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Biomedical subjects

P R Cavanagh

Publications and source records attributed to P R Cavanagh.

At least 91 records · Page 5Linked to original sources
PubMed1987

The biomechanics of lower extremity action in distance running.

The role of quantitative biomechanical measurements in the evaluation of the running patient is discussed. Many techniques are now available to provide insight into the external mechanics of lower extremity action during running, and results from such measurements are presented for symptom-free subjects at distance running speeds. Details of stride length, stride time, and foot placement are first presented followed by a discussion of kinematic data, including stick figures, angle-time graphs, and angle-angle diagrams for the sagittal plane motion of the hip, knee, and ankle joints. The measurement of rearfoot motion, as an approximation of coronal plane subtalar joint movements, is also discussed. Results from acceleration, force, and pressure measurements are considered, and the assertion is made that bilateral asymmetry in many of these measures is a fairly common finding. There are, at present, few reports in the literature of the application of biomechanical techniques to the evaluation of patients with running injuries. It is anticipated that there will be rapid developments in this area in the future and that this will provide considerable insight into the etiology, diagnosis, and treatment of running injuries.

Acceleration↗
PubMed1987

Pressure distribution under symptom-free feet during barefoot standing.

The plantar pressure distributions for a large heterogeneous sample of feet (N = 107) were collected during barefoot standing using a capacitance mat. From these data, the function of the foot during standing was characterized. Peak pressures under the heel (139 kPa) were, on average, 2.6 times greater than forefoot pressures (53 kPa). Forefoot peak pressures were usually located under the second or third metatarsal heads. No significant relationship was found between body weight and the magnitude of peak pressure. The concepts of a transverse arch at the level of the metatarsal heads and a "tripod" theory of load distribution were not substantiated by this study. Load distribution analysis showed that the heel carried 60%, the midfoot 8%, and the forefoot 28% of the weightbearing load. The toes were only minimally involved in the weightbearing process. Examples of unusual distributions are shown; finally, a checklist is provided to aid the clinician in evaluating plantar pressure findings.

Adult↗
PubMed1987

An explanation of the upward drift in oxygen uptake during prolonged sub-maximal downhill running.

The upward drift in oxygen uptake (UDO) that occurs during some prolonged sub-maximal exercises involving eccentric muscle action has received only scant attention in the literature. Those papers reporting UDO have generally used bicycling on an ergometer modified for eccentric exercise as the experimental activity. The purpose of this study was to quantify and propose an explanation for UDO during a different activity involving eccentric muscle action--downhill running. Oxygen consumption, quadriceps muscle electromyography, and stride length were collected from 10 experienced male runners (mean maximal oxygen consumption = 65.0 +/- 5.2 ml X kg X min-1) during two 40-min sub-maximal runs at 3.83 m X s-1. The first run was on a level grade and required 66% of the subjects' mean maximal oxygen consumption. The second run, completed 2 d later, was performed on a 10% downhill grade and elicited 44% of the mean maximal oxygen consumption. Results of the level run showed non-significant changes in oxygen consumption, rectified integrated electromyography, and stride length between minutes 10 and 40. Significant (P less than 0.05) increases in oxygen consumption (10%) and integrated electromyography (23%) were found across the same time period of the downhill run. No significant changes in downhill stride length were observed. Delayed-onset muscle soreness, a presumed indication of muscle damage, occurred only following the downhill run. It is hypothesized that UDO and increasing integrated electromyography during downhill running reflected increased motor unit recruitment within the eccentrically acting muscles caused by an ongoing combination of muscle damage, connective tissue damage, and local muscle fatigue.

Adult↗
PubMed1985

Knee flexor moments during propulsion in cycling--a creative solution to Lombard's Paradox.

The function of two joint muscles in the human lower extremity was studied during a cycling task with efficiency of their action discussed in light of Lombard's Paradox. Special pedals were designed to monitor reaction forces parallel to the sagittal plane of the body. Net moments of force about the hip, knee and ankle and EMG patterns in selected lower extremity muscles were recorded in five subjects pedalling against a constant load. The most original aspect of this study was the clear difference in hip and knee action during the propulsive phase of the pedalling cycle. A knee flexor moment was consistently observed in all subjects starting approximately half way through the propulsive phase of crank rotation (0-180 degrees) and presented as a creative solution to Lombard's Paradox.

Bicycling↗
PubMed1985

Mechanical and muscular factors affecting the efficiency of human movement.

This paper reviews specific examples of how energy expenditure during submaximal exercise is affected by mechanical and muscular factors. Structural biomechanical variables are discussed as a possible reason for economy differences between individuals. The practical question, "Can economy of performing a certain task be modified?" is posed. Examples of how the manipulation of a particular movement pattern results in an energetic minimum (optimal phenomena) are presented. The physiological mechanisms for these phenomena are summarized. The influence of positive vs negative work and storage of elastic energy in relation to the topic of economy and muscular efficiency is considered. The effects of athletic equipment such as footwear, track surfaces, and bicycle components on economy and muscular efficiency are presented. The prospects for improving athletic performance by improving economy are evaluated, and recommendations for future directions are made.

Bicycling↗
PubMed1985

The efficiency of human movement--a statement of the problem.

This paper is an introduction to a multidisciplinary series of papers on the efficiency of human movement. The problem is posed by citing the example of the large variation in oxygen uptake (per kg body weight) within a typical group of subjects running at the same submaximal speed. An analog of the possible causes of this variation is presented where "set points" for biomechanical, physiological, psychological, biochemical, and other factors combine in series to influence the overall energy cost. The various definitions of "efficiency" and "economy" are considered at the whole body and the isolated muscle level, and a discussion of baseline subtraction is presented. The concept of "effectiveness" is reviewed to illustrate the interaction of skilled performance and energy cost. It is recommended that the terms "muscular efficiency," "muscle efficiency," "economy," and "effectiveness" be used in their respective contexts to replace the current diversity of overlapping and, at times, confusing terminology.

Efficiency↗
PubMed1983

A model for the calculation of mechanical power during distance running.

Because widely varying estimates of mechanical power have been calculated for a given speed of running by previous investigators, the effects of various assumptions necessary for mechanical power calculations were evaluated via a segmental energy analysis using 3-D cine data from 31 well-trained subjects running overground at 3.57 ms-1. The magnitude of power calculated was very dependent upon assumptions involving the amount of between segment energy transfer occurring, the relative metabolic cost of positive vs negative work, the amount of the total negative work attributed to muscular work, the effects of elastic storage of energy and on the choice of cutoff frequency in filtering the coordinate data. Mechanical power values ranged from 273 to 1775 W depending on the particular assumptions made and computational methods employed giving efficiency ratios from 0.31 to 1.97. These results point to a need for more definitive research into the role played by energy transfer, negative work, and elastic storage of energy before confidence in measured mechanical power can be established.

Biomechanical Phenomena↗
PubMed1982

The effect of stride length variation on oxygen uptake during distance running.

Ten recreational runners (mean VO2max 64.7 ml . kg-1 . min-1) underwent a 5-d acclimation period to treadmill running at a 7 min . mile-1 pace (3.83 m . s-1) for 30 min each day. During these runs their freely chosen stride lengths were determined and expressed as a percentage of leg length (%LL). On two subsequent testing days stride length was systematically varied over a range of +/- 20% LL about the freely chosen value. O2 uptake was determined by the Douglas Bag method. All subjects exhibited a stride length of which O2 uptake was minimized, although the individual profiles varied considerably. The mean increases in VO2 were 2.6 and 3.4 ml . kg-1 . min-1 at the short- and long-stride length extremes, respectively. During unrestricted running deviations from optimal stride length caused a mean increase in VO2 of 0.2 ml . kg-1 . min-1. The relatively efficient running patterns used by the subjects during unrestricted running indicate either an adaption to the chosen stride length through training or a successful process of energy optimization.

Adaptation, Physiological↗
PubMed1979

Electromechanical delay in human skeletal muscle under concentric and eccentric contractions.

In contraction of skeletal muscle a delay exists between the onset of electrical activity and measurable tension. This delay in electromechanical coupling has been stated to be between 30 and 100 ms. Thus, in rapid movements it may be possible for electromyographic (EMG) activity to have terminated before force can be detected. This study was designed to determine the dependence of the EMG-tension delay upon selected initial conditions at the time of muscle activation. The right forearms of 14 subjects were passively oscillated by a motor-driven dynamometer through flexion-extension cycles of 135 deg at an angular velocity of approximately equal to 0.5 rad/s. Upon presentation of a visual stimulus the subjects maximally contracted the relaxed elbow flexors during flexion, extension, and under isometric conditions. The muscle length at the time of the stimulus was the same in all three conditions. An on-line computer monitoring surface EMG (Biceps and Brachioradialis) and force calculated the electromechanical delay. The mean value for the delay under eccentric condition, 49.5 ms, was significantly different (p less than 0.05) from the delays during isometric (53.9 ms) and concentric activity (55.5 ms). It is suggested that the time required to stretch the series elastic component (SEC) represents the major portion of the measured delay and that during eccentric muscle activity the SEC is in a more favorable condition for rapid force development.

Adult↗
PubMed1976

Asymmetry in bicycle ergometer pedalling.

The effects of changes in speed and resistance setting on the bilateral symmetry of work output on the bicycle ergometer were studied. The cranks of a Monarch bicycle ergometer were instrumented with foil strain gauges and the bridge outputs were integrated on-line and analyzed by a program running in a Hewlett Packard 2115A computer. Twenty male subjects performed three thirty-second trials at each of nine speed and resistance combinations. Indices of asymmetry from 66-178 were found using kicking dominance (n = 20) and 56-135 using a strength dominance classification (n = 13). Day to day reliability of the index of asymmetry was found to be only 0.47; within day reliability was 0.87 for day one and 0.79 for day two. No significant effects for speed or resistance changes were shown on either day for the strength dominant subjects. When kicking dominance was considered main effects were encountered on both days for speed although there was no clear directional trend. The findings of these experiments have important implications for studies where measurements are made on the lower extremity during cycle ergometer exercise, and for competitive cyclists engaged in endurance competition.

Equipment and Supplies↗