Biomedical subjects

M L Hull

Publications and source records attributed to M L Hull.

At least 19 recordsLinked to original sources

PubMed1992

Strain in the anteromedial bundle of the anterior cruciate ligament under combination loading.

Strain within the anteromedial bundle (AMB) of the anterior cruciate ligament (ACL) was measured in 13 human knee specimens in order to determine the combination of external loads most likely to cause injury. Using a load application system that allowed 5 df with the flexion angle being fixed, pure loads of anterior/posterior force, medial/lateral force, varus/valgus torque, and internal/external axial torque were applied at three flexion angles: 0 degrees, 15 degrees, 30 degrees. Combined loads were applied in pairs at two flexion angles: 0 degrees and 30 degrees. Liquid mercury strain gauges were used to measure strain in the ACL. Anterior tibial force was the primary determinant of strain in the anteromedial bundle. This strain was significantly larger at 30 degrees flexion than at 0 degrees. The strain sensitivity of the AMB to medial force was approximately one-half that to pure anterior force. The effect of anterior and medial forces was additive when applied in combination. Neither pure axial torque nor pure varus/valgus torque was observed to strain significantly the AMB at any of the flexion angles investigated. However, valgus torque in combination with anterior force resulted in a significantly larger strain than pure anterior force. Internal axial torque in combination with anterior force also resulted in a larger strain than pure anterior force.

Aged↗

PubMed1992

An activation-recruitment scheme for use in muscle modeling.

The derivation of a new activation-recruitment scheme and the results of a study designed to test its validity are presented. The activation scheme utilizes input data of processed surface EMG signals, muscle composition, muscle architecture, and experimentally determined activation coefficients. In the derivation, the relationship between muscle activation and muscle fiber recruitment was considered. In the experimental study, triceps muscle force was determined for isometric elbow extension tasks varying in intensity from 10 to 100% of a maximum voluntary contraction (MVC) using both a muscle model that incorporates the activation scheme, and inverse dynamics techniques. The forces calculated using the two methods were compared statistically. The modeled triceps force was not significantly different from the experimental results determined using inverse dynamics techniques for average activation levels greater than 25% of MVC, but was significantly different for activation levels less than 25% of MVC. These results lend support for use of the activation-recruitment scheme for moderate to large activation levels, and suggest that factors in addition to fiber recruitment play a role in force regulation at lower activation levels.

Acceleration↗

PubMed1992

The effect of lower-limb anatomy on knee loads during seated cycling.

Overuse knee joint injuries are the primary injuries to cyclists. Overuse injuries have been intuitively linked to the anatomic structure of the foot because external loads are applied to the foot in cycling. Thus, the structure and function of the foot should dictate in part how the loads are transmitted to the knee joint. Therefore, it was hypothesized that patterns in knee loads are related to the anatomic structure of the foot. To test this hypothesis, peak knee loads (dependent variables) were related to anatomical variables (independent variables) through statistical analyses. This required first the detailed evaluation (i.e. measurement) of the anatomical structure of the foot and leg for 23 subjects. Next, three-dimensional knee joint loads were determined for a standardized riding condition. The results of the statistical analyses indicated that a group of cyclists with the most extreme inversion of the forefoot relative to the transverse plane developed significantly greater average posterior knee force and extensive knee moment. In addition, a number of anatomical variables significantly accounted for the variability in peak values of the posterior force, the extensive moment, the varus/valgus moment and the external axial moment. Based on these results, the hypothesis is accepted.

Adult↗

PubMed1992

Three-dimensional knee joint loading during seated cycling.

The hypothesis which motivated the work reported in this article was that neglecting pure moments developed between the foot and pedal during cycling leads to a substantial error in computing axial and varus/valgus moments at the knee. To test this hypothesis, a mathematical procedure was developed for computing the three-dimensional knee loads using three-dimensional pedal forces and moments. In addition to data from a six-load-component pedal dynamometer, the model used pedal position and orientation and knee position in the frontal plane to determine the knee joint loads. Experimental data were collected from the right leg of 11 male subjects during steady-state cycling at 90 rpm and 225 W. The mean peak varus knee moment calculated was 15.3 N m and the mean peak valgus knee moment was 11.2 N m. Neglecting the pedal moment about the anterior/posterior axis resulted in an average absolute error of 2.6 N m and a maximum absolute error of 4.0 N m in the varus/valgus knee moment. The mean peak internal and external axial knee moments were 2.8 N m and 2.3 N m, respectively. The average and maximum absolute errors in the axial knee moment for not including the moment about an axis normal to the pedal were found to be 2.6 N m and 5.0 N m, respectively. The results strongly support the use of three-dimensional pedal loads in the computation of knee joint moments out of the sagittal plane.

Acceleration↗

PubMed1992

Physiological response to cycling with both circular and noncircular chainrings.

The purpose of this study was to compare physiological variables of endurance-trained cyclists riding with four different chainring designs: round, Shimano Biopace, and two engineered ellipse designs. The ellipse designated Eng10 had the crank arm oriented 10 degrees forward of the major (i.e. longer) axis. Eighty degrees further forward, along the minor axis, was the crank arm orientation for the second ellipse, Eng90. With the major to minor axis ratio of 22.9 cm/16.8 cm (1.36), both ellipses imposed a crank angular velocity variation of 27% relative to the highest velocity assuming constant chain velocity. Best described as a skewed ellipse (i.e., major and minor axes not perpendicular), the Biopace had a major to minor axis ratio of 1.09 thus giving a crank angular velocity variation of 8%. Eleven male cyclists rode at a high (80% of maximum VO2) and a low (60% of maximum VO2) workrate using each chainring. The study was conducted over four consecutive days with the presentation order of the chainrings randomized. Open circuit spirometry was used to collect continuous respiratory data. Heart rate, blood lactate, and cadence values also were measured. None of the physiological variables including rates of oxygen consumption showed significant differences among the chainrings. Thus, the gross efficiency of cycling was not improved by any of the noncircular chainrings. For cycling events where efficiency is a determinant of performance, the noncircular chainrings do not offer any advantage over round chainrings.

Adult↗

PubMed1991

A computer simulation of muscle-tendon mechanics.

A computer simulation program was developed to study and illustrate the complex interactions that exist between muscle structure, neural activation, and mechanical characteristics. The software incorporates equations inherent in a comprehensive muscle-tendon model. The software provides a multi-menu interface allowing the user to easily alter quantities related to muscle architecture, kinematics, and activation level. Five different simulations may be performed and graphically displayed including: force-length, force-velocity, force-activation, force-time, and muscle vs tendon length. Up to three different muscle design/contraction condition combinations can be displayed simultaneously for each simulation. Sample simulation results illustrating the mechanical behavior of muscles with different structures are presented.

Biomechanical Phenomena↗

PubMed1991

Apparatus to obtain rotational flexibility of the human knee under moment loads in vivo.

The contributions of this paper are twofold. One is the design and performance evaluation of new equipment to determine the rotational flexibility of the human knee in vivo. Since determining knee flexibility requires the application of external loads and the measurement of knee rotations, the new equipment consists of a load application stand and a triaxial goniometer. The triaxial goniometer noninvasively mounts to the leg and directly measures the relative three degrees-of-freedom rotations of the knee sequentially and independently. The goniometer incorporates several unique design features which enhance measurement accuracy. The load stand applies pure varus/valgus and external/internal axial moments either individually or in combination through the use of motors controlled by the test subject. Unique to this design are features which enable the application of moments to the knee which minimise shear forces. Other unique design features permit the stand to control hip and knee flexion angles, muscle contraction, and axial loading. To assess the accuracy with which rotations are measured during experiments, three tests were conducted with the equipment. One test evaluated the inherent accuracy of the goniometer, a second test assessed the potential for goniometer slippage during loading, and a third explored the effect of goniometer mounting on the repeatability of results. A special verification apparatus facilitated evaluation of goniometer inherent accuracy. A second contribution of the paper is an investigation of the effect of foot constraints (i.e. boundary conditions) on flexibility results. To make this investigation, three subjects were tested with the knee at 15 degrees of flexion. Results revealed large differences in flexibility between constraining the foot in both external/internal and varus/valgus rotations and permitting the foot to rotate freely in the direction not being loaded. Further, constraint moments as high as 23 Nm were also recorded. These results emphasise that in order to obtain accurate flexibility results for isolated loads, the foot must be unconstrained by the loading apparatus.

Biomechanical Phenomena↗

PubMed1991

An angular velocity profile in cycling derived from mechanical energy analysis.

The contributions of this article are twofold. One is procedure for determining the angular velocity profile in seated cycling that maintains the total mechanical energy of both legs constant. A five-bar linkage model (thigh, shank, foot, crank and frame) of seated (fixed hip) cycling served for the derivation of the equations to compute potential and kinetic energies of the leg segments over a complete crank cycle. With experimentally collected pedal angle data as input, these equations were used to compute the total combined mechanical energy (sum of potential and kinetic energies of the segments of both legs) for constant angular velocity pedalling at 90 rpm. Total energy varied indicating the presence of internal work. Motivated by a desire to test the hypothesis that reducing internal work in cycling will reduce energy expenditure, a procedure was developed for determining the angular velocity profile that eliminated any change in total energy. Using data recorded from five subjects, this procedure was used to determine a reference profile for an average equivalent cadence of 90 rpm. The phase of this profile is such that highest and lowest angular velocities occur when the cranks are near vertical and horizontal respectively. The second contribution is the testing of the hypothesis that the reference angular velocity profile serves to effectively reduce internal work for the subjects whose data were used to develop this profile over the range of pedalling rates (80-100 rpm) naturally preferred. In this range, the internal work was decreased a minimum of 48% relative to the internal work associated with constant angular velocity pedalling. The acceptance of this hypothesis has relevance to the protocol for future experiments which explore the effect of reduced internal work on energy expenditure in cycling.

Anthropometry↗

PubMed1991

Rotational flexibility of the human knee due to varus/valgus and axial moments in vivo.

Knee ligamentous injuries persist in the sport of Alpine skiing. To better understand the load mechanisms which lead to injury, pure varus/valgus and pure axial moments were applied both singly and in combination to the right knees of six human test subjects. The corresponding relative knee rotations in three degrees of freedom were measured. Knee flexion angles for each test subject were 15 and 60 degrees for the individual moments and 60 degrees for the combination moments. For both knee flexion angles the hip flexion angle was 0 degrees. Leg muscles were quiescent and axial force was minimal during all tests. Tables of data include sample statistics for each of four flexibility parameters in each loading direction. Data were analyzed statistically to test for significant differences in flexibility parameters between the test conditions. In flexing the knee from 15 to 60 degrees, the resulting knee rotations under single moments depended upon flexion angle with varus, valgus, and internal rotations increasing significantly. Also, rotations were different depending on load direction; varus rotation was significantly different and greater than valgus rotation at both flexion angles. Also external rotation was significantly different and greater than internal at 15 degrees flexion, but not at 60 degrees flexion. Coupled rotations under single moments were also observed. Applying pure varus/valgus moments resulted in coupled external/internal rotations which were inconsistent and hence not significant. Applying pure axial moments resulted in consistent and hence significant varus/valgus rotations; an external axial moment induced varus rotation and an internal axial moment induced valgus rotation. For combination moments, varus/valgus rotations decreased significantly from those rotations at similar load levels in the single moment studies. Also, a varus moment significantly increased external rotation and a valgus moment significantly decreased internal rotation. These differences indicate significant interaction between corresponding load combinations. These results suggest that load interaction is a potentially important phenomenon in knee injury mechanics.

Adult↗

PubMed1990

Goniometric measurement of hip motion in cycling while standing.

The purpose of this study was to develop an instrument for quantifying the motion of the hip relative to the bicycle while cycling in the standing position. Because of the need to measure hip motion on the road as well as in the laboratory, a goniometer which locates the hip using spherical coordinates was designed. The goniometer is presented first, followed by the development of the equations that enable the distance from the joint center to the pedal spindle to be determined. The orientation of this line segment is specified by calculating two angles referenced to the frame. Also outlined are the procedures used to both calibrate the goniometer and perform an accuracy check. The results of this check indicate that the attachment point of the goniometer to the rider can be located to within 2.5 mm of the true position. The goniometer was used to record the hip movement patterns of six subjects who cycled in the standing position on a treadmill. Representative results from one test subject who cycled at 6% grade and 25 km h-1 are presented. Results indicate that the bicycle is leaned from side to side with the frequency of leaning equal to the frequency of pedalling. Extreme lean angles are +/- 6 degrees. The distance from the hip to the pedal varies approximately sinusoidally with frequency equal to pedalling rate and amplitude somewhat less than crank arm length. The absolute elevation of the hip, however, exhibits two cycles for each crank cycle. Asymmetry in the plot of elevation over a single crank cycle indicates that the pelvis rocks from side to side and that the elevation of the pelvis midpoint changes. Extreme values of the pelvis rocking angle are +/- 12 degrees. Highest pelvis midpoint elevations, however, do not occur at the same crank angles as those angles at which the pelvis rocking is extreme. It appears that the vertical motion of the hips affects pedalling mechanics when cycling in the standing position.

Anthropometry↗

PubMed1990

A method for determining lower extremity muscle-tendon lengths during flexion/extension movements.

A study was conducted to examine the relationship between muscle-tendon lengths of 16 lower extremity muscles and the flexion angle(s) of the joint(s) they cross. Anthropometric data from six subjects were obtained. Various lower extremity joint flexion angle combinations were simulated for each subject using computer software. For each simulated lower extremity position, muscle origin and insertion locations were determined based on averaged cadaveric origin/insertion information and individual anthropometric parameters. Corresponding muscle-tendon lengths were computed and normalized to segment lengths. Regression equations were derived which allow normalized muscle-tendon lengths to be estimated from known joint flexion angles. The regression equations obtained for biarticular muscles fit the data quite well giving correlation coefficients greater than 0.92. The correlation coefficients for the equations describing normalized single joint muscle-tendon lengths range from 0.77 to 0.97. The equations were then validated by comparing predicted lengths to those reported by previous investigations. Confirming the utility of the equations, the comparisons were excellent for both uniarticular and biarticular muscles. Used in conjunction with velocity data (obtained by differentiating the length data) and electromyogram recordings, these equations enable a detailed analysis of muscle function.

Adult↗

PubMed1990

Implementation of a five degree of freedom automated system to determine knee flexibility in vitro.

This article describes an automated system designed to study the complete flexibility functions of the knee in vitro. The system allows five degrees of freedom with flexion angle being fixed, though adjustable from 0 to 45 deg. Loads corresponding to each of the five motions can be applied independently and in any combination. The effect of weight bearing on knee flexibility can also be studied by including axial force as one of the five loads. The relative motions are measured with LVDT's and RVDT's, and the loads are measured with strain gage transducers. The system is digitally controlled with a closed feedback loop, allowing for any combination of programmed loads. A control algorithm on an IBM PC/AT monitors the loads on each axis and continuously adjusts stepping motors to correctly follow programmed loads. The machine coordinate system corresponds to clinically accepted definitions of motion yet retains sequence independence for rotations. Results are presented demonstrating the repeatability of using a functional definition of axis placement to align the leg within the machine. Results are also presented demonstrating the utility of the full flexibility functions of the knee, notably in the determination of significant load interactions between anterior/posterior force and internal/external torque, and varus/valgus torque and internal/external torque.

Algorithms↗

PubMed1989

Measurement of strength and loading variables on the knee during Alpine skiing.

The study focusses on the prevention of knee injuries during snow skiing. In order to develop a technology of knee injury prevention, both the strength and loading on the knee during skiing activity must be known. This paper reports measurements of variables influencing both knee strength and loading of the joint. The strength variables measured included the degree of activity in six muscles crossing the knee, the knee flexion angle, and the axial load (i.e. weight bearing) transmitted to the knee. Transducers included surface electrodes to monitor electromyogram signals indicating the degree of muscle activity and a goniometer to measure both hip and knee flexion angles. The complete loading on the knee was derived from a dynamometer which measured the six load components at the boot-dynamometer interface. The transducer data were acquired and stored by a compact, battery powered digital data acquisition-controller system. Three male subjects of similar physical size (nominal was 1.8 m and 75 kg) and skiing ability (advanced intermediate to expert) were tested under similar conditions. Each subject skied a total of four slalom runs--one snowplow and three parallel. The total time of each test was 21 s. Example data plots from different types of runs are presented and discussed. Based on observations from the data, necessary performance features for ski bindings offering improved protection from knee ligamentous injuries are defined.

Adult↗

PubMed1989

Multivariable optimization of cycling biomechanics.

Relying on a biomechanical model of the lower limb which treats the leg-bicycle system as a five-bar linkage constrained to plane motion, a cost function derived from the joint moments developed during cycling is computed. At constant average power of 200 W, the effect of five variables on the cost function is studied. The five variables are pedalling rate, crank arm length, seat tube angle, seat height, and longitudinal foot position on the pedal. A sensitivity analysis of each of the five variables shows that pedalling rate is the most sensitive, followed by the crank arm length, seat tube angle, seat height, and longitudinal foot position on the pedal (the least sensitive). Based on Powell's method, a multivariable optimization search is made for the combination of variable values which minimize the cost function. For a rider of average anthropometry (height 1.78 m, weight 72.5 kg), a pedalling rate of 115 rev min-1, crank arm length of 0.140 m, seat tube angle of 76 degrees, seat height plus crank arm length equal to 97% of trochanteric leg length, and longitudinal foot position on the pedal equal to 54% of foot length correspond to the cost function global minimum. The effect of anthropometric parameter variations is also examined and these variations influence the results significantly. The optimal crank arm length, seat height, and longitudinal foot position on the pedal increase as the size of rider increases whereas the optimal cadence and seat tube angle decrease as the rider's size increases. The dependence of optimization results on anthropometric parameters emphasizes the importance of tailoring bicycle equipment to the anthropometry of the individual.

Anthropometry↗

PubMed1988

Bivariate optimization of pedalling rate and crank arm length in cycling.

The contribution of this paper is a bivariate optimization of cycling performance. Relying on a biomechanical model of the lower limb, a cost function derived from the joint moments developed during cycling is computed. At constant average power, both pedalling rate (i.e. rpm) and crank arm length are systematically varied to explore the relation between these variables and the cost function. A crank arm length of 170 mm and pedalling rate of 100 rpm correspond closely to the cost function minimum. In cycling situations where the rpm deviates from 100 rpm, however, crank arms of length other than 170 mm yield minimum cost function values. In addition, the sensitivity of optimization results to both increased power and anthropometric parameter variations is examined. At increased power, the cost function minimum is more strongly related to the pedalling rate, with higher pedalling rates corresponding to the minimum. Anthropometric parameter variations influence the results significantly. In general it is found that the cost function minimum for tall people occurs at longer crank arm lengths and lower pedalling rates than the length and rate for short people.

Ankle Joint↗

PubMed1988

A mechanically decoupled two force component bicycle pedal dynamometer.

A design is presented for a bicycle pedal dynamometer that measures both normal and tangential forces (i.e. driving forces). Mechanical decoupling is used to reduce the cross-sensitivity of the dynamometer to loads doing no work to propel the bicycle. This obviates the need to measure all six loads for accurate data reduction. A compact strain ring is the transducer element, and a monolithic design eliminates mechanical hysteresis between the strain ring and the dynamometer frame. The angular orientation of the dynamometer with respect to the crank arm is determined with a continuous-rotation potentiometer. Design criteria and design implementation are discussed, sample data are presented, and the performance of the dynamometer is evaluated.

Biomechanical Phenomena↗

PubMed1988

Parameter identification of the human lower limb under dynamic, transient torsional loading.

The response of the lower limb to dynamic, transient torsional loading applied at the foot has been measured for a male test subject. The dynamic loading was provided by a computer controlled pneumatic system which applied single haversine (i.e. half cycle of a sine wave) axial moment pulses of variable amplitude (0-100 Nm) and duration (50-600 ms). Potentiometers measured the absolute rotations of the three leg segments. Test variables included rotation direction, weight bearing and joint flexion. Two approaches were explored for specifying parameters (i.e. inertia, damping, stiffness) of a three degree-of-freedom dynamic system model which best duplicated the measured response. One approach involved identification of linear parameters by means of optimization while the other approach entailed estimation. Parameter estimates, which included non-linear, asymmetric stiffness functions, were derived from the literature. The optimization was undertaken so as to identify parameter dependence on test variables. Results indicate that parameter values are influenced by test variables. Results also indicate that the non-linear, estimated model better approximates the experimental data than the linear, identified model. In addition to identifying parameters of a three degree-of-freedom model, parameters were also identified for a single degree-of-freedom model where the motion variable was intended to indicate the rotation of the in vivo knee. It is concluded that the simpler model offers good accuracy in predicting both magnitude and time of occurrence of peak knee axial rotations. Model motion fails to track the measured knee rotation subsequent to the peak, however.

Ankle Joint↗

PubMed1988

A second generation microcomputer controlled binding system for alpine skiing research.

In the study of sports biomechanics, alpine skiing injuries have always demanded significant attention. In order to aid in understanding the loading phenomena associated with alpine skiing, a new research binding system has been designed which enables both the recording of boot loading data and actively controlled release of the skier's boot from the ski. The new research binding system consists of three hardware components, a dynamometer which senses all six load components at the boot/ski interface, an electromechanical device capable of releasing the boot from the ski, and a new general purpose microprocessor-based data acquisition and release control module. Constructed integrally with the dynamometer, the release mechanism is activated by electrical command from the control module. The mechanical and electrical design features of the dynamometer/release mechanism as well as important features of the hardware and software of the data acquisition and control module are briefly discussed. The system has been tested both in the laboratory and on the ski slopes. The emphasis of this paper is on the boot loading data acquired through field testing and observations on the loading environment during common recreational skiing maneuvers. Through analysis of the data, insight into both the style and safety aspects of alpine skiing is gained.

Athletic Injuries↗