- Email: [email protected]
Mechanical loading and skeletal remodeling during growth
226
Abstracts
independent observations to assess model performance. The model will be used to recommend and loads, and floor and shoe materials to prevent slip.
STRENGTH
CURVES
SINGLE
FOR IMULTIPLE-JOINT
J. G. ANDREWS (The University
DEGREE
cart handle heights
OF FREEDOM
EXERCISES
of Iowa, Iowa City. IA 52242. U.S.A.)
The purposes of this study were (1) to show that the concept of a strength curve for a single joint. one degree of freedom (DOF) exercise can be generalized to include multiple-joint, one DOF exercises, (2) to define the strength curve for such exercises, and (3) to illustrate how this definition applies with a simpleexample. Using an arbitrarily chosen, characteristic angular variable 07 as the one DOF exercise coordinate, the strength curve is defined as the plot of the system joint torque T vs the exercise coordinate 07. Here, T is the algebraic sum of the X L 2 resultant joint torque components T (i = I,. . , N) that (a) act on the distal body segment at each of the subject’s N active joints (i.e. joints that change their configurations during the exercise), and (b)correspond to the N angular variables ei that define the configurations of these N active body joints.
A SYSTEM
FOR ANALYSIS
OF POSTURES
AND FORCES
IN MANUAL
WORK
T. J. ARMSTRONG, M. ROBERTSON, B. BUCHHOLZ, B. S. JOSEPH, C. WOOLLEY and B. SILVERSTEIN (Center for Ergonomics, 1205 Beal, The University of Michigan, Ann Arbor, MI 48109, U.S.A.) Cumulative Trauma Disorders, such as carpal tunnel syndrome and tendinitis. are associated with repetitive work, certain postures and forceful exertions. This paper describes a system designed for analysis of work postures and forces. A video tape recorder is used to record work activities. The tapes are played back in slow motion so that the postural attributes can be determined for each joint. Forces are estimated from surface electromyography. Medial forearm EMG’s are calibrated for each test of each subject by having the subject make graded exertions in all anticipated postures. The EMG signals are integrated and superimposed on the video tape so that they can be synchronized with postures. To facilitate analysis a digital time signal is also superimposed on the video tape.
BASEBALL
PLAYERS
CANNOT
A. TERRY BAHILL (Systems and Industrial
KEEP THEIR
Engineering,
University
EYES ON THE BALL of Arizona.
Tucson, AZ 85721, U.S.A.)
We have measured the head and eye movements ofathletes trying to hit a ball moving along a computer controlled trajectory. We conclude that baseball and tennis players do not ‘keep their eye on the ball’; it is physiologically impossible. Usually they can keep up with the ball only for the first 907” of its flight. Sometimes they track the ball over the first portion of its trajectory, guess its future position, make an anticipatory saccadic eye movement to this predicted location, and then resume tracking. The size and timing of the anticipatory saccade varies from person to person. We have used this data to test a closed-loop control-system model for the head and eye movement control systems.
MECHANICAL
LOADING
AND SKELETAL
REMODELING
A. A. BIEWENER, S. SWARTZ and M. LEE (University
of Chicago,
DURING Chicago,
GROWTH IL, U.S.A.)
Using the chick tibia as our model, these experiments are designed to factor out the importance of differences in strain history on this bone’s remodeling response during growth from 4 to 17 weeks of age. The animals were trained and run on a treadmill at 30 9, of their top speed (constant stride frequency over this age range) for 15 min at five days week-‘. In cico strain recordings were made using both single element and rosette gauges at six sites on the tibia (right tibia: proximal/medial, P/M, cranial midshaft, Cr/M, caudal midshaft, Cd/M, media midshaft, M/M; left tibia: cranial distal, Cr/D, and caudal distal, Cd/D). Recordings were made at 5, 11 and 17 weeks age. Periodic fluorescent bone labels were administered to the animals to correlate loading measurements and age with changes in bone structure. Strain levels were found to vary significantly with gauge location. For instance at 5 weeks, running at 0.96 m s-*, the following strain levels (in microstrain) were recorded: - 710, P/M: + 330, Cr/M; - 1550, Cd/M; -930, M/M; - 1025, Cr/D; + 130, Cd/D. The distribution of loading was similar over a range of speed, but as the animals changed from a walk to a run strain magnitude rose sharply (e.g. 54% at Cd/M). These strains shoHc the chick tibia to be loaded primarily in bending (but in opposite directions at the midshaft and distal
227
Absrracrs
levels). The orientation of maximum principal strains at the midshaft (37. lateral. Cd, M; 40 medial. Cr, MI. however. indicate signiticant torsional loading as well. Strain levels recorded at each age were generally consistent with respect to bone site. The variance in strain magnitude normalized to the levels recorded at vveek 5 ranged from I8 f 5”” at Cd/M to 63 + 21 0, at Cd;D (n = 9). This suggests that the bone cell population regulates its remodeling activity so as to maintain similar patterns of strain during growth. a period when the bone’s mass and length increase ten and two-fold, respectively. (Supported by The Whitaker Foundation & Biomedical Research Support Fund, University of Chicago.)
THE RELATIONSHIP
BETWEEN
ARM MOTIOS
AT ENTRY
AND
W. BODA and L. ABRAHAM (Department of Physical and Health Education, Austin. Austin. TX 78712. U.S.A.)
RIP ENTRlES The University
IN DIVING of Texas at
This study examined the suggestion that arm motion at impact is important in the production of rip entries in competitive diving. Two elite competitive divers were filmed (50 fps) performing both forward and backward spinning dives from the IO m platform. Seventeen dives (nine forward) were analyzed, including eight rip entries (four forward). Six points on the body were digitized to represent the body position. Arm angular velocity and shoulder joint angle were calculated and compared between types of entries. The shoulder joint angles for rip entries ranged from 157 tc 179’; angles for non-rip entries were outside this range. Arm angular velocity at impact was less than 100. s-l for seven of the rip entries but only two of the non-rip entries. These data support the suggestion that arm motion at entry is related to the production of a rip in typical competitive platform dives,
SOME
CHARACTERISTICS OF LAMINAR FLOW VELOCITY SPECTRA 20 MHz PULSED ULTRASOUND DOPPLER
DETECTED
BY A
THOMAS D. BROW? RONALD H. GABEL, DOUGLAS R. PEDERSEN, LAWRENCE D. BELL and WILLIAMSF. BLAIH (Departments oforthopaedic Surgery and Biomedical Engineering. University of Iowa, Iowa City, IA 51242. U.S.A.) To improve
on the accuracy attainable on phasic output from a conventional zero-crossing-detector circuit, a ‘0 MHz pulsed ultrasound Doppler velocimeter has been modified to allow spectral analysis of the frequency shift signal. Spectral analysis is performed using a MINC computer implementing a fast Fourier transform software routine. A benchtop circuit producing fully-developed Poiseville Rows in small-diameter cellulose tubes provided a precise calibration standard for the PUDVM. Of several major spectral indices, the frequency of dominant energy content was found to correlate most closely with true local velocity. The test apparatus was used to evaluate velocity spectrum alterations associated with sample volume geometry changes, with changes in the mechanical mounting configuration of the PUDVM crystal, and with changes in the type and concentration ot reflective particles in the working fluid.
INSTANTANEOUS
IN VITRO
CONTACT STRESS CONDYLES
DlSTRtBUTIONS
THOhtAS D. BROWN and DANIEL T. SHAW (Department of Orthopaedic Pittsburgh, PA 15261. U.S.A.)
Surgery,
ON THE FEMORAL University
of Pittsburgh,
Arrays ofminiature piezoresistivecontact stress transducers were used to sample instantaneous local pressuresat 24 sites on cyclically-loaded femoral condyles, from eleven normal cadavers specimens. Upon calibration and digitizing. the local pressure signals were computationally transformed into continuous spatial contour maps of contact stress distribution. Specimens were tested from 0 to 30’ flexion, and pre- and post-meniscectomy. Numerical integration of the assembled pressure contours showed good agreement with the resultant applied load. The results for the natural kneeaveraged about IS cm2 ofcontact area.and about 8 MPa peak local pressure at maximum physiological load. values which agree well with previous static recordings using surface film techniques. But these transient loading experiments also show that intra-articular pressure patterns are much less sensitive to meniscus removal than appears to be the case under static loading.
Abstracts
independent observations to assess model performance. The model will be used to recommend and loads, and floor and shoe materials to prevent slip.
STRENGTH
CURVES
SINGLE
FOR IMULTIPLE-JOINT
J. G. ANDREWS (The University
DEGREE
cart handle heights
OF FREEDOM
EXERCISES
of Iowa, Iowa City. IA 52242. U.S.A.)
The purposes of this study were (1) to show that the concept of a strength curve for a single joint. one degree of freedom (DOF) exercise can be generalized to include multiple-joint, one DOF exercises, (2) to define the strength curve for such exercises, and (3) to illustrate how this definition applies with a simpleexample. Using an arbitrarily chosen, characteristic angular variable 07 as the one DOF exercise coordinate, the strength curve is defined as the plot of the system joint torque T vs the exercise coordinate 07. Here, T is the algebraic sum of the X L 2 resultant joint torque components T (i = I,. . , N) that (a) act on the distal body segment at each of the subject’s N active joints (i.e. joints that change their configurations during the exercise), and (b)correspond to the N angular variables ei that define the configurations of these N active body joints.
A SYSTEM
FOR ANALYSIS
OF POSTURES
AND FORCES
IN MANUAL
WORK
T. J. ARMSTRONG, M. ROBERTSON, B. BUCHHOLZ, B. S. JOSEPH, C. WOOLLEY and B. SILVERSTEIN (Center for Ergonomics, 1205 Beal, The University of Michigan, Ann Arbor, MI 48109, U.S.A.) Cumulative Trauma Disorders, such as carpal tunnel syndrome and tendinitis. are associated with repetitive work, certain postures and forceful exertions. This paper describes a system designed for analysis of work postures and forces. A video tape recorder is used to record work activities. The tapes are played back in slow motion so that the postural attributes can be determined for each joint. Forces are estimated from surface electromyography. Medial forearm EMG’s are calibrated for each test of each subject by having the subject make graded exertions in all anticipated postures. The EMG signals are integrated and superimposed on the video tape so that they can be synchronized with postures. To facilitate analysis a digital time signal is also superimposed on the video tape.
BASEBALL
PLAYERS
CANNOT
A. TERRY BAHILL (Systems and Industrial
KEEP THEIR
Engineering,
University
EYES ON THE BALL of Arizona.
Tucson, AZ 85721, U.S.A.)
We have measured the head and eye movements ofathletes trying to hit a ball moving along a computer controlled trajectory. We conclude that baseball and tennis players do not ‘keep their eye on the ball’; it is physiologically impossible. Usually they can keep up with the ball only for the first 907” of its flight. Sometimes they track the ball over the first portion of its trajectory, guess its future position, make an anticipatory saccadic eye movement to this predicted location, and then resume tracking. The size and timing of the anticipatory saccade varies from person to person. We have used this data to test a closed-loop control-system model for the head and eye movement control systems.
MECHANICAL
LOADING
AND SKELETAL
REMODELING
A. A. BIEWENER, S. SWARTZ and M. LEE (University
of Chicago,
DURING Chicago,
GROWTH IL, U.S.A.)
Using the chick tibia as our model, these experiments are designed to factor out the importance of differences in strain history on this bone’s remodeling response during growth from 4 to 17 weeks of age. The animals were trained and run on a treadmill at 30 9, of their top speed (constant stride frequency over this age range) for 15 min at five days week-‘. In cico strain recordings were made using both single element and rosette gauges at six sites on the tibia (right tibia: proximal/medial, P/M, cranial midshaft, Cr/M, caudal midshaft, Cd/M, media midshaft, M/M; left tibia: cranial distal, Cr/D, and caudal distal, Cd/D). Recordings were made at 5, 11 and 17 weeks age. Periodic fluorescent bone labels were administered to the animals to correlate loading measurements and age with changes in bone structure. Strain levels were found to vary significantly with gauge location. For instance at 5 weeks, running at 0.96 m s-*, the following strain levels (in microstrain) were recorded: - 710, P/M: + 330, Cr/M; - 1550, Cd/M; -930, M/M; - 1025, Cr/D; + 130, Cd/D. The distribution of loading was similar over a range of speed, but as the animals changed from a walk to a run strain magnitude rose sharply (e.g. 54% at Cd/M). These strains shoHc the chick tibia to be loaded primarily in bending (but in opposite directions at the midshaft and distal
227
Absrracrs
levels). The orientation of maximum principal strains at the midshaft (37. lateral. Cd, M; 40 medial. Cr, MI. however. indicate signiticant torsional loading as well. Strain levels recorded at each age were generally consistent with respect to bone site. The variance in strain magnitude normalized to the levels recorded at vveek 5 ranged from I8 f 5”” at Cd/M to 63 + 21 0, at Cd;D (n = 9). This suggests that the bone cell population regulates its remodeling activity so as to maintain similar patterns of strain during growth. a period when the bone’s mass and length increase ten and two-fold, respectively. (Supported by The Whitaker Foundation & Biomedical Research Support Fund, University of Chicago.)
THE RELATIONSHIP
BETWEEN
ARM MOTIOS
AT ENTRY
AND
W. BODA and L. ABRAHAM (Department of Physical and Health Education, Austin. Austin. TX 78712. U.S.A.)
RIP ENTRlES The University
IN DIVING of Texas at
This study examined the suggestion that arm motion at impact is important in the production of rip entries in competitive diving. Two elite competitive divers were filmed (50 fps) performing both forward and backward spinning dives from the IO m platform. Seventeen dives (nine forward) were analyzed, including eight rip entries (four forward). Six points on the body were digitized to represent the body position. Arm angular velocity and shoulder joint angle were calculated and compared between types of entries. The shoulder joint angles for rip entries ranged from 157 tc 179’; angles for non-rip entries were outside this range. Arm angular velocity at impact was less than 100. s-l for seven of the rip entries but only two of the non-rip entries. These data support the suggestion that arm motion at entry is related to the production of a rip in typical competitive platform dives,
SOME
CHARACTERISTICS OF LAMINAR FLOW VELOCITY SPECTRA 20 MHz PULSED ULTRASOUND DOPPLER
DETECTED
BY A
THOMAS D. BROW? RONALD H. GABEL, DOUGLAS R. PEDERSEN, LAWRENCE D. BELL and WILLIAMSF. BLAIH (Departments oforthopaedic Surgery and Biomedical Engineering. University of Iowa, Iowa City, IA 51242. U.S.A.) To improve
on the accuracy attainable on phasic output from a conventional zero-crossing-detector circuit, a ‘0 MHz pulsed ultrasound Doppler velocimeter has been modified to allow spectral analysis of the frequency shift signal. Spectral analysis is performed using a MINC computer implementing a fast Fourier transform software routine. A benchtop circuit producing fully-developed Poiseville Rows in small-diameter cellulose tubes provided a precise calibration standard for the PUDVM. Of several major spectral indices, the frequency of dominant energy content was found to correlate most closely with true local velocity. The test apparatus was used to evaluate velocity spectrum alterations associated with sample volume geometry changes, with changes in the mechanical mounting configuration of the PUDVM crystal, and with changes in the type and concentration ot reflective particles in the working fluid.
INSTANTANEOUS
IN VITRO
CONTACT STRESS CONDYLES
DlSTRtBUTIONS
THOhtAS D. BROWN and DANIEL T. SHAW (Department of Orthopaedic Pittsburgh, PA 15261. U.S.A.)
Surgery,
ON THE FEMORAL University
of Pittsburgh,
Arrays ofminiature piezoresistivecontact stress transducers were used to sample instantaneous local pressuresat 24 sites on cyclically-loaded femoral condyles, from eleven normal cadavers specimens. Upon calibration and digitizing. the local pressure signals were computationally transformed into continuous spatial contour maps of contact stress distribution. Specimens were tested from 0 to 30’ flexion, and pre- and post-meniscectomy. Numerical integration of the assembled pressure contours showed good agreement with the resultant applied load. The results for the natural kneeaveraged about IS cm2 ofcontact area.and about 8 MPa peak local pressure at maximum physiological load. values which agree well with previous static recordings using surface film techniques. But these transient loading experiments also show that intra-articular pressure patterns are much less sensitive to meniscus removal than appears to be the case under static loading.