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PubMed1983

Isokinetic, isometric and isotonic strength relationships.

Relationships among isokinetic, isometric and isotonic strength measurements in knee and elbow extension and flexion were examined in 16 young, healthy men. Isokinetic and isometric torque measurements were obtained from modified Cybex II apparatus. Isokinetic torque values were obtained at velocities of 36 degrees/sec, 108 degrees/sec, and 180 degrees/sec. An electrogoniometer was used to monitor joint angle. A device similar to a Noland-Kuckhoff (NK) table was employed to determine maximal isotonic capabilities using a 1 repetition maximum procedure. Correlations among the 3 testing modes at joint angles of peak isometric torque were generally high (mean = 0.78, range = 0.97 to 0.47) for all 4 muscle groups. The amounts of common variance suggested that all 3 strength testing modes were measuring a similar phenomenon which could be termed maximal voluntary strength. Within a particular muscle group correlations decreased as isokinetic velocities and joint angles became more widely separated.

Adult↗

PubMed1980

Isometric responses in the denervated diaphragmatic muscle of the guinea pig elicited by antigen and histamine.

Denervated diaphragmatic muscle strips from the guinea pig responded in vitro to varying concentrations of histamine with isometric contractions. Dose-response curves from strips taken from several areas of the muscle (ventral, V; dorsal, D; lateral, L) had slopes which were related in the following manner: D greater than V greater than L. Nevertheless, when the curves were normalized with respect to a dose which produced maximal tension, the slopes were similar and could be superimposed. Preparations taken from animals allergized to either bovine serum albumin or ferritin responded to the antigen with isometric contractions which also differed according to the original location of the strip in the muscle (D greater than V greater than L), but were similar when normalized as above. The results obtained from the normalized curves reflect a uniform sensitivity to histamine and antigen throughout the muscle. The variations in tension developed in the different strips probably are related to their contractile mass. The isometric recordings also revealed the development of spontaneous muscular contractions, as well as the presence of response latencies to both histamine and antigen, but not to acetylcholine.

Animals↗

PubMed1982

Cardiovascular responses to isometric exercise in patients with mitral stenosis. Comparison with normal subjects and patients with depressed ejection fraction.

The hemodynamic response to isometric handgrip was evaluated in 15 patients with mitral stenosis (MS), 12 normal subjects, and 13 patients with severe left ventricular failure (LVF). Acceleration of heart rate and rise in left ventricular systolic pressure were not significantly different between the three groups. Left ventricular end-diastolic pressure did not change in normal subjects and patients with MS during handgrip, but it was raised markedly in patients with LVF. Cardiac index increased in normal subjects but did not change in patients with MS and LVF. Stroke index declined in patients with LVF. In all groups there was a modest and similar increase in oxygen consumption and significant widening of the arteriovenous oxygen difference in patients with LVF. In patients with MS, pulmonary capillary pressure increased by an average of 10.6 mm Hg, with a parallel rise in mean pulmonary vascular resistance. It is concluded that patients with MS demonstrate a normal chronotropic and pressor response to isometric exercise. Normal left ventricular end-diastolic pressure response to isometric handgrip stress in patients with MS suggests good left ventricular performance.

Adult↗

PubMed1980

The effect of elbow angle on the isometric strength and endurance of the elbow flexors in men and women.

Ten male and ten female volunteers served as subjects in these experiments to determine the effect of elbow angle on isometric strength of the biceps muscles and on the ability to sustain an isometric tension to fatigue (endurance). As reported by others, we found that for each individual, there existed one elbow angle at which he or she could exert his greatest isometric strength. When maintaining an absolute work load to fatigue, exercise at this angle resulted in the longest endurance; in contrast, endurance was the same at any work load relative to the maximum strength for a given elbow angle.

Adult↗

PubMed1980

Torque curves produced at the knee during isometric and isokinetic exercise.

Torque curves recorded during knee extension and flexion at various speeds of isokinetic effort and at selected positions of isometric effort were studied to determine the amount of torque generated at selected speeds of motion, the point in the arc of motion where maximal torque output occurred, the relationship between isometric and isokinetic torques, the relative value of knee flexion and extension torques at various speeds, and the constancy of results in isokinetic testing. The isokinetic torques produced were less than isometric values and decreased as the rate of motion increased. Production of peak torque output occurred later in the arc of motion as the speed of contraction increased in extension. No significant change in the relative ability of the flexors and extensors was seen as a rate of motion increased. Isokinetic test-retest differences were similar at the rates of motion tested.

Adult↗

PubMed1996

Isometric strength measurements of knee extensors in women with osteoarthritis of the knee.

OBJECTIVE: To compare torque-angle characteristics of the knee extensors of women with and without osteoarthritis (OA) of the knee, and to determine the reliability of these measures. METHODS: The isometric torque of the knee extensors of both legs was tested on 3 occasions in 17 women with OA of the knee and 17 healthy women. Tests were performed on an isokinetic dynamometer at 3 knee angles (30 degrees, 60 degrees, 90 degrees). The peak torque values were subjected to 4 way analysis of variance (group vs leg vs angle vs time), and intraclass correlation coefficients were calculated. RESULTS: The reliability coefficients for repeated measures of isometric torque varied from 0.83 to 0.94 in the OA group and from 0.90 to 0.95 in the comparison group. The ANOVA and post hoc analyses revealed that the OA group had significantly (p < 0.05) lower knee extensor torque than the comparison group, and that the more symptomatic OA knee had lower torque than the contralateral limb. The torque was different across the 3 angles, but the torque-angle relationship was the same for both groups. CONCLUSION: Isometric torque of the knee extensors can be measured reliably in women with OA of the knee. The torque is lower in women with OA than in women with no knee problems, and the changes are similar across different knee angles.

Aged↗

PubMed1983

Acute effects of alcohol on left ventricular dynamics during isometric exercise in normal subjects.

The aim of this study was to assess whether drinking social amounts of alcohol impairs myocardial contractility in normal humans. To that end, 17 healthy volunteers performed isometric handgrip exercise before and 60 minutes after an intake of 1 g/kg body weight of ethanol within 60 minutes. Left ventricular M-mode echocardiogram, systolic time intervals, and sphygmomanometric arterial blood pressure were recorded before and at the end of 4-min handgrip at 30% of maximum voluntary contraction. The blood ethanol concentration (mean +/- SD) was 24.4 +/- 2.0 mmol/liter. At rest, ethanol increased heart rate (p less than 0.05), and decreased left ventricular end-diastolic diameter (p less than 0.05), end-systolic diameter (p less than 0.01), and circumferential systolic wall stress (p less than 0.05). The indices of left ventricular performance were unchanged except for the maximum circumferential fiber shortening velocity which was increased after ethanol (p less than 0.001). The cardiac response to isometric exercise was similar before and after ethanol except that the handgrip-induced rise in systolic wall stress was smaller postingestion (p less than 0.05). This study does not support the view that drinking small to moderate amounts of alcohol brings about myocardial depression in normal humans. Although preload, afterload, and heart rate were altered by ethanol at rest, myocardial contractility was not impaired even during the afterload stress imposed by isometric exercise.

Adult↗

PubMed2001

Ocular hemodynamics during isometric exercise.

The autoregulatory capacity of the human retina is well documented, but the pressure-flow relationship of the human choroid is still a matter of controversy. Recent data, using laser Doppler flowmetry to measure choroidal blood flow, indicate that the choroid has some autoregulatory potential, whereas most data using other techniques for the assessment of choroidal hemodynamics indicate that the choroidal pressure-flow curve is linear. We used a new laser interferometric technique to characterize choroidal blood flow during isometric exercise. Twenty healthy subjects performed squatting for 6 min during normocapnia and during inhalation of 5% CO2 and 95% air. Ocular fundus pulsation amplitude, flow velocities in the ophthalmic artery, intraocular pressure, and systemic hemodynamics were measured in 2-min intervals. To gain information on choroidal blood flow fundus pulsation amplitude was corrected for changes in flow pulsatility using data from the ophthalmic artery and for changes in pulse rate. Ocular perfusion pressure was calculated from mean arterial pressure and intraocular pressure. The ocular pressure-flow relationship was calculated by sorting data according to ascending ocular perfusion pressure values. In a pilot study in 6 healthy subjects comparable ocular pressure flow relationships were obtained when choroidal blood flow was assessed with the method described above and with laser Doppler flowmetry. In the main study isometric exercise caused a significant increase in mean arterial pressure (56%, P < 0.001), pulse rate (84%, P < 0.001), and intraocular pressure (37%, P 0.004), but decreased fundus pulsation amplitude (-36%, P < 0.001). Significant deviations from baseline choroidal blood flow were observed only at ocular perfusion pressures >69% during normocapnia and 70% during hypercapnia. Our data indicate that during isometric exercise the choroid has a high capacity to keep blood flow constant despite changes in perfusion pressure and that this pressure-flow relationship is not altered by moderate changes in arterial carbon dioxide levels.

Adult↗

PubMed1993

Persistent mechanical effects of decreasing length during isometric contraction of ovarian ligament smooth muscle.

When isometrically-contracting strips of ovarian ligament smooth muscle were suddenly shortened by 10-20% of their length, force fell rapidly and then redeveloped along an exponential time course. The amount of force recovered fell short of that expected in an isometric contraction at the new length, and this force deficit was proportional to the magnitude of the length step (approximately 80% of force was recovered after a 10% shortening). A sudden imposed decrease in length was more effective in reducing subsequent force than was isotonic shortening. Early in the recovery phase the stiffness of the muscle was decreased to less than its expected value; stiffness recovered to expected levels on an exponential time course approximately three to four times faster than force recovery itself. Force-velocity curves made during the redevelopment phase showed a reduced maximal force (Fmax) and an increased maximal shortening velocity (Vmax) when compared with control contractions matched in force, time and length. The curves crossed at approximately 10% of Fmax. During isometric relaxation the muscles showed an increase in their expected stiffness; prior imposed shortening (as above) reduced the relaxation stiffness increase in proportion to the prior force deficit. The persistent effects of early events on the later phases of the contraction, as well as the increase in shortening velocity with very light loads, are consistent with the hypothesis that the sudden shortening detaches crossbridges and that same fail to reattach during force recovery. During isotonic shortening of unperturbed muscle some slowly-cycling crossbridges may act as an internal load and reduce shortening velocity.

Animals↗

PubMed1986

Endurance capacity of untrained males and females in isometric and dynamic muscular contractions.

The capacity to perform isometric and dynamic muscle contractions at different forces has been measured in two separate groups of subjects: 25 men and 25 women performed sustained isometric contractions of the knee-extensor muscles of their stronger leg to fatigue, at forces corresponding to 80%, 50% and 20% of the maximum voluntary force of contraction (MVC). The second experimental model involved a bilateral elbow-flexion weight lifting exercise. Eleven women and 12 men performed repetitions at loads corresponding to 90%, 80%, 70%, 60% and 50% of maximum load (1RM), at a rate of 10 X min-1 to the point of fatigue. Males were stronger (p less than 0.001) than females in both the static (675 +/- 120 N vs 458 +/- 80 N; mean +/- SD) and dynamic (409 +/- 90 N vs 190 +/- 33 N) contractions. Isometric endurance time of the males at a force corresponding to 20% of MVC was less than that of the females (180 +/- 51 s vs 252 +/- 56 s; p less than 0.001) but there was no difference between the sexes at 50% or 80% of MVC. Similarly, when the sexes were compared using dynamic elbow-flexion exercise, the female subjects were able to perform a greater number of repetitions than males at loads of 50% (p less than 0.005), 60% (p less than 0.001) and 70% (p less than 0.025) of 1RM, but there was no difference between the sexes at loads of 80% or 90% of 1RM.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1982

Length dependence of calcium activated isometric force and immediate stiffness in living and glycerol extracted vascular smooth muscle.

Vascular smooth muscle series elasticity was examined in living and glycerinated preparations as a function of the tissue length or calcium elicited force. Isometrically contracted smooth muscle strips were submitted to small quick stretches and releases (rise time 1.5 ms). The resulting immediate tension changes were proportion to the length changes for length steps ranging from -0.5% L0 to +2% L0. Plotting the immediate tension changes versus the length steps resulted in force-extension diagrams of the series elasticity (T1-curves). The linear parts of the T1-curves extrapolated to a common abscissa intercept of about -1% to -2% L0 irrespective of the tissue length or the degree of calcium activated force. The slopes of the T1-curves taken as the stiffness of the series elasticity increased in proportion to the isometric tension and depended on the tissue length or the degree of calcium activation in a similar way as tension. It is concluded that tension changes due to changes in the calcium concentration or the tissue length are caused by a change in the number of attached crossbridges. Results obtained in "skinned" fibres were similar to the one obtained in living fibres indicating that electromechanical coupling was not a major factor in determining the decrease in isometric tension and stiffness at short lengths.

Adenosine Triphosphate↗

PubMed1984

Development of force-velocity relation and rise of isometric tetanic tension measure the time course of different processes.

The time course of the contractile process was investigated in the presence of AR-L 115BS, a twitch potentiator which is thought to increase the rate of the Ca2+ binding by troponin and to improve the Ca2+ mobilization from the sarcoplasmic reticulum. AR-L 115BS increased markedly the rate of development of the force-velocity (T-V) relation and of the isometric tetanic tension. The effect on the rate of development of the T-V relation was however substantially more intense than that on the speed of rise of tetanic tension, thus reducing considerably the isometric tension level at which the T-V relation attained its final characteristics. The velocity of shortening under zero load and the degree of curvature of the T-V relation were not affected by AR-L 115BS. These findings support the view that the development of the T-V relation and the rise of the isometric tetanic tension measure the time course of two different processes.

Animals↗

PubMed1993

Physiological unloading of cardiopulmonary mechanoreceptors by posture change does not influence the pressor response to isometric exercise in healthy humans.

In recent studies in humans the role of cardiopulmonary baroreflexes in modulating the cardiovascular responses to isometric exercise (somatic pressor reflex) has been investigated by performing static handgrip exercise during deactivation of cardiopulmonary receptors produced by low levels of lower body negative pressure; however, findings from these studies have not been consistent. The purpose of this study was to investigate whether a more physiological unloading stimulus of cardiopulmonary baroreceptors, obtained by sequentially changing posture, could influence the pressor response to somatic afferent stimulation induced by isometric exercise. To accomplish this, ten healthy subjects performed a 2-min isometric handgrip (IHG) at 30% maximal voluntary contraction after 10 min of supine rest and, in rapid sequence, after 10 min of sitting and 10 min of standing, at the time when, owing to their transitory nature, the cardiovascular effects, due to arterial baroreceptor intervention should have been minimal. During IHG arterial pressure (BPa) was continuously and noninvasively measured to quantify accurately the blood pressure response to IHG both in magnitude and time course. Results showed that the pressor response to IHG was not significantly influenced by change in posture, either in magnitude or in time course. The mean arterial pressure increased by 17.4 (SEM 2.5), 18.6 (SEM 1.2) and 17.0 (SEM 1.3) mmHg in supine, sitting and standing [2.3 (SEM 0.3), 2.5 (SEM 0.2) and 2.3 (SEM 0.2) kPa] positions, respectively. Also the heart rate response to IHG was unaffected by change in posture.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1989

Specificity of joint angle in isometric training.

Six healthy women (21.8 +/- 0.4 y) did isometric strength training of the left plantarflexors at an ankle joint angle of 90 degrees. Training sessions, done 3 times per week for 6 weeks, consisted of 2 sets of ten 5 s maximal voluntary contractions. Prior to and following the training, and in random order, voluntary and evoked isometric contraction strength was measured at the training angle and at additional angles: 5 degrees, 10 degrees, 15 degrees, and 20 degrees intervals in the plantarflexion and dorsiflexion directions. Evoked contraction strength was measured as the peak torque of maximal twitch contractions of triceps surae. Training increased voluntary strength at the training angle and the two adjacent angles only (p less than 0.05). Time to peak twitch torque was not affected by training. Twitch half relaxation time increased after training (p = 0.013), but the increase was not specific to the training angle. There was a small (1.1%, p less than 0.05) increase in calf circumference after training. Evoked twitch torque did not increase significantly at any joint angle. It was therefore concluded that a neural mechanism is responsible for the specificity of joint angle observed in isometric training.

Adult↗

PubMed1991

The effect of range of motion and isometric pre-activation on isokinetic torques.

The effect of an increased angle of excursion and isometric pre-activation on isokinetic torques of knee extensors was investigated in five male subjects, mean age 35.0 years, SD 9.6. Peak torque and isoangular torque at 0.52 rad from full knee extension (FKE) were measured when contractions were carried out at 3.14, 4.19 and 5.24 rad.s-1 starting: 1) from a standard knee angle (SA) of 1.57 rad from FKE, 2) from the same starting angle as SA, plus an isometric preload (P) equivalent to 25% of isometric maximal voluntary contraction and 3) from an increased angle of knee flexion (IA), 2.09 rad from FKE plus P. Surface integrated electromyograms (iEMG) of the vastus lateralis muscle in SA and IA + P were also recorded. The IA + P had the effect of increasing peak torque, as compared to SA, on average by 12.0%, SD 7.5% (P less than 0.001) at 3.14 rad.s-1, 19.5%, SD 5.5% (P less than 0.001) at 4.19 rad.s-1, 21.6%, SD 10.7% (P less than 0.001) at 5.24 rad.s-1 and of increasing mean iEMG by 15.7%, SD 7.0% (P less than 0.001) at 5.24 rad.s-1. The IA + P also had the effect of increasing the angle from FKE at which peak torque occurred: from means of 0.80 rad, SD 0.11 to 1.00 rad, SD 0.07 at 3.14 rad.s-1, from 0.65 rad, SD 0.11 to 0.92 rad, SD 0.09 at 4.19 rad.s-1 and from 0.60 rad, SD 0.11 to 0.88 rad, SD 0.11 at 5.24 rad.s-1 (P less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1985

Dissociation between mechanical performance and the cost of isometric tension maintenance in Lethocerus flight muscle.

A method for the continuous measurement of ATP hydrolysis (ATPase) by demembranated muscle fibres has been applied to isometrically held, glycerol-extracted flight muscle fibres from the water-bug Lethocerus, under conditions of high MgATP, neutral pH, and varying ionic strength, Ca2+ and extension. These variables caused parallel changes in isometric tension and ATPase. The slope of ATPase upon tension (delta ATPase/delta Tension; incremental tension cost) remained the same upon extension at either different Ca2+ concentrations or different ionic strength. Isometric activation by Ca2+ gave a higher incremental tension cost. The calculated mechanical rate constant of the work-producing process, measured by the small-amplitude behaviour, was increased by either Ca2+ or ionic strength, and little changed by extension; there was therefore a dissociation between its value and that of the incremental tension cost. The results appear to exclude a two-state crossbridge model for fibrillar insect flight muscle.

Adenosine Triphosphate↗

PubMed1981

Effects of fatigue and altered pH on isometric force and velocity of shortening at zero load in frog muscle fibres.

temporaria (0.9-2.5degrees C) were stimulated to produce a 1 s isometric tetanus at regular intervals until constant mechanical responses were attained. Various degrees of force depression ("fatigue") were produced by decreasing the contraction interval from 30 or 15 min (control to 120, 60, 30 and 15s, respectively. In this was the steady-state tetanic force could be reversibly reduced to approximately 70% of the control value. The velocity of shortening at zero load, V0, was determined at each level of fatigue using an approach for direct measurement of V0. V0 was not significantly affected as long as the decrease in force was less than 10%. With further reduction of the isometric tension there was a progressive decline of V0 according to the following empirical relationship between percentage depression of force (delta P0) and maximum speed (delta V0) of shortening: delta V0 = 0.006 delta P02.48- 1.0 (correlation coefficient, 0.86). Cine photographic recording of nylon markers on the fibre surface provided evidence that fatigue developed uniformly along the fibre with no sign of failure of excitation in any segment. The change in mechanical performance during fatigue could be reproduced inthe non-fatigued fibre by reducing the pH of the external medium within the range 8.0-6.6 using a bicarbonate-CO2 buffer. A decrease in pH thus reduced both the rate of rise and the total amplitude of isometric force and prolonged the relaxation phase. Furthermore, there was a drop in V0 that was related to the force decline in approximately the same way as observed during fatigue. The results support the idea the fatigue involves both a reduced state of activation of the contractile system and a specific (activation independent) inhibition of crossbridge turnover. Increased intracellular H+ concentration is likely to contribute to the development of both these effects during fatigue.

Animals↗

PubMed1996

Radiological method for preoperative determination of isometric attachment points of an anterior cruciate ligament graft.

The purpose of this study was to develop a radiological method which would be preoperatively available to help determine the best graft placement (with respect to isometricity as well as absence of graft impingement) for all knees. The radiological method is described in full detail. We also present the most significant experimental work supporting our development. Firstly, we studied the path followed by radio-opaque objects inserted in the mobile tibia around the fixed femur. Secondly, we compared the distances measured between selected femoral and tibial points radiologically (according to our method) and clinically (with a currently available isometer). The main results were: (1) every tibial point considered moves on an arc of a circle centered or a corresponding femoral point. We should then speak of pairs of isometric points instead of a single femoral isometric zone; (2) the more posterior the tibial point, the more anterior and distal the corresponding femoral point and vice versa; (3) the distance variations induced by rotation did not exceed 1.5 to 2.5 mm when measured either radiologically or clinically; (4) on the radiological and clinical measurements, the difference of length variations during flexion was also very small (mean 0.22 mm; SD 1.2 mm). We conclude that this very simple method allows us to find the femoral transition line for every knee (whatever its size, shape or dynamics). It aids preoperative planning in anterior cruciate ligament graft reconstruction.

Anterior Cruciate Ligament↗