Academic Journal
Improved muscle gearing in the medial gastrocnemius of pregnant and lactating rats.
| Title: | Improved muscle gearing in the medial gastrocnemius of pregnant and lactating rats. |
|---|---|
| Authors: | Arias AA; Department of Biology, University of San Diego, San Diego, California, United States., Delargy ML; Department of Biology, University of San Diego, San Diego, California, United States., Danos N; Department of Biology, University of San Diego, San Diego, California, United States. |
| Source: | Journal of applied physiology (Bethesda, Md. : 1985) [J Appl Physiol (1985)] 2026 Oct 01; Vol. 141 (4), pp. 1208-1217. Date of Electronic Publication: 2026 Sep 28. |
| Publication Type: | Journal Article |
| Language: | English |
| Journal Info: | Publisher: American Physiological Society Country of Publication: United States NLM ID: 8502536 Publication Model: Print-Electronic Cited Medium: Internet ISSN: 1522-1601 (Electronic) Linking ISSN: 01617567 NLM ISO Abbreviation: J Appl Physiol (1985) Subsets: MEDLINE |
| Imprint Name(s): | Original Publication: Bethesda, MD : American Physiological Society, c1985- |
| MeSH Terms: | Lactation*/physiology , Muscle, Skeletal*/physiology , Muscle Contraction*/physiology, Adaptation, Physiological/physiology ; Animals ; Female ; Pregnancy ; Rats ; Biomechanical Phenomena ; Rats, Sprague-Dawley |
| Abstract: | Pennate muscles typically contract with complex three-dimensional shape changes that vary in magnitude across muscle force levels, allowing improved muscle fiber force-velocity dynamics across a whole muscle's range of forces (i.e., variable gearing ability). Previous work on the underlying mechanisms that dictate variable gearing suggests that the mechanical properties of intramuscular and extracellular connective tissue can act to constrain muscle bulging and gearing ability. However, it remains unclear whether increased muscle compliance can confer improved gearing ability. Recent work in pregnant and lactating rats suggests adaptations in the medial gastrocnemius (MG) muscle that may influence variable gearing ability and overall function. Here, we used in situ muscle preparations in rats to characterize the range of architectural gear ratios (AGR = muscle velocity/fascicle velocity), force-length properties, and force-velocity properties of isolated gastrocnemii to test the hypothesis that gearing ability improves during pregnancy and lactation. We found that pregnant and lactating rats exhibit a significantly wider range of AGRs and a steeper linear relationship between AGR and muscle force, suggesting an improved ability to fine-tune fiber contractile dynamics to force level during dynamic muscle contractions. This improved gearing ability is underpinned by longer muscle fascicles in pregnant and lactating rats, which have broader implications on in vivo force-velocity dynamics during locomotion. We conclude that young female rats are a viable biological system that naturally varies in gearing ability across different reproductive stages without differences in relative muscle stiffness.NEW & NOTEWORTHY Musculoskeletal remodeling in the medial gastrocnemius of pregnant and lactating rats suggests adaptations that may influence variable gearing ability. Here, we show improved gearing dynamics in pregnant and lactating rats compared with nonpregnant controls due, in part, to longer muscle fascicles. These findings add fascicle length to the list of mechanisms proposed to influence variable gearing in pennate muscle and has broader implications on in vivo force-length dynamics during locomotion in pregnant and lactating animals. |
| Grant Information: | 2239863 National Science Foundation (NSF) |
| Contributed Indexing: | Keywords: architectural gear ratio; lactation; muscle belly gearing; pregnancy; variable gearing |
| Entry Date(s): | Date Created: 20260928 Date Completed: 20261019 Latest Revision: 20261019 |
| Update Code: | 20261020 |
| DOI: | 10.1152/japplphysiol.01083.2025 |
| PMID: | 42804462 |
| Database: | MEDLINE |
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