The effects of length trajectory on the mechanical power output of mouse skeletal muscles.

1997 ◽  
Vol 200 (24) ◽  
pp. 3119-3131 ◽  
Author(s):  
G N Askew ◽  
R L Marsh
Keyword(s):  
Strain Amplitude ◽  
Power Output ◽  
Maximum Power ◽  
Mechanical Power ◽  
Shortening Velocity ◽  
Cycle Frequency ◽  
Maximum Power Output ◽  
Mechanical Power Output ◽  
Evolutionary Context

The effects of length trajectory on the mechanical power output of mouse soleus and extensor digitorum longus (EDL) muscles were investigated using the work loop technique in vitro at 37 degrees C. Muscles were subjected to sinusoidal and sawtooth cycles of lengthening and shortening; for the sawtooth cycles, the proportion of the cycle spent shortening was varied. For each cycle frequency examined, the timing and duration of stimulation and the strain amplitude were optimized to yield the maximum power output. During sawtooth length trajectories, power increased as the proportion of the cycle spent shortening increased. The increase in power was attributable to more complete activation of the muscle due to the longer stimulation duration, to a more rapid rise in force resulting from increased stretch velocity and to an increase in the optimal strain amplitude. The power produced during symmetrical sawtooth cycles was 5-10 % higher than during sinusoidal work loops. Maximum power outputs of 92 W kg-1 (soleus) and 247 W kg-1 (EDL) were obtained by manipulating the length trajectory. For each muscle, this was approximately 70 % of the maximum power output estimated from the isotonic force-velocity relationship. We have found a number of examples suggesting that animals exploit prolonging the shortening phase during activities requiring a high power output, such as flying, jet-propulsion swimming and vocalization. In an evolutionary context, increasing the relative shortening duration provides an alternative to increasing the maximum shortening velocity (Vmax) as a way to increase power output.

scholarly journals The effect of cycle frequency on the power output of rat papillary muscles in vitro.

1995 ◽  
Vol 198 (4) ◽  
pp. 1035-1043 ◽  
Author(s):  
J Layland ◽  
I S Young ◽  
J D Altringham
Keyword(s):  
Phase Shift ◽  
Strain Amplitude ◽  
Power Output ◽  
Maximum Power ◽  
Papillary Muscles ◽  
Cycle Frequency ◽  
Maximum Power Output ◽  
Work Production

Papillary muscles were isolated from the right ventricles of rats and the length for maximum active force generation (Lmax) was determined isometrically. The work loop technique was used to derive the length for maximum work production (Lopt) at the cycle frequency, strain amplitude and stimulation phase shift found to be optimal for power output. Lopt was typically 7% shorter than Lmax and within the physiological length range (87.5% Lmax to Lmax). Net work and power output were measured during sinusoidal strain cycles around Lopt, over the cycle frequency range 1-9 Hz, strain amplitude and phase shift being optimised for work and power at each frequency. Experiments were performed at 37 degrees C. Distinct optima were found in both the work-frequency and the power-frequency relationships. The optimum cycle frequency for net work production was lower than the frequency for maximum power output. The mean maximum power output at 37 degrees C was 8.62 +/- 0.50 W kg-1 (mean +/- S.E.M., N = 9) and was achieved at a cycle frequency of approximately 6 Hz, close to the estimated resting heart rate of 5.8 Hz for the rats used (mean mass 223 +/- 25 g). The cycle frequency, strain amplitude and stimulation phase shift found to be optimal for power output produced an in vitro contraction closely simulating the basal in vivo contraction.

Salbutamol enhances isotonic contractile properties of rat diaphragm muscle

1998 ◽  
Vol 85 (2) ◽  
pp. 525-529 ◽  
Author(s):  
H. F. M. Van Der Heijden ◽  
W. Z. Zhan ◽  
Y. S. Prakash ◽  
P. N. R. Dekhuijzen ◽  
G. C. Sieck
Keyword(s):  
Power Output ◽  
Maximum Power ◽  
Contractile Properties ◽  
Diaphragm Muscle ◽  
Rat Diaphragm ◽  
Shortening Velocity ◽  
Maximum Power Output ◽  
Isometric Twitch ◽  
Camp Levels

The effects of the β2-adrenoceptor agonist salbutamol (Slb) on isometric and isotonic contractile properties of the rat diaphragm muscle (Diamus) were examined. A loading dose of 25 μg/kg Slb was administered intracardially before Diamus excision to ensure adequate diffusion. Studies were then performed with 0.05 μM Slb in the in vitro tissue chamber. cAMP levels were determined by radioimmunoassay. Compared with controls (Ctl), cAMP levels were elevated after Slb treatment. In Slb-treated rats, isometric twitch and maximum tetanic force were increased by ∼40 and ∼20%, respectively. Maximum shortening velocity increased by ∼15% after Slb treatment, and maximum power output increased by ∼25%. During repeated isotonic activation, the rate of fatigue was faster in the Slb-treated Diamus, but both Slb-treated and Ctl Diamusfatigued to the same maximum power output. Still, endurance time during repetitive isotonic contractions was ∼10% shorter in the Slb-treated Diamus. These results are consistent with the hypothesis that β-adrenoceptor stimulation by Slb enhances Diamus contractility and that these effects of Slb are likely mediated, at least in part, by elevated cAMP.

scholarly journals TEMPERATURE, MUSCLE POWER OUTPUT AND LIMITATIONS ON BURST LOCOMOTOR PERFORMANCE OF THE LIZARD DIPSOSAURUS DORSALIS

1993 ◽  
Vol 174 (1) ◽  
pp. 185-197 ◽  
Author(s):  
S. J. Swoap ◽  
T. P. Johnson ◽  
R. K. Josephson ◽  
A. F. Bennett
Keyword(s):  
Power Output ◽  
Maximum Power ◽  
Stride Frequency ◽  
Cycle Frequency ◽  
Maximum Power Output ◽  
Mechanical Power Output ◽  
Cycling Frequency ◽  
Loop Technique ◽  
Fast Twitch

The mechanical power output of fast-twitch fibres from the iliofibularis of the lizard Dipsosaurus dorsalis was measured over a broad body temperature range using the oscillatory work-loop technique. The optimal cycling frequency, that frequency at which mechanical power output is maximal, increases with temperature from 3.3 Hz at 15°C to 20.1 Hz at 42°C. Maximum power output increases with temperature, from 20 W kg-1 at 15°C to 154 W kg-1 at 42°C, the largest power output yet measured using the work-loop technique. At low temperatures (15°C and 22°C), stride frequency during burst running is nearly identical to the optimal cycling frequency for in vitro power output, suggesting that maximum power output may limit hindlimb cycle frequency in vivo. However, at higher temperatures (35°C and 42°C), the optimal cycling frequency of the isolated muscle is significantly higher than the burst stride frequency, demonstrating that contractile events no longer limit hindlimb cycle frequency. At higher temperatures, it is thus unlikely that the fast-twitch fibres of this muscle in vivo attain their potential for maximum power output.

scholarly journals Mechanical Power output from Striated Muscle during Cyclic Contraction

1985 ◽  
Vol 114 (1) ◽  
pp. 493-512 ◽  
Author(s):  
Robert K. Josephson
Keyword(s):  
Power Output ◽  
Muscle Tension ◽  
Single Stimulus ◽  
Mechanical Power ◽  
Work Output ◽  
Shortening Velocity ◽  
Cycle Frequency ◽  
Mechanical Power Output ◽  
Work Done ◽  
Rest Length

1. The mechanical power output of a synchronous insect muscle was determined by measuring tension as the muscle was subjected to sinusoidal length change and stimuli which occurred at selected phases of the length cycle. The area of the loop formed by plotting muscle tension against length over a full cycle is the work done on that cycle; the work done times the cycle frequency is the mechanical power output. The muscle was a flight muscle of the tettigoniid Neoconocephalus triops. The measurements were made at the normal wing-stroke frequency for flight (25 Hz) and operating temperature (30°C). 2. The power output with a single stimulus per cycle, optimal excursion amplitude, and optimal stimulus phase was 1.52 J kg−1 cycle−1 or 37W kg−1. The maximum power output occurs at a phase such that the onset of the twitch coincides with the onset of the shortening half of the length cycle. The optimum excursion amplitude was 5.5% rest length; with greater excursion, work output declined because of decreasing muscle force associated with the more rapid shortening velocity. 3. Multiple stimulation per cycle increases the power output above that available with twitch contractions. In this muscle, the maximum mechanical power output at 25 Hz was 76 W kg−1 which was achieved with three stimuli per cycle separated by 4-ms intervals and an excursion amplitude of 6.0% rest length. 4. The maximum work output during the shortening of an isotonic twitch contraction was about the same as the work done over a full sinusoidal shortening-lengthening cycle with a single stimulus per cycle and optimum excursion amplitude and phase.

scholarly journals Scaling of Power Output in Fast Muscle Fibres of the Atlantic Cod During Cyclical Contractions

1992 ◽  
Vol 170 (1) ◽  
pp. 143-154 ◽  
Author(s):  
M. ELIZABETH ANDERSON ◽  
IAN A. JOHNSTON
Keyword(s):  
Steady State ◽  
Power Output ◽  
Standard Length ◽  
Atlantic Cod ◽  
Maximum Power ◽  
Fast Muscle ◽  
Muscle Fibres ◽  
Cycle Frequency ◽  
Maximum Power Output ◽  
Length Changes

Fast muscle fibres were isolated from abdominal myotomes of Atlantic cod (Gadus morhua L.) ranging in size from 10 to 63 cm standard length (Ls). Muscle fibres were subjected to sinusoidal length changes about their resting length (Lf) and stimulated at a selected phase of the strain cycle. The work performed in each oscillatory cycle was calculated from plots of force against muscle length, the area of the resulting loop being net work. Strain and the number and timing of stimuli were adjusted to maximise positive work per cycle over a range of cycle frequencies at 8°C. Force, and hence power output, declined with increasing cycles of oscillation until reaching a steady state around the ninth cycle. The strain required for maximum power output (Wmax) was ±7-11% of Lf in fish shorter than 18 cm standard length, but decreased to ±5 % of Lf in larger fish. The cycle frequency required for Wmax also declined with increasing fish length, scaling to Ls−0.51 under steady-state conditions (cycles 9–12). At the optimum cycle frequency and strain the maximum contraction velocity scaled to Ls−0.79. The maximum stress (Pmax) produced within a cycle was highest in the second cycle, ranging from 51.3 kPa in 10 cm fish to 81.8 kPa in 60 cm fish (Pmax=28.2Ls0.25). Under steady-state conditions the maximum power output per kilogram wet muscle mass was found to range from 27.5 W in a 10 cm Ls cod to 16.4 W in a 60 cm Ls cod, scaling with Ls−0.29 and body mass (Mb)−0.10 Note: To whom reprint requests should be sent

The effects of adrenaline on the work- and power-generating capacity of rat papillary muscle in vitro.

1997 ◽  
Vol 200 (3) ◽  
pp. 503-509
Author(s):  
J Layland ◽  
I S Young ◽  
J D Altringham
Keyword(s):  
Cardiac Muscle ◽  
Power Output ◽  
Maximum Power ◽  
Maximum Power Output ◽  
Generating Capacity ◽  
Loop Technique ◽  
Maximum Work ◽  
Frequency Relationship ◽  
Work Loop

The work loop technique was used to examine the effects of adrenaline on the mechanics of cardiac muscle contraction in vitro. The length for maximum active force (Lmax) and net work production (Lopt) for rat papillary muscles was determined under control conditions (without adrenaline). The concentration of adrenaline producing the maximum inotropic effect was determined. This concentration was used in the remainder of the experiments. Sinusoidal strain cycles about Lopt were performed over a physiologically relevant range of cycle frequencies (4-11 Hz). Maximum work and the frequency for maximum work increased from 1.91 J kg-1 at 3 Hz in controls to 2.97 J kg-1 at 6 Hz with adrenaline. Similarly, maximum power output and the frequency for maximum power output (fopt) increased from 8.62 W kg-1 at 6 Hz in controls to 19.95 W kg-1 at 8 Hz with adrenaline. We suggest that the power-frequency relationship, derived using the work loop technique, represents a useful index with which to assess the effects of pharmacological interventions on cardiac muscle contractility.

Isotonic contractile and fatigue properties of developing rat diaphragm muscle

1998 ◽  
Vol 84 (4) ◽  
pp. 1260-1268 ◽  
Author(s):  
Wen-Zhi Zhan ◽  
Jon F. Watchko ◽  
Y. S. Prakash ◽  
Gary C. Sieck
Keyword(s):  
Power Output ◽  
Supply And Demand ◽  
Maximum Power ◽  
Diaphragm Muscle ◽  
Fatigue Properties ◽  
Rat Diaphragm ◽  
Shortening Velocity ◽  
Endurance Time ◽  
Early Postnatal Development ◽  
Maximum Power Output

Postnatal transitions in myosin heavy chain (MHC) isoform expression were found to be associated with changes in both isometric and isotonic contractile properties of rat diaphragm muscle (Diam). Expression of MHCneo predominated in neonatal Diam fibers but was usually coexpressed with MHCslow or MHC2A isoforms. Expression of MHCneo disappeared by day 28. Expression of MHC2X and MHC2B emerged at day 14 and increased thereafter. Associated with these MHC transitions in the Diam, maximum isometric tetanic force (Po), maximum shortening velocity, and maximum power output progressively increased during early postnatal development. Maximum power output of the Diam occurred at ∼40% Po at days 0 and 7 and at ∼30% Po in older animals. Susceptibility to isometric and isotonic fatigue, defined as a decline in force and power output during repetitive activation, respectively, increased with maturation. Isotonic endurance time, defined as the time for maximum power output to decline to zero, progressively decreased with maturation. In contrast, isometric endurance time, defined as the time for force to decline to 30–40% Po, remained >300 s until after day 28. We speculate that with the postnatal transition to MHC2X and MHC2Bexpression energy requirements for contraction increase, especially during isotonic shortening, leading to a greater imbalance between energy supply and demand.

scholarly journals LOAD THAT MAXIMIZES POWER OUTPUT IN COUNTERMOVEMENT JUMP

2016 ◽  
Vol 22 (1) ◽  
pp. 13-16 ◽  
Author(s):  
Pedro Jimenez-Reyes ◽  
Victor Cuadrado-Peñafiel ◽  
Fernando Pareja-Blanco ◽  
Juan Párraga-Montilla ◽  
Francisco Javier Toscano Bendala ◽  
...  
Keyword(s):  
Power Output ◽  
Performance Status ◽  
National Level ◽  
Average Power ◽  
Maximum Power ◽  
Mechanical Power ◽  
Countermovement Jump ◽  
Strength And Conditioning ◽  
Maximal Power Output ◽  
Mechanical Power Output

ABSTRACT Introduction: One of the main problems faced by strength and conditioning coaches is the issue of how to objectively quantify and monitor the actual training load undertaken by athletes in order to maximize performance. It is well known that performance of explosive sports activities is largely determined by mechanical power. Objective: This study analysed the height at which maximal power output is generated and the corresponding load with which is achieved in a group of male-trained track and field athletes in the test of countermovement jump (CMJ) with extra loads (CMJEL). Methods: Fifty national level male athletes in sprinting and jumping performed a CMJ test with increasing loads up to a height of 16 cm. The relative load that maximized the mechanical power output (Pmax) was determined using a force platform and lineal encoder synchronization and estimating the power by peak power, average power and flight time in CMJ. Results: The load at which the power output no longer existed was at a height of 19.9 ± 2.35, referring to a 99.1 ± 1% of the maximum power output. The load that maximizes power output in all cases has been the load with which an athlete jump a height of approximately 20 cm. Conclusion: These results highlight the importance of considering the height achieved in CMJ with extra load instead of power because maximum power is always attained with the same height. We advise for the preferential use of the height achieved in CMJEL test, since it seems to be a valid indicative of an individual's actual neuromuscular potential providing a valid information for coaches and trainers when assessing the performance status of our athletes and to quantify and monitor training loads, measuring only the height of the jump in the exercise of CMJEL.

scholarly journals Scaling Effects on Muscle Function: Power Output of Isolated Fish Muscle Fibres Performing Oscillatory Work

1990 ◽  
Vol 151 (1) ◽  
pp. 453-467 ◽  
Author(s):  
JOHN D. ALTRINGHAM ◽  
IAN A. JOHNSTON
Keyword(s):  
Power Output ◽  
Fibre Length ◽  
Fish Muscle ◽  
Maximum Power ◽  
Muscle Fibres ◽  
Scaling Effects ◽  
Cycle Frequency ◽  
Maximum Power Output ◽  
Wide Range ◽  
Length Changes

Bundles of 3–10 live fast fibres were isolated from the abdominal myotomes of cod (Gadus morhua L.) 13–67 cm in length. The preparations performed work under conditions simulating their activity during swimming: sinusoidal length changes were imposed about in situ fibre length, and the fibres were stimulated at a selected phase in each cycle. Strain amplitude, and the number and timing of stimuli were chosen to give maximum power output over a wide range of cycle/tailbeat frequencies. For each preparation power output was maximal at a particular frequency, although the peaks were rather broad. As the size of the fish increased the cycle frequency for maximum power output (fopt) decreased, from 12.5 Hz (13 cm fish) to 5 Hz (67 cm fish) (fopt= 1.67 L−0.52, where L is body length).

scholarly journals Power output and the frequency of oscillatory work in mammalian diaphragm muscle: the effects of animal size

1991 ◽  
Vol 157 (1) ◽  
pp. 381-389 ◽  
Author(s):  
J. D. Altringham ◽  
I. S. Young
Keyword(s):  
Body Mass ◽  
Power Output ◽  
Maximum Power ◽  
Diaphragm Muscle ◽  
Muscle Fibres ◽  
Cycle Frequency ◽  
Maximum Power Output ◽  
Oscillatory Power ◽  
Length Changes ◽  
Animal Size

Bundles of muscle fibres were isolated from the diaphragm of mouse, rat and rabbit. Mean oscillatory power output was determined during phasic stimulation and imposed sinusoidal length changes. Maximum power output was measured over a range of cycle frequencies. The cycle frequency for maximum power output (fopt) decreased with increasing body mass and was described by the equation, fopt = 4.42M-0.16, where M is body mass. A very similar relationship has been reported between body mass and the frequency of the trot-gallop transition in terrestrial, quadrupedal mammals [Heglund et al. (1974), Science 186, 1112–1113), and the significance of this similarity is discussed.

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