Energy approach to human performance evaluation

486

Abstracts

NECK LOADS IN FRONTAL

IMPACT

K. H. YANG, R. CHENG and A. I. KING (Bioengineering Center, Wayne State University, Detroit, MI 48202, U.S.A.) Data from frontal whole body cadaveric impacts were analyzed to explain the severe neck injuries observed when a predeployed driver airbag was used. These injuries did not occur when the cadavers were restrained by an automatic belt system. It was found that the resultant neck loads were much higher for short cadavers in the airbag runs, as a result of the high shear forces encountered during head/bag contact. The load required to cause these injuries is about 10 kN. This paper is an example of the complex nature of neck injuries and indicates a need for further research. No conclusions can be drawn regarding the relative efficacy of the airbag and the automatic belt because the airbag system was not a production version.

J. GAIT AND LOCOMOTION

EFFECTS

OF SPEED AND GAIT UPON FORCES AND IMPULSES RECREATIONAL

MARLENE

RIDING

PRODUCED

BY

HORSES

ADRIAN (University of Illinois at Urbana-Champaign, IL, U.S.A.) and TOM SPLJRGEONand IRIS HUGHES (Washington State University, Pullman, WA, U.S.A.)

The purpose of this research was to determine the changes in force-time patterns and magnitudes of force during support phase of pectoral and pelvic limbs under four conditions: slow walk, fast walk, slow trot and fast trot. The subjects were nine recreational riding horses led along a straight corridor surfaced with sawdust over an imbedded force platform in clay dirt. Significant differences were found between mean gait patterns with respect to maximum vertical force, vertical impulse, duration of support and duration between pelvic and pectoral steps. Although limb differences were noted with respect to horizontal forces and impulses, few differences were found among conditions. A profile was developed for use in clinical practice.

THE INFLUENCE

OF CADENCE AND STEP ANGLE ON THE CHANGE DURING LEVEL WALKING

Y. L. CHOU and I. H. CHEN (Institute of Engineering Science, National Cheng-Kung of China)

OF ENERGY

University, Republic

It is known that cadence, the angles between the legs and the total leg length are primary factors in determining characteristics of human gait under normal conditions. The objective of this report is to establish the relationship with and the effect of these three parameters on energy and momentum during gait. A simple linkage model is used for this study. Experimental verification by using multiple exposure photographs and a force plate is performed. Variations of these parameters through selected test data are computed and compared with those obtained by theoretical modelling. This report also aims on understanding the normal gait pattern during walking. Comparing these normal patterns with experimental data, whether the subject is normal or abnormal, can then be evaluated.

ENERGY APPROACH

TO HUMAN

PERFORlMANCE

EVALUATION

S. Yu. ALESHINSKY(Northern Illinois University, IL, U.S.A.) The energetical approach can serve as the theoretical basis for human movement improvement. Since any improvement usually requires previous evaluation a variety of criteria have been applied to evaluate human movement quality. However, many problems have to be solved to obtain correct results: (1) can a constant baseline be applied to the entire region of intensity of exercise in the calculation of net metabolism, (2) how reliable is the indirect calorimetry procedure when anaerobic mechanisms are activated (even if lactate content in blood is taken into account), (3) which method of apparent work calculation is correct? Even if these problems could be solved, the suggested criteria would not give the understanding of how to improve technique. A different method of human movement quality evaluation and improvement is therefore suggested. This

387

Abstracts

method is based on the analysis of the relationships between the power of ‘energy sources’ (joint forces and moments) and the time rates of the ‘mechanical energy fractions’. Four possibilities of energy economy have been revealed. The ‘coefficients of compensation’ were constructed to provide information related to the location of and reasons for the extra energy expenditure. They can be recommended for human movement optimization.

PERFORlMANCE

CRITERIA

IN NORMAL

HUhIAN

LOCOMOTJON

R. N. MARSHALL, G. A. WOOD and L. S. JENNINGS (Faculty of Physical Education. University of Otago, New Zealand, and the Departments of Human Movement Studies and Mathematics, University of Western Australia,

Australia)

It has been postulated that in highly learned skills (such as walking) the body structures its patterns of movement to minimise or maximise some aspect of its motion. The ability of seven optimisation criteria to predict the segmental kinematics and centre of mass trajectory ofa normal subject walking at his preferred pace during single stance were examined. A non-linear optimal control programme and a generalised simulation package were used to model the body during single stance and predict movement patterns subject to one of the objective functions. The results indicated that functions involving either the sum of the joint torques, the angular ‘jerk’, or the sum of the segmental mechanical energies predicted the segmental kinematics and centre of mass trajectory most accurately. Acceptable walking patterns for all objective functions were developed, although in general a smaller range of movement was predicted for most segments over the single stance phase.

MECHANICAL

WILLIAM L.

INTERACTIONS

OF THE THIGH AND SHANK DURING SWING TASKS

SIMPLE

LEG

SILER and PHILIP E. MARTIN (Exercise and Sport Research Institute Arizona State University, Tempe, AZ 85287, U.S.A.)

Fourteen men were filmed as they performed passive and active leg swing tasks in order to examine the roles of the knee joint reaction force and joint moment in the generation, dissipation and transfer ofenergy to and from the lower leg. For the passive condition, the lower leg energy changes were relatively small and were attributed primarily to a dissipation of energy via the joint moment. For the active condition, the lower leg energy changes were considerably greater than those for the passive condition. The results showed that the joint reaction force made a greater contribution to the work done on the lower leg than the moment. Nevertheless, the joint moment made a significant contribution early in the swing via an energy generation function. The results of the study suggest that the thigh-lower leg combination forms a highly conservative system as the segments interact during these leg swing tasks. This has important implications with respect to the economy of movement.

QUANTITATIVE

FUNCTIONAL

ANATOMY

OF THE LOWER LIMB

J. M. PEREIRA and J. M. MANSOUR (Case Western Reserve University, U.S.A.) A scheme was developed to classify muscles according to their primary, secondary and tertiary functions, e.g. a muscle which produces primarily a flexion moment may also produce secondary abduction and tertiary internal rotation moments. The functions of 37 muscles crossing the hip, knee and ankle joints were computed based upon the changing relative positions of joint centers and muscle origins and insertions during one gait cycle. It was found that the amount of force necessary to produce a given moment about a joint was dependent upon the limb position. In addition, the muscle functions changed significantly with limb position. Electrical stimulation of muscles of a paralyzed subject gave qualitative support to the results. The function of several of the major muscles crossing the hip and knee joints is reported for the different limb positions corresponding to normal gait.