no significant differences were observed in lower limb muscle activity. This study points at effects of inserts on balance parameters which warrants future work in the field. In particular, the effects of long-term use of such inserts needs to be clinically evaluated. Conflict of interest statement No conflict of interest to declare. Acknowledgements The authors wish to express their gratitude to Mr. Heiner Baur for his technical assistance. Partial funding for this project was obtained from Bu-Ali Sina University, Hamedan, Iran. 965 References Arnadottir S.A, Mercer V.S, Effects of footwear on measurements of balance and gait in women between the ages of 65 and 93 years. Phys Ther; 80: Basmajian J.V, De Luca C.J, Muscles Alive (5th edition), Williams and Wilkins, Baltimore, MD; Bell D.G, The influence of air temperature on the EMG/force relationship of the quadriceps. Eur J Appl Physiol Occupational Physiol; 67: Bray J.J, Cragg P.A, Macknight A.D.C, Mills R.G, Human physiology Oxford: Blackwell Science. Chiari L, Rocchi L, Capello A, Stabilometric parameters are affected by arthropometry and foot placement. Clin Biomech ; 17: Eslami M, Begon M, Hinse S, Sadeghi H, Popov P, Effect of foot orthoses on magnitude and timing of rearfoot and tibial motions, ground reaction force and knee moment during running. J Science and Medicine in Sport; 12: Feuerbach J.W, Grabiner M.D, Koh T.J, Weiker G.G, Effect of an ankle orthosis and ankle ligament anesthesia on ankle joint proprioception. Am J Sports Med; 22: Gatev P, Thomas S, Kepple T, Hallet M, Feedforward strategy of balance during quiet stance in adults. J Physiol; 514.3: Hatton A.L, Dixon J, Martin D, Rome K, The effect of textured surfaces on postural stability and lower limb muscle activity. Journal of Electromyography and Kinesiology; 19: Hermens H.J, Freriks B, Merletti R, Hägg G, Stegeman D, Blok J et al., SENIAM 8: European recommendations for surface electromyography. ISBN: , Roessingh Research and Development. Hytönen M, Pyykkö I, Aalto H, Starck J, Postural control and age. Acta Otolaryngol(Stockh); 113(2): James S.L, Bates B.T, Osternig L.R, Injuries to runners. Am. J. Sports Med; 6: Le Clair K, Riach C, Postural stability measures: what to measure and for how long. Clin Biomech; 11:

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