title: Effects of concurrent cognitive task on pre-landing muscle response latency during stepping down activity in older adults with and without a history of falls.
abstract: OBJECTIVE
  To investigate the co-contraction of ankle muscles in older subjects with and without a history of falls during a stepping down activity, and whether the co-contraction was disrupted by a concurrent cognitive task.
  
  
  METHODS
  Ten fallers and 9 non-fallers (mean age = 72.0 +/- 5.0 and 72.1 +/- 7.3 years, respectively) were recruited. Electromyography (EMG) of the tibialis anterior (TA) and medial gastrocnemius (MG) was recorded during stepping down with and without a concurrent cognitive task. Co-contraction was investigated using the time between the EMG onset and the foot touching a force-platform, termed the pre-landing muscle response latency.
  
  
  RESULTS
  The fallers showed longer pre-landing muscle response latencies in the TA compared with non-fallers (141.1 +/- 58.1 ms and 110.9 +/- 68.2 ms, respectively). With a concurrent cognitive task, the pre-landing muscle response latencies in the TA were shortened in fallers significantly more than in non-fallers (44.4% and 15.5%, respectively). No significant difference in MG activation was found between 2 groups in the stepping down activity with and without cognitive task.
  
  
  CONCLUSIONS
  Subjects with history of falls exhibit a greater shortening in the pre-landing muscle response latency than non-fallers when distracted during stepping down. Disruption of their co-contraction in ankle joint might precipitate such older adults to fall.
authors.affiliation: Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Horn, Kowloon, Hong Kong, China. rswtsang@inet.polyu.edu.hk
authors.forename: William W N
authors.initials: WW
authors.lastname: Tsang
authors.forename: Ken Y T
authors.initials: KY
authors.lastname: Lee
authors.forename: Amy S N
authors.initials: AS
authors.lastname: Fu
mesh_terms: D000058:Accidental Falls; D000223:Adaptation, Psychological; D000368:Aged; D000843:Ankle Joint / Q000502:physiology; D010054:Brief Psychiatric Rating Scale; D016022:Case-Control Studies; D004576:Electromyography; D005260:Female; D005684:Gait / Q000502:physiology; D006801:Humans; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology; D004856:Postural Balance; D013647:Task Performance and Analysis; D016138:Walking / Q000502:physiology* / Q000523:psychology*