Effect of stimulus train duration and cycle frequency on the capacity to do work in the pectoral fin muscle of the pumpkinseed sunfish, Lepomis gibbosus

1993 ◽  
Vol 71 (11) ◽  
pp. 2185-2189 ◽  
Author(s):  
Eric A. Luiker ◽  
E. Don Stevens
Keyword(s):  
Duty Cycle ◽  
Length Change ◽  
Lepomis Gibbosus ◽  
Pectoral Fin ◽  
Cycle Frequency ◽  
Pumpkinseed Sunfish ◽  
Train Duration ◽  
Stimulus Train ◽  
Length Changes ◽  
Time Required

The goal of our experiment was to elucidate the effect of stimulus duty cycle (the percentage of the cycle that the muscle was stimulated), phase (the relative timing of the imposed sinusoidal length change and stimulation), and muscle cycle frequency (the speed at which the muscle was cycled) on work and power in the pectoral fin muscle of a labriform swimmer, the pumpkinseed sunfish, Lepomis gibbosus. Stimulus train duration was varied from a twitch to a 40% duty cycle; cycle frequency was varied from 1 to 8 Hz. Work was calculated as the area of work loops produced by muscle contractions while the muscle was undergoing sinusoidal length changes. Maximum net work per cycle (6.2 J/kg) was produced at 1 Hz cycle frequency and a 32% duty cycle. Maximum power (26.7 W/kg) was produced at 5 Hz cycle frequency and a 16% duty cycle. As cycle frequency increased, the duty cycle and the stimulus train duration that produced maximum work decreased. The relatively long relaxation time compared with the length of time required to complete the whole cycle precluded the muscle from doing net positive work at high cycle frequencies.

Effect of temperature and stimulus train duration on the departure from theoretical maximum work in fish muscle

1994 ◽  
Vol 72 (6) ◽  
pp. 965-969 ◽  
Author(s):  
Eric A. Luiker ◽  
E. Don Stevens
Keyword(s):  
Duty Cycle ◽  
Relaxation Times ◽  
Length Change ◽  
Fish Muscle ◽  
Effect Of Temperature ◽  
Temperature Sensitive ◽  
Theoretical Maximum ◽  
Train Duration ◽  
Stimulus Train ◽  
Maximum Work

The goal of the present study was to compare the effect of temperature on contraction kinetic parameters of fish muscle with its effect on oscillatory work. In particular we studied the effect of stimulus train duration or duty cycle (the fraction of the imposed length change that the muscle was stimulated). We compared the actual work done by the muscle with a theoretical maximum work loop that would be achieved if it were fully and instantaneously relaxed at the onset of shortening and fully and instantaneously relaxed at the onset of lengthening. Temperature had a small effect on force but a marked effect on contraction and relaxation times. Thus, work was more temperature sensitive than force. The effect of temperature on work could not be predicted by its effect on any one contraction kinetic parameter. To achieve maximum work at lower temperatures, the duty cycle must be decreased because of the longer relaxation time.

Energetics of rat papillary muscle during contractions with sinusoidal length changes

2000 ◽  
Vol 278 (5) ◽  
pp. H1545-H1554 ◽  
Author(s):  
J. Baxi ◽  
C. J. Barclay ◽  
C. L. Gibbs
Keyword(s):  
High Efficiency ◽  
Length Change ◽  
Mechanical Efficiency ◽  
Left Ventricular ◽  
Force Generation ◽  
Maximum Efficiency ◽  
Cycle Frequency ◽  
Length Changes ◽  
Active Force Generation

The mechanical efficiency of rat cardiac muscle was determined using a contraction protocol involving cyclical, sinusoidal length changes and phasic stimulation at physiological frequencies (1–4 Hz). Experiments were performed in vitro (27°C) using rat left ventricular papillary muscles. Efficiency was determined from measurements of the net work performed and enthalpy produced by muscles during a series of 40 contractions. Net mechanical efficiency was defined as the percentage of the total, suprabasal enthalpy output that appeared as mechanical work. Maximum efficiency was ∼15% at contraction frequencies between 2 and 2.5 Hz. At lower and higher frequencies, efficiency was ∼10%. Enthalpy output per cycle was independent of cycle frequency at all but the highest frequency used. The basis of the high efficiency between 2 and 2.5 Hz was that work output was also greatest at these frequencies. At these frequencies, the duration of the applied length change was well matched to the kinetics of force generation, and active force generation occurred throughout the shortening period.

Effect of stimulus duty cycle and cycle frequency on power output during fatigue in rat diaphragm muscle doing oscillatory work

1993 ◽  
Vol 71 (12) ◽  
pp. 910-916 ◽  
Author(s):  
E. D. Stevens ◽  
D. A. Syme
Keyword(s):  
Duty Cycle ◽  
Muscle Power ◽  
Diaphragm Muscle ◽  
Cycle Duration ◽  
Rat Diaphragm ◽  
Cycle Frequency ◽  
Length Changes ◽  
The Difference ◽  
Work Done ◽  
Measuring Force

Isolated rat diaphragm muscle was stimulated repetitively to induce fatigue, and the work done during each contraction was measured. Work per cycle was calculated by measuring force as the activated muscle was subjected to sinusoidal length changes (from 97 to 103% of L0, where L0 is rest length). Work was calculated from the loop formed when force was plotted against length. Work done was positive when the muscle was shortening and was negative when it was lengthening; net work was the difference. Work output was varied by changing the stimulus duty cycle (4, 8, or 16% of the total cycle duration) and cycle frequency (1, 2, or 4 Hz). The rate and extent of the decrease in power was influenced much more by changes in cycle frequency than by changes in duty cycle. Duty cycle and cycle frequency combinations that resulted in greater power in the prefatigue trials were associated with a more rapid rate of fatigue. However, net positive power at the end of the 15-min fatigue period was greater under these same conditions (i.e., high duty cycle and high cycle frequency). Fatigue in working diaphragm muscle depends more on cycle frequency than on duty cycle.Key words: skeletal muscle, muscle power, respiratory muscle, muscle lengthening.

scholarly journals Medial collateral ligament reconstruction graft isometry is effected by femoral position more than tibial position

2021 ◽  
Author(s):  
Christoph Kittl ◽  
James Robinson ◽  
Michael J. Raschke ◽  
Arne Olbrich ◽  
Andre Frank ◽  
...  
Keyword(s):  
Medial Collateral Ligament ◽  
Knee Flexion ◽  
Length Change ◽  
Collateral Ligament ◽  
Complex Behaviour ◽  
Femoral Attachment ◽  
Attachment Sites ◽  
Custom Made ◽  
Length Changes ◽  
Graft Length

Abstract Purpose The purpose of this study was to examine the length change patterns of the native medial structures of the knee and determine the effect on graft length change patterns for different tibial and femoral attachment points for previously described medial reconstructions. Methods Eight cadaveric knee specimens were prepared by removing the skin and subcutaneous fat. The sartorius fascia was divided to allow clear identification of the medial ligamentous structures. Knees were then mounted in a custom-made rig and the quadriceps muscle and the iliotibial tract were loaded, using cables and hanging weights. Threads were mounted between tibial and femoral pins positioned in the anterior, middle, and posterior parts of the attachment sites of the native superficial medial collateral ligament (sMCL) and posterior oblique ligament (POL). Pins were also placed at the attachment sites relating to two commonly used medial reconstructions (Bosworth/Lind and LaPrade). Length changes between the tibiofemoral pin combinations were measured using a rotary encoder as the knee was flexed through an arc of 0–120°. Results With knee flexion, the anterior fibres of the sMCL tightened (increased in length 7.4% ± 2.9%) whilst the posterior fibres slackened (decreased in length 8.3% ± 3.1%). All fibre regions of the POL displayed a uniform lengthening of approximately 25% between 0 and 120° knee flexion. The most isometric tibiofemoral combination was between pins placed representing the middle fibres of the sMCL (Length change = 5.4% ± 2.1% with knee flexion). The simulated sMCL reconstruction that produced the least length change was the Lind/Bosworth reconstruction with the tibial attachment at the insertion of the semitendinosus and the femoral attachment in the posterior part of the native sMCL attachment side (5.4 ± 2.2%). This appeared more isometric than using the attachment positions described for the LaPrade reconstruction (10.0 ± 4.8%). Conclusion The complex behaviour of the native MCL could not be imitated by a single point-to-point combination and surgeons should be aware that small changes in the femoral MCL graft attachment position will significantly effect graft length change patterns. Reconstructing the sMCL with a semitendinosus autograft, left attached distally to its tibial insertion, would appear to have a minimal effect on length change compared to detaching it and using the native tibial attachment site. A POL graft must always be tensioned near extension to avoid capturing the knee or graft failure.

The location and mechanism of electromotility in guinea pig outer hair cells

1993 ◽  
Vol 70 (2) ◽  
pp. 549-558 ◽  
Author(s):  
R. Hallworth ◽  
B. N. Evans ◽  
P. Dallos
Keyword(s):  
Guinea Pig ◽  
Hair Cells ◽  
Outer Hair Cell ◽  
Length Change ◽  
Opposite Polarity ◽  
Outer Hair Cells ◽  
Response Amplitude ◽  
Change Function ◽  
Length Changes ◽  
Diameter Change

1. The microchamber method was used to examine the motile responses of isolated guinea pig outer hair cells to electrical stimulation. In the microchamber method, an isolated cell is drawn partway into a suction pipette and stimulated transcellularly. The relative position of the cell in the microchamber is referred to as the exclusion fraction. 2. The length changes of the included and excluded segments were compared for constant sinusoidal stimulus amplitude as functions of the exclusion fraction. Both included and excluded segments showed maximal responses when the cell was excluded approximately halfway. Both segments showed smaller or absent responses when the cell was almost fully excluded or almost fully included. 3. When the cell was near to, but not at, the maximum exclusion, the included segment response amplitude was zero, whereas the excluded segment response amplitude was nonzero. In contrast, when the cell was nearly fully included, the excluded segment response amplitude was zero, but the included segment response amplitude was still detectable. A simple model of outer hair cell motility based on these results suggests that the cell has finite-resistance terminations and that the motors are restricted to a region above the nucleus and below its ciliated apex (cuticular plate). 4. The function describing length change as a function of command voltage was measured for each segment as the exclusion fraction was varied. The functions were similar at midrange exclusions (i.e., when the segments were about equal length), showing nonlinearity and saturability. The functions were strikingly different when the segment lengths were different. The effects of exclusion on the voltage to length-change functions suggested that the nonlinearity and saturability are local properties of the motility mechanism. 5. The diameter changes of both segments were examined. The segment diameter changes were always antiphasic to the length changes. This finding implies that the motility mechanism has an active antiphasic diameter component. The diameter change amplitude was a monotonically increasing function of exclusion for the included segment, and a decreasing function for the excluded segment. 6. The voltage to length-change and voltage to diameter-change functions were measured for the same cell and exclusion fraction. The voltage to diameter-change function was smaller in amplitude than the voltage to length-change function. The functions were of opposite polarity to each other, but were otherwise similar in character. Thus it is likely that the same motor mechanism is responsible for both axial and diameter deformations.

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

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