Neuromuscular Coordination of Squat Lifting, I: Effect of Load Magnitude

In a more recent extension of these experiments,we examined the behavior of continuous estimates of coordination, the relative phase between the motion of different joints, and we examined coordination during lowering the load as well.18

John P Scholz

2017

Scholarcy highlights

  • Background and PurposeIn this study, we examined changes in kinematic and electromyographic measurements of the coordination of a squat-lifting task in response to lifting increasing loads.Subjects
  • In a more recent extension of these experiments,we examined the behavior of continuous estimates of coordination, the relative phase between the motion of different joints, and we examined coordination during lowering the load as well
  • Reflective markers were attached to major landmarks of the right extremities and to the trunk using adhesive velcro@.+The markers were placed at the base of the fifth metatarsal, lateral malleolus, lateral femoral condyle, lateral humeral condyle, greater trochanter, posterior superior iliac spine, and immediately inferior to the tip of the acrornial process laterally
  • Onsets and peaks of vastus lateralis muscle activity could not be identified consistently in any subject during this movement phase; VL activity remained relatively constant during lowering. The results of this investigation confirm and extend those of previous studies on the coordination of squat liftir1g.'~-~9,T~h7e,~se results, obtained from experienced workers for whom lifting was part of their job, are generally consistent with the results of similar experiments on college students reported by Scholz.l7,18In particular, both lumbar spine and shoulder joint extension were found to lag further behind knee extension during the lLfting phase of the task when lifting heavier loads
  • The extent of the effect of increasing the load magnitude on kneelumbar spine coordination can be seen qualitatively, in the representative mean relative motion plots depicted in Figure 4
  • For loads greater than 45% maximum llfting capacity, the opposite was true
  • Lumbar spine posture was not prescribed, subjects were told to "keep their backs relatively straight." We found that the spine was slightly more flexed or kyphotic for all subjects prior to lifting the heaviest loads
  • In contrast to erector spinae muscle timing, changes in ner regardless of the weight lifted, or neuromuscular timing of vastus lateralis muscle activity perhaps in the face of changing other did not occur with increases in the task variables such as movement load

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