The distinctive mechanical and structural signatures of residual force enhancement in myofibers

Hessel, Anthony L.; Kuehn, Michel; Palmer, Bradley M.; Nissen, Devin; Mishra, Dhruv; Joumaa, Venus; Freundt, Johanna K.; Ma, Weikang; Nishikawa, Kiisa C.; Irving, Thomas C.; Linke, Wolfgang A.

doi:10.1101/2023.02.19.529125

Cited by 4 publications

(2 citation statements)

References 72 publications

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“…Due to progressive fascicle stretch, this passive element could have progressively increased its force contribution to rFE once it was engaged. We speculate that this passive element, possibly titin (67), was not engaged upon muscle activation at the initially short lengths in our MTU-stretch-hold conditions, but that the passive element became engaged during active muscle stretch around the same muscle length, which resulted in it being stretched similarly across conditions. Subsequently, its passive force contribution remained similar following stretch across our MTU-stretch-hold conditions, which was reflected by similar rFE.…”

Section: Discussionmentioning

confidence: 91%

Eccentric exercise ≠ eccentric contraction

Tecchio,

Raiteri,

Hahn

2024

Journal of Applied Physiology

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Whether eccentric exercise involves active fascicle stretch is unclear due to muscle-tendon unit (MTU) series elasticity. Therefore, this study investigated the impact of changing the activation timing and level (i.e., pre-activation) of the contraction on muscle fascicle kinematics and kinetics of the human tibialis anterior during dynamometer-controlled maximal voluntary MTU-stretch-hold contractions. B-mode ultrasound and surface electromyography were employed to assess muscle fascicle kinematics and muscle activity levels, respectively. While joint kinematics were similar among MTU-stretch-hold contractions (~40° rotation amplitude), increasing pre-activation increased fascicle shortening and stretch amplitudes (9.9-23.2 mm, p ≤ 0.015). This led to increasing positive and negative fascicle work with increasing pre-activation. Despite significantly different fascicle kinematics, similar peak fascicle forces during stretch occurred at similar fascicle lengths and joint angles regardless of pre-activation. Similarly, residual force enhancement (rFE) following MTU stretch was not significantly affected (6.5-7.6%, p = 0.559) by pre-activation, but rFE was strongly correlated with peak fascicle force during stretch ( rrm = 0.62, p = 0.003). These findings highlight that apparent eccentric exercise causes shortening-stretch contractions at the fascicle level rather than isolated eccentric contractions. The constant rFE despite different fascicle kinematics and kinetics suggests that a passive element was engaged at a common muscle length among conditions (e.g., optimal fascicle length). Although it remains unclear whether different fascicle mechanics trigger different adaptations to eccentric exercise, this study emphasizes the need to consider MTU series elasticity to better understand the mechanical drivers of adaptation to exercise.

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Section: Discussionmentioning

confidence: 91%

Eccentric exercise ≠ eccentric contraction

Tecchio,

Raiteri,

Hahn

2024

Journal of Applied Physiology

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“…The mechanisms of rFE and rFD originate at the cellular level. For rFE, in the presence of Ca 2+ and cross-bridge cycling, ‘the molecular spring’ titin becomes stiffer thereby contributing greater tension during and following active lengthening of the muscle (Hahn et al, 2023; Herzog, 2018; Hessel et al, 2023), resulting in a greater contribution of passive force to total force production as compared with a fix-end isometric contraction (Herzog and Leonard, 2002). As well, rFE is greatest following large stretch amplitudes to long muscle lengths (Bakenecker et al, 2022; Fukutani et al, 2017; Rassier and Herzog, 2004).…”

Section: Introductionmentioning

confidence: 99%

Residual force enhancement is not altered while force depression is amplified at the cellular level in old age

Njai,

Hinks,

Patterson

et al. 2024

Preprint

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Residual force enhancement (rFE) and residual force depression (rFD) are history-dependent properties of muscle which refer to increased and decreased isometric force following a lengthening or shortening contraction, respectively. The history-dependence of force is greater in older than younger adults when assessed at the joint level. However, it is unclear whether this amplification of the history-dependence of force in old age is owing to cellular mechanisms or a consequence of age-related remodeling of muscle architecture. Single muscle fibres from the psoas major of old and young F344BN rats were dissected and chemically permeabilized. Single muscle fibres were mounted between a force transducer and length controller, then maximally activated (pCa 4.5). To assess rFD, fibers were actively shortened from 3.1 to 2.5µm at both a slow (0.15Lo/s) and fast (0.6Lo/s) speed, with a fixed-end isometric reference contraction at 2.5µm. To assess rFE, fibers were activated and stretched at 0.3Lo/s from a sarcomere length of 2.2 to 2.5µm, and 2.7 to 3.0µm, and compared to fixed-end isometric reference contractions at 2.5 and 3.0µm, respectively. Isometric force was ≈19% lower in old as compared with young (p<0.001). Upon normalizing to fibre cross-sectional area, there was no age-related difference in specific force (p>0.05). rFD was ≈33% greater in old as compared with young (p<0.05), while rFE did not differ between groups (p>0.05). rFD is amplified in old age at the cellular level, while rFE appears to be unchanged, thus previously reported age-related modification of rFE occurs upstream from the cellular level.

show abstract

Eccentric exercise ≠ eccentric contraction

Tecchio,

Raiteri,

Hahn

2023

Preprint

View full text Add to dashboard Cite

Whether eccentric exercise involves active fascicle stretch is unclear due to muscle-tendon unit (MTU) series elasticity. Therefore, this study investigated the impact of changing the activation timing and level (i.e., pre-activation) on muscle fascicle kinematics and kinetics of the human tibialis anterior during dynamometer-controlled maximal voluntary MTU-stretch-hold contractions. B-mode ultrasound and surface electromyography were employed to assess muscle fascicle kinematics and muscle activity levels, respectively. While joint kinematics were similar for MTU-stretch-hold contractions, increasing pre-activation increased fascicle shortening and stretch amplitudes (9.9 - 23.2 mm,p≤ 0.015). This led to increasing positive and negative fascicle work with increasing pre-activation. Despite significantly different fascicle kinematics, similar peak fascicle forces during stretch occurred at similar fascicle lengths and joint angles regardless of pre-activation. Similarly, residual force enhancement (rFE) following MTU stretch was not significantly affected (6.5–7.6 %,p= 0.559) by pre-activation, but rFE was strongly correlated with peak fascicle force during stretch (rrm= 0.62,p= 0.003). These findings highlight that apparent eccentric exercise causes shortening-stretch contractions at the fascicle level rather than isolated eccentric contractions. The constant rFE despite different fascicle kinematics and kinetics suggests that a passive element was engaged at a common muscle length among conditions (e.g., optimal fascicle length). Although it remains unclear whether different fascicle mechanics trigger different adaptations to eccentric exercise, this study emphasizes the need to consider MTU series elasticity to better understand the mechanical drivers of adaptation to exercise.New & NoteworthyApparent eccentric exercises do not result in isolated eccentric contractions, but shortening-stretch contractions at the fascicle level. The amount of fascicle shortening and stretch depend on the pre-activation during the exercise andcannotbe estimated from the muscle-tendon unit or joint kinematics. As different fascicle mechanics might trigger different adaptations to eccentric exercise, muscle-tendon unit series elasticity and muscle pre-activation need to be considered when eccentric exercise protocols and designed and evaluated.

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The distinctive mechanical and structural signatures of residual force enhancement in myofibers

Cited by 4 publications

References 72 publications

Eccentric exercise ≠ eccentric contraction

Eccentric exercise ≠ eccentric contraction

Residual force enhancement is not altered while force depression is amplified at the cellular level in old age

Eccentric exercise ≠ eccentric contraction

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