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Central and Peripheral Fatigue in Sustained Maximum Voluntary Contractions of Human Quadriceps Muscle

July 1978
Clinical Science 54(6):609-14

Source
PubMed

Authors:

Manchester Metropolitan University

1. The fatigue of force that occurs during the first 60 s of a maximum voluntary contraction of the human quadriceps has been examined by comparing the voluntary force with that obtained by brief tetanic stimulation at 50 Hz in nine healthy subjects. In three subjects the voluntary force declined in parallel with the tetanic force whereas in the remainder it fell more rapidly, suggesting that central fatigue was present. 2. For those subjects who showed little or no central fatigue, surface electromyograph (EMG) activity remained approximately constant while the force declined by about 60%. In the others, EMG activity and force declined in parallel but when an extra effort was made the subjects could briefly increase their force and this was accompanied by a proportionately greater increase in EMG activity (generally up to the original value). 3. It is concluded that in sustained maximum voluntary contractions of the quadriceps (a) central fatigue may account for an appreciable proportion of the force loss, (b) surface EMG recordings provide no evidence that neuromuscular junction failure is the limiting factor determining the loss of force in this muscle.

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Clinical Science and Molecular Medicine

(1978) 54,609-614

Central and peripheral fatigue in sustained maximum

voluntary contractions of human quadriceps muscle

BIGLAND-RITCHIE*, D. A. JONES, G. P. HOSKING AND

R. H. T. EDWARDSt

Jerry

Lewis Muscle Research

Centre,

Royal

Postgraduate Medical

School,

London

(Received 9

May

1977;

accepted 4 January

1978)

Summary

The fatigue of force that occurs during the

first 60 s of a maximum voluntary contraction of

the human quadriceps has been examined by com-

paring the voluntary force with that obtained by

brief tetanic stimulation at SO Hz in nine healthy

subjects. In three subjects the voluntary force

declined in parallel with the tetanic force whereas in

the remainder it fell more rapidly, suggesting that

central fatigue was present.

For those subjects who showed little or no

central fatigue, surface electromyograph (EMG)

activity remained approximately constant while the

force declined by about 60%. In the others, EMG

activity and force declined in parallel but when an

extra effort was made the subjects could briefly

increase their force and this was accompanied by a

proportionately greater increase in EMG activity

(generally up to the original value).

It is concluded that in sustained maximum

voluntary contractions of the quadriceps (a) central

fatigue may account for an appreciable proportion

of the force loss, (b) surface EMG recordings pro-

vide no evidence that neuromuscular junction

failure is the limiting factor determining the loss of

force in this muscle.

•Present address: Quinnipiac College, Hamden, Conn.

06518,

U.S.A.

f Present address: Department of Human Metabolism, Uni-

versity College Hospital Medical School, University Street,

London WC1E6JJ.

Correspondence: Professor R. H. T. Edwards, Department of

Human Metabolism, University College Hospital Medical

School, University Street, London WC1E 6JJ.

Key words: fatigue, muscle, quadriceps, voluntary

contraction.

Abbreviations: EMG, electromyograph; MVC,

maximum voluntary contraction.

Introduction

Force fatigue during maximum voluntary muscular

contractions (MVC) may occur from failure either

at the neuromuscular junction or at sites proximal

or distal to this. Failure proximal to the junction

may be the result of a decreased voluntary effort,

change in motor neuron excitability (direct or due

to inhibition of afferents from the muscle) or to pre-

synaptic block. Which, if any, of these may limit

the extent of voluntary contractions has been the

subject of controversy in the last 50 years (Reid,

1928;

Merton, 1954). A failure of transmission at

the neuromuscular junction may arise from either a

loss of excitability of the postjunctional membrane

or from depletion of acetylcholine stores. Distal

failure may arise if action potentials fail to

propagate, if coupling between the action potential

and the release of

calcium

fails within the

fibre,

or if

the contractile elements fail to function correctly.

We have examined the ability of normal subjects to

maintain maximum voluntary isometric con-

tractions of the quadriceps for periods up to 60 s.

Force and surface electromyograph (EMG) ac-

tivity have been measured and the response of part

of the muscle to maximal electrical stimulation at

different times during the MVC and has been used

609

610

Bigtand-Ritchie et al.

as an index of muscle contractility that is indepen-

dent of central drive.

This work follows our previous studies of

quadriceps muscle function (Edwards, Young,

Hosking & Jones, 1977) and was designed to help

answer the question 'Does the fatigue (i.e. failure to

generate the required force) arise because the

muscle machinery is failing, or because the subject

is not willing to go on driving it with the same

motivation as at the start?'.

Methods

Subjects

We studied nine healthy adult laboratory person-

nel (one female; ages 25-50 years) who were

familiar with the procedures and gave their

informed consent as required by the local Research

Ethics Committee. Both legs were studied and no

consistent differences in the ability to maintain

force were detected.

Measurements of force

The blood supply to leg muscles is occluded

during isometric contractions of more than about

20%

of the maximal voluntary force (Barcroft &

Millen, 1939; Edwards, Hill & McDonnell, 1972),

but since many of the present experiments involved

interruption of the contraction for brief periods of

stimulation, a cuff around the upper thigh was

inflated to 200 mmHg throughout to prevent any

return of blood supply. The force produced by iso-

metric contractions of the quadriceps muscle was

measured with a strain gauge attached to the ankle

while the subject was seated in an adjustable chair

(Edwards et al., 1977) and recorded on a u.v.

oscillograph.

Surface EMG was recorded with two adhesive

cup electrodes filled with electrode paste, one

situated on the skin over the lower third of the

vastus lateralis muscle, the other over the tendon

on the lateral aspect of the knee. An earth electrode

was placed on the lower leg. The EMG activity was

amplified, rectified, smoothed with a time constant

of 0-2 s and displayed on a u.v. oscillograph.

Electrical stimulation

Stimulation of the quadriceps, either per-

cutaneously with surface pad electrodes or by

localized stimulation of the femoral nerve, was

carried out as previously described (Edwards, Hill

& Jones, 1975; Edwards et al., 1977) with a short

stimulus pulse duration (50 ßs) so as to limit

excitation to nerve branches in the muscle. Direct

excitation of human muscle fibres required longer

pulses (100-500 μβ) when studied in vitro (Moulds,

Young, Jones & Edwards, 1977).

Results

To maintain a maximal isometric contraction

(MVC) of the quadriceps for 60 s takes a con-

siderable effort. During the first 30 s discomfort is

mild but between 30 and 45 s pain in the thigh

becomes increasingly severe. There is a pro-

gressive change in the perceived sensations from

the leg with the result that a subject, without visual

feedback, is uncertain of the force exerted towards

the end of the contraction. Pain in the thigh is not

due to ischaemia alone since it largely disappears

as soon as the contraction ceases, even when the

cuff around the thigh remains inflated. To reduce

variation due to pain the results presented here are

all from subjects experienced in the experimental

procedures.

Time course of a sustained MVC

Subjects were first asked to make a series of brief

maximal contractions, the highest of which was

taken as 100% MVC. Aided by visual feedback

subjects were then asked to maintain a contraction

as close as possible to this maximum for 60 s.

During this period force fell to about 30% of the

initial level, but the precise time course varied be-

tween individuals. The consistent performances of

the two subjects with the greatest difference in the

time course are shown in Fig. 1, the records having

been made on several occasions over a 2 months

period.

Central and peripheral fatigue

In one subject the maintained maximum volun-

tary force was compared with the force obtained by

supramaximally stimulating the muscle via the

femoral nerve. In the unfatigued muscle the MVC

was matched by stimulating at 50 Hz, at which

frequency a fully fused tetanus of the quadriceps

develops (Edwards et al., 1977). During each

tetanus the stimulus voltage was increased to con-

firm that nerve stimulation was supramaximal. The

subject then held a MVC which was interrupted

every 15 s for a brief period of stimulation at 50 Hz

(Fig. 2a).

Human muscle fatigue 611

The voluntary and stimulated contractions fell to

a similar extent during the first 30 s. Thus fatigue

during this period could only be due to a failure at

or distal to the neuromuscular junction. After 45 s

the voluntary force was less than the force

produced by the test tetani, indicating that in this

later period a loss of central neural drive con-

tributed to the force fatigue.

Femoral nerve stimulation is painful and carries

a risk of dislocating the patella, whereas per-

cutaneous stimulation of about 50% of the quad-

riceps with large pad electrodes is quite acceptable

(Edwards et al., 1977). Heat measurements during

stimulated and maximal voluntary contractions

indicate that percutaneous stimulation can maxi-

mally activate a portion of the muscle (Edwards,

1975).

The experiment was repeated with the same

subject but, instead with percutaneous stimulation

of the quadriceps at 50 Hz, activating 48% of the

muscle (Fig.

2b,

initial value).

During the first part of

the

MVC voluntary and

stimulated force fell to a similar degree. Thereafter

the voluntary force fell more than the tetanic force

so that the stimulated contraction became 80% of

the voluntary force after 60 s (Fig.

2b).

The relative

changes in the voluntary and stimulated forces

were very similar to those seen in the same subject

with femoral nerve stimulation (Fig. 2a). This

indicates that percutaneous stimulation of

portion

of the muscle can be used to determine function

independently of central drive.

Possible fatigue of the central neural drive during

60 s MVC was assessed, with percutaneous

stimulation, in all subjects. Central fatigue was

considered to be present when the MVC force

declined more rapidly than did the tetanic force

produced by the brief stimulated contractions.

the

nine subjects studied, four showed little or

no central fatigue. In five it amounted to between

24 36

Time (s)

FIG.

1. Time course of uninterrupted maximum voluntary con-

tractions (MVC) of the quadriceps. Subjects were asked to hold

a MVC for 1 min. Points are the mean (±1

SD)

of four separate

contractions for subject D.O. (#), and six contractions for

subject G.H. (O). Force is expressed as a percentage of the

initial value.

•3

140

(a)

500

Time (s) 60

FIG.

2. Comparison of the force obtained by electrical stimulation with the voluntary force during a sustained

maximum voluntary contraction (MVC) of the quadriceps, (o) Femoral nerve stimulation: stimulus marker (shaded

area) gives a record of the stimulation voltage and duration.

(A)

Percutaneous stimulation. Duration of stimulation (at

constant voltage) is indicated by the shaded areas. Force (newtons) and time scales apply to both

records.

Values given

just below the stimulus markers are the tetanic force as a percentage of the voluntary force measured immediately

before the tetani. Results in (a) and (6) are from the same subject.

612

Bigland-Ritchie et al.

Time (s) 45

100

400

g 300

<Ü

200

100

150

100

50 W5

20 30

Time (s) 50

FIG.

3. Force and smoothed, rectified EMG (SREMG) during sustained maximum voluntary contraction (MVC) of

quadriceps in (a) a subject (D.O.) with no central fatigue and (4) in subject D.J. with central fatigue; 'extra efforts'

were made at times shown by the arrows. Force scale is in newtons. The smoothed, rectified EMG is given as a per-

centage of the value at the start of

the

MVC.

10 and 30% of the force loss after 60 s of sustained,

uninterrupted contraction. With practice, the de-

gree of central fatigue generally became less though

these subjects were not able completely to over-

come it.

Surface EMG activity during sustained MVC

The smoothed, rectified EMG activity and force

were measured at intervals throughout the con-

traction in seven of the subjects (Fig. 3). To show

how these vary the ratio of the smoothed, rectified

EMG divided by the force (here called the E/T

ratio) as first used by Stephens & Taylor (1972) is

shown in Fig. 4. The subjects could be divided into

two groups. In group 1, where the smoothed,

rectified EMG declined roughly in proportion to

the fall in force (resulting in relatively constant

E/T

ratios), all the four subjects showed central

fatigue when previously tested, as described above.

In group 2 the smoothed, rectified EMG increased

during the first 10-15 s and then remained high

while the force fell to between 20 and 35% of the

5 ·

Group 2

Group 1

FIG.

4. Relationship between smoothed, rectified EMG

(SREMG) and force during prolonged maximum voluntary con-

traction (MVC) in seven subjects. The SREMG is divided by

force (E/T ratio, ordinate) and the value at the start of

the

con-

traction expressed as 1·0. Group 2 subjects exhibited no central

fatigue but were in brief extra efforts able to achieve E/T ratios

close to those found in group 2 subjects.

fresh MVC. This gave E/T ratios three to five times

the control value at the end of the contraction. The

three subjects in this group had previously shown

no central fatigue.

Human

muscle fatigue 613

Subjects were asked to maintain a MVC and, at

15 s intervals, to make a brief extra effort. Subject

D.O.,

typical of those exhibiting little or no central

fatigue, showed the initial rise in smoothed,

rectified EMG to a value which was then main-

tained until near the end of the contraction (Fig.

3a).

When asked, he could produce virtually no

extra force nor was there any increase in the

smoothed, rectified EMG. The second subject

(DJ.),

in whom approximately 10% central fatigue

had been demonstrated, showed the same initial

rise in smoothed, rectified EMG but after about 10

s the smoothed, rectified EMG and force fell at the

same rate (Fig. 3b). When this subject made an

extra effort both smoothed, rectified EMG and

force increased momentarily but with a greater pro-

portional increase in the electrical activity. If the

ElT ratio was expressed as 1-0 at the start of the

contraction, it became

■

just before the

first

extra

effort, increasing to 1-7 during this brief effort.

After 30 s the value before was again 1-4,

increasing to 2-0 during the brief effort and for the

last effort the values were 1-7 and 2-9 respectively.

Although the 'before' values are similar to those

seen for the group 1 subjects shown in Fig. 4,

values during the brief extra efforts approached

those maintained by group 2 subjects. All the

subjects showing a fall in smoothed, rectified EMG

during the contraction could increase the level pro-

portionately more than the increase in force during

the extra efforts, thus briefly increasing the ElT

ratio.

Discussion

Our studies show that changes occurring proximal

to the neuromuscular junction (i.e. central fatigue)

can consistently account for up to 30% of

the

total

force loss even in apparently well-motivated sub-

jects during sustained contractions of the quad-

riceps. All subjects who showed evidence of central

fatigue could overcome this in brief extra efforts.

The results demonstrate that fatigue cannot be all

attributed to factors at, or distal to, the neuro-

muscular junction, without first ascertaining, par-

ticularly when studies are done on naive subjects,

that central components are not also present.

In experiments on the first dorsal interosseous

muscle Stephens & Taylor (1972) found that the

smoothed, rectified EMG and force declined in

parallel, resulting in a constant ElT ratio

(smoothed, rectified EMG divided by force) during

the first 60 s of the contraction. They interpreted

this to show that fatigue was mainly due to failure

of neuromuscular transmission, having excluded

central fatigue because the evoked synchronous

muscle action potential was also shown to de-

crease.

Although

number of

our

subjects showed a

constant ElT ratio with contractions of the

quadriceps, we believe that for these subjects this

constancy could be accounted for by central

fatigue. For subjects without central fatigue the

smoothed, rectified EMG, after an initial rise,

remained fairly constant at a time when the force

was falling, so that the ElT ratio increased

throughout the contraction. Those subjects with

evidence of central fatigue could briefly increase

their ElT ratios to about the same level by making

brief extra efforts. Our findings for the quadriceps

therefore differ in this respect from those of

Stephens & Taylor (1972) for the first dorsal

interosseous.

The smoothed, rectified EMG signal recorded

during a contraction depends on the number, size

and distribution of active units in the muscle, the

size of the individual fibre action potentials, the

firing frequency and the degree of synchronization

of motor unit activity. The influence of

these

on the

surface recorded signal is not known, and we are

therefore reluctant to speculate about the site of

failure on the basis of smoothed, rectified EMG

data.

It was noticed that towards the end of a

sustained MVC subjects with little central fatigue

appeared actually to improve their voluntary per-

formance as compared with their response to

stimulation at 50 Hz. However, this effort seems

likely to arise from a diminished response to

stimulation at 50 Hz rather than an improvement

in voluntary performance. Parallel studies on the

adductor pollicis (B. Bigland-Ritchie, R. H. T.

Edwards & D. A. Jones, unpublished work) have

shown that fatigued muscle responds to stimulation

at 20 Hz better than at 50 Hz. As a practical con-

sideration, if muscle contractility is to be tested

during the course of a prolonged MVC, a 50 Hz

tetanus is appropriate at the start of the con-

traction but after about 30-45 s stimulation at a

lower frequency (20 Hz) is a better match to the

force of the voluntary contraction, so giving more

reliable information. This suggests that in order to

maintain optimum force during a fatiguing con-

traction the

firing

frequency of motor neurons must

decline, as has been observed (Marsden, Meadows

& Merton, 1971). The smoothed, rectified EMG

might therefore be expected to fall somewhat even

without any neuromuscular block.

In any investigation involving prolonged MVC

614

Bigland-Ritchie et al.

of the quadriceps the possibility

central fatigue

must

taken into account. We suggest that this

should

checked

comparing

the

voluntary

force with tetani

50 Hz during the first 30

s of

the contraction,

and at a

lower frequency there-

after.

would appear that central neural drive pro-

gressively falls during sustained MVC

but

that

subjects

can

overcome this tendency

various

degrees.

Acknowledgments

This work was supported

the Wellcome Trust

and

the

Muscular Dystrophy Group

Great

Britain and also

part by grant NS 09960 from

the U.S.P.H.S. to B.B.-R.

References

BARCROFT,

MILLEN,

J.L.E. (1939) The blood flow through

muscle during sustained contraction. Journal

Physiology

(London),

97,17-31.

EDWARDS,

R.H.T.,

HILL,

D.K. &

MCDONNELL,

M. (1972)

Myothermal

and

intramuscular pressure measurements dur-

ing isometric contractions

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Journal of Physiology (London), 224,

58P-59P.

EDWARDS,

R.H.T. (1975) Muscle fatigue. Postgraduate

Medical Journal, 51,137-143.

EDWARDS,

R.H.T.,

HILL,

D.K. &

JONES,

D.A. (1975) Heat pro-

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EDWARDS,

R.H.T.,

YOUNG,

A.,

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JONES,

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MARSDEN,

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P.A. (1971)

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MERTON,

P.A. (1954) Voluntary strength and fatigue. Journal

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MOULDS,

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Nov 2024
PLOS ONE

Over the course of the physical activity transition, machines have largely replaced skeletal muscle as the source of work for locomotion and other forms of occupational physical activity in industrial environments. To better characterize this transition and its effect on back muscles and the spine, we tested to what extent typical occupational activities of rural subsistence farmers demand higher magnitudes and increased variability of back muscle activity and spinal loading compared to occupational activities of urban office workers in Rwanda, and whether these differences were associated with back muscle endurance, the dominant risk factor for back pain. Using electromyography, inertial measurement units, and OpenSim musculoskeletal modeling, we measured back muscle activity and spinal loading continuously while participants performed occupational activities for one hour. We measured back muscle endurance using electromyography median frequency analysis. During occupational work, subsistence farmers activate their back muscles and load their spines at 390% higher magnitudes and with 193% greater variability than office workers. Partial correlations accounting for body mass show magnitude and variability response variables are positively associated with back muscle endurance (R = 0.39–0.90 [P < 0.001–0.210] and R = 0.54–0.72 [P = 0.007–0.071], respectively). Body mass is negatively correlated with back muscle endurance (R = -0.60, P = 0.031), suggesting higher back muscle endurance may be also partly attributable to having lower body mass. Because higher back muscle endurance is a major factor that prevents back pain, these results reinforce evidence that under-activating back muscles and under-loading spines at work increases vulnerability to back pain and may be an evolutionary mismatch. As sedentary occupations become more common, there is a need to study the extent to which occupational and leisure time physical activities that increase back muscle endurance helps prevent back pain.

Cycling Intensity Effect on Running Plus Cycling Performance among Triathletes

Article

Sep 2024

Running performance is crucial for triathlon performance. However, the prior bout of cycling may affect the running split time. This study compared the triathletes’ cycling plus running (C+R) time, when cycling was performed at three different intensities and running was maximal. A total of 38 athletes (21 males and 17 females) were included. Body composition, maximal oxygen uptake, and functional threshold power (FTP) was evaluated. The participants visited the laboratory three times to cycle 20 km at 80%, 85%, or 90% FTP (in randomized order) and run 5 km as fast as possible. Males ran faster after cycling at 80% FTP than after cycling at 90% FTP (mean difference=35.1 s; CI% 2.2, 68.1 s; p=0.035). The C+R time was faster when cycling at 90% FTP than at 80% FTP (mean difference=57.7 s; CI% 26.1, 89.3 s; p<0.001). For females, no significant difference was observed in the running time after cycling at 80%, 85%, or 90% FTP. The C+R time was faster when cycling at 90% FTP than at 80% FTP (mean difference=80.9 s; CI% 29.7, 132.1 s; p=0.002). In conclusion, to optimize triathlon performance, male and female athletes should cycle at a minimum of 90% FTP.

Supraspinal, spinal, and motor unit adjustments to fatiguing isometric contractions of the knee extensors at low and high submaximal intensities in males

Article

Full-text available

May 2024
J APPL PHYSIOL

Contraction intensity is a key factor determining the development of muscle fatigue and it has been shown to induce distinct changes along the motor pathway. The role of cortical and spinal inputs that regulate motor unit (MU) behaviour during fatiguing contractions is poorly understood. We studied the cortical, spinal, and neuromuscular response to sustained fatiguing isometric tasks performed at 20 and 70% of the maximum isometric voluntary contraction (MVC), together with MUs behaviour of knee extensors in healthy active males. Neuromuscular function was assessed before and after performing both tasks. Cortical and spinal responses during exercise were measured via stimulation of the motor cortex and spinal cord. High density electromyography was used to record individual MUs from the vastus lateralis (VL). Exercise at 70% MVC induced greater decline in MVC ( p = 0.023), and potentiated twitch force compared to 20%MVC ( p < .001), with no difference in voluntary activation ( p = 0.514). Throughout exercise, corticospinal responses were greater during the 20%MVC task (p < 0.001), and spinal responses increased over time in both tasks ( p ≤ 0.042). MU discharge rate increased similarly following both tasks ( p ≤ 0.043) while recruitment and de-recruitment thresholds were unaffected ( p ≥ 0.295). These results suggest that increased excitability of cortical and spinal inputs might be responsible for the increase in MU discharge rate. The increase in evoked responses together with the higher MUs discharge rate might be required to compensate for peripheral adjustments to sustain fatiguing contractions at different intensities.

The effect of fatigue on postural control in individuals with multiple sclerosis: a systematic review

Article

Full-text available

Nov 2023
BMC NEUROL

Background Fatigue is the most disabling symptom for individuals with multiple sclerosis (MS), which can significantly affect postural control (PC) by impairing the ability of the central nervous system to modulate sensory inputs and coordinate motor responses. This systematic review aimed to investigate the effect of fatigue on PC in individuals with MS.. Methods This systematic review is reported according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline and registered in PROSPERO with ID CRD42022376262. A systematic search was performed in the Web of Science, PubMed, Scopus, and Google Scholar until January 2023, and a manual search was performed using the reference lists of included studies. Two authors independently selected the studies, extracted data, and evaluated their methodological quality using the Downs and Black checklist. The process was later discussed with a third author.. Results Five studies were included in this review, of which consistent evidence investigating a direct relationship between fatigue and PC in individuals with MS. All the studies reported negative effects on PC. Four studies employed walking tests as their primary protocol for inducing fatigue, while one study implemented a strength testing protocol for both legs, serving as a fatigue-inducing activity. Conclusions The evidence suggests that individuals with MS may experience PC deficits due to fatigue. However, the present body of literature exhibits limitations regarding its quality and methodology. Gender differences, balance, fatigue task, and muscle function are essential factors that need to be considered when investigating the relationship between fatigue and PC deficits in MS. Further high-quality research is necessary to comprehend the complex interplay between MS-related fatigue and PC deficits after physical activity.

A Study of the Contractility, Biochemistry and Morphology of an Isolated Preparation of Human Skeletal Muscle

Article

Full-text available

Apr 1977
Clin Sci Mol Med

1. A new method of studying isolated human skeletal muscle has been evaluated. This involves the incubation and electrical stimulation of strips of muscle, obtained at surgical biopsy, that are tied at the cut ends of the fibre bundles. 2. Morphological examination showed that the fibres were sealed off at the cut ends. Damage appeared to be restricted to the areas immediately adjacent to the ties. 3. Contractile properties were well maintained for several hours and measurements of tissue metabolites showed that muscle contents of the high-energy phosphate compounds were well preserved. 4. The isolated preparations were found to have the same contractile properties as human quadriceps femoris studied in vivo by the methods described in the preceding paper. 5. Correlation was found between the relaxation speed of the isolated preparations and their fibre-type composition histochemically determined. 6. It is concluded that this technique is a valid addition to the present methods of studying the physiology and pharmacology of human skeletal muscle.

Human Skeletal Muscle Function: Description of Tests and Normal Values

Article

Full-text available

Apr 1977
Clin Sci Mol Med

1. The force produced by isometric contractions of the quadriceps muscle have been studied during maximal voluntary contractions and when a substantial part of the muscle was electrically stimulated via surface electrodes. 2. In normal children and adults, the force of a maximal voluntary contraction of the quadriceps was proportional to body weight. 3. The function of the quadriceps has been described in terms of the force/frequency curve, speed of relaxation and the rate of loss of force during 18 s stimulation at 30 Hz and 100 Hz. 4. The functional characteristics of adductor pollicis when stimulated via the ulnar nerve were essentially similar to those of the quadriceps. 5. Studies of the function of these two muscles are complementary since quadriceps femoris is amenable to needle biopsy investigations of its structure and chemistry whereas adductor pollicis is more suitable for electrophysiological studies.

Muscle fatigue

Article

Mar 1975

R. H. T. Edwards

Muscle fatigue is a common symptom but there are no universally accepted methods for quantitating the function of voluntary muscle. This paper describes three main methods of assessment: simple clinical tests of muscle function; thermal probe measurements of metabolic heat production during muscular contraction; needle biopsy studies of muscle structure and chemistry. These methods, though at a relatively early stage of development, have given promising results which suggest that they could be useful in assessing possible new forms of treatment in patients with neuromuscular disorders.

The Mechanism of Voluntary Muscular Fatigue.

Article

Sep 1927

Reid CH

Heat production and chemical changes during isometric contractions of the human quadriccps muscle (Abstract)

Article

Nov 1975

1. Development of a new thermal probe and use in conjunction with chemical analysis of needle biopsy samples, has made possible a thermodynamic study of the energetics of muscular contraction in the human quadriceps. 2. The observed rate of muscle temperature rise was proportional to the force of the contraction. During maximal contractions the rate of heat production was 54 +/-8-5 W/kg wet muscle (mean +/- s.d.). 3. The observed rates of muscle temperature rise agreed well with the rates calculated from the measured metabolite changes when standard values for the enthalpy changes of the reactions involved were used. 4. During prolonged stimulation of the quadriceps at 15/sec via the femoral nerve, the rate of heat production per unit force fell to nearly half the initial value. It is estimated that this represented a two- to fourfold increased in economy of ATP turn-over required to maintain a given force. 5. Relaxation becomes progressively slower during prolonged contractions and it is suggested that the slowing of relaxation and the increased economy of force maintenance may both be due to an increased cross-bridge cycle time in the fatigued muscle.

Fatigue of maintained voluntary contraction in man

Article

Feb 1972

1. The mechanism of fatigue has been studied in maintained maximal voluntary contractions of the first dorsal interosseous muscle of the hand. 2. Fatigue occurs in two phases. In the first, lasting 1 min, force falls to about 50%. The smoothed rectified e.m.g. (s.r.e.) falls with the same time course and the normal linear relation between s.r.e. and force of unfatigued muscle is preserved. 3. In the second phase, force falls relatively faster than s.r.e. 4. Arterial occlusion does not affect the first phase, but in the second phase causes force to fall to zero, whereas without occlusion it tends to stabilize at about 25%. 5. The size of the synchronous muscle action potential evoked by ulnar nerve stimulation falls to about 65% of normal, most of this fall occurring in the first phase. 6. During recovery after prolonged fatigue, the relation between force and s.r.e. is changed for weak voluntary contractions much more than for strong ones, such that force is less for a given s.r.e. than normal. 7. These results are interpreted as evidence that, in a maximal voluntary contraction, neuromuscular junction fatigue is most important at first, but later, contractile element fatigue increases, particularly when the blood supply is obstructed. 8. Neuromuscular junction fatigue is believed to be most marked in high threshold motor units, while contractile element fatigue more especially affects low threshold units.

Myothermal and intramuscular pressure measurements during isometric contractions of the human quadriceps muscle

Article