title: Mental set can modulate response onset in the lower limb muscles to falls in humans.
abstract: The objective of this study was to investigate the modulation of the ankle muscle electromyographic (EMG) response as a function of mental set. Thirteen young healthy subjects underwent 40 unexpected and self-initiated drops from 30 cm above two separate force-plates. Following unexpected drops, reflex activities were observed in the medial gastrocnemius (MG) and tibialis anterior (TA) at mean latencies (+/- SD) of 83.59 +/- 10.1 and 99.43 +/- 21.82 ms, respectively. Following self-initiated drops, the response latency of the MG was significantly shortened (to 71.98 +/- 10 ms, P<0.05), and the TA was significantly lengthened (to 183.33 +/- 45 ms, P<0.05) when compared with unexpected drops. Such a modulation was associated with a significant reduction of the impact force on landing as compared with unexpected drops (by 17%, P<0.05). Interestingly, a negative correlation was found between the onset of the TA EMG response and the magnitude of the impact force on landing during expected (r= -0.66, P<0.05) but not unexpected drops.
authors.affiliation: Department of Rehabilitation Sciences, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.
authors.forename: S N
authors.initials: SN
authors.lastname: Fu
authors.forename: C W Y
authors.initials: CW
authors.lastname: Hui-Chan
mesh_terms: D000058:Accidental Falls; D000328:Adult; D001696:Biomechanical Phenomena; D003071:Cognition / Q000502:physiology*; D004576:Electromyography; D006801:Humans; D007866:Leg / Q000502:physiology*; D008297:Male; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000502:physiology*; D011187:Posture / Q000502:physiology*; D011930:Reaction Time / Q000502:physiology; D012018:Reflex / Q000502:physiology; D014722:Vestibule, Labyrinth / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology; D014836:Volition / Q000502:physiology*