Force enhancement in the human vastus lateralis is muscle-length-dependent following stretch but not during stretch.

Content Provider	Europe PMC
Author	Bakenecker, Patrick Raiteri, Brent J. Hahn, Daniel
Abstract	PurposeForce enhancement is the phenomenon of increased forces during (transient force enhancement; tFE) and after (residual force enhancement; rFE) eccentric muscle actions compared with fixed-end contractions. Although tFE and rFE have been observed at short and long muscle lengths, whether both are length-dependent remains unclear in vivo.MethodsWe determined maximal-effort vastus lateralis (VL) force-angle relationships of eleven healthy males and selected one knee joint angle at a short and long muscle lengths where VL produced approximately the same force (85% of maximum). We then examined tFE and rFE at these two lengths during and following the same amount of knee joint rotation.ResultsWe found tFE at both short (11.7%, P = 0.017) and long (15.2%, P = 0.001) muscle lengths. rFE was only observed at the long (10.6%, P < 0.001; short: 1.3%, P = 0.439) muscle length. Ultrasound imaging revealed that VL muscle fascicle stretch magnitude was greater at long compared with short muscle lengths (mean difference: (tFE) 1.7 mm, (rFE) 1.9 mm, P ≤ 0.046), despite similar isometric VL forces across lengths (P ≥ 0.923). Greater fascicle stretch magnitude was likely to be due to greater preload forces at the long compared with short muscle length (P ≤ 0.001).ConclusionAt a similar isometric VL force capacity, tFE was not muscle-length-dependent at the lengths we tested, whereas rFE was greater at longer muscle length. We speculate that the in vivo mechanical factors affecting tFE and rFE are different and that greater stretch of a passive component is likely contributing more to rFE at longer muscle lengths.Electronic supplementary materialThe online version of this article (10.1007/s00421-020-04488-1) contains supplementary material, which is available to authorized users.
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ISSN	14396319
Journal	European Journal of Applied Physiology [Eur J Appl Physiol]
Volume Number	120
DOI	10.1007/s00421-020-04488-1
PubMed Central reference number	PMC7674334
Issue Number	12
PubMed reference number	32892321
e-ISSN	14396327
Language	English
Publisher	Springer Berlin Heidelberg
Publisher Date	2020-09-05
Publisher Place	Berlin/Heidelberg
Access Restriction	Open
Rights License	Open AccessThis article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. © The Author(s) 2020
Subject Keyword	Eccentric Force–length relation Knee extensors Muscle history dependence Quadriceps
Content Type	Text
Resource Type	Article
Subject	Orthopedics and Sports Medicine Physiology (medical) Public Health, Environmental and Occupational Health Sports Science