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Development of an upper arm biomechanical model for dynamic simulation of multi-joint reaching movement.

Introduction: Modeling and simulation can provide significant insights into how the neuromuscular and musculoskeletal systems interact to produce movement, and are useful as a complementary means of experimental studies to investigate the biomechanical spinal neural system as a whole for their integrated roles in the control of human reaching movements. Previous models developed to investigate the control of human arm movements only account for single joint (elbow) movements with 2 degrees of freedoms (DOF). Purpose: A complete arm model with multiple joints (elbow and shoulder) and 5 DOFs was developed. This anatomically realistic musculo-skeletal arm model would be one important component of our later complete spinal neuro-skeletal system model (a-? model) to investigate the control of human multi-joint planar reaching movements. Methods: A realistic shoulder arm musculo-skeletal model is constructed using SIMM (MusculoGraphics, Inc.) with realistic bones, muscle origin and insertion (I/O), as well as musculotendon path. The attachment points (I/O points) for the muscles were initially placed on the bones where the muscles anatomically appeared to be correct. The wrapping objects were created and placed accordingly to prevent bone penetration of muscle line as well as provide more realistic moment arm (MA) profiles. The I/O points and wrapping objects was tuned to match experimental MA data available from cadaver as well as human measurements. Results: The resulting SIMM model consists of the fixed clavicle and scapular bone, the shoulder glenohumeral (GH) joint with 3 rotation DOFs, the elbow joint with 1 DOF (flexion/extension), and the forearm pronation/supination with 1 DOF. Muscles include deltoid posterior (DP), middle (DM), and anterial (DA), pectorelis major clavicle portion (PC), biceps brachii (BB) including biceps long (BBlh) and biceps short (BBsh) , triceps brachii (TB) including triceps lateral (TBlt), triceps long (TBlh) and triceps mid (TBmd), brachialis (BS), brachioradialis (BR), pronator teres (PT), supinator (SP) and pronator quadratus (PQ). For elbow flexion MAs, there is a good matching between literature data and model MAs in general, except for TB. As we compared the shoulder muscle MA from SIMM model with experimental MA data obtained at specific shoulder configuration there is a general agreement for BB, TBlh, DA and PC, whereas a big difference for DP. Further more, the BB shoulder to elbow flexion MA ratio (MAsh/MAel) was obtained from SIMM model and compared to the experimental data. The 3-D profile of the ratio with respect to shoulder and elbow flexion angles from SIMM model generally agrees with that from experiment data. However there was a higher value of the ratio when elbow angle is 60 degree (flexed) and shoulder angle is 160 degree (extended) from experimental measurements. Discussion: The big discrepancy for TB elbow flexion MA and DP shoulder flexion MA could be due to the fact that there is complicated wrapping at triceps insertion as well as the shoulder rotator cuff around glenohumeral joint. Since the MA ratios of BB were measured through measuring the joint torque with electrical stimulation of BB, the cross talk between surrounding muscles and BB could be a main factor leading to relatively unreasonable high ratio at the extremity of joint range. This also demonstrated one advantage of computer modeling in controlling individual muscles and variables when studying biomechanics and motor control.

D. Song (2), N. Lan (1), and J. Gordon (1)

Depts. of 1Biokinesiology and Physical Therapy, and 2Biomedical Engineering University of Southern California, Los Angeles, CA 90089,
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Author:Song, D.; Lan, N.; Gordon, J.
Publication:Clinical Kinesiology: Journal of the American Kinesiotherapy Association
Article Type:Clinical report
Geographic Code:1U9CA
Date:Mar 22, 2005
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