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PubMed1997

Visualization of tumor vessels in hepatocellular carcinoma. Power Doppler compared with color Doppler and angiography.

PURPOSE: To assess the visualization of tumor vessels in hepatocellular carcinoma (HCC) by power Doppler sonography. MATERIAL AND METHODS: We examined 40 patients with 47 HCC lesions by means of power Doppler sonography and compared its visualization of tumor vessels with those of color Doppler and angiography. RESULTS: In 38 (81%) of the 47 lesions, power Doppler sonography improved the visualization of tumor vessels compared with color Doppler sonography; in the remaining lesions no significant difference was noted. In lesions located within 7 cm in depth, there was no significant difference between power Doppler sonography and angiography. In 10 (83%) out of 12 small (< or = 2 cm in diameter) lesions and in 11 (85%) out of 13 hypovascular lesions, power Doppler sonography performed considerably better than angiography. In deeper-seated lesions, however, angiography was significantly superior to power Doppler sonography. CONCLUSION: Power Doppler sonography is more sensitive in detecting the fine tumor vessels in most HCCs than color Doppler sonography. In addition, power Doppler sonography can replace angiography in evaluating tumor vascularity in HCCs except in lesions that are deep-seated or located near the heart. In these lesions, angiography can complement power Doppler sonography in demonstrating tumor vessels.

Aged↗

PubMed2003

Cycling on rollers: influence of tyre pressure and cross section on power requirements.

The resistance against a cyclist while riding on rollers is due mainly to rolling resistance produced by the deformation of the tyre as it rolls against small diameter drums. Resistance is then combined with wheel speed to set power output. The effect of tyre pressure and cross-section on power was investigated by systematically altering the pressure (552 kPa, 690 kPa, and 827 KPa) in a 20c, 23c, 25c, and 28c tyre of the same design while riding at a wheel speed of 45 kph. Average power over 1 minute was measured with a Power Tap Hub (Tune Corporation, Cambridge, Massachusetts, USA) on five occasions. Statistical significance was evaluated at p < 0.05. Power requirements increased significantly with each reduction in tyre pressure for all tyres and pressures except the 25c between 690 and 827 kPa. The 20c tyre required significantly more power from the cyclist at each tested tyre pressure when compared to the other tyres (which were not different from each other). The differences in resistance from tyre size were not observed when ridden on the road. Additionally, a slightly different tyre design from the same manufacturer responded similarly in the 20c, but was significantly different in the 23c size. It was also observed that power requirements increased significantly when both the wheels were ridden on the rollers as compared to just the rear wheel. These results indicate that the power requirements may be significantly altered by the cyclist by adjusting tyre pressure, tyre cross-section size, tyre type, and with the number of wheels contacting the rollers. However, the magnitude of these power requirements may not be suitable for intense workouts of trained cyclists.

Bicycling↗

PubMed2003

A test to assess the mechanical power sustainable during everyday activities in older people.

OBJECTIVE: to define with a simple test the power sustainable by older people during everyday occupations. METHODS: nine healthy subjects (65-71 years) performed two series of 5-6 trials on bicycle and arm ergometers at constant power. Throughout the exercise they reported their evaluation of the effort, referred either to perceived whole body exertion or to the working muscles, using Borg's category-ratio, CR10, scale. The exercise was interrupted when CR7 was attained. From a linear regression of the individual data of the work done from the start of each trial to the transition from CR4 to CR5, corresponding to 'somewhat heavy' and 'heavy', and the corresponding duration it was possible to calculate the slope of the work/time relationship. This was considered as the value of power sustainable for leg or arm muscles. RESULTS: on average the sustainable power for the work done on the bicycle ergometer represented 55% of the maximal mechanical power. During the control trial on the bicycle ergometer at a power corresponding to their sustainable power the subjects were able to exercise for 30 min without symptoms of fatigue or discomfort, with an average CR of 3. The average heart rate was 114 bpm and the blood lactate concentration at the end of the exercise was always lower than 4 mmol/l. Sustainable power calculated for the arm muscles was about one quarter that of the leg muscles, but all subjects reported the evaluation of the effort as more difficult. CONCLUSION: the determination of power sustainable for the leg muscles with this simple test appears reliable and accurate.

Activities of Daily Living↗

PubMed2006

An interactive power analysis tool for microarray hypothesis testing and generation.

MOTIVATION: Human clinical projects typically require a priori statistical power analyses. Towards this end, we sought to build a flexible and interactive power analysis tool for microarray studies integrated into our public domain HCE 3.5 software package. We then sought to determine if probe set algorithms or organism type strongly influenced power analysis results. RESULTS: The HCE 3.5 power analysis tool was designed to import any pre-existing Affymetrix microarray project, and interactively test the effects of user-defined definitions of alpha (significance), beta (1-power), sample size and effect size. The tool generates a filter for all probe sets or more focused ontology-based subsets, with or without noise filters that can be used to limit analyses of a future project to appropriately powered probe sets. We studied projects from three organisms (Arabidopsis, rat, human), and three probe set algorithms (MAS5.0, RMA, dChip PM/MM). We found large differences in power results based on probe set algorithm selection and noise filters. RMA provided high sensitivity for low numbers of arrays, but this came at a cost of high false positive results (24% false positive in the human project studied). Our data suggest that a priori power calculations are important for both experimental design in hypothesis testing and hypothesis generation, as well as for the selection of optimized data analysis parameters. AVAILABILITY: The Hierarchical Clustering Explorer 3.5 with the interactive power analysis functions is available at www.cs.umd.edu/hcil/hce or www.cnmcresearch.org/bioinformatics. CONTACT: jseo@cnmcresearch.org

Algorithms↗

PubMed2003

Effect of strength and power training on physical function in community-dwelling older adults.

BACKGROUND: The performance of daily tasks, such as stair climbing or lifting an object, requires both muscle strength and power. Age-associated reductions in strength and power can affect an older adult's ability to complete daily tasks such as stair climbing and lifting a child. METHODS: The purposes of this study were to determine whether power training was more efficacious than strength training for improving whole-body physical function in older adults and to examine the relationship between changes in anaerobic power and muscle strength and changes in physical function. Thirty-nine men and women (mean age +/- SD = 72.5 +/- 6.3 years) with below-average leg extensor power were randomly assigned to control (C, n = 15), strength-training (ST, n = 13) or power-training (PT, n = 11) groups. The ST and PT groups met 3 days per week for 16 weeks; the C group maintained usual activity and attended three lectures during the course of the study. Primary outcome measures included the Continuous Scale Physical Functional Performance test, maximal strength, and anaerobic power. RESULTS: After baseline was controlled for, the Continuous Scale Physical Functional Performance test total score was significantly greater for the PT group than for the ST (p =.033) and C (p =.016) groups. Maximal strength was significantly greater for the ST group than for the C group (p =.015) after the intervention. There was no significant difference between groups for peak anaerobic power. CONCLUSIONS: Power training was more effective than strength training for improving physical function in community-dwelling older adults.

Activities of Daily Living↗

PubMedDate not supplied

Sustained skeletal muscle power for cardiac assist devices: implications of metabolic constraints.

A device to harness power from skeletal muscle contracting in a linear configuration is under development. This application requires a sustained level of power that is dependent upon muscle mechanics and metabolic properties. A biomechanical muscle model and a metabolic model constructed from experimental data were used to predict maximum power available in a sustainable region of loading and stimulation conditions. Latissimus dorsi (LD) of four goats were evaluated in vivo after a 10 week in situ conditioning protocol with an implanted Telectronics myostimulator. The LD insertion was reconnected to a hydraulic loading system, allowing isometric and isotonic contractions for biomechanical characterization. Metabolic utilization was measured by a thermister based myothermic technique. Brief fatigue tests of working isotonic contractions revealed stimulation conditions associated with sustained power. The results show metabolic utilization was dependent on contraction duration, rate, force, and stroke. The region of sustainable contractions was found for a range of durations of 0.1 to 0.6 sec and rates of 10 to 120 bpm. The boundary for the sustainable power region was well approximated by a constant value of metabolic utilization. A constant duty cycle (contraction to cycle duration ratio) also approximated the sustained power but differed by as much as 30% during the shorter contraction durations. The results demonstrate that a mechanical muscle model can predict maximum sustained power when the operating conditions are constrained to a sustainable range determined by a metabolic model. Furthermore, metabolic constraints influence the optimum conditions for sustained power needed in the design of skeletal muscle powered assist devices.

Animals↗

PubMed2005

Power Doppler 'blanching' after the application of transducer pressure.

The aim of this study was to determine if transducer pressure modifies power Doppler assessments of rheumatoid arthritis synovium at the metacarpophalangeal joints and metatarsophalangeal joints. Five rheumatoid arthritis patients of varying degrees of 'disease activity' and damage were assessed with power Doppler ultrasound scanning of the dominant hand second to fifth metacarpophalangeal joints. Two rheumatoid arthritis patients had their dominant foot first to fifth metatarsophalangeal joints assessed with power Doppler ultrasound. Ultrasonography was performed with a high frequency transducer (14 MHz) with a colour mode frequency of 10 Mhz, and a standard colour box and gain. In the joint that showed the highest power Doppler signal, an image was made. A further image was taken after transducer pressure was applied. In all patients, there was increased flow to at least one joint. After pressure was applied, power Doppler signal intensity markedly reduced in all images and in some there was no recordable power Doppler signal. Increased transducer pressure can result in a marked reduction or obliteration in power Doppler signal. This power Doppler 'blanching' shows the need for further studies to evaluate sources of error and standardization before power Doppler ultrasound becomes a routine measure of 'disease activity' in rheumatoid arthritis.

Adult↗

PubMedDate not supplied

Sympathetic regulation in rabbits with heart failure: experience using power spectral analysis of heart rate variability.

1. In five intact rabbits beta-adrenoreceptor blockade (i.v. propranolol), and combined cardiac blockade (i.v. propranolol plus i.v. methscopolamine sulphate) revealed that spectral power of heart rate (HR) variability at low frequencies (LF:0.0625-0.1875 Hz) was modulated predominantly by the sympathetic nervous system and power at high frequencies (HF:0.4373-0.5625 Hz) by vagal influences. 2. In 16 rabbits resting power of HR at LF and changes in LF power in response to maximal treadmill exercise were examined prior to and after 4 and 6 weeks of doxorubicin treatment (1 mg/kg twice weekly). 3. The development of doxorubicin-induced congestive heart failure (CHF) was accompanied by a progressive increase in resting LF power [control, 8.5 +/- 2.1; 4 weeks, 13.4 +/- 1.8; 6 weeks, 21.9 +/- 3.5 (beats/min)2, P < 0.005]. 4. Power spectral analysis (PSA) of HR variability in the immediate post-exercise period showed no change from resting values in normal rabbits [5.3 +/- 1.4 vs 8.5 +/- 2.1 (beats/min)2, P > 0.05] whereas CHF rabbits showed falls in LF power after 4 weeks [4.6 +/- 1.0 vs 13.4 +/- 1.8 (beats/min)2, P < 0.005] and 6 weeks [6.5 +/- 2.4 vs 21.9 +/- 3.5 (beats/min)2, P < 0.005] of doxorubicin treatment. 5. It was concluded that PSA of HR variability reflects the autonomic regulation of sinus node function in conscious rabbits. In doxorubicin-treated animals, the rise in LF power reflects increased sympathetic activity as CHF develops. However, the apparent paradoxical fall in LF power with exercise in these animals underscores the need for caution in interpretation of PSA profiles.

Adrenergic beta-Antagonists↗

PubMed1978

Power relationships in families: a social-exchange perspective.

Although researchers have investigated power relationships in families for twenty-five years, conclusions about normative family power patterns have been inconsistent and contradictory. Comparisons across studies have been difficult owing to different definitions of the construct, multiple methodologies, and inconsistent goals. With such confusion, a new, more integrated theoretical approach to the power issue seems warranted, as is suggested by the present paper. The current individual focus on power as a personal attribute can be replaced by a more dynamic, reciprocal, interactive process. Instead of specific or stable power patterns, power interactions should be fluid and time- or situation- specific. No one member would dominate, since power involves a mutual relationship system that changes its content, though not its rules of operation, across decision-making areas. Furthermore, family adjustment would relate to those rules and the family members' reactions to their particular exchange system but not to specific types of power structures. With these considerations, future research should analyze the process, not the content, of power operations in order to maximize the clinical and theoretical utility of its construct.

Adolescent↗

PubMed2001

Comparison between color power Doppler ultrasound with echo-enhancer and spiral computed tomography in the evaluation of hepatocellular carcinoma vascularization before and after ablation procedures.

OBJECTIVE: Use of new echo enhancers capable of passing the lung filter has extended the clinical applications of color power Doppler flow imaging in many diseases and appears promising in the study of neoplasm vascularization. Levovist (Shering, Berlin Germany) is an ultrasound contrast agent containing galactose microbubbles suspended in palmitic oil. The sensitivity of Levovist-enhanced color power Doppler was compared to that of standard color power Doppler and contrast-enhanced spiral computed tomography (CT) in the detection of vascular signals in hepatocellular carcinoma. METHODS: We examined 29 hepatocellular carcinoma nodules in cirrhotic livers that had appeared avascular on unenhanced color power Doppler. Color power Doppler studies were repeated with and without Levovist enhancement before (15 examinations) and/or after (23 examinations) percutaneous ablation procedures. Findings (vascularized vs nonvascularized) were compared to those obtained with contrast-enhanced spiral computed tomography (gold standard) performed no more than 24 h after each of the 38 Doppler examinations. RESULTS: In pretreatment studies, Levovist-enhanced power Doppler correctly revealed vascularization in 12 of 15 lesions that had appeared avascular without echo enhancement and confirmed the avascularity of one other nodule; the remaining two, which appeared avascular on contrast-enhanced Doppler, displayed vascularization on the spiral CT examination. Levovist-enhanced power Doppler was fully concordant with spiral CT findings in all of the posttreatment examinations. CONCLUSION: Considering the absence of false positive results in this study, echo-enhanced color power Doppler can be considered reliable in diagnosing incomplete necrosis of hepatocellular carcinomas after percutaenous ablation. Spiral computed tomography can thus be reserved for those cases in which the enhanced power Doppler examination reveals no evidence of vascularity.

Carcinoma, Hepatocellular↗

PubMed2001

Effect of power Doppler and digital subtraction techniques on the comparison of myocardial contrast echocardiography with SPECT.

OBJECTIVE: To compare the accuracy and feasibility of harmonic power Doppler and digitally subtracted colour coded grey scale imaging for the assessment of perfusion defect severity by single photon emission computed tomography (SPECT) in an unselected group of patients. DESIGN: Cohort study. SETTING: Regional cardiothoracic unit. PATIENTS: 49 patients (mean (SD) age 61 (11) years; 27 women, 22 men) with known or suspected coronary artery disease were studied with simultaneous myocardial contrast echo (MCE) and SPECT after standard dipyridamole stress. MAIN OUTCOME MEASURES: Regional myocardial perfusion by SPECT, performed with (99m)Tc tetrafosmin, scored qualitatively and also quantitated as per cent maximum activity. RESULTS: Normal perfusion was identified by SPECT in 225 of 270 segments (83%). Contrast echo images were interpretable in 92% of patients. The proportion of normal MCE by grey scale, subtracted, and power Doppler techniques were respectively 76%, 74%, and 88% (p < 0.05) at > 80% of maximum counts, compared with 65%, 69%, and 61% at < 60% of maximum counts. For each technique, specificity was lowest in the lateral wall, although power Doppler was the least affected. Grey scale and subtraction techniques were least accurate in the septal wall, but power Doppler showed particular problems in the apex. On a per patient analysis, the sensitivity was 67%, 75%, and 83% for detection of coronary artery disease using grey scale, colour coded, and power Doppler, respectively, with a significant difference between power Doppler and grey scale only (p < 0.05). Specificity was also the highest for power Doppler, at 55%, but not significantly different from subtracted colour coded images. CONCLUSIONS: Myocardial contrast echo using harmonic power Doppler has greater accuracy than with grey scale imaging and digital subtraction. However, power Doppler appears to be less sensitive for mild perfusion defects.

Aged↗

PubMed2004

Output power levels from mobile phones in different geographical areas; implications for exposure assessment.

BACKGROUND: The power level used by the mobile phone is one of the most important factors determining the intensity of the radiofrequency exposure during a call. Mobile phone calls made in areas where base stations are densely situated (normally urban areas) should theoretically on average use lower output power levels than mobile phone calls made in areas with larger distances between base stations (rural areas). AIMS: To analyse the distribution of power levels from mobile phones in four geographical areas with different population densities. METHODS: The output power for all mobile phone calls managed by the GSM operator Telia Mobile was recorded during one week in four defined areas (rural, small urban, suburban, and city area) in Sweden. The recording included output power for the 900 MHz and the 1800 MHz frequency band. RESULTS: In the rural area, the highest power level was used about 50% of the time, while the lowest power was used only 3% of the time. The corresponding numbers for the city area were approximately 25% and 22%. The output power distribution in all defined urban areas was similar. CONCLUSION: In rural areas where base stations are sparse, the output power level used by mobile phones are on average considerably higher than in more densely populated areas. A quantitative assessment of individual exposure to radiofrequency fields is important for epidemiological studies of possible health effects for many reasons. Degree of urbanisation may be an important parameter to consider in the assessment of radiofrequency exposure from mobile phone use.

Cell Phone↗

PubMed1998

Hepatocellular carcinoma: power Doppler US with a contrast agent--preliminary results.

PURPOSE: To investigate the value of contrast material-enhanced power Doppler ultrasonography (US) in the demonstration and characterization of tumor vascularity in hepatocellular carcinoma (HCC). MATERIALS AND METHODS: Twenty patients with HCC were prospectively evaluated with power Doppler US before and after injection of the contrast agent SH U 508 A. The grade and pattern of tumor vascularity at power Doppler US were analyzed, along with the degree of tumor staining at angiography. RESULTS: Intra- and peritumoral flow signals were detected in 19 HCCs (95%) at unenhanced power Doppler US. After injection of contrast agent, flow signals increased in 19 lesions (95%). At contrast-enhanced power Doppler US, two tumors demonstrated grade 1 vascularity; four, grade 2; three, grade 3; and 11, grade 4. At angiography, two tumors demonstrated grade 1 staining; four, grade 2; eight, grade 3; and six, grade 4. The correlation between vascularity grades at contrast-enhanced power Doppler US and at angiography was statistically significant (P < .0001). Seventeen HCCs (85%) showed the intratumoral or basket pattern of vascularity at unenhanced power Doppler US; after injection of contrast material, 15 HCCs (75%) showed the mixed pattern. CONCLUSION: Contrast-enhanced power Doppler US is superior to unenhanced power Doppler US in the demonstration and characterization of tumor vascularity in HCC.

Adult↗

PubMed1996

Force-velocity and force-power properties of single muscle fibers from elite master runners and sedentary men.

Gastrocnemius muscle fiber bundles were obtained by needle biopsy from five middle-aged sedentary men (SED group) and six age-matched endurance-trained master runners (RUN group). A single chemically permeabilized fiber segment was mounted between a force transducer and a position motor, subjected to a series of isotonic contractions at maximal Ca2+ activation (15 degrees C), and subsequently run on a 5% polyacrylamide gel to determine myosin heavy chain composition. The Hill equation was fit to the data obtained for each individual fiber (r2 > or = 0.98). For the SED group, fiber force-velocity parameters varied (P < 0.05) with fiber myosin heavy chain expression as follows: peak force, no differences: peak tension (force/fiber cross-sectional area), type IIx > type IIa > type I; maximal shortening velocity (Vmax, defined as y-intercept of force-velocity relationship), type IIx = type IIa > type I; a/Pzero (where a is a constant with dimensions of force and Pzero is peak isometric force), type IIx > type IIa > type I. Consequently, type IIx fibers produced twice as much peak power as type IIa fibers, whereas type IIa fibers produced about five times more peak power than type I fibers. RUN type I and IIa fibers were smaller in diameter and produced less peak force than SED type I and IIa fibers. The absolute peak power output of RUN type I and IIa fibers was 13 and 27% less, respectively, than peak power of similarly typed SED fibers. However, type I and IIa Vmax and a/Pzero were not different between the SED and RUN groups, and RUN type I and IIa power deficits disappeared after power was normalized for differences in fiber diameter. Thus the reduced absolute peak power output of the type I and IIa fibers from the master runners was a result of the smaller diameter of these fibers and a corresponding reduction in their peak isometric force production. This impairment in absolute peak power production at the single fiber level may be in part responsible for the reduced in vivo power output previously observed for endurance-trained athletes.

Adult↗

PubMed1997

Optimal shortening velocities for in situ power production of rat soleus and plantaris muscles.

Force-velocity (FV) relationships have been used previously to calculate maximal power production and to identify an optimal velocity of shortening (V(opt)-fv) to produce such power in skeletal muscle. The cyclical nature of muscle position during locomotion for muscles such as the soleus and plantaris is such that either constant force or velocity is rarely attained. In the present study, the work loop technique, a technique developed to measure maximal attainable power output from muscles undergoing cyclic length changes, was undertaken to determine whether simulating in vivo function alters the power-velocity relationship of the soleus and plantaris and, in particular, the velocity of shortening that produces maximal power (V(opt)-wl). FV relationships were determined for both soleus (n = 4) and plantaris (n = 4) muscles in situ from adult female Sprague-Dawley rats by measuring shortening velocities during afterloaded isotonic contractions. The velocity that produced maximal power using FV relationships, V(opt)-fv, was 54.6 +/- 0.7 mm/s for the plantaris vs. 20.2 +/- 1.2 mm/s for the soleus. Then, the work loop technique was employed to measure net power from these same muscles at multiple cycling frequencies (1.5 to 4.0 Hz for the soleus; 4.0 to 8.0 Hz for the plantaris). Multiple power-velocity curves were generated (one at each cycle frequency) by varying the strain (1-8 mm). Thus, at each cycle frequency, V(opt)-wl could be identified. For both the plantaris and soleus, V(opt)-wl at each cycle frequency was not different from their respective V(opt)-fv value. Thus both fast and slow skeletal muscles have inherent optimal shortening velocities, identifiable with FV relationships, that dictate their respective maximal attainable mechanical power production using the work loop technique.

Animals↗

PubMed2005

On averaging power for genetic association and linkage studies.

A power calculation is crucial in planning genetic studies. In genetic association studies, the power is often calculated using the expected number of individuals with each genotype calculated from an assumed allele frequency under Hardy-Weinberg equilibrium. Since the allele frequency is often unknown, the number of individuals with each genotype is random and so a power calculation assuming a known allele frequency may be incorrect. Ambrosius et al. recently showed that the power ignoring this randomness may lead to studies with insufficient power and proposed averaging the power due to the randomness. We extend the method of averaging power in two directions. First, for testing association in case-control studies, we use the Cochran-Armitage trend test and find that the time needed for calculating the averaged power is much reduced compared to the chi-square test with two degrees of freedom studied by Ambrosius et al. A real study is used for illustration of the method. Second, we extend the method to linkage analysis, where the number of identical-by-descent alleles shared by siblings is random. The distribution of identical-by-descent numbers depends on the underlying genetic model rather than the allele frequency. The robust test for linkage analysis is also examined using the averaged powers. We also recommend a sensitivity analysis when the true allele frequency or the number of identical-by-descent alleles is unknown.

Case-Control Studies↗

PubMed2003

Effects of loading and size on maximum power output and gait characteristics in geckos.

Stride length, stride frequency and power output are all factors influencing locomotor performance. Here, we first test whether mass-specific power output limits climbing performance in two species of geckos (Hemidactylus garnoti and Gekko gecko) by adding external loads to their bodies. We then test whether body size has a negative effect on mass-specific power output. Finally, we test whether loading affects kinematics in both gecko species. Lizards were induced to run vertically on a smooth wooden surface with loads of 0-200% of body mass (BM) in H. garnoti and 0-100% BM in G. gecko. For each stride, we calculated angular and linear kinematics (e.g. trunk angle, stride length), performance (maximum speed) and mean mass-specific power output per stride. The addition of increasingly large loads caused an initial increase in maximum mass-specific power output in both species, but for H. garnoti, mass-specific power output remained constant at higher loads (150% and 200% BM), even though maximum velocity declined. This result, in combination with the fact that stride frequency showed no evidence of leveling off as speed increased in either species, suggests that power limits maximum speed. In addition, the large gecko (G. gecko) produced significantly less power than the smaller H. garnoti, despite the fact that both species ran at similar speeds. This difference disappeared, however, when we recalculated power output based on higher maximum speeds for unloaded G. gecko moving vertically obtained by other researchers. Finally, the addition of external loads did not affect speed modulation in either species: both G. gecko and H. garnoti increase speed primarily by increasing stride frequency, regardless of loading condition. For a given speed, both species take shorter but more strides with heavier loads, but for a given load, G. gecko attains similar speeds to H. garnoti by taking longer but fewer strides.

Analysis of Variance↗

PubMed1995

The mechanical power output and hydromechanical efficiency of northern pike (Esox lucius) fast-starts

The mechanical power output and hydrodynamic efficiency of northern pike, Esox lucius, during acceleration from rest (fast-start) are calculated from hydrodynamic theory for two kinematic patterns, C-starts (used in escape) and S-starts (used in prey capture). The Weihs model is employed and modified to calculate the mechanical power produced by a fish during a fast-start. A term is included for the power required to accelerate body sections laterally. Lateral deceleration of fish body sections and their associated added mass are expressed as an active process requiring energy expenditure or as a passive process requiring no energy expenditure. In addition, two methods of calculating useful power (the power used to accelerate the virtual mass of the fish, i.e. fish body mass + longitudinal added mass, in the direction of motion), one derived from the Weihs model and the second by summing the changes in kinetic energy of the virtual mass of the fish during a fast-start, are compared and found to give similar estimates of useful power (not significantly different; differences average 22 %). Comparisons of the kinematics and performance of C- and S-starts reveal that C-starts are consistently terminated after two tail flips (stages 1 and 2) whereas S-starts continue for 36 tail flips (stages 36). In addition, acceleration during C-starts is more rapid and velocities are higher (2.32.8 m s-1) than during S-starts (0.81.8 m s-1) over the first 100 ms. However, the peak velocities achieved during S-starts and C-starts are similar over the duration of a fast-start. The superior acceleration rates achieved during the initial stages of a C-start can be explained, in part, by the use of greater maximum angles of attack, higher lateral and perpendicular velocities and larger maximum forces by the caudal fin. Hydrodynamic efficiencies for fast-starts range from 0.16 to 0.39, values that are lower than those observed during either burst-and-coast or steady swimming. Efficiencies are lower for S-starts than for C-starts during the first two tail beats. S-start efficiencies increase with each subsequent tail flip and the maximum efficiencies realised are similar to those achieved during C-starts. Power output during C- and S-starts (449.0 and 394.9 W kg-1 muscle fibre, respectively) approaches the theoretical maximum for vertebrate striated muscle (500 W kg-1). Also, the inferred muscle stress is close to the predicted optimum for maximum power output, at 30 % of the maximum isometric stress recorded for isolated fast muscle fibres. These measurements suggest that fast-start performance is near a physiological limit and is probably constrained by muscle function. The superior acceleration rates achieved by C-starts over S-starts are explained in part by differences in hydrodynamic efficiency, whereas power outputs are similar.

Journal Article↗