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Biomedical subjects

M L Hull

Publications and source records attributed to M L Hull.

At least 109 records · Page 6Linked to original sources
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↗
PubMed1988

Carrier detection of Duchenne dystrophy by frequency analysis of the electromyogram.

A new method for Duchenne muscular dystrophy (DMD) carrier detection based on frequency analysis of electromyograms (EMG) taken from relative force contractions shows great promise in classifying possible carriers. Nine carriers were examined and compared to nineteen normals in an attempt to define a discriminant function that would be effective in classification of possible carriers of the gene responsible for DMD. EMG data were taken at 20%, 40%, and 60% of maximum effort from the biceps brachii using a specially designed dynamometer apparatus. The apparatus was able to isolate the biceps muscle group and allowed for adjustment to accommodate different body sizes. Three signal processing methods were used to find variables in the frequency domain that would provide the best discriminant function based on the jackknife classification method. Of these methods, the most promising appears to be the high-to-low ratio method at 20% maximum contraction. When combining the high and low values found with this test in conjunction with the peak cepstrum values also found at 20% maximum contraction, discrimination was found to be 83.8% accurate. Because this classification is not based solely on definite carriers, and appears to be independent of serum creatine phosphokinase (CPK) values, it would seem that classification based on a definite carrier population could be performed with greater accuracy, especially with the addition of CPK values.

Electromyography↗
PubMed1986

On the relation between joint moments and pedalling rates at constant power in bicycling.

Joint moments are of interest because they bear some relation to muscular effort and hence rider performance. The general objective of this study is to explore the relation between joint moments and pedalling rate (i.e. cadence). Joint moments are computed by modelling the leg-bicycle system as a five-bar linkage constrained to plane motion. Using dynamometer pedal force data and potentiometer crank and pedal position data, system equations are solved on a computer to produce moments at the ankle, knee and hip joints. Cadence and pedal forces are varied inversely to maintain constant power. Results indicate that average joint moments vary considerably with changes in cadence. Both hip and knee joints show an average moment which is minimum near 105 rotations min-1 for cruising cycling. It appears that an optimum rotations min-1 can be determined from a mechanical approach for any given power level and bicycle-rider geometry.

Bicycling↗
PubMed1986

Prediction of pedal forces in bicycling using optimization methods.

The bicycle-rider system is modeled as a planar five-bar linkage with pedal forces and pedal dynamics as input. The pedal force profile input is varied, maintaining constant average bicycle power, in order to obtain the optimal pedal force profile that minimizes two cost functions. One cost function is based on joint moments and the other is based on muscle stresses. Predicted (optimal) pedal profiles as well as joint moment time histories are compared to representative real data to examine cost function appropriateness. Both cost functions offer reasonable predictions of pedal forces. The muscle stress cost function, however, better predicts joint moments. Predicted muscle activity also correlates well with myoelectric data. The factors that lead to effective (i.e. low cost) pedalling are examined. Pedalling effectiveness is found to be a complex function of pedal force vector orientation and muscle mechanics.

Bicycling↗
PubMed1986

Analysis of EMG measurements during bicycle pedalling.

Activity of eight leg muscles has been monitored for six test subjects while pedalling a bicycle on rollers in the laboratory. Each electromyogram (EMG) data channel was digitized at a sampling rate of 2 kHz by a minicomputer. Data analysis entailed generating plots of both EMG activity regions and integrated EMG (IEMG). For each test subject, data were recorded for five cases of pedalling conditions. The different pedalling conditions were defined to explore a variety of research hypotheses. This exploration has led to the following conclusions: Muscular activity levels of the quadriceps are influenced by the type of shoes worn and activity levels increase with soft sole shoes as opposed to cycling shoes with cleats and toeclips. EMG activity patterns are not strongly related to pedalling conditions (i.e. load, seat height and shoe type). The level of muscle activity, however, is significantly affected by pedalling conditions. Muscular activity bears a complex relationship with seat height and quadriceps activity level decreases with greater seat height. Agonist (i.e. hamstrings) and antagonist (i.e. quadriceps) muscles of the hip/knee are active simultaneously during leg extension. Regions of peak activity levels, however, do not overlap. The lack of significant cocontraction of agonist/antagonist muscles enables muscle forces during pedalling action to be computed by solving a series of equilibrium problems over different regions of the crank cycle. Regions are defined and a solution procedure is outlined.

Bicycling↗
PubMed1985

A method for biomechanical analysis of bicycle pedalling.

This paper reports a new method, which enables a detailed biomechanical analysis of the lower limb during bicycling. The method consists of simultaneously measuring both the normal and tangential pedal forces, the EMGs of eight leg muscles, and the crank arm and pedal angles. Data were recorded for three male subjects of similar anthropometric characteristics. Subjects rode under different pedalling conditions to explore how both pedal forces and pedalling rates affect the biomechanics of the pedalling process. By modelling the leg-bicycle as a five bar linkage and driving the linkage with the measured force and kinematic data, the joint moment histories due to pedal forces only (i.e. no motion) and motion only (i.e. no pedal forces) were generated. Total moments were produced by superimposing the two moment histories. The separate moment histories, together with the pedal forces and EMG results, enable a detailed biomechanical analysis of bicycle pedalling. Inasmuch as the results are similar for all three subjects, the analysis for one subject is discussed fully. One unique insight gained via this new method is the functional role that individual leg muscles play in the pedalling process.

Adult↗
PubMed1985

A microcomputer controlled snow ski binding system--I. Instrumentation and field evaluation.

This paper presents the design and field evaluation of the first microcomputer controlled ski binding system. This system incorporates an Intel 8086 microcomputer controller and an integral binding/dynamometer. This instrumentation system not only undertakes real time control, but also it records dynamometer data via a miniature digital cassette tape recorder. The integral binding/dynamometer offers the same operational and mounting convenience of commercially available mechanical bindings. The binding may be released either manually or electrically via the controller. Comprised of four octagonal half strain rings, the strain gage dynamometer measures the three moment load components at the boot. To enable the user to conveniently operate the computer, extensive operating software was developed. The operating software is discussed in relation to both the acquisition and storage of data from the dynamometer and the control of the electro-mechanical snow ski binding. The binding system has been used successfully to both record boot moment components and control ski binding release during actual skiing maneuvers. Moment histories typical of three common recreational skiing maneuvers are presented.

Athletic Injuries↗
PubMed1985

A microcomputer controlled snow ski binding system--II. Release decision theories.

A hierarchy of release decision theories for both tibia fracture and knee ligamentous injury are defined and simulated on a computer. Moment loading data, recorded during actual skiing by the microcomputer-based ski binding system described in Part I, are processed by the various release decision theories. At the bottom of the hierarchy is the simplest theory which treats boot loading as quasi-static and compares moment components to threshold levels. Another stage of the hierarchy defines an analytic expression for a combined loading failure locus. Note that this is the first formulation of a combined loading release decision theory. Yet another stage of the hierarchy computes bone moments via dynamic system leg models. The various release decision theories are evaluated by comparing processed results to both pain and bone failure limits. For the data generated by the field tests conducted to date, the simplest release decision theory satisfied the retention requirement for pain limits in the presence of muscle activity for both torsion and forward bending. For pain limits in the absence of muscle activity the retention requirement was not satisfied however. Another result is that leg dynamics are significant. A final result is that combined loading considerations lead to a more conservative theory.

Athletic Injuries↗
PubMed1984

Dynamic simulation of the leg in torsion.

This paper analytically investigates the dynamic response of the leg in torsion with application to snow ski injuries. A biomechanical model of the leg system is developed and injury mechanisms to the ankle, knee and tibia are presented. The objective is to determine how torsional leg system dynamics influence injuries to the ankle, knee and tibia under impulse loading. The results of the study indicate that ankle, knee and tibial injuries exhibit identical dynamic behavior which is characteristic of a single degree-of-freedom system. In addition, analysis of the injury response to flexible vs rigid thigh tissue shows that the above results are not especially sensitive to flesh effects. Finally, a release decision algorithm for implementation in actively controlled ski bindings is presented.

Ankle Injuries↗
PubMed1981

Design of an actively controlled snow ski release binding.

A new electronic ski binding has been designed which may better protect skiers from lower extremity injuries. A four-step procedure for developing binding release criteria aimed at preventing specific injuries is outlined. Using simplified biomechanical models, the release criteria for tibia fracture in both torsion and flexion are derived. A binding design which embodies the derived release criteria is described. The binding consists of three subsystems: 1) a dynamometer, 2) an analog computer controller, and 3) an electromechanical release mechanism. The strain gage dynamometer directly measures torsion and bending moments between the boot and ski. An analog computer controlled processes dynamometer signals. Dual release mode capability is achieved by parallel solution of differential equations which model the leg in both medial-lateral rotation and flexion. When the model solution reaches a critical value, the controller actuates the release mechanism. The release mechanism incorporates a unique closed circuit hydraulic system which rigidly locks the boot to the ski until release. Laboratory tests on a prototype confirm that the computer-controlled binding prevents inadvertent release under noninjurious high-magnitude, short-duration loads but releases before quasi-static loads reach injurious levels.

Athletic Injuries↗