In Vivo Sarcomere Lengths Become More Non-uniform upon Activation in Intact Whole Muscle
The sarcomere force-length relationship has been extensively used to predict muscle force potential. The common practice is to measure the mean sarcomere length (SL) in a relaxed muscle at a single location and at a given length, and this mean SL is assumed to represent the SLs at other locations ac...
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| Format: | Article |
| Language: | English |
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Frontiers Media S.A.
2017-12-01
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| Series: | Frontiers in Physiology |
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| Online Access: | http://journal.frontiersin.org/article/10.3389/fphys.2017.01015/full |
| _version_ | 1811300592317890560 |
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| author | Eng Kuan Moo Timothy R. Leonard Walter Herzog |
| author_facet | Eng Kuan Moo Timothy R. Leonard Walter Herzog |
| author_sort | Eng Kuan Moo |
| collection | DOAJ |
| description | The sarcomere force-length relationship has been extensively used to predict muscle force potential. The common practice is to measure the mean sarcomere length (SL) in a relaxed muscle at a single location and at a given length, and this mean SL is assumed to represent the SLs at other locations across the muscle. However, in a previous study, we found that SLs are highly non-uniform across an intact passive muscle. Moreover, SL non-uniformity increases during activation in single myofibril experiments. Myofibrils lack some structural proteins that comprise an intact muscle, and therefore, the increased SL dispersion upon activation seen in myofibrils may not occur in intact whole muscle. The objectives of the current study were (i) to measure the distribution of SLs in an activated intact muscle; and (ii) to assess the feasibility of using the mean SL measured at a specific location of the muscle to predict muscle force. Using state-of-the-art multi-photon microscopy and a miniature tendon force transducer, in vivo sarcomeres in the mouse tibialis anterior were imaged simultaneously with muscle force during isometric tetanic contractions. We found that in vivo SL dispersion increased substantially during activation and reached average differences of ~1.0 μm. These differences in SL are associated with theoretical force differences of 70–100% of the maximal isometric force. Furthermore, SLs measured at a single location in the passive muscle were poor predictors of active force potential. Although mean SLs in the activated muscle were better predictors of force potential, predicted forces still differed by as much as 35% from the experimentally measured maximal isometric forces. |
| first_indexed | 2024-04-13T06:53:30Z |
| format | Article |
| id | doaj.art-d51abe528ef34b77b5edfb72b5ab777b |
| institution | Directory Open Access Journal |
| issn | 1664-042X |
| language | English |
| last_indexed | 2024-04-13T06:53:30Z |
| publishDate | 2017-12-01 |
| publisher | Frontiers Media S.A. |
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| series | Frontiers in Physiology |
| spelling | doaj.art-d51abe528ef34b77b5edfb72b5ab777b2022-12-22T02:57:20ZengFrontiers Media S.A.Frontiers in Physiology1664-042X2017-12-01810.3389/fphys.2017.01015315950In Vivo Sarcomere Lengths Become More Non-uniform upon Activation in Intact Whole MuscleEng Kuan MooTimothy R. LeonardWalter HerzogThe sarcomere force-length relationship has been extensively used to predict muscle force potential. The common practice is to measure the mean sarcomere length (SL) in a relaxed muscle at a single location and at a given length, and this mean SL is assumed to represent the SLs at other locations across the muscle. However, in a previous study, we found that SLs are highly non-uniform across an intact passive muscle. Moreover, SL non-uniformity increases during activation in single myofibril experiments. Myofibrils lack some structural proteins that comprise an intact muscle, and therefore, the increased SL dispersion upon activation seen in myofibrils may not occur in intact whole muscle. The objectives of the current study were (i) to measure the distribution of SLs in an activated intact muscle; and (ii) to assess the feasibility of using the mean SL measured at a specific location of the muscle to predict muscle force. Using state-of-the-art multi-photon microscopy and a miniature tendon force transducer, in vivo sarcomeres in the mouse tibialis anterior were imaged simultaneously with muscle force during isometric tetanic contractions. We found that in vivo SL dispersion increased substantially during activation and reached average differences of ~1.0 μm. These differences in SL are associated with theoretical force differences of 70–100% of the maximal isometric force. Furthermore, SLs measured at a single location in the passive muscle were poor predictors of active force potential. Although mean SLs in the activated muscle were better predictors of force potential, predicted forces still differed by as much as 35% from the experimentally measured maximal isometric forces.http://journal.frontiersin.org/article/10.3389/fphys.2017.01015/fullsecond harmonic generation microscopyactive contractionin vivonon-uniformityforce-length relationshipskeletal muscle properties |
| spellingShingle | Eng Kuan Moo Timothy R. Leonard Walter Herzog In Vivo Sarcomere Lengths Become More Non-uniform upon Activation in Intact Whole Muscle Frontiers in Physiology second harmonic generation microscopy active contraction in vivo non-uniformity force-length relationship skeletal muscle properties |
| title | In Vivo Sarcomere Lengths Become More Non-uniform upon Activation in Intact Whole Muscle |
| title_full | In Vivo Sarcomere Lengths Become More Non-uniform upon Activation in Intact Whole Muscle |
| title_fullStr | In Vivo Sarcomere Lengths Become More Non-uniform upon Activation in Intact Whole Muscle |
| title_full_unstemmed | In Vivo Sarcomere Lengths Become More Non-uniform upon Activation in Intact Whole Muscle |
| title_short | In Vivo Sarcomere Lengths Become More Non-uniform upon Activation in Intact Whole Muscle |
| title_sort | in vivo sarcomere lengths become more non uniform upon activation in intact whole muscle |
| topic | second harmonic generation microscopy active contraction in vivo non-uniformity force-length relationship skeletal muscle properties |
| url | http://journal.frontiersin.org/article/10.3389/fphys.2017.01015/full |
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