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Anticipatory Muscular Activity in Stable and Unstable Standing: A Study on Ankle and Trunk Muscles during Voluntary Arm

This study examines the anticipatory muscular activity in ankle and trunk muscles during the initial phase of voluntary arm movements in both stable and unstable standing conditions. The aim is to investigate proximal to distal compensatory adjustments on a short base of support.

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Anticipatory Muscular Activity in Stable and Unstable Standing: A Study on Ankle and Trunk Muscles during Voluntary Arm

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  1. Anticipatory muscular activity during stable and unstable standing David Conradsson David Conradsson 2 januari 2020 1

  2. Postural control • Postural stability: the ability to control the body Centre of Mass (CoM) in relation to the base of support (BoS). • Postural orientation:maintenances of a posture of the body that is appropriate for performance of the specific task. Sensory input (visual, vestibular, somatosensory). Motor output Horak FB, Macpherson, 1996

  3. Postural adjustments Anticipatory mechanism (feed-forward) - Prediction of disturbance of CoM in which preparatory responses is produced. - Precede the onset of the movement. Aims to maintain postural stability – orientation, and to provide a dynamic support to the chain of movement for improved performance (force, velocity). Compensatory/reactive mechanism (feedback): - Initiated by sensory input that detect postural instability/perturbation. - Occur after/during the movement. (Bouisset 2008, Horak FB, Macpherson, 1996)

  4. Unstable standing – MBT-shoes Rounded sole = increased degree of instability Based on qualitative/clinical experience…

  5. Brief review… • Balance • Improvement of certain aspects of standing balance (CoP-parameters) in women (>50 years). (Ramstrand et al 2010) • Gait characteristics • Decreased hip and knee ROM, increased dorsiflexion during initial stand phase (Nigg et al 2006, Romkes et al 2006) • Decreased trunk flexion (New & Pearce 2007) • Disability • Decreased perceived LBP (VAS 23mm) in amateur golfers (Nigg et al 2009)

  6. Aim • Study anticipatory muscular activity for ankle and trunk muscles during initial phase of voluntary arm movements in stable and unstable standing. • Proximal to distal compensatory adjustments on short base of support. (Horak & Nashner 1986)

  7. Method Subject: Wim! Healthy, athletic… Test procedure: - Rapid bilateral arm flexion holding a weight in each hand (2kg) - Regular shoes (STABLE) vs unstable shoes (UNSTABLE) - 3 trials for each condition - Narrow stance width (0.2m) - Instructions and test trials before measurement

  8. Laboratory measurement Kinematics: right wrist Muscular activity, EMG: Rectus abdominus Erector spinae Gastrocnemius lateralis Tibialis anterior

  9. Data management and analysis • Onset for the arm movement - kinematic marker on the wrist. • EMG records 150ms before and 200ms after the onset of the arm movement were analyzed. • Definition of muscular onset • Visual inspection. • EMG activity >3SD above mean baseline activity, EMG-burst >30ms. • Postural adjustments - Anticipatory/preparatory: -150ms before and +50ms after the arm movement. - Compensatory/reactive: >50ms after the arm movement. (Aruin & Latash 1995)

  10. Data management

  11. Results

  12. Discussion, questions…

  13. References Aruin AS, Latash ML. Directional specificity of postural muscles in feed-forward postural reactions during fast voluntary arm movements. Exp Brain Res.03(2):323-32. 1995 Horak FB, Macpherson JM, Shepard J, et al. Postural orientation and equilibrium. Handbook of Physiology: Section 12, Integration of Motor, Circulatory, Respiratory and Metabolic Control During Exercise. New York: Oxford Univ. Press, 1996:47-9. New P, Pearce J. The effects of Masai Barefoot Technology* footwear on posture: an experimental designed study. Physiotherapy Research International.12(4): 202. 2007 Nigg BM, Davis E, Lindsay D et al. The effectiveness of an unstable sandal on low back pain and golf performance. Clin J Sport Med. 19(6):464-70. 2009 Nigg B, Hintzen S, Ferber R. Effect of an unstable shoe construction on lower extremity gait characteristics. Clin Biomech (Bristol, Avon). 2006. 21(1):82-8. Ramstrand N, Thuesen AH, Nielsen DB et al. Effects of an unstable shoe construction on balance in women aged over 50 years. Clin Biomech (Bristol, Avon). 2010 Feb 20. Romkes J, Rudmann C, Brunner R. Changes in gait and EMG when walking with the Masai Barefoot Technique. Clin Biomech (Bristol, Avon). 2006. 21(1):75-81.

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