SEARCH · PubMed Health

Results for “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 991 records · Page 55Linked to original sources

PubMed2000

The relationship between isometric force requirement and forelimb tremor in the rat.

To explore the effects of isometric force of rodent forelimb contraction on forelimb tremor, rats were trained to press downward on an isometric force transducer to raise a water-filled dipper cup and maintain force to keep the dipper in the raised position while licking. Force requirements were then manipulated parametrically to measure the effects of escalating force output on forelimb tremor and other variables. In the Peak-Force greater than Hold-Force (PF > HF) manipulation, the forces required to raise the dipper were 20, 40, and 60 g (each condition for about 2 weeks), while the force required to maintain the dipper in the raised position remained 6.7 g for all three conditions. In the Peak-Force equal to the Hold-Force (PF = HF) manipulation, rats were required to maintain the "dipper-raising" force throughout the response. The forces required were 20 g, 40 g, and 60 g (each for 2 weeks). For all force requirement manipulations, data were analyzed within and across conditions. As expected, force output increased with increased force requirements. Spectral analysis of force-time records revealed that during all manipulations, high-frequency (>10 Hz) forelimb tremor increased with increased force output, an effect that is consistent with human studies, and that may reflect increases in the number of motor units firing at higher rates. Additionally, with the exception of the 60-g PF = HF condition, there were within-condition decreases in tremor and increases in task engagement, evidence suggesting increased muscle strength as a function of experience (i.e., "physical training"). Taken together, the results suggest that the rodent-based method may provide a valuable, noninvasive functional assay for animal models of disorders that affect skeletal muscle control in humans.

Animals↗

PubMed2002

Unintentional forces developed during isometric test of the shoulder.

OBJECTIVE: To study unintentional, spontaneous forces developed during isometric shoulder strength testing. DESIGN: An experimental study. BACKGROUND: During torque measurements, subjects may apply forces in directions other than requested, thereby obscuring the interpretation of the results. METHODS: A shoulder strength test was performed with a strength test device permitting measurements of force in the requested direction as well as perpendicular to it. Nine fishermen and nine welders performed isometric abduction and elevation with the arm held in various angles. Moreover four rotational postures were investigated. RESULTS: Spontaneous force deviations from requested direction were found in almost all posture tested, with errors--defined as 100 times the ratio of the magnitude of intentional torque to the magnitude of unintentional (erroneous) torque generated perpendicular to it--of more than 30% found for some postures. Abduction in 45 degrees horizontal flexion was better controlled than abduction in 90 degrees horizontal flexion. Detailed analysis indicated some groupwise differences between fishermen and welders. Also pairwise comparison of handiness indicated some differences. CONCLUSIONS: Considerable deviations from requested direction of action can arise during strength tests. Thus, one must either monitor these deviations or minimize them by a proper design of the examination to get relevant data. As the error can differ between certain subject categories depending on posture this indicate a new tool for discriminating between musculo-skeletal problems. RELEVANCE: Muscle strength devices must be used with care as their measurement setups may mask the truce muscle action of the patients.

Adult↗

PubMed2002

The effects of age and feedback on isometric knee extensor force control abilities.

OBJECTIVE: To investigate the effects of age and feedback on submaximal isometric force control abilities in the knee extensors. DESIGN: Analysis of a force control task in a quasi-experimental design. BACKGROUND: The ability to control submaximal strength is important to accomplish activities of daily living. The purpose of this study was to investigate the effects of age, feedback, and force level on force control ability in knee extension, which is often used to accomplish daily activities. METHODS: The performance of an isometric force control task was measured in young (mean age 26, SD 2.7 yrs) and older (mean age 72, SD 2.0 yrs) adult healthy male participants. Each participant maintained a steady force in knee extension at two levels of force (20% and 60% MVC) with and without visual bandwidth feedback. Age, force level, and feedback effects were examined on the dependent variables of force variability, bias, and time in bandwidth. RESULTS: Both groups were fairly accurate at accomplishing the task, particularly at the lower force level. The higher force was harder to control, particularly when feedback was absent. The absence of feedback did not affect variability during force control. Older adults performed with less variability and a higher safety margin. Both groups performed better in time spent in bandwidth and safety margin with visual feedback, compared to the no-feedback condition. CONCLUSIONS: Healthy older and younger adults performed quite similarly regardless of feedback being provided or not. The intermittent feedback condition may have been more closely aligned with a no feedback condition rather than a continuous feedback condition. RELEVANCE: Clinical evaluation of submaximal force control ability may be useful for delineating impairments in motor skill and measuring outcomes of intervention programs. To be useful in the clinic, force control assessments must be both sensitive and specific to underlying impairments. The current study investigated the normal range of force control variability to allow the detection of true impairments.

Adult↗

PubMed2000

The dynamics of human isometric pointing movements under varying accuracy requirements.

The goal of the present study was to explore the relation between speed-accuracy trade-off phenomena and action kinematics in the case of pointing under isometric conditions. Increasing task difficulty resulted in a linear increase in movement time (as predicted by Fitts' law) and in systematic changes in the spatio-temporal patterning of force production. The observed changes in motion topology were similar to those reported for isotonic tasks and adequately captured by a limit cycle model derived for the latter type of task. These results indicate that, for isometric force control as for isotonic position control, the reasons underlying the emergence of Fitts' law might be sought in dynamic trajectory formation processes.

Adult↗

PubMed1985

Electromyographic analysis of the thumb: a study of isometric forces in pinch and grasp.

An electromyographic study of thumb muscles was performed on eight subjects by means of integrated polyelectromyography and simultaneous recordings of isometric flexion-extension, abduction-adduction, and prehensile pinch and grasp of the thumb. The integrated electromyographic signal proved to be an excellent index of thumb muscle activity, with a linear relationship found at low to middle levels of muscle strength. To facilitate understanding of thumb function, thumb muscles can be classified as primary or secondary on the basis of electrical potential activity. In isometric flexion, the flexor pollicis longus (FPL) was primary, whereas in extension, the extensor pollicis longus (EPL) and abductor pollicis longus were primary. In adduction, the adductor pollicis and EPL were primary and the FPL was secondary. In abduction, the abductor pollicis brevis and opponens pollicis were primary. The adductor pollicis, and FPL were nearly equal during pinch and grasp, with significant electrical activity increasing with greater force requirements. The first dorsal interosseous and EPL contributed secondarily in both pinch and grasp. When surgeons consider tendon transfers for nonfunctioning thumb muscles, the primary muscles should be replaced first to best restore pinch and grasp strength.

Biomechanical Phenomena↗

PubMed2002

Isometric arm counter-pressure maneuvers to abort impending vasovagal syncope.

OBJECTIVES: We hypothesized that isometric arm exercises were able to increase blood pressure (BP) during the phase of impending vasovagal syncope and allow the patient to avoid losing consciousness. BACKGROUND: Hypotension is always present during the prodromal phase of vasovagal syncope. METHODS: We evaluated the effect of handgrip (HG) and arm-tensing in 19 patients affected by tilt-induced vasovagal syncope. The study consisted of an acute single-blind, placebo-controlled, randomized, cross-over tilt-table efficacy study and a clinical follow-up feasibility study. RESULTS: In the acute tilt study, HG was administered for 2 min, starting at the time of onset of symptoms of impending syncope. In the active arm, HG caused an increase in systolic blood pressure (SBP) from 92 +/- 10 mm Hg to 105 +/- 38 mm Hg, whereas in the placebo arm SBP decreased from 91 +/- 11 mm Hg to 73 +/- 21 mm Hg (p = 0.008). Heart rate behavior was similar in the two arms. In the active arm, 63% of patients became asymptomatic, versus 11% in the control arm (p = 0.02); conversely, only 5% of patients developed syncope, versus 47% in the control arm (p = 0.01). The patients were trained to self-administer arm-tensing treatment as soon as symptoms of impending syncope occurred. During 9 +/- 3 months of follow-up, the treatment was actually performed in 95/97 episodes of impending syncope (98%) and was successful in 94/95 (99%). No patients suffered injury or other adverse morbidity related to the relapses. CONCLUSIONS: Isometric arm contraction is able to abort impending vasovagal syncope by increasing systemic BP. Arm counter-pressure maneuvers can be proposed as a new, feasible, safe, and well accepted first-line treatment for vasovagal syncope.

Adolescent↗

PubMed2002

EMG activity of trunk muscles and torque output during isometric axial rotation exertion: a comparison between back pain patients and matched controls.

Abnormal patterns of trunk muscle activity could affect the biomechanics of spinal movements and result in back pain. The present study aimed to examine electromyographic (EMG) activity of abdominal and back muscles as well as triaxial torque output during isometric axial rotation at different exertion levels in back pain patients and matched controls. Twelve back pain patients and 12 matched controls performed isometric right and left axial rotation at 100%, 70%, 50% and 30% maximum voluntary contractions in a standing position. Surface EMG activity of rectus abdominis, external oblique, internal oblique, latissimus dorsi, iliocostalis lumborum and multifidus were recorded bilaterally. The primary torque in the transverse plane and the coupling torques in sagittal and coronal planes were measured. Results showed that there was a trend (P = 0.08) of higher flexion coupling torque during left axial rotation exertion in back pain patients. Higher activity for external oblique and lower activity for multifidus was shown during left axial rotation exertion in back pain group when compared to the control group. In right axial rotation, back pain patients exhibited lesser activity of rectus abdominis at higher levels of exertion when compared with matched controls. These findings demonstrated that decreased activation of one muscle may be compensated by overactivity in other muscles. The reduced levels of activity of the multifidus muscle during axial rotation exertion in back pain patients may indicate that spinal stability could be compromised. Future studies should consider these alternations in recruitment patterns in terms of spinal stability and internal loading. The findings also indicate the importance of training for coordination besides the strengthening of trunk muscles during rehabilitation process.

Abdominal Muscles↗

PubMed1998

Evoked isometric muscle contractions in myopathies: analysis of pathophysiological properties by different stimulus patterns.

Isometric twitches of the adductor pollicis muscle following ulnar nerve stimulation were investigated in healthy subjects (n = 35) and patients with different types of myopathies (myotonic dystrophy, n = 19; limb girdle muscular dystrophy, n = 10; metabolic myopathy, n = 6). The changes within the rising part (i.e. within the contraction time, CT) of the isometric twitches after single stimuli were similar in myotonic and limb girdle dystrophies: the first part of CT, which lasts until the maximal contraction rate is achieved, was shortened, whereas the following second part of CT, which lasts until the maximal twitch force is achieved, was normal. In metabolic myopathies the first part was normal, whereas the second part was prolonged. The relaxation was prolonged in all types of myopathies, particularly in metabolic myopathies. Using double stimuli with short interstimulus intervals (ISI), the absolute refractory period of the muscle contraction (healthy subjects: 1.35 +/- 0.16 ms) was shortened in patients with myotonic dystrophy (1.02 +/- 0.11 ms). In the other types of myopathies, the absolute refractory period was only shortened provided that the single twitch force was clearly reduced. A similar dependence on a reduced single twitch force was also found with regard to the maximal force development with two stimuli and the corresponding ISI: the force contributed by a second stimulus was pathologically enhanced if the single twitch force was clearly reduced. The ISI related to the maximal force with two stimuli was shifted towards very short values (healthy subjects: 10.5 ms, myotonic dystrophy: 4.6 ms, limb girdle dystrophies: 5.0 ms). Our results can be attributed to altered kinetics of calcium release and uptake by the sarcoplasmic reticulum in myopathies.

Adolescent↗

PubMed2001

Feedback-dependent modulation of isometric force control: an EEG study in visuomotor integration.

The primary purpose of this investigation was to examine the cortical mechanisms underlying visuomotor integration in an experiment directly manipulating visual feedback (control-signal gain) as participants executed a grasping task. This was accomplished by assessing human electroencephalograms in both time and frequency domains and relating these measures to the performance accuracy of isometric force control. The basic experimental manipulation consisted of subjects controlling a grip dynamometer and the subsequent force trace displayed on a computer monitor at various magnitudes of force output and control-signal gain. Several findings from this study were of interest. First, the effects of control-signal gain and its interplay with the magnitude of force were most evident across the parietal and frontocentral electrode locations--areas specifically related to multi-modal sensory evaluation (parietal lobe) and higher-order movement control (supplementary and mesial premotor areas). Second, electroencephalography (EEG) measures in the time domain, i.e., slow-wave potentials, were sensitive to control-signal gain only during the ramp phase of force production (period of reaching the target force), not the static phase (period of maintaining the target force level). Third, EEG measures within the frequency domain (event-related desynchronization), unlike the slow-wave potential measures, were sensitive to control-signal gain during the static phase of force production--a sensitivity that was directly related to improvements in the accuracy of isometric force control. The findings of this investigation are described in relation to the existent literature on human visuomotor integration with special attention paid to the distinct spatial and temporal electrocortical patterns exhibited under varying degrees of visual feedback and magnitudes of force output during grasping.

Adult↗

PubMed2000

Different neuromuscular recruitment patterns during eccentric, concentric and isometric contractions.

Aim. The purpose of this study was to determine the neuromuscular fatigue profiles during 100 s isometric (ISO), concentric (CON), and eccentric (ECC) activity.Methods. Twelve subjects (age 25.1+/-3.7 years, mass 70.1+/-8.2 kg, mean+/-SD) performed ISO, CON and ECC maximal voluntary contractions and 100 s endurance trials on an isokinetic dynamometer. Raw EMG data were recorded throughout each trial from the rectus femoris of the right limb. Corresponding data for integrated electromyography (IEMG), percentile frequency shifts (MPFS) and peak torque output were divided into five 5 s epochs and subsequently normalised with the first epoch being the reference point, in order to assess changes over time.Results. There were no significant differences between ECC, CON and ISO peak torque output (211+/-63 vs 169+/-41 vs 177+/-61 Nm; ECC, CON, ISO) and IEMG activity (280+/-143 vs 305+/-146 vs 287+/-143 mV; ECC, CON, ISO) during maximal contractions. Serial reductions in torque output were greatest in ISO in which torque output during the final epoch was 31+/-13% of initial values, similar to the final torque values in CON (58+/-15%), but significantly less than ECC (108.6+/-38.6%; P<0. 001) values. In CON and ECC, IEMG was maintained (95+/-27% and 93+/-21%; CON and ECC), whereas IEMG for ISO decreased to 38+/-13% of initial values. The greatest reduction in MPFS occurred in CON (69+/-10%) compared to ISO (78+/-9%; P<0.05) and ECC (93+/-6%; P<0.001).Conclusion. These data demonstrate distinct neuromuscular fatigue profiles for the different types of muscle contraction. Whereas eccentric activity was largely fatigue resistant, isometric and concentric contractions displayed different neuromuscular fatigue profiles.

Adult↗

PubMed2003

Is the coactivation of biceps femoris during isometric knee extension affected by adiposity in healthy young humans?

This study aimed to verify if the level of biceps femoris antagonist activity measured during isometric knee extension was affected by the individual degree of adiposity in 14 young healthy subjects of both genders aged between 18 and 24. Surface EMG signals were recorded from the biceps femoris muscle of the dominant leg during isometric knee extension at three levels of voluntary contraction: maximum (MVC), 80% MVC and 200 N, respectively. In addition, whole-body percentage of fat, volume of the thigh and skinfold thickness below the electrodes were achieved. Biceps femoris coactivation values were: 28.5 +/- 17.9%, 30.9 +/- 17.7% and 25.3 +/- 17.5% for MVC, 80% MVC and 200 N trials, respectively (NS). Neither the whole-body percentage of fat nor the skinfold thickness influenced percentage coactivation, irrespective of the intensity of contraction. However, an increase in the whole-body percentage of fat showed a tendency to augment the biceps femoris coactivation (P(I)=0.079; P(II)=0.575). No differences in coactivation were observed between genders. In addition, the duration of contraction did not affect the level of coactivation.

Adipose Tissue↗

PubMed1998

Extrapolation of time series of EMG power spectrum parameters in isometric endurance tests of trunk extensor muscles.

The aim of the present study was to test the viability of using short isometric contractions of trunk extensor muscles to perform an assessment of their endurance capacity. To this aim two types of analysis were performed. First, electromyographic (EMG) mean power frequency (MPF) slopes with respect to time as estimated over shorter fixed periods were compared to slopes estimated over the full contraction period of a contraction sustained until the endurance time. Second, the relationship between MPF slope estimates as estimated over various periods and the endurance time of the muscle group was evaluated. Five subjects performed three isometric trunk endurance tests at 25%, 50% and 75% of their maximum voluntary contraction (MVC), respectively. EMG signals of the left and right multifidus, iliocostalis and longissimus muscles were continuously recorded and spectral parameters were calculated. The MPF appeared to decrease consistently during all endurance tests. The extrapolation from a MPF time series of half the estimated contraction period to the time series of the complete contraction period gave reasonable results at all force levels, when data from several electrode locations were incorporated in a single slope estimate (mean or steepest slope). The accuracy of the prediction of trunk extensor endurance on the basis of these parameters describing the MPF time series over half the estimated contraction period was satisfactory. Endurance time predictions from yet shorter periods were unreliable.

Adult↗

PubMed1998

EMG variability during maximum voluntary isometric and anisometric contractions is reduced using spatial averaging.

Electromyography (EMG) is a commonly used tool that can be plagued with poor signal-to-noise ratios. One result of poor signal-to-noise ratios is increased within- and between-subject variability of quantified EMG variables, for example, the integrated EMG. Methods that reduce within- and between-subject variability of quantified EMG variables can increase the statistical power of an experimental design and aid in the functional interpretation of experimental results. The purpose of this investigation was to determine the effectiveness of spatially averaging the surface EMG signal to reduce the variability of the quantified EMG obtained during maximum voluntary contractions (MVC). The present study extends the work of earlier investigators describing the enhanced signal characteristics obtained by spatially averaging the surface EMG measured during submaximum voluntary isometric contractions and stretch reflexes. Ten subjects performed maximum voluntary isometric and anisometric (concentric and eccentric) contractions of the elbow flexors. Four electrodes, forming two pairs of bipolar electrodes were placed over both the biceps brachii and brachioradialis muscles. Four rectified and integrated EMG signals from the electrode array were compared. Data from each subject's contraction condition and from each muscle were used to compute a coefficient of variation that was considered representative of the within-subject variability. These data were analysed with a multifactorial repeated measures analysis of variance (ANOVA). The results revealed a muscle-specific, statistically significant superiority of one of the methods in reducing the variability of the rectified and integrated EMG signal. Summing the rectified and integrate signals from each bipolar pair of electrodes in the array was shown to reduce significantly the within-subject variability.

Adult↗

PubMed2002

Comparison of virtual and real electric powered wheelchair driving using a position sensing joystick and an isometric joystick.

There are limited interface options for electric powered wheelchairs, which results in the inability of some individuals to drive independently. In addition, the development of new interface technologies will necessitate the development of alternative training methods. This study compares a conventional position sensing joystick to a novel isometric joystick during a driving task in a virtual environment and a real environment. The results revealed that there were few differences in task completion time and root-mean-square error (RMSE) between the two types of joysticks. There were significant correlations between the RMSE in the virtual environment and the real environment for both types of joysticks. The data indicate that performance in the virtual environment was representative of driving ability in the real environment, and the isometric joystick performed comparably to the position sensing joystick.

Algorithms↗

PubMed1999

Temperature effect on the rates of isometric force development and relaxation in the fresh and fatigued human adductor pollicis muscle.

The purpose of the present study was to investigate the effect of temperature on the rates of isometric force development and relaxation in electrically activated fresh and fatigued human adductor pollicis muscle. Following immersion of the lower arm for 20 min in water baths of four different temperatures, muscle temperatures were approximately 37, 31, 25 and 22 C. Maximal isometric force was reduced by 16.8 +/- 1.5 % at 22 C. The stimulation frequency-force and -rate of force development relationships were shifted to the left at lower temperatures. Q10 values for the maximal rates of force development and relaxation, and the times for 100 to 50 % and 50 to 25 % force relaxation, were about 2.0 between 37 and 25 C and about 3.8 between 25 and 22 C. However, the time for 50 to 25 % force relaxation had a relatively high Q10 value between 25 and 22 C (6.9) and this parameter also appeared to be more sensitive to fatigue compared to the other indices of relaxation. Nevertheless, the effect of fatigue on all parameters decreased with cooling over the entire (37-22 C) temperature range.

Adult↗

PubMed1998

Acute and sustained effects of isometric and lengthening muscle contractions on high-energy phosphates and glycogen metabolism in rat tibialis anterior muscle.

Previous studies have shown that lengthening contractions, in contrast to isometric contractions, readily result in sustained malfunctioning of the exercised muscles. The present study was performed to investigate whether an exercise period with many (240) lengthening contractions (LC) results in alterations in muscle high-energy phosphates and inosine monophosphate (IMP) content, different from muscles performing a few (60) lengthening or a few (60) or many (240) isometric contractions (IC). Moreover, we sought for a possible cause(s) of the inability to replenish muscle glycogen stores following LC. Rat tibialis anterior muscles were subjected in vivo to either 60 or 240 LC or IC. Structural muscle damage occurred only after 240 LC. The fact that tissue glycogen levels declined to a similar extent during LC and IC suggests that the energy demand was comparable during both types of exercise. Nevertheless, the observation that on the one hand tissue stores of adenine nucleotides showed a greater decline, and on the other hand the tissue content of IMP increased to a significantly higher level after LC than after IC, clearly indicates that muscle energy metabolism is more disturbed during LC than during IC. The high tissue levels of IMP may contribute to impaired mechanical function as previously observed in muscles subjected to LC. In contrast to 240 IC, 24 hours after 240 LC, tissue glycogen stores and high-energy phosphate levels were not restored to control values. The present findings indicate that depressed glycogen synthase activity and impaired activity of the mitochondrial marker enzyme cytochrome C oxidase probably contribute to a continuous disturbance of energy metabolism in the exercised muscles during the 24 hours following 240 LC.

Adenosine Diphosphate↗

PubMed2001

A comparison of effects measured with isotonic and isometric recording: I. Concentration-effect curves for agonists.

Concentration-effect curves were obtained with carbachol tested on isolated preparations of guinea-pig ileum taken from adjacent sites in the same animal, one recorded isotonically, the other isometrically: similar experiments were made with histamine as agonist and with carbachol on rat uterus (in oestrus). The position and steepness of the curves was expressed as the values of [EC(50)] and the exponent, P: with carbachol or histamine on guinea-pig ileum the curves were significantly steeper with isotonic recording (P<0.02, sign test) and displaced towards lower concentrations (P<0.005) but there were significant correlations (P<0.05) between values obtained with tissues from the same animal. The curves for carbachol on the rat uterus were very steep: with isotonic recording the exponent (often eight or more) was consistently higher than with isometric (P<0.001): there was no significant displacement but there was a significant correlation (P<0.05) between values of [EC(50)] obtained with tissues from the same animal. Although the results obtained by the two methods are different, they are correlated. These effects are to be expected because with isotonic recording there can be no change in length until the tension exceeds the load and the tissue bulk sets an upper limit to shortening: the range within which an effect can be measured (the "operational window") is smaller. The observed effects on [EC(50)] and P have been reproduced with theoretical data.

Animals↗

PubMed1982

Baroreceptor stimulation and isometric exercise in normotensive and borderline hypertensive subjects.

1. The effects of carotid baroreceptor stimulation (neck chamber) on systemic haemodynamics were determined for normotensive and borderline hypertensive subjects during periods of resting and isometric exercise. 2. Both groups reacted to baroreceptor stimulation with a similar decrease in mean arterial pressure and cardiac index at rest and during isometric exercise, but baseline heart rate decreased more in borderline hypertensive patients. 3. Baroreceptor stimulation elicited the same haemodynamic response at rest and during exercise-induced arterial pressure increase. Since the magnitude of arterial pressure had no bearing on the subsequent response, these data suggest resetting of baroreceptors during this short-term blood pressure increase.

Adult↗