Contraction isotonic

In terms of muscle function, muscle is very adaptable. Depending on the type of stimulation, muscle can either twitch or contract tetanically for a variable length of time. If the ends are held fixed, then it contracts isometrically and the force produced is maximal. If one or both ends of the muscle are not held fixed then the muscle is able to shorten. The muscle can shorten at a fixed load (isotonic contraction) where the velocity of shortening is also constant. Power output (force X velocity) is maximum where the velocity of shortening is about one third of the maximal rate. Finally, the muscle can shorten at maximum velocity (unloaded shortening). However, the molecular basis of the interaction of myosin with actin to produce force, or shortening, is the same in each case. 

Isotonic contraction occurs when the muscle shortens under a constant load. For example, when an object is lifted, the muscle contracts and becomes shorter although the weight of the object remains constant. In addition to moving external objects, isotonic contractions are performed for movements of the body, such as moving the legs when walking. 

Many activities require both types of muscle contraction. An example is running when one of the legs hits the ground, isometric contraction of the muscles within this limb keep it stiff and help to maintain body support. At the same time, isotonic contractions in the opposite leg move it forward to take the next stride. 

Figure 8. Original tracings showing the effects of (R)a-methylhistamine (MHA, pM), thioperamide (TH, pM), the selective a2 adrenoceptor agonist UK-14304 (UK, nM) and the a2-adrenoceptor antagonist idazoxan (ID, pM) on different in vitro assays from the guinea pig ileum A) Electrically-evoked longitudinal contractions of the whole ileum B) Peristaltic waves of the perfused ileum, C) Reflex-evoked circular muscle contractions Vertical calibrations represent (A and C) centimeters of isotonic contractions or (B) changes in perfusion pressure. Horizontal calibration is the chart speed, w = washing of the preparation...

Martin-Femandez, M. L., Bordas, J., Diakun, G., Harries, J., Lowy, J., Mant, G. R., Svennson, A., and Towns-Andrews, E. (1994). Time-resolved X-ray diffraction studies of myosin head movements in live frog sartorius muscle during isometric and isotonic contractions./. Mus. Res. CellMotil. 15, 319-348. 

Mechanical Cutting vessel removes stretch with shortening (isometric to isotonic contraction) Reflex Segmental contraction of vessel Contraction by autopharmacodynamic agents SVPx, adrenalin, serotonin, histamine released locally from platelets, adrenochrome from sympathetic endings... 

Figure 8.17 shows computed isotonic contractions for different fixed loads. Although not shown, this muscle model exhibits an inverse relation between isotonic load and amount of shortening, and a direct relation between initial length and shortening (Starhng s law). Results are also consistent with experiments,... 

FIGURE 8.17 Isotonic contractions for muscle strip computed from Equation 8.15 for three intermediate and one isometric load. Top shows muscle length (right y-axis). 

The idea for this distributed muscle fiber model arose in 1990 [44]. At that time, muscle fibers were assumed to be functionally similar to muscle strips. Recently, experiments on isolated muscle libers show this to be the case. Predictions from the model have recently been borne out, for example, the magnitude of computed peak isometric force compared to that measured on isolated guinea pig myocytes [34]. Peak isometric stress measured on isolated rabbit myocytes (5.4 mN/mm ) is very close to peak stress from rabbit papillary muscle strips (6.4 mN/mm ) [45]. The distributed model generates peak isometric stress of 2.5 mN/mm. Other muscle phenomena measured on the isolated fiber include a quadratic force-length relation [45], inotropic changes in contractile state [37], quick release and stretch [37,39], and isotonic contractions [46], all in agreement with model predictions. 

Brutsaert, D.L., Claes, V. A., and SonnenbHck, E.H. 1971. Effects of abrupt load alterations on force-velocity-length and time relations during isotonic contractions of heart muscle load clamping. /. Physiol. 216 319. 

M. Amin, Theory of Muscle Contraction II Isotonic Contraction, J. Biol. Phys. 11, 123-126 (1984). 

Figure 1.7. Shown are the first reported data of the conversion by an elastic-contractile model protein of chemical energy due to an increase in concentration of acid into the mechanical work of contraction. A Length changes at constant force (isotonic contraction) in phosphate-buffered saline. B Force changes at constant length (isometric contraction) in phosphate-buffered saline. (Reproduced from Urry et al. )...

Performance of Mechanical Work with an Isometric Contraction Followed by an Isotonic Contraction with Relaxation to Initial Force... 

Stimull/s 20 Stimuli/s 50 Stimuli/s Frog muscle, 20°C, approx. Isotonic contraction... 

Bundles of about 60 gel filaments with such structure and ( ) = 25 pm immersed alternatively in alkaline and acidic solutions responded by elongation/contraction cycles under a constant load of 0.75 kg/cm (isotonic contraction). Some dynamic characteristics of the described contractile system are presented in Figure 4.13 and Table 4.3. 

Figure 4.33. Schematic representation of chemomechanical contraction of a PMAA membrane by polymer-membrane complexation (a) isotonic contraction) (b) isometric contraction [131].

Another type of reaction control realized by isotonic contraction of a PMAA membrane is shown in Fig. 27 In this case the invertase solution was placed in a glass tube, the lower part of which was loosely wrapped with the PMAA membrane. The contraction of the membrane, bringing about the shrinkage of the pore radius (isotonic contraction cf. Fig. 20 a) interferes with the permeation of the substrate molecules from outside. Fig. 27 shows the effects of pH change and addition of PEG on the rate of hydrolysis. It is seen that the addition of a small amount of PEG impedes the hydrolysis completely, whereas a pH change has no effect on the rate. PEG molecules adsorbed on the PMAA membrane can be removed by rinsing with a dilute NaOH... 

Fig. 27. Effect of isotonic contraction caused by pH change and PEG addition on the rate of hydrolysis of saccharose. Invertase solution 2 ml Saccharose 20 wt. % 10 ml HCl 0.1 mol/1 NaOH 0.1 raol/1 PEG added 5.8 X iO mol/1, Temp. 25 °C...

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