title: Influence of long-term wearing of unstable shoes on compensatory control of posture: an electromyography-based analysis.
abstract: OBJECTIVE
  This study investigated the influence of long-term wearing of unstable shoes (WUS) on compensatory postural adjustments (CPA) to an external perturbation.
  
  
  METHODS
  Participants were divided into two groups: one wore unstable shoes while the other wore conventional shoes for 8 weeks. The ground reaction force signal was used to calculate the anterior-posterior (AP) displacement of the centre of pressure (CoP) and the electromyographic signal of gastrocnemius medialis (GM), tibialis anterior (TA), rectus femoris (RF) and biceps femoris (BF) muscles was used to assess individual muscle activity, antagonist co-activation and reciprocal activation at the joint (TA/GM and RF/(BF+GM) pairs) and muscle group levels (ventral (TA+RF)/dorsal (GM+BF) pair) within time intervals typical for CPA. The electromyographic signal was also used to assess muscle latency. The variables described were evaluated before and after the 8-week period while wearing the unstable shoes and barefoot.
  
  
  RESULTS
  Long-term WUS led to: an increase of BF activity in both conditions (barefoot and wearing the unstable shoes); a decrease of GM activity; an increase of antagonist co-activation and a decrease of reciprocal activation level at the TA/GM and ventral/dorsal pairs in the unstable shoe condition. Additionally, WUS led to a decrease in CoP displacement. However, no differences were observed in muscle onset and offset.
  
  
  CONCLUSIONS
  Results suggest that the prolonged use of unstable shoes leads to increased ankle and muscle groups' antagonist co-activation levels and higher performance by the postural control system.
authors.affiliation: Escola Superior da Tecnologia de Saúde do Porto, Instituto Politécnico do Porto, Área Científica de Fisioterapia, Centro de Estudos de Movimento e Actividade Humana, Rua Valente Perfeito 322, 4400-330 Vila Nova de Gaia, Portugal; Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Portugal. Electronic address: asp@estsp.ipp.pt.
authors.forename: Andreia S P
authors.initials: AS
authors.lastname: Sousa
authors.forename: Andreia
authors.initials: A
authors.lastname: Silva
authors.forename: Rui
authors.initials: R
authors.lastname: Macedo
authors.forename: Rubim
authors.initials: R
authors.lastname: Santos
authors.forename: João Manuel R S
authors.initials: JM
authors.lastname: Tavares
mesh_terms: D000328:Adult; D000843:Ankle Joint / Q000502:physiology; D004576:Electromyography / Q000379:methods*; D005260:Female; D005528:Foot / Q000502:physiology* / Q000503:physiopathology*; D006801:Humans; D008297:Male; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D012775:Shoes; D013997:Time Factors
keywords: Adaptation; Electromyography; Postural control; Unstable shoe wearing