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PubMed1992

A test of the maximum-power stimulus theory for strength.

The main purpose was to test the hypothesis that the true force and power in weightlifting were related significantly to the strengthening stimulus. Secondary hypotheses were (a) slower, heavier weight training for strength would increase strength, not maximum power, (b) faster, lighter weight training for maximum power would increase maximum power, not strength and (c) there would be no significant difference between force = mass (F = m) and true force = mass multiplied by acceleration (F = ma) for arm weightlifting. Using an optical encoder, digital recorder and a data-logging computer on an arm weightlifting machine, F = m and F = ma were significantly different between 25% and 94%, contrary to published reports, but not at 100% of strength. A second-order polynomial equation predicted force, F = ma, as a multiple of the weight lifted, from the velocity of the lift with R2 = 0.997. A group was trained for strength and a matched group was trained for maximum power. The strength group gained significantly in maximum power and the power group gained significantly in strength and maximum power. Both groups gained significantly in velocity, but not force, at maximum power. The correlations between strength and maximum power were high (r = 0.95-0.98, P < 0.02), consistent (before and after training) and valid (gain in standard error of estimate of 6 N or 2% of strength). The evidence suggested that maximum power was the strength stimulus. The maximum-power stimulus theory may unify and simplify theories of response and adaptation of structure and function induced by muscle.

Adult↗

PubMed1999

Assessment of aortic pressure power components and their link to overall elastic and resistive arterial properties.

This paper reviews the analytical expressions for in-phase and quadrature aortic power components associated with the real and imaginary parts of aortic input admittance, respectively. It is shown that active power Wact, and its steady, Wstdy, and pulsatile, Wpuls, components logically follow from in-phase power. Reactive power follows from quadrature power only for sinusoidal signals. The definition of reactive power indexes for real aortic pressures and flows requires extreme care. The link between overall arterial properties and pressure power components (and indexes) is investigated, making use of a three-element windkessel model and ascending aortic pressure and flow data taken from eight anaesthetised dogs, under basal state and after treatment with a vasoconstrictor (methoxamine). Seven dogs are normotensive in the baseline state (NBA cases, n = 7), the average (+/- SE) of mean pressure being 86.5 +/- 5.2 mmHg. The eighth dog has a baseline mean pressure of 134 mmHg and is considered to be hypertensive. The two experimental cases from this dog are grouped with those from the other seven dogs after vasoconstriction, to form the NVC + H group (n = 9). On average, fitting the model to the experimental data yields a 100% increase (p < 0.05) in total peripheral resistance, a 63% decrease (p < 0.01) in total arterial compliance and a 10% decrease (p > 0.05) in aortic characteristic impedance, from the NBA group to the NVC + H. Correspondingly, the peak-to-peak amplitude of quadrature power shows a 69% increase (p < 0.02). Wact, Wstdy, and Wpuls show a 28% increase (p > 0.05), a 40% increase (p < 0.02) and a 43% decrease (p > 0.05), respectively. Energetic efficiency of the arterial system, Eart = 1 - (Wpuls/Wact), increases by 8% (p < 0.02). From analysis of the estimates of power components and arterial parameters in relation to low-frequency phase angles of aortic impedance, it is concluded that the decrease in total arterial compliance with increasing pressure reduces the power lost in pulsation. This happens at the expense of an increase in quadrature power and absolute values of related reactive power indexes.

Animals↗

PubMed2004

Shoulder and elbow joint power differ as a general feature of vertical arm movements.

Consistent patterns of joint power underlie coordinated lower extremity behaviors such as running and walking. Recent work found that shoulder and elbow power consistently differed during reaching movements in the horizontal plane. Moreover, joint power during horizontal reaching appears correlated with motor cortical activity. It is not known if the feature of differential joint power extends to vertical plane reaches or to reaches of different movement conditions. The purpose of this study was to test for differential shoulder and elbow power during the acceleratory and deceleratory phases of fast and normal speed vertical reaches in sitting and supine positions. Our results suggest that shoulder and elbow power typically differed both within and across conditions. First, shoulder power values were positive or negative dependent largely on movement direction and movement phase. That is, for each direction and phase, the shoulder either generated or absorbed energy independent of speed or body position. Second, and unexpectedly, reaches of certain condition combinations had similar shoulder power magnitudes across directions. In contrast, elbow power values for each direction varied between positive and negative values depending on phase, speed and position, and no two condition combinations overlapped across directions. Third, as target direction, movement phase and body position varied, shoulder power at fast and normal speeds were linearly correlated, as was shoulder power in sitting and in supine. In contrast, elbow power was linearly correlated only between speeds. These results join other studies to suggest that the neuromotor control of the shoulder may be less complex as compared to the elbow as a general feature of reaching movements. This differential control has important implications for the study of reaching impairments in neurorehabilitation populations, and provides a potentially important variable in the study of cortical firing patterns.

Acceleration↗

PubMed1993

Monitoring airborne dust in a high density coal-fired power station region in North Yorkshire.

Concerns about the levels of dust deposition in the vicinity of coal-fired power stations in North Yorkshire, in particular Drax Power Station, prompted the commissioning of a detailed monitoring study in the area. This paper describes the first two years' work. The first 12-month study concentrated on the village of Barlow close to Drax Power Station, whilst in the second 12-month study, monitoring sites were spread along a transect passing through the power station belt formed by Ferrybridge, Eggborough and Drax Power Stations. Two monitoring sites were common to both 12-month studies, thus giving two years of continuous monitoring. Pairs of wet Frisbee dust deposit gauges (based on inverted Frisbees) were located at each site. Undissolved particulate matter from each gauge was weighed and characterized by microscopic examination of individual particles. The first 12-month study revealed a downward gradient in dust deposition rate and cenosphere content with distance from Drax Power Station. The high cenosphere content at Barlow, especially at the eastern end, suggested that there was a significant contribution from coal-fired power stations. In the second year, the overall pattern of dust deposition rate and cenosphere content across the power station belt suggested that power stations were contributing to higher levels. In particular, relatively high levels were again found at Barlow. Wind direction correlations point to the fly-ash tip next to Drax Power Station as being the source of cenospheres arriving at Barlow. It is concluded that in both years the fly-ash tip Drax Power Station was making a significant contribution to higher than expected dust deposition rates at Barlow, particularly its eastern end. Other villages in the area may also have been affected by dust originating from coal-fired power stations.

Journal Article↗

PubMed2006

Inadequate statistical power of negative clinical trials in urological literature.

PURPOSE: Negative studies provide valuable information. However, conducting studies with inadequate power is unethical and an inefficient use of resources. The purpose of this study was to determine the prevalence of negative studies with inadequate power in urological literature. MATERIALS AND METHODS: The Journal of Urology, Urology and BJU International (formerly British Journal of Urology) from 1982 to 2002 were searched using the Ovid MEDLINE database. All clinical trials that contained the phrase "no difference" were identified. Data necessary for power calculation were extracted from applicable studies. RESULTS: Of the 417 articles identified in the MEDLINE search, 127 were negative studies that contained enough information to be analyzed. There were 70 (55%) articles from The Journal of Urology, 35 (28%) from BJU International and 22 (17%) from Urology. Of the studies that used continuous variables 65% had adequate power (greater than 80%) to detect a 50% difference between groups and 32% had adequate power to detect a 25% difference. Of the studies that used dichotomous variables only 33% had adequate power to detect a 50% difference between groups and 23% had adequate power to detect a 25% difference. Levels of adequate power in negative studies did not improve over time (p = 0.258). CONCLUSIONS: Many negative studies in urological literature are inconclusive because they lack adequate power to detect even large differences between groups. Inadequately powered studies often result in false conclusions that alter clinical behavior and deter further research. Therefore, it is imperative to consider power when interpreting literature. When designing future investigations power calculations should be performed to ensure sufficient patient recruitment to attain clinically meaningful results.

Bibliometrics↗

PubMed2001

Power vector analysis of the optical outcome of refractive surgery.

PURPOSE: To demonstrate the power vector method of representing and analyzing spherocylindrical refractive errors. SETTING: School of Optometry, Indiana University, Bloomington, Indiana, USA. METHODS: Manifest and keratometric refractive errors were expressed as power vectors suitable for plotting as points in a 3-dimensional dioptric space. The 3 Cartesian coordinates (x, y, z) of each power vector correspond to the powers of 3 lenses that, in combination, fulfill a refractive prescription: a spherical lens of power M, a Jackson crossed cylinder of power J0 with axes at 90 degrees and 180 degrees, and a Jackson crossed cylinder of power J45 with axes at 45 degrees and 135 degrees. The Pythagorean length of the power vector, B, is a measure of overall blurring strength of a spherocylindrical lens or refractive error. Changes in refractive error due to surgery were computed by the ordinary rules of vector subtraction. RESULTS: Frequency distributions of blur strength (B) clearly demonstrate the effectiveness of refractive surgery in reducing the overall blurring effect of uncorrected refractive error. CONCLUSIONS: Power vector analysis also revealed a reduction in the astigmatic component of these refractive errors. Paired comparisons revealed that the change in manifest astigmatism due to surgery was well correlated with the change in keratometric astigmatism. Power vectors aid the visualization of complex changes in refractive error by tracing a trajectory in a uniform dioptric space. The Cartesian components of a power vector are mutually independent, which simplifies mathematical and statistical analysis of refractive errors. Power vectors also provide a natural link to a more comprehensive optical description of ocular refractive imperfections in terms of wavefront aberration functions and their description by Zernike polynomials.

Astigmatism↗

PubMed2003

Counter intuitive relations between in vivo RF lesion size, power, and tip temperature.

BACKGROUND: Radiofrequency (RF) lesion size in vitro is positively correlated with applied power and catheter tip temperature. However, the relation between RF lesion size, power, and tip temperature in vivo remains unclear. We hypothesized that due to flow, anatomy and tip contact effects in vivo, increased tip temperature would be inversely related to applied power and RF lesion size. METHODS: RF lesions were created on the endocardium of 16 pigs using 5, 6, and 7 Fr catheters. The ablation generator was set to achieve a temperature of 70 degrees C. RF lesions were created in different regions of the heart so as to encompass a wide range of blood flow and catheter movement conditions. RF lesions were measured acutely (DIMEN, mm) and correlated with average power applied (POWER, W), and average tip temperature (TEMP, degrees C). The POWER and TEMP relation was also examined. RESULT: For TEMPs below 55 degrees C, the power output from the generator was typically maximized at 50 W. At TEMPs above 55 degrees C, POWER decreased exponentially with increasing TEMP (POWER = 50 - exp(-((41-TEMP)/7)), r = 0.98, p < 0.05). Further, DIMEN tended to be inversely related to TEMP (Slope: -0.07 +/- 0.04, r = -0.15, p = 0.07); but, was positively related to POWER (Slope: 0.04 +/- 0.02, r = 0.23, p < 0.05). These relations varied by tip size and estimated local blood flow characteristics. CONCLUSION: In vivo, variable tissue contact and flow yield DIMEN-POWER-TEMP relations opposite to those found in vitro. These counterintuitive results suggest that maximum in vivo RF lesion size is achieved when power is maximized at tip temperatures between 50 and 60 degrees C.

Animals↗

PubMed1992

Anaerobic and aerobic power in arms and legs of elite senior wrestlers.

UNLABELLED: The purpose of this study was to characterize anaerobic power and aerobic power (power at peak oxygen uptake, or peak VO2) of elite senior (post-collegiate) wrestlers. Subjects (n = 14) from the U.S. national senior freestyle and Greco Roman wrestling teams were evaluated at separate tests using cycle ergometry for peak VO2 of the arms, peak VO2 of the legs, arm anaerobic peak power, and leg anaerobic peak power. Power output at peak VO2 was recorded for each test and compared to the anaerobic power of the appropriate body segment. The results (mean +/- SD) showed that wrestlers produced 2.3 +/- 0.4 W.kg body weight-1 at arm peak VO2 (43.7 +/- 4.6 ml.kg body weight-1. min-1), 4.2 +/- 0.5 W.kg body weight-1 at leg peak VO2 (50.9 +/- 5.1 ml.kg body weight-1.min-1), arm PP of 7.7 +/- 1.0 W.kg body weight-1, and leg PP of 10.5 +/- 1.7 W.kg body weight-1. Comparing power output during anaerobic and aerobic tests, the subjects performed at 3.4 +/- 0.6 times their peak oxygen uptake during arm anaerobic ergometry, whereas leg anaerobic peak power was 2.7 +/- 0.4 times the power at peak oxygen uptake for the legs (p < 0.05 for difference between ratios). CONCLUSION: relative to aerobic power, elite senior wrestlers may produce power anaerobically in the upper body at significantly higher levels than in the lower body.

Adult↗

PubMedDate not supplied

Electromagnetic thermal therapy power optimization for multiple source applicators.

The optimization of power deposition for electromagnetic (EM) thermal therapy is investigated. Several goal or objective functions are examined using a generalized mathematical formulation. These include maximization of: (1) target power absorption, (2) the ratio of target to non-target power absorption, (3) target power absorption weighted by the ratio of target to non-target power absorption, and (4) target power absorption subject to the constraint that the non-target high power volume ('hot spot' volume) is below a chosen level. The merit of these functions was retrospectively tested using an anatomic data base containing 38 cancer patients that were clinically heated with EM phased arrays. CT and/or MRI image data were used to define relevant anatomic geometries and tissue properties for finite element numerical models. Power optimization is achieved by variation of seven available control parameters (four amplitudes and three phases) for these clinical array devices. The results indicate that site dependent improvements in target power absorption can be achieved using these goal functions relative to a configuration that utilizes equal phase and amplitude for the sources. The relative merit among these various functions favours an optimization strategy that maximizes the target power absorption weighted by the ratio of target power to non-target power absorption.

Biophysical Phenomena↗

PubMed2006

Lower extremity strength and power are associated with 400-meter walk time in older adults: The InCHIANTI study.

BACKGROUND: It has been suggested that lower extremity muscle power is more important for physical function in older adults compared to strength, and that there is a nonlinear relationship between power or strength and physical function that might be indicative of a threshold above which the association between muscle function and physical function is no longer evident. This study examined the association between lower extremity strength or power with the time to complete a 400-meter walk, and attempted to identify thresholds within the relationship. METHODS: A cross-sectional analysis of a sample of 384 females and 336 males aged > or = 65 years from the InCHIANTI study ("Invecchiare in Chianti," i.e., Aging in the Chianti Area) was conducted. Measures included 400-meter walk time, lower extremity strength and power, comorbidities, and sociodemographic variables (age, gender, height, education, cognitive function, depression). RESULTS: Linear regression models showed that both lower extremity strength and power were significant predictors of 400-meter walk time, although power explained marginally more of the variance in 400-meter walk time. Quadratic models of lower extremity strength and power fit the data slightly better than the linear models. Regardless of gender, comorbidities, or normalization scheme for strength and power, the curvilinear form of the relationship between strength or power and 400-meter walk time remained the same. CONCLUSIONS: Lower extremity muscle strength and power are both important predictors of the 400-meter walk time. Although curvilinear relationships existed between muscle strength and power and the 400-meter walk time, the data do not indicate a clear threshold for either strength or power above which the performance in the 400-meter walk test plateaus.

Aged↗

PubMed1996

A new method for the calculation of constant supra-VO2peak power outputs.

This investigation compared the variance in times to exhaustion among four different methods of supra-VO2peak power output calculation. Ten male subjects cycled to exhaustion at power outputs equivalent to 1) 120% VO2peak, 2) 6 W.kg-1, 3) 100% VO2peak + 10% of the peak anaerobic scope (PAS), and 4) 100% VO2peak + 20% of the mean anaerobic scope (MAS). PAS was defined as the difference between the peak power output (PPO) during a 30-s all-out cycle sprint and the power output at VO2peak MAS was defined as the difference between the mean power output (MPO) during a 30-s all-out cycle sprint and the power output at VO2peak. While the mean times to exhaustion for the four methods were not significantly different, the supra-VO2peak power output calculated as 120% VO2peak resulted in significantly more variance (P = 0.0173) in the times to exhaustion than did the power output equivalent to 20% MAS + 100% VO2peak (SE 16.2 s vs 6.9 s). The variance in time to exhaustion was significantly higher with the power output of 6 W.kg-1 than for the remaining three methods, while the variance in times to exhaustion at a power output of 10% PAS + 100% VO2peak was not significantly different from either 120% VO2peak or 20% MAS + 100% VO2peak. These results indicate that a supra-VO2peak power output that accounts for both aerobic ability and anaerobic work capacity (20% MAS + 100% VO2peak) results in less variance in time to exhaustion than a method which extrapolates the submaximal power output-VO2 relationship to a supramaximal intensity (120% VO2peak).

Adolescent↗

PubMed2000

Inertial effects on mechanically braked Wingate power calculations.

PURPOSE: The standard procedure for determining subject power output from a 30-s Wingate test on a mechanically braked (friction-loaded) ergometer includes only the braking resistance and flywheel velocity in the computations. However, the inertial effects associated with accelerating and decelerating the crank and flywheel also require energy and, therefore, represent a component of the subject's power output. The present study was designed to determine the effects of drive-system inertia on power output calculations. METHODS: Twenty-eight male recreational cyclists completed Wingate tests on a Monark 324E mechanically braked ergometer (resistance: 8.5% body mass (BM), starting cadence: 60 rpm). Power outputs were then compared using both standard (without inertial contribution) and corrected methods (with inertial contribution) of calculating power output. RESULTS: Relative 5-s peak power and 30-s average power for the corrected method (14.8 +/- 1.2 W x kg(-1) BM; 9.9 +/- 0.7 W x kg(-1) BM) were 20.3% and 3.1% greater than that of the standard method (12.3 +/- 0.7 W x kg(-1) BM; 9.6 +/- 0.7 W x kg(-1) BM), respectively. Relative 5-s minimum power for the corrected method (6.8 +/- 0.7 W x kg(-1) BM) was 6.8% less than that of the standard method (7.3 +/- 0.8 W x kg(-1) BM). The combined differences in the peak power and minimum power produced a fatigue index for the corrected method (54 +/- 5%) that was 31.7% greater than that of the standard method (41 +/- 6%). All parameter differences were significant (P < 0.01). The inertial contribution to power output was dominated by the flywheel; however, the contribution from the crank was evident. CONCLUSIONS: These results indicate that the inertial components of the ergometer drive system influence the power output characteristics, requiring care when computing, interpreting, and comparing Wingate results, particularly among different ergometer designs and test protocols.

Adult↗

PubMed1995

Calculation of stopping-power ratios using realistic clinical electron beams.

The Spencer-Attix water/air restricted mass collision stopping-power ratio is calculated in realistic electron beams in the energy range from 5-50 MeV for a variety of clinical accelerators including the Varian Clinac 2100C, the Philips SL75-20, the Siemens KD2, the AECL Therac 20, and the Scanditronix Medical Microtron 50. The realistic clinical beams are obtained from full Monte Carlo simulations of the clinical linear accelerators using the code BEAM. The stopping-power ratios calculated using clinical beams are compared with those determined according to the AAPM and the IAEA protocols which were calculated by using monoenergetic parallel beams. Using the energy-range relationship of Rogers and Bielajew [Med. Phys. 13, 687-694 (1986)] leads to the most consistent picture in which the stopping-power ratios at dmax derived from mono-energetic calculations underestimate the stopping-power ratios calculated with the realistic beam by 0.3% at 5 MeV and up to 1.4% at 20 MeV. The stopping-power ratios at dmax determined according to the AAPM TG-21 protocol (1983) are shown to overestimate the realistic stopping-power ratios by up to 0.6% for a 5-MeV beam and underestimate them by up to 1.2% for a 20-MeV beam. Those determined according to the IAEA (1987) protocol overestimate the realistic stopping-power ratios by up to 0.3% for a 5-MeV beam and underestimate them by up to a 1.1% for a 20-MeV beam at reference depth. The causes of the differences in the stopping-power ratios between the realistic clinical mono-energetic beams are analyzed quantitatively. The changes in the stopping-power ratios at dmax are mainly due to the energy spread of the electron beam and the contaminant photons in the clinical beams. The effect of the angular spread of electrons is rather small except at the surface. Data are presented which give the corrected stopping-power ratios at dmax or reference depth starting from those determined according to protocols for any energy of clinical electron beams with scattering foils. For scanned clinical electron beams the correction to stopping-power ratios determined according to protocols is found to be less than 0.5% at dmax or reference depth for all beam energies studied. We quantify the differences in the stopping-power ratios determined using the depth of 50% ionization level and the depth of 50% dose level. The differences are very small except for very-high-energy beams (50 MeV) where they can be up to 0.8%.

Electrons↗

PubMed1992

Power-afterload relation in the failing human ventricle.

Animal studies have shown that the power output of the left ventricle is related to afterload by a bell-shaped curve. Furthermore, the normal ventricle operates at the maximum power point, whereas the diseased ventricle operates off the maximum power point because of increased afterload. We studied this relation in eight patients with dilated cardiomyopathy. A high-fidelity catheter with micromanometer pressure and electromagnetic velocity transducers was used to measure blood pressure and flow velocity in the ascending aorta. The latter was converted into volumetric flow by calibrating with the simultaneously determined thermodilution cardiac output. Ventricular power was calculated by dividing the integral of the aortic blood pressure-flow product by the duration of the cardiac cycle. Intravenous nitroprusside was used to alter afterload and the power-afterload relation was obtained by plotting power against mean aortic blood pressure. In all patients, as blood pressure was lowered initially, the power output of the left ventricle increased. As the dose of nitroprusside was increased further, the total power either plateaued or actually decreased. The averaged power and the mean blood pressure at control were 1.00 +/- 0.62 W and 92 +/- 9.3 mm Hg, respectively. The averaged maximum increase in power with nitroprusside was 22%, to 1.22 +/- 0.73 W, and this occurred at a mean pressure of 80 +/- 8.8 mm Hg. This study showed that the power-afterload relation in the human ventricle has a maximum power point at some intermediate level of afterload, similar to that found in animal studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2000

The influence of temperature on power production during swimming. II. Mechanics of red muscle fibres in vivo.

We found previously that scup (Stenotomus chrysops) reduce neither their stimulation duration nor their tail-beat frequency to compensate for the slow relaxation rates of their muscles at low swimming temperatures. To assess the impact of this 'lack of compensation' on power generation during swimming, we drove red muscle bundles under their in vivo conditions and measured the resulting power output. Although these in vivo conditions were near the optimal conditions for much of the muscle at 20 degrees C, they were far from optimal at 10 degrees C. Accordingly, in vivo power output was extremely low at 10 degrees C. Although at 30 cm s(-)(1), muscles from all regions of the fish generated positive work, at 40 and 50 cm s(-)(1), only the POST region (70 % total length) generated positive work, and that level was low. This led to a Q(10) of 4-14 in the POST region (depending on swimming speed), and extremely high or indeterminate Q(10) values (if power at 10 degrees C is zero or negative, Q(10) is indeterminate) for the other regions while swimming at 40 or 50 cm s(-)(1). To assess whether errors in measurement of the in vivo conditions could cause artificially reduced power measurements at 10 degrees C, we drove muscle bundles through a series of conditions in which the stimulation duration was shortened and other parameters were made closer to optimal. This sensitivity analysis revealed that the low power output could not be explained by realistic levels of systematic or random error. By integrating the muscle power output over the fish's mass and comparing it with power requirements for swimming, we conclude that, although the fish could swim at 30 cm s(-)(1) with the red muscle alone, it is very unlikely that it could do so at 40 and 50 cm s(-)(1), thus raising the question of how the fish powers swimming at these speeds. By integrating in vivo pink muscle power output along the length of the fish, we obtained the surprising finding that, at 50 cm s(-)(1), the pink muscle (despite having one-third the mass) contributes six times more power to swimming than does the red muscle. Thus, in scup, pink muscle is crucial for powering swimming at low temperatures. This overall analysis shows that Q(10) values determined in experiments on isolated tissue under arbitrarily selected conditions can be very different from Q(10) values in vivo, and therefore that predicting whole-animal performance from these isolated tissue experiments may lead to qualitatively incorrect conclusions. To make a meaningful assessment of the effects of temperature on muscle and locomotory performance, muscle performance must be studied under the conditions at which the muscle operates in vivo.

Animals↗

PubMed2001

The influence of thermal acclimation on power production during swimming. II. Mechanics of scup red muscle under in vivo conditions.

We have previously shown that the power output of red muscle from warm-acclimated scup is greatly reduced when the fish swim at low temperatures. This reduction occurs primarily because, despite the slowing of muscle relaxation rate at cold temperatures, warm-acclimated scup swim with the same tail-beat frequency and the same stimulation durations, thereby not affording the slower-relaxing muscle any extra time to relax. We hypothesize that power output during swimming could be increased if the stimulus duration were reduced or if the relaxation rate of the red muscle were increased during cold acclimation. Scup were acclimated to 10 degrees C (cold-acclimated) and 20 degrees C (warm-acclimated) for at least 6 weeks. Cold acclimation dramatically increased the ability of scup red muscle to produce power at 10 degrees C. Power output measured from cold-acclimated muscle bundles driven through in vivo conditions measured from cold-acclimated scup swimming at 10 degrees C (i.e. work loops) was generally much greater than that from warm-acclimated muscle driven through its respective in vivo conditions at 10 degrees C. The magnitude of the increase depended both on the anatomical location of the muscle and on swimming speed. Integrated over the length of the fish, the red musculature from cold-acclimated fish generated 2.7, 8.9 and 5.8 times more power than the red musculature from warm-acclimated fish while swimming at 30 cm s(-)(1), 40 cm s(-)(1) and 50 cm s(-)(1), respectively. Our analysis suggests that the cold-acclimated fish should be able to swim in excess of 40 cm s(-)(1) with just their red muscle whereas the warm-acclimated fish must recruit their pink muscle well below this speed. Because the red muscle is more aerobic than the pink muscle, cold acclimation may increase the sustained swimming speed at which scup perform their long seasonal migrations at cool temperatures. We then explored the underlying mechanisms for the increase in muscle power output in cold-acclimated fish. Contrary to our expectations, cold-acclimated muscle did not have a faster relaxation rate; instead, it had an approximately 50 % faster activation rate. Our work-loop studies showed that this faster activation rate, alone, can increase the mechanical power production during cyclical contractions to a surprising extent. By driving cold-acclimated muscle through warm- and cold-acclimated in vivo conditions, we were able to partition the improvement in power production associated with increased activation rate and the approximately 20 % reduction in the duration of electromyographic activity found in the accompanying study. Depending on the position and swimming speed, approximately 60 % of the increase in power output was due to the change in the red muscle's contractile properties (i.e. faster activation); the remainder was due to the shorter stimulus duty cycle of cold-acclimated scup. Thus, by both shortening the in vivo stimulation duration and speeding up the rate of muscle activation as part of cold-acclimation, scup achieve a very large increase in the power output of their red muscle during swimming at low temperature. This increase in power output probably results in an increase in muscle efficiency and, hence, a reduction in the energetic cost of swimming. This increase in power output also reduces reliance on the less aerobic and less fatigue-resistant pink muscle. Both these abilities may increase the swimming speed at which prolonged aerobic muscle activity can occur and thus reduce the travel time for the long seasonal migrations in which scup engage.

Adaptation, Physiological↗

PubMed2002

Mechanical power output during running accelerations in wild turkeys.

We tested the hypothesis that the hindlimb muscles of wild turkeys (Meleagris gallopavo) can produce maximal power during running accelerations. The mechanical power developed during single running steps was calculated from force-plate and high-speed video measurements as turkeys accelerated over a trackway. Steady-speed running steps and accelerations were compared to determine how turkeys alter their running mechanics from a low-power to a high-power gait. During maximal accelerations, turkeys eliminated two features of running mechanics that are characteristic of steady-speed running: (i) they produced purely propulsive horizontal ground reaction forces, with no braking forces, and (ii) they produced purely positive work during stance, with no decrease in the mechanical energy of the body during the step. The braking and propulsive forces ordinarily developed during steady-speed running are important for balance because they align the ground reaction force vector with the center of mass. Increases in acceleration in turkeys correlated with decreases in the angle of limb protraction at toe-down and increases in the angle of limb retraction at toe-off. These kinematic changes allow turkeys to maintain the alignment of the center of mass and ground reaction force vector during accelerations when large propulsive forces result in a forward-directed ground reaction force. During the highest accelerations, turkeys produced exclusively positive mechanical power. The measured power output during acceleration divided by the total hindlimb muscle mass yielded estimates of peak instantaneous power output in excess of 400 W kg(-1) hindlimb muscle mass. This value exceeds estimates of peak instantaneous power output of turkey muscle fibers. The mean power developed during the entire stance phase increased from approximately zero during steady-speed runs to more than 150 W kg(-1) muscle during the highest accelerations. The high power outputs observed during accelerations suggest that elastic energy storage and recovery may redistribute muscle power during acceleration. Elastic mechanisms may expand the functional range of muscle contractile elements in running animals by allowing muscles to vary their mechanical function from force-producing struts during steady-speed running to power-producing motors during acceleration.

Acceleration↗

PubMed2003

Acute negative effect of a hypertrophy-oriented training bout on subsequent upper-body power output.

Athletes regularly combine maximal strength, power, and hypertrophy-oriented training within the same workout. Traditionally, it has been suggested that power-oriented exercises precede strength and hypertrophy-oriented training within a workout to avoid the possible negative effects that the latter types of training may have on power output. However, with regard to upper-body training, little study has been performed to verify this commonly held belief. The purpose of this study was to determine the extent, if any, of a high-repetition, short-rest-period, hypertrophy-oriented training dose on upper-body power output. Twenty-seven college-aged rugby league players were tested for average power output during bench press throws with a resistance of 40 kg (BT P40). The experimental group (Hyp, n = 15) then performed a typical hypertrophy-oriented work bout (3 x 10 at 65% 1 repetition maximum bench press, 1RM BP) before being retested for power output with the same resistance. In comparison with the control group (Con, n = 12), whose power output remained unchanged between the pre- and posttest periods, the Hyp group experienced a large, significant decrease in BT P40 power output. Even after further passive rest of 7 minutes, power output remained suppressed from the pretest values. Furthermore, the strongest 5 subjects experienced significantly larger percentage declines in power output than did the 5 less strong subjects. This study shows that a high-repetition, short-rest-period training can acutely decrease power output. Coaches should plan the order of exercises carefully when combining power and hypertrophy training.

Adolescent↗