PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “overcoming isometric”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1988

Methods for measurement of muscle function. Methodological aspects, reference values for children, and clinical applications.

In children isometric muscle force can be measured with acceptable reproducibility by using a simple hand-held dynamometer. Reference values for 10 different muscle groups are given for children aged 3.5-15 years. If age and weight are known, the force can be predicted. The most pronounced differences between the dominant and the non-dominant side were found in the elbow flexors, 3 of the 6 age groups showing greater force on the dominant side, and in the wrist extensors, the 2 oldest age groups being stronger on the dominant side. Sex differences were present as early as 9.5-11 years of age, boys being stronger than girls. Isokinetic muscle torque of the dorsiflexors of the ankle increased with age. Reference values are given for peak torque in children 6, 9, 12, and 15 years of age. The most intense force development occurs between 12 and 15 years of age in boys, and earlier in girls. Sex differences appear in early puberty. In young children the dominant leg was the stronger at the highest velocities. In the older children the non-dominant leg was the stronger at low velocities. Isokinetic measurements are time-consuming and require experience, and should be regarded as complementary to isometric testing. In muscle groups that are too weak to overcome gravity isometric and isokinetic methods cannot be used. Functional tests of motor ability are especially useful in patients with severely impaired muscle function when other test methods are inadequate or difficult to evaluate. The natural course of Duchenne muscular dystrophy was followed in 16 boys by means of functional tests, isometric tests, isokinetic tests of concentric muscle contraction, and manual tests. Of these only the isokinetic method proved unreliable, possibly because of difficulty in activating the muscles at different speeds. The function of adductor pollicis was studied by supramaximal electrical stimulation of the ulnar nerve. Force-frequency curves and reference values for relaxation rate and half contraction time to tetanus for children aged 9, 12, and 15 years are presented. The half contraction time to tetanus was briefer in the older children than in the younger. The relative force developed at a stimulation of 10 Hz increased with age. Apart for the increase in muscle force with increasing age, no other differences emerged between the different age groups. No sex differences were found. The electrical stimulation test is rather painful, and only about 60% of the children persevered to the end of the test.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
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 &#xb1; 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&#xb0; 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↗
PubMed2004

Isometric shoulder muscle activation patterns for 3-D planar forces: a methodology for musculo-skeletal model validation.

OBJECTIVE: To present an isometric method for validation of a shoulder model simulation by means of experimentally obtained electromyography and addressing all muscles active around the shoulder joints. BACKGROUND: Analysis of muscle force distribution in the shoulder by means of electromyography during motion tasks is hampered by artificial and non-linear amplitude modulation and is often limited to downward directed external forces. This application of EMG is therefore inadequate and insufficient for the validation of shoulder model simulations. We suggest an isometric method including multi-directional forces to overcome these problems. METHODS: A force with constant magnitude is actively rotated stepwise in 20 directions perpendicular around the arm while kept in one position. The isometric muscle activation (EMG) is a function of the clockwise-rotated force angle, characterized by baseline activation, and a section of increased muscle activation characterized by baseline interception and direction and magnitude of maximum muscle activation. Comparison of the parameterized muscle activation with predicted muscle forces from model simulation illustrates the applicability for musculo-skeletal model validation. RESULTS: All recorded shoulder muscles were active over a section of force angles of at least 180 degrees. Some muscles demonstrated two activation sections. The estimated model sensitivity for the baseline interception was SD=5 degrees -10 degrees. The Principal Action was the most reliable parameter (SD=4 degrees ). A correlation of 0.778 was observed between model simulations and EMG recordings. CONCLUSIONS: The methodology addresses all shoulder muscles over a substantial section of planar force directions. This enables the comparison of experimentally determined direction of activation on- and offset and direction of maximum activation with equivalent muscle forces, predicted from model simulation.

Algorithms↗
PubMed2005

Overcoming abnormal joint torque patterns in paretic upper extremities using triceps stimulation.

The goal of this research project was to quantitatively assess whether transcutaneous triceps stimulation can overcome the expression of abnormal torque patterns in the paretic upper limb of subjects with hemiparetic stroke. Abnormal torque patterns consist of strong coupling between shoulder abduction (SAB) and elbow flexion (EF) or between elbow extension (EE) and shoulder adduction (SAD) torques. Both patterns reduce the active range of motion during arm movements. Eight chronic stroke subjects with moderate to severe (Fugl-Meyer assessment scores of 21/66-36/66) upper limb motor impairment participated in this study. Shoulder and elbow joint torques were measured with a 6-degrees-of-freedom load cell under isometric conditions, while the triceps muscle was stimulated to generate EE torques. At the same time the subjects were asked to lift up their arm to generate different SAB torque levels. The obtained isometric results showed that electrical stimulation can overcome abnormal torque patterns in chronic stroke subjects while generating SAB. This is likely to have potential benefits to increase the reaching workspace of the paretic arm.

Adult↗
PubMed2004

Maximum isometric lifting strengths of men in teamwork.

This study reexamined the additivity of maximum isometric teamwork lifting strength using experienced and height-matched young male participants. The maximum isometric lifting strength was measured for four exertion heights (45, 75, 105, and 140 cm) and four lifting styles (one-, two, three-, and four-person exertions). The results showed that actual teamwork strength could be greater or lower than the sum of individual strengths. If it was greater, the difference between the two could be either significant or nonsignificant, but if it was lower, there was no significant difference between the two. Actual teamwork strength ranged from 90.0% to 134.8% of the sum of individual strengths, indicating that experienced and height-matched participants could overcome the problem of lack of coordination in isometric teamwork lifting. The results also showed that some teamwork members, especially weaker members, might be forced to exert strengths higher than their maximum individual voluntary strengths in teamwork lifting. To avoid such overexertion in teamwork, it is recommended that the weight of the handled load be controlled and lower than the sum of all members' strengths. Additionally, members with significantly different strength abilities should not be assigned to the same team. Actual or potential applications of this research include designing member assignments in teamwork lifting tasks.

Adult↗
PubMed1993

Dissociation of [H+] from fatigue in human muscle detected by high time resolution 31P-NMR.

Previous in vivo studies of skeletal muscle fatigue have demonstrated significant relationships between the decline of muscular force and changes in muscle metabolism. However, these studies performed measurements over relatively long time intervals or during steady state exercise, thereby obscuring rapid metabolic changes occurring at the onset of exercise and recovery. To overcome these limitations, fatigue of human calf musculature during sustained isometric foot plantar flexion was quantified continuously as the decline in maximal voluntary contraction force (MVC), while concentrations of phosphocreatine (PCr), inorganic phosphate (Pi), intracellular free hydrogen ion (H+), and monovalent phosphate (H2PO4-) were simultaneously measured at 2-second intervals by 31P nuclear magnetic resonance. The first major finding was that [H+], which has been thought to be a mediator of muscle fatigue, actually declined during the first 10 seconds of exercise when force was declining and rose immediately postexercise, when force partially recovered. Second, the correlations of [H+], [H2PO4-] and Pi with MVC during the first minute of exercise were determined to be curvilinear and not linear as previously suggested. Furthermore, using either a linear or curvilinear regression model, [H2PO4-] and Pi demonstrated a closer correlation to MVC than [H+] during the first minute of exercise. Thus, these results reveal nuances in the relationships of MVC to metabolites previously undetected by low time-resolution measurements. These findings suggest that during sustained isometric exercise, rising [H+] is not likely to be the sole mechanism of muscle fatigue and are consistent with the view that a rise of Pi or [H2PO4-] is a major causation factor in force reduction.

Adolescent↗
PubMed1998

Two-step, predictive, isometric force model tested on data from human and rat muscles.

Functional electrical stimulation can assist paralyzed individuals to perform functional movements, but muscle fatigue is a major limitation to its practical use. An accurate and predictive mathematical model can facilitate the design of stimulation patterns that optimize aspects of the force transient while minimizing fatigue. Solution nonuniqueness, a major shortcoming in previous work, was overcome with a simpler model. The model was tested on data collected during isometric contractions of rat gastrocnemius muscles and human quadriceps femoris muscles under various physiological conditions. For each condition tested, parameter values were identified using the force response to one or two stimulation trains. The parameterized model was then used to predict forces in response to other stimulation patterns. The predicted forces closely matched the measured forces. The model was not sensitive to initial parameter estimates, demonstrating solution uniqueness. By predicting the force that develops in response to an arbitrary pattern of stimulation, we envision the present model helping identify optimal stimulation patterns for activation of skeletal muscle during functional electrical stimulation.

Animals↗
PubMed2006

Compensatory strategies during normal walking in response to muscle weakness and increased hip joint stiffness.

Compared to young adults, older adults exhibit a slower walking speed, smaller step length, shorter swing phase time and decreased range of motion in their lower extremity joints. The underlying mechanisms causing these gait adaptations is not well understood, with various musculoskeletal parameters being put forth as contributing factors, including increased joint stiffness and decreased isometric muscle strength. The objective of this study was to identify the necessary compensatory mechanisms to overcome such musculoskeletal deficits and regain a normal walking pattern. Understanding these mechanisms has important implications for designing effective rehabilitation interventions for older adults that target specific muscle groups and properties (e.g., isometric strength versus joint stiffness) to improve gait performance. Muscle-actuated forward dynamics simulations of normal walking were analyzed to quantify compensatory mechanisms in the presence of muscle weakness in specific muscle groups and increased hip joint stiffness. Of particular importance were the compensatory mechanisms provided by the plantar flexors, which were shown to be able to compensate for many musculoskeletal deficits, including diminished muscle strength in the hip and knee flexors and extensors and increased hip joint stiffness. This importance was further highlighted when a normal walking pattern could not be achieved through compensatory action of other muscle groups when the uniarticular and biarticular plantar flexor strength was decreased as a group. Thus, rehabilitation or preventative exercise programs may consider focusing on increasing or maintaining plantar flexor strength, which appears critical to maintaining normal walking mechanics.

Adaptation, Physiological↗
PubMed1983

[Method of measuring the modulus of elasticity of human muscle tissue].

An experimental method is described for estimating the mechanical properties of human soft tissues by calculating Young's modulus which was defined according to the slope of the hysteresis curve of the test subject, reflecting the dependence of its deformation on the force applied. The main causes of numerous difficulties in obtaining such data and the ways for their overcoming are considered. Experiments were made on the biceps in the isometric mode under different degrees of internal tension. It has been shown that the higher the physical development of the test subject the less the magnitude of Young's modulus. The dependence of its magnitude on the degree of muscular tension is sublinear in character in the group with good physical development and superlinear in that with poor physical development.

Adult↗
PubMed1985

Effects of intense "stretching"-flexibility training on the mechanical profile of the knee extensors and on the range of motion of the hip joint.

The sample for the study involved 12 volunteer male, active but not specially trained secondary school students. They averaged 15.33 years with a mean height of 168.20 cm, and a mean mass of 55.08 kg. Changes, if any, in the mechanical properties (MVC, half-relaxation time, fast isometric contraction, concentric contraction of the knee extensors) and flexibility of the hip joints were studied. The subjects executed passive, purely slow stretching as well as range-of-motion flexibility exercises for the knee extensors and the hip joints for 7 weeks three times a week. Pre- and post-measurements for flexibility and stride frequency on the spot showed significant improvement as did half-relaxation time, fast isometric force development, and speed of concentric contractions when low loads were to be overcome. In addition to studies in which improvements reported were attributed to and related to myoelectrical, reflex, and connective tissue changes, in the present study it was concluded that stretching exercises influence intrinsic muscle mechanical character along with a simultaneous improvement in range of motion of the joints exercised.

Adolescent↗
PubMed1993

Vascular and electromyographic responses evoked in forearm muscle by isometric contraction of the contralateral forearm.

There is controversy over whether isometric contraction of the forearm evokes vasoconstriction or vasodilatation in the muscles of the contralateral forearm. In the present study we have investigated in normal man, the effects of isometric contraction of one arm at 75, 50 and 25% maximum voluntary contraction (MVC) on arterial pressure, heart rate, blood flow and vascular resistance of the contralateral forearm and on electromyographic (EMG) activity recorded from that same arm with sensitive, surface electrodes. When EMG activity was not being recorded from the 'resting' arm, isometric contraction of the contralateral arm for 2 min evoked increases in arterial pressure and heart rate whose magnitudes were graded with % MVC and an increase in forearm blood flow and a decrease in forearm vascular resistance at 75, 50 and 25% MVC, indicating vasodilatation. Further experiments in which EMG activity was recorded from the 'resting' arm demonstrated that the decrease in forearm vascular resistance evoked by 75% MVC was associated with a substantial increase in EMG activity of the extensor and flexor muscles of that arm. By contrast, when forearm contraction was performed at 75% MVC whilst subjects viewed the EMG activity in the 'resting' arm on an oscilloscope and kept EMG activity minimal, vascular resistance increased in that arm, indicating vasoconstriction. Further, when subjects performed contraction at 25% MVC whilst showing minimal EMG activity in the contralateral arm, vascular resistance in that same arm increased (from 78 +/- 16 to 124 +/- 29 mmHg/ml/min/100 ml tissue). These results are discussed in relation to those of previous studies. We propose, that in normal man, isometric contraction of the forearm evokes primary vasoconstriction in the muscles of the contralateral forearm, but that this response may be overcome by muscle vasodilatation occurring secondary to unintended muscle contraction or as part of the alerting response to acute stress.

Adult↗
PubMed1983

Inhibition by propranolol of the contractile response of the rat diaphragm to tetanic field stimulation in vitro.

Contraction of the rat isolated diaphragm in response to maximal tetanic stimulation was examined before and after isoprenaline or propranolol. Isoprenaline (10(-4)M) did not affect maximum isometric force, whereas propranolol depressed maximum force in a concentration-dependent manner (10(-6)-10(-4)M). Inhibition due to propranolol (10(-4)M) could not be overcome by increasing the intensity or duration of electrical stimulation, and was only partially reversed (mean 73% +/- 10 s.e. mean) after washing. Pretreatment with isoprenaline did not alter the response of the muscle to propranolol, nor did neuromuscular blockade with (+)-tubocurarine. The response to either stereoisomer of propranolol was similar to that obtained with the racemate. Atenolol, a beta-adrenoceptor blocking agent without membrane stabilizing activity, had minimal (less than 10%) depressant effects on diaphragmatic force development. Lignocaine (8.5 X 10(-6)-8.5 X 10(-5)M) produced a concentration-related decrease in isometric force, similar to that with propranolol. It is concluded that propranolol decreases the contractile force of the rat isolated diaphragm by a mechanism related to stabilization of excitable membranes.

Animals↗
PubMed1996

Distension reduces the vasoreactivity of the internal mammary artery.

Although the vasoreactivity of internal mammary artery grafts is beneficial in the long term, after mobilisation, vasospasm reduces flow through the vessel. This may be overcome and flow improved by distension. To assess the effects of distension on the vasoreactivity of the artery we have measured changes in isometric tension in rings of distended and undistended human internal mammary artery. For an equivalent wall tension, the diameter of the distended artery was 1922 microns (CL 1858 to 1986) and undistended 1684 microns (CL 1628 to 1739), (P < 0.001). In response to 25 mM potassium the increase in isometric tension, as a percent of resting tension, was 35% (CL 31 to 39) in undistended and 5% (CL 3 to 6) in distended segments (P < 0.001), with 10 microM noradrenaline increases were 57% (CL 47 to 66) and 3% (CL 2 to 5), respectively (P < 0.001). The reduction in developed tension in segments contracted with potassium and relaxed with 1 microM acetylcholine was 65% (CL 47 to 83) in undistended, and 15% (CL -1 to 32) in distended (P < 0.01). With 10 microM glyceryl trinitrate relaxation was 96% (CL 87 to 105) and 17% (CL -9 to 43), respectively (P < 0.01). Similarly, after contraction by noradrenaline, with acetylcholine, undistended segments relaxed by 50% (CL 44 to 55) and distended by 14% (CL 8 to 21) (P < 0.01), with glyceryl trinitrate relaxation was 90% (CL 80 to 99) and 7% (CL -4 to 19), respectively (P < 0.001). Distension produces a profound reduction in vasoreactivity of the internal mammary artery which is not due to endothelial damage alone.

Adult↗
PubMed2006

Scaling properties of pyramidal neurons in mice neocortex.

Dendritic morphology is the structural correlate for receiving and processing inputs to a neuron. An interesting question then is what the design principles and the functional consequences of enlarged or shrinked dendritic trees might be. As yet, only a few studies have examined the effects of neuron size changes. Two theoretical scaling modes have been analyzed, conservative (isoelectrotonic) scaling (preserves the passive and active response properties) and isometric scaling (steps up low pass-filtering of inputs). It has been suggested that both scaling modes were verified in neuroanatomical studies. To overcome obvious limitations of these studies like small size of analyzed samples and restricted validity of utilized scaling measures, we considered the scaling problem of neurons on the basis of large sample data and by employing a more general method of scaling analysis. This method consists in computing the morphoelectrotonic transform (MET) of neurons. The MET maps the neuron from anatomical space into electrotonic space using the logarithm of voltage attenuation as the distance metric. The theory underlying this approach is described and then applied to two samples of morphologically reconstructed pyramidal neurons (cells from neocortex of wildtype and synRas transgenic mice) using the NEURON simulator. In a previous study, we could verify a striking increase of dendritic tree size in synRas pyramidal neurons. Surprisingly, in this study the statistical analysis of the sample MET dendrograms revealed that the electrotonic architecture of these neurons scaled roughly in a MET-conserving mode. In conclusion, our results suggest only a minor impact of the Ras protein on dendritic electroanatomy, with non-significant changes of most regions of the corresponding METs.

Algorithms↗
PubMed2002

A conserved C-terminal region in Gp71 of the small isometric-head phage LL-H and ORF474 of the prolate-head phage JCL1032 is implicated in specificity of adsorption of phage to its host, Lactobacillus delbrueckii.

Thirty-five phage-resistant mutants of Lactobacillus delbrueckii subsp. lactis ATCC 15808 were selected. Thirty-three of these mutants were assigned to the Bes group, while the remaining two were grouped under the Ads designation. Bes group mutants adsorbed phage LL-H but did not allow efficient phage development. Preliminary evidence suggests that these strains exhibit a mutation that changes the DNA specificity of a restriction-modification system. The Ads group mutants did not adsorb the small isometric-head phage LL-H. The results suggest that there are at least three different types of phage receptors in L. delbrueckii: two that are specific for small isometric-head phages and one that is specific for prolate-head phage JCL1032. Five LL-H host-range mutants which could overcome the adsorption block (a-type mutants) were selected and investigated by sequencing the genes g71 and g17, which encode minor and major tail proteins, respectively. Each of the a-type mutants carried a nucleotide change at the 3' end of gene g71. No mutations were observed in gene g17. Comparison of the gene product of g71 of phage LL-H with its homolog in JCL1032 (ORF474) showed that these proteins had very similar C-terminal regions. No similarities were found at the N-terminal part of the proteins. We conclude that the C-terminal portion of the protein encoded by g71 of phage LL-H and its homolog in phage JCL1032 determines the adsorption specificities of these phages on L. delbrueckii.

Amino Acid Sequence↗
PubMed2003

Coexistence of potentiation and low-frequency fatigue during voluntary exercise in human skeletal muscle.

The role of muscle potentiation in overcoming low-frequency fatigue (LFF) as it developed during submaximal voluntary exercise was investigated in eight males (age 26.4 +/- 0.7 years, mean +/- SE) performing isometric leg extension at approximately 30% of maximal voluntary contraction for 60 min using a 0.5-duty cycle (1 s contraction, 1 s rest). At 5, 20, 40, and 60 min, exercise was interrupted for 3 min, and the maximum positive rate of force development (+dF/dtmax) and maximal twitch force (Pt) were measured in maximal twitch contractions at 0, 1, 2, and 3 min of rest (R0, R1, R2, R3); they were also measured at 15 min of recovery following the entire 60-min exercise period. These measures were compared with pre-exercise (PRE) as an indicator of potentiation. Force at low frequency (10 Hz) was also measured at R0, R1, R2, and R3, and at 15 min of recovery, while force at high frequency (100 Hz) was measured only at R0 and R3 and in recovery. Voluntary exercise increased twitch +dF/dtmax at R0 following 5, 20, 40, and 60 min of exercise, from 2553 +/- 150 N/s at PRE to 39%, 41%, 42%, and 36% above PRE, respectively (P<0.005). Twitch +dF/dtmax decayed at brief rest (R3) following 20, 40, and 60 min of exercise (P<0.05). Pt at R0 following 5 and 20 min of exercise was above that at PRE (P<0.05), indicating that during the early phase of moderate-intensity repetitive exercise, potentiation occurs in the relative absence of LFF. At 40 and 60 min of exercise, Pt at R0 was unchanged from PRE. The LFF (10 Hz) induced by the protocol was evident at 40 and 60 min (R0-R3; P<0.05) and at 15 min following exercise (P<0.05). High-frequency force was not significantly compromised by the protocol. Since twitch force was maintained, these results suggest that as exercise progresses, LFF develops, which can be compensated for by potentiation.

Adult↗
PubMed2003

Eye muscle force development and saccadic velocity in thyroid-associated ophthalmopathy.

BACKGROUND: Ocular motility disturbances are very common in patients with thyroid-associated ophthalmopathy (TAO). The force duction test has demonstrated that limitations of eye movements may be caused by mechanical restrictions in the muscles. A quantitative evaluation of isometric force production and ocular motility in all directions of gaze could further elucidate the mechanism of the movement disorder. METHODS: In eight patients with TAO and eight controls of the same age range, horizontal and vertical saccadic movements of both eyes were recorded by means of electro-oculography (EOG). The corresponding force development in muscles of the more affected eye in patients and the non-dominant eye in normals was measured, using a suction contact lens/strain gauge technique. RESULTS: Steady-state tension in the patients was increased in all directions of gaze both horizontally and vertically, most markedly for vertical fixations in the upper field of gaze. However, peak tension was increased only for the downward movements in the upper field of gaze and for the horizontal movements in the abduction field of gaze. Vertical saccadic velocity was slower than normal in downward movements, and horizontal saccadic velocity was reduced in the abduction field of gaze. CONCLUSION: The increased active eye muscle tension in different directions of gaze could represent an adaptational mechanism of the ocular motor system to overcome the eye movement restriction in TAO.

Aged↗