scholarly journals Energy Cost of Force Production After a Stretch-Shortening Cycle in Skinned Muscle Fibers: Does Muscle Efficiency Increase?

2021 ◽  
Vol 11 ◽  
Author(s):  
Venus Joumaa ◽  
Atsuki Fukutani ◽  
Walter Herzog
Keyword(s):  
Steady State ◽  
Energy Cost ◽  
Muscle Force ◽  
Metabolic Energy ◽  
Total Force ◽  
Force Enhancement ◽  
Residual Force ◽  
Stretch Shortening Cycle ◽  
Residual Force Enhancement ◽  
Shortening Contractions

Muscle force is enhanced during shortening when shortening is preceded by an active stretch. This phenomenon is known as the stretch-shortening cycle (SSC) effect. For some stretch-shortening conditions this increase in force during shortening is maintained following SSCs when compared to the force following a pure shortening contraction. It has been suggested that the residual force enhancement property of muscles, which comes into play during the stretch phase of SSCs may contribute to the force increase after SSCs. Knowing that residual force enhancement is associated with a substantial reduction in metabolic energy per unit of force, it seems reasonable to assume that the metabolic energy cost per unit of force is also reduced following a SSC. The purpose of this study was to determine the energy cost per unit of force at steady-state following SSCs and compare it to the corresponding energy cost following pure shortening contractions of identical speed and magnitude. We hypothesized that the energy cost per unit of muscle force is reduced following SSCs compared to the pure shortening contractions. For the SSC tests, rabbit psoas fibers (n = 12) were set at an average sarcomere length (SL) of 2.4 μm, activated, actively stretched to a SL of 3.2 μm, and shortened to a SL of 2.6 or 3.0 μm. For the pure shortening contractions, the same fibers were activated at a SL of 3.2 μm and actively shortened to a SL of 2.6 or 3.0 μm. The amount of ATP consumed was measured over a 40 s steady-state total isometric force following either the SSCs or the pure active shortening contractions. Fiber stiffness was determined in an additional set of 12 fibers, at steady-state for both experimental conditions. Total force, ATP consumption, and stiffness were greater following SSCs compared to the pure shortening contractions, but ATP consumption per unit of force was the same between conditions. These results suggest that the increase in total force observed following SSCs was achieved with an increase in the proportion of attached cross-bridges and titin stiffness. We conclude that muscle efficiency is not enhanced at steady-state following SSCs.

scholarly journals Influence of muscle length on the stretch-shortening cycle in skinned rabbit soleus

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Atsuki Fukutani ◽  
Tadao Isaka
Keyword(s):  
Muscle Force ◽  
Muscle Length ◽  
Relative Increase ◽  
Mechanical Work ◽  
Skinned Fibers ◽  
Force Enhancement ◽  
Residual Force ◽  
Stretch Shortening Cycle ◽  
Residual Force Enhancement

AbstractMuscle force generated during shortening is instantaneously increased after active stretch. This phenomenon is called as stretch-shortening cycle (SSC) effect. It has been suggested that residual force enhancement contributes to the SSC effect. If so, the magnitude of SSC effect should be larger in the longer muscle length condition, because the residual force enhancement is prominent in the long muscle length condition. This hypothesis was examined by performing the SSC in the short and long muscle length conditions. Skinned fibers obtained from rabbit soleus (N = 20) were used in this study. To calculate the magnitude of SSC effect, the SSC trial (isometric-eccentric-concentric-isometric) and the control trial (isometric-concentric-isometric) were conducted in the short (within the range of 2.4 to 2.7 μm) and long muscle (within the range of 3.0 to 3.3 μm). The magnitude of SSC effect was calculated as the relative increase in the mechanical work attained during the shortening phase between control and SSC trials. As a result, the magnitude of SSC effect was significantly larger in the long (176.8 ± 18.1%) than in the short muscle length condition (157.4 ± 8.5%) (p < 0.001). This result supports our hypothesis that the magnitude of SSC effect is larger in the longer muscle length condition, possibly due to the larger magnitude of residual force enhancement.

scholarly journals Modifiability of the history dependence of force through chronic eccentric and concentric biased resistance training

2019 ◽  
Vol 126 (3) ◽  
pp. 647-657 ◽  
Author(s):  
Jackey Chen ◽  
Geoffrey A. Power
Keyword(s):  
Steady State ◽  
Resistance Training ◽  
Isometric Force ◽  
Eccentric Training ◽  
Force Enhancement ◽  
History Dependence ◽  
Force Depression ◽  
Residual Force ◽  
Residual Force Enhancement ◽  
Concentric Training

The increase and decrease in steady-state isometric force following active muscle lengthening and shortening are referred to as residual force enhancement (RFE) and force depression (FD), respectively. The RFE and FD states are associated with decreased (activation reduction; AR) and increased (activation increase; AI) neuromuscular activity, respectively. Although the mechanisms have been discussed over the last 60 years, no studies have systematically investigated the modifiability of RFE and FD with training. The purpose of the present study was to determine whether RFE and FD could be modulated through eccentric and concentric biased resistance training. Fifteen healthy young adult men (age: 24 ± 2 yr, weight: 77 ± 8 kg, height: 178 ± 5 cm) underwent 4 wk of isokinetic dorsiflexion training, in which one leg was trained eccentrically (−25°/s) and the other concentrically (+25°/s) over a 50° ankle excursion. Maximal and submaximal (40% maximum voluntary contraction) steady-state isometric torque and EMG values following active lengthening and shortening were compared to purely isometric values at the same joint angles and torque levels. Residual torque enhancement (rTE) decreased by ~36% after eccentric training ( P < 0.05) and increased by ~89% after concentric training ( P < 0.05), whereas residual torque depression (rTD), AR, AI, and optimal angles for torque production were not significantly altered by resistance training ( P ≥ 0.05). It appears that rTE, but not rTD, for the human ankle dorsiflexors is differentially modifiable through contraction type-dependent resistance training. NEW & NOTEWORTHY The history dependence of force production is a property of muscle unexplained by current cross bridge and sliding filament theories. Whether a muscle is actively lengthened (residual force enhancement; RFE) or shortened (force depression) to a given length, the isometric force should be equal to a purely isometric contraction—but it is not! In this study we show that eccentric training decreased RFE, whereas concentric training increased RFE and converted all nonresponders (i.e., not exhibiting RFE) into responders.

scholarly journals Force enhancement after stretch of isolated myofibrils is increased by sarcomere length non-uniformities

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Ricarda M. Haeger ◽  
Dilson E. Rassier
Keyword(s):  
Steady State ◽  
Sarcomere Length ◽  
Isometric Force ◽  
Force Production ◽  
Force Enhancement ◽  
Residual Force ◽  
Residual Force Enhancement ◽  
State Force ◽  
Isometric Forces

AbstractWhen a muscle is stretched during a contraction, the resulting steady-state force is higher than the isometric force produced at a comparable sarcomere length. This phenomenon, also referred to as residual force enhancement, cannot be readily explained by the force-sarcomere length relation. One of the most accepted mechanisms for the residual force enhancement is the development of sarcomere length non-uniformities after an active stretch. The aim of this study was to directly investigate the effect of non-uniformities on the force-producing capabilities of isolated myofibrils after they are actively stretched. We evaluated the effect of depleting a single A-band on sarcomere length non-uniformity and residual force enhancement. We observed that sarcomere length non-uniformity was effectively increased following A-band depletion. Furthermore, isometric forces decreased, while the percent residual force enhancement increased compared to intact myofibrils (5% vs. 20%). We conclude that sarcomere length non-uniformities are partially responsible for the enhanced force production after stretch.

scholarly journals Effect of Active Lengthening and Shortening on Small-Angle X-ray Reflections in Skinned Skeletal Muscle Fibres

2021 ◽  
Vol 22 (16) ◽  
pp. 8526
Author(s):  
Venus Joumaa ◽  
Ian C. Smith ◽  
Atsuki Fukutani ◽  
Timothy R. Leonard ◽  
Weikang Ma ◽  
...  
Keyword(s):  
Steady State ◽  
Small Angle ◽  
Isometric Contraction ◽  
Sarcomere Length ◽  
Force Enhancement ◽  
X Ray ◽  
Cross Bridge ◽  
Residual Force ◽  
Residual Force Enhancement ◽  
Cross Bridges

Our purpose was to use small-angle X-ray diffraction to investigate the structural changes within sarcomeres at steady-state isometric contraction following active lengthening and shortening, compared to purely isometric contractions performed at the same final lengths. We examined force, stiffness, and the 1,0 and 1,1 equatorial and M3 and M6 meridional reflections in skinned rabbit psoas bundles, at steady-state isometric contraction following active lengthening to a sarcomere length of 3.0 µm (15.4% initial bundle length at 7.7% bundle length/s), and active shortening to a sarcomere length of 2.6 µm (15.4% bundle length at 7.7% bundle length/s), and during purely isometric reference contractions at the corresponding sarcomere lengths. Compared to the reference contraction, the isometric contraction after active lengthening was associated with an increase in force (i.e., residual force enhancement) and M3 spacing, no change in stiffness and the intensity ratio I1,1/I1,0, and decreased lattice spacing and M3 intensity. Compared to the reference contraction, the isometric contraction after active shortening resulted in decreased force, stiffness, I1,1/I1,0, M3 and M6 spacings, and M3 intensity. This suggests that residual force enhancement is achieved without an increase in the proportion of attached cross-bridges, and that force depression is accompanied by a decrease in the proportion of attached cross-bridges. Furthermore, the steady-state isometric contraction following active lengthening and shortening is accompanied by an increase in cross-bridge dispersion and/or a change in the cross-bridge conformation compared to the reference contractions.

scholarly journals Residual force enhancement exceeds the isometric force at optimal sarcomere length for optimized stretch conditions

2008 ◽  
Vol 105 (2) ◽  
pp. 457-462 ◽  
Author(s):  
Eun-Jeong Lee ◽  
Walter Herzog
Keyword(s):  
Steady State ◽  
Sarcomere Length ◽  
Isometric Force ◽  
Passive Component ◽  
Force Enhancement ◽  
Single Fibers ◽  
Length Relationship ◽  
Residual Force ◽  
Residual Force Enhancement ◽  
Isometric Forces

Residual force enhancement (FE) following stretch of an activated muscle is a well accepted property of skeletal muscle contraction. However, the mechanism underlying FE remains unknown. A crucial assumption on which some proposed mechanisms are based is the idea that forces in the enhanced state cannot exceed the steady-state isometric force at a sarcomere length associated with optimal myofilament overlap. Although there are a number of studies in which forces in the enhanced state were compared with the corresponding isometric forces on the plateau of the force-length relationship, these studies either did not show enhanced forces above the plateau or, if they did, they lacked measurements of sarcomere lengths confirming the plateau region. Here, we revisited this question by optimizing stretch conditions and measuring the average sarcomere lengths in isolated fibers, and we found that FE exceeded the maximal isometric reference force obtained at the plateau of the force-length relationship consistently (mean ± SD: 4.8 ± 2.1%) and by up to 10%. When subtracting the passive component of FE from the total FE, the enhanced forces remained greater than the isometric plateau force (mean ± SD: 4.3 ± 2.0%). Calcium-induced increases in passive forces, known to be present in single fibers and myofibrils, are too small to account for the FE observed here. We conclude that FE cannot be explained exclusively with a stretch-induced development of sarcomere length nonuniformities, that FE in single fibers may be associated with the recruitment of additional contractile force, and that isometric steady-state forces in the enhanced state are not uniquely determined by sarcomere lengths.

scholarly journals The influence of residual force enhancement on spinal and supraspinal excitability

PeerJ ◽  
2018 ◽  
Vol 6 ◽  
pp. e5421 ◽  
Author(s):  
Caleb T. Sypkes ◽  
Benjamin J. Kozlowski ◽  
Jordan Grant ◽  
Leah R. Bent ◽  
Chris J. McNeil ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Steady State ◽  
Evoked Potentials ◽  
Isometric Contraction ◽  
Motor Evoked Potentials ◽  
Isometric Force ◽  
Force Enhancement ◽  
Active Muscle ◽  
Residual Force ◽  
Residual Force Enhancement

Background Following active muscle lengthening, there is an increase in steady-state isometric force as compared with a purely isometric contraction at the same muscle length and level of activation. This fundamental property of skeletal muscle is known as residual force enhancement (RFE). While the basic mechanisms contributing to this increase in steady-state isometric force have been well documented, changes in central nervous system (CNS) excitability for submaximal contractions during RFE are unclear. The purpose of this study was to investigate spinal and supraspinal excitability in the RFE isometric steady-state following active lengthening of the ankle dorsiflexor muscles. Methods A total of 11 male participants (20–28 years) performed dorsiflexions at a constant level of electromyographic activity (40% of maximum). Half of the contractions were purely isometric (8 s at an ankle angle of 130°), and the other half were during the RFE isometric steady-state following active lengthening (2 s isometric at 90°, a 1 s lengthening phase at 40°/s, and 5 s at 130°). Motor evoked potentials (MEPs), cervicomedullary motor evoked potentials (CMEPs), and compound muscle action potentials (M-waves) were recorded from the tibialis anterior during the purely isometric contraction and RFE isometric steady-state. Results Compared to the purely isometric condition, following active lengthening, there was 10% RFE (p < 0.05), with a 17% decrease in normalized CMEP amplitude (CMEP/Mmax) (p < 0.05) and no change in normalized MEP amplitude (MEP/CMEP) (p > 0.05). Discussion These results indicate that spinal excitability is reduced during submaximal voluntary contractions in the RFE state with no change in supraspinal excitability. These findings may have further implications to everyday life offering insight into how the CNS optimizes control of skeletal muscle following submaximal active muscle lengthening.

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