Scaling and non-scaling of muscle activity, kinematics, and dynamics in sit-ups with different degrees of difficulty

Paul J. Cordo, Paul W. Hodges, Terrence C. Smith, Simon Brumagne, Victor S. Gurfinkel

Research output: Contribution to journalArticlepeer-review

12 Scopus citations


The purpose of this study was to investigate how the CNS adjusts motor patterns for variants of a complex axial movement-the sit-up. Adjustments were induced by changing the support surface contact and mass distribution of the body. Healthy adults performed straight-legged sit-ups, 3 s in duration, with support added to or removed from the lumbar trunk, or with mass added to the head or to the legs. Each of these interventions either increased or decreased the difficulty of the task. The study addressed the extent to which changes in sit-up difficulty are compensated by scaling of muscle activity, kinematics, and dynamics versus the extent to which they are compensated by changing discretely the motor pattern. The analysis of muscle activity, kinematics, and dynamics focused on the first 30-40% of the sit-up-the trunk flexion phase-since this is the most critical part of the movement. Our results demonstrate that, in some respects, sit-up kinematics and dynamics scaled with difficulty, but in other respects, they did not. Muscle activity also scaled, in many respects, but in more difficult sit-ups, abdominal flexor activity decreased instead of increased. Non-scaling changes in these parameters suggest that complex movements, such as the sit-up, may require discrete changes in motor pattern in order to deal with large loads, which challenge the available leverage.

Original languageEnglish (US)
Pages (from-to)506-521
Number of pages16
JournalJournal of Electromyography and Kinesiology
Issue number5
StatePublished - Oct 2006
Externally publishedYes


  • Axial movement
  • Coordination
  • EMG
  • Human
  • Kinematics
  • Perturbations

ASJC Scopus subject areas

  • Neuroscience (miscellaneous)
  • Biophysics
  • Clinical Neurology


Dive into the research topics of 'Scaling and non-scaling of muscle activity, kinematics, and dynamics in sit-ups with different degrees of difficulty'. Together they form a unique fingerprint.

Cite this