BIOMECHANICAL
RESEARCH IN SPACE
By
Gideon Ariel, Ph.D.
ABSTRACT
Aerospace engineers are now calling for development of space as a new frontier. To accomplish safe flights and landing, we faced with great challenges. One of the biggest challenge is the human physiological machinery. The goal of the present project is to minimize the effects of deconditioning during spaceflight. Some of these effects are physiological and mechanical demands of microgravity is by deconditioning of the cardiovascular, musculoskeletal, and neuromuscular systems. Deconditioning produces a multitude of physical changes such as loss of muscle mass, decreases in bone density and body calcium; it is also responsible for decreased muscle performance, strength and endurance.
Extravehicular activity (EVA) in space require the most physically demanding task that astronaut perform on orbit. Therefore, it is necessary to develop exercise programs as well as exercise device to countermeasure these effects.
Biomechanics in space is fundamental to understanding the work performance capabilities of humans in space. Biomechanics as practiced by NASA has the primary goal to conducting operationallyoriented research focusing on maximizing astronaut on--orbit performance capabilities.
At the present time the following biomechanics prioritized research objectives are designed for immediate research projects:
Ail the biomechanical analysis integrate a high speed videography, EMG and force plates. In addition, a computer controlled dynamometer is programmed to provide specific exercise prescriptions to the astronauts in order to maximize their muscular strength and endurance to perform the require tasks which analyzed by the integrated movement analysis.
BIOMECHANICAL RESEARCH IN SPACE
by
Gideon Ariel, Ph.D.
INTRODUCTION
Aerospace engineers are now calling for development of space as a new frontier. They maintain that a high frontier in space can produce the same kind of boom conditions that existed for Europe after 1500 and for the United States during early days of its experience when an ever expanding West helped to produce a growing, spirited America. Specifically, space frontier can provide unlimited low-cost energy, available to everyone rather than just to those nations favored with large reserves of fossil or nuclear fuels. Provide unlimited new lands to provide living space of higher quality than that now possessed by most of the human race. And provide an unlimited materials source, available without stealing or killing or polluting.
When Americans reflect on the space program, there are two events that stand out more prominently than others. The first moon landing and the Challenger disaster.
On July 21, 1969, an Apollo spacecraft carried Neil A. Armstrong, Edwin E. Aldrin, and Michael Collins to the moon. Aldrin, became the first man on the moon. When Neil Armstrong touch his foot to the moon's surface he said:
The second event, the Challenger disaster, took the lives of seven astronauts, including the school teacher Christa McAuliffe, when the rocket boosters of the space shuttle exploded 73 seconds after lift-off on January 28, 1986.
Neil Armstrong fixed the ultimate significance of his deed by what he said; Christa McAuliffe did the same by who she was. Armstrong, in the midst of a historic event, had the vision to say the right thing. McAuliffe, although a nonprofessional astronaut, had the vision to become part of the quest.
We stand before a frontier of apparently infinite proportions. It constitutes perhaps the ultimate quest. As we proceed in this exploration, we are outfitted with the most sophisticated and rapidly expanding technologies the world has ever known. Authentic heroes have helped us to understand that "the right stuff" must be complemented with "the right reasons" when we undertake such a task.
To accomplish the "right stuff" we faced with great challenges. One of the biggest challenge is the human physiological machinery. Man, having evolved as an upright, bipedal animal, cannot consciously take the rapid onset of acceleration that would be required for long distance space travel. Additionally, the physiological adaptations of a microgravity environment are poorly understood, and it can arguable be said that long term weightlessness results in significant postflight deleterious changes that may be permanently debilitating.
COUNTERMEASURES
The goal of the present project is to minimize the effects of deconditioning during spaceflight using individualized exercise "prescriptions" and inflight exercise facilities combine with extensive biomechanical analysis of movement in microgravity.
Background:
One of the ways the human body reacts to the reduced physiological and mechanical demands of microgravity is by deconditioning of the cardiovascular, musculoskeletal, and neuromuscular systems. Deconditioning produces a multitude of physical changes such as loss of muscle mass, decreases in bone density and body calcium; it is also responsible for decreased muscle performance, strength and endurance, orthostatic intolerance, and overall decreases in aerobic and anaerobic fitness.
Deconditioning presents operational problems during spaceflight and upon return to 1-G. Muscular and cardiovascular deconditioning contribute to decreased work capacity during physically demanding extravehiculr activities (EVAs); neuromuscular and perceptual changes can precipitate alterations in magnitude estimation, or the socalled "input-offset" phenomenon; and finally, deceased vascular compliance can lead to syncopal episodes upon reentry and landing.
Extravehicular Activity (EVA) is the most physically demanding task that astronauts perform on-orbit. Space Station Freedom and manned Lunar and Mars missions will greatly increase the number, frequency, and complexity of EVA's within the next 10 to 20 years.
Countermeasures are efforts to counteract these problems by interrupting the body's adaptation process. Effective countrmeasures will assure mission safety, maximize mission success, and maintain crew health.
Results from experiments on the Gemini, Apollo, and Skylab missions suggest that regular exercise is helpful in minimizing several aspects of spaceflight deconditioning (7,9,10). In fact, exercise is the only countermeasure that can potentially counteract the combined cardiovascular, musculoskeletal and neuromuscular effects of adaptation. Biomechanics in space is fundamental to understanding the work performance capabilities of humans in space. Biomechanics as practiced by NASA has the primary goal to conducting operationallyoriented research focusing on maximizing astronaut on-orbit performance capabilities. The purpose of biomechanical analysis in space is to provide a program of exercise countermeasures that will minimize the operational consequences of microgravityinduced deconditioning. Biomechanical analysis of movement in space will provide individualized exercise "prescriptions" for each crew member to optimize required tasks in microgravity environment. Through characterizing the tasks requirement in the musculoskeletal and neuromuscular systems induced by microgravity, develop training protocols to address deconditioning in these systems that will serve as the basis for training prescriptions. To achieve these training protocols it is necessary to develop flight exercise hardware and associated software related to biomechanical measurement devices.
Critical Questions:
Some of the critical questions to be addressed the present goals are:
These are few of the questions to be answer to understand the possible countermeasures to be efficient. On Wednesday, September 20, 1989, the following 23 topics were suggested by members of the Biomechanics group, of which I was one of the members:
At the present time the following biomechanics prioritized research objectives are designed for immediate research projects:
Biomechanical Performance and Modeling Predictions
-prediction model vs actual performance
-integrate biomechanics with physiology
-movement notes
Telescience, Automation, and Tool Design
-development of robotic tools to perform some tasks
-power tools (smart tools)
-increase mechanical advantage of existing tools
-development of universal tool
Human Motor Control Strategy
-training
-subject feedback
One of the first biomechanical project underway at the present time is to investigate landing and normal egress.
Task Analysis of Landing and Normal Egress:
The following is one of the biomechanical studies to evaluate landing and normal egress. ABSTRACT: This study requires using the astronauts preflight; during egress training, and postflight; during landing, (out of seat egress) and during normal exit from the shuttle to a ground level. A total of ten (N=10) manifested astronauts are requested, five Pilots and 5 Mission Specialists, to participate so that comparisons can be made on post mission walk-out performance.
Video cameras and force plate instrumentation will record simulated tasks associated to landing and egress during normal training in the high fidelity mockup. During training, crew will be video recorded as they perform the actual tasks that will be idiospecific to their flight tasks. Normal, walk-out of orbiter, egress will also be video recorded, however, specifying that the first 3-4 steps on level ground be done on the Force Plate for force patterning and gait analysis. At landing, video cameras in the orbiter will record landing procedures in upper and middecks and for out of seat egress. Additional video cameras will also record normal walk-out egress from the orbiter with the first 3-4 steps on level ground being done on the Force Plate. This study is the first of several studies to scientifically quantify the forces, movement patterns, center of gravity and force velocities of motion
during landing and egress tasks. This base investigation shall be further expanded to evaluate ground based emergency egress of volunteer subjects and counermeasure interaction and effectiveness on egress performance of astronaut crewmembers.
Another task is to design an exercise dynamometer to be able to exercise and analyze muscle functions and efficiencies. The goal is to utilize biomechanical research to utilize the most efficient means to counteract the effect of deconditioning in space.
Fitness technology, in both theory and practice, exhibits two problems common to many modern, rapidly emerging disciplines. First, a lack of clearly defined and commonly accepted standards has resulted in a marketplace rife with conflicting claims and approaches to both attaining and maintaining fitness. In general, both vendors and consumers of fitness technology have been unable to provide a sound scientific answer to the simple question, "Are we doing the right thing?" Second, a lack of the proper tools and techniques for measuring fitness and the effectiveness of a given technology to the attainment of fitness has made it quite difficult to evaluate existing products in order to select the ones that really work.
Some of the requirements to in/flight 0-G exercise dynamometer are as follows:
Mechanism for the Required Dynamometer:
A standard hydraulic cylinder is attached to an exercise bar by a mechanical linkage. As the bar is moved, the piston in the hydraulic cylinder moves pushing non inflammable liquid out of one side of the cylinder, through a valve, and back into the other side of the cylinder. When the valve is fully open there is no resistance to the movement of the liquid and thus no resistance to the movement of the bar. As the valve is closed, it becomes harder to push the liquid from one side of the cylinder to the other and thus harder to move the bar. When the valve is fully closed, liquid cannot flow and the bar will not move. In addition to the cylinder, the resistance mechanism contains sensors to measure the applied resistance mechanism contains sensors to measure the applied force on the bar and the motion of the bar. Now assume the valve is at some intermediate position and the bar is being moved at some velocity with some level of resistance. If the computer senses that the bar velocity is too high or that bar resistance is too low, it will close the valve by a small amount and then check the velocity and resistance values again. If the values are not correct, it will continue to close the valve and check the values until the desired velocity or resistance is achieved. Similarly if the bar velocity is too low or the bar resistance is too high, the computer will open the valve by a small amount and then recheck the values. This feedback loop will continue with the valve being opened by small amounts until desired velocity or resistance is achieved. The feedback cycle occurs hundreds of times a second so that the user will not experience perceptible variations from the desired parameters of exercise.
There are a number of advantages in such a resistance mechanism. One significant advantage is safety. The passive
hydraulic mechanism provides resistance only when the user pushes or pulls against it. The user may stop exercising at any time, such as during rehabilitation if pain or discomfort is experienced, and the exercise bar will remain motionless. Another advantage is that of bidirectional exercise. the hydraulic mechanism can provide resistance with the bar moving in either direction.
This computer controlled exercise device has been designed to consider every movement or exercise performed by a user to be a pattern of continuously varying velocity or resistance. This pattern may be set using direct measurement of subject motion by the system, it may be copied from the results of performance analysis, or the pattern may be "designed" or created by the user or practitioner as a goal of training or rehabilitation. Exercise patterns are stored in computer memory and can be recalled and used each time a subject trains. During exercise, the computer uses the pattern to adjust bar velocity or bar resistance as the subject moves through the full range of motion. In this manner, the motion parameters of almost any activity can be really duplicated by the exercise system. Thus, assessment, training, or rehabilitation may be performed using the same pattern as the activity itself.
The value of applying the principles of biomechanics to the assessment of fitness in space has been clearly demonstrated. Performance analysis provides the means to quantify human activity and to provide insight into the mechanisms that contribute either to superior or inferior levels of performance. At the same time, it has been shown that fitness technology has been presented that permits exercise and countermeasure means patterns to biomechanically duplicate the target activity.
The integration of movement analysis with measurements such as E.M.G. activity with forces measured in load cells and force plates allow to analyze the astronauts in various gravitational conditions and allow the design of optimal technique and equipment to optimize space missions.
BIOMECHANICS IN SPACE AND THE DESIGN OF EXERCISE
AND ANALYSIS DYNAMOMETER AND SOFTWARE SYSTEM
AS AN IN/FLIGHT, O-G, EXERCISE DYNAMOMETER
SYSTEM
Fitness technology, in both theory and practice, exhibits two problems common to many modern, rapidly emerging disciplines. First, a lack of clearly defined and commonly accepted standards has resulted in a marketplace rife with conflicting claims and approaches to both attaining and maintaining fitness. In general, both vendors and consumers of fitness technology have been unable to provide a sound scientific answer to the simple question, "Are we doing the right thing?" Second, a lack of the proper tools and techniques for measuring fitness and the effectiveness of a given technology to the attainment of fitness has made it quite difficult to evaluate existing products in order to select the ones that really work.
Some of the requirements to in/flight 0-G exercise dynamometer are as follows:
-
The flexibility of performing exercises and diagnostics in isotonic,
isokinetic, isometric, accommodating velocity at variable loads as well
as accommodating resistance at variable speeds or any combination of
these exercise controlled modes.
-
The ability to perform exercises and diagnostics from a preprogrammed
sequence of tests and exercises stored on disk. The investigator can
prescribe for object, testing and rehabilitation programs from a library
of specialized programs or create specific protocol tailored for that
subject.
-
To offer user-friendly, menu-driven software packages which can be
easily learned and are simple to operate.
-
Allows for data transfer to other commercial or custom software packages
for extraordinary graphing, data report formats, statistical analysis,
etc.
-
Allow for external analog data acquisition that can be correlated with
the acquired force curves such as E.M.G. data and load cells.
-
All dynamometer functions can be controlled or monitored either from the
keyboard, hard disk storage, or a remote location, via telephone modem
and satellites.
Biomechanics in space is fundamental to understanding the work performance capabilities of humans in space. Biomechanics as practiced by NASA has the primary goal to conducting operationally-oriented research focusing on maximizing astronaut on-orbit performance capabilities. The purpose of biomechanical analysis in space is to provide a program of exercise countermeasures that will minimize the operational consequences of microgravityinduced deconditioning. Biomechanical analysis of movement in space will provide individualized exercise "prescriptions" for each crew member to optimize required tasks in microgravity environment. Through characterizing the tasks requirement in the musculoskeletal and neuromuscular systems induced by microgravity, develop training protocols to address deconditioning in these systems that will serve as the basis for training prescriptions. To achieve these training protocols it is necessary to develop flight exercise hardware and associated software related to biomechanical. measurement devices.
Critical Questions:
Some of the critical questions to be addressed the present goals are:
-
1. What type of exercise devices such as weight training, bicycling, rowing,
swimming, running, etc. are necessary to train all of the organ systems
affected by deconditioning?
-
2. Which indices are the most reliable indicators of changes in fitness?
-
3. Which reliable indicators of changes in fitness best describe the changes
caused by deconditioning?
-
4. How does training in microgravity differ from training in 1-G ?
-
5. What are the differences between training that includes impact forces and
training that uses nonimpact forces?
-
6. Can an artificial intelligence expert system be developed to aid in
monitoring, controlling, and adjusting prescriptions?
-
7. How does inflight exercise training affect the adaptation process?
-
8. Which muscle groups are critical in the performance of egress, landing,
and EVAs?
-
9. Which of the indicators of microgravity-induced change in muscle function
can be correlated with possible difficulty in performing egress, landing, and
EVAs?
These are few of the questions to be answer to understand the possible countermeasures to be efficient. On Wednesday, September 20, 1989, the following 23 topics were suggested by members of the Biomechanics group, of which I was one of the members:
-
Identify and analyze tasks by mission.
-
Focus studies to examine the functions of upper extremities during space
flight.
-
Integration of Biomechanics and Physiology to fully understand "the
complete picture."
-
Examine the use of power tools to enhance performance and reduce fatigue
of the crew members.
-
Compare the use of a robotic hand to EVA crew interaction.
-
Investigate "tweaking" existing tools to a give a greater
mechanical advantage.
-
Use of the prediction of work and tools required to perform a given
task.
-
What jobs/tasks are needed on orbit?
-
What are the energy expenditures for on orbit activity.
-
Comparison of perceived target accuracy and spatial orientation to
actual target accuracy and spatial orientation.
-
Comparison of gross tasks to fine motor control.
-
Quantify performance of metabolism, muscles, forces, etc.
-
Determination of the scope of biomechanics operations vs. those of
medical science.
-
Evaluation of muscle, EMG, etc. of crew members.
-
Evaluation of hormones and metabolic information.
-
Investigation of hardware issues such as the development of a universal
tool.
-
Integration of protocols including recovery, strength, power, endurance,
and frequency.
-
Development of work related tests incorporating dynamometers, force
plates, etc.
-
definition of specified joint axes.
-
Investigation into the use of a robot glove as an extension of the space
suit.
-
Development and use of a flight qualified dynamometer and determination of
what information should be measured (i.e. power, endurance, etc.).
-
Development of an immediate recovery dynamometer to measure post-flight
crew strength.
At the present time the following biomechanics prioritized research objectives are designed for immediate research projects:
-
Flight Dynamometer -on-orbit data collection -EVA tools/work tasks -single
joint articulations
-
Task Analysis and Efficiency (IVA/EVA) upper body work tasks -mechanical
efficiency -metabolic efficiency - psychomotor efficiency/accuracy
Biomechanical Performance and Modeling Predictions
-prediction model vs actual performance
-integrate biomechanics with physiology
-movement notes
-
Biomechanical Countermeasures -short arm centrifuge - skeletal system impact
loading -vertebral column/locomotion skeletal muscles
-
Biomechanics of Space Suit Assembly -development of flexible, high
performance space suit -glove design
-
Telescience, Automation, and Tool Design -development of robotic tools to
perform some tasks -power tools (smart tools) - increase mechanical
advantage of existing tools
-
-development of universal tool
Human Motor Control Strategy
-
-training
-
-subject feedback
TASK ANALYSIS OF LANDING AND NORMAL EGRESS
-
Objectives: 1. Identify the normal biomechanical and kinematic
requirements of landing and walk-out of shuttle egress using video
motion analysis. 2. Identify specific tasks associated with individual
crewmembers during ELE. 3. Quantify the forces of gait during normal
walkout egress. 4. Suggest physiological parameters that might be tested
in a laboratory that may mimic tasks that are performed during landing
and normal walk-out egress.
The following is one of the biomechanical studies to evaluate landing and normal egress. ABSTRACT: This study requires using the astronauts preflight; during egress training, and postflight; during landing, (out of seat egress) and during normal exit from the shuttle to a ground level. A total of ten (N=10) manifested astronauts are requested, five Pilots and 5 Mission Specialists, to participate so that comparisons can be made on post mission walk-out performance.
Video cameras and force plate instrumentation will record simulated tasks associated to landing and egress during normal training in the high fidelity mockup. During training, crew will be video recorded as they perform the actual. tasks that will be idiospecific to their flight tasks. Normal, walk-out of orbiter, egress will also be video recorded, however, specifying that the first 3-4 steps on level ground be done on the Force Plate for force patterning and gait analysis. At landing, video cameras in the orbiter will record landing procedures in upper and middecks and for out of seat egress. Additional video cameras will also record normal walk-out egress from the orbiter with the first 3-4 steps on level ground being done on the Force Plate. This study is the first of several studies to scientifically quantify the forces, movement patterns, center of gravity and force velocities of motion during landing and egress tasks. This base investigation shall be further expanded to evaluate ground based emergency egress of volunteer subjects and counermeasure interaction and effectiveness on egress performance of astronaut crewmembers.
-
The ability to simulate real task activities for comparison of strength and
endurance in 1 and 0 Gs.
-
All exercise program variables, such as intensity, frequency, duration,
sets, work load, percent fatigue, can be controlled and changed from the
control keyboard or by remote modem.
-
The software is an artificial intelligence expert system that monitors,
controls and adjusts prescriptions according to the measured output of the
exerciser.
Mechanism for the Required Dynamometer:
A standard hydraulic cylinder is attached to an exercise bar by a mechanical linkage. As the bar is moved, the piston in the hydraulic cylinder moves pushing non inflammable liquid out of one side of the cylinder, through a valve, and back into the other side of the cylinder. When the valve is fully open there is no resistance to the movement of the liquid and thus no resistance to the movement of the bar. As the valve is closed, it becomes harder to push the liquid from one side of the cylinder to the other and thus harder to move the bar. When the valve is fully closed, liquid cannot flow and the bar will not move. In addition to the cylinder, the resistance mechanism contains sensors to measure the applied resistance mechanism contains sensors to measure the applied force on the bar and the motion of the bar. Row assume the valve is at some intermediate position and the bar is being moved at some velocity with some level of resistance. If the computer senses that the bar velocity is too high or that bar resistance is too low, it will close the valve by a small amount and then check the velocity and resistance values again. If the values are not correct, it will continue to close the valve and check the values until the desired velocity or resistance is achieved. Similarly if the bar velocity is too low or the bar resistance is too high, the computer will open the valve by a small amount and then recheck the values. This feedback loop will continue with the valve being opened by small amounts until desired velocity or resistance is achieved. The feedback cycle occurs hundreds of times a second so -that the user will not experience perceptible variations from the desired parameters of exercise.
There are a number of advantages in such a resistance mechanism. One significant advantage is safety. The passive hydraulic mechanism provides resistance only when the user pushes or pulls against it. The user may stop exercising at any time, such as during rehabilitation .if pain or discomfort is experienced, and the exercise bar will remain motionless. Another advantage is that of bidirectional
exercise. the hydraulic mechanism can provide resistance
with -the bar moving in either direction.This computer controlled exercise device has been designed to consider every movement or exercise performed by a user to be a pattern of continuously varying velocity or resistance. This pattern may be set using direct measurement of subject motion by the system, it may be copied from the results of performance analysis, or the pattern may be "designed" or created by the user or practitioner as a goal of training or rehabilitation. Exercise patterns are stored in computer memory and can be recalled and used each time a subject trains. During exercise, the computer uses the pattern to adjust bar velocity or bar resistance as the subject moves through the full range of motion. In this manner, the motion parameters of almost any activity can be really duplicated by the exercise system. Thus, assessment, training, or rehabilitation may be performed using the same pattern as the activity itself.
INTEGRATION OF PERFORMANCE ANALYSIS AND COMPUTERIZED
EXERCISE IN ACHIEVING OPTIMUM FITNESS
The value of applying the principles of biomechanics to the assessment of fitness in space has been clearly demonstrated. Performance analysis provides the means to quantify human activity and to provide insight into the mechanisms that contribute either to superior or inferior levels of performance. At the same time, it has been shown that fitness technology has been presented that permits exercise and countermeasure means patterns to biomechanically duplicate the target activity.
The integration of movement analysis with measurements such as E.M.G. activity with forces measured in load cells and force plates allow to analyze the astronauts in various gravitational conditions and allow the design of optimal technique and equipment to optimize space missions.
Application of High Technology to Performance Analysis
Gideon 'B. Ariel '
Ariel Performance Analysis System, Inc.
b Alicante, Trabuco Canyon. California 92679
ABSTRACT
Biomechanics is the study of the motion of living things and, as an established disciplines it has evolved from a fusion of the classic disciplines of anatomy, physiology, physics, and engineering. New technological enhancements now available may provide the tools to accurately describe and quantify motion exercises work environments, and/or any motion related protocols.
MOTION ANALYSIS
The Ariel Performance Analysis System is a computer-based system to measures analyzes and present movement characteristics. This Performance Analysis System provides a means to quantity motion utilizing input information from any or all of the following mediums: visual (video or film), electromyography (EMS), and force platforms. The theoretical bases of the system models the human body as a mechanical system of moving segments upon which muscular! gravitational! inertial, and reaction forces are applied. Although the physical and mathematical model for such a system is complex! it is well defined (isbs7).
The Ariel Analysis System provides a means of measuring human motion based on a proprietary technique for the processing of multiple high-speed film or video recordings of a subject's performance (2!12!13). This technique demonstrates significant advantages over other common approaches to the measurement of human performance. First, except in those specific applications requiring EMS or kinetic (force platform) data, it is noninvasive. No wires! sensors, or markers need be attached to the subject. In fact! the subject need not be aware that data is being collected. Seconds it is portable and does not require modification of the performing environment. Cameras can be taken to the location of the activity and positioned in any convenient manner so as not to interfere with the subject. Activities in the ,workplaces homes hospital, therapist's offices health club, or athletic field can be studied with equal ease. Thirds the scale and accuracy of measurement can be set to whatever levels are required for the activity being performed. Camera placements lens selections shutter and film speed may be varied within wide limits to collect data on motion of only a few centimeters or of many meters! with a duration from a few milliseconds to a number of seconds. Video equipment technology currently available is sufficiently adequate for most applications requiring accurate motion analysis, although special applications may require very
high-speed cameras, powerful lenses, and high levels of illumination. Determination of the problem, error level, degree of quantification, and price will all affect the input device selection. Fourth, in studies with subjects who are aware of the filming process, multiple trials with each individual can be collected with ease. Multiple trials and subjects enhance the development of biomechanical models, task descriptions, and performance protocols as well as allowing statistical analyses.
A typical kinematic analysis consists of four distinct phases -- data collection (filming), digitizing, computation, and presentation of the results. Data collection is the only phase that is not computerized. "In this phase, film or video recordings of an activity,are made using two or more cameras with only a few restrictions: (1) All cameras must record the action simultaneously; (2) the cameras must not move during the activity or between the recording of the activity and the recording of the calibration points: (3) the activity must be clearly seen throughout its duration from at least two camera views! (4) the location of at least six fixed noncoplanar points visible from each camera view (calibration points) must be known. These points need not be present during the activity as long as they can be seen before or after the activity. Usually they are provided by some object or "apparatus" of known dimensions that is placed in the general area of the activity, filmed and then removed! (5) the speed of each of the cameras (frames/second) must be accurately known, although the speeds do not have to be the same; and (6) some event or time signal must be recorded simultaneously by all cameras during the activity in order to provide synchronization.
These rules for data collection allow great flexibility in the recording of an activity. Information about the camera location and orientation, the distance from camera to subject, and the focal length of the lens is not needed. The image space is "self-calibrating" through the use of calibration points that do not need to be present during the actual performance of the activity. Different types of cameras and different film speeds can be used and the cameras do not need to be mechanically or electronically synchronized. The best results are obtained when camera viewing axes are orthogonal (9U degrees apart), but variations of 20 to 30 degrees can be accommodated while introducing almost negligible error.
Digitizing is the second phase of analysis. Initially, the video image is captured by the computer and stored in memory. This eliminates any further need for the video apparatus. The image sequence is then retrieved from computer memory and is displayed, one frame at a time, on the digitizing monitor. The grabbed image can be enhanced or altered in several ways. These include zooming the whole frame or a defined, isolated portion of the view. Changing the size may help the person digitizing to
more accurately.determine a particular joint which in the unenlarged viewcould not be identified. It is also possible to adjust the coloring, shading, and intensities of the image for each frame. Thus, alterations of the video image, in a manner similar to camera adjustments, can assist in the digitizing process.
Following the selection and storage of the video image, the digitizing phase continues. Using a video cursor, the location of each of the subject's body joints (e.g. ankle, knee, hip, shoulder, elbow) is selected and entered into the computer. As each point is selected, it is displayed within the video image on the monitor. The person digitizing may select an additional option which causes the previous one or two digitized frame points to appear while the current frame is being traced. This allows the digitizer .to evaluate. his current joint selection choice with the perspective of the previously identified joint center. Another useful feature is the "rubber band" effect. This situation occurs when the previously selected joint in the current frame is "fixed" while the next joint is being located. The computer connects the preceeding joint center with the curser. As the curser is moved to establish the joint center location, a line is created which moves according to the curser motion. This assists in digitizing since the connection between the two points represents the segment between the two joints. The digitizer can examine the alignment of the segment based on the perceived joint center while making the current joint center choice.
Another option available when there is difficulty locating a joint center is the "missing" and "estimated" point notation. If the joint center is completely blocked from view and no appropriate estimate can be made, the particular point can be designated as "missing" and the subsequent processing phase will ignore it. If the digitizer believes that the location is approximately correct, the joint center can be designated as "estimated" with subsequent processing utilizing a weighting factor in calculating that point.
In addition, a fixed point, which is a point in the field of view that does not move, is digitized for each frame as an absolute reference. This allows for the simple correction of any registration or vibration errors introduced during recording or playback. At some point during the digitizing of each view, a synchronizing event must be identified and, additionally, the location of the calibration points as seen from that camera must be digitized and saved in the computer memory. This sequence of events is repeated for each camera view.
Digitizing is primarily a manual process. It is performed, however, under computer control and the digitizing of video images is computer assisted. An automatic digitizing option is also available. Automatic digitizing can be performed utilizing
brightness, color resolution, and kinetic parameters. However, under manual control, user participation in the digitizing process, however, provides an opportunity for error checking and visual feedback which rarely slows the digitizing process adversely. A trained operator with a reasonable knowledge of anatomy and a consistent pattern of digitizing can rapidly produce highquality digitized images. Because all subsequent information is based on the data provided in this phase, it is essential that the points are selected precisely.
The computation phase of analysis is performed after all camera views have been digitized. The purpose of this phase is to compute the true threedimensional image space coordinates of the subject's body joints from the twodimensional digitized coordinates of each camera's view. Computation is performed using a direct linear transformation. This transformation is determined by first relating the known image space locations of the calibration points to the digitized coordinate locations of those points. The transformation is then applied to the digitized body joint locations to yield true image space locations. This process is performed under computer control with a small amount of timing information provided by the user. This information includes starting and ending points if all the data are not to be useds as well as a frame rate for the image sequence that may differ from the frame rates of the cameras used to record the sequence.
When transformation is complete, a smoothing or filtering operation is performed on the image coordinates to remove small random digitizing errors and to compute body joint velocities and accelerations. Smoothing options include cubic and quintic splines as well as a Butterworth 2nd order digital filter (14,16,19). Smoothing may be performed automatically by the computer or interactively with the user controlling the amount of smoothing applied to each joint. In addition, error measurements from the digitizing phase may be used to optimize the amount of smoothing selected. In those cases involving impact, such as hitting a golf-ball, the point of impact can be identified during the smoothing process. The operator can select that point and several points on either side of the event so that the smoothing algorithm will adjust to this violent activity in an appropriate manner. That is to say, the motion before and after impact as well as impact itself can be more accurately calculated during the smoothing process. At the completion of smoothing the true threedimensional body joint displacements, velocities and accelerations have been computed on a continuous basis throughout the duration of the sequence.
At this point, optional kinetic calculations may be performed to complete the computation phase. Body joint displacements, velocities and accelerations are combined with body segment mass distribution to compute dynamic forces and moment at each of the body joints. Muscular contribution to these forces and moments
can then be computed by selectively removing the inertial and gravitational kinetic components.
The presentation phase of analysis allows computed results to be viewed and recorded in a number of different formats. Body position and body motion can be presented in both still frame and animated "stick figure" format in three dimensions. Multiple .stick figures may be displayed simultaneously for comparison purposes. Joint velocity and acceleration vectors may be added to the stick figures to show the magnitude and direction of body motion parameters. Color hard copies of these displays can also be produced for reporting and publication.
Results can also be reported graphically. Plots of body joint and segment linear and angular displacements, velocities, accelerations, forces and moments can be produced in a number of format options. An interactive graphically oriented user interface makes the selection and plotting of such results simple and straightforward. In addition, results may also be reported in numerical form. All quantities that can be selected for graphing may also be printed in tables of body motion parameters.
The reliablity of the system are high with reliability coefficients ranging from .95 to .99. Coefficient variability is affected by poor and/or inappropriate video quality, inexact calibration points, and the skill level of the digitizing operators.
Consider, for example a hypothetical situation. The civilian authorities of A City must describe, evaluate, promote or demote, train, and, perhaps, rehabilitating various professionals. These professions could include fire fighters, police personnel, sanitation workers, bus drivers, postal workers, etc. Modern societal demands insist that job related decisions must not discriminate but no effectively objective, accurate measurement devices have been available for the personnel selection process. How then could these authorities handle this hypothetical personnel situation?
Imagine the following scenario. Fire fighters from A City choose a panel of their peers who select certain tasks that are the most frequently demanded in their jobs. These tasks are unanimously agreed upon and some specifically selected individuals, whom all fire fighters agree are superior examples of their profession, are chosen for testing. Biomechanical data is obtained on all those individuals as they perform each task. This data is processed to quantify a "generic" fire fighter so that guidelines for task performance can be described in precise, accurate, and duplicable form. Performance levels may be required for hiring, promotion, alternative assignments, and/or
termination. The critical factor, however, is that biomechanical
quantification can provide exact results without bias.
The same sequential procedures could be utilized for testing the efficacy of a drug. For example, what is the difference between a type of operation and a new drug for patients afflicted with Parkinson's disease? Individuals could be analyzed biomechanically before and after the applications. In addition, evaluation of their fitness relative to their abilities to perform tasks could be monitored in terms of patterns of motion as well as strength.
Physical therapy (15,18) and job retraining are other fields which provide numerous opportunities for the quantification of performance. ..If data has been recorded on the individual before an injury, comparison can easily be made to determinine level of recovery and/or disability. If an adequate data base has been created, it is also possible to compare an individual's activity with an "ideal" or "average" performance level.
Other obvious examples for quantification of performance can be found in sports 13,17). Specific performance parameter measurements for various occupations coupled with actual performance analysis of individual's will allow better job description, work related performance criteria, and rehabilitation programs to be established.
Biomechanical analyses and computer technology have increased the parameters upon which performance can be considered. Biomechanics provides a precise, objective, and quantifiable criterion for performance evaluation. Obviously, data about the arteries, the functioning capacities of various internal organs, and other anatomical or physiological data are not provided by biomechanical testing. However, the mare blind men employed to touch the elephant, the greater the chance to know what the elephant actually is. However, as the definitions and the evaluative instruments become more precise, it can only be hoped that the blind will be able to see.
REFERENCES
1. G.B. Ariel, "Computerized Biomechanical Analysis of Human Performance," Mechanics and Sport, Vol. 4, pp. 267-275, The American Society of Mechanical Engineers, New York, 1973.
2. G.B. Ariel, "The Effect of Knee Joint Angle on Harvard Step Test Performance," Ergonomics. Vol.12, pp. 33-37, 1969.
3. G.B. Ariel, "Computer Application of Biomechanical Analysis of Human Performance in Sport and Industry," Canadian Congress of Sport and Physical Activity. Abstracts, Oct., 1973.
4. G.B. Ariel, "Computerized Biomechanical Analysis of the Knee Joint during Deep Knee Bend with Heavy Load," Biomechanics IV. Edited by Richard C. Nelson and Chauncey A. Morehouse, Fourth
International.Seminar on Biomechanics Volume IV. The Pennsylvania State University, 1973.
5. G.B. Ariel, "Shear and Compression Forces in the Knee Joint during Deep Knee Bends" XXth World Congress in Sports Medicine Handbook, Melbourne, Australia, 1974.
6. G.B. Ariel, "Computerized Biomechanical Analysis of Human Performance," XXth World Con ress..in Sports Medicine Handbook, Melbourne, Australia, 1974.
7. G.B. Ariel, "Method for Biomechanical Analysis of Human Performance," Research Quarterly, Vol. 45, pp. 72-79, 1974.
8. G.B. Ariel, "Biomechanical Consideration in the Design and Construction of Resistance Exercise Equipment," Proceedings of the 1st Annual Meeting, Canadian Society for Biomechanics. University of Alberta, Edmonton, Alberta, Canada, pp.25-34, 1974.
9. G.B. Ariel, "The Biomechanics of Athletic Shoe Designs" Medicine and Science in Sports, (Abstract), Vol. 7, pp. 78, 1975.
10. G.B. Ariel, "Computer Method of Analyzing Locomotive Patterns of Handicapped Children," Final Report of the State of the Art Research Review and Conference on the Psychomotor Development in Preschool Handicapped Children for the Bureau of Education. Prepared for the Bureau of Education for the Handicapped Office of Education, Department of Health, Education, and Welfare. Contract No., 300-75-0225. pp. 16-25, 1976.
11. G.B. Ariel, "Neural Control of Locomotion - A Kinetic Analysis of the Trot in Cats," In Neural Control of Locomotion. Edited by R.M. Herman, et al. pp. 759-762, Plenum Publishing Corp., 1976.
12. G.B. Ariel, "Human Movements Analysis," Applied Ergonomics, Vol. 11, pp. 61-62, 1980.
13. G.B. Ariel, "Biomechanics," In Scientific Foundations of Sports Medicine. Edited by Carol C. Teitz, M.D., Chapter 12, pp. 271-297, Toronto: B.C. Decker, Inc., 1989.
14. J.F. Kaiser, "Digital Filters," Digital Filters and the Fast Fourier Transform, Edited by D. Liu, pp. 5-79, Dowden, Hutchinson & Ross, Stroudsburg, 1975.
15. I. Llacera and R. Squires. "An Analysis of the Shoulder Musculature during the Forehand Racquetball Serve," presented at American Physical Therapy Association meeting, Las Vegas, June, 1988.
16. C. Reinsch, "Smoothing by Spline Functions," Numerische Mathematik, Vol. 10, pp. 177-183, 1967.
17. P. Susanka, "Biomechanical Analyses of Men's Handball," Internationale Handball Federation 12th Men's Handball World Championship, Charles University, Prague, Czechoslovakia, 1990.
18. R.W. Wainwright, R.R. Squires, R.A. Mustich, "Clinical Significance of Ground Reaction Forces in Rehabilitation and Sports Medicine," presented at the Canadian Society for Biomechanics, 5th Biannial Conference on Biomechanics and Symposium on Human Locomotion, 1988.
19. G.A. Wood and L.S. Jennings, "On the Use of Spline Functions for Data Smoothing," J. of Biomechanics. Vol. 12 (6?, pp. 477-479, 1975.