THE EFFECT OF FATIGUE 
ON 
VOLUNTARY MUSCULAR 
CONTRACTIONS. 
by 
j 
Warren P. Lombard, M. D. 
REPRINT 
FROM 
Thb American Journal of Psychology. 
January, 1890. THE EFFECT OF FATIGUE ON VOLUNTARY MUS- 
CULAR CONTRACTIONS.1 
Warren P. Lombard, M. D. 
In March, 1889, I had the good fortune to spend three 
weeks in the physiological laboratory of the University of 
Turin. It is with much pleasure that I take this opportunity 
to express my appreciation of the great courtesy of Professor 
Angelo Mosso and his assistants. It was only by their 
advice and aid that I was able to make the research recorded 
in this paper. 
Apparatus and Method. 
The research was begun at the suggestion of Professor 
Mosso, who proposed that I should continue Dr. Maggiora’s2 
work on the fatigue of voluntary muscles, and who placed the 
apparatus which Dr, Maggiora had used entirely at my disposal. 
This apparatus, which is very simple and satisfactory, has 
been described at length by Professor Mosso—Li Ligi Fafica 
Studiate nei Muscullo dell Uomo, R. Academia dei Lincei, 
1889. 
All the experiments were made upon men, and most of 
them on the flexor muscles of the second finger. The mus- 
cles were stimulated voluntarily or electrically, and the 
corresponding movements of the finger were registered. 
The record was made by a pen which was carried by a little 
car. The car was supported by two parallel horizontal steel 
rods, upon which it slid with very little friction. A string, 
fastened by a leather loop to the finger, pulled the car in one 
direction, and a cord, which passed over a pulley to a weight, 
drew the car in the opposite direction. Thus, when the 
muscles contracted, the finger was flexed and the car was 
drawn forward, and when the muscles relaxed, the weight 
caused the finger and the car to return to their original posi- 
1 This paper was read before the Physiological Congress at Basel- 
Sept. 29th, 1889. 2 
LOMBARD: 
tions. The movements of the car were recorded by a pen on 
the horizontal drum of a Baltzar kymographion. 
The subject was seated during the experiments. The hand 
and arm were securely fixed on a convenient rest, and, in 
spite of the violent muscular contractions which were often 
required by the experiments, made no movement of a kind to 
influence the record. This question was carefully studied. 
Also the action of the finger was watched, to see that all the 
joints moved with each contraction, in other words, that all 
the muscles which assist to flex the finger were contracted . 
Discovery of the Periodicity, 
As the first step of the proposed research, it was necessary 
for me to ascertain the normal curve of fatigue of my mus- 
cles, because Dr. Maggiora had found that this varies in dif- 
ferent individuals. In these experiments, I voluntarily con- 
tracted the flexor muscles of the second finger of the left hand 
every two seconds. The signal was the sound made by the 
interrupter of an electric clock. Each contraction was the 
strongest possible, and, as the weight was three kilograms, 
the muscles soon began to weary. The drum revolved slowly 
and the following curve of fatigue was recorded:— 
fig. i. 
Several records closely resembling this were obtained. On 
the second day, however, the work was continued in one 
experiment longer than usual, because I was determined to 
fatigue the muscle so completely that no contraction should 3 
MUSCULAE CONTE ACTION. 
be possible. After 110 seconds of continuous work, I could 
hardly stir the weight, and thought the experiment nearly at 
an end. To my surprise, however, I began to recover the lost 
power, and during the next half minute each of the succeed- 
ing contractions was higher than the one which had preceded 
it. The effect of fatigue then began to manifest itself again, 
and the contractions became smaller. I concluded that I 
had made a mistake, that I had not exerted all my will power 
before, and I determined for the rest of the experiment to do 
my best. As the contractions grew smaller I threw all my 
energy into each attempt to raise the weight. I was conscious 
that, as is always the case during violent muscular exercise, 
I was contracting many muscles of the body, and that my 
face was flushing under the strain; nevertheless, the con- 
tractions became gradually less, and I supposed that I had 
finally succeeded in tiring out the muscle, when, to my 
astonishment, I began to recover my power a second time. 
The contractions became stronger, reached a maximum and 
fell, only again to recover. In short, for some inexplicable 
reason, during the twelve minutes that the work was per- 
formed, the ability to voluntarily contract the muscles with 
sufficient strength to raise the weight, decreased and 
recovered five times. During the intervals of decreased 
strength the power was almost entirely lost, while during 
the periods of recovery, the force was equal to that shown 
half a minute after the beginning of the work. Fig. 11, Plate 
I, is a better witness than any words. 
The recovery of power which I observed in this and in 
similar experiments interested me so much that I gave up 
the intended research and devoted my time to studying its 
nature and cause. 
A few days of work showed that the observations which 
have been described were not exceptional, but that in my 
case, at least, the periodic loss and recovery of force could be 
found every day and at all times in the day ; on the muscles 
of both arms, and on the extensors as well as flexors; with 
weights of y2, 1, 2, 3 and 4 kilos.; and when the muscles were 
contracted at intervals of 1, 2 and 4 seconds. 
Constancy of the Phenomenon. 4 
LOMBARD: 
Experiments upon Others. 
Unfortunately, lack of time prevented extended experiments 
upon others; nevertheless, the power to voluntarily contract 
the muscles was seen to vary in a like manner in the case of 
two other strong, healthy men. Fig. 111, Plate 11, is a 
reproduction of the record obtained from one of these experi- 
ments. 
The phenomenon is, therefore, normal. It is, however, far 
from sure that it can be found well marked with all men. I 
failed to obtain it in a few experiments which I made on six 
other men, although in some of them suggestive irregularities 
were seen. As has been said, the phenomenon is distinctly a 
result of fatigue, and, therefore, the experiments are not 
agreeable. Men are very differently constituted, both as 
regards their ability to concentrate their efforts, and to con- 
tinue muscular work after fatigue has made it painful. One 
sees this exemplified in races, on the march, and whenever 
long continued and violent muscular exertion is required. I 
do not know that these constitutional differences have ever 
been satisfactorily explained, or, indeed, that anyone has a 
well defined idea of the physiological conditions which are 
essential to endurance and tenacity. 
Study of a Characteristic Experiment. 
In long continued experiments with weights lighter than 
that which was employed in the experiments recorded in Fig. 
11, Plate I, the alternating loss and recovery of power, 
though appearing later, is even more striking. Fig. IV, 
Plate I, records an experiment on the flexor muscles of the 
second finger of the left hand, with a weight of half a 
kilogramme. The muscles were voluntarily contracted every 
two seconds, and each time with the utmost force. In this 
case the difference between the height of the contractions 
during the interval in which the voluntary power was lost, 
and the periods when the muscle responded well to the will 
impulse, was very great. For the first half minute of this 
experiment, the height of the contractions varied from 53 to 
57 mm., and averaged 55 mm. They then began to decrease 
in size, and at the end of minutes had fallen to 5 mm. The MUSCULAR CONTRACTION. 
5 
change during the last half minute was very rapid. In the 
preceding half minute the contractions were irregular and 
varied from 17 to 32 mm., but averaged 24 mm., while during 
the last half minute they were, viz.—22, 23, 17, 19, 17, 12, 
15, 11, 15, 12, 8, 6, 7, 6, 5. 
From this time on the alternating intervals of loss and 
periods of recovery of power became well marked, as is seen 
in the reproduction of the curve, Fig. IY, Plate I, and in 
the following table. 
The table records the variations in the size of the contractions 
during the first eleven successive periods. The size of the 
contractions is stated in millimeters. Each column of the 
table contains the contractions which occurred from the time 
that the power began to be recovered until it was lost 
again. 
1 
2 
3 
4 
5 
TABLE I. 
6 7 
8 
9 
10 
11 
6 
9 
6 
9 
rt 
I 
7 
12 
10 
10 
10 
12 
6 
10 
8 
22 
9 
6 
11 
18 
14 
10 
12 
8 
11 
23 
44 
7 
7 
10 
15 
10 
23 
15 
14 
17 
44 
47 
9 
9 
12 
22 
14 
42 
20 
11 
12 
46 
44 
11 
10 
29 
26 
16 
47 
34 
11 
26 
45 
46 
21 
10 
45 
44 
34 
47 
45 
14 
43 
46 
45 
26 
15 
47 
49 
42 
48 
46 
15 
41 
48 
45 
46 
20 
47 
47 
45 
50 
48 
27 
43 
42 
44 
47 
44 
39 
39 
47 
48 
45 
46 
42 
47 
37 
47 
46 
30 
30 
46 
45 
46 
48 
44 
40 
25 
33 
49 
13 
21 
44 
38 
45 
46 
45 
29 
14 
27 
40 
9 
18 
44 
38 
40 
34 
42 
20 
10 
13 
20 
10 
44 
36 
38 
38 
45 
10 
8 
11 
12 
6 
49 
14 
40 
42 
41 
7 
5 
8 
11 
48 
10 
38 
41 
36 
11 
7 
7 
45 
7 
40 
42 
30 
11 
6 
50 
30 
47 
25 
7 
50 
14 
42 
16 
5 
47 
8 
39 
10 
46 
45 
10 
36 
47 
5 
40 
48 
5 
48 
39 
4 
47 
41 
41 
37 
48 
40 
30 
33 
15 
35 
17 
25 
11 
8 
8 6 
LOMBARD: 
The difference between the size of the contractions during 
the periods of power and intervals of weakness was remark- 
ably constant. This is well seen in the following table, in which 
the highest contraction of each period is placed by the side 
of the lowest contraction of the following interval. The height 
of the contractions is stated in millimeters. 
Highest contraction of 
TABLE II. 
Lowest contraction of the 
the period. 
following interval. 
48 
8 
45 
4 
48 
5 
47 
47 
6 
49 
7 
47 
9 
50 
40 
7 
48 
7 
47 
47 
8 
48 
13 
48 
47 
8 
47 
48 
4 
49 
• • . . . 4 
The regularity seen in this table is the more surprising when 
one reflects that it depended not only on the action of mechan- 
isms within the spinal cord, of the nerves, the nerve ends and 
muscle fibers, but also on the ability of the subject of the exper- 
iment to give each time the strongest will impulse possible. 
The fact remains the same, however, that in each of the periods 
of recovered power the highest contraction was of about the 
same size, and that it was nearly as vigorous as the contrac- 
tions which were made at the beginning of the experiment. 
It is also noteworthy that during the intervals of decreased 
force the strength was lost each time to almost exactly the 
same degree. 
On the other hand there was but little regularity in the 
length of the succeeding periods. Stated in seconds their 
lengths were, viz.—66, 48, 38, 30, 34, 32, 24, 28, 62, 32, 34, 
28, 44, 26, 28, 38, 34, 26. 
There was also great difference in the time elapsing before 
the highest contraction of each of the successive periods was MUSCULAR CONTRACTION. 
7 
reached. Stated in seconds these times were, viz.—22, 24, 
16, 8, 18, 22, 14, 4, 30, 16, 16, 4, 38, 14, 10, 14, 12, 12. 
Likewise the time between the highest contraction of a 
period and the next lowest contraction varied greatly, viz., 
44, 24, 22, 18, 16, 10, 10, 14, 26, 16, 18, 24, 6, 12, 18, 24, 
22, 6. 
It is unnecessary to calculate the work accomplished in 
each period. A glance at the curve discloses that it was not 
the same in any two periods. 
To summarize these results one may say that nine and one 
half minutes elapsed before the first interval of decreased 
power was reached. During the succeeding ten minutes the 
power to raise the weight was regained and lost fifteen times. 
The periods of recovered power varied greatly in length. 
The lowest contractions of the intervals and the highest con- 
tractions of the periods were irregularly distributed. In no 
two periods was the same amount of work accomplished. 
Finally the highest contractions were of about the same size 
in all the periods and were nearly equal to the contractions 
occurring at the beginning of the experiment, though in the 
intervals of decreased force the contractions had almost no 
power. 
Search for the Seat of the Changes which Produce the 
Periods. 
When a muscle is voluntarily contracted many chains of 
mechanisms are thrown into action. All these chains are 
connected with the areas of the brain originating the will 
impulse. The successive links are formed by the mechan- 
isms within the central nervous system, the centrifugal 
nerves, the nerve ends, and the muscle fibres. Which of 
these organs is the seat of the changes which cause the loss 
and recovery of voluntary power? 
The periods do not appear until after considerable work 
has been performed. The greater the weight and the more 
frequent the contractions the sooner they occur. Indeed, 
they seem to be essentially connected with the fatigue of the 
mechanisms involved in the voluntary movement. It is well 
known that muscles weary rapidly if deprived of blood, and 8 
LOMBARD 
as Dr. Maggiora has shown they recover their strength with 
equal rapidity if treated with massage during the intervals of 
repose. These facts suggest that the periods are the result 
of circulatory changes in the muscle. 
With the hope of ascertaining the truth of this supposition 
I made the following experiment. I contracted the flexor 
muscles of the second finger, weighted with 2800 grammes, 
every two seconds, and each time as vigorously as possible. 
When fatigue had become great, and the intervals of loss and 
periods of recovery 'of force were very marked, the muscle was 
subjected to massage. The work was continued during the mas- 
sage with the same regularity. At the end of a few minutes, 
the effect of the massage was seen in the flushed skin and in 
the fact that the muscular contractions during the intervals 
of decreased power were somewhat higher than before. 
Nevertheless, the periods continued to occur. In other 
words, the increased circulation caused by the massage, 
though slightly strengthening the muscle, did not remove the 
periodicity. Fig. V, Plate 11, is a reproduction of the record 
of this experiment. The arrow marks the moment at which 
the massage was applied. 
Another form of experiment was then resorted to, in order 
to see if the irritability or strength of the muscle was less at 
the moment that the voluntary contraction was weakest. The 
condition of the muscle was tested at the beginning of the 
experiment by a tetanizing induction current, applied at 
intervals of two seconds, during about half a second, the 
muscle raising a kilogramme at each contraction. After ten 
contractions the electricity was stopped, and the subject 
began to voluntarily contract the muscle every two seconds, 
and always with his whole force. When the periodicity had 
become well defined, the muscle was again tested with elec- 
tricity. The test was made during an interval when the most 
vigorous voluntary effort was incapable of raising the weight. 
It was found that the response to electricity was about the 
same, and that the muscle was still capable of doing work. 
Moreover, although the electric stimulations were applied 
regularly, every two seconds, for some minutes, no recurrence 
of the periodicity was seen. When the electricity was dis- 9 
MUSCULAR CONTRACTION. 
continued and voluntary contractions again commenced, tlie 
periods soon returned. It is worthy of note that the period- 
icity did not appear immediately, however. It seemed as if 
the mechanism which was the seat of the changes producing 
the phenomena, had had an opportunity to partially recover 
during the time that the muscle was contracting in response 
to the electric irritations. The difference in the form of the 
record obtained, when the muscle is irritated directly by elec- 
tricity, and when it is stimulated voluntarily, is well illus- 
trated in Fig. YI, Plate 11. The whole curve is the record 
of one continuous experiment, and contains two groups of 
periods, obtained when the muscle was voluntarily contract- 
ed, and, between them, the series of contractions which were 
called out by direct electrical stimulation of the muscle. 
These experiments, and others in which the muscle was stim- 
ulated by electricity every two seconds for a long time, and 
was seen to weary without any sign of periodic loss and 
recovery of power showing itself, forced me to conclude that 
the phenomenon did not originate in the muscle. 
The nerves and nerve ends were next studied. The record 
of one of the experiments is given in Fig. YII, Plate I. The 
median and ulnar nerves were irritated by a tetanizing induc- 
tion current, applied every two seconds, for about half a 
second, one of the moist electrodes being placed on the skin 
over the sternum, the other over the region of the nerves on 
the inside of the upper arm. The record was taken from the 
second finger, and the weight was one kilogramme. It was 
with difficulty that the most favorable point for simultaneous- 
ly stimulating both nerves was found; at last, however, all 
the phalanges were seen to move in response to the irritation, 
and it was evident that all the muscles which help to flex the 
finger were receiving the nerve impulse. 
After the muscles had contracted ten times, (see a on 
curve,) the irritation was stopped and the muscles were 
voluntarily contracted every two seconds, and always with 
all the force possible. The periodicity appeared in this case 
sooner than was usual, perhaps because the subject was tired, 
on account of the many experiments of the preceding days. 
After 209 contractions, about seven minutes’ work, when the 10 
LOMBARD: 
periods had become very decided, the effect of electrical 
stimulation of the nerves was again tried (see & on curve); 
the muscle contracted less than at the beginning of the exper- 
iment, but, though the irritations were given every two 
seconds for nearly two minutes, no periodicity manifested 
itself. When the voluntary contractions were begun again 
the periods occurred as before. 
It is worthy of observation, that, in this case, as in that 
already referred to, of direct electrical stimulation of the muscle 
the first period after the electrical stimulation was stopped 
was longer than those which occurred just before the stimu- 
lation with electricity, which suggests that the mechanisms 
which are the seat of the changes which cause the periodicity, 
had time, while the nerves and muscles were working under 
the influence of the electrical irritations, to partly recover 
from their fatigue. That the recovery was incomplete, was 
shown in the rapidity with which short periods made their 
appearance. 
During this experiment the subject had the curiosity to try 
the effect of continuous voluntary contractions of the muscles. 
He avoided looking at the curve lest he should be influenced 
by it. He raised the weight as high as possible and did his 
best to keep it at that height. He was conscious of the loss 
and gain of power, but was not aware, until afterwards, that 
his finger had written a curve which corresponded to a 
silhouette of the records of the intervals of loss and periods of 
gain of power which were recorded when the muscles were 
contracted every two seconds. 
The effect of electrical stimulation of the muscles was tried 
a third time, and it was found that the muscles contracted 
higher than at the beginning of the experiment, (see c on 
Fig. VII, Plate I.) The writer lays but little stress on the 
difference in the height of the contractions obtained with the 
electric current in the three observations of this experiment, 
because it is probable that they were caused by slight 
changes in the position of the electrode on the arm. The 
important fact demonstrated by this experiment is the absence 
of periods from the curves obtained by stimulating the nerves 
by electricity, and, that too, at a time when the periodic MUSCULAR CONTRACTION. 
11 
variations during the voluntary contractions were very 
marked. 
By chance, the third time that the voluntary contractions 
were begun coincided with the part of the period when a vigor- 
ous contraction was possible and one high contraction was 
recorded. Immediately after, however, the cause which pro- 
duces the intervals asserted itself, and the contractions be- 
came smaller. The record looks as if part of a period had 
been cut off; (see the first contraction following series marked 
cin Fig. VII, Plate I.) This chance observation, which was 
repeated in another part of the experiment not given in the 
plate, is very important, because it shows, both by its shape 
and the time of its occurrence, that the changes which cause 
the periods continue after the voluntary action has ceased. 
Although the foregoing experiments suffice to show that 
the periodic variations were of central rather than peripheral 
origin, I sought a method of experimentation which would 
enable me to form a clearer idea of the relative influence 
exerted on the height of the contractions by the fatigue of the 
muscles and the changes occurring in the central nervous 
system. At the suggestion of Professor Mosso the following 
form of experiment was adopted. The flexor muscles of the 
second finger, weighted with one kilogramme, were stimulat- 
ed every two seconds. Two different forms of stimuli were 
employed, electrical and voluntary stimuli, and they were 
applied alternately. During the electrical irritation, the 
nerves and muscles were stimulated by a tetanizing induc- 
tion current, one of the electrodes being placed over the 
sternum, the other over the muscle. Fig. YIII gives the 
results of a part of this experiment, and looks as if the records 
of the response of the nerves and muscles to electrical stimuli 
and to voluntary impulses had been superimposed. 12 
LOMBARD; 
FIG. VIII. 
The records of the voluntary contractions differ entirely 
from those written by the contractions produced by the elec- 
trical stimulation of the nerve. The voluntary contractions 
do not begin to decrease in size as soon, and when they com- 
mence they lessen much more rapidly. There is a moment 
when the response to the two forms of irritation is about the 
same, but the voluntary contractions soon begin to increase 
in height, and from this time on, the shape of the two records 
is as different as possible. The condition of peripheral 
organs, as shown by the response of the nerves and muscles 
to electricity, varies but slightly and irregularly, while that of 
the central nervous mechanisms, as shown by the extent of 
the voluntary contractions, undergoes marked and rhyth- 
mical alterations. The difference in the relative height of the 
two curves is due in part to differences in strength and effec- 
tiveness of the two forms of irritation. 
These and other similar experiments convinced me that the 
changes producing the periodicity, do not occur in the nerves, 
the nerve ends, or the muscles, and that they take place in 
the central nervous system. MUSCULAR CONTRACTION. 
13 
Which of the central mechanisms is the seat of these 
changes? The will power seemed to the subject to be un- 
abated, and experiments showed that he was capable of con- 
tracting other muscles vigorously at the moment that he was 
unable to lift the weight with the finger. The result of one 
of these experiments is to be seen in Fig. IX, Plate I. The 
letter f marks the beginning of the voluntary contractions of 
the flexors of the finger, and t the beginning of the voluntary 
contraction of the extensors of the thumb. In this experi- 
ment two cords were attached to the recording apparatus ; 
one was fastened to the second finger, the other to the thumb. 
The second finger was then contracted voluntarily at intervals 
of two seconds, each time raising a weight of 2800 grammes 
as high as possible. After a few minutes the periods became 
well developed. In one of the intervals, when the power to 
move the second finger was lost, the subject ceased to try to 
move the finger and raised the weight by voluntarily con- 
tracting the extensors of the thumb. These muscles respond- 
ed well, and they were used until fatigue set in, and they in 
their turn demonstrated the periods. Then, at a moment 
when the ability to extend the thumb was lost, the work was 
taken up by the flexors of the finger and they were found to 
be capable of raising the weight nearly as high as at the 
beginning of the experiment. 
The facts just stated prove that the loss and recovery of 
the ability to voluntarily contract the muscles is not depen- 
dent on changes in the strength of the will, but on alterations 
which take place in some of the mechanisms between the 
areas of the brain originating the will impulse and the cen- 
trifugal nerves. It also shows that the seat of the changes 
which produce the periods is different for each of the muscles, 
and that the change occurs in the central mechanisms which 
control the different muscles, independently.1 
The successive periods, though sometimes occurring with 
great regularity, more frequently show many variations, 
1 Last August I made a few experiments on this subject in the Physio- 
logical Laboratory of Leipzig with Dr. Max von Frey. These experi- 
ments showed still more clearly that the will power is unabated at times 
when voluntary contractions are markedly decreased. The results of 
these experiments will be reported in full hereafter. 14 
LOMBARD 
which prevent ns from attributing them solely to a rhyth- 
mical action peculiar to the central mechanisms. See statement 
at bottom of page 29. In another experiment the lengths of 
thirteen successive periods were, in seconds, viz., 24, 28, 24, 
38, 26, 28, 40, 82, 24, 20, 18, 24, 32. 
In still another experiment in which the muscles were 
voluntarily contracted every four seconds, against a weight 
of 2800 grammes, the following results were obtained. The 
first period appeared in about fourteen minutes, and during 
the next forty-five minutes, forty-seven periods were record- 
ed. The number of contractions forming a period and the 
number of contractions which failed to raise the weight, dur- 
ing the intervals of decreased power, gradually increased. 
These changes caused by the fatigue of the central mechan- 
isms displayed, however, many irregularities. There were 
many moments when it seemed as if the periodic changes had 
ceased. Thus the 29th and 46th periods contained respec 
tively 48 and 33 contractions, instead of six or seven, the num- 
ber found in many of the other periods. The following table 
will give a good idea of the eccentricities of the phenomenon. It 
states the number of contractions which occurred in each 
period, and the number of unsuccessful contractions during 
each interval. A contraction which failed to raise the weight 
half a millimetre was considered an unsuccessful contraction. 
As a matter of fact the muscle always contracted somewhat. MUSCULAR CONTRACTION. 
15 
TABLE III. 
Number of contrac- 
Number of unsuc- 
Number of contrac- 
Number of unsuc- 
tions in a period. 
cessful 
in the 
terval. 
contractions 
following in- 
tions in a period. 
cessful contractions 
in the following in- 
terval. 
206 
.... 0 
1 
1 
12 
.... 0 
7 
1 
12 
.0 
1 
2 
13 
.... 0 
6 
0 
20 
.... 0 
17 
0 
18 
.... 0 
48 
4 
15 
.... 1 
7 
1 
11 
.... 2 
2 
1 
16 
.... 1 
6 
2 
19 
.... 0 
12 
3 
7 
.... 3 
5 
11 
.... 4 
6 
1 
12 
.... 3 
1 
1 
15 
.... 0 
6 
5 
4 
.... 4 
7 
1 
13 
. . . 2 
8 
7 
11 
. . . . 1 
7 
3 
11 
.... 7 
6 
3 
12 
.... 7 
6 
6 
9 
.... 2 
7 
4 
6 
.... 4 
6 
12 
9 
7 
0 
V 
9 
33 
3 
7 
. . . . 2 
7 
1 
I found that if I voluntarily contracted a muscle frequently, 
and each time raised a weight with my utmost force, the 
mechanisms involved in the action gradually wearied, the 
contractions weakened and after a time scarcely stirred the 
weight. If, however, I continued, regardless of the result, 
to strive with the whole power of my will to frequently con- 
tract the muscle, sooner or later my force began to return. 
The recovery, for a short time, might be almost complete. 
Soon, however, the power began to be lost for a second time 
and throughout the rest of the experiment intervals of almost 
entire loss of power to voluntarily contract the muscle were 
seen to alternate with periods of nearly complete recovery. 
Not only are the variations in the strength of the contrac- 
Summary of Results and Conclusions. 16 
LOMBARD; 
tion of the muscle wholly out of the control of the subject, 
but he does not even know, when he wills a contraction, 
whether the muscle will respond vigorously or not. 
The phenomenon was observed in the case of the extensors 
as well as the flexors ; on the muscles of both arms; with 
weights of 1, 2, 3 and 4 kilogrammes; and when the 
muscles were contracted at intervals of 1, 2 and 4 seconds. 
The alternate loss and recovery of power which has been 
described is evidently the result of fatigue, because it is well 
marked only after the work has been continued for a consid- 
erable time, and it appears more quickly when the contrac- 
tions are frequent, and the weight is large. 
That the periodic loss and recovery of voluntary control 
over the muscle is not due to nutritive changes in the muscle 
itself, is shown by the fact that massage, though strengthen- 
ing the muscle, does not do away with the periodicity. More- 
over, they do not seem to be dependent on variations in the 
irritability of the nerves, the nerve ends, or the muscle, be- 
cause at a moment when a voluntary contraction is almost 
impossible, the muscle responds well either to direct electri- 
cal stimulation, or to electrical stimulation of its nerve. 
Moreover, periodic variations of the force of the contractions 
are never seen in experiments in which the muscle or its 
nerve are frequently stimulated with electricity. Further, 
if a muscle be voluntarily contracted vigorously and frequent- 
ly, until the periodic loss and recovery of force has become 
well marked, and then the voluntary contractions be replaced 
for a minute or two by contractions called out by electrical 
stimulation of the nerve, the periods immediately cease, 
although they return again as soon as voluntary contractions 
are resumed. Finally, it is worthy of note, that, in such an 
experiment, the periods are somewhat less frequent when the 
voluntary contractions are first resumed than they were just 
before the electricity was applied. In other words, that, 
while the nerve and muscle were working in response to the 
electric stimuli, the mechanism which was the seat of the 
changes causing the periodic variations of force had time to 
partially recover from its fatigue. 
It seems almost certain, therefore, that the periodic loss MUSCULAR CONTRACTION. 
and recovery of power to make vigorous voluntary muscular 
contractions, which 'was seen in the experiments that have 
been described, was due to changes which occurred not in 
the peripheral mechanisms, but in the central nervous sys- 
tem. The periods do not, however, seem to be due to varia- 
tions in the strength of the will power, because at a moment 
when it is impossible to make a strong voluntary contraction 
of one muscle, other muscles can be contracted with the 
usual vigor. The alterations which cause the periodicity 
must therefore be considered as located in some of the central 
nervous mechanisms, which lie between the areas of the 
brain which originate the will impulse, and the centrifugal 
nerves. 
The experiments threw but little light on the nature of 
these changes. As has been said they are the result of 
fatigue, and they do not cease to occur as soon as the volun- 
tary contractions cease, but their influence may be recognized 
for some minutes, at least, after the work has been stopped. 
The fact that the extensor of the thumb worked well when 
the flexors of the finger refused to obey the will, and vice 
versa, shows that the changes occurred independently in 
the mechanisms controlling each of these muscles. Though 
the periods were often almost rhythmical, they displayed so 
many variations that one cannot attribute them solely to a 
functional rhythm peculiar to these mechanisms. Indeed, it 
is probable that they were the result of a number of conflict- 
ing influences. 
In addition to the marked periodic variations which have 
been discussed, there were observed even at the beginning of 
the experiment, when none of the mechanisms were fatigued, 
slight variations in the strength of the contractions. These 
were irregularly distributed, and were probably due, in part, 
to the inability of the subject to give his whole attention to 
the work and to always make the strongest possible volun- 
tary effort. On the other hand, it may be remarked that 
most processes which depend on the activity of the central 
nervous system are subject to similar variations, and that 
such irregularities may well be considered as characteristic 
of the action of the higher nervous mechanisms. LOMBARD: 
The results here given were obtained from experiments 
which were made on the writer at twenty-five different times. 
In the few experiments which were made upon others, the 
periodicity was found well developed in the case of two 
strong and healthy young men, but failed to appear with 
definiteness in the case of six others. There can be but 
little doubt that the phenomenon is normal. Its absence in 
six out of the nine men examined, may be explained, in part, 
by the difficulties of the experiment, but was probably chief- 
ly the result of the functionally different nervous systems of 
the men examined. 
That fatigue should cause, the strength of voluntary muscu- 
lar contractions to vary periodically is less surprising when 
one recalls that fatigue causes a periodicity of many proces- 
ses which depend on the action of the central nervous system. 
If one listens to the ticking of a distant watch, the sound 
is heard with periodically varying distinctness. If one looks 
long at a white sky, darkness sweeps from time to time over 
the field of vision. The intensity of 1 i after-images ’7 is subject 
to rhythmical variation. If one seeks to count the waves in 
a curve which record the vibrations of a tuning fork, he finds 
that, as he wearies, his ability to continue the counting 
varies more or less periodically. Much the same thing is 
true of such mental processes as adding a long column of 
figures, or the following of a long continued exact line of 
thought. There are intervals when the mind refuses to 
work, and these are soon followed by periods of almost 
unusual clearness. 
Other Similar Phenomena. 
Undoubtedly these phenomena would impress us more if 
we did not unconsciously yield to fatigue, and did not fre- 
quently rest ourselves. Even slight intervals of rest are 
sufficient to prevent the amount of fatigue which is necessary 
to reveal the phenomenon in marked degree. 
In experiments made by the writer in Leipzig, 1 1884, he 
found that if a constant temperature, high enough to cause 
1 Die raumliche und zeitliche Aufeninanderfolge reflectoriseh coutra- 
hirter Muskeleu. Du Bois-Reyrn end’s Archiv. 1885. PLATE 1. PLATE II MUSCULAR CONTRACTION. 
reflex movements, but not so high as to rapidly destroy the 
tissues, were continually applied to the skin of the leg of a 
decapitated frog, the resulting reflex action was not a contin- 
uous tetanus, but a series of tetani, which followed one 
another with considerable regularity. In the intervals be- 
tween the tetani, the muscles entirely relaxed, and the 
succeeding tetani were of nearly the same height. This 
phenomenon seemed to be dependent upon almost rhythmical 
changes occurring within the spinal cord, and closely resem- 
bles the results obtained in the experiments described in this 
paper. 
Still another process, which naturally suggests itself as 
perhaps of similar nature to that under discussion, is the 
“ Chene-Stokes respiration.” 
It is not impossible that the gaining of the so-called 
11 second wind,” so well known to runners, may depend, in 
part, at least, upon conditions similar to those which caused 
the first recovery noticed in my experiments; further the 
variation in the amount of difficulty experienced in maintain- 
ing long continued violent muscular action, is probably 
caused by functional changes, the same as those which pro- 
duced the succeeding periods which have been described. 
We have as yet but few and for the most part unsatisfac- 
tory tests of the functional activity of the central nervous 
system. Every new method which enables us to approach 
this difficult question is, therefore, of great importance.