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A Compact Portable Data Acquisition Module for Sports Biomechanics Research

Jeff Newmiller and Maury L. Hull

This article describes a new portable digital data acquisition module, which has been developed for the measurement and temporary storage of signals from mobile biomechanical phenomena in the field. The module’s performance capabilities include 32 available analog input channels, a 12-bit analog-to-digital converter, maximum throughput of 57,040 samples per second, and a temporary storage capacity of up to 253,000 samples. The portable power source is a rechargeable battery pack, and the appropriate sensors and sensor signal conditioning circuits are supplied by the user to meet the particular needs of the phenomena under study. The size of the signal conditioning, battery pack, and data acquisition module is such that it can be carried in a belt pack worn by a subject under study and weighs less than 3 kgf. To facilitate the use of the module, operating software complements the hardware. The software is comprehensive functionally in that routines are provided for acquiring data, for transferring acquired data serially to a general purpose microcomputer for storage on magnetic media, and for monitoring equipment setup. Further, the software is versatile in that the various parameters necessary to customize the operation to a particular application may be readily set. Finally, the menu-driven structure ensures that the software is easy to use.

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An Alpine Ski Binding with Electrically Modulated Twist Release

Kevin Eseltine and Maury L. Hull

This article describes the design of a new binding for Alpine skiing wherein the release level of the toepiece in twist is modulated based on the level of neural stimulation of one of the vastii muscles in the quadriceps group. A conventional binding toepiece that relies on the force of a compressed spring to resist the release of the boot was modified. To modulate the release level to either a high or a low state, a special solenoid activated mechanism that alters the binding spring constant was designed. The design details of this special mechanism are described and the computations necessary to ensure reliable activation with a low force solenoid are summarized. Also described is the special circuitry that was designed to actuate the solenoid. To demonstrate the workability of both the mechanism and the circuitry, a prototype binding system was constructed and tested. The results of this testing are described as well.

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Design and Evaluation of a Multi-Degree-of-Freedom Foot/Pedal Interface for Cycling

Dennis Wootten and Maury L. Hull

Described is the design of a foot/pedal interface intended as a research tool in the study of overuse knee injuries in cycling. The interface enables the systematic variation of factors that may affect loads transmitted by the knee joint. It permits two degrees of freedom of movement, inversion/eversion and abduction/adduction rotations, either separately or in combination. The movement permitted by each degree of freedom can be either free or resisted by spring assemblies. Sample data were collected to demonstrate the function of the foot/pedal interface. With no spring resistance, the interface functioned as intended by allowing free movement of the foot. Significant interaction was seen between the two degrees of freedom, with more motion and a larger absolute mean occurring when both degrees of freedom were allowed simultaneously. This emphasizes the need for a multi-degree-of-freedom interface when undertaking a comprehensive study of the factors affecting loads transmitted by the knee.

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A New Electromechanical Ski Binding with Release Sensitivity to Torsion and Bending Moments Transmitted by the Leg

Rick Neptune and Maury L. Hull

This paper describes the design of a new electromechanical ski binding whereby release in both twist and forward bending is controlled electronically and the release level in twist is modulated electronically based on the neural stimulation of muscles in the quadriceps group. To provide signals for controlling release in the two modes, the binding incorporates two dynamometers. Each dynamometer measures loads that have been shown to correlate strongly (r 2>0.90) to torsional and bending moments at the lower leg injury sites. Although the binding consists of both a toepiece and heelpiece, the toepiece does not permit release of the boot from the ski in the twist mode but rather serves as one of the dynamometers. Consequently the heelpiece was designed to provide the release function in both modes. Release is realized by a low-force solenoid that actuates a multilink trigger mechanism. To prove feasibility, a prototype was constructed and evaluated.

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Rider/Bicycle Interaction Loads during Standing Treadmill Cycling

Cal Stone and Maury L. Hull

This paper provides measurements of rider-induced loads during standing cycling. Two strain gauge dynamometers were used to measure these loads while three subjects rode bicycles on a large motorized treadmill; the cycling situation simulated hill climbing while standing. Comparing the results to those previously published for seated cycling revealed that the loading for standing cycling differed fundamentally from that for seated cycling in certain key respects. One respect was that the maximum magnitude normal pedal force reached substantially higher values, exceeding the weight of the subject, and the phase occurred later in the crank cycle. Another respect was that the direction of the handlebar forces alternated indicating that the arms pulled up and back during the power stroke of the corresponding leg and pushed down and forward during the upstroke. Inasmuch as these forces were coordinated (i.e., in phase) with the leaning of the bicycle, the arms developed positive power.

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Methods for Determining Hip Movement in Seated Cycling and Their Effect on Kinematics and Kinetics

Richard R. Neptune and Maury L. Hull

In a previous paper (Neptune & Hull, 1995), a new video-based method (ASIS) for locating the hip joint center (HJC) in seated cycling was shown to be more accurate than tracking a marker placed over the superior aspect of the greater trochanter (TRO). The main goal of the present study was to see if the conclusions presented in Neptune and Hull (1995) may be applied to other cyclists. Lower limb kinematic and pedal force data were collected from 7 cyclists at nine combinations of pedaling rate and work rate. ASIS produced significantly different hip joint movement patterns than TRO, which resulted in significantly different power and work calculations developed by the intersegmental hip joint force, at all combinations except one. A significant quadratic trend was evident as a function of pedaling rate, and a significant linear trend was evident for work rate. At naturally preferred pedaling rates (~90 rpm) and lower work rates (<225 W), the hip joint movement was minimum. Under these conditions, the fixed hip assumption is least prone to error.

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A Biomechanical Approach to Alpine Ski Binding Design

Glenn S. Wunderly and Maury L. Hull

A new approach to ski binding design is advanced. It begins with a release locus derived from injury mechanics research and knowledge of the expected loading conditions and then incorporates these into the final binding design. A mechanical ski binding designed by following the new approach is presented. This binding offers a number of performance features not found in commercially available designs. One feature is the ability to eliminate the axial force supported by the tibial shaft from affecting release in forward bending. A second feature is the binding’s ability to release according to virtually any preprogrammed locus of the combination of moments in both bending and torsion. A third feature is a release mechanism that is insensitive to the common frictional forces that affect the release consistency of conventional heel/toe bindings. In addition to these features, the binding offers a variety of operational conveniences. The presentation of the binding not only describes the design details but also evaluates the release performance (i.e., locus and consistency) based upon laboratory tests under quasistatic loading.

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The Effect of Pedal Platform Height on Cycling Biomechanics

Maury L. Hull and Hiroko K. Gonzalez

Using a five-bar linkage model of the leg/bicycle system in conjunction with experimental kinematic and pedal force data, the inverse dynamics problem is solved to yield the intersegmental moments. Among the input data that affect the problem solution is the height of the pedal platform. This variable is isolated and its effects on the total joint moments are studied as it assumes values over a ±4-cm range. Platform height variation affects the total joint moment peak values by up to 13%. Relying on a cost function derived from the hip and knee moments, it is found that the platform height that minimizes the cost function is +2 cm. The sensitivity of the cost function to the platform height variable is low; over the variable range the cost function increases 2% above the minimum. These results hold for a pedaling rate of 90 rpm. As pedaling rate is varied above and below 90 rpm, the sensitivity of the cost function increases. The platform heights that minimize the cost function are the lower and upper limits for 60 and 120 rpm, respectively. Thus the platform height variable interacts with pedaling rate, requiring a compromise in platform height adjustment. The compromise height depends on the individual’s preferred pedaling rate range.

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A New Force Plate Design Incorporating Octagonal Strain Rings

Maury L. Hull, Richard Brewer, and David Hawkins

This paper reports on the design, fabrication, and performance evaluation of a new force plate. The force plate is unique in that it can be manufactured “in house” using conventional machine tools for substantially lower cost than commercially available units. To achieve these attributes, the force plate embodies four octagonal strain ring sensing elements that are instrumented with conventional strain gauges. Strain gauge signals are amplified by simple signal conditioning circuits with a low component count. Despite the simplicity of the design, a calibration and accuracy check revealed root mean squared errors of 14 N for the vertical force component and less than 11 N for the horizontal force components.

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Optimization of Pedaling Rate in Cycling Using a Muscle Stress-Based Objective Function

Maury L. Hull, Hiroko K. Gonzalez, and Rob Redfield

Relying on a five-bar linkage model of the lower limb/bicycle system, intersegmental forces and moments are computed over a full crank cycle. Experimental data enabling the solution of intersegmental loads consist of measured crank arm and pedal angles together with the driving pedal force components. Intersegmental loads are computed as a function of pedaling rate while holding the average power over a crank cycle constant. Using an algorithm that avoids redundant equations, stresses are computed in 12 lower limb muscles. Stress computations serve to evaluate a muscle stress-based objective function. The pedaling rate that minimizes the objective function is found to be in the range of 95–100 rpm. In solving for optimal pedaling rate, the muscle stresses are examined over a complete crank cycle. This examination provides insight into the functional roles of individual muscles in cycling.