scholarly journals Sustained force development: specializations and variation among the vertebrates

1985 ◽  
Vol 115 (1) ◽  
pp. 239-251 ◽  
Author(s):  
I. A. Johnston
Keyword(s):  
Aerobic Capacity ◽  
Power Output ◽  
Significant Proportion ◽  
Force Production ◽  
Membrane Properties ◽  
Energy Requirements ◽  
Motor Endplates ◽  
Force Development ◽  
Contraction Speed ◽  
Mechanical Power Output

The kinds of muscle fibre that are recruited for sustained force production by different vertebrates are described. Although aerobic metabolism always accounts for a significant proportion of their ATP turnover, no single characteristic such as colour, number and form of motor endplates, membrane properties, myosin isotype or contraction speed is diagnostic of such muscles. As mechanical power output increases, there is a tendency for a decrease in fatigue resistance with repetitive usage and an increase in both aerobic capacity and the fraction of energy requirements derived from glycolysis.

scholarly journals The changes in power requirements and muscle efficiency during elevated force production in the fruit fly Drosophila melanogaster.

1997 ◽  
Vol 200 (7) ◽  
pp. 1133-1143 ◽  
Author(s):  
F O Lehmann ◽  
M H Dickinson
Keyword(s):  
Drosophila Melanogaster ◽  
Power Output ◽  
Force Production ◽  
Fruit Fly ◽  
Reynolds Numbers ◽  
Power Input ◽  
Mechanical Power ◽  
Total Power ◽  
Mechanical Power Output ◽  
The Cost

The limits of flight performance have been estimated in tethered Drosophila melanogaster by modulating power requirements in a 'virtual reality' flight arena. At peak capacity, the flight muscles can sustain a mechanical power output of nearly 80 W kg-1 muscle mass at 24 degrees C, which is sufficient to generate forces of approximately 150% of the animal's weight. The increase in flight force above that required to support body weight is accompanied by a rise in wing velocity, brought about by an increase in stroke amplitude and a decrease in stroke frequency. Inertial costs, although greater than either profile or induced power, would be minimal with even modest amounts of elastic storage, and total mechanical power energy should be equivalent to aerodynamic power alone. Because of the large profile drag expected at low Reynolds numbers, the profile power was approximately twice the induced power at all levels of force generation. Thus, it is the cost of overcoming drag, and not the production of lift, that is the primary requirement for flight in Drosophila melanogaster. By comparing the estimated mechanical power output with respirometrically measured total power input, we determined that muscle efficiency rises with increasing force production to a maximum of 10%. This change in efficiency may reflect either increased crossbridge activation or a favorable strain regime during the production of peak forces.

Hummingbird hovering performance in hyperoxic heliox: effects of body mass and sex.

1996 ◽  
Vol 199 (12) ◽  
pp. 2745-2755 ◽  
Author(s):  
P Chai ◽  
R Harrykissoon ◽  
R Dudley
Keyword(s):  
Power Output ◽  
Aerodynamic Force ◽  
Force Production ◽  
Power Input ◽  
Flight Mechanics ◽  
Flight Performance ◽  
Metabolic Power ◽  
Significant Extent ◽  
Mechanical Power Output ◽  
Stroke Amplitude

Owing to their small size and hovering locomotion, hummingbirds are the most aerobically active vertebrate endotherms. Can hyperoxia enhance the flight performance of this highly oxygen-dependent group? Hovering performance of ruby-throated hummingbirds (Archilochus colubris) was manipulated non-invasively using hyperoxic but hypodense gas mixtures of sea-level air combined with heliox containing 35% O2. This manipulation sheds light on the interplay among metabolic power input, mechanical power output and aerodynamic force production in limiting flight performance. No significant differences in flight mechanics and oxygen consumption were identified between hyperoxic and normoxic conditions. Thus, at least in the present experimental context, hyperoxia did not change the major metabolic and mechanical parameters; O2 diffusive capacities of the respiratory system were probably not limiting to a significant extent. Compared with hummingbirds in our previous studies, the present experimental birds were heavier, had resultant shorter hover-feeding durations and experienced aerodynamic failure at higher air densities. Because hummingbirds have relatively stable wingbeat frequencies, modulation of power output was attained primarily through variation in stroke amplitude up to near 180 degrees. This result indicates that maximum hovering performance was constrained geometrically and that heavier birds with greater fat loads had less margin for enhancement of power production. Sexual dimorphism in flight adaptation also played a role, with males showing more limited hovering capacities, presumably as a trade-off for increased maneuverability.

scholarly journals Lack of increased rate of force development after strength training is explained by specific neural, not muscular, motor unit adaptations

2021 ◽  
Author(s):  
Alessandro Del Vecchio ◽  
Andrea Casolo ◽  
Jakob Lund Dideriksen ◽  
Per Aagaard ◽  
Francesco Felici ◽  
...  
Keyword(s):  
Strength Training ◽  
Motor Unit ◽  
Discharge Rate ◽  
Force Production ◽  
Population Data ◽  
Motor Units ◽  
Rate Of Force Development ◽  
Force Development ◽  
Maximal Force ◽  
Contraction Speed

While maximal force increases following short-term isometric strength training, the rate of force development (RFD) may remain relatively unaffected. The underlying neural and muscular mechanisms during rapid contractions after strength training are largely unknown. Since strength training increases the neural drive to muscles, it may be hypothesized that there are distinct neural or muscular adaptations determining the change in RFD independently of an increase in maximal force. Therefore, we examined motor unit population data acquired from surface electromyography during the rapid generation of force before and after four weeks of strength training. We observed that strength training did not change the RFD because it did not influence the number of motor units recruited per second or their initial discharge rate during rapid contractions. While strength training did not change motoneuron behaviour in the force increase phase of rapid contractions, it increased the discharge rate of motoneurons (by ~4 spikes/s) when reaching the plateau phase (~150 ms) of the rapid contractions, determining an increase in maximal force production. Computer simulations with a motor unit model that included neural and muscular properties, closely matched the experimental observations and demonstrated that the lack of change in RFD following training is primarily mediated by an unchanged maximal recruitment speed of motoneurons. These results demonstrate that maximal force and contraction speed are determined by different adaptations in motoneuron behaviour following strength training and indicate that increases in the recruitment speed of motoneurons are required to evoke training-induced increases in RFD.

In vivo pectoralis muscle force-length behavior during level flight in pigeons (Columba livia)

1998 ◽  
Vol 201 (24) ◽  
pp. 3293-3307 ◽  
Author(s):  
A. A. Biewener ◽  
W. R. Corning ◽  
B. W. Tobalske
Keyword(s):  
Power Output ◽  
Muscle Length ◽  
Columba Livia ◽  
Length Change ◽  
Pectoralis Muscle ◽  
Fascicle Length ◽  
Force Development ◽  
Mechanical Power Output ◽  
Muscle Shortening

For the first time, we report in vivo measurements of pectoralis muscle length change obtained using sonomicrometry combined with measurements of its force development via deltopectoral crest strain recordings of a bird in free flight. These measurements allow us to characterize the contractile behavior and mechanical power output of the pectoralis under dynamic conditions of slow level flight in pigeons Columba livia. Our recordings confirm that the pigeon pectoralis generates in vivo work loops that begin with the rapid development of force as the muscle is being stretched or remains nearly isometric near the end of the upstroke. The pectoralis then shortens by a total of 32 % of its resting length during the downstroke,generating an average of 10.33.6 J kg-1 muscle (mean s.d.) of work per cycle for the anterior and posterior sites recorded among the five animals. In contrast to previous kinematic estimates of muscle length change relative to force development, the sonomicrometry measurements of fascicle length change show that force declines during muscle shortening. Simultaneous measurements of fascicle length change at anterior and posterior sites within the same muscle show significant (P<0.001, three of four animals) differences in fractional length (strain) change that averaged 1912 %, despite exhibiting similar work loop shape. Length changes at both anterior and posterior sites were nearly synchronous and had an asymmetrical pattern, with shortening occupying 63 % of the cycle. This nearly 2:1 phase ratio of shortening to lengthening probably favors the ability of the muscle to do work. Mean muscle shortening velocity was 5.381.33 and 4.881.27 lengths s-1 at the anterior and posterior sites respectively. Length excursions of the muscle were more variable at the end of the downstroke (maximum shortening), particularly when the birds landed,compared with highly uniform length excursions at the end of the upstroke(maximum lengthening). When averaged for the muscle as a whole, our in vivo work measurements yield a mass-specific net mechanical power output of 70. 2 W kg-1 for the muscle when the birds flew at 5-6 m s-1, with a wingbeat frequency of 8.7 Hz. This is 38 % greater than the value that we obtained previously for wild-type pigeons, but still 24-50 % less than that predicted by theory.

scholarly journals Effect of Accommodating Elastic Bands on Mechanical Power Output during Back Squats

Sports ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 151 ◽  
Author(s):  
Takafumi Kubo ◽  
Kuniaki Hirayama ◽  
Nobuhiro Nakamura ◽  
Mitsuru Higuchi
Keyword(s):  
Power Output ◽  
Random Order ◽  
Mechanical Power ◽  
Muscular Force ◽  
Force Output ◽  
Elastic Band ◽  
Free Weight ◽  
Mechanical Power Output ◽  
Elastic Bands ◽  
Acceleration And Deceleration

The aim of this study was to investigate whether accommodating elastic bands with barbell back squats (BSQ) increase muscular force during the deceleration subphase. Ten healthy men (mean ± standard deviation: Age: 23 ± 2 years; height: 170.5 ± 3.7 cm; mass: 66.7 ± 5.4 kg; and BSQ one repetition maximum (RM): 105 ± 23.1 kg; BSQ 1RM/body mass: 1.6 ± 0.3) were recruited for this study. The subjects performed band-resisted parallel BSQ (accommodating elastic bands each sides of barbell) with five band conditions in random order. The duration of the deceleration subphase, mean mechanical power, and the force and velocity during the acceleration and deceleration subphases were calculated. BSQ with elastic bands elicited greater mechanical power output, velocity, and force during the deceleration subphase, in contrast to that elicited with traditional free weight (p < 0.05). BSQ with elastic bands also elicited greater mechanical power output and velocity during the acceleration subphase. However, the force output during the acceleration subphase using an elastic band was lesser than that using a traditional free weight (p < 0.05). This study suggests that BSQ with elastic band elicit greater power output during the acceleration and deceleration subphases.

Pinacidil-primed ATP-sensitive potassium channels mediate feedback control of mechanical power output in isolated myocardium of rats and guinea pigs

2010 ◽  
Vol 628 (1-3) ◽  
pp. 116-127 ◽  
Author(s):  
Diethart Schmid ◽  
Dawid L. Staudacher ◽  
Christian A. Plass ◽  
Hans G. Loew ◽  
Eva Fritz ◽  
...  
Keyword(s):  
Feedback Control ◽  
Potassium Channels ◽  
Power Output ◽  
Guinea Pigs ◽  
Mechanical Power ◽  
Mechanical Power Output ◽  
Isolated Myocardium

Power output by an asynchronous flight muscle from a beetle

2000 ◽  
Vol 203 (17) ◽  
pp. 2667-2689 ◽  
Author(s):  
R.K. Josephson ◽  
J.G. Malamud ◽  
D.R. Stokes
Keyword(s):  
Power Output ◽  
Flight Muscle ◽  
Muscle Length ◽  
Mechanical Power ◽  
Effect Of Temperature ◽  
Muscle Temperature ◽  
Work Output ◽  
Stroke Frequency ◽  
Mechanical Power Output ◽  
Wing Stroke

The basalar muscle of the beetle Cotinus mutabilis is a large, fibrillar flight muscle composed of approximately 90 fibers. The paired basalars together make up approximately one-third of the mass of the power muscles of flight. Changes in twitch force with changing stimulus intensity indicated that a basalar muscle is innervated by at least five excitatory axons and at least one inhibitory axon. The muscle is an asynchronous muscle; during normal oscillatory operation there is not a 1:1 relationship between muscle action potentials and contractions. During tethered flight, the wing-stroke frequency was approximately 80 Hz, and the action potential frequency in individual motor units was approximately 20 Hz. As in other asynchronous muscles that have been examined, the basalar is characterized by high passive tension, low tetanic force and long twitch duration. Mechanical power output from the basalar muscle during imposed, sinusoidal strain was measured by the work-loop technique. Work output varied with strain amplitude, strain frequency, the muscle length upon which the strain was superimposed, muscle temperature and stimulation frequency. When other variables were at optimal values, the optimal strain for work per cycle was approximately 5%, the optimal frequency for work per cycle approximately 50 Hz and the optimal frequency for mechanical power output 60–80 Hz. Optimal strain decreased with increasing cycle frequency and increased with muscle temperature. The curve relating work output and strain was narrow. At frequencies approximating those of flight, the width of the work versus strain curve, measured at half-maximal work, was 5% of the resting muscle length. The optimal muscle length for work output was shorter than that at which twitch and tetanic tension were maximal. Optimal muscle length decreased with increasing strain. The curve relating work output and muscle length, like that for work versus strain, was narrow, with a half-width of approximately 3 % at the normal flight frequency. Increasing the frequency with which the muscle was stimulated increased power output up to a plateau, reached at approximately 100 Hz stimulation frequency (at 35 degrees C). The low lift generated by animals during tethered flight is consistent with the low frequency of muscle action potentials in motor units of the wing muscles. The optimal oscillatory frequency for work per cycle increased with muscle temperature over the temperature range tested (25–40 degrees C). When cycle frequency was held constant, the work per cycle rose to an optimum with increasing temperature and then declined. We propose that there is a temperature optimum for work output because increasing temperature increases the shortening velocity of the muscle, which increases the rate of positive work output during shortening, but also decreases the durations of the stretch activation and shortening deactivation that underlie positive work output, the effect of temperature on shortening velocity being dominant at lower temperatures and the effect of temperature on the time course of activation and deactivation being dominant at higher temperatures. The average wing-stroke frequency during free flight was 94 Hz, and the thoracic temperature was 35 degrees C. The mechanical power output at the measured values of wing-stroke frequency and thoracic temperature during flight, and at optimal muscle length and strain, averaged 127 W kg(−1)muscle, with a maximum value of 200 W kg(−1). The power output from this asynchronous flight muscle was approximately twice that measured with similar techniques from synchronous flight muscle of insects, supporting the hypothesis that asynchronous operation has been favored by evolution in flight systems of different insect groups because it allows greater power output at the high contraction frequencies of flight.

Mitochondrial ATP-sensitive K+ channels influence force development and anoxic contractility in a flatfish, yellowtail flounderLimanda ferruginea, but not Atlantic codGadus morhuaheart

2002 ◽  
Vol 205 (10) ◽  
pp. 1411-1418 ◽  
Author(s):  
Tyson J. MacCormack ◽  
William R. Driedzic
Keyword(s):  
Atlantic Cod ◽  
Force Production ◽  
Katp Channels ◽  
Cardiac Performance ◽  
K Channels ◽  
Yellowtail Flounder ◽  
Force Development ◽  
Cardiac Responses ◽  
Resting Tension ◽  
Cardiac Hypoxia

SUMMARYThe influence of ATP-sensitive K+ channels (KATPchannels) on cardiac performance during anoxia and reoxygenation was investigated in two species of fish showing different cardiac responses to anoxia. Force production in isometrically contracting ventricular muscle preparations from yellowtail flounder is potentiated at the onset of anoxia,while force immediately declines in Atlantic cod preparations. Glibenclamide,a general KATP blocker, impaired oxygenated force development in yellowtail flounder heart but was without effect on cod preparations. The mitochondrial KATP (mKATP)-specific blocker 5-hydroxydecanoic acid (5HD) improved oxygenated force production in yellowtail flounder heart without influencing contractility during anoxia or reoxygenation. The specific mKATP agonist diazoxide preserved resting tension and eliminated anoxic force potentiation in yellowtail flounder heart preparations. Neither 5HD nor diazoxide affected contractility in cod ventricle preparations. Results indicate that KATP channels can modulate contractility in yellowtail flounder heart and are potentially important in cardiac hypoxia survival in this species.

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