Gradation of isometric tension by different activation rates in motor units of cat flexor carpi radialis muscle

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Abstract

1. Single motor units of the flexor carpi radialis (FCR) muscle were activated with a series of constant-rate stimulus trains to study the relation between the frequency of activation and isometric tension development (F-T relation). The tension produced by each stimulus train was expressed as a percentage of the maximum tension-time area (A(max)) found for a given unit. 2. Between 25 and 75% A(max) a clear separation was seen in the rates needed to produce the same relative tension for the F-T curves of slow-twitch (type S) and fast-twitch (type F) units. Over the steepest portion of the F-T curve (25-50% A(max)), where tension output was most sensitive to changes in activation rate, type F units required substantially higher stimulation rates (30 pps) to achieve the same relative tension output as type S units. Furthermore, the frequency range that corresponded to the steep portion of the curve was 2.3 times greater for type F units. 3. For both type S and F units, twitch duration was deemed to be an important determinant of the F-T curve, as has been shown previously. A direct continuous relation was seen between the integrated twitch time (ITT) and the stimulus interval needed to produce 50% A(max) (r = 0.94, P < 0.001). Thus, units that had relatively brief twitches required higher activation rates to achieve the same relative percentage of A(max). 4. Comparison of F-T curves from FCR with those derived by other investigators for cat hindlimb units (medial gastrocnemius and peroneus longus; Ref. 34) revealed that significant differences in activation rates were needed to produce the same percentage of A(max) throughout the midrange of the F-T curve. At 50% A(max), type F units in FCR required activation rates ~20 pps higher than type F units in the hindlimb. Type S units in FCR required only slightly higher rates (~5 pps). 5. Based on a number of well-founded assumptions, F-T curves derived from FCR units were used to estimate the potential contribution of rate coding to total muscle tension by type S and F units. This analysis leads to the conclusion that rate modulation is a potentially important factor in the gradation of tension for the FCR muscle.

Original languageEnglish (US)
Pages (from-to)494-506
Number of pages13
JournalJournal of Neurophysiology
Volume56
Issue number2
StatePublished - 1986

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Hindlimb
Cats
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Muscle Tonus
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ASJC Scopus subject areas

  • Physiology
  • Neuroscience(all)

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@article{3e2aacd0d10244518a4cfeeb2b26f9ff,
title = "Gradation of isometric tension by different activation rates in motor units of cat flexor carpi radialis muscle",
abstract = "1. Single motor units of the flexor carpi radialis (FCR) muscle were activated with a series of constant-rate stimulus trains to study the relation between the frequency of activation and isometric tension development (F-T relation). The tension produced by each stimulus train was expressed as a percentage of the maximum tension-time area (A(max)) found for a given unit. 2. Between 25 and 75{\%} A(max) a clear separation was seen in the rates needed to produce the same relative tension for the F-T curves of slow-twitch (type S) and fast-twitch (type F) units. Over the steepest portion of the F-T curve (25-50{\%} A(max)), where tension output was most sensitive to changes in activation rate, type F units required substantially higher stimulation rates (30 pps) to achieve the same relative tension output as type S units. Furthermore, the frequency range that corresponded to the steep portion of the curve was 2.3 times greater for type F units. 3. For both type S and F units, twitch duration was deemed to be an important determinant of the F-T curve, as has been shown previously. A direct continuous relation was seen between the integrated twitch time (ITT) and the stimulus interval needed to produce 50{\%} A(max) (r = 0.94, P < 0.001). Thus, units that had relatively brief twitches required higher activation rates to achieve the same relative percentage of A(max). 4. Comparison of F-T curves from FCR with those derived by other investigators for cat hindlimb units (medial gastrocnemius and peroneus longus; Ref. 34) revealed that significant differences in activation rates were needed to produce the same percentage of A(max) throughout the midrange of the F-T curve. At 50{\%} A(max), type F units in FCR required activation rates ~20 pps higher than type F units in the hindlimb. Type S units in FCR required only slightly higher rates (~5 pps). 5. Based on a number of well-founded assumptions, F-T curves derived from FCR units were used to estimate the potential contribution of rate coding to total muscle tension by type S and F units. This analysis leads to the conclusion that rate modulation is a potentially important factor in the gradation of tension for the FCR muscle.",
author = "Botterman, {B. R.} and Iwamoto, {G. A.} and Gonyea, {W. J.}",
year = "1986",
language = "English (US)",
volume = "56",
pages = "494--506",
journal = "Journal of Neurophysiology",
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publisher = "American Physiological Society",
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T1 - Gradation of isometric tension by different activation rates in motor units of cat flexor carpi radialis muscle

AU - Botterman, B. R.

AU - Iwamoto, G. A.

AU - Gonyea, W. J.

PY - 1986

Y1 - 1986

N2 - 1. Single motor units of the flexor carpi radialis (FCR) muscle were activated with a series of constant-rate stimulus trains to study the relation between the frequency of activation and isometric tension development (F-T relation). The tension produced by each stimulus train was expressed as a percentage of the maximum tension-time area (A(max)) found for a given unit. 2. Between 25 and 75% A(max) a clear separation was seen in the rates needed to produce the same relative tension for the F-T curves of slow-twitch (type S) and fast-twitch (type F) units. Over the steepest portion of the F-T curve (25-50% A(max)), where tension output was most sensitive to changes in activation rate, type F units required substantially higher stimulation rates (30 pps) to achieve the same relative tension output as type S units. Furthermore, the frequency range that corresponded to the steep portion of the curve was 2.3 times greater for type F units. 3. For both type S and F units, twitch duration was deemed to be an important determinant of the F-T curve, as has been shown previously. A direct continuous relation was seen between the integrated twitch time (ITT) and the stimulus interval needed to produce 50% A(max) (r = 0.94, P < 0.001). Thus, units that had relatively brief twitches required higher activation rates to achieve the same relative percentage of A(max). 4. Comparison of F-T curves from FCR with those derived by other investigators for cat hindlimb units (medial gastrocnemius and peroneus longus; Ref. 34) revealed that significant differences in activation rates were needed to produce the same percentage of A(max) throughout the midrange of the F-T curve. At 50% A(max), type F units in FCR required activation rates ~20 pps higher than type F units in the hindlimb. Type S units in FCR required only slightly higher rates (~5 pps). 5. Based on a number of well-founded assumptions, F-T curves derived from FCR units were used to estimate the potential contribution of rate coding to total muscle tension by type S and F units. This analysis leads to the conclusion that rate modulation is a potentially important factor in the gradation of tension for the FCR muscle.

AB - 1. Single motor units of the flexor carpi radialis (FCR) muscle were activated with a series of constant-rate stimulus trains to study the relation between the frequency of activation and isometric tension development (F-T relation). The tension produced by each stimulus train was expressed as a percentage of the maximum tension-time area (A(max)) found for a given unit. 2. Between 25 and 75% A(max) a clear separation was seen in the rates needed to produce the same relative tension for the F-T curves of slow-twitch (type S) and fast-twitch (type F) units. Over the steepest portion of the F-T curve (25-50% A(max)), where tension output was most sensitive to changes in activation rate, type F units required substantially higher stimulation rates (30 pps) to achieve the same relative tension output as type S units. Furthermore, the frequency range that corresponded to the steep portion of the curve was 2.3 times greater for type F units. 3. For both type S and F units, twitch duration was deemed to be an important determinant of the F-T curve, as has been shown previously. A direct continuous relation was seen between the integrated twitch time (ITT) and the stimulus interval needed to produce 50% A(max) (r = 0.94, P < 0.001). Thus, units that had relatively brief twitches required higher activation rates to achieve the same relative percentage of A(max). 4. Comparison of F-T curves from FCR with those derived by other investigators for cat hindlimb units (medial gastrocnemius and peroneus longus; Ref. 34) revealed that significant differences in activation rates were needed to produce the same percentage of A(max) throughout the midrange of the F-T curve. At 50% A(max), type F units in FCR required activation rates ~20 pps higher than type F units in the hindlimb. Type S units in FCR required only slightly higher rates (~5 pps). 5. Based on a number of well-founded assumptions, F-T curves derived from FCR units were used to estimate the potential contribution of rate coding to total muscle tension by type S and F units. This analysis leads to the conclusion that rate modulation is a potentially important factor in the gradation of tension for the FCR muscle.

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