The proportional work of lifting the center of mass during walking.

The present study determined the proportion of energy consumption used to lift the center of mass vertically during walking. By assuming that the vertical oscillations of the trunk were identical to those of the center of mass, the complexity of studying the human gait was simplified. The work performed on the center of mass, defined as lift work, was calculated using the subject's mass and the vertical displacement of the trunk. Compensating for the fact that human muscles are approximately 25% efficient in performing external work, the mechanical work was compared with the total energy expenditure, determined using an expired air analysis. At 1.34 and 1.79 m/s, 53.2 +/- 9.3% and 62.8 +/- 8.6%, respectively, of the total energy can be explained by lift work. At 0.45 and 0.90 m/s, the proportions are considerably less, 21.6 +/- 6.6% and 37.6 +/- 8.2%, respectively. These findings provide a rationale for why the metabolic energy cost per unit distance is greater at slower speeds than comfortable or fast speeds of walking. The total energy consumption can be accounted for by changes in the potential and kinetic energies and internal muscular work, defined as the less readily observable work probably needed for balance. The present study demonstrated that the metabolic energy cost of changing the potential energy of the center of mass during walking is significantly less relative to the total energy consumption at slower speeds than at higher speeds. Because kinetic energy is proportional to the square of the velocity, the metabolic energy cost of changing this energy is relatively small at slower speeds. Internal muscular work must therefore play a large role in total energy consumption at slow speeds of walking.

A tool to assess biomechanical gait efficiency; a preliminary clinical study.

A goal of many physiatric interventions is to improve biomechanical walking efficiency. Thus, a tool that helps assess this efficiency, independent of cardiac, pulmonary, psychologic, or other nonbiomechanical factors, would be useful. Currently used methods to measure efficiency, including comfortable walking speed, are not specific to biomechanical variables. A potential tool, the biomechanical efficiency quotient (BEQ), which uses three variables--average stride length, vertical displacement of the trunk during walking, and sacral height during standing--is proposed and preliminarily tested. This quotient is based on Saunders, Inman, and Eberhart's theories and on a prior study in able-bodied subjects. The BEQ was computed in 20 consecutive patients with neurologically based gait disability referred for gait laboratory evaluation who subjectively reported that one or two ankle-foot-orthoses (AFOs) reduced the effort necessary to walk. The quotient was calculated with and without the AFO(s) by dividing the average vertical displacement of the sacrum, which was measured with an optoelectronic system, and by a predicted displacement, which was based on the patient's sacral height and average stride length. The mean BEQ with the AFO(s) (6.3 +/- 4.4) was significantly less than the mean BEQ without the AFO(s) (9.7 +/- 7.1); P = 0.005. Furthermore, the BEQ was less with the AFO(s) compared with trials without the AFO(s) in all subjects. Percent change in BEQ with the AFO(s) (26.8 +/- 19.6) correlated with percent change in comfortable walking velocity (24.8 +/- 31.8), r = 0.73, P<0.001, across all subjects. The BEQ may be useful in specifically assessing the effect on biomechanical efficiency of physiatric interventions, despite variable nonbiomechnical factors. An instrument to measure vertical trunk displacement during walking outside of the gait laboratory would be extremely useful for further necessary longitudinal studies.

Measured versus predicted vertical displacement of the sacrum during gait as a tool to measure biomechanical gait performance.

The vertical displacement of the sacrum during walking is proposed as an estimation of the overall biomechanical performance of walking, independent of cardiopulmonary factors. Vertical sacral displacement during walking was measured using an optoelectronic motion analysis system in 10 normal volunteers at variable speeds. Oxygen consumption was simultaneously measured. The actual vertical displacement of the sacrum, when correlated with body weight, reliably predicted oxygen consumption (r2 = 0.91). The relationship between vertical sacral displacement and oxygen consumption persisted when controlling for the variables, velocity, square of velocity, cadence or stride length, each known to co-vary with cardiopulmonary performance. A mathematic model designed to predict the vertical displacement of the sacrum, based on sacral height and average stride length, was tested. The actual vertical sacral displacement correlated with predicted displacement (r = 0.94). Unilateral immobilization of each subject's knee resulted in a greater average vertical sacral displacement during gait than predicted. Comparing measured with predicted vertical sacral displacement may provide a clinically useful and specific overall assessment of biomechanical gait performance.

Assistive technology: problems and policy alternatives.

Assistive technology (AT), defined as any device or product system that increases the physical functioning or independence of persons with disabilities, is transforming the way disabled Americans live and work. Numerous studies show increases in independence, employment, and life satisfaction; yet, the acquisition of AT presents many problems for disabled persons, such as lack of funds to purchase AT, no centralized information and evaluation system, fraud and abuse by some providers, and denials of needed equipment by third-party payers. The proposed Health Security Act could provide a potential mechanism to address these problems, but whether AT should be covered under the Act has received little national attention. In this article we document the need and current funding alternatives for AT, and suggests possible short and long-range strategies to make AT more available for individuals with disabilities.

Use it or lose it--the hazards of bed rest and inactivity.

Professional experience and lay wisdom teach us the benefits of exercise and the hazards of idleness. Yet the myth persists that "bed rest is good for you" when ill or convalescing. Abundant scientific evidence in the past 50 years has demonstrated the specific damage done to each of the body's organ systems by inactivity. Both aging and inactivity lead to strikingly similar kinds of deterioration. I summarize the data from military and veterans' hospitals, rehabilitation experience, aerospace research, and gerontology and review the physiologic and metabolic changes of aging and inactivity, along with strategies to help prevent the iatrogenic complications of bed rest.

Cardiac disability. The impact of coronary heart disease on patients' daily activities.

We studied 100 men with clinically stable coronary heart disease. Their capacity for exertion as defined by treadmill test was compared with the physical and social avocational activities they carried out in their daily routine, as reported by them. Exercise capacity (treadmill time) was strongly correlated with a physician's independent assessment of symptomatic status (anginal history). Although participation in some relatively strenuous elective activities was related slightly to exercise capacity, participation in many household duties and social undertakings bore no relationship to exercise capacity or to other measures of the severity of the underlying heart disease. The patients' own perceptions of their cardiac limitation varied for different activities and for some activities it was determined as much by their own concern and outside advice as by cardiac symptoms. Decreased capacity for exertion seems to exert surprisingly little influence on a cardiac patient's daily routine and interventions aimed at altering one of these measures of performance will not necessarily affect the other.

Independent living outcomes in spinal cord injury: multivariate analyses.

This paper presents results of a study designed to isolate those medical, personal, and environmental factors that best predict a spinal cord injured (SCI) person's ability to live independently following discharge from medical rehabilitation. A formal research model is used to identify the most promising dependent and independent variables. The principal data source is an extensive data file of 111 persons with SCI who were discharged from 10 medical rehabilitation centers across the nation. The two main independent living (IL) outcome variables are (1) a person's ability to live in a less restrictive environment, and (2) a person's ability to live productively--not only in terms of gainful employment but also in terms of other contributions to community and family life. Using multiple regression analysis, the paper reports that approximately 63% of the variance in IL outcome can be explained. The most important predictors of IL outcome are marital status, education, transportation barriers, economic disincentives, and the severity of a person's disability as measured by the Barthel index. All predictors are statistically significant. The paper concludes with implications for medical rehabilitation practice and disability policy.

Comparison of bile acid synthesis determined by isotope dilution versus fecal acidic sterol output in human subjects.

Fecal acidic sterol output has been found to be much lower than bile acid synthesis determined by isotope dilution (J. Lipid Res. 17: 17, 1976). Because of this confusing discrepancy, we compared these 2 measurements done simultaneously on 13 occasions in 5 normal volunteers. In contrast to previous findings, bile acid synthesis by the Lindstedt isotope dilution method averaged 16.3% lower than synthesis simultaneously determined by fecal acidic sterol output (95% confidence limit for the difference - 22.2 to -10.4%). When one-sample determinations of bile acid pools were substituted for Lindstedt pools, bile acid synthesis by isotope dilution averaged 5.6% higher than synthesis by fecal acidic sterol output (95% confidence limits -4.9 to 16.1%). These data indicate that the 2 methods yield values in reasonably close agreement with one another. If anything, fecal acidic sterol outputs are slightly higher than synthesis by isotope dilution.

Sports medicine and the physiology of wheelchair marathon racing.

In the past three decades, wheelchair sports have become an international reality. Disabled athletes are exercising their right to accept the challenges and risks taken by able-bodied athletes. Marathon racing over a 26-mile, 385-yard course is the latest and most strenuous of the wheelchair athletic events. The small amount of available research data on wheelchair sports has been summarized, as well as some relevant data from exercise physiology studies on able-bodied subjects. Physicians and other health professionals who work with disabled people should be knowledgeable about the risks and benefits of wheelchair sports. Much more basic research is needed to improve the safety, training techniques, and performance of wheelchair athletes.

Energy expenditure of ambulation in patients with above-knee amputations.

Oxygen consumption during ambulation was measured in nine middle-aged or elderly subjects having above-knee amputations, in an effort to determine the mode of ambulation and prosthetic prescription requiring the least energy expenditure. Studies revealed that crutch walking and prosthetic ambulation require the same energy expenditure; that there is no significant difference between the energy requirements of ambulating with knee locked or unlocked; and that 65 percent more energy is required at approximately one-half the normal speed of ambulation for above-knee amputees as compared to normal persons.