Reliability of knee extension and flexion measurements using the Con-Trex isokinetic dynamometer

The aim of this study was to evaluate the reliability of isokinetic and isometric assessments of the knee extensor and the flexor muscle function using the Con-Trex isokinetic dynamometer. Thirty healthy subjects (15 males, 15 females) were tested and retested 7 days later for maximal strength (isokinetic peak torque, work, power and angle of peak torque as well as isometric maximal voluntary contraction torque and rate of torque development) and fatigue (per cent loss and linear slope of torque and work across a series of 20 contractions). For both the knee extensor and the flexor muscle groups, all strength data - except angle of peak torque - demonstrated moderate-to-high reliability, with intraclass correlation coefficients (ICC) higher than 0.86. The highest reliability was observed for concentric peak torque of the knee extensor muscles (ICC = 0.99). Test-retest reliability of fatigue variables was moderate for the knee extensor (ICC range 0.84-0.89) and insufficient-to-moderate for the knee flexor muscles (ICC range 0.78-0.81). The more reliable index of muscle fatigue was the linear slope of the decline in work output. These findings establish the reliability of isokinetic and isometric measurements using the Con-Trex machine.     

Muscle fatigue of the elbow flexor muscles during two intermittent exercise protocols with equal mean muscle loading

OBJECTIVE: Whether different muscle-loading patterns with the same mean load have a similar influence on the resultant muscle fatigue is still unknown. This study investigated the influence of two intermittent exercise protocols, with equal mean muscle loading, on the mechanical and myoelectrical signs of fatigue in the elbow flexor muscles. DESIGN: Ten subjects performed two 20-min long intermittent isometric elbow flexion tasks. The exercise period load for the low force intermittent test was 25% of the maximum voluntary contraction, with a work-cycle time of 20 s and a duty cycle of 0.5. The high force intermittent exercise protocol had an exercise period load of 50% maximum voluntary contraction, a cycle time of 20 s and a duty cycle of 0.25. METHODS: Muscle fatigue was quantified both by measuring the maximal voluntary contraction torque before and after the intermittent exercises, and also by the temporal changes observed in the electromyography signal. RESULTS: Both muscle-loading patterns induced a 15% decrease in maximum voluntary contraction. However, the electromyographic spectral changes during the intermittent static contractions varied between the two protocols. CONCLUSIONS: Variation in muscle load without loss in productivity can affect the physiological responses. The results also showed that different methods to assess muscle fatigue sometimes provide different information on the resultant fatigue.     

Endurance and fatigue characteristics of the neck flexor and extensor muscles during isometric tests in patients with postural neck pain

Sustained postural loading of the cervical spine during work or recreational tasks may contribute to the development of neck pain. The aim of this study was to compare neck muscle endurance and fatigue characteristics during sub-maximal isometric endurance tests in patients with postural neck pain, with asymptomatic subjects. Thirteen female patients with postural neck pain and 12 asymptomatic female control subjects completed timed sub-maximal muscle endurance tests for the neck flexor and extensor muscles. Muscle fatigue, defined as the time-dependent decrease in median frequency electromyography (EMG), was examined using surface EMG analysis during the tests. The median extensor test holding time was lower but not significantly different in the neck pain group (165 s) that the control group (228 s) (p = 0.17). There was no difference between groups in the flexor test holding time (neck pain = 36 s, controls = 38 s) (p = 0.96). The neck pain group was characterised by greater variability in neck flexor (p = 0.03) and extensor (p = 0.006) muscle endurance. For both tests, the rate of decrease in median frequency EMG was highly variable within and between groups with no significant difference between groups for the flexor or extensor test (p = 0.05-0.82). Patients with postural neck pain did not have significant impairment of neck muscle endurance or accelerated fatigue compared to control subjects. However, the greater variability in these indices of muscle function may reflect patient-specific changes in muscle function associated with neck pain disorder.     

Muscle function during repetitive moderate-intensity muscle contractions in myoadenylate deaminase-deficient Dutch subjects

We investigated whether the capacity for repetitive submaximal muscle contraction was reduced in a group of subjects (n=8) with a primary deficiency of myoadenylate deaminase (MAD). Quadriceps femoris muscle fatigue was evaluated using voluntary and electrically stimulated contractions during 20 min of repetitive voluntary isometric contractions at 40% of maximal force-generating capacity (MFGC). After 5 min of exercise, MFGC had declined significantly to 70.6+/-4.1% (mean+/-S.E.M.) and 87.2+/-1.6% of baseline values in MAD-deficient and sedentary control subjects (n=8) respectively (P=0.002 between groups). After 5 min of exercise, the half-relaxation time had increased significantly to 113.4+/-6.1% of baseline in MAD-deficient muscle, but had decreased significantly to 94.1+/-1.3% in control subjects (P=0.003 between groups). All control subjects completed the 20-min exercise test. Five of the MAD-deficient subjects had to stop exercising due to early muscle fatigue; however, three of the MAD-deficient subjects were able to complete the 20-min exercise test. In conclusion, although the capacity for repetitive submaximal isometric muscle contractions for the group of MAD-deficient subjects was significantly decreased, it remains uncertain whether MAD deficiency is the sole cause of pronounced muscle fatigue.     

Neuromuscular efficiency of the sternocleidomastoid and anterior scalene muscles in patients with chronic neck pain

PURPOSE: This study compared the neuromuscular efficiency (NME) of the sternocleidomastoid (SCM) and anterior scalene (AS) muscles between 20 chronic neck pain patients and 20 asymptomatic controls. METHOD: Myoelectric signals were recorded from the sternal head of SCM and the AS muscles as subjects performed sub-maximal isometric cervical flexion contractions at 25 and 50% of the maximum voluntary contraction (MVC). The NME was calculated as the ratio between MVC and the corresponding average rectified value of the EMG signal. Ultrasonography was used to measure subcutaneous tissue thickness over the SCM and AS to ensure that differences did not exist between groups. RESULTS: For both the SCM and AS muscles, NME was shown to be significantly reduced in patients with neck pain at 25% MVC (p<0.05). Subcutaneous tissue thickness over the SCM and AS muscles was not different between groups. CONCLUSIONS: Reduced NME in the superficial cervical flexor muscles in patients with neck pain may be a measurable altered muscle strategy for dysfunction in other muscles. This aberrant pattern of muscle activation appears to be most evident under conditions of low load. NME, when measured at 25% MVC, may be a useful objective measure for future investigation of muscle dysfunction in patients with neck pain.     

Neck flexor muscle fatigue is side specific in patients with unilateral neck pain.

Despite the evidence of greater fatigability of the cervical flexor muscles in neck pain patients, the effect of unilaterality of neck pain on muscle fatigue has not been investigated. This study compared myoelectric manifestations of sternocleidomastoid (SCM) and anterior scalene (AS) muscle fatigue between the painful and non-painful sides in patients with chronic unilateral neck pain. Myoelectric signals were recorded from the sternal head of SCM and the AS muscles bilaterally during sub-maximal isometric cervical flexion contractions at 25% and 50% of the maximum voluntary contraction (MVC). The time course of the mean power frequency, average rectified value and conduction velocity of the electromyographic signals were calculated to quantify myoelectric manifestations of muscle fatigue. Results revealed greater estimates of the initial value and slope of the mean frequency for both the SCM and AS muscles on the side of the patient's neck pain at 25% and 50% of MVC. These results indicate greater myoelectric manifestations of muscle fatigue of the superficial cervical flexor muscles ipsilateral to the side of pain. This suggests a specificity of the effect of pain on muscle function and hence the need for specificity of therapeutic exercise in the management of neck pain patients.     

The relationship between EMG median frequency and low frequency band amplitude changes at different levels of muscle capacity

OBJECTIVE: To test the validity of high and low frequency band amplitudes of the surface electromyography (EMG) profile as representation of muscle fatigue. DESIGN: A within subjects (n=10) repeated measures design was used to collect surface EMG signals from the biceps during an isometric contraction under two levels of fatigue status. BACKGROUND: The use of the shift in the median frequency of the surface EMG power spectrum is a well known method of assessing muscle fatigue. Fatigue also results in amplitude changes of the specific frequency bands. The use of frequency band analysis may be an alternative option for the assessment of muscle fatigue in specific experimental settings. METHODS: Surface EMG profiles of the biceps were recorded at 1024 Hz during a sustained isometric hold at 60% of the individuals fresh and fatigued maximal voluntary isometric torque. The median frequency of the power spectrum was compared with changes in the low frequency (15-45 Hz) and high frequency (>95 Hz) bands.Results. There was a close association between median frequency shift and the amplitude of the 15-45 Hz bandwidth and the high-low frequency amplitude ratio. The association was similar for performance under different muscle capacity states. CONCLUSIONS: Frequency band amplitude analysis provides similar information to median frequency shift under isometric conditions and may be suited to specific experimental protocols in workplace fatigue studies. RELEVANCE: The use of amplitude band analysis that closely approximates the standard median frequency changes allows greater possibility of assessing muscle fatigue in different experimental settings and the use of lower sampling rates.     

Median frequency of the myoelectric signal in cervical paraspinal muscles

Objective measurements of the function of cervical paraspinal muscles (CPM) are lacking. Changes in the frequency spectrum of the myoelectric (ME) signal have been used in the limb muscles as an objective measurement of muscle function. Based on our previous investigational work on limb muscles, we attempted to measure parameters related to median frequency (MF) of the ME signal to measure localized muscle fatigue in cervical paraspinal muscles in 14 healthy subjects. The ME signals were recorded bilaterally using surface electrodes placed posteriorly at the C3 to C6 level. Sustained isometric neck extensions were performed at 20%, 50%, 80%, and 100% of maximum voluntary contractions (MVC). Initial median frequency (IMF) and slope of the MF during sustained isometric contraction were obtained by analyzing the ME signal using an IBM-XT computer, a laboratory interface system, and custom-designed software. The results indicated that the MF of the CPM behave somewhat differently from limb muscles, and that the CPM are less fatigable than limb muscles. The test-retest reliability, using our system, was found to be high, and data processing showed a variability of 4 to 8Hz. These results imply that neck muscles appear to behave differently at high and low force levels in response to daily functional demand. The MF measurements appear to be a useful objective technique for evaluating muscle function of cervical musculature.     

The relationship between submaximal activity of the lumbar extensor muscles and lumbar posteroanterior stiffness

BACKGROUND AND PURPOSE: Some patients with low back pain are thought to have increased lumbar posteroanterior (PA) stiffness. Increased activity of the lumbar extensors could contribute to this stiffness. This activity may be seen when a PA force is applied and is thought to represent much less force than occurs with a maximal voluntary contraction (MVC). Although MVCs of the lumbar extensors are known to increase lumbar PA stiffness, the effect of small amounts of voluntary contraction is not known. In this study, the effect of varying amounts of voluntary isometric muscle activity of the lumbar extensors on lumbar PA stiffness was examined. SUBJECTS: Twenty subjects without low back pain, aged 26 to 45 years (X=34, SD=5.6), participated in the study. METHODS: Subjects were asked to perform an isometric MVC of their lumbar extensor muscles with their pelvis fixed by exerting a force against a steel plate located over their T4 spinous process. They were then asked to perform contractions generating force equivalent to 0%, 10%, 30%, 50%, and 100% of that obtained with an MVC. Posteroanterior stiffness at L4 was measured during these contractions. RESULTS: A Friedman one-way analysis of variance for repeated measures demonstrated a difference in PA stiffness among all levels of muscle activity. CONCLUSION AND DISCUSSION: Voluntary contraction of the lumbar extensor muscles will result in an increase in lumbar PA stiffness even at low levels of activity.     

Influence of prolonged unilateral cervical muscle contraction on head repositioning – Decreased overshoot after a 5-min static muscle contraction task

The ability to reproduce a specified head-on-trunk position can be an indirect test of cervical proprioception. This ability is affected in subjects with neck pain, but it is unclear whether and how much pain or continuous muscle contraction factors contribute to this effect. We studied the influence of a static unilateral neck muscle contraction task (5 min of lateral flexion at 30% of maximal voluntary contraction) on head repositioning ability in 20 subjects (10 women, 10 men; mean age 37 years) with healthy necks. Head repositioning ability was tested in the horizontal plane with 30° target and neutral head position tests; head position was recorded by Zebris^®, an ultrasound-based motion analyser. Head repositioning ability was analysed for accuracy (mean of signed differences between introduced and reproduced positions) and precision (standard deviation of the differences). Accuracy of head repositioning ability increased significantly after the muscle contraction task, as the normal overshoot was reduced. An average overshoot of 7.1° decreased to 4.6° after the muscle contraction task for the 30° target and from 2.2° to 1.4° for neutral head position. The increased accuracy was most pronounced for movements directed towards the activated side. Hence, prolonged unilateral neck muscle contraction may increase the sensitivity of cervical proprioceptors.     

Cranio-cervical flexor muscle impairment at maximal, moderate, and low loads is a feature of neck pain

Impairment of the cranio-cervical flexor (CCF) muscles is a feature of painful cervical spine disorders. The aim of this study was to investigate if CCF muscle impairment is present over a range of contraction intensities (maximal, moderate, low) in neck pain sufferers compared to individuals with no history of neck pain. Isometric CCF muscle strength (isometric maximal voluntary contraction (MVC)), and endurance at moderate (50% of MVC), and low (20% of MVC) loads was compared in 46 participants with neck pain (Neck Disability Index (NDI): mean+/-SD; 22.8+/-5.2) and 47 control participants (NDI: 2.6+/-2.6). Compared to the control group, the neck pain group had a significant deficit (15.9%, P=0.037) in their MVC peak torque recordings, as well as a significantly reduced capacity to sustain isometric CCF muscle contractions to task failure at 20% of MVC (35% deficit, P=0.03) and 50% of MVC (27% deficit, P=0.002). Neck pain participants also demonstrated poorer accuracy in maintaining their MVC(20) contraction at the nominated isometric CCF torque amplitude (P=0.02), compared to control participants. It would appear that impairment in isometric CCF muscle performance exists over a range of contraction intensities in neck pain sufferers, which may benefit from specific therapeutic intervention.     

Gender influence on fatigability of back muscles during intermittent isometric contractions: a study of neuromuscular activation patterns

BACKGROUND: Gender difference in the fatigability of muscles can be attributed to muscle mass (or strength) and associated level of vascular occlusion, substrate utilization, muscle composition, and neuromuscular activation patterns. The purpose of this study was to assess the role of neuromuscular activation patterns to explain gender differences in back muscle fatigability during intermittent isometric tasks. METHODS: Sixteen males and 15 females performed maximal voluntary contractions (Strength) and a fatigue test to exhaustion (fatigue criterion=time to exhaustion), while standing in a static dynamometer measuring L5/S1 extension moment. The fatigue test consisted of repetitions of an 8-s cycle (1.5 s ramp to reach 40% of maximal voluntary contraction +5s plateau at 40% of maximal voluntary contraction +1.5s rest). Surface electromyography signals were collected bilaterally from 4 back muscles (multifidus at the L5 level, iliocostalis lumborum at L3, and longissimus at L1 and T10). FINDINGS: Males were stronger (P<0.05) than females (316, SD 82>196, SD 25 Nm) but showed significantly shorter time-to-exhaustion values (7.1, SD 5.2<13.0, SD 6.1 min.), the latter result being corroborated by electromyographic indices of fatigue. However, the gender effect on time to exhaustion disappeared when accounting for Strength, thus supporting the muscle mass hypothesis. Among the various electromyographic indices computed to assess neuromuscular activation patterns, the amount of alternating activity between homolateral and between contralateral muscles showed a gender effect (females>males). INTERPRETATION: These results support the muscle mass hypothesis as well as the neuromuscular activation hypothesis to explain gender differences in back muscle fatigability.     

Neuromuscular efficiency of the sternocleidomastoid and anterior scalene muscles in patients with chronic neck pain

Purpose:?This study compared the neuromuscular efficiency (NME) of the sternocleidomastoid (SCM) and anterior scalene (AS) muscles between 20 chronic neck pain patients and 20 asymptomatic controls.

Method:?Myoelectric signals were recorded from the sternal head of SCM and the AS muscles as subjects performed sub-maximal isometric cervical flexion contractions at 25 and 50% of the maximum voluntary contraction (MVC). The NME was calculated as the ratio between MVC and the corresponding average rectified value of the EMG signal. Ultrasonography was used to measure subcutaneous tissue thickness over the SCM and AS to ensure that differences did not exist between groups.

Results:?For both the SCM and AS muscles, NME was shown to be significantly reduced in patients with neck pain at 25% MVC (p?<?0.05). Subcutaneous tissue thickness over the SCM and AS muscles was not different between groups.

Conclusions:?Reduced NME in the superficial cervical flexor muscles in patients with neck pain may be a measurable altered muscle strategy for dysfunction in other muscles. This aberrant pattern of muscle activation appears to be most evident under conditions of low load. NME, when measured at 25% MVC, may be a useful objective measure for future investigation of muscle dysfunction in patients with neck pain.     

The reliability of isometric strength and fatigue measures in patients with knee osteoarthritis

Patients with knee osteoarthritis have both poor strength and endurance of their quadriceps muscles. It is possible to assess muscle fatigue by monitoring frequency spectrum using electromyography (EMG). This study used the closed kinetic chain approach to muscle assessment. Fifty-five subjects with knee osteoarthritis were examined twice within 1 week. To test maximum voluntary isometric contraction into extension an isokinetic dynamometer, with a closed kinetic chain "leg press" attachment was used. EMG assessment of signal median frequency was done by measuring median frequency shift associated with fatiguing of muscle during a 60s isometric contraction at 60% of maximum isometric contraction. Intra-class correlation coefficients with 95% confidence intervals, standard errors of measurement and smallest detectable differences were calculated. Results showed the reliability of the maximum voluntary isometric contraction extension strength test was ICC 0.99 and SEM 3.95Nm. The initial median frequency indices also demonstrated excellent ICC and SEM statistics (ICC 0.84-0.91, SEM 9.2-11Hz) for the three heads of the quadriceps; however, the fatigue slopes for all three muscles were unreliable with poor ICCs (0.04-0.72) and SDD values (2207-4000%). The assessment of peak muscle torque using a closed kinetic chain isometric technique is reliable, as is the determination of median frequency values for the quadriceps. Error for the assessment of fatigue was of an unacceptable scale. While the use of a closed kinetic chain leg press technique provides a reliable measurement of lower limb strength, EMG power spectrum decrease during an isometric contraction is of little value.     

Idiopathic Headaches: A Neuropsychological and Computerized Electromyographic Study

SYNOPSIS
Considerable disagreement is found in the literature regarding the correlations between the degree of the electromyographically recorded tension of the head and cervical muscles, and muscle contraction headache.
31 patients were admitted to the study and divided into 3 groups according to the diagnostic criteria of Ad Hoc Committee: vascular headache, muscle tension and mixed headache, in addition to 5 control subjects. The EMG recording was carried out with superficial electrodes on neck muscles during rest conditions (base EMG), under stress conditions (stress EMG), and finally during isometric contraction against resistance (max EMG).
The exclusion from the study of patients with clinical characteristics definable as "psychogenic" headaches made it possible to obtain a homogeneous sample of patients with the diagnosis of muscle tension headache.
Higher values of muscle tension in the group of patients suffering from muscle tension headache as compared to other groups of patients and to control subjects were found.     

Temporal effects of isometric contraction maneuvers on threshold sural amplitude

OBJECTIVE: To investigate the effect of isometric biceps brachii contraction and neck flexion on the time course of threshold sural amplitude. DESIGN: Twelve healthy subjects, who were asked to lie supine on an examination bench, performed 1 min of muscle contraction. The sural sensory nerve action potential was recorded before, immediately after, and at 2-min intervals after muscle contraction. The preexercise level of stimulus intensity remained unchanged for sural readings throughout the entire course of the experiment. RESULTS: The temporal changes in sensory nerve action potential amplitudes for both maneuvers were similar (P = 0.9734, two-way interaction). The mean sural amplitude after neck flexion increased from 6.0 +/- 2.9 microV (SD) to 10.6 +/- 6.6 microV (SD) 10 min after contraction. Similarly, mean sural amplitude increased from 6.5 +/- 1.8 microV (SD) to 14.5 +/- 9.7 microV (SD) 8 min after biceps brachii contraction. Statistical analysis performed using repeated measures with post hoc least significant difference showed a significant temporal effect in the two groups (P = 0.04). CONCLUSION: The temporal responses of threshold sural amplitudes after isometric biceps brachii contraction and central reinforcement neck flexion maneuvers are nearly identical with regard to increase in the amplitude.     

Cervical muscles weakness in chronic whiplash patients

BACKGROUND: Isometric cervical strength has been used for assessing the severity of cervical spine pathologies. However there is a conspicuous dearth of information relating to cervical strength data in patients suffering from chronic whiplash. Therefore the objective of this study was to compare absolute and ratio-based isometric cervical strength scores in chronic whiplash patients with reported corresponding scores in healthy subjects. METHODS: Isometric cervical strength was measured in the directions of flexion, extension, right and left lateral flexion in 97 patients, 51 women and 46 men, using a wall-mounted dynamometer. FINDINGS: Compared to published values of normal subjects, whiplash patients suffered sharp reductions of about 90% in both genders and in all directions. The consistency of the isometric cervical strength scores as indicated by the mean coefficient of variation was relatively low, 17% and 20% in men and women respectively. The flexion/extension strength ratio ranged 0.8--0.9, slightly higher than the reported range for normal subjects. This ratio was highly correlated (r=0.91, P=0.01) with the mean coefficient of variation in a subgroup of 9 patients. INTERPRETATION: In the absence of an obvious reason such as sever atrophy or grossly dysfunctional neurological control the indicated weakness of the cervical muscles may be associated with learned pain avoidance behavior which is typical among this group of patients.     

颈部肌群等长抗阻训练配合针刺及牵引疗法治疗颈型颈椎病的临床研究

目的:探讨颈部肌群等长抗阻训练配合针刺加牵引疗法治疗颈型颈椎病生理曲度异常的临床疗效。方法:将符合纳入标准的84例颈型颈椎病患者按照随机化原则平均分为2组,2组均给予针刺、牵引治疗,观察组另外给予颈部肌群等长抗阻训练。结果:治疗10次、20次后,2组症状体征积分、VAS、NDI评分均较治疗前明显降低(P0.01),观察组治疗10次、20次后状体征积分、NDI评分更低于对照组(P0.05,0.01),治疗10次后,2组VAS评分差异无统计学意义,治疗20次后,观察组VAS评分更低于对照组(P0.05)。2组颈椎生理曲度测量值较治疗前均明显增加(P0.05),观察组更大于对照组(P0.05)。2组临床疗效比较,观察组临床愈显率明显优于对照组(P0.05)。结论:颈部肌群等长抗阻训练有利于颈椎生理曲度异常的恢复或纠正。     

Quantifying human muscle strength, endurance and fatigue

Physiologic methods have been developed to objectively quantify muscle strength, endurance, and fatigability. Isometric force and rectified/integrated electromyogram were simultaneously recorded during the three phases of a recording session: pre-fatigue, fatigue (1 min duration) and post-fatigue recovery (up to 10 min). Five parameters of muscle performance were computed: Maximum force (MF) exerted during isometric voluntary contraction (muscle strength); Force-time integral--area under force-time plot (endurance); Fatigue index (FI) (% reduction in MF); Neuromuscular efficiency (force/mV of EMG recruited), and Recovery time (RT). Normal values based on data from 20 normal subjects were determined for four muscles: index finger abductor, elbow flexors, knee extensors, and ankle dorsiflexors. Neuromuscular efficiency (NME) decreased significantly (20 to 70%) at the end of the fatigue phase; it generally increased to the pre-fatigue level in 2 to 10 min, during the recovery phase. The period needed to reach pre-fatigue level was referred to as RT. The elbow flexors had the highest mean FI (48%) and the longest RT (greater than 6 min); the ankle dorsiflexors had the lowest mean FI (34%) and the shortest RT (1.5 min). These methods have been used also to evaluate the effects of weight training in two patients with neuromuscular disorders.