Authors: Daniel J Cleather Jon E Goodwin Anthony M J Bull
Publish Date: 2011/06/29
Volume: 39, Issue: 9, Pages: 2476-2478
Abstract
The authors had previously demonstrated that this approach to the inverse dynamics problem permitted the notional intersegmental joint moment to exceed that calculated by a traditional inverse dynamics analysis However when the joint contact force due to the biarticular muscles is included it can be shown analytically that the notional intersegmental joint moment is equivalent to the traditional approachGiven the notional intersegmental joint moments are equivalent between all the cases presented in the revised analysis the activation of the musculature is more constrained than in the original paper In particular this results in the activity of the biarticular muscles being generally 02 – 06 × BW lower than in the original paper This also results in a commensurate decrease in the calculated joint reaction forces but these differences are generally small The largest decreases are seen at the hip and at the PFJ during landing with the largest being seen at the hip during landing 12 × BW – 17The difference between the TRADB and BI methods is due to the formalization of different optimization problems On the one hand the TRADB method is based purely upon a consideration of joint moments where each biarticular muscle is modeled as two monoarticular muscles that are constrained to have the same force In contrast the BI approach is based upon segmental considerations This permits a more realistic representation of the biarticular muscles Figure A1 contrasts the two approaches to modeling a biarticular muscle Although it can be shown that the net moment acting on the intermediate segment is equivalent between the two approaches it is clear that the moments impressed at either end of the intermediate segment are differentDuring vertical jumping it is common for a biarticular muscle to be an agonist at one joint and an antagonist at the other which when modelled in this way under the traditional approach constrains its activity Alternatively in the segment based approach the biarticular muscles cause the rotation of three segments and during vertical jumping can often act to assist the rotation of two segments while impeding the other This difference in the optimization problem thus permits the difference in activity of the biarticular muscles between the two approachesIn summary if the effect of the joint contact forces due to the biarticular muscles is included in Eq 6 the TRADB and BI cases are more similar than previously presented Despite this there are still differences between the two cases due to the formalization of different optimization problems The authors therefore suggest that the method presented here represents a more faithful interpretation of the biarticular muscles and should therefore be preferred in future work
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