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PubMed1998

Test-retest reliability of isometric and isoinertial testing in symmetric and asymmetric lifting.

The aim of this study was to evaluate test-retest reliability of a dynamometer in measuring lifting strength or force parameters under several combinations of ergonomic factors. Thirteen healthy participants were tested on peak force (PF), related variables and isometric strength (IS) twice, at intervals of 3 months. Correlation coefficients for all parameters in the sagittal plane were 0.60-0.85. Coefficients of variations (CVs) of methodology error for PF in the sagittal plane were 6.2-6.9%. Correlation coefficients and CVs for IS at 90 degrees to the lateral plane were 0.51-0.54 and 16.6-17.9%, respectively. In paired t-tests of the parameters under all conditions, there was a significant difference between test and retest. In the test and retest, ratings of perceived exertions for the low back and the right arm in isometric lifting were significantly higher than those in dynamic lifting. It was concluded that the test-retest reliability of dynamic forces in the dynamometer was high. The peak force in the sagittal plane was considered reliable. In isometric lifting, isometric strength in the sagittal plane seemed reliable, while that at right angles to the lateral plane was considered to be less reliable.

Adult↗

PubMed2000

The effect of knee angle on the external validity of isometric measures of lower body neuromuscular function.

The aim of this study was to evaluate the effect of varying knee angle (120 degrees and 90 degrees) on the external validity of an isometric leg press test with reference to vertical jump performance. Isometric peak force (PF120 and PF90), rate of force development (RFD120 and RFD90), and maximum height reached with a squat jump and counter-movement jump were measured in 14 males. Although RFD120 was significantly correlated with squat jump and counter-movement jump performance (r = 0.71 and 0.69), and the correlations with PF120 approached statistical significance (r = 0.53 and 0.50), neither PF90 nor RFD90 was significantly related to vertical jump performance. Furthermore, although both RFD120 and PF120 were significantly different between the best five and the worst five jumpers, RFD90 and PF90 did not differentiate between individuals' vertical jump performance. We conclude that the choice of joint angle affects the external validity of isometric strength testing. Based on our results, we recommend accurate control of biomechanical specificity and assessment at different angles to find the position at which isometric strength testing is most comfortable.

Adult↗

PubMed2002

Maximal-intensity isometric and dynamic exercise performance after eccentric muscle actions.

A well-documented observation after eccentric exercise is a reduction in maximal voluntary force. However, little is known about the ability to maintain maximal isometric force or generate and maintain dynamic peak power. These aspects of muscle function were studied in seven participants (5 males, 2 females). Knee extensor isometric strength and rate of fatigue were assessed by a sustained 60 s maximal voluntary contraction at 80 degrees and 40 degrees knee flexion, corresponding to an optimal and a shortened muscle length, respectively. Dynamic peak power and rate of fatigue were assessed during a 30 s Wingate cycle test. Plasma creatine kinase was measured from a fingertip blood sample. These variables were measured before, 1 h after and 1, 2, 3 and 7 days after 100 repetitions of the eccentric phase of the barbell squat exercise (10 sets x 10 reps at 80% concentric one-repetition maximum). Eccentric exercise resulted in elevations in creatine kinase activity above baseline (274+/-109 U x l(-1); mean +/- s(x)) after 1 h (506+/-116 U x l(-1), P < 0.05) and 1 day (808+/-117 U x l(-1), P < 0.05). Isometric strength was reduced (P < 0.05) for 7 days (35% at 1 h, 5% at day 7) and the rate of fatigue was lower (P < 0.05) for 3 days at 80 degrees and for 1 day at 40 degrees. Wingate peak power was reduced to a lesser extent (P < 0.05) than isometric strength at 1 h (13%) and, although the time course of recovery was equal, the two variables differed in their pattern of recovery. Eccentrically exercised muscle was characterized by an inability to generate high force and power, but an improved ability to maintain force and power. Such functional outcomes are consistent with the proposition that type II fibres are selectively recruited or damaged during eccentric exercise.

Adult↗

PubMed1997

Effect of increased maxillo-mandibular relationship on isometric strength in TMD patients with loss of vertical dimension of occlusion.

The effect on isometric strength of the shoulders and limbs while biting in habitual occlusion, on a bite-elevating appliance and on a placebo appliance was analyzed. Twenty female volunteer patients, presenting with temporomandibular pain dysfunction syndrome and obvious loss of vertical dimension, served as subjects. All were weaker to the manual application of the isometric Deltoid Press (IDP) when biting, as opposed to maintaining the mandible in an unsupported rest position. Two intraoral appliances were fabricated for each subject: a bite-elevating appliance (BEA) set by a functional criterion of peak strength to the IDP and a placebo appliance which did not interfere with occlusion but was "set" with a mock IDP procedure. Testing was carried out by the Neuromuscular Research Testing Laboratory of the Neurology Department of Tufts New England Medical Center. Testing was independent of the dentist who fabricated and set the appliances. A standard neuromuscular test with the Maximal Voluntary Isometric Contraction apparatus was used to assess strength of right and left shoulder, elbow and knee flexion and extension as is routinely performed with all neuromuscular disease patients. Twelve strength tests were carried out for each of three conditions: 1. Baseline-biting in habitual occlusion; 2. Elevated-biting on the BEA; and 3. Placebo-biting with the placebo appliance inserted. The order of conditions 2 and 3 was counterbalanced without knowledge of the subjects. Twelve repeated measures ANOVAs (each subject as their own control) were conducted for each of the 12 strength measures. All F-tests indicated a significant main effect for treatment differences (p < 0.0001). Mean strength biting on the BEA was consistantly greater (p < 0.001) than Baseline or Placebo strength. Baseline and Placebo condition were equivalent. These findings confirmed previous observations at this TMD Center: individuals with loss of vertical dimension of occlusion respond to a bite raising appliance by increased isometric-strength.

Analysis of Variance↗

PubMed1999

The effect of vertical dimension and mandibular position on isometric strength of the cervical flexors.

This study compared the peak isometric strength of the cervical flexors in deep bite temporomandibular dysfunction (TMD) patients while biting in four bite positions: habitual occlusion, edge-to-edge, lateral shift and retruded. These values were then compared to those of the same subjects' bite positions elevated to a functional criterion (maximum isometric strength of the deltoid muscles). The mean height increase was 2.4 mm with a range of 1.5-3.8 mm. Fifteen of eighteen deep bite subjects met an inclusionary criterion, at least 13.3 Newtons (N) stronger cervical muscle strength with mandible relaxed open than habitual bite. Peak strength biting edge-to-edge was significantly greater than biting in habitual occlusion. Strength was found to increase significantly when biting in each of four mandibular positions when the bite was elevated to the functional criterion. The greatest strength was obtained from elevated habitual and edge-to-edge positions. The findings are of clinical significance, suggesting that cervical muscle isometric strength is affected by bite position and vertical dimension of occlusion. The results suggest that when biting, individuals with deep bite may be functioning at about 60% of their potential cervical flexor, isometric strength. The interaction between occlusal position, vertical dimension and cervical muscle function suggests a craniomandibular-cervical masticatory system.

Adult↗

PubMed2002

The diurnal rhythm in isometric muscular performance differs with eumenorrheic menstrual cycle phase.

The aim of this study was to examine the effect of the interaction of circamensal and diurnal rhythms in temperature upon the production of maximal voluntary muscle force. Ten eumenorrheic females (mean age: 24 +/- 3 yr mean body mass: 58.4 +/- 6.9 kg) participated in the experiment at both 06:00 and 18:00h at the mid-point of both the follicular and luteal phases of the menstrual cycle. Subjects performed tasks of maximal isometric lifting strength (MILS) at knee height, and endurance time (t) for lifting 45% of MILS, upon an isometric lift dynamometer. Body temperature was elevated at 18:00h and in the luteal phase by 0.52 +/- 0.4 and 0.26 +/- 0.35 degrees C, respectively. The amplitude of the diurnal variation in temperature was blunted by 0.3 degrees C within the luteal phase. Maximal isometric performance was elevated by 8% at 18:00h in the luteal phase of the cycle (p < 0.05 interaction for MILS) but unaffected by time of day in the follicular phase. Endurance time was unaffected by time or phase (p > 0.05). It should be noted that the classic diurnal rhythm in maximal voluntary isometric muscle force may not be evident in all phases of the female menstrual cycle.

Adult↗

PubMed1994

Maximal isometric strength and mobility among 75-year-old men and women.

The purpose of this study was to examine the association between maximal isometric strength and mobility among 75-year-old men and women. All those born in 1914 and resident in the city of Jyväskylä in August 1989 comprised the study group (n = 388); 355 persons were interviewed at their homes (92%): 101 men (81% of all male residents) and 186 women (75%) participated in the laboratory strength tests. As part of the home interview the person's mobility at home, on stairs and outdoors was assessed using a four-point scale:--1 able, 2--able with difficulty, 3--needs help, 4--unable. Poor mobility was more common among the drop-outs than among the strength-tested subjects in both sexes. Maximal isometric strength of hand grip, arm flexion, knee extension and trunk flexion and extension were measured using specially constructed dynamometers. The strength results were adjusted for body weight. The study also included a stair-mounting test and measurement of maximal walking speed. The body-weight adjusted maximal forces were consistently significantly associated with mobility. Those who claimed no problems in the mobility interview and performed better in the walking and stair-mounting tests exhibited greater maximal isometric strength. The present results indicate that maximal isometric strength tests provide useful information about physical functional capacity among elderly people. These findings also suggest that the maintenance of adequate strength could be favourable to the mobility of older persons.

Activities of Daily Living↗

PubMed1987

Filling pressures in post-myocardial infarction patients: comparison between isometric and dynamic exercise.

The purpose of this study was to determine if isometric exercise (handgrip) using a substantial muscle mass and intensity could be substituted for dynamic exercise in the assessment of left ventricular function in myocardial infarct (MI) patients. Forty patients with documented MI were assigned, on the basis of their previous exercise ECG responses, to either an exercise-induced ischaemic group (Group 1) or to a non-exercise ischaemic group (Group 2). Eight apparently healthy males served as controls. Pulmonary capillary pressure (PCP) was measured at rest, during volume loading and during isometric and dynamic exercise. Mean PCP in Group 1 increased progressively from 7.5 +/- 2.9 mmHg at rest, to 11.6 +/- 3.8 mmHg during volume loading, to 18.8 +/- 10.2 mmHg during the isometric exercise and to 25.2 +/- 10.1 mmHg during the dynamic exercises. For Group 2, the respective values were 9.6 +/- 6.3, 13.1 +/- 6.4, 18.7 +/- 13.7 and 18.4 +/- 9.8 and for the controls 8.9 +/- 1.9, 11.3 +/- 1.2, 13.3 +/- 3.3 and 11.8 +/- 3.6 mmHg. The results of this study indicate that isometric exercise of 50% MVC using both hands can adequately replace dynamic exercise in the diagnosis of left ventricular function in post MI patients.

Adult↗

PubMed2003

Creatine supplementation enhances isometric strength and body composition improvements following strength exercise training in older adults.

We sought to determine whether creatine monohydrate (CrM) supplementation would enhance the increases in strength and fat-free mass that develop during resistance exercise training in older adults. Twenty-eight healthy men and women over the age of 65 years participated in a whole-body resistance exercise program 3 days per week for 14 weeks. The study participants were randomly allocated, in a double-blind fashion, to receive either CrM (5 g/d + 2 g of dextrose; n = 14) or placebo (7 g of dextrose; n = 14). The primary outcome measurements included the following: total body mass, fat-free mass, one-repetition maximum strength for each body part, isometric knee extension, handgrip, and dorsiflexion strength, chair stand performance, 30-m walk test, 14-stair climb performance, muscle fiber type and area, and intramuscular total creatine. Fourteen weeks of resistance exercise training resulted in significant increases in all measurements of strength and functional tasks and muscle fiber area for both groups (p <.05). CrM supplementation resulted in significantly greater increases in fat-free mass and total body mass, as compared with placebo (p <.05). The CrM group also showed a greater increase in isometric knee extension strength in men and women, as compared with placebo (p <.05), and also greater gains in isometric dorsiflexion strength (p <.05), but in men only. There was a significant increase in intramuscular total creatine in the CrM group (p <.05). Finally, there were no significant side effects of treatment or exercise training. This study confirms that supervised heavy resistance exercise training can safely increase muscle strength and functional capacity in older adults. The addition of CrM supplementation to the exercise stimulus enhanced the increase in total and fat-free mass, and gains in several indices of isometric muscle strength.

Age Factors↗

PubMed1988

A comparison of isometric exercise, cold pressor stimulation and dynamic exercise in patients with coronary heart disease.

Isometric exercise and cold pressor stimulation have been proposed as alternatives to dynamic exercise in the evaluation of patients with coronary heart disease. We evaluated all three, by gated radionuclide ventriculography, in 13 male controls and 44 male patients with coronary heart disease. In controls, mean left ventricular ejection fraction did not change during isometric exercise or cold pressor stimulation (64 +/- 2 to 63 +/- 2 and 63 +/- 3) but fell significantly in patients (56 +/- 1 to 53 +/- 1 and 53 +/- 1, both P less than 0.001). During dynamic exercise, mean left ventricular ejection fraction rose in controls (64 +/- 2 to 84 +/- 2, P less than 0.001) but did not change in patients (56 +/- 1 to 56 +/- 2). There was considerable overlap between the groups in the left ventricular ejection fraction response to isometric exercise and cold pressor stimulation; only dynamic exercise discriminated between them. Isometric exercise and cold pressor stimulation are of little value in the diagnosis of coronary heart disease by radionuclide ventriculography.

Adult↗

PubMed1977

The influence of isometric exercise and passive stretch on hip joint motion.

A method was designed to compare the effects of isometric contractions and passive stretch on modifying joint range of motion in 30 normal men. Subjects were randomly assigned into a control group, a passive stretch group, or an isometric contraction group. Each subject assumed a left sidelying position on the force table. Stabilization was applied to the pelvis and left lower extremity. The cuff, to which the force cable was attached, was applied to the right lower extremity. Force measurements produced by the isometric contractions or passive stretch procedures were stored on computer tape. The results of the mean differences in pelvifemoral angle measurements indicated that both treatment groups significantly increased their range of passive hip flexion with the knee extended when compared to the control group. Comparisons between the two treatment groups indicated that the isometric contraction and passive stretch procedures had significant and similar effects.

Adult↗

PubMed1980

Strength of isometric and isokinetic contractions: knee muscles of men aged 20 to 86.

Maximum isometric and isokinetic torques of the knee flexor and extensor muscles were measured at three knee joint positions in 72 normal, health men in three age groups from 20 to 86 years. The isokinetic contractions were performed at a speed of 36 degrees per second. The isometric contractions were sustained for five seconds. Strength of the men in the older age groups was significantly less than that of the youngest group. The strength of the isokinetic contractions was significantly less than that of the isometric contractions for all joint positions. The men in the oldest age group generally took longer than the younger men to reach peak torque during the isometric contractions. The torque values provide base-lines for evaluating patients with knee joint disabilities.

Adult↗

PubMed1998

Isometric and dynamic exercise studied with echo planar magnetic resonance imaging (MRI).

PURPOSE: The effect of different types of exercise upon echo planar (EP) magnetic resonance (MR) images was examined during and after both dynamic and isometric dorsi-flexion exercises at matched workloads and durations. METHODS: Healthy untrained subjects performed either dynamic exercise through a full range of motion and against a constant resistance or isometric exercise at the center of the range of motion and against a constant resistance at 25 or 70% their measured maximum voluntary contraction (MVC). EP MR images were acquired at 1.5 T every 4 s before (4 images), during (27 images), and after (29-65 images) exercise. A spin echo EP sequence was employed with TE = 30 ms, TR = 4000 ms, FOV = 20 x 40 cm, 64 x 128 matrix. The changes in proton transverse relaxation rate (deltaR2, [s(-1)]) relative to values obtained before exercise were calculated from individual images at different times during and after exercise. RESULTS: At both 70 and 25% of MVC, the maximum deltaR2 after dynamic exercise (-8.38+/-0.32 s(-1) (70%), -6.47+/-1.23s(-1) (25%)) was significantly greater (P < or = 0.05) than after isometric exercise (-5.91+/-0.67 s(-1) (70%), -3.80+/-0.87s(-1) (25%)). Throughout the period that recovery was monitored, the recovery patterns of deltaR2 following isometric and dynamic exercise at both workloads remained parallel. CONCLUSIONS: We conclude that exercise-induced changes in MR images are influenced not only by workload and exercise duration but also by the type of exercise, and we postulate that these differences result from the different physiological responses elicited by the different types of exercise.

Adult↗

PubMed2001

Effects of creatine supplementation on isometric force-time curve characteristics.

PURPOSE: To assess the effects of creatine monohydrate on isometric force-time curve parameters of sedentary college males aged 18-25 yr. METHODS: This double-blind study randomly assigned subjects to either a treatment (with creatine (Cr)) group (N = 11) or placebo group (P) (N = 8). The Cr group received 20 g x d(-1) of Cr for the first 5 d, in 5-g doses, four times daily (loading period) followed by a 5-g x d(-1) dose for the next 5 d (maintenance phase) and then no Cr ingestion for 7 d (washout period). Each 5-g dose was mixed with 250 mL of Gatorade. The P group received a placebo (cornstarch) following the exact same dosage regimen and protocol as the Cr group. All subjects were sedentary and had not used any nutritional supplements for 6 months before the study. Measurements of isometric force production of four muscle groups (elbow flexors and extensors; knee flexors and extensors) were characterized by a number of force-time parameters including strength (MF), time to maximal force (TMF), rate of force development (MRFD), and intermittent endurance (total impulse (TI) and percent force decrement (PFD)). Testing was done at pretreatment, after the 10-d loading and maintenance phases, and after the washout phase. RESULTS: Repeated measures ANOVA indicated no significant group effect for any muscle group concerning the maximal strength parameters and only two significant time effects for the knee flexors during MF and MRFD. Similarly, there were no significant group effects for any muscle group during the endurance trials; however, there was a significant time effect concerning TI for each muscle group tested. CONCLUSION: Our findings indicate that oral supplementation with creatine monohydrate in untrained males does not positively influence isometric strength but may enhance intermittent isometric muscular endurance.

Adolescent↗

PubMed1997

Spectral and temporal responses of trunk extensor electromyography to an isometric endurance test.

STUDY DESIGN: This study investigated the effect of trunk extensor muscle location on the spectral and temporal electromyographic activity of the muscles during a fatiguing isometric extension of the torso against gravity. OBJECTIVES: To determine the spectral responses of the trunk extensor muscles at more locations than have been studied previously, to determine if fatigue in the knee flexors limits this test, and to quantify the recruitment patterns of the trunk extensor muscles in a group of healthy subjects. SUMMARY OF BACKGROUND DATA: Isometric endurance tests appear to have more value than strength tests in predicting the occurrence of low back pain. Electromyographic activity of trunk extensor muscles during these tests may provide clues to the etiology of neuromuscular-based low back pain. Spectral electromyographic measures appear to be successful discriminators between low back pain patient and normal populations, although which muscles provide the best information is unclear. Likewise, the recruitment patterns of the trunk extensors during fatiguing isometric tasks is not well quantified. METHODS: Ten healthy men performed an isometric trunk endurance test. Surface electromyography was recorded from the erector spinae medially and laterally at vertebral levels of L1 and L3, medially at L5, and from the biceps femoris and gastrocnemius. Spectral parameters were calculated from the Fast Fourier Transform, and temporal parameters were calculated from the root mean square of the raw data. Linear regression was used to determine their responses as a function of time. RESULTS: There was a significant effect of vertebral level and medial-lateral location on the initial median frequency and linear slope of the median frequency regressions. No significant evidence of fatigue in the lower extremities was observed. For most subjects, the temporal response of the surface electromyography was parabolic (concave-down), peaking at 30-50% of the endurance time. CONCLUSION: Establishment of which muscle locations provide the best information and knowledge of the recruitment patterns are essential for the development of clinical diagnostic procedures and rehabilitation protocols.

Adult↗

PubMed1999

Maximal isometric strength of the cervical musculature in 100 healthy volunteers.

STUDY DESIGN: A descriptive study involving maximal isometric strength measurements of the cervical musculature. OBJECTIVES: To determine the maximal isometric strength of the flexors and extensors and of the cervical musculature in 100 healthy volunteers (50 men and 50 women). SUMMARY OF BACKGROUND DATA: The literature contains only a few descriptive studies pertaining to strength levels of the cervical musculature. These studies include small subject populations, and measurement methods have demonstrated weak reliability. METHODS: Testing was carried out using strain-gauge technology on a neck muscle training apparatus. RESULTS: A reliability study demonstrated acceptable intraday and day-to-day values. Maximal isometric strength was approximately 20% to 25% higher in male subjects than female subjects in both flexion and extension from the third to the sixth decades. In the seventh decade, the women's strength levels surpassed values for men in both flexion and extension. Extension-flexion ratios were approximately 1.7 to 1 in both the men and women participants. The men demonstrated a significant decrease in maximal isometric strength with increasing age in both flexion and extension, whereas the women were able to maintain strength values in the ages tested. CONCLUSIONS: Men and women demonstrate impressive levels of muscular strength in the flexors and extensors of the cervical spine and can maintain these values until the seventh decade of life. Successful rehabilitation of the cervical musculature will require considerable resistance for sufficient stimulation of the cervical musculature.

Adult↗

PubMed2002

Posture-dependent isometric trunk extension and flexion strength in normal male and female subjects.

The objective of this study was to quantify the relationship between trunk posture and trunk muscle function in a group of young, normal male and female subjects. Ten male and 10 female subjects performed isometric flexion and extension tasks using a trunk dynamometer. Peak isometric torque was recorded in flexion and extension at 10 degrees increments over a sagittal posture range of -20 degrees extension to +50 degrees of flexion. Significant differences in trunk strength (isometric torque) were found between males and females, at various sagittal plane trunk postures, and between flexion (F) and extension (E) tasks. Flexion torque was greatest at 20 degrees to 30 degrees flexion, whereas extension torque was greatest at 50 degrees flexion. Gender-specific differences in trunk strength were markedly reduced when the torque data were normalized by the subject's height multiplied by body weight. The E/F torque ratio showed a relatively linear, over twofold increase with increasing flexion angle, and was significantly greater for female subjects compared with male subjects at most sagittal postures. The baseline trunk isometric strength data provided by this study should help clinicians to use strength testing more precisely and specifically in prevention and diagnosis of patients at risk for back disorders.

Adult↗

PubMed2004

Metabolic cost of lengthening, isometric and shortening contractions in maximally stimulated rat skeletal muscle.

AIM: The present study investigated the energy cost of lengthening, isometric and shortening contractions in rat muscle (n = 19). METHODS: With electrical stimulation the rat medial gastrocnemius muscle was maximally stimulated to perform 10 lengthening, isometric and shortening contractions (velocity 25 mm s(-1)) under experimental conditions (e.g. temperature, movement velocity) that resemble conditions in human movement. RESULTS: Mean +/- SD force-time-integral of the first contraction was significantly different between the three protocols, 2.4 +/- 0.2, 1.7 +/- 0.2 and 1.0 +/- 0.2 N s, respectively (P < 0.05). High-energy phosphate consumption was not significantly different between the three modes of exercise but a trend could be observed from lengthening (7.7 +/- 2.7 micromol approximately P muscle(-1)) to isometric (8.9 +/- 2.2 micromol approximately P muscle(-1)) to shortening contractions (10.4 +/- 1.6 micromol approximately P muscle(-1)). The ratio of high-energy phosphate consumption to force-time-integral was significantly lower for lengthening [0.3 +/- 0.1 micromol approximately P (N s)(-1)] and isometric [0.6 +/- 0.2 micromol approximately P (N s)(-1)] contractions compared with shortening [1.2 +/- 0.2 micromol approximately P (N s)(-1)] contractions (P < 0.05). CONCLUSION: The present results of maximally stimulated muscles are comparable with data in the literature for voluntary human exercise showing that the energy cost of force production during lengthening exercise is approximately 30% of that in shortening exercise. The present study suggests that this finding in humans probably does reflect intrinsic muscle properties rather than effects of differential recruitment and/or coactivation.

Animals↗