Multi-digit maximum voluntary torque production on a circular object

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Journal of Biomechanics 2006, Vol. 39 (Suppl 1)

4836 Mo, 09:15-09:30 (P6) An exploratory investigation of the discomfort of clutch pedal operation using a musculoskeletal biomechanical model F. Fraysse, X. Wang, L. Ch~ze. LBMH, INRETS-UCBL, Lyon, France Ergonomic simulation is one of the numerous applications of biomechanical models of the human body. However, previous studies [Wang et al., 2004] have shown that the kinematical or dynamical parameters are not very well correlated with discomfort. We believe that discomfort modeling requires detailed muscular activities simulation. The aim of the present study is therefore to investigate possible correlation between muscular activities during a clutch pedal operation and perceived discomfort. In order to compute muscle forces, a musculoskeletal biomechanical model of the lower limb has been developed using Matlab® software. This model is based on the skeletal geometry of the HUMOS model (European project HUMOS). It consists of 4 rigid segments representing pelvis, thigh, leg and foot, and forty muscles. Each muscle's average attachment sites were taken from published cadaver studies. The palpable bony points were used to scale the overall model. The muscles lines of action connect the attachment sites, with joint wrapping to better fit the real muscular geometry. From the kinematical (segments positions) and dynamical (joints torques) data, an optimization method was used to compute the muscular loads. The model was validated by simulating loaded flexion-extension of the hip, knee and ankle joints, and by comparing the results with experimental data. The model was then used to calculate muscular exertion during a clutch pedal operation. Data were obtained from a previous study, which investigated the influence of four design parameters of clutch pedal on discomfort. The present work has shown that discomfort was not noticeably better explained by calculated muscular forces than by joint torques. This may be due to the fact that muscle force-length and force-velocity relationships are not included in the current model, certainly affecting the muscle force prediction. Optimisation criteria should also be improved, especially by taking into account muscular anticipation. References Wang X., Le Breton-Gadegbeku L., Bouzon L. (2004). Biomechanical evaluation of the comfort of automobile clutch pedal operation. International Journal of Industrial Ergonomics, 2004; 34: 209-221. 5949 Mo, 11:00-11:30 (P8) Relaxation after isokinetic shoulder abductions in subjects with trapezius myalgia compared to controls K. S~gaard, L.L. Andersen, G. Sj~gaard. National Institute ef Occupational

Health, Copenhagen, Denmark Introduction: During repetitive work tasks with low force demands lack of relaxation has been suggested as an aetiological factor in trapezius myalgia. The aim of the present study was to evaluate the ability to relax the shoulder muscles after standardized isokinetic maximal contractions. Methods: 13 females clinically diagnosed with trapezius myalgia (TM; 45±6 yrs, 166±6cm, 72±14kg) and 9 healthy female controls (CON; 45±8 yrs, 168±5 cm, 68±9 kg) participated in the study. Bipolar surface EMG measurements were obtained from the trapezius and deltoideus muscles. Isometric shoulder abduction MVC was performed to obtain max isometric torque and EMG in the two muscles. In a Biodex dynamometer isokinetic concentric (60°/s and 180°/s) and eccentric (60°/s) shoulder abductions were performed. Four sweeps were performed, giving a total of 12 isokinetic contractions for each subject. For each contraction peak isokinetic torque and EMG were obtained. Immediately after each contraction the subjects placed their hands in the lap and resting EMG was obtained over a 10s period. Results: Max isometric abduction torque was similar for TM and CON (36±5 vs 38±4Nm, respectively). Peak isokinetic trapezius EMG corresponded to 97±59% and 96±24% of peak isometric EMG for TM and CON, respectively. Resting EMG was expressed as the percentage of peak EMG in the preceding contraction. If all sweeps are averaged TM compared to CON showed significantly larger resting activity in both trapezius (2.1±3.1 vs 0.9±0.8%) and deltoid muscle (0.6±0.5 vs 0.3±0.3%). However, if the lowest value for each contraction type was compared between TM and CON there were no significant differences for neither the trapezius or deltoid muscle. Discussion and Conclusion: Normalised maximal muscle activation during isokinetic shoulder abduction was not reduced in women with TM compared to CON. Further, evaluated from the lowest resting activity they had the ability to reduce activity to the same level as controls. However, TM did not use the opportunity to relax the muscles to the same extent as the CON. Therefore lack of relaxation in breaks during the workday may be a contributing factor in development of trapezius myalgia.

Oral Presentations 5677 Mo, 11:30-11:45 (P8) Hand motion analysis during touch-typing using VICON system with finger force plate N. Sakai, S. Shimawaki. Biomechanics Laboratory, Utsunomiya University,

Japan Introduction: Finger force plate, which is linked to 3-D motion analysis system VICON, was developed and used for study on the mechanical motion analysis of the touch typing, concerning with the carpal tunnel syndrome. Method: The subject was ten male computer users which mean of age was 23.0 years. Finger force plate composed of force sensor of the FES system (Nitta Co., Japan) which is the six-axial force transducer measuring the compressive and tensile force in x, y, z-direction (Fx, Fy, Fz), and the moment around x, y, z-axis (Mx, My, Mz). The platform of 3 3cm in size was placed on the force sensor and the fingertip force vector was measured. Finger motion analysis was performed by VICON (Oxford Metrics Co.) using the micro-reflective markers of 3 mm in diameter on the dorsal side of the index finger, dorsal hand, and dorsal forearm. A keyboard switch of personal computer PC-98 (NEC, Co.) was attached on the platform of finger force plate, and the subjects tapped the switch with their right index finger. The hand had six different position, high, middle, low position on the desk, and close, middle, distant position to the keyboard. Both data of the finger force plate and of the VICON system was linked, and flexion angle of the wrist and finger joint, and the joint moment were compared among six kind hand positions. Result: Maximum and minimum flexion angle of the wrist joint at the close position to the keyboard was significantly (p<0.05) larger than the distant position. Similarly, maximum and minimum flexion angle of the MCP joint at close position was significantly (p < 0.05) larger than distant position, while the other PIP and DIP joint had no significant difference. Change in height of the hand position showed no significant difference in flexion angle of the writs and finger joints. Moments in finger joints showed a significant (p < 0.05) difference between the close and the distant position, while change in height showed no difference. Discussion: Change in distance between the hand and the keyboard showed a significant difference in both the flexion angle and joint moment, while change in height of hand position showed no difference. This result suggest that the distance is more important factor for cause of the carpal tunnel syndrome of typists. 6663 Mo, 11:45-12:00 (P8) Multi-digit maximum voluntary torque production on a circular object J.K. Shim 1,2, J. Huang 1, M.L. Latash3, V.M. Zatsiorsky3. 1Department ef

Kinesiology, University of Maryland, College Park, MD, USA, 2Bioengineering Program/Neuroscience and Cognitive Science Program, University of Maryland, College Park, MD, USA, 3Department of Kinesiology, Penn State University, University Park, PA, USA Manipulation of circular objects, such as twisting a valve, opening a jar lid, or rotating a door knob is a part of everyday activities. These activities usually involve torque production (a twisting action) on a grasped circular object. Repetitive and forceful performances of such tasks during labour movements may increase the risk of injury and motor disorders. We studied the individual digit-tip forces and moments during torque production on a mechanically fixed circular object. During the experiments, subjects positioned each digit on a 3-dimensional force/moment sensor attached to a circular aluminum handle and produced the maximum voluntary torque on the handle. Two independent variables, the torque direction and the orientation of the axis of rotation with respect to the subject's body, were systematically varied. The goal of the study was to investigate the magnitudes of total force and moment under different torque directions and axes, the relative contributions of individual digit force/moment to the total force and moment, and the relations between normal and tangential forces at individual digit contacts. We concluded that (1) the maximum torque in the closing (clockwise) direction was larger than in the opening (counter clockwise) direction, (2) the thumb and little finger, respectively, had the largest and the smallest share of both total normal force and total moment, (3) the sharing of individual digit moments was not affected by the orientation of the torque axis or the torque direction while the sharing of individual digit normal forces changed with torque direction, and (4) the normal force safety margins had the largest and smallest values in the thumb and little finger, respectively. From the first conclusion, switching the current design of opening and closing directions of circular valves and jar caps was suggested. 5977 Mo, 12:00-12:15 (P8) Maximum one-handed pull force under constrained conditions and its relation to shoulder geometry K. Gielo-Perczak. Liberty Mutual Research Institute for Safety, Hopkinton,

MA, USA Shoulder strength is a limiting factor in upper extremity exertion capability. This study hypothesizes that by isolating the influences of the contact surface