Determination of centers of gravity of man.

Data are presented coacerning the location of the center of gravity of the adult male in various body positione and the ability to shift the c.g. voluntarily with various body motions. M,•imum possible shifts of the e.g. from tbat of an erect standing posture were found to be IMI inches toward the head, 10 inches toward the feet, 8 inches anteriorly, 4% inches posteriorly and 41 inches laterally. INTRODUCTION EQUIPMENT AND PROCEDURE The data presented in this report concerning A number of different techniques for locating the location of the center of gravity of the and recordin~g the e.g. were tested 4nd the foladult male and the ability to shift the e.g. with lowing chosen for use in this study. The equipvarious body motions were originally published ment consists essentially of five platforms as a Civil Aviation Medical Research Laboratory (Fig. la) mounted one above the other. The Report in 1953 (CAA Project No. 53-203). top platform, which supports the subject, conDuring the past nine years these data have sists, of an adjustable seat with arm" and foot proved most useful in studies to determine rests. The bottom of the seat, the foot rest (1) effective restraint devices for protection and the arm rests are adjustable to different against crash forces, (9.) flight and balance angles and can be counterbalanced in each posicharacteristics of one-man helicopters, (3) detion by a sliding weight on the back of the seat. sign of flotation equipment, (4) orientation in This adjustable chair can be rotated about a falls and parachute jttmps, (5) capsule stabilhorizontal axis from the horizontal through apity, and (6) flying platform characteristics, proximately 20' to a second position and locked With the advent of the space age it is felt that in position. The second and third platforms these data deserve wider distribution as they slide horizontally at right -angles to one another will have obvious application in the design of by means of jack screws. Each of 'these platartificial gravity fields, space work capsules for forms also has its own connterbalance system. assembling space stations, lunar and planetary keeping the equipment as a whole in pertect landing equipment, and locomotion devices on balarne, regardless of position with .'eerence to planets with gravit...onal fields greater or less the bottomt platform. I.tails of these counterthan one g. balance systems are ihown in ri6. 2. The fourth For these reasons the author is taking the platform is separated from the bottom platform liberty of republishing the data as a CARl by means of a ball and socket joint in the center report. and four electrical contact points, one at each corner of this four foot square platform. E.iach be within uiie-cighth of an inch with rel of these contact points lights a light ini its correadings on the same subject not varying m ner if the platform is tilted in th'at direction. than one-fourth inch. The latter variation Hence, the platform may be assumed to be in probably caused by slight differences in balance when all four lights are out. A horiposition of the subject as he reaiounted zontal scale with one-fourth inch increments platform. was mounted on the supporting structure of During this study it became apparent tha the tilt chair with its zero in vertical alignment any point on the pelvic structure was cho with the rcfcrencc point on the seat. as a reference point the centers of gravity A vertical cable was stretched taut from the all men fell in a very small area. For, I ceiling to the base platform in front of the reason all vertical distances to the centers horizontal scale and a camera s:ght set up apgravity are measured from the inferior spine proximately ten feet from the platform. The the isehium. Horizontal measurements camera sight, vertical cable and ball and socket either from the anterinr or posterior plan.e fulcrum were in alignment. A similar arrangethe body, depending upon the type of mot ment was placed at the end of the platform for involved. For convenience of discussion I ;.eading lateral displac.-nients of e.g. The suhsixty-scven dilfetent body posi-tkrns studied : ject was then placed in the supporting struetui e divided into three groups: sitting, maximi with the seat back in the horizontal position displacement of e.g., and the effects on i (Fig. la), the equipment balanced by means e.g. of adding various weights to the body. of turning the jack screws and a reading taken on the horizontal scale. This reading repreTHE SAMPLE sents the vertical height of the e.g. of the subThe number of subjects tested was limit ject above the reference point when the subject by the large number of positions being studi, is 'in normal upright sitting posture. The seat telarge mber tost bein g studse was then tilted approximately 200, locked in Only five men were tested in all sixty-se% position (Fig. 'lb) and rebalanced, The readpositions, but they were carefully chosen to ing from the horizontal scale obtained as deelude a wide range of body sizes and weigh srinbed above was then set on the base leg of a Authropometric measurements of these st special adjustable T-square and the base of this. jects are presented in Table Ia. In addition T-square placed upon the seat back with the the five tested in all positions, an additioi zero of the square at the line of intersection of twenty-seven men were check tested in o the seat back and seat bottom. A second readsitting and one standing position. In the s ing (the horizontal distance of the e.g. of the ting position (Fig. 4, B-sitting with hands subject from the reference point) was then lap) the centers of gravity of all but one su takenct troug the caferae s oiht) whe then p ject (97%) were found, to fall within the ran taken through the camera sight where the peretbih df rt eoii a i es b et .I pendicular member of the adjustable T-square established for the original five subjects. In t intersected the vertical cable. By this method standing position, all but three (91%) fell wit the location of the center of gravity of the subin the established range. An analysis of t ject was determined directly with reference to anthropometris measurements of these 1 o the seat, subjects (Table Ib, subjects number 12 sitti• and .7, 10, and 24 standing) shows the ve Although the total weight of the equipment abnormal distribution of weight between tf and subject on the fulcrum may have reached trunk and legs. Subject number 12 has t6 800 pounds, the equipment was sensitive major portion of his 202 pounds in his tru enough that the weight of a silver half dollar with very short, light legs. His center of g-' placed on one comer would light the light in ity falls 3/4 inch above the eltablished ran) that comer. The breaker-over distance the platfor the sitting pestion. Subject number 7 hi for m had to le moved by turning the jack screw extremely long, heavy !egs and a short, lig to turn out one pair of lights and turn on thtA)ptrunk, causing his e.g. to fall 7/8 inch below tl posite pair was about one-eighth inch. For established range for the standing positio reason, accuracy of reading is believed to Body characteristics of subjects 10 and 24 cau -2their c,. to fall 1 inch above the established determine the best position for passenger range for the standing position. Their a,,throthe event of a crash. pometric measurements are 1w,•seitted in Table 1b. MAXIMUM DISPLACEMENT OF C.G. SITTING In this study of shift of the center of gra with maximum movements of the body Studies were made on three diffe,'ent sitting pelvis remains fixed and all movable body p groups. The first group (Fig. 4) represents were shifted on the pclvis in a given direct man in the normal sitting position; that is, trunk In the first group (Fig. 9) the shift of the ( erect, tl'ighs 900 to the trunk and legs 900 to ter of gravity accompanying ,arious ante thighs, and presents data showing the effects movements of body parts was studied and upon the center of gravity of rw*oving one and corded. This included flexing the head both arms to various positions. In addition to ward, extending both arms straight forwr the arm movements, two tests were made to flexing the trunk forward (note the sp show the shift of center of gravity when the amount of flexion of the trunk when trunk was flexed forward from the sitting posipelvis is held rigid), extending the legs scrai .ion. The vertical hcrgiit uf the center of grayforward and the final test irt which all L, ity was measured either from the seat bottom or parts were moved in unison to the rpaxim from the ischium, as it was assumed that the anterior position. The center of gravity % iselifum was in contact with the seat bottom. measured as the vertical height above the Horizontal distances to the e.g. in these tests chium and the horizontal distance from were measured from the seat back. posterior body plane. The second group (Figs. 5, 6 and7) conFor the posterior motions (Fig. 10) t( cerns itself with the study of various pilot posisimilar to those de.sribed in the anterior grc tions and shows the shift of center of gravity if were made. These individual tests were me the arms are moved to various positions for to determine the effect on the center of gray operation of controls with the legs at the comfor posterior motions of head, arms, trunk, h fort angle ""' where the knees are 1100, ±t'50, and all body parts moved in posterior directii and, in addition, two extreme positiouns for the Again the center of gravity was measured v feet, one in which the feet are back under the tically from the ischium and horizontally fr( chair and one where the legs are fully extended. the anterior body plane. The third group (Fig 8) represents the comIn the study of lateral shifts of e.g. (Fig. 1 mercial airline passenger in the full reclining individual tests were made for location of t position and shows the displacement of the center of gravity with the head flexed to t center of gravity of the body for the passenger side, with the left arm extended laterally, wi when the arms are moved to various positions the right arm across the chest, with the he. and when the feet are on the floor or on the and trunk flexed to one side, with the left I foot rest of the seat immediately in front. In in maximum abduction, with the left leg a 'this position the seat back makes an angle of ducted and the right leg adducted, and a fir. 1150 with the seat cushion. However, since test with all body parts moved laterally as f both the trunk and pelvis are reclining at this as possible. In all tests the pelvis was n angle, these tests and measurements were made moved and the center of gravity was measurn by dropping the legs to the 1150 angle. It vertically from the ischium and horizontal must be noted here that vertical distances of from the mid-sagittal plane. the center of gravity were measured from the In tests to move the centcr of gravity as f ischium parallel to the plane of the subject's as possible toward the head (cephauae back, while boiizontal distances of the e.g were (Fig. 12) inrxl,"dual tesl,; for both arms e perp-ndicular distances from this plane. In tended over the head a~id for both legs flex( F of Fig. 8 the passerger is not reclining but is '-,ward the head as well as ene final test, wit assuming one posivion in a current study to both legs and both arms in maximum cephah, direction, were made. 'A these tests the center the body; for example, para-hut Ick packs, of gravity was rcasured ver.ically from the chest packs, etc. isehium and horizont.'lv from the posterior body plane. RESULTS Only two tests were made for shifting center The results are presented bot graphical of gravity toward the feet (caudad) (Fig. 13), (Figs. 4 through 16) and tabu. Tables II one with *he subject standing with the trunk through XIV) form with sma agramatic flexed as far as possible withouw exte:cding t%.e arms and the second with the arms extended. fies rranyine p on t nof the Here the pelvis was allowed to rotate but the a or any ontepsion ga omralli vertical distance of the center of gravity wth average of the centers of gray .f all five measured from the rosition of the ischium besuhjects is shown as a black . n Figs. 4 fore flexion of the trunk in order to show the through 14 along with an are of :le which, total caudad shift due to these movements, if completed, would include the al centers The horizontal distance of the'e.g. was measof gravity of all subjects. tired from the posterior body plane. Finall,, "5st6 to determine shifts of center DISCUSSION AND CONCLUS of gravity accompanying maximum abduction of arms and legs were made (Fig. 14 and 15). It will he noted from a sttidy ( se graphs Individual tests were made to determine the that the variation between s.ibje i any one e.g. for abduction of the arms, for abduction of position is sometime great.:r th; e shift of the legs and for simultaneous abduction of the center of gravity of the groi te to any arms and legs. For reference, the results of particular motion. Fig. 3 presel -tual centhese tests are presented first showing the shift ters of gravity of each of the fi, ting subof the e.g. in the free body as measured from jects for three different arm positi nd shows the isehium andsecondly the shift of the e.g. the location of the geometrical a ,es of the of man standing giving vertical height of the group. It will be noted from t] "aph that e.g. from the ground. the shifts of e.g. of all subjects f ' a definite pattern. The completed cireh Figs. 4, 5, ADDITION OF WEIGHTS TO BODY 6, and 7 enclose areas that inclu( i subjects Studie-s were made to locate the center of and all arm positions. In Fig this area Studes eremad t lo e nt has a two inch radius while a rad :one and gravity of man sitting and standing with a one-half inches suffices in Figs. 5 nd 7. twenty pound pack on his back (Fig. 16), with the center of gravity of the pack 18-5/8 inches Analysis of tests of maximun ft shows above the ischium and 6 inches posterior to that man is capable of shifting hi . roughly the back. The center of gravity of man wear11-1/2 inches toward the head 12), 10 ing this pack in the two positions studied was inches toward the feet (Fig. 13) iches anfound experimentally on the balancing equipteriorly (Fig. 9), 4-1/2 inch, )steriorly ment and then checked by mathematical calcu(Fig. 10), and 4-1/2 inches later, Fig. 11) lations, using data previously obtained fn this from that of an erect standing p L. study for the center of gravity of man without The maximum shift. of e.g. ipanying the pack. We were pleased to find that the the movement of all body parts i given dicalculated and the experimental data checked rection is not the sum cf the sh )roduced within one-fourth inch. The significance of by moving each part separately. these tests is obvious as they show that the This study shows that in spite he wide d(L•. presented in this report may be used as a variety of body sizes and mass ributions basis for mathematical calcula--uns of location there is surpiisingly little variatio; the locaof the center Of gravity of man !n variol~s position of the body e.g. when inca: from a tions with the addition of various weights to reference point on the pelvis. In *en body -4position the c.g. ,'-f at least 901 of the adult male Report No. 1, 27th AAF Base Unit, AAF population fal] within a sphece 2 inches in School of Aviation Medicine, Randolph diameter. Field, Te.;, 15 August 1945. RE;ERENCES 2. Swearingen, J. J., Determination of the most comfortable knee angle for piluts, Civil 1. Elbel, E. R., Leg strength and !eg endurAeronautics Medical Rcsearch Laboratory, ance in relation to height, weight, and Project No. Biotechnology 3-48, Report other body measurements, Project No. 318, No. 1.