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PubMed2002

[Contraction-relaxation coupling of skeletal muscle in patients susceptible to malignant hyperthermia].

OBJECTIVE: To assess whether halothane exposure could influence contraction-relaxation coupling of human skeletal muscle with malignant hyperthermia susceptibility. STUDY DESIGNED: Laboratory investigation. MATERIAL AND METHODS: Muscle biopsies from 14 patients, including six classified as susceptible to MH (MHS) and eight as classified as non-susceptible (MHN) according to criteria of the European MH group. Mechanical parameters of strips were obtained before and after 3 vol% halothane exposure. The contraction and relaxation parameters were measured under isotonic and isometric conditions: maximum shortening and lengthening velocities (respectively maxVc and maxVr); peak of the positive (+dP/dtmax) and negative (-dP/dtmax) twitch tension derivative; ratio R1 = maxVc/maxVr and ratio R2 = (+dP/dtmax) (-dp/dtmax). RESULTS: In MHN muscle, halothane markedly increased maxVc and maxVr, so that the ratio R1 was unchanged. Both +dP/dtmax and -dP/dtmax increased such that the ratio R2 did not vary. In MHS muscle, halothane induced a significant decrease in maxVr (p < 0.05) without changes in maxVc, so that the ratio R1 increased significantly. +dP/dtmax remained unchanged whereas -dP/dtmax decreased significantly; the ratio R2 increased (p < 0.05). CONCLUSION: Our results indicated that, in MHN muscle the contractility property is improved with halothane exposure. In MHS muscle, halothane caused an impairment of relaxation. The mechanical abnormalities observed in this study might be related to sarcoplasmic reticulum dysfunction in MH diseases.

Anesthetics, Inhalation↗
PubMed1997

[Dynamic 31phosphorus magnetic resonance spectroscopy of the quadriceps muscle: metabolic changes under 2 different forms of loading].

PURPOSE: The aim of the present investigation was to examine the metabolism of the quadriceps muscles of normal young individuals using dynamic 31phosphorus magnetic resonance spectroscopy. METHODS: 22 normal individuals were examined in a 1.5T-MRT using a 6 cm surface coil. The metabolic changes in the quadriceps muscle as shown by the phosphorus spectrum were evaluated during rest, exercise (isometric and isotonic exercise) and during a 36-second period of recovery. RESULTS: The Pi/PCr quotient rose from its resting value of 0.11 +/- 0.02 following exercise to a maximum of 0.83 +/- 0.47 (isometric) or 1.40 +/- 0.59 (isotonic) (difference p = 0.0001). Half-time recovery of Pi/PCr was 35 +/- 11 s or 31 +/- 10 s, respectively (p = 0.13). During the recovery phase Pi/PCr fell briefly but significantly below its rest value. Following an initial rise in pH, there was a continual fall. Minimum pH (6.68 +/- 0.21 and 6.53 +/- 0.27 respectively; p = 0.01) occurred in the early recovery phase. The recovery process of pH values lasted longer following isotonic than after isometric exercise (half-value recovery time 229 +/- 72 s and 146 +/- 55 s, respectively; p = 0.001). CONCLUSION: Compared with isometric exercise, isotonic stress is more expensive in terms of metabolism. Dynamic 31phosphorus MRT spectroscopy can differentiate changes in muscle metabolism during different forms of exercise.

Adult↗
PubMed2006

Quantitative EMG changes during 12-week DeLorme's axiom strength training.

Strength training is one of the most common exercises practiced in the field of physical therapy or sports training. However, limited methodology is available to evaluate its effect on the target muscle. This study aimed to test the hypothesis that surface electromyographic (EMG) data from both isometric and isotonic exercise can express changes within the muscle during a 12-week strength training program. Ten healthy male volunteer students (5 for training, 5 for controls) from Yonsei University were recruited for evaluation in this study. DeLorme's axiom was practiced for 12 weeks in the dominant elbow flexors and knee extensors of the training group. Tension for 1 repetition maximum and maximal voluntary isometric contraction, and surface EMG information such as the integrated EMG and three variables from the regression line of median frequency (MDF) data were measured at weeks 0, 3, 6, 9, and 12. The limb circumference was measured at weeks 0 and 12. During the strength training, which was enough for the increment of muscle strength and limb circumference, the rectified-integrated EMG and initial MDF increased with a significant linear pattern in both types of contraction. The two surface EMG variables were able to monitor the physiologic muscle changes during the training. Based on these results, we propose that these two surface EMG variables can be used for monitoring electrophysiological changes in the specific muscle that is undergoing the training program, under conditions where the contraction mode for EMG data collection is either static or dynamic.

Adult↗
PubMed1991

A comparison of three muscle pennation assumptions and their effect on isometric and isotonic force.

Three different pennation angle assumptions are compared to experimental data from Huijing and Woittiez (Neth. J. Zool. 34, 21-32, 1984) that relate fibre length to angle of pennation changes. The assumptions tested are: (1) neglecting pennation; (2) assuming a fixed pennation; and (3) assuming a constant muscle volume and thickness resulting in pennation angle being dependent on fibre length. Each assumption is compared by transforming fibre force/length and force/velocity characteristics to muscle properties. In general, the fixed pennation assumption provides the worst estimate of muscle force output with a peak error of 0.31 Fo during isometric contractions at small muscle lengths. A better estimate of muscle force output was provided by neglecting pennation entirely. The assumption that the pennation angle changed with fibre length maintained an error of less than 0.05 Fo for most lengths and velocities tested and provided the best estimate of muscle force output.

Elasticity↗
PubMed1991

Cardiac mechanics at the cellular level.

The active mechanical properties of heart muscle are load, length, and time-dependent. The capability for investigating cardiac mechanisms at the cellular level may help to distinguish between those properties of the myocardium which arise from myocardial cells and those which arise from the tissue architecture and extracellular matrix of connective fibers. We present here, for the first time, a general approach for subjecting single heart cells to isometric, isotonic, afterloaded, or physiological loading sequences, while obtaining on-line measures of cell force and length. This approach has been implemented and tested on freshly dissociated, adult frog ventricular myocytes. Examples are presented for each of the four loading sequences.

Animals↗
PubMed1991

Global analysis of myocardial isotonic shortening: comparison with isometric dynamics.

Although potentially analytically useful, a global empirical model of the myocardial isotonic curve, L(t), has not been described. We propose the following relation: L(t) = C(t/A)B-1e-(t/A)B, where A, B, and C are global parameters, L is length, and t is time. We evaluated this model in nine in situ canine papillary muscles studied with a servo-system to produce isotonic twitches at different isotonic forces (F). For each twitch, the parameters were determined by nonlinear curve fitting. The model fit the observed curves of L(t) closely, with the coefficient of determination being 0.995 +/- 0.002. C changed with F, but A and B varied little with F, averaging 0.262 +/- 0.021 s and 2.76 +/- 0.17, respectively. Our predictions that A reflects chronotropic, B reflects lusitropic, and C reflects heterotonic (different afterloads) and inotropic states were supported. Comparison done in five muscles showed that A was the same but B was higher for isotonic than for isometric twitches: 0.270 +/- 0.020 vs. 0.264 +/- 0.038 s (P = not significant) for A and 2.79 +/- 0.18 vs. 2.39 +/- 0.05 (P less than 0.008) for B. Dobutamine increased A but not B in isotonic twitches. Thus shortening is lusitropic but leaves no lusitropic reserve to be mobilized by dobutamine. The relation L(t) = C(t/A)B-1e-(t/A)B provides a framework that undergirds global analysis of myocardial shortening and enables comparison with isometric dynamics.

Animals↗
PubMed1994

Knee-joint proprioception during 30-day 6 degrees head-down bed rest with isotonic and isokinetic exercise training.

To determine if daily isotonic exercise or isokinetic exercise training coupled with daily leg proprioceptive training, would influence leg proprioceptive tracking responses during bed rest (BR), 19 men (36 +/- SD 4 years, 178 +/- 7 cm, 76.8 +/- 7.8 kg) were allocated into a no-exercise (NOE) training control group (n = 5), and isotonic exercise (ITE, n = 7) and isokinetic exercise (IKE, n = 7) training groups. Exercise training was conducted during BR for two 30-min periods.d-1, 5 d.week-1. Only the IKE group performed proprioceptive training using a new isokinetic procedure with each lower extremity for 2.5 min before and after the daily exercise training sessions; proprioceptive testing occurred weekly for all groups. There were no significant differences in proprioceptive tracking scores, expressed as a percentage of the perfect score of 100, in the pre-BR ambulatory control period between the three groups. Knee extension and flexion tracking responses were unchanged with NOE during BR, but were significantly greater (*p < 0.05) at the end of BR in both exercise groups when compared with NOE responses (extension: NOE 80.7 +/- 0.7%, ITE 82.9* +/- 0.6%, IKE 86.5* +/- 0.7%; flexion: NOE 77.6 +/- 1.5%, ITE 80.0 +/- 0.8% (NS), IKE 83.6* +/- 0.8%). Although proprioceptive tracking was unchanged during BR with NOE, both isotonic exercise training (without additional proprioceptive training) and especially isokinetic exercise training when combined with daily proprioceptive training, significantly improved knee proprioceptive tracking responses after 30 d of BR.

Adult↗
PubMed1993

Time-resolved equatorial X-ray diffraction measurements in single intact muscle fibres.

Equatorial X-ray diffraction techniques have been successfully applied to the intact single muscle fibre preparation under length clamp and "fixed end" conditions. 10 and 11 intensity changes and stiffness have been measured in the same preparation. Under isometric conditions, equatorial signals and stiffness led force by 14-20ms during the rise of tetanic tension. During relaxation, stiffness and equatorial signals lagged force. The time course of the intensity changes suggests a low force crossbridge state is present to a greater extent during the rise of tetanic tension and during relaxation than at the tetanus plateau. During isotonic shortening at Vmax, stiffness fell to 30% of its isometric level, while equatorial signals fell to 60%. Since stiffness and equatorial signals are thought to detect attached crossbridges, either the average stiffness per attached bridge measured at 4kHz during shortening is less than at the plateau, or the relation between equatorial intensities and the proportion of attached crossbridges during isotonic shortening differs from that measured under isometric conditions. Active tension also affects the lattice spacing. The myosin lattice was compressed during the development of longitudinal force. This implies a radial component of crossbridge tension. The lattice compression was smaller in a compressed lattice and larger in an expanded lattice.

Animals↗
PubMed2006

[Fatigability evaluation on multiple sclerosis patients by using a hand held dynamometer].

Fatigue is one of the most common disabling symptoms in multiple sclerosis (MS). The aim of this study was to evaluate the fatigability on patients with MS by the application of hand grip isotonic and isometric exercises with dynamometer. As results the fatigability, the isometric strength and time were statistically similar in the control group and in MS. We conclude that although fatigue is a frequent subjective complaint on MS, the fatigability and the recover after exercises seems to be normal.

Adult↗
PubMed1991

A comparison of static and dynamic characteristics between rectus eye muscle and linear muscle model predictions.

The characteristics of a muscle model are analyzed using rectus eye muscle parameter values and compared to rectus eye muscle data. The muscle is modeled as a viscoelastic parallel combination connected to a parallel combination of active state tension generator, viscosity element, and length tension elastic element. Each of the elements is linear and their existence is supported with physiological evidence. The static and dynamic properties of the muscle model are compared to rectus eye muscle data. The length-tension characteristics of the model are in good agreement with the data within the operating region of the muscle. With the muscle model incorporated into a lever system to match the isotonic experiment paradigm, simulation results for this linear system yield a nonlinear force-velocity curve. Moreover, the family of force-velocity curves generated with different stimulus rates reported in the literature match the predictions of the model without parametric changes. The results of this paper are important in studies involving the oculomotor plant and oculomotor neural networks. Additionally, these results may be applicable to other muscles.

Isometric Contraction↗
PubMed1993

[Effects of aging on mechanical performance of Wistar rat papillary muscles].

PURPOSE: To evaluate the effects of age on mechanical performance of rat myocardium. METHODS: Left ventricular papillary muscles were isolated from male Wistar rats at 1, 3, 6 and 12 months of age. Muscles were studied isometrically and isotonically, stimulated at 0.2 Hz, perfused with Krebs-Henseleit solution having an external calcium concentration of 2.52 mM, and maintained at 28 degrees C. RESULTS: Peak isometric developed tension was significantly higher in 1 month than 3, 6 and 12 months. Peak rate of isometric tension rise decreased substantially between 1, 3 and 12 months. Time to peak isometric developed tension showed a significant increase of both 3 and 12 months of age. Time to half relaxation increased significantly from 3 to 6 and from 3 to 12 months. Maximum rate of tension decline decreased from 3 to 6 and from 3 to 12 months. No difference in resting tension was noted among any group. Isotonically, peak shortening and time to peak shortening increased from 1 to 3 months of age. Time to half re-lengthening increased from 3 to 6 and from 3 to 12 months of age. No difference in peak shortening velocity, peak relaxation velocity and relative change in muscle length was noted among any groups. CONCLUSION: The maturation affects the mechanical performance of cardiac muscle.

Aging↗
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↗
PubMed1993

Skeletal muscle mechanics: implications for rehabilitation.

Skeletal muscles are the primary organ system responsible for force generation and movement. As such, an improved understanding of normal movement can be obtained by understanding skeletal muscle mechanical properties. In this review, we present the basic mechanical properties of skeletal muscle in a way that relates to their normal function. First, isometric force production is discussed, followed by a presentation of isotonic force production. Then, skeletal muscle architectural properties are presented as a strategy for muscles to specialize in either force production or excursion. Finally, we discuss the relationship between muscles and joints and the significance of this relationship for understanding strength. Based on this presentation, the therapist will have an improved understanding of normal movement and may have insights into developing rehabilitation protocols that can improve function.

Actins↗
PubMed1994

Electrophysiological characteristics of tension receptors in the abomasal antrum of sheep.

Unitary impulse activity from tension receptors in the abomasal antrum in sheep anaesthetized with chloralose was studied with concurrent measurements of isometric tension in the antral wall, intraluminal pressures and electromyography (EMG). Rhythmical background activity had a close correlation with intraluminal pressure changes and usually a close correlation with local increases in EMG activity and isometric tension. Impulse frequencies increased, but were not sustained, following changes from isotonic to isometric conditions. Tension receptors were excited by transmural compression, by antral distension and by local intra-arterial injections of acetylcholine (2.5-25 micrograms), pentagastrin (10-20 micrograms), 5-hydroxytryptamine (1-20 micrograms), adrenaline (10 micrograms) cholecystokinin-8 (1-5 micrograms) or bradykinin (0.5-20 micrograms), and by systemic injections of bethanecol (5-1000 micrograms). Local intra-arterial perfusions of atropine (50 micrograms) and hexamethonium (100 micrograms) did not abolish spontaneous antral movements or affect the enhanced impulse activity evoked by acetylcholine or 5-hydroxytryptamine. Most antral tension receptors were excited by increases in antral tension or passive distension; they therefore functioned 'in series' with the muscularis externa. The discharges of three tension receptors were 'off-loaded' early during the contraction evoked by local injections of pentagastrin (10-20 micrograms).

Abomasum↗
PubMed1995

Dynamic muscle strength as a predictor of bone mineral density in elderly women.

Although muscle strength has been shown to predict bone mineral density (BMD) in older adults, the variance explained by isometric and isokinetic testing has been generally low (< 20%) and limited to only a few exercises and muscle groups. To elucidate the relationship of muscle strength to BMD at multiple sites, and to ascertain the most robust predictor of BMD using isotonic strength testing apparatus, we examined dynamic muscle strength and BMD in 40 healthy elderly women aged 65-82 years. BMD of the spine (L2-4), proximal femur (neck, trochanter, Ward's triangle), forearm (midradius), and whole body were measured by dual-energy X-ray absorptiometry. Dynamic strength (1-RM), utilizing isotonic weight-lifting equipment, was assessed for 10 standard upper and lower body exercises. In stepwise multiple regressions, leg press was the only independent predictor of spine (R2 = 0.11), neck and trochanter (R2 = 0.21 and 0.18), forearm (R2 = 0.21), and whole body BMD (R2 = 0.19), while bench press was an independent predictor of Ward's BMD (R2 = 0.12). The most robust predictor of regional and whole body BMD using isotonic equipment was the leg press, which may reflect overall skeletal health in this population. The portion of variance explained by dynamic muscle strength (11-21%) is similar to that reported when strength is assessed by isometric and isokinetic testing. The relationship of dynamic strength to BMD was not generally site-specific.

Absorptiometry, Photon↗
PubMed2000

System for measuring isolated rat soleus muscle belly response to tetanic stimulation.

A novel system for simultaneous measurements of isotonic muscle contraction and transversal muscle belly displacement in the isolated rat soleus muscle was designed. The system simultaneously records tetanic contraction of the muscle and transversal displacements of the muscle belly. The tetanic rise times (TRT) and muscle belly displacement times (BDRT) were measured at different proton loads induced by CO2 at 1%, 5% and 30%. The measurements of muscle belly displacement enabled us to follow the water shift into the muscle tissue during the tetanic activity. Acidosis provoked by 30% CO2 irreversibly increased the BDRT, however the TRT were not changed.

Acidosis↗
PubMed1996

A modified aortic multiple-ring preparation for functional studies.

A comparison is made of four rat aortic preparations, that is, single ring, spiral strip, zig-zag strip, and multiple-ring, on the basis of the responses to norepinephrine (NE) and acetylcholine (ACh). The single ring preparation was suitable under isometric, but not under isotonic conditions, because of the small isotonic tension which developed in response to the contractile agonist. The spiral and the zig-zag strips showed a discontinuity in the relaxant activity of the ACh, probably because of the removal, or not, of the endothelium from the preparation. The reproducibility of both contracturant and relaxing responses in the multiple-ring preparation makes this the most suitable of all four for the study of vasoactive drugs.

Acetylcholine↗
PubMed2005

The effects of isotonic and isokinetic muscle stretch on the excitability of the spinal alpha motor neurones in patients with muscle spasticity.

To examine the effect of isotonic (with and without weight bearing) and isokinetic muscle stretch on the excitability of the spinal alpha motor neurones (alphaMN) in patients with spasticity and to establish whether this effect is maintained for at least 24 h after the intervention. A single 20-min session of isotonic muscle stretch (with or without weight bearing) or isokinetic stretch was delivered to the ankle plantar flexors in patients with post-stroke lower limb spasticity and healthy control subjects. The effect of these types of muscle stretch on the excitability of alphaMN was assessed by measuring the latency of the Hoffmann reflex (H-reflex) and the ratio of the amplitude of the maximum H-reflex (H(max)) to that of the maximum action motor potential of the soleus muscle (M(max)). Sixty-six hemiplegic stroke patients and 21 healthy control subjects were recruited and completed the trial. The H(max):M(max) ratio was significantly higher in patients with spasticity than in healthy control subjects. However, there were no statistically significant differences in the H-reflex latency or the change in H(max):M(max) ratio between the baseline values and those recorded immediately after the therapy intervention or 24 h later for each type of muscle stretch. Similarly, there were no significant differences in these variables between the interventions. In the present study neither isotonic muscle stretch (with or without weight bearing) or isokinetic stretch had a statistically significant effect on the excitability of the alphaMN in patients with muscle spasticity. This suggests that the previously reported reduction in spasticity after muscle stretch is because of mechanisms other than the direct effect on alphaMN. However, the lack of a demonstrable benefit of treatment may be due the fact that we examined the effects of a single, rather than repeated treatment cycles.

Aged↗