Motor units within the normal rat medial gastrocnemius

Einsiedel, L.J.; Luff, A. R.

doi:10.1113/expphysiol.1993.sp003691

Cited by 6 publications

(7 citation statements)

References 26 publications

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“…P tw :P tet was higher in FF than in S, FR, or FI motor units. Previous studies found similar differences between FF and S motor units in twitch:tetanus ratio, but all F units had similar values (Celichowski and Grottel 1993;Einsiedel and Luff 1993). A greater degree of twitch potentiation (i.e., lower P tw :P pot ratio) was seen in F than in S motor units; this was FIG. 11.…”

Section: Relationship Between Sag and Other Motor Unit Propertiessupporting

confidence: 54%

“…Stimulation at 40 Hz is the de facto standard of motor unit typing in cats (Burke et al 1973). However, CT tw of TS motor units is substantially shorter in rats (Bakels and Kernell 1993b;Chamberlain and Lewis 1989;Einsiedel and Luff 1993;Gardiner 1993;Grottel and Celichowski 1990) than that in cats (Burke 1967;Burke et al 1973;Proske and Waite 1974;Wuerker et al 1965). Therefore a higher stimulation frequency was chosen to maintain a comparable degree of tetanic fusion.…”

Section: Electrophysiological Recordingmentioning

confidence: 99%

“…Studies of rat triceps surae (TS) motor unit contractile properties have produced qualitatively similar results, but there has not been general agreement on the specific criteria for type identification. The presence or absence of sag as a lone predictor of the speed of contraction has been confirmed in some studies (Chamberlain and Lewis 1989;Einsiedel and Luff 1993;Kanda and Hashizume 1989) but not in others (Bakels and Kernell 1993a,b;Grottel and Celichowski 1990). In these studies, sag was evaluated under widely varying conditions (e.g., at fixed stimulation frequencies or at frequencies based on the speed of contraction and with single trains or with batteries of trains at different stimulation frequencies).…”

mentioning

confidence: 95%

“…In these studies, sag was evaluated under widely varying conditions (e.g., at fixed stimulation frequencies or at frequencies based on the speed of contraction and with single trains or with batteries of trains at different stimulation frequencies). Sag has been demonstrated to be present at some stimulation frequencies in a given unit, but not all units display the same pattern of frequency dependence or even the same force envelope shapes (Celichowski 1992a;Einsiedel and Luff 1993;Gardiner 1993;Grottel and Celichowski 1990). Thus it is not surprising that a consistent classification scheme for F versus S units has not emerged for rat motor units.…”

mentioning

confidence: 99%

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Sag During Unfused Tetanic Contractions in Rat Triceps Surae Motor Units

Carp

Herchenroder

Chen

et al. 1999

Journal of Neurophysiology

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Contractile properties and conduction velocity were studied in 202 single motor units of intact rat triceps surae muscles activated by intra-axonal (or intra-myelin) current injection in L5 or L6 ventral root to assess the factors that determine the expression of sag (i.e., decline in force after initial increase during unfused tetanic stimulation). Sag was consistently detected in motor units with unpotentiated twitch contraction times <20 ms. However, the range of frequencies at which sag was expressed varied among motor units such that there was no single interstimulus interval (ISI), with or without adjusting for twitch contraction time, at which sag could be detected reliably. Further analysis indicated that using the absence of sag as a criterion for identifying slow-twitch motor units requires testing with tetani at several different ISIs. In motor units with sag, the shape of the force profile varied with tetanic frequency and contractile properties. Simple sag force profiles (single maximum reached late in the tetanus followed by monotonic decay) tended to occur at shorter ISIs and were observed more frequently in fatigue-resistant motor units with long half-relaxation times and small twitch amplitudes. Complex sag profiles reached an initial maximum early in the tetanus, tended to occur at longer ISIs, and were more common in fatigue-sensitive motor units with long half-relaxation times and large twitch amplitudes. The differences in frequency dependence and force maximum location suggested that these phenomena represented discrete entities. Successive stimuli elicited near-linear increments in force during tetani in motor units that never exhibited sag. In motor units with at least one tetanus displaying sag, tetanic stimulation elicited large initial force increments followed by rapidly decreasing force increments. That the latter force envelope pattern occurred in these units even in tetani without sag suggested that the factors responsible for sag were expressed in the absence of overt sag. The time-to-peak force (TTP) of the individual contractions during a tetanus decreased in tetani with sag. Differences in the pattern of TTP change during a tetanus were consistent with the differences in force maximum location between tetani exhibiting simple and complex sag. Tetani from motor units that never exhibited sag did not display a net decrease in TTP during successive contractions. These data were consistent with the initial force decrement of sag resulting from a transient reduction in the duration of the contractile state.

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Section: Relationship Between Sag and Other Motor Unit Propertiessupporting

confidence: 54%

Section: Electrophysiological Recordingmentioning

confidence: 99%

mentioning

confidence: 95%

mentioning

confidence: 99%

See 2 more Smart Citations

Sag During Unfused Tetanic Contractions in Rat Triceps Surae Motor Units

Carp

Herchenroder

Chen

et al. 1999

Journal of Neurophysiology

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“…Einsiedel and Luff,22 in physiological studies of the functional characteristics of motor units, described ‘ the existence of a motor unit continuum ’. They found that from the smallest fatigue-resistant slow units to the larger fast-fatiguable units, ‘ an almost continuous range of fatigue resistance and motor unit force exists ’.…”

Section: Histochemical Muscle Fibre Types: Are the Assumptions Correct?mentioning

confidence: 99%

Six issues in muscle disease

Swash

2017

J Neurol Neurosurg Psychiatry

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Parameter interdependence and success of skeletal muscle modelling

Huijing

1995

Human Movement Science

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In muscle and movement modelling it is almost invariably assumed that force actually exerted is determined by several independent factors. This review considers the fact that length force characteristics are not a relatively fixed property of muscle but should be considered the product of a substantial number of interacting factors. Level of activation and recruitment are influential factors in relation to aspects of muscle architecture. For the level of activation effects of its short term history (potentiation, fatigue in sustained contractions) have to be taken into account and are reviewed on the basis of recent experimental results as well as available literature. History is also an important determinant for the effect of length changes. This concept is introduced on the basis of recent experimental evidence as well as available literature. Regarding effects of muscle architecture, the concepts of primary and secondary distribution of fibre mean sarcomere length are introduced as well as effects of muscle geometry for mono-and bi-articular muscles on those distributions. Implications for motor control are discussed and the need for intramuscular coordination indicated.

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Motor units within the normal rat medial gastrocnemius

Abstract: SUMMARYThe contractile properties, fatiguability and axonal conduction velocity were

Cited by 6 publications

References 26 publications

Sag During Unfused Tetanic Contractions in Rat Triceps Surae Motor Units

Sag During Unfused Tetanic Contractions in Rat Triceps Surae Motor Units

Six issues in muscle disease

Parameter interdependence and success of skeletal muscle modelling

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