The relations between sarcomere length and characteristics of isometric twitch contractions of frog sartorius muscle

Close, R.

doi:10.1113/jphysiol.1972.sp009733

Cited by 115 publications

(74 citation statements)

References 24 publications

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“…The sarcomere length values were those existing at the time the extrapolated tension was reached. Previous studies using serw) control of the length of a segment of fiber (Gordon et al, 1966 b), and data from isometric tetani of whole muscles (Close, 1972) show a similar correspondence between sarcomere length and extrapolated tension. The relation, therefore, does not seem to depend critically upon the experimental procedure.…”

Section: The Sarcomere Length-tension Relationmentioning

confidence: 79%

The sarcomere length-tension relation in skeletal muscle.

Keurs¹,

Iwazumi²,

Pollack³

1978

The Journal of General Physiology

155

114

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Tension development during isometric tetani in single fibers of frog semitendinosus muscle occurs in three phases: (a) in initial fast-rise phase; (b) a slow-rise phase; and (c) a plateau, which lasts greater than 10 s. The slow-rise phase has previously been assumed to rise out of a progressive increase of sarcomere length dispersion along the fiber (Gordon et al. 1966. J. Physiol. [Lond.]. 184:143--169;184:170--192). Consequently, the "true" tetanic tension has been considered to be the one existing before the onset of the slow-rise phase; this is obtained by extrapolating the slowly rising tension back to the start of the tetanus. In the study by Gordon et al. (1966. J. Physiol. [Lond.] 184:170--192), as well as in the present study, the relation between this extrapolated tension and sarcomere length gave the familiar linear descending limb of the length-tension relation. We tested the assumption that the slow rise of tension was due to a progressive increase in sarcomere length dispersion. During the fast rise, the slow rise, and the plateau of tension, the sarcomere length dispersion at any area along the muscle was less than 4% of the average sarcomere length. Therefore, a progressive increase of sarcomere length dispersion during contraction appears unable to account for the slow rise of tetanic tension. A sarcomere length-tension relation was constructed from the levels of tension and sarcomere length measured during the plateau. Tension was independent of sarcomere length between 1.9 and 2.6 microgram, and declined to 50% maximal at 3.4 microgram. This result is difficult to reconcile with the cross-bridge model of force generation.

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Section: The Sarcomere Length-tension Relationmentioning

confidence: 79%

The sarcomere length-tension relation in skeletal muscle.

Keurs¹,

Iwazumi²,

Pollack³

1978

The Journal of General Physiology

155

114

View full text Add to dashboard Cite

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“…Close, 1972 Initial and reactivation latencies Some records used for studying latency and early tension development are illustrated in Fig. 1.…”

Section: Resultsmentioning

confidence: 99%

Activation delays in frog twitch muscle fibres.

Close¹

1981

The Journal of Physiology

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SUMMARY1. The length dependence of the mechanical latent period and early tension development, uncomplicated by latency relaxation, was determined from responses of single muscle fibres to restimulation at the peak of the isometric twitch at 15 'C.2. The onset of the reactivation response showed little (< 1x X 1O-7 N) or no latency relaxation.3. Reactivation latency was minimal (2-8 msec) and constant at 1P9-21 ,tm sarcomere length and it increased by about 3 msec with sarcomere extension to 3-2,sm.4. Reactivation responses showed two stages of early tension development, an initial phase in which tension acceleration increased, and a phase of maximum responsiveness in which tension acceleration was constant; the transition between the two phases occurred about 4-5 msec after the start of the stimulus at 2-2 jum sarcomere length and was delayed about 4 msec with increase in sarcomere length to 3-2 ,um.5. The square root of the maximum tension acceleration was directly proportional to the degree of overlap of thick and thin filaments in the sarcomere length range 2-3-3-2 ,um.6. It is proposed that the onset of the phase of constant tension acceleration marks the end of the period during which the activator, calcium, is distributed throughout the sarcomere.7. Analysis of early tension transients in relation to myofibril structure showed that length-dependent changes in reactivation latency and time of onset of constant tension acceleration were probably brought about mainly by alteration of the kinetics of distribution of activator within the myofibril and by changes in the diffusion distance between activator-release sites near the end of the sarcomere and the tension-generating sites.8. There was a 2 msec myofibril priming delay in the rise of tension in twitch responses that was not seen in reactivation responses; the possible origin of that delay is discussed in relation to structural changes accompanying activation and to competition between calcium-binding structures.9. The onset of twitch latency relaxation occurred within about 250 ,gsec after the time corresponding to latency of the earliest reactivation responses and appeared to signal the start of a process that took place after the arrival of calcium among the myofilaments. The origin of latency relaxation is discussed.

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“…This pattern closely matches that seen in the soleus and plantaris muscles, but not the medial gastrocnemius (Fig.·8). The assessment of such a relationship is hampered, however, by the complicated changes in activation-deactivation kinetics, which occur as a result of changes in strain (Brown et al, 1999;Close, 1972;Josephson and Stokes, 1999), motor unit firing frequency (Roszek et al, 1994) and muscle fascicle strain rates (Brown and Loeb, 2000). Activation-deactivation kinetics may also have influenced motor unit recruitment patterns as the result of a recruitment strategy to maximise metabolic efficiency.…”

Section: Motor Unit Recruitment Related To Activation-deactivation Kimentioning

confidence: 99%

Motor unit recruitment patterns 1: responses to changes in locomotor velocity and incline

Hodson-Tole

Wakeling

2008

Journal of Experimental Biology

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SUMMARYMammalian skeletal muscles are composed of a mixture of motor unit types, which contribute a range of mechanical and physiological properties to the muscle. For a muscle to effectively contribute to smooth, co-ordinated movement it must activate an appropriate number and combination of motor units to generate the required force over a suitable time period. Much evidence exists indicating that motor units are activated in an orderly fashion, from the slowest through to the fastest. A growing body of evidence, however, indicates that such a recruitment strategy does not always hold true. Here we investigate how motor unit recruitment patterns were influenced by changes in locomotor velocity and incline. Kinematics data and myoelectric signals were collected from three rat ankle extensor muscles during running on a treadmill at nine velocity and incline combinations. Wavelet and principal component analysis were used to simultaneously decompose the signals into time and frequency space. The relative frequency components of the signals were quantified during 20 time windows of a stride from each locomotor condition. Differences in signal frequency components existed between muscles and locomotor conditions. Faster locomotor velocities led to a relative increase in high frequency components, whereas greater inclines led to a relative increase in the low frequency components. These data were interpreted as representing changes in motor unit recruitment patterns in response to changes in the locomotor demand. Motor units were not always recruited in an orderly manner, indicating that recruitment is a multi-factorial phenomenon that is not yet fully understood.

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The relations between sarcomere length and characteristics of isometric twitch contractions of frog sartorius muscle

Cited by 115 publications

References 24 publications

The sarcomere length-tension relation in skeletal muscle.

The sarcomere length-tension relation in skeletal muscle.

Activation delays in frog twitch muscle fibres.

Motor unit recruitment patterns 1: responses to changes in locomotor velocity and incline

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