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PubMed1993

Isometric hip abductor strength following total hip replacement and its relationship to functional assessments.

Despite the rehabilitative emphasis on hip abductor strength following total hip replacement (THR), it is unclear how muscular strength is related to function. The purposes of this study were to examine changes in hip abductor strength during the first 6 months following THR and to determine the relationship between hip abductor strength and functional performances. Forty-three patients (mean age 64 +/- 7 years) completed strength assessments before surgery and at 1, 6, 12, and 24 weeks after surgery, and functional assessments before surgery and at 12 and 24 weeks after surgery. Both hip abductor strength and functional performance were significantly improved at each assessment (p < 0.01). The correlation between isometric hip abductor torques and the distance walked in 6 minutes was modestly high (r = 0.48-0.51; p < 0.01). This study provides baseline data for isometric hip abductor strength that can be used comparatively to assess patient progress and to help set clinical goals. Although strength is related to function, isometric measurements of strength should not be relied upon as the sole predictors of function in patients who have undergone THR.

Bone Cements↗

PubMed1997

Assessment of isometric contractions performed with maximal subjective effort: corresponding results for EEG changes and force measurements.

In order to find a parameter or parameters that can be attributed to movements performed with maximal subjective effort, EEG recordings and force measurements were taken in connection with isometric muscle contractions performed with 80% of the subjective maximal force (IMC80) or with maximal subjective effort (IMC100). Criteria based on EEG recordings and force measurements have been considered as indicators for maximal subjective effort in a given movement. The following criteria were selected: A. If the mean spectral theta amplitude across the parieto-occipital area decreases from IMC80 to IMC100 then the isometric contraction is taken to be performed with maximal effort; B. If the obtained force values can be fitted to a switch function and if the achieved forces are only a predetermined percentage lower than the maximal force value obtained over all trials then this isometric contraction is accepted to be performed with maximal effort. 18 out of 24 cases fulfill the EEG criterion whereas the criterion for force measurements is fulfilled in 16 out of 24 trials. The comparison between the results obtained by means of the EEG criterion and by means of criterion for force measurement shows that the results are in agreement in 22 out of 24 cases (p < .001). The high correspondence of the assessments allows us to suspect that both criteria specify the same phenomenon, namely the performance of a motor task with maximal subjective effort.

Adult↗

PubMed1985

Plasma adrenaline and noradrenaline during mental stress and isometric exercise in man. The role of arterial sampling.

Plasma adrenaline and noradrenaline were measured in arterial blood and in forearm venous blood during isometric exercise and during a mental stress test. In both conditions arterial plasma adrenaline increased significantly, whereas arterial plasma noradrenaline remained unchanged. During isometric exercise the increase in plasma adrenaline was greater in venous blood from the exercising arm than from the resting arm. The extraction of adrenaline in the forearm was greater in the resting than in the exercising arm. Venous plasma noradrenaline showed a rebound phenomenon after isometric exercise and tended to decrease during the mental stress test. The results indicate that it is preferable to measure arterial concentrations of adrenaline as an indicator of sympathoadrenal activity rather than venous concentrations since the extraction of adrenaline in forearm might not be constant. It is suggested that a selective increase in arterial plasma adrenaline as opposed to an increase in both plasma adrenaline and noradrenaline may indicate a selective increase in sympathoadrenal activity in visceral organs.

Adult↗

PubMed1996

Methods for measuring maximal isometric grip strength during short and sustained contractions, including intra-rater reliability.

The purposes of this study were to develop methods for measuring maximal isometric grip strength during short and sustained contractions in a laboratory setting, and to evaluate the test-retest reliability of these methods in short- and long-term perspectives. Eleven healthy men and women were assessed on four occasions. Maximal voluntary isometric grip strength (MVC) was measured in standardized and optional positions, and sustained maximal isometric strength (SMVC) in the standardized position. The results indicated that three trials in a session might be insufficient to obtain a true measure of MVC. The within-session and test-retest reliability of the described multi-trial procedure was considered satisfactory. The mean score of the last three trials tended to show the highest short-term and long-term variability. There were no clear differences between scores obtained in standardized and optional positions. The standardized position seemed more consistently to yield higher test-retest reliability and lower variability over time. The described method for measuring SMVC, expressed as area and peak score, had high test-retest reliability and an acceptable degree of short-term and long-term variability. The time taken to reach the peak score was not a reliable measure.

Adult↗

PubMed2006

[Effects of isometric contraction training by electrostimulation on Type I and II hindlimb muscles in cerebral ischemia model rats].

PURPOSE: The purpose of this study was to examine the effects of cerebral ischemia on Type I(soleus) and Type II(plantaris, gastrocnemius) muscles, and to determine the effects of isometric contraction training by electrostimulation on Type I and II muscles in cerebral ischemia model rats. METHOD: Twenty-five male Sprague-Dawley rats were randomly divided into four groups: ST(stroke), STES(stroke+electrostimulation), SH(sham) and SHES (sham+electrostimulation). The ST and STES groups received a transient right middle cerebral artery occlusion operation. The SH and SHES groups received a sham operation. The STES and SHES groups had daily isometric contraction training by electrostimulation(100 Hz, 45 mA, 7.5 V) on hindlimb muscles for 7 days. RESULT: Plantaris and gastrocenmius muscle weight, myofibrillar protein contents of soleus and gastrocnemius, and the muscle fiber cross-sectional area of gastrocnemius in the ST group significantly decreased compared with the SH group. Soleus, plantaris, gastrocnemius muscle weight, myofibrillar protein contents of soleus and gastrocnemius, and the Type I muscle fiber cross-sectional area of soleus and the Type II muscle fiber cross-sectional area of gastrocnemius in the STES group significantly increased compared with the ST group. CONCLUSION: Hindlimb muscle atrophy occurs after acute stroke and isometric contraction training by electrostimulation during early stages of a stroke attenuates muscle atrophy of Type I and Type II muscles.

Animals↗

PubMed1999

Reliability and validity of a new device to measure isometric strength in polyarticular exercises.

BACKGROUND: The purpose of this study was to assess the validity of a new device to evaluate isometric strength during multi-joint exercise such as the squat or bench press. METHODS: The device used an electric motor-driven bar to simultaneously generate and measure forces during weight lifting exercises. This new device and a force platform measured the forces generated by either the motor on a fixed telescopic steel girder (passive condition) or a subject pushing vertically against the bar from three squat positions (active condition). In the passive condition, 252 measurements were made, with 3 trials for 6 bar heights and 14 bar loads. In the active condition, 8 young physically active students (age, height and body mass were 25.1 +/- 2.6 years, 179.3 +/- 7.2 cm and 82.0 +/- 9.9 kg, respectively) performed 3 maximal isometric strength (MIS) trials in each of the 3 squat exercise positions (parallel, half and quarter squat), and 3 additional MIS trials in one position randomly assigned two weeks later to test inter-day reliability. RESULTS: In the passive condition, no differences were observed between the forces measured by the force platform and the new device. The coefficient of linear regression (r) and the coefficient of variation (CV) were 1 and below 0.23%, respectively. In the active condition, the peak MIS measured was 2828 N and the values of r and CV were above 0.982 and below 5.96%, respectively. The assessment of inter-day reliability showed an r value of 0.984 and a CV of 3.98%. CONCLUSIONS: This study demonstrated that the new electric motor-driven exerciser provides valid and reliable data when used to generate forces and measure isometric strength throughout the load and motion ranges commonly used in squat exercise.

Adult↗

PubMedDate not supplied

Electromyography tension and frequency spectrum analysis of some masticatory muscles at rest, isotonic and isometric contractions.

On a population of 52 subjects surface electromyographic recordings of temporals and masseters, simultaneously with mandible dynamic of closure and clenching, were performed, in order to study tension and frequency behaviour in three postural conditions: rest, isotonic and isometric contractions. Frequency was studied using the median resulting from FFT calculation, and a new computing method, which presents the proportion of frequencies making up the whole EMG signal, by steps of 50 Hz. Tension was calculated as well. The results permit us to draw the following conclusions: 1. a period of EMG silence was present in 51 of 52 subjects at mandible closure (SPA--Silent Period Area); 2. SPA onset was before teeth contact (22.5 msec., during the motion of the mandible), while its end was after closure (10.2 msec., during motionless phase of clenching). This allowed to use the SPA as a tool to clearly distinguish isotonic from isometric contraction; 3. the comparison of tension and frequency, expressed as median, showed that at rest a muscle presents low frequency and low tension. In active contraction both increase their values. Nevertheless, in active contraction, while no differences were found in frequency behaviour, tension showed a difference: although higher than at rest, isotonic contraction presented lower values than during isometric contraction; 4. the study performed by the new program showed that the low frequency at rest was due to the high proportion (30-40%) of frequencies of less than 50 Hz, while the increase at function was due to the parallel increase of frequencies comprised between 100 and 250 Hz. Because it is known that muscles are composed of fibers at low frequency and at high frequency of discharge, which play different functional roles, the last finding suggests that the mathematical analysis of the spectrum of frequencies, could provide a functional-histological image of the muscle.

Adolescent↗

PubMedDate not supplied

The effect of free isotonic and maximal isometric contraction exercises of the hip adduction on vastus medialis oblique muscle: an electromyographic study.

The purpose of this study was to analyse the activity of the vastus medialis oblique (VMO) muscle electromyographically during free isotonic and maximal isometric contraction of the hip adduction with knee extension performing exercises at sitting and in decubitus lateralis positions. Using a 8 channels Nicolet Electromyograph and Beckman surface mini electrodes, the activity of the vastus medialis oblique muscle was recorded among 15 healthy subjects, aged 19 to 33 years, (mean = 24.4, SD = 4.1) without prior knee and hip joints pathology. The sign was recorded in root mean square (RMS), expressed in microvolts. The data were statistically calculated employing an analysis of variance (ANOVA) and the Tukey test, at 5% of significance. The results showed that the electromyographic (EMG) activity of the vastus medialis oblique muscle was significantly greater in both exercises of maximal contraction when compared with free isotonic at decubitus lateralis. On the other hand, there was no significant difference of the electromyographic activity of the vastus medialis oblique muscle between the two exercises of maximal isometric contraction. These findings, within the experimental conditions used, suggest that prior stages of patellofemoral dysfunction, the exercises of hip adduction with knee extension could be performed isometrically or isotonically, at sitting and in decubitus lateralis positions, depending on the biological conditions of each patient.

Adult↗

PubMedDate not supplied

Muscle fiber conduction velocity during isometric contraction and the recovery period.

Changes of muscle fiber conduction velocity (MFCV) detected by surface array electrodes during an isometric contraction and the recovery period were evaluated. The location on skin measured for action potentials of muscle fiber in m. biceps brachii was a distance of 5 mm and 30 mm from the end-plate to the distal tendon. The MFCV was evaluated by averaging raw EMG waves. The MFCVs at both locations declined gradually during the loads of sustained isometric contractions of 30, 50, and 70% of the maximum voluntary contraction (MVC). The degree of the decrease of the MFCV was extremely intense during a sustained contraction of 70% MVC. The values of the MFCV at the location of 5 mm from the end-plate in the period close to the exhaustion state showed a significant decrease compared with the values in the initial period during the contractions for the above three kinds of loads, while the decrease of the MFCV at the location of 30 mm from the end-plate was not found to be so significant during the contractions. In the recovery period, the contraction of 5% MVC was maintained, and the resultant MFCVs restored gradually to the value of the initial period. At the location of 5 mm from the end-plate, the MFCVs at 15 minutes after the end of the load were significantly higher than those just after the end of the load. At the location of 30 mm from the end-plate, the increases of the MFCVs during the recovery period did not show significant changes. Changes of the MFCV during the isometric contraction and the recovery period depend greatly on the location of the electrodes measured for the action potentials of the muscle fibers.

Adult↗

PubMed2001

Characteristics of isometric and dynamic strength loss following eccentric exercise-induced muscle damage.

Angle-specific isometric strength and angular velocity-specific concentric strength of the knee extensors were studied in eight subjects (5 males and 3 females) following a bout of muscular damaging exercise. One hundred maximal voluntary eccentric contractions of the knee extensors were performed in the prone position through a range of motion from 40 degrees to 140 degrees (0 degrees = full extension) at 1.57 rads(-1). Isometric peak torque was measured whilst seated at 10 degrees and 80 degrees knee flexion, corresponding to short and optimal muscle length, respectively. Isokinetic concentric peak torque was measured at 0.52 and 3.14 rad x s(-1). Plasma creatine kinase (CK) activity was also measured from a fingertip blood sample. These measures were taken before, immediately after and on days 1, 2, 4, and 7 following the eccentric exercise. The eccentric exercise protocol resuited in a greater relative loss of strength (P< 0.05) at short muscle length (76.3 +/- 2.5% of pre-exercise values) compared to optimal length (82.1 +/- 2.7%). There were no differences in the relative strength loss between isometric strength at optimal length and isokinetic concentric strength at 0.52 and 3.14 rad x s(-1). CK activity was significantly elevated above baseline at days 4 (P < 0.01) and 7 (P < 0.01). The greater relative strength loss at short muscle length appeared to persist throughout the seven-day testing period and provides indirect evidence of a shift in the angle-torque relationship towards longer muscle lengths. The results lend partial support to the popping sarcomere hypothesis of muscle damage, but could also be explained by an impairment of activation at short muscle lengths.

Adult↗

PubMed2002

Mechanomyographic and electromyographic responses to unilateral isometric training.

The purpose of this investigation was to examine the effects of unilateral, isometric training of the forearm flexors on strength and the mechanomyographic (MMG) and electromyographic (EMG) responses of the biceps brachii in the trained and untrained limb at three joint angles. Seventeen adult females (mean age +/- SD = 21 +/- 2 years) were randomly assigned to a control (CTL; N=7) or a training (TRN; N=10) group. The TRN group performed isometric training of the non-dominant forearm flexors on a Cybex II Dynamometer at a joint angle such that the Cybex lever arm was positioned 60 degrees above the horizontal plane. The training consisted of 3 to 5 sets of 8, 6-second repetitions at 80% of maximal voluntary contraction 3 times per week for 8 weeks. The results indicated a significant increase in flexed arm circumference as well as isometric strength in the trained limb at all three joint angles. There were, however, no changes in MMG or EMG amplitude in the trained or untrained limb and no cross-training effect for strength or flexed arm circumference. These findings suggested that the increased strength may have been due to factors associated with hypertrophy, independent of neural adaptations in the biceps brachii. Furthermore, hypertrophy may have had counteractive effects on the MMG signal that could be responsible for the lack of a training-induced change in the MMG amplitude.

Adult↗

PubMed2003

[Effects of isometric exercise on the diastolic function in patients with severe aortic stenosis].

The objective of the study was to determine the effects of isometric exercise on the diastolic function in patients with aortic stenosis without coronary lesion (group 1, G1, n = 9) and with coronary lesion (group 2, G2, n = 11). Patients subjected to a cardiac catheterization performed isometric exercise until their heart rate increased in 32 +/- 9% compared to baseline. The left ventricular systolic pressure, the +dP/dtmax, and the end diastolic pressure (LVEDP) were measured, and the time constant of pressure decay (tau, tau) was calculated. The +dP/dtmax increased in G1 and G2 during exercise, from a value of 1989 +/- 190 and 2428 +/- 220 mmHg/sec up to 2286 +/- 214 y 2661 +/- 230 mmHg/sec, respectively, returning afterwards to its baseline value. The LVEDP increased during exercise in G1 and G2 from a value of 30.1 +/- 2.7 and 26.5 +/- 2.2 mmHg up to 38.4 +/- 1.7 and 36.1 +/- 4.0 mmHg, respectively (p < 0.05), returning to its baseline value only in G1. The tau (tau) increased during exercise in G1 and G2 from a value of 42.8 +/- 6.8 and 44.8 +/- 4.2 m/sec up to 55.3 +/- 9.2 and 60.4 +/- 5.9 msec respectively (p < 0.05), and remained elevated after exercise in both groups although it was statistically significant only in G2. The isometric exercise decreases the relaxation rate and increases the LVEDP in patients with aortic stenosis and left ventricular hypertrophy. After exercise, relaxation remained altered in the group of patients with coronary lesion. Alteration in the lusitropism and the increase of LVEDP after exercise suggest the presence of myocardial stunning.

Aortic Valve Stenosis↗

PubMed1992

Isokinetic and isometric testing of knee musculature in young female patients with patellofemoral pain syndrome.

By using a Cybex II+ isokinetic dynamometer, we performed isokinetic and isometric tests of the knee musculature in 29 female patients (aged 17-45 years) with patellofemoral pain syndrome (PFPS) and the same number of age- and weight-matched female controls. The pain was unilateral in 11 patients and bilateral in 18. The isokinetic testing was set at speeds of 60 degrees, 120 degrees and 180 degrees/sec; the isometric testing was set at 30 degrees and 60 degrees of knee flexion. The results showed that the lowest torque values occurred on the affected side of the unilateral group, followed by both sides of the bilateral group, the sound side of the unilateral group, and the control group, sequentially. The highest rate of abnormal torque values for all PFPS patients occurred in the quadriceps at 60 degrees/sec of isokinetic contraction: 33%. In this study, five (17%) patients showed abnormal torque curves and 10 (34%) patients complained of pain or soreness at either the lowest speed of isokinetic testing or during the isometric testing of the quadriceps muscles. The bilateral torque difference was highest in the unilateral group.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1992

The effects of treadmill running on the isometric fatigue of the handgrip muscles.

Twelve male subjects, ages 18-32, performed low, moderate, and high intensity systemic treadmill exercise to examine its effect on isometric strength and fatigue of the handgrip muscles. Baseline handgrip values were recorded, as well as maximal oxygen uptake and ventilatory threshold (VT), to determine the intensity for each of the three exercise conditions. Task A involved a 10-min treadmill run at 20% below VT, task B was given at VT, and task C was 20% above VT. Immediately following the endurance treadmill run the subjects were given a 2-min isometric contraction at maximum intensity. Heart rate and blood pressure were also measured. No significant differences were found between control measures and the strength and endurance variables. Rates of fatigue were similar for all conditions, and heart rate and blood pressure remained elevated during the handgrip fatigue task. It is concluded that isometric strength and endurance of non-involved muscles are not affected by prior endurance exercise.

Adolescent↗

PubMed2004

Active finite element analysis of skeletal muscle-tendon complex during isometric, shortening and lengthening contraction.

An active finite element model was developed to predict the mechanical behaviors of skeletal muscle-tendon complex during isometric, shortening and lengthening contraction. The active finite element was created through incorporation of a user-defined material property into ABAQUS finite element code. The active finite element is controlled by a motor element that is activated by a mathematical function. The nonlinear passive behavior of the muscle was defined by the viscoelastic elements and can be easily altered to other properties by using other elements in the material library without the need of re-defining the constitutive relation of the muscle. The isometric force-length relationship, force-strain relations of the muscle-tendon complex during both shortening and lengthening contraction and muscle relaxation response were predicted using the proposed finite element model. The predicted results were found to be in good agreement with available experimental data. In addition, the stress distribution in the muscle-tendon complex during isometric, shortening and lengthening contractions was simulated. The location of the maximum stress may provide useful information for studying muscle damage and fatigue in the future.

Algorithms↗

PubMed2004

Combined effects of age and maturation on maximum isometric leg press strength in young basketball players.

AIM: Muscular strength of the leg extensor muscles in children can be affected by several factors such as age, sexual maturation, body mass and training status of the subjects. The purpose of the study was to examine maximal isometric strength characteristics of young male basketball players taking into consideration the combined effects of chronological age and sexual maturation. METHODS: One hundred and twenty male basketball players, aged from 12 to 17 years divided into 6 equivalent age subgroups performed maximum bilateral isometric leg press efforts. The parameters analysed were the maximal voluntary isometric force (MVC), relative strength (MVC/body mass and MVC/fat free mass), starting strength (F50: force exerted during the first 50 ms of the contraction) and speed strength index (the ratio of maximal force to time to attain maximal force). RESULTS: The results indicated that in almost all absolute force parameters, the 12-and 13-year olds demonstrated significantly (p<0.05) lower values compared with the 15(-1)6-and 17-years old groups. Age differences were also significant (p<0.05) when the effects of sexual maturation were taken into consideration in the statistical analysis but they were reduced when strength was adjusted for body mass. Finally, no significant differences for strength per unit of fat free mass were found (p>0.05). CONCLUSIONS: Maximum absolute strength of basketball players is significantly increased from 12 to 17 years and as sexual maturation stage increases. It also appears that body mass and fat free mass should be taken into consideration when examining age effects on strength in basketball players.

Adolescent↗

PubMed2005

The impact of rosiglitazone on cardiovascular responses and endurance during isometric exercise in patients with Type 2 diabetes.

BACKGROUND: Vascular endothelial function is compromised in people with diabetes reducing tissue blood flow. The present investigation was a logical extension of a previous work, examining isometric exercise performance and recovery in people with diabetes and the impact of the insulin sensitizer rosiglitazone, a drug shown to improve endothelial function. MATERIAL/METHODS: Blood pressure, heart rate and limb blood flow were examined in 12 control subjects and 8 subjects with type 2 diabetes during a series of 2 fatiguing isometric contractions at a tension of 40% of the maximum strength of the handgrip muscles; 5 minutes of rest were allowed between the contractions. RESULTS: Endurance of the first and the second contraction was significantly less in subjects with diabetes (p<0.01). HR increased significantly (p<0.01) by over three fold during exercise in control subjects compared to subjects with diabetes. There was no statistical difference in the increase in either systolic or diastolic BP during isometric exercise comparing controls to subjects with Type 2 diabetes (p>0.05), however, resting and peak blood pressures were greater in subjects with type 2 diabetes (p<0.01). Forearm blood flow, which was significantly lower at rest (p<0.01) in subjects with diabetes, only increased by about half as much during the exercise in subjects compared to control subjects. These differences were partially reversed after 3 months administration of rosiglitazone. CONCLUSIONS: Microcirculatory damage in diabetes impairs exercise performance and recovery and can be partially reversed after rosiglitazone administration.

Adult↗

PubMed2006

Characterization of isometric contractions of rat skeletal muscle in vivo: duty cycle effects.

Many work related injuries stem from the exertion of skeletal muscle forces over an extended period of time. Musculoskeletal injury can be caused by muscle's inability to maintain force during occupational exposure. The goal of the present study is to test how various rest times (duty cycles) between long isometric contractions will affect decrements in force, and develop a model that characterizes force decrements due to skeletal muscle fatigue. All tests were performed in vivo on the tibialis anterior muscle of anesthetized Sprague-Dawley rats. Animals were randomly assigned to either a 10 second (N=8), 1 minute (N=8), or 5 minute (N=8) duty cycle group. All animals were then subjected to 7 isometric contractions (duration of 2.8 seconds). A model was constructed to characterize forces changes over the duration of a contraction and over multiple contractions. The model consisted of a power law and an exponential component; these two components were combined by using an exponential weighting function. Overall, the combination of a power law and exponential model with a weighting function satisfactorily characterized the changes in isometric force for the 10 second duty cycle, but a simpler exponential model could be used where longer duty cycles are performed.

Animals↗