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PubMed2001

Muscle power patterns in the mid-acceleration phase of sprinting.

To assess the role of the lower limb joints in generating velocity in the mid-acceleration phase of sprinting, muscle power patterns of the hip, knee and ankle were determined. Six male sprinters with a mean 100 m time of 10.75 s performed repeated maximal sprints along a 35 m indoor track. A complete stride across a force platform, positioned at approximately 14 m into the sprint, was video-recorded for analysis. Smoothed coordinate data were obtained from manual digitization of (50 Hz) video images and were then interpolated to match the sampling rate of the recorded ground reaction force (1000 Hz). The moment at each joint was then calculated using inverse dynamics and multiplied by the angular velocity to determine the muscle power. The results showed a proximal-to-distal timing in the generation of peak extensor power during stance at the hip, the knee and then the ankle, with the plantar flexors producing the greatest peak power. Apart from a moderate power generation peak towards toe-off, knee power was negligible despite a large extensor moment throughout stance. The role of the knee thus appears to be one of maintaining the centre of mass height and enabling the power generated at the hip to be transferred to the ankle.

Acceleration↗

PubMed2001

Reliability of power output measurements during repeated treadmill sprinting in rugby players.

The non-motorized treadmill system initially reported by Lakomy in 1984 has been used extensively to assess sprinting performance. However, there has been limited research into the reliability of power output measurement using such systems. The aim of this study was to design a system and protocol capable of measuring treadmill sprinting performance in rugby players and to assess the reliability of this system for measuring power output. Twenty-seven rugby players, all of whom were familiar with treadmill sprinting, performed three maximal 6 s sprints with 2 min recovery between sprints, on two occasions 1 week apart. Both tests were performed on a non-motorized Woodway tramp treadmill, interfaced to a data acquisition system. There were no significant differences (P > 0.05) between power output for repeated trials on the same day (between trials) or for repeated trials on different days (between days). Limits of agreement for maximum average power (the average of 100 readings per second) were 4+/-98 and 30+/-157 W for between trials and between days, respectively. When reported as ratio limits of agreement, these were 1.07 (*/divided 1.12) and 1.03 (*/divided 1.16), respectively. The limits of agreement for maximum instantaneous power (the highest of 100 readings per second) were 51+/-464 and 105+/-588 W for between trials and between days, respectively. When reported as ratio limits of agreement, these were 1.02 (*/divided 1.20) and 1.04 (*/divided 1.21) for between trials and between days, respectively. The coefficients of variation for all measures of power output were less than 9.3%. Hence, the treadmill system and protocol developed in this study provide a reliable measure of power output for rugby players.

Adult↗

PubMed2001

Muscle power in "high-risk" preterm infants at 12 and 24 weeks corrected age: a measure for early detection.

UNLABELLED: A group of 72 "high-risk" preterm infants was studied at the corrected ages of 12 and 24 wk. Only infants with a high risk for developmental deviance with gestational ages below 32 wk and/or birthweights of less than 1500 g were included in the study. In addition, the infants were categorized according to their medical history, as confirmed by the "Neonatal Medical Index" (NMI I to V), with category I describing infants with few medical problems and V characterizing those with the most serious complications. In this study we included only "high-risk" infants as categorized in NMI III to V, since infants with a "low risk" have been described earlier. Apart from the standard paediatric follow-up, an age-adequate neurological assessment was made, with special emphasis on the relationship between active and passive muscle power. When development is optimal, these two components of muscle power should be in balance in order to create a stable posture and fluent motility. We compared muscle power at the corrected ages of 12 and 24 wk to determine whether the method employed to assess muscle power could enhance early detection of deviant development. At 12 wk of age, only 5 infants showed overall optimal muscle power, while at 24 wk this figure had increased to 27. Significantly more infants in NMI III had optimal outcomes at 24 wk of age. When muscle power in the different parts of the body was studied separately at 24 wk, outcomes in shoulders and trunk still showed significant discrepancies in all NMI groups. At this age, fewer asymmetries were found compared to outcomes at 12 wk. CONCLUSION: Our method of assessing muscle power is useful in detecting preterm infants at risk for pathological development.

Age Factors↗

PubMed1999

Increased exposure to pollutant aerosols under high voltage power lines.

PURPOSE: To assess increased exposure to airborne pollutants near power lines by investigating theoretically and experimentally the behaviour of 222Rn decay product marker aerosols in the 50 Hz electric field under power lines. MATERIALS AND METHODS: The behaviour of aerosols in outdoor air including those carrying 222Rn decay products was modelled theoretically in the presence of an AC field. TASTRAK alpha-particle spectroscopy was used to characterize 218Po and 214Po aerosols outdoors. Sampling points were chosen along a line at right angles up to 200 m from a number of high voltage power (transmission) lines. Each sampling point comprised an arrangement of mutually orthogonal TASTRAK detectors. Exposures were carried out at different power line locations in various weather conditions. RESULTS: The model predicts a two- to three-fold increase in deposition of aerosols on spherical surfaces mimicking the human head under high voltage power lines. Experimental measurements using detectors mounted on grounded metal spheres showed an enhanced deposition of both 218Po and 214Po aerosols. Enhanced 218Po deposition on 400 kV lines ranged from 1.96+/-0.15 to 2.86+/-0.32. Enhanced 214Po deposition on 275 kV and 132 kV lines were 1.43+/-0.07 and 1.11+/-0.21, respectively, where the latter value was not significant. CONCLUSIONS: The observations demonstrate a mode of increased exposure to pollutant aerosols under high voltage power lines by increased deposition on the body. The total (indoor + outdoor) 218Po and 214Po dose to the basal layer of facial skin is estimated to be increased by between 1.2 and 2.0 for 10% of time spent outdoors under high voltage power lines.

Aerosols↗

PubMed2006

Techniques and considerations for determining isoinertial upper-body power.

Power is an integral aspect of many sports. Although power output of the lower body is often measured during jumping and cycling movements, much less is known about power as pertains to the upper body musculature. Recently, isoinertial methods--with constant gravitational load--of power testing have become common, but little is known of the reliability and criterion validity of these tests as they pertain to sport performance. In addition, the varied methodology makes a lucid model more evasive. The aims of this review are to examine the various methods of assessing upper body power, to establish its role in predicting athletic performance, and to assess the body of literature that has assessed power output of the upper extremities by isoinertial methods. To our knowledge, only two studies on isoinertial upper-body power have shown a direct correlation to sporting ability (Baker, 2001; Baker et al., 2001); therefore, many unanswered questions exist as to the efficacy of these tests as predictors of athletic ability or as a method to track athletes' training over time. From this review we hope to allow the sport coach to assess the overall utility of these tests in terms of availability, safety and external validity.

Arm↗

PubMedDate not supplied

Upper body contribution during leg cycling peak power in teenage boys and girls.

This study investigated gender differences in upper-body contribution to cycle muscle power in 23 adolescents. All subjects performed two 5-s and one 20-s cycling sprint, using two protocols: with handgrip (WG) and without handgrip (WOG). Maximal handgrip strength was assessed for each individual. Absolute peak and mean cycling power was corrected for total fat-free mass (FFM) and for lean leg volume (LLV). Males showed higher cycling performance than females. Peak power and 20-s mean power (flywheel inertia included), but not optimal velocity, were higher WG than WOG. Especially for peak power, absolute differences between both protocols were higher in males than in females, and were significantly related to handgrip strength. The significant contribution of the upper body suggested that, for standardisation of cycle muscle power, total FFM is a more relevant variable compared with LLV. Furthermore, in adolescents, the higher contribution of the upper body musculature in males partly explained gender differences in peak power.

Adolescent↗

PubMed2000

Power of linkage versus association analysis of quantitative traits, by use of variance-components models, for sibship data.

Optimal design of quantitative-trait loci (QTL) mapping studies requires a precise understanding of the power of QTL linkage versus QTL association analysis, under a range of different conditions. In this article, we investigate the power of QTL linkage and association analyses for simple random sibship samples, under the variance-components model proposed by Fulker et al. After a brief description of an extension of this variance-components model, we show that the powers of both linkage and association analyses are crucially dependent on the proportion of phenotypic variance attributable to the QTL. The main difference between the two tests is that, whereas the power of association is directly related to the QTL heritability, the power of linkage is related more closely to the square of the QTL heritability. We also describe both how the power of linkage is attenuated by incomplete linkage and incomplete marker information and how the power of association is attenuated by incomplete linkage disequilibrium.

Chi-Square Distribution↗

PubMed2000

The power of genomic control.

Although association analysis is a useful tool for uncovering the genetic underpinnings of complex traits, its utility is diminished by population substructure, which can produce spurious association between phenotype and genotype within population-based samples. Because family-based designs are robust against substructure, they have risen to the fore of association analysis. Yet, if population substructure could be ignored, this robustness can come at the price of power. Unfortunately it is rarely evident when population substructure can be ignored. Devlin and Roeder recently have proposed a method, termed "genomic control" (GC), which has the robustness of family-based designs even though it uses population-based data. GC uses the genome itself to determine appropriate corrections for population-based association tests. Using the GC method, we contrast the power of two study designs, family trios (i.e., father, mother, and affected progeny) versus case-control. For analysis of trios, we use the TDT test. When population substructure is absent, we find GC is always more powerful than TDT; furthermore, contrary to previous results, we show that as a disease becomes more prevalent the discrepancy in power becomes more extreme. When population substructure is present, however, the results are more complex: TDT is more powerful when population substructure is substantial, and GC is more powerful otherwise. We also explore general issues of power and implementation of GC within the case-control setting and find that, economically, GC is at least comparable to and often less expensive than family-based methods. Therefore, GC methods should prove a useful complement to family-based methods for the genetic analysis of complex traits.

Alleles↗

PubMed2001

Electrovaporization of prostate at power settings below 100 W.

BACKGROUND AND PURPOSE: Prostate electrovaporization has usually been performed at high power settings in the pure cut mode, using traditional electrosurgical generators. However, this practice is empirically based on the fact that a vaporization electrode is larger than a cutting wire loop. The role of the electrosurgical unit (ESU) in prostate electrovaporization has not been studied in detail. METHODS: In this Phase II cohort comparison study, we evaluated two different ESUs, coupled to the most clinically efficient vaporization roller electrode available in our opinion, to determine the lowest panel power settings that permit consistent tissue removal despite the desiccation normally produced during electrovaporization. RESULTS: One of these ESUs, the Excalibur Plus, permitted prostate electrovaporization at panel settings below 100 W for the first time, without compromising satisfactory early clinical outcomes. In a small number of cases, the spiked VaporTrode-Force 2 combination permitted effective electrovaporization at a lower power setting (180 W) than has previously been described when this ESU was coupled with the grooved VaporTrode, regardless of prostate size. During bench tests, a comparison of the actual power output curves in the clinically effective panel power setting range for each ESU revealed that the Force 2 overestimated the actual power output as impedance increased, while the Excalibur Plus underestimated it. This difference may explain why tissue could be vaporized at such low panel settings without the use of computer-controlled technology. CONCLUSION: These findings indicate a potential for improving the safety and efficiency of tissue clearance during prostate electrovaporization through future modifications in monopolar electrode design coupled with use of a generator that can either maintain or slowly increase actual power output as impedance increases at low panel settings. A Phase III clinical study would be justified on the basis of our preliminary results.

Benchmarking↗

PubMed2006

The loss in power when the test of differential expression is performed under a wrong scale.

One of the most common and important goals of microarray studies is to identify genes that are differentially expressed between cells of different conditions. T-test and ANOVA models on the expression data are common practices to gauge the significance of the observed difference in expression levels. Transformation of the microarray data is often applied in order to satisfy the model assumptions being entertained. However, the distributional properties of the expression are gene specific, and it is impractical to find a single transformation that is universally optimal for all the genes. This difficulty results in the situation that some genes have to violate the assumptions of the model (e.g., homogeneity in variance, normality). It is thus the interest of this paper to evaluate the impact on the inference of differential expression when the test is performed under an inappropriate scale. Particularly, we quantitatively assess the loss of power when the test is performed under a wrong scale. Normal distribution and log-normal distribution of the expression data are considered. The loss in power is investigated in two scenarios: a transformation is misused, or a transformation fails to be applied. Log transformation and power transformation are particularly considered due to the fact that Box-Cox types of transformation are commonly used in practice. The impact of using a wrong scale is investigated analytically and based on simulations. The loss in power is assessed both as a function of the degree to which the assumptions are violated and as a function of the effect size. Simulations are conducted to quantitatively assess the power loss when tests are performed under a wrong scale. A public experimental microarray dataset is used to illustrate the impact of transformation on the results of testing differential expression. The results show that the loss of power is a function of CV and fold-change (effect size). The loss in power depends on the true model and on how severely the assumptions are violated.

Databases, Genetic↗

PubMed1997

Longitudinal sleep EEG power spectral analysis studies in adolescents with minor head injury.

Power spectral analysis (PSA) was used to evaluate the longitudinal overnight electroencephalographic (EEG) sleep recordings of eight subjects, between the ages of 15 and 19 years, who had sustained a minor head injury (MHI). Recordings occurred within 72 h, 6 weeks, and 12 weeks following MHI. A conditioning night preceded the first study night during which EEG electrodes were in place and subjects slept at least 7.5 h with a mean sleep efficiency of 91%. PSA was performed on four channels of EEG data recorded from fronto-temporal (F3-T3, F4-T4), and temporal (T3-T5, T4-T6) electrodes. The three waveforms associated with sleep, Delta, Theta, and Alpha-1 were all significantly elevated within 72 h post-MHI. Over time all wave forms decreased in mean log power. Theta in rapid eye movement (REM) sleep Cycle 1 decreased significantly within 6 weeks postinjury. The greatest number of significant changes, over the 12-week period were recorded during the non-REM (NREM) sleep. Changes included (1) significant decreases in mean log power of Theta and Alpha-1 in Cycle 1 from fronto-temporal leads; (2) significant decreases in Delta, Theta, and Alpha-1 in Cycle 2 from fronto-temporal leads, and (3) significant decreases in Delta and Theta for consistency during Cycle 2 from temporal leads. The intrusion of Theta into the first REM cycle within 6 weeks and its subsequent decrease within 6 weeks suggested the initiation of recovery toward baseline values. This was followed by decreased levels of Theta power during NREM Cycles 1 and 2, and Delta power in Cycle 2, both of which approached their lowest levels within 12 wks. The decrease in Alpha-1 power occurred last. Alpha-1 remained elevated through both Cycles 1 and 2 of the 6th week and then showed a precipitous decrease between the sixth and twelfth week. These findings suggested that following MHI, the brain has a specific sequence of recovery as illustrated by Delta, Theta, and Alpha-1 powers requiring different time frames to reach their lowest levels.

Adolescent↗

PubMed1997

Age-associated loss of power and strength in the upper extremities in women and men.

Cross-sectional and longitudinal age-associated reductions in power and isometric strength are described for the upper extremities. Over a 25-year period, repeated measures were taken approximately every 2 years from men and women in the Baltimore Longitudinal Study of Aging (BLSA). The longitudinal measures covered an average 9.6 years, range 1-25 years for men and an average 4.6 years, range 1-8 years for women. Strength and power declined beginning by age 40 in both women and men. Thereafter, power declined about 10% more than strength in men, while no significant differences were found in women. Age had a statistically independent influence on strength and power measures after adjusting for gender, height, weight, caloric expenditure, and muscle mass. Twenty-five-year longitudinal analyses in men confirmed the declines observed cross-sectionally, while no changes were observed in women over the 4-5 years of longitudinal data available. Further longitudinal studies are needed to understand the relationships between strength and power losses with age in women. The differences between power and strength changes with age in men argue for the importance of factors other than strength affecting power.

Adult↗

PubMed2002

Anaerobic power and physical function in strength-trained and non-strength-trained older adults.

BACKGROUND: Challenging daily tasks, such as transferring heavy items or rising from the floor, may be dependent on the ability to generate short bursts of energy anaerobically. The purposes of this study were to determine if strength-trained (ST) older adults have higher anaerobic power output compared with non-strength-trained (NST) older adults and to determine the relationship between anaerobic power and performance-based physical function. METHODS: Thirty-five men and women (age 71.5 +/- 6.4 years, mean +/- SD; NST: n = 18, ST: n = 17) were grouped by training status. Outcome variables included relative anaerobic power (Wingate test), physical function measured with the Continuous Scale Physical Functional Performance Test (CS-PFP, scaled 0 to 100), and anthropometric lean thigh volume (LTV). Analysis of covariance (with age and sex as covariates) was used to determine group differences in the dependent variables listed above. Pearson's r was used to determine the relationship between anaerobic power, CS-PFP total score (TOT), and CS-PFP lower body strength domain score (LBS). RESULTS: The ST group had significantly higher mean anaerobic power (NST 58.9 +/- 16 W/l, ST 96.3 +/- 23 W/l), CS-PFP total (NST 61.2 +/- 13, ST 73.7 +/- 8), and LBS (NST 54.1 +/- 17, ST 70.9 +/- 8) compared with the NST group (p <.05). However, LTV was similar for both groups (NST 3.323 +/- 0.75; ST 3.179 +/- 0.79), which suggests that the ST group had higher muscle quality compared with the NST group. Anaerobic power was significantly related to TOT (r =.611, p =.001) and LBS (r =.650, p =.001). CONCLUSIONS: High levels of physical function in ST older adults may in part be explained by higher levels of anaerobic power associated with strength training.

Aged↗

PubMed2005

Triceps surae muscle power, volume, and quality in older versus younger healthy men.

This study investigated whether loss of power with aging is fully accounted for by a decrease in muscle volume. Triceps surae power and volume (VOL) were measured in 18 older (OM: 69-82 years) and 12 younger men (YM: 19-35 years). Isokinetic peak torque was measured to determine torque-velocity and power-velocity relationships. Both peak power observed (PP(obs)) and peak power estimated from Hill's equation (PP(est)) were markedly reduced in the OM (PP(obs) was 45% and PP(est) was 43% of those of the YM). VOL was 81% of that of the YM (p <.001). Specific power (PP(est)/VOL) of the OM was 55.2% of that of the YM (p <.001). Torque at PP(est) accounted for a greater proportion of the decline in PP(est) in the OM than did optimum velocity (50% vs 13%, respectively). Hence, the present results showed that only approximately half of the loss in triceps surae peak power in old age is due to decreases in muscle VOL.

Adolescent↗

PubMed1991

The EEG as a monitor of midazolam amnesia: changes in power and topography as a function of amnesic state.

In order to identify EEG parameters that might be specific for identifying amnesia during midazolam infusion, we examined changes in the EEG power spectrum associated with a period of amnesia, determined by inability to recall a sequence of numbers and objects presented verbally, after intravenous midazolam 0.07 mg/kg in ten normal volunteers. Measurements were taken at baseline, during infusion immediately before and after the onset of amnesia, immediately at end of infusion, and 0.5 and 1.5 h after infusion. All subjects had onset of amnesia during infusion, were completely amnesic by the end of infusion, partially amnesic 0.5 h after infusion, and had complete recall by 1.5 h after infusion. The EEG beta power increased and alpha power decreased during amnesic periods. The beta 1/alpha power ratio was the parameter most specific for amnesia. From a baseline value of 0.20 +/- 0.05 (standard error of the mean [SEM]), it increased to 0.96 +/- 0.26 at the end of infusion and decreased to 0.61 +/- 0.15 0.5 h after infusion. By 1.5 h after infusion, all EEG parameters had returned to baseline values. Beta power changes associated with midazolam amnesia were most pronounced in the Fz and Cz lead positions, and alpha power changes were most pronounced in the Oz position. We conclude that 1) EEG power values, particularly the beta 1/alpha ratio, can identify periods of amnesia after midazolam infusion; 2) specific EEG changes and the presence of amnesia vary with the probable serum concentration of midazolam; and 3) the characteristic EEG pattern during partial or complete amnesia varies as one moves across the cerebral cortex.

Adult↗

PubMed2001

Muscle power compensatory mechanisms in below-knee amputee gait.

OBJECTIVE: This three-dimensional and bilateral gait study on five below-knee amputees was undertaken to demonstrate the following: (1) how hip muscle powers can compensate for the lack of ankle function on the amputated side; and (2) how these compensatory mechanisms can influence muscle power activities in the sound limb. DESIGN: Gait data were assessed by an eight-camera high-speed video system synchronized to two force plates. The three-dimensional mechanical muscle powers were calculated at the joints of the lower limbs. Significant differences between each limb were determined using the Student's t test for paired data with P < 0.05. RESULTS: In the absence of ankle plantar flexor power, hip extensors and flexors as well as hip external rotators became the major power generators, whereas hip abductors and adductors and knee extensors muscle powers became the main source of absorption. For the sound limb, increased hip extensor activity was observed, accompanied by less hip abduction-adduction activity. CONCLUSIONS: Perturbations in below-knee amputee gait affected the hip muscle powers on the amputated side in all three planes, although the hip frontal plane balance was modified in the sound limb.

Adult↗

PubMed1994

Timing of pressure release affects power of breathing and minute ventilation during airway pressure release ventilation.

OBJECTIVES: To evaluate the effects of interference between spontaneous and mechanical breaths on the power of breathing (rate at which work is done) and ventilatory support during airway pressure release ventilation. DESIGN: Multitrial tests under simulated clinical conditions using a mechanical respiratory system model. SETTING: A research laboratory at a university medical center. INTERVENTIONS: Simulated spontaneous breathing augmented with continuous positive airway pressure and airway pressure release ventilation. Variation in synchrony between spontaneous breathing and mechanical ventilation was accomplished by adjusting the time lag between detection of the spontaneous inspiration and the airway pressure release from 0 to 3 secs in increments of 0.25 secs. MEASUREMENTS AND MAIN RESULTS: Pressures and volumes were measured at the inlet of the lung and chest wall compartment of the respiratory system model. Pressure and volume changes measured at the inlet of the chest wall compartment were used to generate pressure/volume loops and to calculate the power of the spontaneous breathing. Minute ventilation was greater (p < .01) during all airway pressure release ventilation settings compared with those values of continuous positive airway pressure. Nonconflicting airway pressure release ventilation was associated with a higher minute ventilation (p < .001) than asynchronous airway pressure release ventilation. When spontaneous inspiration was synchronous with restoration of continuous positive airway pressure, minute ventilation was lower (p < .001) than during nonconflicting airway pressure release ventilation settings. Power of spontaneous breathing was highest when airway pressure release and spontaneous inspiration coincided, and lowest when spontaneous inspiration and restoration of continuous positive airway pressure were synchronized. Power of breathing was significantly lower during nonconflicting than during asynchronous airway pressure release ventilation (p < .01). No difference was observed between the power of spontaneous breathing and airway pressure release ventilation either with spontaneous expiration synchronized with airway pressure release or with nonconflicting airway pressure release ventilation. When calculated per liter of ventilation, power of spontaneous breathing was significantly lower (p < .01) during all airway pressure release ventilation settings compared with continuous positive airway pressure. CONCLUSION: Asynchronous airway pressure release may increase the power of spontaneous breathing and reduce effective mechanical ventilatory support during airway pressure release ventilation. A clinical study is required to assess the effect of synchronous and asynchronous interference between spontaneous and mechanical breaths during airway pressure release ventilation.

Airway Resistance↗

PubMed1996

Effects of active recovery on plasma lactate and anaerobic power following repeated intensive exercise.

The purpose of this study was to investigate the effects of active recovery (AR) on plasma lactate concentration [La] and anaerobic power output as measured during repeated bouts of intense exercise (6 s) against increasing braking forces. Ten male subjects performed two randomly assigned exercise trials: one with a 5-min passive recovery (PR) after each exercise bout and one with a 5-min active recovery (AR) at a workload corresponding to 32% of maximal aerobic power. Blood samples were taken at rest, at the end of each exercise bout (S1) and at the 5th minute between bout-recovery (S2) for plasma lactate assay. During the tests, [La]S1 was not significantly different after AR and PR, but [La]S2 was significantly lower after AR for power outputs obtained at braking forces 6 kg (5.66 +/- 0.38 vs 7.56 +/- 0.51 mmol.l-1) and peak anaerobic power (PAnP) (6.73 +/- 0.61 vs 8.54 +/- 0.89 mmol.l-1). Power outputs obtained at 2 and 4 kg did not differ after AR and PR. However, when compared with PR, AR induced a significant increase in both power outputs at 6 kg (842 +/- 35 vs 798 +/- 33 W) and PAnP (945 +/- 56 vs 883 +/- 58 W). These results showed that AR between bouts of intensive exercise decreased blood lactate concentration at high braking forces. This decrease was accompanied by higher anaerobic power outputs at these forces.

Adult↗