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PubMed2005

[Measurement of the isometric dorsiflexion and plantar flexion force in the ankle joint].

This article describes an easy to use test equipment for measuring the isometric force in the ankle joints in dorsiflexion and plantar flexion. The combination of the test equipment for measuring the voluntary maximal isometric muscle force in the ankle joint, the surface electromyograms and the motion analysis of the measured leg allow an objective comparison of the strength of the muscular force between the left and right leg. It might be also used as a control setup during rehabilitation after surgical treatment or injuries.

Ankle Joint↗

PubMed1996

An isometric predictor for maximum acceptable weight of lift for Chinese men.

The aim of this study was to examine the practicality of the modified isometric strength tests to predict the maximum acceptable weight of lift (MAWL) of Chinese men. The modified strength tests allow the participant to pull on the load cell in front of the body and to apply force in a functional free posture. Both the modified and the standard strength data of each participant were used as predictors for the MAWLs. The prediction models were constructed and evaluated under task conditions of two lifting ranges, two box sizes, and three lifting frequencies. To realize the effect of modifications, testing posture was recorded and the joint angles were calculated. A stepwise multiple regression analysis indicated that modified composite strength (MCS), chest circumference, and acromial height accounted for 86% to 91% of the variance. Because the strength of the upper extremity body was also recruited in the test, the weak upper extremity strength of the Chinese participants would therefore be better reflected. Evidence for the existence of a close match between MAWL and MCS values, as well as the task conditions for its existence, suggest that a simple isometric strength measure is a good predictor for the MAWL.

Adult↗

PubMed2004

The importance of isometric maximum strength and peak rate-of-force development in sprint cycling.

This study was designed to investigate the relationship of whole-body maximum strength to variables potentially associated with track sprint-cycling success. These variables included body composition, power measures, coach's rank, and sprint-cycling times. The study was carried out in 2 parts. The first part (n = 30) served as a pilot for the second part (n = 20). Subjects for both parts ranged from international-caliber sprint cyclists to local-level cyclists. Maximum strength was measured using an isometric midthigh pull (IPF). Explosive strength was measured as the peak rate-of-force development (IPRFD) from the isometric force-time curve. Peak power was estimated from countermovement (CMJPP) and static vertical jumps (SJPP) and measured by modified Wingate tests. Athletes were ranked by the U.S. national cycling coach (part 1). Sprint times (from a standing start) were measured using timing gates placed at 25, 82.5, 165, 247.5, and 330 m of an outdoor velodrome (part 2). Maximum strength (both absolute and body-mass corrected) and explosive strength were shown to be strongly correlated with jump and Wingate power. Additionally, maximum strength was strongly correlated with both coach's rank (parts 1 and 2) and sprint cycling times (part 2). The results suggest that larger, stronger sprint cyclists have an advantage in producing power and are generally faster sprint cyclists.

Adult↗

PubMed2002

Mechanomyogram and electromyogram responses of upper limb during sustained isometric fatigue with varying shoulder and elbow postures.

To investigate the behavior of mechanomyogram (MMG) and electromyogram (EMG) signals in the time and frequency domains during sustained isometric contraction, MMG and surface EMG were obtained simultaneously from four muscles: upper trapezius (TP), anterior deltoid (DL), biceps brachii (BB), and brachioradialis (BR) of 10 healthy male subjects. Experimental conditions consisted of 27 combinations of 9 postures [3 shoulder angles (SA): 0 degree, 30 degrees, 60 degrees and 3 elbow angles (EA): 120 degrees, 90 degrees, 60 degrees] and 3 contraction levels: 20%, 40%, and 60% of maximum voluntary contraction (MVC). Subjective evaluations of fatigue were also assessed using the Borg scale at intervals of 60, 30, and 10 sec at 20%, 40%, and 60% MVC tests, respectively. The mean power frequency (MPF) and root mean square (RMS) of both signals were calculated. The current study found clear and significant relationships among physiological and psychological parameters on the one hand and SA and EA on the other. EA's effect on MVC was found to be significant. SA had a highly significant effect on both endurance time and Borg scale. In all experimental conditions, significant correlations were found between the changes in MPF and RMS of EMG in BB with SA and EA (or muscle length). In all four muscles, MMG frequency content was two or three times lower than EMG frequency content. During sustained isometric contraction, the EMG signal showed the well-known shift to lower frequencies (a continuous decrease from onset to completion of the contraction). In contrast, the MMG spectra did not show any shift, although its form changed (generally remaining about constant). Throughout the contraction, increased RMS of EMG was found for all tests, whereas in the MMG signal, a significant progressive increase in RMS was observed only at 20% MVC in all four muscles. This supports the hypothesis that the RMS amplitude of the MMG signal produced during contraction is highly correlated with force production. Possible explanations for this behavioral difference between the MMG and EMG signals are discussed.

Adult↗

PubMed1980

Blood flow of the ipsilateral and contralateral lower limbs after isometric contraction.

Calf and thigh blood flows in both of right and left legs were measured simultaneously after isometric contraction of the right thigh muscle. Isometric contraction was performed at a force of about 50% of maximal voluntary contraction for 15 sec. The thigh blood flow of the right leg increased immediately after voluntary contraction in all subjects, while the calf blood flow of right leg decreased conversely in spite of exercised ipsilateral leg.

Adult↗

PubMed1985

Laser diffraction patterns during isometric and auxotonic contractions in frog skeletal muscle.

The changes in laser diffraction patterns during contraction of frog skeletal muscle are investigated under auxotonic as well as isometric conditions. Muscle fiber is connected to the double lever system of Huxley and Peachey's type so that the illuminated portion can be kept immobile during the muscle shortening. Under isometric conditions, the first order diffraction lines show rapid decreased in intensity at the start of contraction, but they stay at a nearly steady level during maintained tension. Meanwhile, noticeable changes in line width are not observed. The first order diffraction lines show further transient decrease in intensity at the onset of relaxation after the end of stimulation and then return almost to the initial resting state when relaxation is completed. These changes in diffraction lines are not obvious in sarcomeres longer than 3.3 micrometers, where only small tensions are developed. If the muscle is allowed to shorten under auxotonic conditions, not only decrease in intensity but also expansion in width is observed. The possible origins of changes in diffraction lines are considered to be non-uniform activation in excitation-contraction coupling, in addition to the displacement, bending, or transformation of the diffractive gratings. The disordering of the sarcomere arrangements also contributes to the change in diffraction patterns during muscle shortening.

Animals↗

PubMed1990

[Muscle activities in the region of neck, shoulder and back during isometric horizontal jaw exercises in various postures].

Eleven healthy participants were made to perform isometric horizontal jaw movements with maximum voluntary efforts in various postures. Surface EMGs from the laterocervical, nucha, shoulder and back regions were bilaterally picked up, and simultaneously recorded with jaw force. The results obtained were as follows: 1. Electromyographic power value in these regions depended on the directions of the jaw exercises (posteriorly pull greater than posterolaterally pull greater than anteriorly push not equal to anterolaterally push, P less than 0.0001). 2. The directional effects mentioned above were significantly obvious in the inferior laterocervical (Electrode No. 2) and back Electrode No. 5) regions (P less than 0.0001). 3. The postural effects on the power value were varied with the directions of the jaw exercises (P not equal to 0.03); i.e., the highest value during jaw pull was observed in an upright position, while that during jaw push was found in a supine position. 4. From above results, it would be considered that occlusal habits with sustained isometric jaw retrusion might have higher probability to provoke the discomfortableness in the neck, shoulder and back regions than those with protrusion, and that the habits with the retrusion might be more injurious in a supine than in an upright position, while those with the protrusion more injurious in an upright position.

Adult↗

PubMed1990

[Electromyographic studies on the exhibition of isometric protrusive and lateral protrusive mandibular forces].

To study the mechanism of exertion of horizontal mandibular force, the myoelectric effect of mandibular isometric protrusive and lateral protrusive contraction under four forces (1/4, 2/4, 3/4, or 4/4 of the maximum voluntary contraction) at three different jaw positions (O: centric occlusion, half: middle position between O and max, and max: maximum eccentric protrusive or lateral protrusive mandibular positions) was measured in six male subjects with normal jaw function. Electromyographic recordings of the inferior part of the lateral pterygoid (LPt), posterior temporalis (Tp) and masseter (Mm) muscles were taken bilaterally, and forces were measured with force transducer. EMG activities in the bilateral LPt during isometric protrusive contraction and in the contralateral LPt during lateral protrusive contraction increased with load intensity. Mm bilaterally during protrusive contraction, ipsilateral Tp and contralateral Mm during lateral protrusive contraction played an auxiliary role in exertion of horizontal mandibular force. EMG activities in the contralateral LPt during lateral protrusive contraction with every force and in the bilateral LPt during protrusive contraction with 1/4, 2/4, 3/4 force, were significantly increased under the eccentric mandibular position. However, EMG activities in the bilateral LPt during protrusive contraction with 4/4 force did not increase under the eccentric mandibular position. EMG activity in the LPt during protrusive contraction were higher than that during lateral protrusive contraction at every mandibular position and with every force. It was concluded that the LPt was predominantly concerned with exertion of horizontal mandibular force.

Electromyography↗

PubMed1996

Relationship between motoneuron pool excitability and parameters of timing and force in an isometric ankle-extension movement.

The changes in peak facilitation and slope of facilitation of the H-reflex were compared to the parameters of an isometric plantarflexion task. The amplitude of the reflex was significantly greater for reflexes elicited within 50 msec. of the onset of soleus muscle activity. Neither peak amplitude of the reflex nor slope correlated with rate of rise of isometric force; however, they did show a modest relationship between premotor time and reaction time.

Adult↗

PubMed1994

Q angle: effects of isometric quadriceps contraction and body position.

The quadriceps femoral angle (Q angle) has been linked with several knee disorders, but Q-angle measurement procedures have not been standardized. The purpose of this study was to examine the effects of isometric quadriceps contraction in the standing and supine positions on the Q angle. The Q angles of the right knees of 30 men and 30 women were measured goniometrically during four test conditions: 1) quadriceps relaxed in standing, 2) quadriceps contracted in standing, 3) quadriceps relaxed in supine, and 4) quadriceps contracted in supine. The pelvic widths were also measured as the distance between the anterior superior iliac spines in standing and supine. A two-way multivariate analysis of variance showed a significant difference between genders (p < 0.001) and among the four test conditions (p < 0.001) (N = 60). Separate one-way analyses of variance (ANOVAs) with two grouping factors (contraction and position) showed significant effects of contraction (p < 0.001) for both men and women, but no significant effect of positions. A dependent t-test showed that the pelvic width differed between standing and supine for both men and women (p < 0.001). The results showed that isometric quadriceps contraction affects the Q angle with the subjects standing or supine, even though the pelvic width differed significantly between the two positions. Clinicians and researchers should consider the results of this study in order to standardize procedures for measuring the Q angle.

Adult↗

PubMed1994

Estimation of aerobic and anaerobic metabolism in isometric forearm exercise.

The aim was to evaluate the energy turnover in the forearm during isometric submaximal exercise. Eight subjects performed isometric handgrip contractions until exhaustion at 10%, 25% and 40% of maximal voluntary contraction (MVC). Blood samples were drawn frequently from the cubital vein of the exercising arm during exercise and a 60 minutes recovery period, and forearm blood flow (plethysmography) was monitored during the same periods. Oxygen uptake and lactate release were used to quantify aerobic and anaerobic energy expenditure. Electromyography (frequency analysis) was monitored during exercise. Anaerobic glycolysis contributed 4%, 31% and 37% of the ATP production in the three experiments, respectively, but total ATP production from anaerobic glycolysis was the same, suggesting a maximal anaerobic glycolytic capacity (MAGC). MAGC may be a limiting factor for muscle performance at 25 and 40% MVC, but not at 10% MVC. Judging from the match between oxygen debt or estimated oxygen deficit vs the anaerobic energy production, the muscles recovered during 60 min rest after 10% MVC and 40% MVC. However, recovery after 25% MVC may have been incomplete.

Adult↗

PubMed1997

Circadian rhythm in the torque developed by elbow flexors during isometric contraction. Effect of sampling schedules.

Time-dependent changes in elbow flexion torque have been documented according to two different sampling schedules. Seven physical education students took part in the first series of experiments, and 7 other similar subjects in the second. In both sets of experiments, the subjects performed isometric contractions: maximal and submaximal at 90 degrees in the first experiments and maximal at different angular positions in the second. After a 30-minute rest period, the torque developed was measured at 00:00, 06:00, 09:00, 12:00, 15:00, 18:00, and 21:00 h on the day of the experiment. These subjects remained in the laboratory for 24 h. In the second series of experiments, the torque developed was measured at 01:00, 05:00, 09:00, 13:00, 17:00, and 21:00 h over the subsequent 6 days with only one test session per day. In this case, there was an interval of 20 h between two successive test sessions. In the first experiment, a significant time-of-day effect was observed for the torque of the elbow flexors under isometric conditions with an acrophase at 17:58 h. The 24 h normalized mean score was 92.85% with an amplitude of 7.63% of the daily mean. In the second series of experiments, there was evidence of a circadian rhythm in the torque developed by the elbow flexors at every angle position, especially at 90 degrees, the angle investigated in the first set of experiments. The peak torque was calculated to have occurred at 17:55 h. The amplitude of the rhythm was equal to 6.99% of the daily mean. There were no statistically significant differences in the characteristics of the circadian rhythm observed between the two experimental designs. We concluded that an experiment extending over several days could be employed to evaluate circadian rhythms in muscular activity reliably.

Adult↗

PubMed1985

Temporal relationships between isometric force, phosphorylase, and protein kinase activities in vascular smooth muscle.

Vascular smooth muscle contractility is tightly coupled to ATP production by intermediary metabolism. To elucidate mechanisms underlying coordination of metabolism and contractility we studied the time course of isometric force, and the activation of phosphorylase and cAMP-dependent protein kinases during stimulation of bovine coronary arterial strips with KCl. Isometric force reached a maximum after 10 min of exposure to 30 mM KCl (ED90) and was sustained throughout the subsequent 20-min period of contraction. In contrast, activation of phosphorylase was biphasic: enzymic activity reached a maximum (176 +/- 10% of control) after 3 min of contraction and then, though remaining above control, activity declined to a lower level (135 +/- 7% of control). However, no change occurred in the activity ratios for cAMP-dependent protein kinase assessed in either the presence (type II isozyme) or absence (type I isozyme) of 0.5 M NaCl. These data suggest that the activation of phosphorylase during K+-induced contraction is independent of the cAMP system. The biphasic activation of phosphorylase may reflect transient changes in the intracellular concentration of Ca2+ or the activation of a phosphatase(s) during the response.

Animals↗

PubMed1987

Performance of papillary muscles from the aging spontaneously hypertensive rat: temporal changes in isometric contraction parameters.

Myocardial mechanics in the male spontaneously hypertensive rat (SHR) and Wistar-Kyoto rat (WKY) at 18 months of age were studied. Left ventricular hypertrophy was documented in the SHR by an increase in left ventricle/body weight and left ventricle/tibial length ratios when compared to the WKY (P less than 0.001). Isolated left ventricular papillary muscles were studied at 28 degrees C while contracting 12 times/min at the apex of the length-tension curve. Active and passive length-tension relations were measured at relatively early (65 +/- 3 min) and late (200 +/- 5 min) times following sacrifice. No significant differences in passive length-tension relations between strains were observed. Between early and late measurements, a significant decrease in passive tension within the length spectrum 89-100% Lmax occurred in both SHR and WKY, accompanied by a significant increase in passive stiffness (P less than 0.01, SHR; P less than 0.001, WKY). Isometric performance was measured at relatively early (81 +/- 3 min) and later (190 +/- 5 min) times following sacrifice. Strain differences in active muscle performance were of a greater electromechanical delay time (EMD) (P less than 0.05, early: P less than 0.001, late) and time-to-peak tension (TPT) (P less than 0.001, late) in SHR compared to WKY. Between early and late measurements, decreases in EMD (P less than 0.01, SHR; P less than 0.001, WKY), TPT (P less than 0.001; P less than 0.001), the half-time of relaxation (P less than 0.001; P less than 0.001), and the resting tension (P less than 0.01; P less than 0.001) were observed, and the maximum rate of fall of tension increased (P less than 0.01; P less than 0.01). We conclude that studies must be precisely referenced from the time of sacrifice of the animal in order to accurately evaluate the effects of experimental hypertrophy on isolated muscle performance. No evidence for the depression of papillary muscle isometric performance was seen in the 18-month SHR when compared to the WKY, although prolonged EMD and TPT were observed.

Aging↗

PubMed2005

Decreased isometric skeletal muscle force in critically ill patients.

QUESTION UNDER STUDY: Critically ill patients can develop muscle weakness that prolongs recovery. The aim of this study was to evaluate contractile parameters of the involuntary isometric skeletal muscle forces as measures of muscle weakness in critically ill patients. METHODS: Prospective, controlled trial performed in an intensive care unit (ICU) of a university hospital. SUBJECTS: 19 critically ill patients (diagnoses: intracranial bleeding n = 9; sepsis n = 6; others n = 4), who were ventilated and completely immobilised for one week. 20 healthy volunteers served as controls. We measured peak torques (PT), contraction times, half-relaxation times, peak rates of torque development and decay and torque latencies of the ankle dorsiflexors of the foot after peroneal nerve stimulation. RESULTS: Patients (median Acute Physiology and Chronic Health Evaluation II score 21) had reduced PTs, medians 3.3 Nm (interquartile range 2.5 Nm) vs 4.1 Nm (2.0 Nm) in controls (P = 0.0003) for single pulse, 4.9 (4.7) vs 8.1 Nm (3.8) (P = 0.0001) for 2-pulse, 6.1 (6.3) vs 10.3 Nm (3.9) (P = 0.0009) for 3-pulse and 7.3 (6.4) vs 11.6 Nm (7.8), (P = 0.006) for 4-pulse stimulations, respectively. Contraction times were reduced and half-relaxation times increased compared with controls. CONCLUSIONS: Assessment of involuntary isometric skeletal muscle forces can be readily measured in critically ill patients. After one week of critical illness, these patients have decreased force compared with healthy controls. This assessment approach will be further evaluated in a long-term study with a larger patient population.

APACHE↗

PubMedDate not supplied

Repeatability study of mechanomyography in submaximal isometric contractions using coefficient of variation and intraclass correlation coefficient.

The within-day and between-day repeatability of the mechanomyogram (MMG) was assessed using the coefficient of variation (CV) and the intraclass correlation coefficient (ICC) and was compared with that of the electromyogram (EMG). The MMG and EMG were recorded simultaneously during isometric elbow flexion trials at different submaximal levels of 10% to 90% MVC. The testing session consisting of 9 submaximal trials was repeated 8 times on the same day for estimation of the within-day variation. In order to examine the between-day variation, the same testing session was also performed 8 times over 3 weeks with a 2-day rest interval between each session. The CVs within-day and between-day in both the MMG and EMG did not demonstrate any significant differences relating to the magnitude of force exerted. The CVs combined over all the force levels were approximately 10% within the same day and 25% between days for both the MMG and EMG. These corresponded to the within-day ICC of approximately 0.95 and the between-day ICC of 0.80. The repeatability of the MMG during submaximal isometric contractions of biceps brachii muscles is considered to be similar to that of the more established EMG.

Adult↗

PubMed1999

Isometric strength measurements in children with arthritis: reliability and relation to function.

OBJECTIVE: To examine the reliability of testing strength in children with juvenile arthritis (JA), and to determine the relationship between strength and function. METHODS: Children with JA were tested for grip and pinch strength (n = 32). Isometric force produced by hip abductors and knee extensors was tested with a hand-held dynamometer (n = 29). Two therapists both performed each of the tests twice so that intrarater and interrater reliability could be examined. Function was measured by means of the Childhood Health Assessment Questionnaire (CHAQ) and performance on a 50-meter run. Reliability was examined with intraclass correlations (ICC). The relationships of strength and function were determined with Pearson and Spearman correlations. RESULTS: All measures demonstrated good intrarater (ICC = 0.92-0.97) and interrater (ICC = 0.80-0.95) reliability. Grip strength and pinch were correlated with the CHAQ (r = -0.45 and -0.33, respectively), while hip abduction and knee extension torque were correlated with rankings on the 50-meter run (rho = -0.34 and -0.38, respectively). CONCLUSION: Isometric strength can be reliably measured in children with arthritis in a clinical setting.

Activities of Daily Living↗

PubMed2000

On the inter- and intra-subject variability of the electromyographic signal in isometric contractions.

The objective of the present study was to evaluate the variability of the surface EMG signal of the same muscle in healthy subjects, because of lack of reproducibility of the EMG signal for the same subject and muscle in different trials of maximal isometric voluntary contraction. The results showed an EMG coefficient of variability of 21.61%, indicating that this variability must be considered in experiments with an inappropriate condition for normalization procedures, such as EMG biofeedback in rehabilitation sessions, or normalization procedures by the maximal isometric voluntary contraction.

Adult↗