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PubMed1996

Modulation of pressure pain thresholds during and following isometric contraction in patients with fibromyalgia and in healthy controls.

This study aimed at evaluating the influence of submaximal isometric contraction on pressure pain thresholds (PPTs) in 14 fibromyalgia (FM) patients and 14 healthy volunteers, before and after skin hypoesthesia. PPTs were determined with pressure algometry over m. quadriceps femoris before, during and following an isometric contraction. Maximum voluntary contraction (MVC) was assessed using a computerized dynamometer. A contraction of 22% MVC on average was held until exhaustion (max. 5 min) and PPTs were assessed every 30 sec. A local anesthetic cream and a control cream were applied following a double-blind design and PPTs were reassessed. In healthy volunteers PPTs increased during contraction (P < 0.001), then decreased after the end of contraction (P < 0.001) but remained above precontraction values during the 5 min of post-contraction assessments (P < 0.001). In FM patients PPTs decreased in the middle of the contraction period (P < 0.05) and remained below precontraction levels during the rest of the contraction period (P < 0.05) and during the 5 min of post-contraction assessment (immediately post-contraction NS; 2.5 min post-contraction P < 0.01; 5 min post-contraction P < 0.05). The normalized PPTs were significantly lower in patients than in controls during contraction (start P < 0.01; middle P < 0.001; end P < 0.001) and at all times during post-contraction assessments (P < 0.001). Anesthetic cream raised PPTs at rest in controls (P < 0.01) but not in FM patients, and did not influence contraction or post-contraction PPTs in either group. Therefore, the increased pressure pain sensibility in FM patients is more pronounced deep to the skin. The observed decrease of PPTs during isometric contraction in FM patients could be due to sensitization of mechanonociceptors caused by muscle ischemia and/or dysfunction in pain modulation during muscle contraction.

Adult↗

PubMed1988

Hemodynamic, ventilatory and metabolic effects of light isometric exercise in patients with chronic heart failure.

Light isometric exercise, such as lifting or carrying loads that require 25% of a maximal voluntary contraction, is frequently reported to cause dyspnea in patients with heart failure. The pathophysiologic mechanisms responsible for the appearance of this symptom, however, are unknown. Accordingly, hemodynamic, metabolic and ventilatory responses to 6 min of light isometric forearm exercise were examined and compared in 20 patients with chronic heart failure and abnormal ejection fraction (24 +/- 9%) and 17 normal individuals. In contrast to findings in normal volunteers, exercise cardiac index did not increase whereas exercising forearm and mixed venous lactate concentrations increased (p less than 0.05) above levels at rest in patients with heart failure; at 90 s of recovery, blood lactate concentration remained elevated (p less than 0.05). The venous lactate concentration of the nonexercising arm, unlike that of the exercising forearm, was not altered. Oxygen uptake, carbon dioxide production and minute ventilation increased similarly in patients and normal subjects during exercise, but only in patients did each increase further (p less than 0.05) during recovery. Thus, in patients with heart failure, light isometric forearm exercise represents an anaerobic contraction with lactate production. The subsequent increase in carbon dioxide production leads to a disproportionate increase in minute ventilation and oxygen uptake during recovery that may be perceived as breathlessness.

Adult↗

PubMed1988

Effect of topical cheek surface anesthesia on isometric contractions of the human masseter muscle.

To study the possibility of interactions between buccal cutaneous sensory receptors and voluntary maximum isometric contractions of the masseter muscles, six adult subjects exercised maximum teeth clenching before and after spraying the right cheek surface with aerosol containing 20% benzocaine. The right cheek and masseter muscle served as the experimental side, the left cheek and masseter muscle as the control side. Isometric motor outputs, on the right and left sides, were monitored by integrated surface electromyography over periods of 10 seconds. Topical surface anesthesia provided no evidence of motor modulation by cutaneous tactile receptors. Before and after anesthesia, the two muscles showed nearly identical and well-coordinated motor innervation patterns. It is suggested that the cortical motor commands of maximum isometric contractions, with recruitment of practically all available motor units, overrule all modulatory inputs except those of fatigue.

Adult↗

PubMed2006

Isometric muscle torque in children 5 to 15 years of age: normative data.

OBJECTIVE: To establish reference values of arm and leg muscle strength as measured by isometric torque production in healthy children. DESIGN: Measurement of isometric muscle strength in healthy children. SETTING: Public school. PARTICIPANTS: Healthy children (N=149; 76 boys, 73 girls) ages 5 to 15 years. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Isometric torque values of 12 arm and leg muscle groups of healthy children as measured by a handheld dynamometer. RESULTS: Normative data were obtained for children 5 to 15 years of age. There was an increase in torque with age and weight and a strong correlation with both age and weight. There were few differences between boys and girls. Equations for predicted torque taking into account age, weight, and sex were calculated. The agreement between examiners was excellent. CONCLUSIONS: Studies on growing children require comparison to healthy (normal) children to assess the amount of deviation from normal and to be able to draw conclusions of change over time. The reference values for torque in combination with a predicted value based on the child's age, weight, and sex make it possible to compare over time and between subjects and provide a tool for evaluation of physical status and efficacy of therapy.

Adolescent↗

PubMed2004

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

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

Algorithms↗

PubMed2004

In vivo forces generated by finger flexor muscles do not depend on the rate of fingertip loading during an isometric task.

Risk factors for activity-related tendon disorders of the hand include applied force, duration, and rate of loading. Understanding the relationship between external loading conditions and internal tendon forces can elucidate their role in injury and rehabilitation. The goal of this investigation is to determine whether the rate of force applied at the fingertip affects in vivo forces in the flexor digitorum profundus (FDP) tendon and the flexor digitorum superficialis (FDS) tendon during an isometric task. Tendon forces, recorded with buckle force transducers, and fingertip forces were simultaneously measured during open carpal tunnel surgery as subjects (N=15) increased their fingertip force from 0 to 15N in 1, 3, and 10s. The rates of 1.5, 5, and 15N/s did not significantly affect FDP or FDS tendon to fingertip force ratios. For the same applied fingertip force, the FDP tendon generated more force than the FDS. The mean FDP to fingertip ratio was 2.4+/-0.7 while the FDS to tip ratio averaged 1.5+/-1.0 (p<0.01). The fine motor control needed to generate isometric force ramps at these specific loading rates probably required similar high activation levels of multiple finger muscles in order to stabilize the finger and control joint torques at the force rates studied. Therefore, for this task, no additional increase in muscle force was observed at higher rates. These findings suggest that for high precision, isometric pinch maneuvers under static finger conditions, tendon forces are independent of loading rate.

Adult↗

PubMed2005

Aging, regularity and variability in maximum isometric moments.

This study examined the variability and regularity of maximum isometric moment production of the plantar flexors in young and old subjects. It was hypothesized that in the development of maximum isometric moments there would be greater regularity in the moment profiles for older subjects compared with young subjects, due to the reduced number of motor units present in elderly muscle. Two groups of subjects produced three maximal isometric plantar flexions (young: n=11, mean age 23.8+/-2.8 years, mean mass 81.2+/-10.4 kg, mean height 1.78+/-0.05 m; elderly: n=13, mean age 74.0+/-3.3 years, mean mass 78.5+/-3.4 kg, mean height 1.73+/-0.05 m). The plateau of the moment-time curve was analyzed for each trial. A repeat measures analysis of variance showed the young subjects produced statistically greater peak plantar flexion moments than the elderly subjects, but similar coefficients of variation. Signal regularity was determined by computing the signal's approximate entropy, which demonstrated that the older group had greater regularity in their generation of moment profiles. The hypothesis was accepted, with a potential explanation for this increased regularity in old age being the reduced number of motor units to coordinate.

Adult↗

PubMed2004

Are hamstrings activated to counteract shear forces during isometric knee extension efforts in healthy subjects?

The hamstring muscles have the potential to counteract anterior shear forces at the knee joint by co-contracting during knee extension efforts. Such a muscle recruitment pattern might protect the anterior cruciate ligament (ACL) by reducing its strain. In this study we investigated to what extent co-activation of the knee flexors during extension efforts is compatible with the hypothesis that this co-activation serves to counteract anterior tibial shear forces during isometric knee extension efforts in healthy subjects. To this aim, it is investigated whether co-activation varies with the required knee extension moment, with the knee joint angle, and with the position of the external flexing force relative to the knee joint. With unaltered moment and muscle activation, distal positioning of the flexing force on the tibia causes higher resultant (muscular plus external) forward shear forces at the knee as compared to proximal positioning. In ten subjects, knee flexor and extensor EMG was measured during a quasi-isometric positioning task for a range (5-50 degrees) of knee flexion angles. It was found that the co-activation of the knee flexors increased with the extension moment, but this increase was less than proportional (p<0.001). The extension moment increased 2.7 to 3.4 times, whereas the activation of Biceps Femoris and Semitendinosus increased only a factor 1.3 to 2.0 (joint angle dependent). Furthermore, a strong increase in co-activation was seen near full extension of the knee joint. The position of the external extension load on the tibia did not affect the level of co-contraction. It is argued that these results do not suggest a recruitment pattern that is directed at reduction of anterior shear forces in the knee joint during sub-maximal isometric knee extension efforts in healthy subjects.

Adaptation, Physiological↗

PubMed2004

Comparison of surface electromyography and myotonometric measurements during voluntary isometric contractions.

OBJECTIVES: Muscle stiffness increases during muscle contraction. The purpose of this study was to determine the strength of the correlation between myotonometric measurements of muscle stiffness and surface electromyography (sEMG) measurements during various levels of voluntary isometric contractions of the biceps brachii muscle. SUBJECTS: Eight subjects (four female; four male), with mean age of 30.6 +/- 8.23, volunteered to participate in this study. METHODS: Myotonometer and sEMG measurements were taken simultaneously from the right biceps brachii muscle. Data were obtained: (1) at rest, (2) while the subject held a 15 lb (6.8 kg) weight isometrically and, (3) during a maximal voluntary isometric contraction. Myotonometer force-displacement curves (amount of tissue displacement to a given unit of force applied perpendicular to the muscle) were compared with sEMG measurements using Pearson's product-moment correlation coefficients. RESULTS: Myotonometer and sEMG measurement correlations ranged from -0.70 to -0.90. The strongest correlations to sEMG were from Myotonometer force measurements between 1.00 and 2.00 kg. CONCLUSIONS: Myotonometer and sEMG measurements were highly correlated. Tissue stiffness, as measured by the Myotonometer, appears capable of assessing changes in muscle activation levels.

Adult↗

PubMed2005

Experimental muscle pain increases mechanomyographic signal activity during sub-maximal isometric contractions.

This study was designed to investigate the local effect of experimental muscle pain on the MMG and the surface EMG during a range of sub-maximal isometric contractions. Muscle pain was induced by injections of hypertonic saline into the biceps brachii muscle in 12 subjects. Injections of isotonic saline served as a control. Pain intensity and location, MMG and surface EMG from the biceps brachii were assessed during static isometric (0%, 10%, 30%, 50% and, 70% of the maximal voluntary contraction) and ramp isometric (0-50% of the maximal voluntary contraction) elbow flexions. MMG and surface EMG signals were analyzed in the time and frequency domain. Experimentally induced muscle pain induced an increase in root mean square values of the MMG signal while no changes were observed in the surface EMG. Most likely this increase reflects changes in the mechanical contractile properties of the muscle and indicates compensatory mechanisms, i.e. decreased firing rate and increased twitch force to maintain a constant force output in presence of experimental muscle pain. Under well-controlled conditions, MMG recordings may be more sensitive than surface EMG recordings and clinically useful for detecting non-invasively increased muscle mechanical contributions during muscle pain conditions.

Adaptation, Physiological↗

PubMed2005

Inevitable joint angular rotation affects muscle architecture during isometric contraction.

The purpose of this study was to quantify the influence of inevitable ankle joint motion during an isometric contraction on the measured change of the gastrocnemius medialis muscle (GM) architecture in vivo during the loading and the unloading phase. Sitting on a dynamometer subjects performed isometric maximal voluntary contractions as well as contractions induced by electrostimulation. Synchronous joint angular motion, plantarflexion moment, foot's centre of pressure and real-time ultrasonography of muscle architecture changes of the GM were obtained. During the contraction the ankle joint position altered and significantly affected the change in muscle architecture. At maximal tendon force (1094+/-323 N), the measured fascicle length overestimated the change in fascicle length due to the tendon force by 1.53 cm, while the measured pennation angle overestimated the change in pennation angle due to the tendon force by 5.5 degrees . At the same tendon force the measured fascicle length and pennation angle were significantly different between loading and unloading conditions. After correcting the values for the change in ankle joint angle no differences between the loading and the unloading phase at the same tendon force were found. Concerning the estimation of GM fascicle length-force and pennation angle-force curves during the loading and unloading phase of an isometric contraction, these findings indicate that not accounting for ankle joint motion will produce unreliable results.

Ankle Joint↗

PubMed2006

Time and frequency domain responses of the mechanomyogram and electromyogram during isometric ramp contractions: a comparison of the short-time Fourier and continuous wavelet transforms.

The purposes of this study were to examine the mechanomyographic (MMG) and electromyographic (EMG) time and frequency domain responses of the vastus lateralis (VL) and rectus femoris (RF) muscles during isometric ramp contractions and compare the time-frequency of the MMG and EMG signals generated by the short-time Fourier transform (STFT) and continuous wavelet transform (CWT). Nineteen healthy subjects (mean+/-SD age=24+/-4 years) performed two isometric maximal voluntary contractions (MVCs) before and after completing 2-3, 6-s isometric ramp contractions from 5% to 100% MVC with the right leg extensors. MMG and surface EMG signals were recorded from the VL and RF muscles. Time domains were represented as root mean squared amplitude values, and time-frequency representations were generated using the STFT and CWT. Polynomial regression analyses indicated cubic increases in MMG amplitude, MMG frequency, and EMG frequency, whereas EMG amplitude increased quadratically. From 5% to 24-28% MVC, MMG amplitude remained stable while MMG frequency increased. From 24-28% to 76-78% MVC, MMG amplitude increased rapidly while MMG frequency plateaued. From 76-78% to 100% MVC, MMG amplitude plateaued (VL) or decreased (RF) while MMG frequency increased. EMG amplitude increased while EMG frequency changed only marginally across the force spectrum with no clear deflection points. Overall, these findings suggested that MMG may offer more unique information regarding the interactions between motor unit recruitment and firing rate that control muscle force production during ramp contractions than traditional surface EMG. In addition, although the STFT frequency patterns were more pronounced than the CWT, both algorithms produced similar time-frequency representations for tracking changes in MMG or EMG frequency.

Adult↗

PubMed1999

Effect of cold pressor stimulation (4 degrees C) on human masseter muscle haemodynamics during and after sustained isometric contraction.

The effect of cold pressor (CP) stimulation and sustained isometric contraction on the blood volume of the right masseter muscle was examined in seven healthy males, who performed 1 min of isometric jaw clenching at 50% of their maximum voluntary contraction without, with and again without a 4 degrees C CP stimulation. Total haemoglobin was measured in the masseter before, during and after the contraction task using near-infrared spectroscopy. CP stimulation during the isometric contraction diminished the magnitude of the contraction-induced decrease of blood volume when compared to the trials without CP stimulation. However, in the immediate post-contraction period (while the CP stimulation was still in place), no increase in blood volume above the usual post-contraction hyperaemia was evident. Once the CP stimulation had been removed, there was a clear decrease (faster return to baseline) in the vasodilation occurring in the post-contraction period. This diminished period of vasodilation occurred in spite of the fact that the vascular resistance (blood pressure) and heart rate were still substantially elevated by the CP effect during this same period. These data suggest that the strong CP stimulation produced a biphasic response. First, there was an early-onset strong vasodilation (during CP), which was followed by a period of diminished vasodilation, suggesting that an active, but delayed, vasoconstrictive drive may be induced by the CP stimulus.

Adult↗

PubMed1995

Electromyographic analysis of four techniques for isometric trunk muscle exercises.

Posture to avoid hyperextension of the lumbar spine during isometric trunk muscle exercises has been widely recommended. However, there are no common standards for cervical and pelvic alignment during exercises. To investigate the effects of four different techniques regarding cervical and pelvic alignment, electromyographic (EMG) and radiological studies were performed on 30 healthy subjects. The four different postures were: (1) maximally extended neck, (2) neutral neck, (3) maximally flexed neck, and (4) maximally flexed neck with pelvic stabilization through muscle contraction. During flexion exercises, the largest increase in EMG activity in the abdominal muscles was observed with the flexed neck with pelvic stabilization (p < .01). During extensor exercises, the largest increase in EMG activity in the erector spinae was also obtained in the same position (p < .01). An increase of EMG activity in antagonist muscles (eg, erector spinae on flexion, and rectus and oblique muscles on extension) was also greatest with the flexed neck and pelvic stabilization. From the radiographic study, degrees of lumbar lordosis were least with the flexed neck and pelvic stabilization (p < .01). This study showed that neck and pelvic alignment can influence the EMG activity of trunk flexors and extensors during isometric trunk exercises. For isometric trunk muscle exercises, a maximum flexed neck with pelvic stabilization through muscle contraction seems to be the most optimal posture for decreasing the lumbar lordosis and for activating trunk flexors and extensors most effectively.

Abdominal Muscles↗

PubMed1998

Age, sex, and body mass index as determinants of back and hip extensor fatigue in the isometric Sørensen back endurance test.

OBJECTIVE: To study the ability of a widely used isometric back endurance test to measure lumbar back erector muscle fatigue and to assess the influence of age, sex, and body mass index (BMI) on back and hip extensor muscle fatigability (EMG spectral indices). DESIGN: Cross-sectional study of men and women without back problems. SETTING: Occupational health center and rehabilitation clinic in Finland. SUBJECTS: Experiment 1 consisted of 233 consecutive occupational health center customers (133 women, 100 men) without back problems. Experiment 2 consisted of 20 healthy women. INTERVENTION: Subjects performed the isometric Sørensen back endurance test up to 240sec in experiment 1 and to the limit of endurance in experiment 2. OUTCOME MEASURES: Raw surface EMG was recorded bilaterally over the belly of lumbar erector spinae muscles at L1-L2 and L4-L5 levels in experiment 1, and bilaterally over the medial paraspinal muscles at L1-L2, L3-L4, and L5-S1 levels and over the major hip extensor muscles (gluteus maximus and biceps femoris) in experiment 2. In both experiments, time to endurance was recorded (in experiment 1 up to 240sec). The EMG spectral median frequency (MF) decrease over time was used for the assessment of back and hip extensor fatigability. RESULTS: In experiment 1, the rate of change in paraspinal MF was greater in men than in women, indicating greater paraspinal fatigability in men. Multiple regression analysis indicated that the rate of MF decrease (fatigue) during the test was dependent on age and BMI in both sexes and that the effects of age and BMI were more pronounced in women than in men. Correlation analysis revealed that the rate of paraspinal muscle MF decrease was associated with endurance time and BMI in women and with endurance time and age in men. In experiment 2, the paraspinal muscles, as well as the hip extensor muscles, biceps femoris, and gluteus maximus, showed clear decreases in MF during the isometric endurance test in women. MF decrease was highly related to endurance time and BMI in women. CONCLUSIONS: Lumbar paraspinal muscle fatigability during the Sørensen test is influenced by subject characteristics. Further, the hip extensor muscles also significantly fatigue, indicating load sharing between back and hip extensor muscles during the test. According to these results, the validity of this widely used back endurance test in specifically measuring lumbar paraspinal muscle endurance is questionable, as is the direct comparison of test results between women and men.

Aging↗

PubMed1999

Tropomyosin modulates pH dependence of isometric tension.

We investigated the effect of pH on isometric tension in actin filament-reconstituted and thin filament-reconstituted bovine cardiac muscle fibers in the pH range of 6.0-7.4. Thin filament was reconstituted from purified G-actin with either bovine cardiac tropomyosin (Tm) or rabbit skeletal Tm in conjunction with cardiac or skeletal troponin (Tn). Results showed that isometric tension decreased linearly with a decrease in pH. The slope of the pH-tension relation, DeltaF/DeltapH (Deltarelative tension/Deltaunit pH), was 0.28 and 0.44 in control cardiac fibers and skeletal fibers, respectively. In actin filament-reconstituted fibers without regulatory proteins, DeltaF/DeltapH was 0.62, namely larger than that in cardiac or skeletal fibers. When reconstituted with cardiac Tm-Tn complex (nTm), DeltaF/DeltapH recovered to 0.32, close to the value obtained in control cardiac fibers. When reconstituted with skeletal nTm, DeltaF/DeltapH recovered to 0.48, close to the value for control skeletal fibers. To determine whether Tm or Tn is responsible for the inhibitory effects of nTm on the tension decrease caused by reduced pH, thin filament was reconstituted with cardiac Tm and skeletal Tn, or with skeletal Tm and cardiac Tn. When cardiac Tm was used, pH dependence of isometric tension coincided with that of control cardiac fibers. When skeletal Tm was used, the pH dependence coincided with that of control skeletal fibers. Furthermore, closely similar results were obtained in fibers reconstituted with actin and either cardiac or skeletal Tm without Tn. These results demonstrate that Tm but not Tn modulates the pH dependence of active tension.

Actins↗

PubMed2002

Modeling the length dependence of isometric force in human quadriceps muscles.

Functional electrical stimulation is used to restore movement and function of paralyzed muscles by activating skeletal muscle artificially. An accurate and predictive mathematical model can facilitate the design of stimulation patterns that produce the desired force. The present study is a first step in developing a mathematical model for non-isometric muscle contractions. The goals of this study were to: (1) identify how our isometric force model's parameters vary with changes in knee joint angle, (2) identify the best knee flexion angle to parameterize this model, and (3) validate the model by comparing experimental data to predictions in response to a wide range of stimulation frequencies and muscle lengths. Results showed that by parabolically varying one of the free parameters with knee joint angle and fixing the other parameters at the values identified at 40 degrees of knee flexion, the model could predict the force responses to a wide range of stimulation frequencies and patterns at different muscle lengths. This work showed that the current isometric force model is capable of predicting the changes in skeletal muscle force at different muscle lengths.

Biomechanical Phenomena↗

PubMed2003

Correlation between active and passive isometric force and intramuscular pressure in the isolated rabbit tibialis anterior muscle.

The purpose of this study was to quantify the relationship between intramuscular pressure (IMP) and muscle force during isometric muscle contraction of the rabbit tibialis anterior (TA) absent the effect of either bone or fascia. To quantify this relationship, length-tension experiments were performed on the isolated TA of the New Zealand White rabbit (mass=2.5+/-0.5kg, n=12). The knee was fixed in a custom jig, the distal tendon of the TA was attached to a servomotor, and a 360 microm fiber optic pressure transducer was inserted into the TA. The peroneal nerve was stimulated to define optimal length (L(0)). The length-tension curve was created using 40Hz isometric contractions with 2-min rest intervals between each contraction. Measurements began at L(0)-50%L(f) and progressed to L(0)+50%L(f), changing the length-tension in 5% L(f) increments after each contraction. Qualitatively, the length-tension curve for isometric contractions was mimicked by the length-pressure curve for both active and passive conditions. Linear regression was performed individually for each animal for the ascending and descending limb of the length-tension curve and for active and passive conditions. Pressure-force coefficients of determination ranged from 0.138-0.963 for the active ascending limb and 0.343-0.947 for the active descending limb. Passive pressure coefficients of determination ranged from 0.045-0.842 for the ascending limb and 0.672-0.982 for the descending limb. These data indicate that IMP measurement provide a fairly accurate index of relative muscle force, especially at muscle lengths longer than optimal.

Animals↗