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PubMed1999

Lean body mass and leg power best predict bone mineral density in adolescent girls.

PURPOSE: We evaluated anthropometric and performance measures that best predict bone mineral density (BMD) and bone mineral content (BMC) in 54 adolescent girls (14.6 +/- 0.5 yr; 22.7 +/- 14.0 months past menarche). METHODS: Whole body, femoral neck, greater trochanter, lumbar spine (L2-L4), and mid-femoral shaft BMD and BMC, and whole body bone-free lean mass and fat mass were assessed using DXA (Hologic QDR 1000/W). Knee extensor strength and leg power were assessed by isokinetic dynamometry and the Wingate Anaerobic Power Test, respectively. RESULTS: Whole body lean mass was correlated with BMD at all bone sites (r = 0.45-0.77; P < 0.001) and was more highly correlated with bone at all sites than was body weight. Leg power was also associated with BMD at all sites (r = 0.41-0.67; P < 0.001), whereas leg strength correlated significantly with all sites (r = 0.41-0.53; P < 0.001) except the lumbar spine. Stepwise regression analyses revealed that 59% of the variance in whole body BMD was predicted by lean mass alone. No other variables, including fat mass, height, months past menarche, leg power, or leg strength, contributed additionally to the regression model. Similarly, lean mass was the only predictor of lumbar spine and femoral shaft BMD (R2 = 0.25, R2 = 0.37, respectively), while femoral neck and trochanteric BMD were best predicted by leg power (R2 = 0.38, R2 = 0.36, respectively). Similar but stronger models emerged using BMC as the outcome, with lean mass and leg power explaining the most variance in BMC values. CONCLUSION: In this group of adolescent girls, lean body mass and leg power best predicted BMC and BMD of the whole body, lumbar spine, femoral shaft, and hip, which may suggest an important role for muscle mass development during growth to maximize peak bone density.

Absorptiometry, Photon↗

PubMed1999

Racing cyclist power requirements in the 4000-m individual and team pursuits.

PURPOSE: The purpose of this paper is: 1) to present field test data describing the power requirements of internationally competitive individual and team pursuiters, and 2) to develop a theoretical model for pursuit power based upon on these tests. METHODS: In preparing U.S. cycling's pursuit team for the 1996 Atlanta Olympics, U.S. team scientists measured cycling power of seven subjects on the Atlanta track using a crank dynamometer (SRM) at speeds from 57 to 60 kph. By using these field data and other tests, mathematical models were devised which predict both individual and team pursuit performance. The field data indicate the power within a pace line at 60 kph averages 607 W in lead position (100%), 430 W in second position (70.8%), 389 W in third position (64.1%), and 389 W in fourth position (64.0%). A team member requires about 75% of the energy necessary for cyclists riding alone at the same speed. These results compare well with field measurements from a British pursuit team, to recent wind tunnel tests, and to earlier bicycle coast down tests. RESULTS: The theoretical models predict performance with reasonable accuracy when the average power potential of an individual or team is known, or they may be used to estimate the power of pursuit competitors knowing race times. The model estimates that Christopher Boardman averaged about 520 W when setting his 1996, 4000-m individual pursuit record of 4 min 11.114 s and the Italian 4000-m pursuit team averaged about 480 W in setting their record of 4:00.958. Both used the "Superman" cycling position. CONCLUSIONS: These records would be very difficult to break using less aerodynamic riding positions, due to the extraordinarily high power requirements.

Bicycling↗

PubMed2000

Reliability of an air-braked ergometer to record peak power during a maximal cycling test.

PURPOSE: To assess the reliability of the Kingcycle ergometer, this study compared peak power recorded using a Kingcycle and SRMTM power meters during Kingcycle maximal aerobic power tests. METHODS: The study was completed in two parts: for part 1, nine subjects completed three maximal tests with a stabilizing kit attached to the Kingcycle rig and calibration of the Kingcycle checked against SRM (MAP(C)); and for part 2, nine subjects completed two maximal tests without the stabilizing kit and the Kingcycle calibrated using the standard procedure (MAP(S)). Each MAP(C) test was separated by 1 wk; however, MAPs tests were separated by 54 +/- 32 d, (mean +/- SD). Testing procedure was repeated for each MAP and peak power output was calculated as the highest average power output recorded during any 60-s period of the MAP test using the Kingcycle (King(PPO)) and SRM (SRM(PPO)). RESULTS: Coefficient of variations (CVs) for King(PPO) were larger than those of SRM(PPO); 2.0% (95%CI = 1.5-3.0) versus 1.3% (95%CI = 1.0-2.0) and 4.6% (95%CI = 2.7-7.6) versus 3.6% (95%CI = 2.1-6.0) for MAPC( and MAP(S), respectively. During all tests, King(PPO) was higher than SRM(PPO) by an average of approximately 10% (P < 0.001). CONCLUSIONS: Investigators should be aware of the discrepancy between the two systems when assessing peak power and that SRM cranks provide a more reproducible measure of peak power than the Kingcycle ergometer.

Bicycling↗

PubMed2001

Validity of lower extremity strength and power utilizing a new closed chain dynamometer.

PURPOSE: The purpose of this study was to compare selected variables measured on a traditional isokinetic dynamometer (Cybex II) with a new lower extremity, closed chain dynamometer (Omnikinetic, OmK). METHODS: Twelve subjects (6 male, 6 female, age = 28+/-5 yr, mean +/- SD) performed Cybex II knee flexion and extension at 1.05, 3.14, and 5.23 rad x s(-1). A maximal effort of 10 repetitions of lower extremity concentric extension and eccentric flexion at 36% of subject's 1-RM was performed on the OmK. Crank power and joint (ankle, knee, and hip) kinetics were recorded as a mean of 10 repetitions. RESULTS: t-Tests revealed right versus left leg differences (P < 0.05) for Cybex II peak torque flexion at 5.23 rad x s(-1), and OmK knee and hip peak power and hip root mean square power (RMS) power. Cybex peak knee torques were related (Pearson r values 0.78-0.92, P < 0.01) to OmK peak knee torques. Cybex average power was related to OmK knee power (Pearson r values 0.71-0.96, P < 0.01) and OmK crank power (r = 0.62-0.94, P < .01). Correlations tended to be stronger comparing the OmK with the fastest (5.23 rad x s(-1)) Cybex II speed. CONCLUSIONS: These results suggest that the OmK knee and crank kinetic data are comparable to Cybex It isokinetic dynamometry. The ability to evaluate lower extremity joint exercise at a subject's maximal movement speed, in addition to the use of a closed-chain, multi-joint motion, may allow for the OmK to provide a more global evaluation of lower extremity kinetics during seated concentric-extension, eccentric-flexion exercise.

Adult↗

PubMed2002

Pedal trajectory alters maximal single-leg cycling power.

PURPOSE: Muscular power produced during in vitro cyclic contraction has been reported to vary with muscle-length trajectory. The purpose of this study was to determine whether maximal human single-leg cycling power could be similarly altered by manipulating pedal trajectory. METHOD: Seven trained cyclists performed maximal single-leg cycle ergometry. Pedal trajectory was manipulated by repositioning the ergometer drive sprocket off-center with respect to the crank axle, such that the leg-extension phase occupied 42, 50, or 58% of the cycle time (LEP42, LEP50, and LEP58, respectively). RESULTS: Maximum instantaneous power was 12% greater for LEP58 (1984 +/- 143 W) than LEP50 (1838 +/- 126 W), which was 8% greater than that for LEP42 (1645 +/- 112 W). Maximum power, averaged over a complete revolution of the crank, was 4% greater for LEP58 (636 +/- 59 W) than for LEP50 (613 +/- 53 W), which was 18% greater than that for LEP42 (520 +/- 43 W). CONCLUSIONS: These findings, paralleling those for an in vitro model, confirmed our hypothesis that maximal single-leg cycling power could be altered by manipulating pedal trajectory. Alterations in power were likely due to concomitant effects of muscle-shortening velocity, muscle excitation, and biomechanical constraints. Additional research is needed to determine whether greater leg-extension phase ratios can elicit further increases in power and whether similar results can be obtained during bilateral cycling.

Adult↗

PubMed2002

Mixed-methods resistance training increases power and strength of young and older men.

PURPOSE: This study examined the effects of mixed-methods resistance training on young and older men to determine whether similar increases in muscle power were elicited. METHODS: Effects of 10 wk of a periodized resistance-training program designed to increase muscle size, strength, and maximal power on isometric squat strength, time course of force development, muscle fiber characteristics, and muscle activation (iEMG), as well as force and power output during squat jumps, were compared in young (YM, 30 +/- 5 yr, N = 8) and older men (OM, 61 +/- 4 yr, N = 10). RESULTS: Isometric squat strength was higher in the YM compared with OM at all testing occasions and increased over the training period by 23 +/- 15% and 40 +/- 42% for the YM and OM, respectively. The early phase of the force-time curve was shifted upward in both groups over the course of the training. During the squat jumps, the YM produced higher force and power at all test occasions and at all loads tested compared with the OM. The YM increased power output by 15 +/- 14%, 33 +/- 16%, and 26 +/- 12%, and the OM by 7 +/- 5%, 36 +/- 23%, and 25 +/- 16% for the 17 kg, and 30% and 60% 1RM loads, respectively. CONCLUSION: Although the results of this study confirm age-related reductions in muscle strength and power, the older men did demonstrate similar capacity to young men for increases in these variables via an appropriate periodized resistance-training program that includes rapid, high-power exercises.

Adult↗

PubMed1978

Changes in hydrogel contact lens power due to flexure.

When a hydrogel lens is placed on the eye, its power may change because of flexing of the lens. The correcting power of the lens when on the eye can be calculated by assuming that the lens flexes to the shape of the underlying cornea. Actual measurements of the correcting power of Hydrocurve lens on the eye were not in agreement with the calculated values. Assuming that the front and back surfaces of the lens flex by the same amount, the presence of a fluid lens between the hydrogel lens and the cornea would account for this discrepancy. For minus lenses of moderate and high power, it was found that the change in power was in the direction of more plus; for low minus and all plus lenses, the change was in the direction of more minus. Under the conditions of the present investigation, correcting power measured with the lens on the eye was in agreement with the calculated value for regular-thickness Hydrocurve lenses of -2.00 D and thin lenses of -0.75 D. This is interpreted to mean that lenses of these powers conform to the shape of the cornea so that the fluid lens is thin and plano. The clinical implications are discussed.

Contact Lenses, Hydrophilic↗

PubMed1982

Lens weight as a function of density, shape, and power.

An equation to determine the weight of a spherical lens as a function of its density, shape, and power is presented. I found that if center thickness and size are held constant, lens weight increases as the lens power increases in minus or decreases in plus. A way to calculate the power at which two lenses are equal in weight when they differ only in density is also presented. This power is the endpoint of a range of powers above which one of the two lenses is heavier, whereas below this power it is lighter than the other lens. A way to reduce the weight of a lens by altering the surface powers is also suggested.

Eyeglasses↗

PubMed1998

On-eye power characteristics of soft contact lenses.

BACKGROUND: The power of a soft contact lens on the eye is a function of its off-eye power, the manner in which the lens flexes on the eye, lens hydration changes, and the corneal topography. METHODS: In the present study, we used a high illumination keratometer, which allowed us to obtain front and back surface keratometric readings when the lenses were in position on the eye. The on-eye power of the lens could then be calculated from these readings, with the assumption that the center thickness and refractive index of the lens corresponded to those in vitro. RESULTS: The estimates of the on-eye powers agreed closely with the results indicated by over-refraction. Moreover, comparison of in vitro with in vivo power estimates indicated that the positive lenses lost power on-eye, whereas the negative ones maintained their power. CONCLUSIONS: The present study confirms the results of earlier workers, who suggested that soft lenses drape to fit the cornea. Our findings appeared to be in agreement with the predictions of most of the models developed in the past.

Contact Lenses, Hydrophilic↗

PubMed2005

Powered instrumentation and tissue effects in the nose and paranasal sinuses.

PURPOSE OF REVIEW: The technologic cornerstones of endoscopic sinus surgery initially rested on the endoscope and CT scanning. In the mid-1990s, the advent of powered instrumentation, in particular the microdebrider, advanced the surgeon's ability to treat polypoid disease, sinus and nasal disease in a bleeding field, choanal atresia, antral choanal polyps, and inferior turbinate hypertrophy. This review evaluates both positive and negative tissue effects secondary to powered instrumentation. RECENT FINDINGS: Recent reports of deleterious outcomes with powered instrumentation require a reevaluation of the role of powered instrumentation and consideration of factors that lead to injury. The rapidity of injury makes the powered instrument especially dangerous in inexperienced hands. One third of participants in a recent survey were unaware that powered instruments could be involved in orbital injury and half were unaware that cranial injuries could be secondary to powered instrumentation. SUMMARY: Microdebriders will continue to advance the field of endoscopic surgery, providing clearer operative fields and causing less tissue trauma in experienced hands. However, the severity of complications, including the potential for rapidly aspirating orbital and cerebral contents when laminae are violated, must be appreciated and respected.

Debridement↗

PubMed2006

Effect of tilt on the tilted power vector of a thin lens.

PURPOSE: The purpose of this study is to derive the equation for the effect of tilt on the tilted power vector of a possibly astigmatic thin lens. METHODS: The analysis makes use of the equation for tilted power in terms of the dioptric power matrix. RESULTS: A simple equation is obtained for the tilted power vector of a thin lens in terms of the untilted power vector of the lens. A solution of the equation provides a means for compensating spectacle lenses for tilt. Numerical examples are presented in the (available online at www.optvissci.com). CONCLUSIONS: The equation gives insight and is useful for researchers and clinicians working in terms of power expressed as power vectors.

Astigmatism↗

PubMed2003

The theoretical limits to the power output of a muscle-tendon complex with inertial and gravitational loads.

When a muscle delivers power to an inertial load through a spring, the peak power can exceed the maximum that the muscle alone could produce. Using normalized differential equations relating dimensionless quantities we show, by solving the equations either analytically or numerically, that one dimensionless constant (Xi), representing the inertial load, is sufficient to specify the behaviour during shortening of a muscle-tendon complex with linear force-velocity and force-extension properties. In the presence of gravity, an additional constant (Gamma), representing the gravitational acceleration, is required. Nonlinear force-velocity and force-extension relationships each introduce an additional constant, representing their curvature. In the absence of gravity the power output delivered to an inertial load is limited to approximately 1.4 times the maximum power of the muscle alone, and when gravity is present the power delivered is limited to approximately twice the power of muscle alone. These limits are found for the purely inertial load at Xi ca. 1 and with gravity acting at XiGamma = 0.5 with Xi arbitrarily small. The effects of nonlinear muscle and tendon properties tend to cancel each other out and do not produce large deviations from these optima. A lever system of constant ratio between muscle and load does not alter these limits. Cams and catches are required to exceed these limits and attain the high power outputs sometimes observed during explosive animal movement.

Animals↗

PubMed1984

Assimilatory Power (Postillumination CO(2) Uptake) in Leaves: Measurement, Environmental Dependencies, and Kinetic Properties.

Assimilatory power was measured in ten C(3) species by means of a rapid-response gas exchange device as the total amount of CO(2) fixed in N(2)-CO(2) atmosphere after switching the light off. Different steady-state levels of the assimilatory power were obtained by varying light intensity and O(2) and CO(2) concentrations during the preexposition periods in the leaf chamber.Within the limits of the linear part of the CO(2) curve of photosynthesis in N(2), the assimilatory power is constant, being sufficient for the assimilation of about 20 nanomoles CO(2) per square centimeter leaf. The pool starts to decrease with the onset of the CO(2) saturation of photosynthesis. Increase in O(2) concentration from 0 to 100% at 350 microliters CO(2) per liter produces a considerable decrease in the assimilatory power.THE MESOPHYLL CONDUCTANCE (M) WAS FOUND TO BE PROPORTIONAL TO THE ASSIMILATORY POWER (A): M = mA. The most frequently occurring values of the proportionality constant (m) (called the specific efficiency of carboxylation) were concentrated between 0.03 and 0.04 centimeter per second per nanomole A per square centimeter but the measured extreme values were 0.01 and 0.06 centimeter per second per nanomole A per square centimeter. The specific rate of carboxylation (the rate per unit A) showed a hyperbolic dependence on CO(2) conentration with the most frequent values of K(m) (CO(2)) ranging from 25 to 35 micromolar in the liquid phase of mesophyll cells (extremes 23 and 100 micromolar).It is concluded that the CO(2(-) ) and light-saturated rate of photosynthesis is limited by the reactions of the formation of the assimilatory power and not by ribulose-1,5-bisphosphate carboxylase. O(2) is a competitive consumer of the assimilatory power, and the inhibitory effect of O(2) on photosynthesis is caused mainly by a decrease in the pool of the assimilatory power at high O(2) concentrations. In intact leaves, the kinetic properties of ribulose-1,5-bisphosphate carboxylase seem to be variable.

Journal Article↗

PubMed1992

Optimal power deposition with finite-sized, planar hyperthermia applicator arrays.

Improved hyperthermia applicator technology is allowing finer spatial power resolution within the heated tissue volume. Effective utilization of these planar applicator arrays requires an understanding of the interrelationships between the lateral dimensions of the tumor and the applicators, the power field produced by the applicators, the amount of surface cooling, the tumor tissue blood perfusion, and the normal tissue blood perfusion. These interrelationships are investigated using three-dimensional power patterns and temperature fields produced by optimizing the power amplitudes of the individual applicators located within an array of small, but finite, planar applicators. Five major conclusions are obtained. First, optimization works and is effective in determining optimal power fields. Second, for optimal treatments the lateral dimensions of a single superficial applicator need to extend beyond the tumor boundary. Third, surface cooling is needed to reduce the high normal tissue temperatures at shallow depths. Fourth, finer power resolution becomes more important as the tumor size decreases, but, little improvement in the temperature field is achieved beyond a 3 x 3 array configuration. Fifth, increasing the normal blood perfusion rate can decrease the temperature on the tumor boundary if direct power deposition on that boundary is unavailable.

Equipment Design↗

PubMed2006

An improved adaptive power line interference canceller for electrocardiography.

Power line interference may severely corrupt a biomedical recording. Notch filters and adaptive cancellers have been suggested to suppress this interference. We propose an improved adaptive canceller for the reduction of the fundamental power line interference component and harmonics in electrocardiogram (ECG) recordings. The method tracks. the amplitude, phase, and frequency of all the interference components for power line frequency deviations up to about 4 Hz. A comparison is made between the performance of our method, former adaptive cancellers, and a narrow and a wide notch filter in suppressing the fundamental power line interference component. For this purpose a real ECG signal is corrupted by an artificial power line interference signal. The cleaned signal after applying all methods is compared with the original ECG signal. Our improved adaptive canceller shows a signal-to-power-line-interference ratio for the fundamental component up to 30 dB higher than that produced by the other methods. Moreover, our method is also effective for the suppression of the harmonics of the power line interference.

Algorithms↗

PubMed2003

Cyclic and radial variation of the Doppler power from porcine whole blood.

The Doppler power from porcine blood was observed in a mock flow loop to have cyclic and radial variation during a pulsatile cycle. It was found to decrease with shear rate under steady flow, except near the center of the tube at which other mechanisms such as the effects of radial distribution on the rouleaux might be involved. Under pulsatile flow, the timing of the peak of the Doppler power measured at the center of the tube became closer to the peak systole from 20 to 60 beats/minute (BPM), and the power and velocity peaks coincided at 60 BPM. The overall radial variation of the Doppler power during a whole pulsatile cycle was prominent due to the increase of shear rate from the center to 4.5 mm radial position within a tube of 6.35 mm radius. The cyclic variation of the Doppler power varied with the radial position, being relatively large at the center, reaching a minimum at an intermediate radial position, and increasing again near the wall. The peak of the Doppler power occurred at early systole near the tube wall and lagged the flow closer to the center. The "black hole" phenomenon was observed only over portions of the flow cycle. All these complex variations of the Doppler power across the tube over a cycle are thought to be the result of red cell aggregation, which can be affected by shear rate and acceleration.

Acceleration↗

PubMedDate not supplied

Detecting blickets: how young children use information about novel causal powers in categorization and induction.

Three studies explored whether and when children could categorize objects on the basis of a novel underlying causal power. To test this we constructed a "blicket detector," a machine that lit up and played music when certain objects were placed on it. First, 2-, 3- and 4-year-old children saw that an object labeled as a "blicket" would set off the machine. In a categorization task, other objects were demonstrated on the machine. Some set it off and some did not. Children were asked to say which objects were "blickets." In an induction task, other objects were or were not labeled as "blickets." Children had to predict which objects would have the causal power to set off the machine. The causal power could conflict with perceptual properties of the object, such as color and shape. In an association task the object was associated with the machine's lighting up but did not cause it to light up. Even the youngest children sometimes used the causal power to determine the object's name rather than using its perceptual properties and sometimes used the object's name rather than its perceptual properties to predict the object's causal powers. Children rarely categorized the object on the basis of the associated event. Young children also sometimes made interesting memory errors-they incorrectly reported that objects with the same perceptual features had had the same causal power. These studies demonstrate that even very young children will easily and swiftly learn about a new causal power of an object and spontaneously use that information in classifying and naming the object.

Age Factors↗

PubMed1993

EEG spectral power analysis of phasic and tonic REM sleep in young and older male subjects.

EEG spectral power was studied during periods of rapid eye movements (REMs) and tonic intervals in REM sleep of 7 young and 7 older male subjects. Significant symmetrical decreases in alpha and beta1 power at central and occipital sites, concurrent with an increase in frontal theta power, were observed during the production of REMs. The former findings are discussed as sleep analogues to changes in alpha and beta1 during waking, showing increased information processing and behavioural activation, and that of theta is tentatively presented as reflecting an increase in afferent thresholds. Independent of the phasic-tonic REM distinction, total EEG power markedly decreased as a function of time of night and did not interact with age. Significant age differences in the overall spectral composition of the EEG were obtained, namely, a lower level of delta power and a relative shift towards more power in frequencies above 12 Hz for the older group. Further, older subjects also demonstrated a more uniform topographical distribution of alpha and sigma power.

Journal Article↗