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Results for “yielding isometric”

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PubMed2026

Comparing the Effects of Push and Hold Isometric Training on Strength and Musculotendinous Adaptations: A Within-Subject Randomized Controlled Trial.

Lum, D, Oranchuk, DJ, Chen, SE, and Kong, PW. Comparing the effects of push and hold isometric training on strength and musculotendinous adaptations: A within-subject randomized controlled trial. J Strength Cond Res 40(9): 1050-1058, 2026-Despite recent interest in delineating pushing (PIMA) and holding (HIMA) isometric muscle actions, training-induced adaptations have not been examined. As such, we compared the strength and morphological adaptations between PIMA and HIMA training. Twenty limbs across 10 adults (5 men, 5 women, age: 31.4 ± 6.5 years) were randomly assigned to PIMA or HIMA conditions and underwent 12 training sessions over 6 weeks. PIMA required subjects to exert force against a fixed lever while the HIMA limb maintained a set joint angle while resisting an isotonic lever. During each contraction, subjects had to exert force at 70% of maximal voluntary contraction for 20 seconds at an 80° knee angle, for 4-6 repetitions. Subjects completed isometric, concentric, and eccentric knee extension assessments for both limbs before and after the intervention. Pre- and postintervention ultrasound scans were performed to determine quadriceps muscle architecture and patellar tendon thickness. Increased isometric torque was found following both conditions (p < 0.05, g = 0.30-0.36), while concentric (p < 0.05, g = 0.31) and eccentric (p < 0.01, g = 0.50) torque only increased following PIMA. Both conditions increased muscle thickness (p < 0.05, g = 0.27-0.88) and vastus lateralis fascicle length (p < 0.05, g = 0.20-0.31). Only HIMA increased patellar tendon thickness (p < 0.05, g = 0.12). The increase in total quadriceps (p < 0.05, g = 0.46) and especially rectus femoris (p < 0.05, g = 1.44) thickness was greater in HIMA. The results suggest that PIMA may be more effective at improving strength, while HIMA may be superior for inducing morphological adaptations. Larger sample sizes and more ecologically valid training programs are warranted to further elucidate potential differences between different isometric types.

Humans↗

PubMed1978

Sarcomere relaxation in intact cardiac muscle.

The process of tension decay in the absence of sarcomere motion was studied in intact heart muscle isolated from rats. Sarcomere length, observed by an infrared light diffraction technique, was controlled and the effect on force dissipation measured. Distribution of the diffracted light suggested that sarcomere length was uniform immediately after contraction than prior to the next. When sarcomeres - as distinct from the total muscle length - are kept isometric, the rate of tension decay (a) reaches its maximum sooner, and (b) appears to be constant throughout relaxation. Slow stretch (about 3% sarcomere length) prolonged cardiac muscle tension during early relaxation without direct evidence of sarcomere 'yielding'. The dynamics of isometric relaxation and the effect of stretch were qualitatively the same at external calcium concentrations of 0.6 and 1.9 mM. For a specified sequence of sarcomere length changes during relaxation, the dynamics of tension decay were independent of preloaded sarcomere length when the sarcomeres are kept isometric. The data suggest that lowering contractile tension enhanced relative relaxation rate (sec-1) at a sarcomere length of 2.0 micron. The results clarify the physiological mechanism regulating the dynamics of myocardial fiber relaxation.

Animals↗

PubMed1977

Incidence and properties of temperate bacteriophages induced from lactic streptococci.

Sixty-three strains of lactic streptococci isolated from commercial lactic streptococcal starter cultures were examined for lysogeny by treatment with ultraviolet light or mitomycin C. After treatment with the inducing agent, all strains, whether or not they lysed, were examined for evidence of phage release by electron microscopy. Thirty-eight strains yielded intact phages or phage particles of varying morphology. All the temperate phages had isometric heads and noncontractile tails; some had collars and structurally distinctive baseplates. Indicator host strains were found for phages induced from seven different strains. Three strains that released phages spontaneously yielded titers of 10(3) to 10(4) plaque-forming units per ml. When strains that spontaneously released phages were grown in mixed culture with indicator strains, increased phage titers of 10(6) to 10(7) plaque-forming units per ml were observed. These findings indicate that lysogenic lactic streptococcal strains may serve as a reservoir for phages that attack sensitive strains in mixed- or multiple-strain lactic starter cultures.

Bacteriophages↗

PubMed1977

Structure of pyruvate dehydrogenase complex. Comparison between freeze-etching and negative staining.

Pyruvate dehydrogenase complex (pyruvate : lipoate oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1), from pig heart, was studied by spray freeze etching and negative staining. From freeze etching experiments an average particle weight of 7-10(6) was estimated. Negative staining after glutaraldehyde fixation and freeze etching of unfixed and prefixed enzyme solutions yielded no significant difference in particle dimensions: the majority of the isometric complex molecules measured approximately 400 A in diameter. Tantalum tungsten shadowed freeze etch replicas indicated that the surface of the complex is built up of globular units. The relative positions of these units are in good agreement with the model still under discussion.

Animals↗

PubMed1976

[Effect of curarization on sensitivity of chicken latissimus dorsi to electric current].

(1.) To test the sensitivity to electric current of the latissimus dorsi and, therefore, its ability to yield action potential, we have studied the effect of curarisation on the amplitude of the isometric tetanus during "massive" stimulations by alternative current. (2.) Curarisation causes a considerable but reversible reduction of the tetanic tension of the latissimus dorsi anterior (L.D.A.) but has no effect on the tetanus of the latissimus dorsi posterior (L.D.P.). It is concluded that a part of the L.D.A. is not sensitive to electric current and is thus unable to yield action potentials, unlike the opinion of some authors. (3.) Rising the temperature has an inverse effect on the speed of the tetanus ascending phase, depending on whether the L.D.A. has been curarised or not. This show the existence of two types of excitation processes of very different nature in this muscle. (4.) Direct current is much less efficient than alternative current on the curarised L.D.A.

Action Potentials↗

PubMed1979

Shortening velocity, active force and homogeneity of contraction during electrically evoked twitches in smooth muscle from rabbit urinary bladder.

Force-velocity relations obtained by the quick release technique were studied at different times during the twitch at 25 degrees C in electrically stimulated longitudinal smooth muscle from rabbit urinary bladder. The results show that maximal shortening velocity (Vmax) and maximal tension (Po) reach their highest values during the rising phase of the twitch. Maximum Vmax was calculated to be 0.30 +/- 0.04 1/s (S.E., n -= 9). Vmax declines rapidly with time and at the peak of the twitch it is only about 70% of the maximum value. On the other hand Po at the peak does not differ significantly from its maximum value during the rising phase. In the relaxation phase of the twitch, both Vmax and Po decrease progressively. Photographic studies of preparations marked with charcoal grains did not show any considerable inhomogeneity of contraction during isometric twitches, maximum movement of grains never exceeding 4% of total muscle length. No yield at the ends of the preparations were seen. The different time course of Vmax and Po can therefore not be explained by longitudinal inhomogeneity of activation or deactivation of the preparations.

Activation Analysis↗

PubMed1977

Isokinetic and isometric torque force relationships.

The torque forces of elbow extensor musculature of 28 men were tested with an isokinetic dynamometer to determine the relationships between maximal isokinetic torque generated at various speeds and maximal isometric forces at specified angles in the arc of elbow extension. The men were tested at constant velocities ranging from 5 to 25 rpm and at angles of elbow extension ranging from 10 degrees to 90 degrees. Product-moment correlation coefficients were calculated between the maximum isometric torque developed at each of the measured angles and the isokinetic torque generated at each of the predetermined speeds. Of the 81 correlation coefficients calculated, 13 differed significantly from zero. There were slight tendencies for the significant correlations to cluster toward the slower speeds and toward the greater angles of elbow flexion. It was suggested that the slight tendency for higher correlations to cluster toward the slower speeds may be due to slower speeds stimulating isometric effort. The slight tendency for the higher correlations to cluster toward the greater angles of elbow flexion may be due to variances in the consistency of muscular strength at different muscle lengths. Since the highest correlation attained yielded a common variability of less than 24% between the two variables tested, it was concluded that measures of isokinetic strength cannot be used to predict isometric strength capabilities.

Adult↗

PubMed2026

Age-related differences in motor unit behaviours and maximal strength: A systematic review and meta-analysis.

Ageing is associated with a decline in strength; however, the neural mechanisms underpinning these changes remain poorly understood. Motor unit discharge rate (MUDR) and recruitment threshold (MURT) regulate the magnitude of motoneuron output through rate coding and orderly recruitment, while discharge rate variability (MUDRV) reflects the steadiness of motoneuron output. Yet, age-related differences in these properties remain inconsistent across the literature. Therefore, this systematic review and meta-analysis quantified age-related differences in motor unit behaviours and their contribution to maximal isometric strength. Electronic databases (Medline, Embase, Scopus, PsycINFO, Ovid Emcare, CENTRAL, and Web of Science) were searched up to May 2025, yielding 1493 records; of these, 48 studies met the inclusion criteria. Standardised mean differences (SMDs) were calculated using random-effects models to compare older and younger adults, and methodological quality was assessed using the AXIS tool. Older adults exhibited markedly lower maximal strength than younger adults (SMD = -1.01; 95% CI -1.22, -0.79). MUDR was lower in older adults across all contraction intensities, with greater reductions at high forces (> 60% maximal voluntary contraction (MVC): SMD = -0.65; 95% CI -0.96, -0.34) compared to low forces (< 30% MVC: SMD = -0.34; 95% CI -0.50, -0.18). Discharge rate variability was greater (SMD = 0.44; 95% CI 0.15, 0.72), whereas recruitment thresholds relative to MVC were lower (SMD = -0.42; 95% CI -0.80, -0.03) in older adults. Collectively, these findings suggest that age-related alterations in motor unit discharge behaviour may contribute, at least in part, to reduced maximal strength in older adults.

Aging↗

PubMed1978

Togaviridae.

The family Togaviridae is described; it contains four genera--Alphavirus, Flavivirus, Pestivirus and Rubivirus--and additional members. The main characteristics of the family are as follows: single-stranded, linear RNA, molecular weight about 4 X 10(6). Virions have isometric nucleocapsids surrounded by a lipoprotein envelope containing host cell lipid and virus-specified polypeptides including one or more glycopeptides. Virions yield infectious RNA. There are at least 80 members; all the alphaviruses and most flaviviruses are arboviruses in the biological sense.

Arboviruses↗

PubMed2026

Acute Performance, Mechanical and Thermal Effects of Isometric Conditioning Versus Standardized Volleyball Pre-Training Activation in Highly Trained Male Players.

This study compared acute performance, neuromuscular, and thermal responses to a maximal isometric conditioning activity (ICA) versus a standardized volleyball pre-training activation (VPA) in highly trained male volleyball players, and to explore putative mechanisms underpinning post-activation performance enhancement (PAPE) considering training load. In a randomized crossover, 14 men (27 ± 3 y) completed two sessions: VPA (mobility/plyometric drills; 9 min), and ICA comprising 3×5×3-s maximal isometric back-squat contractions (knee angle 120°; 3-min inter-set rest). Countermovement jump (CMJ) height (primary), relative peak power (PP), RSImod, and contraction time (CT) were recorded pre and 3, 6, 9, and 12 min post. Rectus femoris muscle viscoelastic properties and skin surface temperature (SST) were assessed at matched time points. Analyses used repeated-measures ANOVA, responder analysis, correlations, and regression. Period×Sequence interactions favored ICA for CMJ and PP when delivered in Period 2 (lower training volume): ∆CMJ was higher under ICA versus VPA (p = 0.005, d = 1.20); PP likewise greater (p = 0.026, ηp2 = 0.35). ICA yielded more beneficial responders than VPA (9/14 vs 1/14; McNemar exact p = 0.021). In Period 2, reductions in rectus femoris muscle stiffness independently predicted CMJ gains (β_std = -0.495, p = 0.005), whereas SST changes did not (p = 0.974). RSImod and CT showed no differences. A brief, high-effort isometric squat protocol was associated with superior acute improvements in jump performance compared with a standard volleyball warm-up, but this advantage emerged specifically when the preceding training volume was reduced (Period 2), suggesting that residual fatigue from training may reduce the effects of PAPE. Gains align with neuro-mechanical rather than thermal mechanisms, supporting ICA as a practical, equipment-minimal priming strategy for elite volleyball.

Humans↗

PubMed1978

Ventricular premature beats. Reliability in various measurement methods at rest and during exercise.

The yield and reproducibility of various methods of ventricular premature beat (VPB) detection are examined in otherwise healthy middle-aged men first found to have VPB in a 2-min lead I ECG rhythm strip. With a combination of an isometric and treadmill exercise test, VPB were repeatedly detected in 83%. Test-retest reliability in classifying the subjects by frequency of VPB was 67%. The reliability of detecting complex VPB was 47% for multiform VPB, 35% for pairs of VPB, 17% for runs and 36% for VPB showing the R-on-T phenomenon. These data suggest that simple and complex VPB detected by the described methods among normal men are poorly reproducible in the individual. Taking the VPB reproducibility for the group as a whole, the proportion of subjects having different frequency or kinds of ectopic beats is reasonably stable for the different test occasions.

Adult↗

PubMed1977

Effect of hemolysin produced by Vibrio parahaemolyticus on membrane conductance and mechanical tension of rabbit myocardium.

The mechanisms of the action of hemolysin extracted from Vibrio parahaemolyticus in the S-A node and right atrium cells of rabbit were studied by means of the single sucrose gap and isometric tension recording methods. Hemolysin caused the membrane to depolarize reversibly without affecting the action potential generating mechanism. Lowering of [Na+]o inhibited membrane depolarization in the presence of hemolysin while the readmission of normal Tyrode solution induced depolarization. Tetrodotoxin (TTX) barely antagonized the depolarizing action of hemolysin but slowed the rate of development of depolarization. Therefore, this depolarization is considered to be primarily due to the increase in conductance to Na which TTX may not block. The dose-response relationship was obtained by measuring a change in membrane resistance. The concentration necessary to yield one-half of the maximum reduction of the membrane was determined to by 7.5 micrograms/ml. Accumulation of Na within the cell may be responsible for an increase of twitch tension observed during the action of a low concentration of hemolysin. On the other hand, a higher concentration of hemolysin seemed to promote exchange of intracellar Na with extracellular Ca, especially when the Na concentration of the perfusing solution was reduced, and led to stronger contracture.

Animals↗

PubMed1979

Pentobarbitone and skeletal muscle contractions: on the interaction with the effect elicited by the beta-adrenoceptor agonist, terbutaline.

The soleus, a slow-contracting muscle, and the extensor digitorum longus (EDL), a fast-contracting muscle from guinea-pig were prepared for isometric recording in vitro. Subtetanic contractions were evoked by transmural field-stimulation. Pentobarbitone increased the force of contraction in both muscles. In the soleus it shifted the stimulation frequency-response curve to the left. Terbutaline caused a decrease in the force of subtetanic contractions of the soleus, an effect which was dependent on the stimulation frequency. In the presence of pentobarbitone, the stimulation frequency had to be lowered by about 2 HZ in order to maintain the optimum response to terbutaline. The EDL responded to terbutaline with an increased force of contraction. In this case the stimulation frequency was less critical and the effects were the same in the presence and in the absence of pentobarbitone. Experiments with alpha-chloralose yielded results similar to those obtained with pentobarbitone.

Animals↗