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PubMed1983

Spin label measurement of platelet alignment in a clot induced by isometric tension.

A spin label technique was applied to examine the alignment of platelet membranes in the platelet-fibrin clot. The ESR spectrum of the clot in the control experiment was typical of isotropically oriented membranes, while the ESR spectrum of the clot which was kept isometric was quite different from that of the control experiment. These spectra were simulated with a computer and explained to indicate that the shape of platelets in the clot was transformed to a cylindrical form under the isometric tension so that axes of all membrane cylinders were directed parallel to the generated force.

Animals↗

PubMed1978

Isometric torque of the finger extensors at the metacarpophalangeal joints.

A pilot study was undertaken to evaluate the isometric torque produced at the metacarpophalangeal joint during finger extension. Fifteen women with normal right hands, aged 21 to 29 years, participated. Each subject was tested for maximal force of isometric extension at the metacarpophalangeal joint angles of 0, 30, and 60 degrees on each of the four fingers. Torque was computed by multiplying the recorded tension and measured length of the proximal phalanx (lever arm). The mean torque for the long finger was significantly greater than the average torque for each of the other three fingers. The mean torque at the joint angle of 60 degrees was significantly greater than at 0 degrees but not at 30 degrees. Reasons for the findings are discussed.

Adult↗

PubMed1983

Isometric, isotonic, and isokinetic torque variations in four muscle groups through a range of joint motion.

The purpose of this investigation was to describe and examine variations in maximal torque produced by knee extension, knee flexion, elbow extension, and elbow flexion through a range of joint motion. Subjects were young, healthy men (n = 16) and women (n = 15). Torque was measured isometrically and isokinetically using a modified Cybex apparatus. Isotonic torque was calculated from a one-repetition maximum using a modified N-K device. Joint angles were monitored with an electrogoniometer. Torque-joint angle curves were constructed for both men and women for each muscle group. Isometric torque was highest, followed by isotonic and isokinetic torque. Torque declined with increasing isokinetic velocity. The angle of peak torque was found to be highly variable in individual subjects. Variations in torque curves were explained in terms of mechanical characteristics of the musculoskeletal system. Muscle group capability was generally found to be well matched to the mechanical requirements of the movement.

Adult↗

PubMed1988

Reliability of isometric muscle testing of knee flexor and extensor muscles in patients with connective tissue disease.

This two-part study evaluated the reliability of inexpensive devices for isometric muscle testing on patients. First, the relationship between gauge readings of the devices and known weights was evaluated. Coefficients of determination and regression lines were used to determine the strength and nature of this relationship, which was determined to be linear. Second, intratester reliability for force measurements of isometric knee extension and flexion motions was determined for 30 patients with connective tissue diseases. Right knee extensor and flexor muscle forces were measured during two sessions. The measurements between sessions were compared for degree of agreement using intraclass correlation coefficients. Intraclass correlation coefficients ranged from .90 to .95 for knee flexor force measurements and from .75 to .85 for knee extensor force measurements. Based on the results of this study, this measuring device can be used reliably to measure knee extensor muscle force at 50 degrees and knee flexor muscle force at 30 and 70 degrees.

Adolescent↗

PubMedDate not supplied

Effect of isometric contraction on threshold somatosensory evoked potentials.

We previously described the augmentation of sensory nerve action potential amplitudes after near and remote isometric muscle contraction. In this study, we wished to determine if the sensory cortex was involved in this process. In this prospective, intrinsically controlled study, we studied threshold somatosensory evoked potentials in 12 normal subjects with stimulation of the median nerve at 5.1 Hz. The subjects were tested during the following conditions: baseline, 25%, and 75% maximum isometric abductor digiti minimi contraction for 4 min. Each of these conditions was recorded before, during, and 4 min and 8 min after contraction. Results showed that at 25% contraction, there was a significant temporal increase in N9 amplitude (2.1-2.6 microV; P = 0.05, analysis of variance, repeated measures) and a decrease in N20 amplitude with 75% contraction (1.9-1.6 microV; P = 0.03, analysis of variance, repeated measure). No significant changes were noted in the spinal cord or brainstem recordings. In conclusion, it appears that augmentation of the brachial plexus peripheral nervous system recording occurs concurrently with central inhibitory gating. The possibility of peripheral nervous system adaptability will be discussed.

Adult↗

PubMedDate not supplied

Temporal effects of isometric contraction maneuvers on threshold sural amplitude.

OBJECTIVE: To investigate the effect of isometric biceps brachii contraction and neck flexion on the time course of threshold sural amplitude. DESIGN: Twelve healthy subjects, who were asked to lie supine on an examination bench, performed 1 min of muscle contraction. The sural sensory nerve action potential was recorded before, immediately after, and at 2-min intervals after muscle contraction. The preexercise level of stimulus intensity remained unchanged for sural readings throughout the entire course of the experiment. RESULTS: The temporal changes in sensory nerve action potential amplitudes for both maneuvers were similar (P = 0.9734, two-way interaction). The mean sural amplitude after neck flexion increased from 6.0 +/- 2.9 microV (SD) to 10.6 +/- 6.6 microV (SD) 10 min after contraction. Similarly, mean sural amplitude increased from 6.5 +/- 1.8 microV (SD) to 14.5 +/- 9.7 microV (SD) 8 min after biceps brachii contraction. Statistical analysis performed using repeated measures with post hoc least significant difference showed a significant temporal effect in the two groups (P = 0.04). CONCLUSION: The temporal responses of threshold sural amplitudes after isometric biceps brachii contraction and central reinforcement neck flexion maneuvers are nearly identical with regard to increase in the amplitude.

Action Potentials↗

PubMed1989

Effects of sustained-release verapamil on 24-hour ambulatory blood pressure and on pressor response to isometric exertion in hypertensive patients.

The antihypertensive effect of a drug should be present not only at rest, but also during usual daily activities and pressor stimuli. In our study, we tested the impact of a new formulation of sustained-release (SR) verapamil (240-mg tablets), given once or twice daily, on 24-h ambulatory blood pressure (BP) and on pressor response to isometric exercise (handgrip). Fourteen mildly to moderately essential hypertensive patients were included in a single-blind placebo-controlled trial. The mean titrated dose of verapamil required to normalize office BP was 430 +/- 28 mg/day. Mean 24-h waking (7 a.m.-11 p.m.) and sleeping (11 p.m.-7 a.m.) blood pressures were significantly lower after verapamil than after placebo. The absolute levels of BP achieved at peak of handgrip (30% of maximal voluntary contraction for 3 min) were significantly reduced by verapamil with respect to placebo. However, due to the lower starting values, the pressor increment to the isometric work was not significantly modified by the active treatment. In conclusion, SR verapamil seems to provide a blood pressure lowering effect during all times of the day. It attenuates the surges in BP associated with handgrip exercise.

Adult↗

PubMed1991

Cardiac performance in elderly hypertensive patients with left ventricular hypertrophy: responses to isometric exercise and beta-agonists.

To assess the cardiac functional reserve of elderly hypertensive patients with left ventricular hypertrophy (LVH) we studied cardiac function after isometric exercise and beta-adrenergic stimulation. Forty-five elderly hypertensive and 16 normotensive patients (NC group) were recruited for the study. The hypertensive patients were divided into two groups: those with LVH (n = 17) mass index (LV mass index greater than 130 g/m2; H1 group) and those without LVH (n = 28) (H2 group). Echocardiographic studies were performed before and after isometric exercise (handgrip) and isoproterenol (ISP) administration. We measured the LV mass index, fractional shortening (FS), isovolumic relaxation time (IRT), and the ratio of late and early diastolic transmitral flow velocity (A/E). The FS at rest in the H1 group was significantly higher than those in the H2 and NC groups. In the H1 group, the IRT was elongated and A/E was greater than in the NC group, which indicated the impaired diastolic function in the H1 group. After the HG stress, the FS in the H1 group significantly decreased whereas it did not change in the H2 or NC groups. The FS increased in all three groups after the infusion of ISP, although the increment of FS was smaller in the H1 group. In conclusion, (a) diastolic function was impaired whereas systolic function was supranormal at rest in the hypertrophied heart of the elderly hypertensive patients and (b) when exercise or pharmacological stress was loaded, the systolic function deteriorated, suggesting the impairment of cardiac reserve in those patients.

Aged↗

PubMed1996

Pressor response to isometric exercise in patients with multiple sclerosis.

The purpose of this study was to determine whether patients with multiple sclerosis (MS) would show attenuated heart rate and/or pressor responses to isometric handgrip exercise. Patients with MS (30 males, 74 females, aged 23-61 yr) and control subjects (9 males, 16 females, aged 25-47 yr) performed isometric handgrip exercise at 30% of maximal voluntary contraction (MVC) to fatigue. Systolic, diastolic, and mean arterial pressure (MAP) increased linearly in both groups, but were significantly lower (P < 0.05) in patients with MS at 20%, 40%, 60%, 80%, and 100% of exercise duration. Mean change in MAP at fatigue was +47.9 mm Hg for controls and +28.2 mm Hg for patients with MS, with 18 patients with MS between -6 mm Hg and +15 mm Hg. Heart rate increased normally in patients with MS. To predict change in MAP at fatigue in patients with MS, stepwise regression analysis using six variables yielded an R2 of 0.26. These data suggest that in some patients MS lesions exist in areas of autonomic cardiovascular control that result in attenuated pressor responses to exercise. In 17% of patients tested, attenuation was profound. Data also suggest an abnormal dissociation between the heart rate and pressor response to static work in patients with MS.

Adult↗

PubMed2001

Electromechanical delay in isometric actions initiated from nonresting levels.

PURPOSE: The purpose of this study was to determine whether electromechanical delay (EMD) was associated exclusively with the onset of tension from a resting state and whether EMD remained constant across different rates of force development. METHODS: Twenty-four subjects (23.9 +/- 5.4 yr, 171.7 +/- 7.3 cm, 72.9 +/- 12.8 kg) performed isometric elbow flexion trials in the transverse plane by using the dominant arm during which isometric force data and surface EMG activity were collected. Subjects completed three trials to establish a maximal force (MF) reference. Subjects then completed trials in which pulse forces of varying magnitudes were elicited at a frequency of 1 Hz from different baseline intensities. All forces were expressed relative to MF. Three trials of the following conditions (baseline-pulse) were performed in random order: 0-25%, 25-50%, 50-75%, 0-50%, and 0-75%. EMG and force data were collected for 10 pulse cycles during these trials. EMD was defined as the temporal shift that maximized a normalized cross-correlation function. RESULTS: EMD for a 25% pulse force developed from rest (83.5 +/- 12.9 ms) was significantly longer than that developed from 25% (66.3 +/- 11.5 ms) or 50% (60.6 +/- 16.6 ms) baselines. EMD values were not different when force was developed from 25% and 50% baselines. EMD associated with a 25% pulse force from rest was significantly longer than 50% (70.3 +/- 10.0 ms) and 75% (68.9 +/- 8.7 ms) pulse forces from rest. EMD for 50% and 75% pulse forces from rest were not statistically different. CONCLUSION: It was concluded that EMD is present during exertions initiated from both resting and nonresting states but is reduced when exertions are initiated from non-resting states and with higher rates of force development.

Adolescent↗

PubMed2006

Activation of nitric oxide modulator effect by isometric contraction in rat resistance arteries.

The participation of nitric oxide (NO) as a modulator of the isometric contraction, as well as the underlying mechanism, was investigated in rat small mesenteric arteries. In the presence of a functional endothelium, L-NAME and L-NA similarly increased the contractions induced by phenylephrine, dependently on the level of contraction. However, no effect was observed in the absence of a functional endothelium. In the presence of selective inhibitors of protein kinase C (PKC) and phosphatidyl-inositol 3-kinase (PI3K), calphostin-C and wortmannin, respectively, the effect of L-NAME was not modified. The same observation was done in the presence of the tyrosine kinase inhibitors, genistein and tyrphostin A-23. However, in the presence of a Ca2+-independent tyrosine kinase inhibitor, erbstatin-A, and on the presence of a non-selective kinase inhibitor, staurosporine, a strong reduction was observed. Our results suggest that protein kinases are involved in the activation of nitric oxide modulator effect on isometric contractions in resistance arteries.

Animals↗

PubMed1995

The nasal response to isometric exercise.

The cardiovascular response to isometric exercise is well understood. However, the response of the nasal mucosa is less well known. We have attempted to document this response in normal individuals. Ten individuals with no history of nasal disease or allergy were studied. All subjects were asked to perform sustained handgrip on the side of the obstructed nostril for a period of 5 min at 30% of maximum voluntary effort. Nasal cross-sectional area was measured on both sides of the nose using an acoustic rhinometer. The individuals were then rested for at least 30 min and the test repeated with pressure applied by the opposite hand. Statistical analysis was performed by non-parametric methods. There was a significant fall in nasal cross-sectional area on the side of exercise median change = 0.09 cm2, P < 0.01) while cross-sectional area in the contralateral nasal passage increased (median change = 0.35 cm2, P = 0.01). There was no significant differences between these results and those obtained by handgrip on the opposite side. The results indicate that isometric exercise produces nasal obstruction (isotonic exercise) and both afferent and efferent arms of this reflex are side-specific.

Blood Pressure↗

PubMed2000

Preferential role of intracellular Ca2+ stores in regulation of isometric force in NIH 3T3 fibroblast fibres.

Fibroblast contraction plays a major role in wound repair, but the regulatory mechanisms are not well known. We investigated the relations between isometric force and intracellular calcium concentration ([Ca2+]i) in fibroblast fibres. These fibres were made with mouse NIH 3T3 fibroblasts cultured with native collagen in a three-dimensional matrix. Calf serum (CS; 30%) elicited a monotonic increase in force that attained a maximum within 15 min and could be sustained indefinitely. In contrast, [Ca2+]i increased to a peak at 3 min after CS stimulation, then returned to baseline levels by 10 min. Pretreatment with Ca2+-free medium or the Ca2+-channel antagonist nicardipine (10 microM) blocked the CS-induced [Ca2+]i increase, but force was not affected. KCl (50 mM) stimulation on the other hand, elicited a prolonged increase in [Ca2+]i but did not increase force. Inhibition of the endoplasmic reticulum Ca2+ release with Ca2+-ATPase inhibitors cyclopiazonic acid (5 microM) or thapsigargin (5 microM) nearly abolished (<20% control) the increase in [Ca2+]i and force response to CS. Treatment with ryanodine (10 microM) and caffeine (20 mM) had a similar effect. The phospholipase C inhibitor U73122 (3 microM) reduced the CS-induced increases in [Ca2+]i and force by 70 and 40%, respectively. We conclude that fibroblast isometric force is not coupled to Ca2+ arising from transmembrane influx but is correlated with the transient [Ca2+]i increase due to release from intracellular stores. Store-released Ca2+ may initiate activation pathways for fibroblast force development, but is not required for force maintenance.

3T3 Cells↗

PubMed1996

Differential effects of tert-butyl-benzohydroquinone, a putative SR Ca2+ pump inhibitor, on isometric relaxation during the staircase in the rabbit and rat ventricle.

1. The effects of 2,5 di-(tert-butyl)-1,4-benzohydroquinone (TBQ), a putative inhibitor of the sarcoplasmic reticulum Ca2+ pump, on mechanical relaxation and contraction-relaxation coupling have been studied at different frequencies (0.5-3 Hz) in isometrically contracting isolated right ventricular preparations of rabbit and rat at 37 degrees C. Two types of mechanical responses have been studied: the twitch tension and the force transient (rewarming spike, RSp) following a rapid cooling contracture (RCC, an index of sarcoplasmic reticulum Ca2+ content) on return to 37 degrees C. 2. The coupling between contraction and relaxation was assessed by two methods: (a) by evaluation of the variation of the slope relating the maximal rate of tension fall to twitch peak tension; (b) by modelling the twitch according to the following equation: TwT (t) = C x (t/A)B x exp(1-(t/AB) where TwT(t) is the time course of isometric tension, t is time, C and A are an inotropic and a chronotropic index respectively and B, a contraction-relaxation coupling index (Nwasokwa, 1993). 3. In the rabbit ventricle, 30 microM TBQ did not prevent the frequency-induced shortening of the twitch time to half-relaxation (t1/2) and of the time constant (tau) describing the final part of the RSp relaxation (tau decreased from 140 ms (0.5 Hz) to 133 ms (3 Hz) in control and from 253 ms (0.5 Hz) to 197 ms (3 Hz) after exposure to TBQ). By contrast, at a given frequency, the prolongation of relaxation induced by TBQ was proportional to its inotropic effect (unchanged slopes and B values) but TBQ did not prevent the acceleration of relaxation observed at high frequencies: B increased from 2.02 (0.5 Hz) to a peak value of 2.18 (1 Hz) in control and from 1.88 (0.5 Hz) to a maximum of 2.48 (2 Hz) after TBQ exposure. TBQ significantly attenuated the decay of RCCs elicited after increasingly longer periods of muscle quiescence as normally observed in control conditions. 4. In the rat ventricle, TBQ depressed relaxation more than expected on the basis of its negative inotropic effects (B decreased from 2.16 to 1.84 at 0.5 Hz and from 2.15 to 1.66 at 3 Hz). TBQ also slowed the rate of RSp relaxation (tau increased from 95 ms to 168 ms at 0.5 Hz, and from 109 ms to 149 ms at 3 Hz) and increased twitch t1/2. By contrast with the results obtained in the rabbit ventricle, B, tau and t1/2 were frequency-insensitive whether or not TBQ was present. 5. TBQ exerts negative inotropic effects consistent with inhibition of the SR Ca2+ pump. In the rabbit ventricle, the TBQ-induced potentiation of relaxation acceleration at high pacing frequencies suggests the involvement of counteracting Ca(2+)-mediated mechanisms probably via Ca(2+)-calmodulin-activated kinases. In the rat ventricle, TBQ did not have any differential effect on relaxation depending on the frequency, probably because the extent of the negative staircase was small in the present experimental conditions.

Action Potentials↗

PubMed1995

Intramuscular pressure and torque during isometric, concentric and eccentric muscular activity.

Intramuscular pressures, electromyography (EMG) and torque generation during isometric, concentric and eccentric maximal isokinetic muscle activity were recorded in 10 healthy volunteers. Pressure and EMG activity were continuously and simultaneously measured side by side in the tibialis anterior and soleus muscles. Ankle joint torque and position were monitored continuously by an isokinetic dynamometer during plantar flexion and dorsiflexion of the foot. The increased force generation during eccentric muscular activity, compared with other muscular activity, was not accompanied by higher intramuscular pressure. Thus, this study demonstrated that eccentric muscular activity generated higher torque values for each increment of intramuscular pressure. Intramuscular pressures during antagonistic co-activation were significantly higher in the tibilis anterior muscle (42-46% of maximal agonistic activity) compared with the soleus muscle (12-29% of maximal agonistic activity) and was largely due to active recruitment of muscle fibers. In summary, eccentric muscular activity creates higher torque values with no additional increase of the intramuscular pressure compared with concentric and isometric muscular activity.

Adult↗

PubMed1976

Isometric and isotonic length-tension relations and variaitonsin cell length in longitudinal smooth muscel from rabbit urinary bladder.

Isometric and isotonic length-tension relations of longitudinal smooth muscle from rabbit urinary bladder were studied together with muscle cell length and tissue structure as revealed histologically. In vivo strip length at a bladder volume of 10 m1 is referred to as L10. The smooth muscle was relaxed by Ca2+-free solution and contracted by K+-high solution with different Ca2+-concentrations. Maximal active force, 12.5+/-0.4 N/cm2 (S.E., n =11), for wholestrips was attained at a length of 206+/-4% (S.E., n=5) of L10. Passive tension at this length was about 15% of total tension. After correction for amount of connective tissue, maximal active tension of pure muscle bundles was 19 N/cm2. Up to about 165% of L10 isometric and isotonic length-tension relations were identical; if the muscle was stretched beyond this, it failed to shorten isotonically to the same length as when contracting from a shorter starting length. This decreased shortening capacity was reversible if the muscle was shortened passively. The extent of shortening against zero load was dependent on degree of activation suggesting an internal resistance to shortening. A linear relationship was found between bladder radius and muscle cell length, indicating that no slippage occurs between the cells when the bladder is filled. Mean cell diameter in the nuclear regionat L10 was 7.2+/-0.2 mum (S.D.,n=10). Mean macimal active tension per cell was calculated to be 2.3-10(-6) N and occurred at a cell length of 655 mum.

Animals↗

PubMed1978

Isometric strength performance and muscle fibre type distribution in man.

Maximal isometric one-leg strength (MIS) was determined in 31 physical education students displaying a wide range in muscle fibre type distribution (21-79% fast twitch (FT) muscle fibres) in their vastus lateralis muscles. A linear positive correlation was found between MIS and the relative distribution of FT fibres (p less than 0.001). This should mean that not only muscle mass involved but also the quality of muscle will be decisive for the ability to develop high isometric strength.

Adult↗

PubMed1976

The responses of human muscle spindle endings to vibration during isometric contraction.

1. An human subjects, vibration of amplitude 1-5 mm and frequency 20-220 Hz was applied to the tendons of muscles in the leg to examine the effects on the discharge of primary and secondary endings during manoeuvres designed to alter the level of fusimotor drive. 2. In four experiments, the peroneal nerve was completely blocked with lidocaine proximal to the recording site in order to de-efferent spindle endings temporarily. The responses to muscle stretch and vibration, as seen in multi-unit recordings and in single unit recordings, were similar during the block as in the relaxed state prior to the block. Thus, these experiments provided no evidence for a functionally effective resting fusimotor drive. 3. The responses to vibration of nine primary endings and four secondary endings were examined during isometric voluntary contractions of the receptor-bearing muscles. Providing that the endings were responding submaximally in the relaxed state, voluntary contraction enhanced the response to vibration, suggesting co-activation of the fusimotor system sufficient to compensate for mechanical unloading. Unloading effects were observed during contractions of neighbouring synergistic muscles, indicating a close spatial relationship between the co-activated skeletomotor and fusimotor outflows. 4. Recordings were obtained from ten primary endings and seven secondary endings during isometric reflex contractions resulting from the vibratory stimulus (TVR contractions). For twelve endings, the appearance of the tonic vibration reflex in the receptor-bearing muscle resulted in a significant decrease in the response to vibration, suggesting that the endings were unloaded by the extrafusal contraction. On voluntary suppression of the reflex contraction spindle responses reverted to their previous levels. 5. These results suggest that the tonic vibration reflex, like the tendon jerk reflex, operates predominantly or exclusively on alpha motoneurones and that it does not utilize the same cortically originating efferent pathways as are used in the performance of voluntary contractions.

Action Potentials↗