Computer analysis of the surface EMG during isometric exercise

doi:10.1016/0010-4825(80)90025-6

Computers in Biology and Medicine

Volume 10, Issue 2, 1980, Pages 83-95

https://doi.org/10.1016/0010-4825(80)90025-6 Get rights and content

Abstract

A computer program is described which can provide either on-line or off-line analysis of the surface electromyogram (EMG) in man during submaximal isometric contractions. The intention of the program was to quantify the tension developed by, and the degree of fatigue induced in muscle during this form of exertion from the surface EMG. Six male and female volunteers served as subjects to test the program by exerting brief isometric contractions of their handgrip muscles at tensions ranging from 3 to 100% of their maximum strength and fatiguing isometric contractions at tensions ranging between 20 and 95% of their maximum strength. The results of these experiments showed that the program was able to estimate the tension developed by muscle within an average of 2.4% of the subject's maximum strength and estimate the duration of fatigue contractions within an average of 3.5% of the actual recorded endurance. The applications of this form of analysis to work physiology are discussed.

References (29)

R.D. Fusfeld
Analysis of electromyographic signals by measurement of wave duration
Electroenceph. clin. Neurophysiol.
(1971)
B. Bigland et al.
The relation between force, velocity, and integrated electrical activity in human muscles
J. Physiol.
(1971)
F.S. Cenkovich et al.
Fourier analysis of the normal human electromyogram
Am. J. Physiol. Med.
(1963)
D.B. Chaffin
Electromyography — a method of measuring local muscle fatigue
J. Methods — Time Measurements
(1969)
H. Clamann
Activity of single motor units during isometric tension
Neurology
(1970)
R.S.J. Clarke et al.
The duration of sustained contractions of the human forearm at different muscle temperatures
J. Physiol., Lond.
(1958)
S. Cobb et al.
Electromyographic studies of muscular fatigue in man
Am. J. Physiol.
(1923)
A. Dasgupta et al.
Relation between firing frequency of motor units and muscle tension in the human
Electromyography
(1962)
H.A. De Vries
Method of evaluation of muscle fatigue and endurance from electromyographic curves
Am. J. phys. Med.
(1968)
R. Eason
Electromyographic study of local and generalized muscular impairment
J. appl. Physiol.
(1960)

R.G. Edwards et al.

The relation between force and the integrated electrical activity in fatigued muscle

J. Physiol., Lond.

(1956)

R.H.T. Edwards et al.

Effect of temperature on muscle energy metabolism and endurance during successive isometric contractions sustained to fatigue of the quadriceps muscle in man

J. Physiol., Lond.

(1972)

E. Kaiser et al.

Muscle action potentials studied by frequency analysis and duration measurements

Acta neurologica scand.

(1965)

J. Karlsson et al.

Constituents of human muscle in isometric fatigue

J. appl. Physiol.

(1975)

Cited by (35)

Interrelationships between body fat and skin blood flow and the current required for electrical stimulation of human muscle
2008, Medical Engineering and Physics
There is variability between individuals in the current needed to elicit a contraction in human muscle with surface electrodes. To understand what might be causing some of this variability, 25 subjects whose average age was 24.4 ± 2.3 years, whose height was 165.5 ± 9.5 cm, and whose average weight was 70.3 ± 21 kg were examined. Electrical stimulation was applied above the motor point of the quadriceps, biceps, and lateral gastrocnemius muscles. To assess body fat, 2D ultrasound was used with a 1 cm stand off. Electrical stimulation was applied with sine wave stimulation at 100 μs pulse width and at a frequency of 30 Hz. To alter skin blood flow, aside from the natural difference in skin blood flow at rest, hot packs and cold packs were used for 5 min. The average fat thickness below the quadriceps and gastrocnemius muscles was 0.75 ± 0.13 cm and under the biceps was 0.48 ± 0.16 cm. Without the use of hot or cold packs, the currents for the quadriceps and gastrocnemius muscles were significantly higher than that of the biceps (p < 0.01). While there was some relationship between stimulation current and blood flow without the application of hot or cold packs, when hot packs were applied, skin blood flow increased as did the current required to stimulate muscle to threshold. When cold packs were applied, there was a decrease in the current required to stimulate these muscles. In conclusion, there is a causal relationship between skin blood flow, the thickness of the fat layer below the skin, and the current required to stimulate the muscle.
The nature of the sense of effort and its neural substrate
2006, Revue Neurologique
Quels sont la nature et le substratum neural de la perception de la force musculaire volontaire ? État des connaissances. Les données expérimentales démontrent que des signaux efférents dérivés de la commande motrice jouent un rôle dominant dans le processus par lequel la force volontaire est perçue. Ceci signifie que la perception de la force volontaire est réalisée, avant tout, par l’intermédiaire d’un sens de l’effort, et non pas par l’intermédiaire d’un sens de la tension intramusculaire. De nombreuses études montrent néanmoins que les informations en provenance des capteurs sensoriels participent au sens de l’effort. Leur rôle ne consiste pas à engendrer un signal d’effort, mais plutôt à moduler et à calibrer l’intensité de celui-ci. Les études de neuro-imagerie et de neuropsychologie révèlent par ailleurs que de nombreuses structures corticales participent à la perception de la force musculaire volontaire. Perspectives et conclusion Dans ce type de tâche, les ganglions de la base pourraient assurer la mise en cohérence de l’activité corticale.
What are the nature and the neural substrate of voluntary force perception? State of art. Experimental findings demonstrate that efferent signals related to motor command play a dominant role in perceiving voluntary muscular force. This suggests that voluntary force perception is provided through a sense of effort and not through a sense of intramuscular tension. Nevertheless, experimental data show that the contribution of sensory input to effort awareness must not be dismissed. Sensory signals are not involved in generating a signal of effort but rather in calibrating and modulating its magnitude. Neuroimaging and neuropsychological studies revealed that many cortical structures are activated during tasks of voluntary muscular force perception. Perspectives and conclusion. In such tasks, the basal ganglia might support the coherence of cortical activity.
Electromyographical indication of muscular fatigue in occupational field studies
2000, International Journal of Industrial Ergonomics
Citation Excerpt :
The most often used measures to characterize EMG power spectral distribution are the Median Frequency (MF) according to Stulen and De Luca (1981) and the Mean Power Frequency (MPF) as defined by Kwatny et al. (1970). Measurements have been performed to study the MPF and MF as a function of the muscular force and torque level during both static and dynamic contractions (e.g. Komi and Viitasalo, 1976; Viitasalo and Komi, 1977, 1978; Petrofsky, 1980; Petrofsky and Lind, 1980; Petrofsky et al., 1982; Hagberg and Ericson, 1982; Broman et al., 1985; Moritani and Muro, 1987; Nagata et al., 1990; Bilodeau et al., 1990, 1991, 1992a, b). A collation of literature data regarding the relationship between the force and both spectral measures is provided for studies on extremity muscles in Fig. 2.
Surface electromyography offers a valuable tool for the indication of muscular fatigue in occupational field studies. For this purpose, the time course of the electromyogram (EMG) has to be analysed, in order to detect typical fatigue-induced changes such as an increase in EMG amplitude or a shift in the spectral distribution towards lower frequencies. Such procedures need a detailed knowledge about the actual activity of the person and muscle under test for the total working time. This can be attained by encoding the activity of the person during the work and recording an electrical code signal together with the electrophysiological signals. For the indication of muscle fatigue, EMGs for situations connected with similar muscle load should only be compared, since the EMG amplitude as well as the spectrum do not only depend upon the fatigue state, but also upon the produced muscle force. This demand can be fulfilled by (i) interrupting the work and performing test contractions of known force in a predefined body posture or (ii) by comparing situations connected with a certain reference activity. (iii) In a recently developed approach for the joint analysis of EMG amplitude and spectrum (JASA) changes in the amplitude and the spectrum are considered simultaneously. This method permits the discrimination between fatigue-induced and force-related EMG changes. Using this procedure, changes in the EMG can be attributed to categories like fatigue or recovery as well as increase or decrease in the force production of the muscle under test. Applications from field studies during manual materials handling in a weaving mill, price recording at scanner checkouts in a supermarket and the performance of surgical work using endoscopic operation techniques in urology demonstrate the appropriateness of electromyography for fatigue indication in occupational physiology and ergonomics. Nevertheless, the commonly used measures of muscular fatigue such as increase in EMG amplitude and left shift in EMG spectrum are primarily related to the electrical activation and its propagation along the muscle fibres. Their connection to the fatigue-induced reduction in the force generating capacity of the muscle under test includes complex physiological implications. Therefore, the need for further development of fatigue indicators which are more directly related to muscular force is recognized.
Relevance to industry
In occupational health and ergonomics indication of muscular fatigue is needed, since activities inducing muscular fatigue can be performed for a limited time, only, and the quality of work can be influenced negatively. Electromyography offers valuable tools for the indication of fatigue and the appropriate assessment of ergonomic design measures.
The effects of mats on back and leg fatigue
1994, Applied Ergonomics
Prolonged standing is common in many industrial workplaces. It is also quite common for workers to complain of discomfort in the back and legs as a result of prolonged standing. Mats are often provided for the worker to relieve this fatigue. However, there is no quantitative evidence that these mats relieve leg and back fatigue. Five subjects were asked to stand on a concrete surface and two mat surfaces for prolonged periods of time. Spectral electromyographic analyses indicated that mats reduced localized muscle fatigue in the erector spinae muscle only. Furthermore, this fatigue reduction occurred only with the more compressible of the two mats tested. These results imply that localized muscular fatigue in the leg may not be relieved with ‘anti-fatigue’ mats, and some of these mats only benefit the back.
On the assessment of muscle fatigue rate via various EMG frequency spectral parameters
1989, International Journal of Industrial Ergonomics
A research study was undertaken to investigate the fatigue process of quadriceps muscle during sustained isometric contraction at several work load levels using root-mean-squared (RMS) voltage and frequency parameters of EMG frequency spectral distribution. Its objective was to evaluate the possibility of using those parameters to indicate muscle fatigue rate. Twelve male subjects participated in an experiment which required them to exert and maintain isometric knee extension forces at 25%, 40%, 55%, and 70% of their maximal voluntary contraction (MVC) force levels. The results showed that both initial mean power frequency (MPF) and median power frequency (MF) (as determined from MPF and MF versus time curves) were not significantly influenced by muscle contraction level (p > 0.1). RMS voltage, MPF, and MF linear slopes, on the other hand, were significantly correlated to muscle contraction level ( $p < 0.001$ ) which suggested that they could be used to represent muscle fatigue rate. The exponential relationship found in this study showed that quadriceps fatigued at an increasing rate as the work load increased. Further, an improvement in the coefficient of correlation between their linear slopes and muscle work load was found when expressing muscle work load in terms of the ratio of force to body weight. This finding indicated the possibility of using body weight as a basis of determining work load level which could help to improve the quality of quantitative assessment of muscle fatigue.
Motor preparation and the achilles tendon reflex: The role of background muscle tension
1986, Biological Psychology
The effects of instructed tension or relaxation of the soleus muscles on the amplitude of the Achilles tendon reflex were investigated. Reflexes were evoked during the foreperiod of a warned reaction time experiment with a plantar flexion of the right foot serving as the response, and during isometric contractions of the right soleus muscle at different low levels of tension. The tension levels were related to the subject's maximal voluntary contraction force. The results were comparable in the two tasks. When background muscle tension was present in the right leg the reflexes in that leg were depressed, whereas in the contralateral leg reflexes were increased. This difference in amplitude was roughly proportional to the amount of tension and independent of whether the antagonist muscle was also activated during the contraction. It was argued that the differential reflex effect found in the two soleus muscles during motor preparation need not be a reflection of a selective neural inhibition. It could also be explained by a reduced effectiveness of the tendon tap in stretching the muscle, due to stiffening of the muscle during contraction. It was concluded that during motor preparation, only reflex changes recorded in the absence of muscle tension can be considered reflections of subliminal changes in spinal reactivity.

View all citing articles on Scopus

View full text

Computer analysis of the surface EMG during isometric exercise

Abstract

Electroenceph. clin. Neurophysiol.

The relation between force, velocity, and integrated electrical activity in human muscles

J. Physiol.

Fourier analysis of the normal human electromyogram

Am. J. Physiol. Med.

Electromyography — a method of measuring local muscle fatigue

J. Methods — Time Measurements

Activity of single motor units during isometric tension

Neurology

The duration of sustained contractions of the human forearm at different muscle temperatures

J. Physiol., Lond.

Electromyographic studies of muscular fatigue in man

Am. J. Physiol.

Relation between firing frequency of motor units and muscle tension in the human

Electromyography

Method of evaluation of muscle fatigue and endurance from electromyographic curves

Am. J. phys. Med.

Electromyographic study of local and generalized muscular impairment

J. appl. Physiol.

The relation between force and the integrated electrical activity in fatigued muscle

J. Physiol., Lond.

Effect of temperature on muscle energy metabolism and endurance during successive isometric contractions sustained to fatigue of the quadriceps muscle in man

J. Physiol., Lond.

Muscle action potentials studied by frequency analysis and duration measurements

Acta neurologica scand.

Constituents of human muscle in isometric fatigue

J. appl. Physiol.