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Author Notes:

Author to whom correspondence should be addressed: Paul Stapley, Balance and Voluntary Movement Laboratory (BVML), Department of Kinesiology and Physical Education, McGill University, 475 Pine Ave West, H2W 1S4, Montréal (Québec), CANADA, Tel: +1-514-398-4184, x0783, Fax: +1-514-398-4186, paul.stapley@mcgill.ca.


Research Funding:

Supported by CFI and NSERC grants to PJS. HT held a Georgia Tech President’s Research Fellowship and a Michael Birnbaum Scholarship.


  • Science & Technology
  • Life Sciences & Biomedicine
  • Neurosciences
  • Neurosciences & Neurology
  • Human
  • Posture
  • Feedforward
  • Feedback
  • Reaching
  • CAT

Postural responses to unexpected perturbations of balance during reaching


Journal Title:

Experimental Brain Research


Volume 202, Number 2


, Pages 485-491

Type of Work:

Article | Post-print: After Peer Review


To study the interaction between feedforward and feedback modes of postural control, we investigated postural responses during unexpected perturbations of the support surface that occurred during forward reaching in a standing position. We examined postural responses in lower limb muscles of nine human subjects. Baseline measures were obtained when subjects executed reaching movements to a target placed in front of them (R condition) and during postural responses to forward and backward support-surface perturbations (no reaching, P condition) during quiet stance. Perturbations were also given at different delays after the onset of reaching movements (RP conditions) as well as with the arm extended in the direction of the target, but not reaching (P/AE condition). Results showed that during perturbations to reaching (RP), the initial automatic postural response, occurring around 100 ms after the onset of perturbations, was relatively unchanged in latency or amplitude compared to control conditions (P and P/AE). However, longer latency postural responses were modulated to aid in the reaching movements during forward perturbations but not during backward perturbations. Our results suggest that the nervous system prioritizes the maintenance of a stable postural base during reaching, and that later components of the postural responses can be modulated to ensure the performance of the voluntary task.

Copyright information:

© 2009 Springer-Verlag.

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