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PubMed1992

Estimates of mechanical work and energy transfers: demonstration of a rigid body power model of the recovery leg in gait.

Many studies concerning the mechanical work and efficiency of human motion have used models based on segmental energy. It has been shown theoretically that such work estimates may be in error due to offsetting compensations in power sources underlying the energy profiles. Further, mechanical energy transfers calculated from these energy models have been interpreted as metabolic energy-saving mechanisms. This paper examines the use of mechanical power analysis to calculate work and energy transfer estimates, using the motion of the recovery leg in walking and running for one subject as a demonstrative example. Work and energy transfer estimates from both energy and power models are compared and contrasted. The energy model underestimates the work of the recovery leg in both walking (54% of power model estimate) and running (38%), due to muscle powers at joints opposing each other in energy generation and absorption. Energy transfers calculated with energy models are shown to suffer the same problem of offsetting power sources. In contrast, the power model identifies four energy transfer mechanisms (pendulum, whip, tendon, and joint force transfers), which contribute to energy change within the leg in varying amounts. For the recovery leg, the joint force and whip transfer mechanisms have the greatest magnitude, while the pendulum and tendon transfers are much smaller. These energy transfers can be observed on a time-varying basis throughout a motion sequence and illustrate differences in energy distribution between walking and running. These power-based transfers are discussed in terms of their nature regarding metabolic energy cost and mechanical energy distribution within a multisegmented system. It is suggested that the work and energy transfers calculated from the power analysis are more accurate than those calculated from mechanical energy models and are more useful for understanding performance.

Biomechanical Phenomena↗

PubMed1990

The behaviour of the mean power frequency of the surface electromyogram in biceps brachii with increasing force and during fatigue. With special regard to the electrode distance.

The present study aims to investigate: a) the relationship between force and mean power frequency of the EMG, and b) how the distance between surface electrodes influences the mean power frequency. The study consisted of three parts: 1) a gradually increasing contraction upto 100% MVC, 2) contractions performed at 5 different levels from 20% upto 100% MVC with rest in between, and 3) an endurance test at 30% MVC. Nine healthy women participated. The elbow was flexed 90 degrees and EMG signals were obtained from the biceps brachii. The surface electrodes were placed so that electrode distances of 10 mm, 20 mm and 30 mm were obtained. The mean power frequency increased upto 60% MVC. Above 60% MVC no change in mean power frequency occurred. No differences in the mean power frequency with respect to the electrode distances existed at each force level. No significant differences were found at each contraction level between the gradually increasing contraction and the stepwise increasing contractions. The mean power frequency decreased linearly during the endurance test without any differences with respect to the electrode distances. It is concluded that the different electrode distances do not affect the mean power frequency-force relationship or the decrease in mean power frequency during fatigue. It is proposed that the increase in mean power frequency, on group level, can be used as an indicator of motor unit recruitment. However, this proposal was found to be complicated when individual analyses were made.

Adult↗

PubMed1981

Longitudinal study of aerobic power in superior junior athletes.

The effects of endurance training on aerobic power, and the relationship between aerobic power and running performance were investigated in 11 junior runners over a period of 5-to-7 years, starting from the age of 14. Aerobic power was measured using treadmill running and a protocol that involved increasing speed. The six subjects who comprised group I were those who continued competitive training, while the five in group II had stopped training by the age of 18. The subjects in group I demonstrated greater aerobic power (l x min-1) and better running performance than those in group II. Aerobic power for group I increased from 3.54 l x min-1 (65.4 ml x kg-1 x min-1) to 4.49 l x min-1 (75.5 ml x kg-1 x min-1) between the ages of 14.8 and 18.8 yr. The increase in l x min-1 and ml x kg-1 x min-1 was statistically significant (p less than 0.01, p less than 0.05). The greatest aerobic power found in subject A corresponds to the data from world-class runners: 3.63 l x min-1 (61.5 ml x kg-1 x min-1) at age 14.7 yr; 4.67 l x min-1 (74.6 ml x kg-1 x min-1) at 17.8 yr; and 5.04 l x min-1 (76.3 ml x kg-1 x min-1) at 20.7 yr. After their training was discontinued, aerobic power for those in group II decreased to the level of ordinary schoolboys. Improvement in running performance was closely related to the increase of aerobic power in l x min-1. Superior running performance seems to be associated with high aerobic power in l x min-1, rather than in ml x kg-1 x min-1 for junior runners.

Adolescent↗

PubMed1993

Statistical power in the detection of matrix effects.

Matrix-induced bias can adversely affect the performance evaluation a clinical laboratory receives on proficiency testing results. Therefore, it is vital that matrix effects from a matrix-biased system are detected and that laboratories using these systems are not falsely penalized on their proficiency testing results. The College of American Pathologists has developed an experimental protocol to test whether an observed bias is, in fact, due to the proficiency testing sample matrix rather than true performance or calibration problems. The probability of detecting a matrix effect using this protocol given a matrix-biased system is defined as statistical power. Five parameters are known to affect the probability of detection: (1) size of the bias in the proficiency testing material, (2) lack of fit coefficient of variation-natural variation in patient samples used to define the relationship between the test and reference methods, (3) pure error coefficient of variation-random variation in the test method, (4) the number of fresh patient samples, and (5) the number of replicates for each sample. The level of significance of the statistical test will also affect the probability of detection. Power curves are generated to show the effect these five parameters have on the determination of power. With the exception of bias, power is most influenced by the components of variance, lack of fit (nonlinear), and pure (random) error. Of these two components, the lack of fit error, which represents an uncontrollable source of error, is usually more influential than pure error, which can be reduced by a larger number of replicates. A large increase in power will result from an increase of fresh patient samples from 10 to 20, and a moderate increase in power will result from an increase of fresh patient samples from 20 to 40; no noticeable increase in power is seen with greater than 40 fresh patient samples. Large increases in power were observed for increases in the number of replicates per sample from one to two, two to three, and three to five. To markedly increase power further, 10 replicates would have to be assayed.

Bias↗

PubMed1995

Sympathetic, parasympathetic and non-autonomic contributions to cardiovascular spectral powers in unanesthetized spontaneously hypertensive rats.

OBJECTIVE: To determine whether spectral powers of blood pressure and pulse interval can specifically reflect sympathetic and parasympathetic effects in unanesthetized, free-moving spontaneously hypertensive rats (SHR). DESIGN: Spectral powers were observed before and after various autonomic interventions in chronically instrumented rats. MATERIALS AND METHODS: Chemical sympathectomy was produced in 12-week-old SHR by repeated injections of 6-hydroxydopamine, while control rats were given vehicle alone. Chronic arterial and venous catheters were inserted in the femoral artery and vein. Blood pressure was recorded beat-to-beat for 90 min in free-moving rats; further recording sessions were obtained under additional alpha-receptor blockade with phenoxybenzamine at 1 mg/kg and/or additional cholinergic blockade with atropine at 0.8 mg/kg. Off-line computer analysis (fast Fourier transform) provided estimates of low- (0.025-0.1 Hz), mid- (0.1-0.6 Hz) and high-frequency (0.8-3.0 Hz) powers for blood pressure and pulse interval over consecutive periods of 100 s. RESULTS: The most noticeable findings were that sympathectomy produced a striking increase in the low-frequency power of blood pressure and a tendency (borderline statistical significance) to reduce the mid-frequency power of blood pressure. Additional alpha-receptor blockade had no effect on any spectral power whereas additional cholinergic blockade caused a further increase in the low-frequency blood pressure power and a drastic reduction in all pulse interval powers. CONCLUSIONS: In the unanesthetized SHR, sympathetic activity opposes low-frequency and marginally promotes mid-frequency blood pressure fluctuations; the pulse interval spectral expression of vagal effects is spread throughout the range of frequencies explored and is not confined to the high-frequency band. These data indicate that in SHR no spectral power can specifically reflect the effects of either autonomic limb.

Adrenergic Fibers↗

PubMed1989

Power in college students' contraceptive decisions.

Excluding Hollerbach (1980), previous fertility researchers have paid little attention to contraceptive power bases, relationships that become the source of changes in birth control values and behavior. Eight contraceptive power bases, each evaluated as a direct or obvious strategy, were identified in a pilot study involving 25 college students as participants and 10 undergraduate raters. Two-hundred college students completed a questionnaire which included the Bem Sex Role Inventory, inquired into their sexual and contraceptive behavior, and asked about contraceptive power bases. There were highly significant main effects for both students' personal experiences with contraceptive power bases and for their opinions about the comfort and effectiveness of same. Coercion was the most popular and legitimate power was the least popular power base. Women were more likely than men to be the targets of contraceptive power bases, the majority of which were stereotyped as feminine by women in particular. Sex role identification was unrelated to students' experiences with contraceptive power bases. The implications of these findings for family-planning researchers and practioners are addressed.

Adolescent↗

PubMed2004

Effects of affiliation and power motivation arousal on salivary progesterone and testosterone.

Following up on earlier research suggesting a link between implicit affiliation motivation and progesterone (P) and implicit power motivation and testosterone [T; Schultheiss, O.C., Dargel, A., Rohde, W., 2003. Implicit motives and gonadal steroid hormones: Effects of menstrual cycle phase, oral contraceptive use, and relationship status. Horm. Behav. 43, 293-301.], we tested whether arousal of affiliation motivation increases P levels and whether arousal of power motivation increases T levels. Sixty subjects were randomly assigned to watch 30 min of either Bridges of Madison County (affiliation arousal) or The Godfather II (power arousal), or a documentary about the Amazon (control condition). Levels of P and T were assessed in saliva samples taken before (T1), immediately after (T2), and 45 min after the movie (T3). The efficacy of experimental conditions to differentially arouse motives was verified by assessment of changes in affiliation and power motive imagery expressed in imaginative stories written before and after the movie. After the movie, salivary P levels (T2 and T3) in the affiliation-arousal group were significantly higher than in the control group and marginally higher than in the power-arousal group. Subjects' postmovie T responses (T3) depended on premovie T levels: in men, higher premovie T levels predicted a greater likelihood of postmovie T increases in the Power Arousal condition but not in the other conditions, whereas in women, higher premovie T levels tended to be associated with postmovie T decreases in the Power Arousal condition but not in the other conditions. These findings suggest that aroused affiliation motivation has a specific stimulatory effect on P, whereas aroused power motivation has a specific stimulatory effect on T in men, but not in women, with high baseline T levels.

Adult↗

PubMed2004

A question of place: medical power in rural Australia.

In Australia, like many countries, government, medicine and the community have maintained an interdependent and symbiotic relationship based on mutual resource dependency and reciprocity. The services of medicine have been indispensable to government and the community and in return medicine has achieved power, elitism and financial gain. Traditionally, doctors have controlled and directed medical knowledge in an absolute manner and this has been the basis of increasing power and dominance. There are, however, claims that medicine's power and dominance over the health care system is being eroded by the emergence of major social trends. The corporatization of medicine, manageralism and proletarianization are touted as factors that are increasingly countervailing medical dominance and power. Whilst it could be suggested that as these trends become more firmly established government and the community gain greater discretionary control over how the resources of medicine can be allocated and utilized, this article argues that the geographic and social dimensions of the community in which doctors practice must be considered. Using a qualitative descriptive approach research was conducted in rural Victoria, Australia. The overall aim of the study was to identify the issues that impact upon service delivery in rural hospitals. The most significant issue that emerged related to medical relationships. The results of this research indicate that in this rural area the power of medicine is strengthened and institutionalized by geographically determined resource control. The sustainability of rural communities is linked to the ability of the town to attract and retain the services of a doctor. Crucial shortages of rural doctors provide medicine with a mandate to dictate the way in which medical resources will be allocated and used by hospitals and the community. Organizations that control critical resources are in an extremely powerful position to control others. Doctors in rural Victoria maintain a position of strength and use their power to exert control over the state, the community and the hospital. Although medical power and dominance may be declining in some areas, in rural Victoria it remains firmly entrenched.

Community Participation↗

PubMed2000

Social motives and cognitive power-sex associations: predictors of aggressive sexual behavior.

The present study investigated whether implicit social motives and cognitive power-sex associations would predict self-reports of aggressive sexual behavior. Participants wrote stories in response to Thematic Apperception Test pictures, which were scored for power and affiliation-intimacy motives. They also completed a lexical-decision priming task that provided an index of the strength of the cognitive association between the concepts of "power" and "sexuality." For men, high levels of power motivation and strong power-sex associations predicted more frequent aggression. There was also an interaction: Power motivation was unrelated to aggression for men with the weakest power-sex associations. For women, high levels of affiliation-intimacy motivation were associated with more frequent aggression. Strong power-sex associations were also predictive for women but only when affiliation-intimacy motivation was high.

Adult↗

PubMed2002

Relationship power, condom use and HIV risk among women in the USA.

Women's ability to negotiate safer sexual practices, particularly condom use, is a vital component of HIV/STD prevention strategies. Gender-based power imbalances may constrain women's negotiation ability, yet few empirical studies have tested the hypothesis that sexual relationship power constitutes a key factor in condom use negotiation. In this investigation, a new measure - the Sexual Relationship Power Scale (SRPS) - was applied. Data were collected from 388, mostly Latina, women at an urban community health centre in Massachusetts. Women with high levels of relationship power were five times as likely as women with low levels to report consistent condom use, after controlling for sociodemographic and psychosocial variables (p < 0.05). Population attributable risk estimates indicate that 52% of the lack of consistent condom use among women can be attributed to low sexual relationship power. The strong association between the Sexual Relationship Power Scale and consistent condom use supports the hypothesis that relationship power plays a key role in safer sex decision making. These findings underscore the importance of including the issue of relationship power in the design and implementation of programmes that promote sexual and reproductive health, as well as research investigating condom use and HIV risk.

Adolescent↗

PubMed2003

A method for assessing occupational exposure to power-frequency magnetic fields for electricity generation and transmission workers.

A new method for assessing both current and historical occupational exposures to magnetic fields has been developed and used in health studies involving a cohort of electricity generation and transmission workers in England and Wales. The exposure values are derived by calculation from engineering and operational data about the power stations rather than from measurements. They are provided for each of 11 job categories for each year of operation of each power station represented in the cohort. The engineering data are used to determine the average magnetic fields in specified areas of work within the power station and then applied to information about the time spent in these areas by each of the job categories. The operational data are used to adjust the exposures for each year according to the power station output for the year. Earlier methods used measurements or the advice of panels of experts to provide exposure scores for a number of job categories across all power stations and years. Such methods were not able to distinguish exposures from different power facilities or during the different years of their operation. Measurement surveys at 10 power stations of the magnetic fields in the work areas gave confidence that the calculations were realistic. Exposure measurements on 215 workers at three power stations were compared in job groups with the exposures predicted by the method. The Pearson correlation coefficient was 0.86 and the slope and intercept of the line of best fit were 0.87 and 0.07 microT respectively. The method gives a good prediction of measured exposure and is being used for studies of occupational exposure to magnetic fields and leukaemia, and of cardiovascular disease, and a reanalysis of brain cancer.

Electric Wiring↗

PubMed1984

Uncertainty in the amount of power delivered by CO2 medical lasers.

Carbon dioxide medical lasers are being used for various clinical applications with considerable success. Despite the bulk of the generating equipment, the use of light, articulated arms to deliver the power beam to either hand-held or microscope-mounted aiming heads allows accurate power placement. In addition, the beam can be focussed to a small spot size, minimizing damage to adjacent tissue provided that the output power and the precise duration of application are known, and the shielding of deeper tissue has been adequate. In an attempt to assess the reliability of the laser beam as a significant surgical tool (particularly suitable for fine cutting functions in microsurgical procedures), we tested the power output of some of the CO2 surgical lasers now available in Australia. An alarming discrepancy was found between the actual power delivered and the higher power value displayed as being delivered. As these medical lasers were tested and passed as fully functioning by their local agents, it is suggested that purchasers of CO2 lasers should be aware of these possible power inadequacies and subject their equipment to frequent power checks. Otherwise much longer applications of the laser beam will be needed to accomplish the cutting action required, with the consequent infliction of more damage to the surrounding tissues.

Australia↗

PubMed2005

Beliefs about power and its relation to emotional experience: a comparison of Japan, France, Germany, and the United States.

This research examined the concept of power in Japan, France, Germany, and the United States, as well as beliefs about the emotions persons in power tend to elicit in others and about powerful people's regulation (specifically, inhibition) of certain emotions. Definitions of power were assessed by examining the importance of two main components: control over self versus other and freedom of action vis-à-vis social norms. Beliefs about both positive (pride, admiration) and negative (jealousy, contempt) emotions were measured. Analyses revealed that the concept of power differed across countries and that the definitions of power as well as country of origin significantly predicted beliefs about the emotions that are elicited in others by powerful people and also the regulation of expression of emotion by powerful people.

Adult↗

PubMed2001

Theoretical and perceived balance of power inside Spanish public hospitals.

BACKGROUND: The hierarchical pyramid inside Spanish public hospitals was radically changed by the Health Reform Law promulgated in 1986. According to it, the manpower of the hospitals was divided into three divisions (Medical, Nursing, General Services/Administration), which from then on occupied the same level, only subject to the general manager. Ten years after the implementation of the law, the present study was designed in order to investigate if the legal changes had indeed produced a real change in the balance of power inside the hospitals, as perceived by the different workers within them. MATERIALS AND METHODS: A questionnaire was administered to 1,027 workers from four different public hospitals (two university-based and two district hospitals). The participants belonged to all divisions, and to all three operative levels (staff, supervisory and managerial) within them. The questionnaire inquired about the perceived power inside each division and hierarchical level, as well as about that of the other divisions and hierarchical levels. RESULTS: Every division attributed the least power to itself. The Nursing and the Administrative division attributed the highest power to the physicians, and these attributed the highest power to the General Services/Administrative division. All hierarchical levels (including the formal top of the pyramid) attributed significantly more power to the other than to them. CONCLUSIONS: More than ten years after the implementation of the new law, the majority of workers still perceive that the real power within the hospitals is held by the physicians (whereas these feel that it has shifted to the administrators). No division or hierarchical level believes it holds any significant degree of power, and this carries with it the danger of also not accepting any responsibility.

Attitude of Health Personnel↗

PubMed2004

Does perceived behavioural control mediate the relationship between power beliefs and intention?

OBJECTIVES: In order to determine whether the relationship between power beliefs (Sigma(p)) and health-related behavioural intentions is mediated by perceived behavioural control (PBC) we used structural equation modelling of eight cross-sectional data sets. METHOD: Eight studies that examined health-related behaviours and employed representative samples totalling N = 4663 participants were analysed. All studies involved power belief items derived from pilot testing and employed standard multi-item measures of power beliefs, PBC and intention that were highly reliable. RESULTS: Confirmatory factor analysis confirmed the discriminant validity of power beliefs, PBC and intention. Structural equation modelling of relevant paths indicated that PBC only partially mediated the relationship between power beliefs and intention (Z(Sobel) = 5.15, p < .001; Z(Baron&Kenny) = 5.16, p < .001). Power beliefs had a significant direct relationship with intention even after PBC had been taken into account. CONCLUSION: The findings undermine Ajzen's contention that PBC mediates the power beliefs-intention relationship and suggests that it is important to employ measures of power beliefs in addition to measures of PBC in order to enhance the prediction of intentions to perform health-risking, or health-promoting, behaviours.

Adolescent↗

PubMed1999

[Determining power factors of clinical departments in a medical center].

The intradepartmental power factors in a medical center were studied. 3 strategic contingency factors were examined, based on the model of Hickson et al. (1971): centrality, substitutability, and coping-with uncertainty. Only coping-with-uncertainty contributed directly to departmental power, and not the summation of the 3. Power derives from department resources, connections and influence outside the medical center. Aspects related to inpatient treatment or teaching of residents did not contribute directly to departmental power status. Power is gained in stages: in the first the department contributes to the factor of centrality (mainly patient treatment, teaching and research). In the middle stage, power is gained due to the factor of substitutability--the unique services and research which the department has developed. The third stage contributes directly to power-coping with uncertainty. This implies the ability of a department to solve crucial problems of the medical center. Surprisingly, the clinical field (i.e. surgery) did not contribute significantly to power. The current trend is toward empowering ambulatory units in the medical center.

Hospital Departments↗

PubMed1992

Feeling personal power.

Feelings of personal power are important for personal feelings of well-being. Although feelings of personal power relate to authority, either given by others or acquired with the job, personal power is largely a personal feeling that is created and can be developed. Careful assessment of position power, expertise power, and personal characteristics that add or detract from personal power can increase self-awareness and cause strong areas to be maximized and weak areas to be developed. With the development of feelings of personal power come feelings of confidence in a nursing role. Feelings of personal power also benefit the nursing profession because this enables the profession to grow in strength and pride.

Attitude↗

PubMed2004

Tooth whitening through the removal of extrinsic stain with a power toothbrush: results of four randomized, examiner blind, positive controlled clinical studies.

PURPOSE: To assess the "whitening" through stain removal benefit delivered by a prototype power toothbrush and a positive control power toothbrush over a 2-week period. METHODS: Four independent studies with identical protocols were conducted to examine tooth whitening through the removal of extrinsic stain with power toothbrushes. These were randomized, positive-controlled, two treatment, parallel group, examiner-blind, 2-week studies involving approximately 20 healthy adults with longstanding visible extrinsic stain on the facial surfaces of the 12 anterior teeth. Approximately 10 subjects per group were enrolled into the study for each of the two treatment groups; a prototype-powered toothbrush group (Crest SpinBrush Pro Whitening) and a positive control powered toothbrush group (Sonicare Personal 4100). RESULTS: In these four studies, the positive control sonic power toothbrush statistically significantly (P < 0.05) reduced stain scores by 84%, 77%, 44% and 49% following 2 weeks of brushing. Importantly, the prototype whitening power toothbrush statistically significantly (P < 0.05) reduced stain scores by 88%, 65%, 59% and 57% following 2 weeks of brushing. In both the individual studies and a combined analysis involving all four studies, the adjusted mean changes between treatment groups did not differ significantly between the two treatment groups. In the combined analysis, a one-sided upper 95% confidence bound on the difference in stain reduction scores between the two toothbrushes (positive control minus prototype) was found to be 8.3% of the prototype toothbrush adjusted mean change. This supports that the prototype power toothbrush removed extrinsic stain at least as well as the positive control toothbrush across these four studies.

Adult↗