Effects of initial foot position on postural responses to lateral standing surface perturbations in younger and older adults |
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| Institution: | 1. Department of Physical Therapy and Rehabilitation Science, University of Maryland School of Medicine, Baltimore, MD, USA;2. Department of Kinesiology, University of Texas at Austin, Austin, TX, USA;1. Yeditepe University, Institute of Health Sciences, Department of Physiotherapy and Rehabilitation, Istanbul, Turkey;2. Yeditepe University, Faculty of Health Sciences, Department of Physiotherapy and Rehabilitation, Istanbul, Turkey;3. Istanbul Kültür University, Faculty of Health Sciences, Department of Physiotherapy and Rehabilitation, Istanbul, Turkey;4. Istanbul University, Institute of Health Sciences, Department of Developmental Neurology, Istanbul, Turkey;5. Istanbul University, Istanbul Faculty of Medicine, Department of Orthopaedics and Traumatology, Istanbul, Turkey;1. Shriners Hospitals For Children, Portland, 3101 SW Sam Jackson Park Road, Portland, OR 97239, United States;2. Shriners Hospitals For Children, Northern California, 2425 SW Stockton Blvd, Sacramento, CA 95817, United States;3. University of California, Los Angeles, Department of Orthopaedics, 1000 Veteran Ave, Rehab Building 22-64, Los Angeles, CA 90025, United States;4. University of California Davis Medical Center, Department of Physical Medicine, 4869 Y Street, Suite 3850, Sacramento, CA 95817, United States;1. St. Vincent’s Hospital Melbourne, Physiotherapy Department, PO Box 2900, Fitzroy, Victoria, 3065, Australia;2. School of Allied Health, Faculty of Health Sciences, Curtin University, GPO Box U1987, Perth, Western Australia, 6845, Australia;3. School of Health and Behavioural Science, T3.29, University of the Sunshine Coast, Sippy Downs, Queensland, 4556, Australia;4. Rehabilitation Ageing and Independent Living (RAIL) Research Centre, School of Primary and Allied Health Care, Monash University (Peninsula Campus), McMahons Road, Frankston, Victoria, 3199, Australia;1. Department of Orthopedics, University of Colorado School of Medicine, Aurora, CO, USA;2. Sports Medicine Center, Children’s Hospital of Colorado, Aurora, CO, USA;3. Department of Pediatrics, University of Colorado School of Medicine, Aurora, CO, USA |
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| Abstract: | BackgroundAn age-related decline in standing balance control in the medio-lateral direction is associated with increased risk of falls. A potential approach to improve postural stability is to change initial foot position (IFP).Research questionsIn response to a lateral surface perturbation, how are lower extremity muscle activation levels different and what are the effects of different IFPs on muscle activation patterns and postural stability in younger versus older adults?MethodsTen younger and ten older healthy adults participated in this study. Three IFPs were tested Reference (REF): feet were placed parallel, shoulder-width apart; Toes-out with heels together (TOHT): heels together with toes pointing outward; Modified Semi-Tandem (M-ST): the heel of the anterior foot was placed by the big toe of the posterior foot]. Unexpected lateral translations of the standing surface were applied. Electromyographic (EMG) activity of the lower extremity muscles, standard deviation (SD) of the body’s CoM acceleration (SD of CoMAccel), and center of pressure (CoP) sway area were compared across IFPs and age.ResultsActivation levels of the muscles serving the ankle and gluteus medius were greater than for the knee joint muscles and gluteus maximus in the loaded leg across all IFPs in both groups. TOHT showed greater EMG peak amplitude of the soleus and fibularis longus compared to REF, and had smaller SD of CoMAccel and CoP sway area than M-ST. Compared to younger adults, older adults demonstrated lower EMG peak amplitude and delayed peak timing of the fibularis longus and greater SD of CoMAccel and CoP sway area in all IFPs during balance recovery.SignificanceDuring standing balance recovery, ankle muscles and gluteus medius are important active responders to unexpected lateral surface perturbations and a toes-out IFP could be a viable option to enhance ankle muscle activation that diminishes with age to improve postural stability. |
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| Keywords: | Initial foot position Lateral perturbation Older adults EMG Balance |
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