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

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

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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.

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HILL,

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MCDONNELL,

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Dec 2020

Etienne Gouraud

La drépanocytose est une maladie caractérisée par la production d’une hémoglobine mutée, l’hémoglobine S, dont les formes les plus répandues sont la forme homozygote S/S et double hétérozygote composite S/C. L’hémoglobine S possède la capacité de polymériser au sein du globule rouge en condition désoxygénée modifiant sa morphologie provoquant ainsi des complications cliniques multi-organiques. Ces patients présentent une capacité à l’exercice réduite dont les causes sont des altérations cardio-vasculaires cependant l’implication du muscle squelettique n’est pas encore totalement caractérisée dans la drépanocytose. En effet, le muscle squelettique drépanocytaire présente une amyotrophie, un remodelage profond de la microcirculation et une diminution de sa capacité à produire de la force cependant la présence d’une dysfonction musculaire à l’exercice n’a pas encore été décrite. Plusieurs études suggèrent que le stress oxydatif pourrait être élevé dans le muscle drépanocytaire expliquant ainsi en partie les altérations observées. Chez les sujets sains, l’exercice chronique aérobie est connu pour améliorer la capacité antioxydante musculaire notamment par l’augmentation de l’activité des enzymes antioxydantes. Cependant, les effets de ce type d’exercice sur le stress oxydatif n’ont pas encore été caractérisés dans la drépanocytose. Ainsi, les objectifs de cette thèse sont de 1) mettre en évidence une dysfonction musculaire chez des patients drépanocytaires S/S et S/C et de 2) déterminer les modifications induites par un exercice chronique aérobie sur le stress oxydatif au sein du muscle squelettique dans un modèle murin drépanocytaire. Lors d’une première étude, des sujets sains (A/A) et patients drépanocytaires S/S et S/C ont effectué un exercice mono-articulaire sous-maximal du quadriceps à une intensité correspondant à 25% de leur force maximale isométrique (Fmax) suivi d’un test de marche de 6 minutes (T6M). Fmax a été mesurée avant et après cet exercice mono-articulaire, et après le T6M et la perte de Fmax a été utilisée pour quantifier la fatigabilité musculaire. Au cours du protocole, les activités électromyographiques du Vastus Lateralis (VL) et du Vastus Medialis ainsi que l’oxygénation musculaire par spectroscopie proche infrarouge du VL ont été mesurés au cours de l’exercice. Le principal résultat de cette étude est que les patients drépanocytaires S/S et S/C présentent une fatigabilité musculaire accrue comparés aux sujets A/A. Cette fatigabilité accrue semble être provoquée par des altérations musculaires plutôt qu’une modification de l’oxygénation musculaire. De plus, il semblerait que les mécanismes d’apparition de la fatigue musculaire soient différents entre les S/S et S/C comme le suggère les modifications des paramètres électromyographiques. Ainsi, le muscle des patients S/C semble moins altéré que celui des patients S/S. Dans une seconde étude, des souris Townes A/A et S/S ont suivi un exercice chronique aérobie d’intensité modérée de 8 semaines puis la mesure de marqueurs permettant de caractériser la balance pro/anti-oxydant a été effectuée dans le gastrocnemius, le plantaris et le soleus. A l’issue de ces 8 semaines, nous avons observé des modifications uniquement dans le gastrocnemius des souris S/S entraînées. En effet, l’activité de la NADPH oxydase ainsi que de la superoxyde dismutase et de la catalase étaient plus élevées chez les souris S/S entraînées. Ces résultats suggèrent une altération de la balance pro/antioxydante en réponse à un exercice chronique aérobie d’intensité modérée au sein du muscle squelettique drépanocytaire. Enfin, contrairement aux souris S/S entraînées, nous n’observons pas de modifications de la balance pro/antioxydante dans les souris S/S sédentaires indiquant que le stress oxydatif ne serait pas augmenté dans le muscle drépanocytaire.

EEG-Based Spectral Analysis Showing Brainwave Changes Related to Modulating Progressive Fatigue During a Prolonged Intermittent Motor Task

Article

Full-text available

Mar 2022
FRONT HUM NEUROSCI

Repeatedly performing a submaximal motor task for a prolonged period of time leads to muscle fatigue comprising a central and peripheral component, which demands a gradually increasing effort. However, the brain contribution to the enhancement of effort to cope with progressing fatigue lacks a complete understanding. The intermittent motor tasks (IMTs) closely resemble many activities of daily living (ADL), thus remaining physiologically relevant to study fatigue. The scope of this study is therefore to investigate the EEG-based brain activation patterns in healthy subjects performing IMT until self-perceived exhaustion. Fourteen participants (median age 51.5 years; age range 26−72 years; 6 males) repeated elbow flexion contractions at 40% maximum voluntary contraction by following visual cues displayed on an oscilloscope screen until subjective exhaustion. Each contraction lasted ≈5 s with a 2-s rest between trials. The force, EEG, and surface EMG (from elbow joint muscles) data were simultaneously collected. After preprocessing, we selected a subset of trials at the beginning, middle, and end of the study session representing brain activities germane to mild, moderate, and severe fatigue conditions, respectively, to compare and contrast the changes in the EEG time-frequency (TF) characteristics across the conditions. The outcome of channel- and source-level TF analyses reveals that the theta, alpha, and beta power spectral densities vary in proportion to fatigue levels in cortical motor areas. We observed a statistically significant change in the band-specific spectral power in relation to the graded fatigue from both the steady- and post-contraction EEG data. The findings would enhance our understanding on the etiology and physiology of voluntary motor-action-related fatigue and provide pointers to counteract the perception of muscle weakness and lack of motor endurance associated with ADL. The study outcome would help rationalize why certain patients experience exacerbated fatigue while carrying out mundane tasks, evaluate how clinical conditions such as neurological disorders and cancer treatment alter neural mechanisms underlying fatigue in future studies, and develop therapeutic strategies for restoring the patients' ability to participate in ADL by mitigating the central and muscle fatigue.

SAĞLIKLI KADINLARDA TÜM VÜCUT ViBRASYON EĞİTİMİ VE PİLATES EGZERSİZLERİNİN FİZİKSEL UYGUNLUK, YORGUNLUK VE FİZİKSEL BENLİK ALGISI ÜZERİNE ETKİLERİNİN KARŞILAŞTIRILMASI

Thesis

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Feb 2019

The Transitional Effect of Fatigue Due to a Period of Physical and Mental Activity on the Level of Learning a Motor Skill

Article

Full-text available

Jan 2020

Internatinal Journal of Motor Control and Learning

Background: All of the amazing advances of the present world are the result of human learning. Durability and survival of human being in the world is possible by creating and discovering new ways of teaching and learning. Objective: The purpose of this study was to investigate the transitional effect of fatigue due to a period of physical and mental activity on the level of learning a motor skill. Method: Participants in this research were all of the students of a non-profit female school; among which 36 students, aged between 15-18 years, were selected in simple random method and divided into 3 groups of mental activity, a physical activity and a control group-each group consisting of 12 individuals. The present study was semi-experimental and of repeated measurement type and included three experimental groups. The exercise protocol was considered for 4 weeks, 3 sessions per week. For each session, 5 close and 20 attempts were considered. AAHPERD standard test was used in acquisition, retention and transfer tests. Statistical method of variance analysis with repeated measurements was used to analyze the data. Results: The results showed that the physical activity group had a significant difference compared to the control group, while the mental activity group did not show significant difference. There was also a significant difference between physical activity and mental activity in motor skill variable. Conclusion: The overall conclusion that can be drawn is that, learning motor skill is not equal in all individuals and could be affected by all negative factors.

Zbornik-radova-2021-2 Uticaj sporta na fizički razvoj djece predškolskog i ranog školskog uzrasta

Conference Paper

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May 2021

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
Br Med J

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