Maximal Force Generation Research Articles

Efficacy of Rapid Inspiratory Bouts Followed by Sustained Expiration on Maximal Force Generation During Isometric Exercise

Efficacy of Rapid Inspiratory Bouts Followed by Sustained Expiration on Maximal Force Generation During Isometric Exercise

Changes in strength performance of highly trained athletes after COVID-19

Introduction This study aimed to explore the impact of COVID-19 on strength performance in highly trained athletes. Method A force plate was employed to measure squat jump height (SJH), counter-movement jump height (CMJH), and drop jump reactive strength index (DJRSI) in 27 highly trained athletes before infection, and at one week, two weeks, and four weeks post-recovery. Additionally, an Isometric Mid-thigh Pull (IMTP) test was conducted to record maximum isometric strength (MIS) and the rate of force development of the initial phase (RFD 0–50; RFD 0–100). Repeated measures analysis of variance was utilized to compare variations in these indicators across different time points. Results One week post-recovery, SJH (-7.71%, P = 0.005), CMJH (-9.08%, P < 0.001), DJRSI (-28.88%, P < 0.001), MIS (-18.95%, P < 0.001), RFD 0–50 (-64.98%, P < 0.001), and RFD 0–100 (-53.65%, P < 0.001) were significantly lower than pre-infection levels. Four weeks post-recovery, SJH (-2.08%, P = 0.236), CMJH (-3.28%, P = 0.277), and MIS (-3.32%, P = 0.174) did not differ significantly from pre-infection levels. However, DJRSI (-11.24%, P = 0.013), RFD 0–50 (-31.37%, P = 0.002), and RFD 0–100 (-18.99%, P = 0.001) remained significantly lower than pre-infection levels. Conclusion After COVID-19, highly trained athletes exhibited a significant reduction in maximum strength, explosive strength, reactive strength, and initial phase force generation capability. By four weeks post-recovery, their maximum and explosive strength had returned to near pre-infection levels, yet their reactive strength and initial phase force generation capability remained significantly impaired.

Sex differences in neuromuscular and biological determinants of isometric maximal force.

Force expression is characterized by an interplay of biological and molecular determinants that are expected to differentiate males and females in terms of maximal performance. These include muscle characteristics (muscle size, fiber type, contractility), neuromuscular regulation (central and peripheral factors of force expression), and individual genetic factors (miRNAs and gene/protein expression). This research aims to comprehensively assess these physiological variables and their role as determinants of maximal force difference between sexes. Experimental evaluations include neuromuscular components of isometric contraction, intrinsic muscle characteristics (proteins and fiber type), and some biomarkers associated with muscle function (circulating miRNAs and gut microbiome) in 12 young and healthy males and 12 females. Male strength superiority appears to stem primarily from muscle size while muscle fiber-type distribution plays a crucial role in contractile properties. Moderate-to-strong pooled correlations between these muscle parameters were established with specific circulating miRNAs, as well as muscle and plasma proteins. Muscle size is crucial in explaining the differences in maximal voluntary isometric force generation between males and females with similar fiber type distribution. Potential physiological mechanisms are seen from associations between maximal force, skeletal muscle contractile properties, and biological markers.

Abstract 18445: Rigorous Mechanics in Engineered Heart Tissues

Introduction: Heart failure can develop or be exacerbated by mechanical stressors, including increased diastolic strain (preload) and increased systolic impedance (afterload). Recent advances in human induced pluripotent stem cell (iPSC) technology and tissue engineering have enabled long term culture and maturation of engineered heart tissues (EHTs). Most current platforms do not allow for mechanical assessment under a range of loading conditions. Here, we develop a technique to engineer cardiac tissues that allow for non-destructive rigorous phenotyping of tissue mechanics. Methods: Custom tissue anchors were 3D printed using Boston Micro Fabrication HTL Resin and placed within polydimethylsiloxane tissue casting molds. iPS cardiomyocytes and ventricular fibroblasts were mixed 5:1 in 2 mg/mL collagen and cast in rectangular molds. Tissues were compacted around custom tissue anchors over 14 days. Tissues were dismounted from the molds and fixed for immunostaining or hooked onto a force transducer for length-tension, force-frequency, and work-loop analysis. Results: 3D printed tissue anchors accommodated EHT molding and compaction. EHTs spontaneously contracted after 3 days in culture, and compacted to 15.9±0.8% their initial tissue area by 14 days of culture. Engineered tissues were cell dense and mature, with bands of aligned sarcomeres. During isometric testing, tissues display a physiologic length-tension relationship, with linear increases in force with stretch between L 0 (slack length) and L max (length at maximum active force generation, 4.3±0.7 mN/mm 2 ; r 2 =0.96). These are coupled with increases in contraction and relaxation velocities. EHTs were capable of mimicking physiologic work loops. Conclusions: In summary, we have shown the ability to grow and mature three-dimensional human engineered heart tissues capable of rigorous mechanical assessment, enabling future studies on load-dependent cardiac remodeling.

The Effect of Skeletal Fixation on Nerve Healing in a Rat

Objective To investigate the effect of rigid internal skeletal fixation of a rat femoral shaft fracture on the healing of an induced sciatic nerve crush injury as assessed by functional outcomes. Methods Thirty-six male Lewis rats were divided into two groups. A unilateral sciatic nerve crush injury and a same-level transverse femur fracture were created in all animals. Animals in the first group underwent immediate open reduction internal fixation (ORIF) with a stainless steel plate and screws. Animals in the second group were treated non-operatively (NON) without internal or external fixation or bracing. At each of the six-time points relevant to different nerve degeneration and regeneration stages, three animals in each group underwent bilateral limb assessments of electrophysiology, muscle mass, and nerve histomorphometry. Results Outcome measurements of the ORIF group (n=17) and NON group (n=16) showed the ORIF group to have both significantly greater tibialis anterior muscle force generation and sciatic nerve conduction velocity across the zone of injury for the overall groups. Force and conduction velocity measurements were greater for the ORIF group at selective time points in the subgroup analysis. Histologic analysis confirmed a greater cross-sectional area of the sciatic nerve in the ORIF group. Conclusion This study provides information about the influence of the stability of the skeletal and soft tissue environment on the nerve healing process. The significantly greater maximum force generation and conduction velocity and the increased cross-sectional areas with greater axon counts observed in our ORIF group support our hypothesis that rigid internal skeletal fixation of a fracture promotes superior recovery of a concomitant peripheral nerve injury. The findings of this study suggest that superior healing of the peripheral nerve injury may occur with stable skeletal fixation.

New Methods to Quantify Functional Strength for Young Children: Laboratory and Task Design Considerations

Strength data for children are needed to improve the safety of products. Currently, minimal information on strength is available for children under age 6 years. This paper describes the development of methods to measure functional, task-relevant strength for children ages 24 to 71 months. Strength measurement methods used for adults and older children must be adapted substantially to obtain meaningful data from this younger cohort. This paper discusses the challenges associated with gathering volitional, maximal force-generation capability for this age cohort with attention to applicability, repeatability, and reproducibility.

C-type natriuretic peptide induces inotropic and lusitropic effects in human 3D-engineered cardiac tissue: Implications for the regulation of cardiac function in humans.

The role of C-type natriuretic peptide (CNP) in the regulation of cardiac function in humans remains to be established as previous investigations have been confined to animal model systems. Here, we used well-characterized engineered cardiac tissues (ECTs) generated from human stem cell-derived cardiomyocytes and fibroblasts to study the acute effects of CNP on contractility. Application of CNP elicited a positive inotropic response as evidenced by increases in maximum twitch amplitude, maximum contraction slope and maximum calcium amplitude. This inotropic response was accompanied by a positive lusitropic response as demonstrated by reductions in time from peak contraction to 90% of relaxation and time from peak calcium transient to 90% of decay that paralleled increases in maximum contraction decay slope and maximum calcium decay slope. To establish translatability, CNP-induced changes in contractility were also assessed in rat ex vivo (isolated heart) and in vivo models. Here, the effects on force kinetics observed in ECTs mirrored those observed in both the ex vivo and in vivo model systems, whereas the increase in maximal force generation with CNP application was only detected in ECTs. In conclusion, CNP induces a positive inotropic and lusitropic response in ECTs, thus supporting an important role for CNP in the regulation of human cardiac function. The high degree of translatability between ECTs, ex vivo and in vivo models further supports a regulatory role for CNP and expands the current understanding of the translational value of human ECTs. NEW FINDINGS: What is the central question of this study? What are the acute responses to C-type natriuretic peptide (CNP) in human-engineered cardiac tissues (ECTs) on cardiac function and how well do they translate to matched concentrations in animal ex vivo and in vivo models? What is the main finding and its importance? Acute stimulation of ECTs with CNP induced positive lusitropic and inotropic effects on cardiac contractility, which closely reflected the changes observed in rat ex vivo and in vivo cardiac models. These findings support an important role for CNP in the regulation of human cardiac function and highlight the translational value of ECTs.

Dependence of cardiomyocyte force, velocity, and power generation on ATP concentration

Theoretical analysis and computer modeling of myocardial energy metabolism under physiological and heart failure conditions predicts that cytoplasmic ATP and ADP levels both fall roughly in proportion to reductions in total adenine nucleotide pool observed in heart failure. Assessing sub-maximal force and velocity in loaded myocardial muscle at MgATP levels in the range of 2 to 8 mM, Beard et al. ( Biophys. J. 2022. 121: 3213–3223) observed effects of MgATP on myocardial power generation that suggest that although maximal force and velocity are not substantially sensitive to differences in [MgATP] that occur in the normal versus failing myocardium, maximal power generation, which occurs at submaximal force and velocity, is sensitive to [MgATP]. Previously developed computational models are not able to reproduce the observed dependence on MgATP. The goals of the present study are to construct and analyze a computational model of muscle dynamics to analyze data on the dependence of maximal force, velocity, and power generation on [MgATP] in order to determine a potential mechanism to explain the MgATP-dependent phenomena. Model development and identification was guided by dynamic measurements on permeabilized mouse trabecular fibers. The data include force-velocity relation and time constant of tension development. The mathematical model used to simulate cardiomyocyte crossbridge mechanics was based on the previous crossbridge and calcium models from Tewari et al. (J Mol Cell Cardiol, 2016. 96: 11-25) and Campbell et al. (Biophys J, 2018. 115: 543-553). The developed model includes strain- and metabolite-dependent transition between attachment states, and ATP-dependent destabilization of the super-relaxed (SRX) myosin state. Model-based analysis of force and velocity dyanmics is consistent with the hypothesis that ATP assocition with the myosin protein influence the kinetics and thermodynamics of transitions between the SRX and disorded (DRX) states. Funding: Department of Veterans Affairs Merit Review Award I01BX000740 (A.J.B.) and National Heart, Lung, and Blood Institute grant R01 HL154624 (A.J.B., D.A.B.) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

A classification of the plantar intrinsic foot muscles based on the physiological cross-sectional area and muscle fiber length in healthy young adult males

BackgroundPlantar intrinsic foot muscles (PIFMs) are composed of 10 muscles and play an essential role in achieving functional diversity in the foot. Previous studies have identified that the morphological profiles of PIFMs vary between individuals. The morphological profiles of a muscle theoretically reflect its output potentials: the physiological cross-sectional area (PCSA) of a muscle is proportional to its maximum force generation, and the muscle fiber length (FL) is its shortening velocity. This implies that the PCSA and FL may be useful variables for characterizing the functional diversity of the individual PIFM. The purpose of this study was to examine how individual PIFMs can be classified based on their PCSA and FL.MethodsIn 26 healthy young adult males, the muscle volume and muscle length of seven PIFMs (abductor hallucis, ABDH; abductor digiti minimi, ABDM; adductor hallucis oblique head, ADDH-OH; ADDH transverse head, ADDH-TH; flexor digitorum brevis, FDB; flexor hallucis brevis, FHB; quadratus plantae, QP) were measured using magnetic resonance imaging. The PCSA and FL of each of the seven PIFMs were then estimated by combining the data measured from the participants and those of muscle architectural parameters documented from cadavers in previous studies. A total of 182 data samples (26 participants × 7 muscles) were classified into clusters using k-means cluster analysis. The optimal number of clusters was evaluated using the elbow method.ResultsThe data samples of PIFMs were assigned to four clusters with different morphological profiles: ADDH-OH and FHB, characterised by large PCSA and short FL (high force generation and slow shortening velocity potentials); ABDM and FDB, moderate PCSA and moderate FL (moderate force generation and moderate shortening velocity potentials); QP, moderate PCSA and long FL (moderate force generation and rapid shortening velocity potentials); ADDH-TH, small PCSA and moderate FL (low force generation and moderate shortening velocity potentials). ABDH components were assigned equivalently to the first and second clusters.ConclusionsThe approach adopted in this study may provide a novel perspective for interpreting the PIFMs’ function based on their maximal force generation and shortening velocity potentials.

Prolonged static stretching increases the magnitude and decreases the complexity of knee extensor muscle force fluctuations.

Static stretching decreases maximal muscle force generation in a dose-response manner, but its effects on the generation of task-relevant and precise levels of submaximal force, i.e. force control, is unclear. We investigated the effect of acute static stretching on knee extensor force control, quantified according to both the magnitude and complexity of force fluctuations. Twelve healthy participants performed a series of isometric knee extensor maximal voluntary contractions (MVCs) and targeted intermittent submaximal contractions at 25, 50 and 75% MVC (3 x 6 seconds contraction separated by 4 seconds rest, with 60 seconds rest between each intensity) prior to, and immediately after, one of four continuous static stretch conditions: 1) no stretch; 2) 30-second stretch; 3) 60-second stretch; 4) 120-second stretch. The magnitude of force fluctuations was quantified using the standard deviation (SD) and coefficient of variation (CV), while the complexity of fluctuations was quantified using approximate entropy (ApEn) and detrended fluctuation analysis (DFA) α. These measures were calculated using the steadiest 5 seconds of the targeted submaximal contractions at each intensity (i.e., that with the lowest SD). Significant decreases in MVC were evident following the 30, 60 and 120-second stretch conditions (all P < 0.001), with a significant correlation observed between stretch duration and the magnitude of decrease in MVC (r = -0.58, P < 0.001). The 120-second stretch resulted in significant increases in SD at 50% MVC (P = 0.007) and CV at 50% (P = 0.009) and 75% MVC (P = 0.005), and a significant decrease in ApEn at 75% MVC (P < 0.001). These results indicate that the negative effects of prolonged static stretching extend beyond maximal force generation tasks to those involving generation of precise levels of force during moderate- to high-intensity submaximal contractions.

Intramuscular Nanofat Injection Promotes Inflammation-Induced Gastrocnemius Regeneration in a Syngeneic Rat Sciatic Nerve Injury Model.

Mechanical emulsification of adipose tissue to concentrate protein and stromal cell components (ie, nanofat) has gained considerable interest in clinical practice. Although the regenerative potential of nanofat has largely been used in aesthetic applications, these effects have considerable potential in reconstruction as well. Here, the authors investigated the therapeutic properties of nanofat injected directly into the denervated gastrocnemius after a sciatic nerve injury in Lewis rats. Muscle denervation was induced by transecting and immediately repairing the sciatic nerve. Inguinal and subcutaneous adipose was harvested from donor rodents, processed into nanofat, and then injected intramuscularly into the gastrocnemius. Gait analysis was performed weekly. Rodents were euthanized at 9 and 12 weeks, after which tetanic contraction force was measured, and gene expression, histology, and cytokine multiplexing were performed. Intramuscular injection of nanofat significantly increased maximum tetanic force generation at 9 and 12 weeks. The forces of the nanofat-injected gastrocnemii were better correlated to their contralateral gastrocnemii relative to controls. Muscle repair-associated inflammatory gene expressions were significantly up-regulated in nanofat-injected gastrocnemii. Cytokines interleukin (IL)-1β, IL-18, vascular endothelial growth factor, granulocyte-macrophage colony-stimulating factor, and tissue inhibitor of metalloproteinase-1 were significantly higher in nanofat-injected gastrocnemii relative to control gastrocnemii, and the tetanic force was linearly and significantly correlated to IL-1β and IL-18 and their interacting effects. Intramuscular injection of emulsified adipose tissue (nanofat) significantly increased gastrocnemii contraction force after sciatic nerve injury, with prolonged reconstructive inflammation by means of CD68, inducible nitric oxide synthase, IL-1β, and IL-18 all being potential mechanisms for this recovery. This application could potentially increase the therapeutic breadth of nanofat to include muscular recovery after nerve injury. The authors' study investigates a clinically translatable therapy to mitigate muscle atrophy after nerve injury.

Abstract 12713: Increased Calcium Sensitivity in Hypoplastic Left Heart Syndrome Hearts With Systolic Failure

Introduction: Systolic failure of the systemic right ventricle (RV) in children with hypoplastic left heart syndrome (HLHS) is a significant cause of death and a growing indication for heart transplantation. However, the underlying etiology of RV systolic failure in this population remains ill-defined. Hypothesis: We hypothesize that cardiomyocyte autonomous defects in contractility, characterized by increased calcium sensitivity, may contribute to systolic failure in HLHS. Methods: Explanted RV tissue was collected and flash frozen at the time of heart transplant in pediatric subjects with HLHS. HLHS subjects were classified by their primary indication for transplant: HLHS subjects with normal systolic function (HLHS-NF, N=2) were transplanted secondary to refractory protein losing enteropathy, and HLHS-F subjects (N=9) had end-stage heart failure due to decreased systolic function. Cardiomyocytes were isolated from frozen RV tissue, permeabilized, and glued to a force transducer and length controller. Force generated by the cardiomyocyte at different calcium concentrations was measured and force-calcium dose response curves were generated (modified Hill equation). pCa50 denotes the negative log of calcium concentration required to generate 50% maximal tension. Results: Less calcium is required to generate 50% maximal tension in HLHS-F cardiomyocytes (n=33 cardiomyocytes) when compared to HLHS-NF (n=5 cardiomyocytes), demonstrated by a higher pCa50 (5.62 vs. 5.46, p=0.027). Maximal force generation is similar between HLHS-NF and HLHS-F cardiomyocytes (55.5 mN/mm2 vs. 54.8 mN/mm2, p=0.96). Conclusions: Cardiomyocytes isolated from HLHS-F demonstrate increased calcium sensitivity when compared to those from HLHS-NF. Although future studies are needed, the presence of intrinsic alterations in sarcomeric properties in HLHS-F supports the hypothesis that cardiomyocyte autonomous defects may contribute to systolic failure in HLHS.

Corn Snakes Show Consistent Sarcomere Length Ranges Across Muscle Groups and Ontogeny.

The force-generating capacity of muscle depends upon many factors including the actin-myosin filament overlap due to the relative length of the sarcomere. Consequently, the force output of a muscle may vary throughout its range of motion, and the body posture allowing maximum force generation may differ even in otherwise similar species. We hypothesized that corn snakes would show an ontogenetic shift in sarcomere length range from being centered on the plateau of the length-tension curve in small individuals to being on the descending limb in adults. Sarcomere lengths across the plateau would be advantageous for locomotion, while the descending limb would be advantageous for constriction due to the increase in force as the coil tightens around the prey. To test this hypothesis, we collected sarcomere lengths from freshly euthanized corn snakes, preserving segments in straight and maximally curved postures, and quantifying sarcomere length via light microscopy. We dissected 7 muscles (spinalis, semispinalis, multifidus, longissimus dorsi, iliocostalis (dorsal and ventral), and levator costae) in an ontogenetic series of corn snakes (mass = 80–335 g) at multiple regions along the body (anterior, middle, and posterior). Our data shows all of the muscles analyzed are on the descending limb of the length-tension curve at rest across all masses, regions, and muscles analyzed, with muscles shortening onto or past the plateau when flexed. While these results are consistent with being advantageous for constriction at all sizes, there could also be unknown benefits of this sarcomere arrangement for locomotion or striking.

Reduced cardiac muscle power with low ATP simulating heart failure

For patients with heart failure, myocardial ATP level can be reduced to one-half of that observed in healthy controls. This marked reduction (from ≈8 mM in healthy controls to as low as 3–4 mM in heart failure) has been suggested to contribute to impaired myocardial contraction and to the decreased pump function characteristic of heart failure. However, in vitro measures of maximum myofilament force generation, maximum shortening velocity, and the actomyosin ATPase activity show effective KM values for MgATP ranging from ≈10 μM to 150 μM, well below the intracellular ATP level in heart failure. Thus, it is not clear that the fall of myocardial ATP observed in heart failure is sufficient to impair the function of the contractile proteins. Therefore, we tested the effect of low MgATP levels on myocardial contraction using demembranated cardiac muscle preparations that were exposed to MgATP levels typical of the range found in non-failing and failing hearts. Consistent with previous studies, we found that a 50% reduction in MgATP level (from 8 mM to 4 mM) did not reduce maximum force generation or maximum velocity of shortening. However, we found that a 50% reduction in MgATP level caused a 20%–25% reduction in maximal power generation (measured during muscle shortening against a load) and a 20% slowing of cross-bridge cycling kinetics. These results suggest that the decreased cellular ATP level occurring in heart failure contributes to the impaired pump function of the failing heart. Since the ATP-myosin ATPase dissociation constant is estimated to be submillimolar, these findings also suggest that MgATP concentration affects cross-bridge dynamics through a mechanism that is more complex than through the direct dependence of MgATP concentration on myosin ATPase activity. Finally, these studies suggest that therapies targeted to increase adenine nucleotide pool levels in cardiomyocytes might be beneficial for treating heart failure.

Chromatin sequesters pioneer transcription factor Sox2 from exerting force on DNA

Biomolecular condensation constitutes an emerging mechanism for transcriptional regulation. Recent studies suggest that the co-condensation between transcription factors (TFs) and DNA can generate mechanical forces driving genome rearrangements. However, the reported forces generated by protein-DNA co-condensation are typically below one piconewton (pN), questioning its physiological significance. Moreover, the force-generating capacity of these condensates in the chromatin context remains unknown. Here, we show that Sox2, a nucleosome-binding pioneer TF, forms co-condensates with DNA and generates forces up to 7 pN, exerting considerable mechanical tension on DNA strands. We find that the disordered domains of Sox2 are required for maximum force generation but not for condensate formation. Furthermore, we show that nucleosomes dramatically attenuate the mechanical stress exerted by Sox2 by sequestering it from coalescing on bare DNA. Our findings reveal that TF-mediated DNA condensation can exert significant mechanical stress on the genome which can nonetheless be attenuated by the chromatin architecture.

SUMOylation does not affect cardiac troponin I stability but alters indirectly the development of force in response to Ca2.

Post-translational modification of the myofilament protein troponin I by phosphorylation is known to trigger functional changes that support enhanced contraction and relaxation of the heart. We report for the first time that human troponin I can also be modified by SUMOylation at lysine 177. Functionally, TnI SUMOylation is not a factor in the development of passive and maximal force generation in response to calcium, however this modification seems to act indirectly by preventing SUMOylation of other myofilament proteins to alter calcium sensitivity and cooperativity of myofilaments. Utilising a novel, custom SUMO site-specific antibody that recognises only the SUMOylated form of troponin I, we verify that this modification occurs in human heart and that it is upregulated during disease.

Analysis of Biomechanical and Biochemical Markers of Rat Muscle Soleus Fatigue Processes Development during Long-Term Use of C60 Fullerene and N-Acetylcysteine.

The development of an effective therapy aimed at restoring muscle dysfunctions in clinical and sports medicine, as well as optimizing working activity in general remains an urgent task today. Modern nanobiotechnologies are able to solve many clinical and social health problems, in particular, they offer new therapeutic approaches using biocompatible and bioavailable nanostructures with specific bioactivity. Therefore, the nanosized carbon molecule, C60 fullerene, as a powerful antioxidant, is very attractive. In this study, a comparative analysis of the dynamic of muscle soleus fatigue processes in rats was conducted using 50 Hz stimulation for 5 s with three consistent pools after intraperitoneal administration of the following antioxidants: C60 fullerene (a daily dose of 1 mg/kg one hour prior to the start of the experiment) and N-acetylcysteine (NAC; a daily dose of 150 mg/kg one hour prior to the start of the experiment) during five days. Changes in the integrated power of muscle contraction, levels of the maximum and minimum contraction force generation, time of reduction of the contraction force by 50% of its maximum value, achievement of the maximum force response, and delay of the beginning of a single contraction force response were analyzed as biomechanical markers of fatigue processes. Levels of creatinine, creatine phosphokinase, lactate, and lactate dehydrogenase, as well as pro- and antioxidant balance (thiobarbituric acid reactive substances, hydrogen peroxide, reduced glutathione, and catalase activity) in the blood of rats were analyzed as biochemical markers of fatigue processes. The obtained data indicate that applied therapeutic drugs have the most significant effects on the 2nd and especially the 3rd stimulation pools. Thus, the application of C60 fullerene has a (50–80)% stronger effect on the resumption of muscle biomechanics after the beginning of fatigue than NAC on the first day of the experiment. There is a clear trend toward a positive change in all studied biochemical parameters by about (12–15)% after therapeutic administration of NAC and by (20–25)% after using C60 fullerene throughout the experiment. These findings demonstrate the promise of using C60 fullerenes as potential therapeutic nanoagents that can reduce or adjust the pathological conditions of the muscular system that occur during fatigue processes in skeletal muscles.

Seed fate in ant‐mediated dispersal: Seed dispersal effectiveness in the Ectatomma ruidum (Formicidae)—Zanthoxylum ekmanii (Rutaceae) system

AbstractPlants are often dispersal limited relying on passive or active agents to find suitable microhabitats for germination. Seeds of pioneer tree species, for example, require light gaps for growth but have short median dispersal distances and often do not provide a food reward to encourage animal dispersal. Zanthoxylum ekmanii seeds are frequently moved by ants but evaluating the effectiveness of ant‐mediated seed removal requires knowledge of the species moving the seeds, how far they are moved, and the deposition site. To assess the effectiveness of ants as seed dispersers of Z. ekmanii, we utilized the seed dispersal effectiveness framework. We tracked the movement of seeds from caches on the forest floor, revealing that foragers of Ectatomma ruidum moved 32.8% of seeds an average first distance of 99.8 cm with 68.3% of those seeds taken into a colony. The quality of deposition location was assessed using a seedling emergence study where freshly germinated seeds were buried at different depths. Seedlings were primarily able to emerge from the shallowest depths. Wax castings of E. ruidum colonies demonstrated that seeds brought into the colony were deposited in chambers that had larvae present and experienced more damage than seeds unhandled by ants. Foragers, however, did not have a strong enough bite force to rupture Z. ekmanii seeds likely because their muscle morphology is not structured to maximize force generation. Overall, E. ruidum may help fine tune deposition location, incorporating seeds into the topsoil, though few seeds will likely emerge if soil bioturbation is low.Abstract in Spanish is available with online material

Physiological tremor is suppressed and force steadiness is enhanced with increased availability of serotonin regardless of muscle fatigue.

Although there is evidence that 5-HT acts as an excitatory neuromodulator to enhance maximal force generation, it is largely unknown how 5-HT activity influences the ability to sustain a constant force during steady-state contractions. A total of 22 healthy individuals participated in the study, where elbow flexion force was assessed during brief isometric contractions at 10% maximal voluntary contraction (MVC), 60% MVC, MVC, and during a sustained MVC. The selective serotonin reuptake inhibitor, paroxetine, suppressed physiological tremor and increased force steadiness when performing the isometric contractions. In particular, a main effect of drug was detected for peak power of force within the 8-12 Hz range (P = 0.004) and the coefficient of variation (CV) of force (P < 0.001). A second experiment was performed where intermittent isometric elbow flexions (20% MVC sustained for 2 min) were repeatedly performed so that serotonergic effects on physiological tremor and force steadiness could be assessed during the development of fatigue. Main effects of drug were once again detected for peak power of force in the 8-12 Hz range (P = 0.002) and CV of force (P = 0.003), where paroxetine suppressed physiological tremor and increased force steadiness when the elbow flexors were fatigued. The findings of this study suggest that enhanced availability of 5-HT in humans has a profound influence of maintaining constant force during steady-state contractions. The action of 5-HT appears to suppress fluctuations in force regardless of the fatigue state of the muscle.NEW & NOTEWORTHY Converging lines of research indicate that enhanced serotonin availability increases maximal force generation. However, it is largely unknown how serotonin influences the ability to sustain a constant force. We performed two experiments to assess physiological tremor and force steadiness in unfatigued and fatigued muscle when serotonin availability was enhanced in the central nervous system. Enhanced availability of serotonin reduced physiological tremor amplitude and improved steadiness regardless of muscle fatigue.

The Effects of Core Stabilization Training Program on Endurance and Balance in Cricketers

Background and Purpose: Core stability 1 is seen as being pivotal for efficient biomechanical functionto maximize force generation and minimize joint loads in all types of activities ranging from running tothrowing. The purpose of the study is to evaluate the effectiveness of core stabilization training program onendurance and balance in cricketers. Materials and Methods: A total of 40 male cricketers of age group 15-25yrs were included in the study and randomly assigned into two groups, 20 in each group. Group A -controlgroup, who did not receive any training and Group B -core strengthening group, who received six weeks ofcore training. Before the start of the study and again after 6 weeks of training, 2 tests were used to measurecore endurance and balance- Sorensen back endurance test and Star Excursion Balance Test. Statisticalanalysis: Analyzed by calculating mean, standard deviation, and comparison within the groups by pairedt-test and between groups by unpaired t-test. Results: The results showed significant improvements in bothSorenson and Star excursion balance tests for the group undertaking the core training program (p &lt;0.05).Conclusion: Core endurance measured using Sorensen also showed increase in trunk holding time after 6weeks of core exercise training, among the two tests Star excursion balance test improved more compare tocore endurance after 6 weeks of training.