Force enhancement in the human vastus lateralis is muscle-length-dependent following stretch but not during stretch
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ORIGINAL ARTICLE
Force enhancement in the human vastus lateralis is muscle‑length‑dependent following stretch but not during stretch Patrick Bakenecker1 · Brent J. Raiteri1 · Daniel Hahn1,2 Received: 24 May 2020 / Accepted: 29 August 2020 © The Author(s) 2020
Abstract Purpose Force 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. Methods We 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. Results We 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
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