672

THE COLLIERY GUARDIAN

October 1, 1915.

INDUSTRIAL FATIGUE.

Experiments on Colliers.

An interim report on an investigation of industrial fatigue
by physiological methods, carried out by A. F. Stanley Kent,
M.A., D.Sc. (Oxon), Henry Overton Wills Professor of
Physiology in the University of Bristol, has been published
as a White Paper [Cd. 8056].

Some account is given therein of an attempt undertaken on
behalf of the Home Office to discover a test for recognising
the presence, and a gauge for estimating the degree, of fatigue
as met with under factory conditions. The work is to be
regarded as preliminary, and is published now in order that
others, interested in the subject, may be informed of the
progress made and of the relative value to be placed on the
methods described.

Fatigue is a term used in connection with various struc-
tures and bearing different meanings accordingly. In some
cases fatigue of various organs—of muscle, of nerve, and of
central organs — may be associated in the production of
general fatigue, and this is especially likely to be the case in
the problem under consideration. The term “ fatigue ” is
used in the report as a general term, and may be taken to
include a general lowering of the functions of the body as a
result of extreme or prolonged activity.

The report describes the various tests employed, and the
experiments carried out to determine their value.

Experiments were carried out, first, upon two students in
the laboratory, and subsequently upon four assistants in the
department. In these experiments the muscles were used
until completely exhausted, and a period of five minutes then
allowed for recovery, followed by a second record. From
the experiments carried out on these lines, it appeared that in
this power of recovery from fatigue there existed an index
of the general condition of an individual which might be
of great use in the investigation under consideration. Labor-
atory experiments made in the way indicated were carried
on for some months, the results showing that in a majority
of cases the power of recovery was distinctly less at the end
of the day’s work than at the commencement. The chief
difficulty was that fatigue, in its graver aspects, was not
present. Difficulties, however, were experienced owing to the
inconstancy of the results and the smallness of the differences
observed.

Laboratory experiments having been completed, arrange-
ments were made to commence investigations under factory
conditions. The results obtained were irregular, however,
and indicate that some modifications should be introduced
into the method before it can be regarded as suitable for
measuring the fatigue of factory operatives. For this reason
an endeavour was made to discover a method of experiment
which should be free from these defects, and to apply it in
a wider range of industries, including such as involved more
physical strain.

Tests on Colliers.

The main interest of the report concerns the special senses
—tests having been made upon the. special senses of sight
and hearing. These tests, to which, in view of the simplicity
of application and consistency in results obtained, Dr. Kent
attaches a high value, were carried out upon three distinct
categories of workers : (a) colliers, engaged in coal mining;
(5) chemical works men; and (c) three men and three women
engaged in letterpress printing. In each of these classes,
tests both of sight and hearing are shown to be capable of
indicating distinctly fatigue of only moderate severity, such
as occurs at the end of the eight-hour shift,’whilst in some
cases the general acuity of sight and of hearing both before
and after labour, are found to be markedly lowered towards
the end of the week, thus indicating an accumulation of
fatigue.

With regard to blood pressure the results of the present
investigation seem to show that an estimation of this cannot
be accepted as a reliable test of the existence of fatigue,
although the charts appear to bring out an interesting rela-
tion between height of blood pressure and power of response.

The examinees from the colliery (Talk-o’-th’-Hill) were
four colliers (Nos. 1, 3, 4, and 5) aged 46, 32, 37, and 39
respectively, the first two having to walk four miles in order
to reach work, and the last two f mile and | mile respec-
tively; and two loaders (Nos. 2 and 6), aged 31 and 21
respectively, who had to walk four miles and f mile
respectively.

The experiments were carried out at the beginning and at
the end of an eight hours “ shift,” in each case. The
colliers commenced work on what is called the “ afternoon
shift at 3 p.m. on Monday. They went down the pit
between 2 and 3 p.m., so as to be ready to start work at 3.
They then worked, with one 20 minutes’ interval, till 11p.m.,
and came up the pit some time between 11 and 12 p.m. This
continued until Friday. Saturday and Sunday were rest
days. The men started again on Monday, but this time they
were engaged on the “ morning shift,” that is, from 6 a.m.
till 2 p.m. During this week they would put in six “ shifts.”
The loaders would work the same hours as the colliers.

Reaction Time Tests.

In the experiment on colliers to show the reaction time
(chart 1), of the six individuals examined on the first day,
three are seen to have reacted less quickly after work than
before, whilst three reacted more quickly after work than
before. The results are thus evenly divided, and the average
comes out exactly the same before and after work. In seek-
ing an explanation of this result, it must be remembered :—
(1) That the test was made after several days’ rest; (2) that
the test was unfamiliar to the examinees. It is therefore
possible that the first period of work after a prolonged rest
was not sufficient to produce a grade of fatigue capable of
detection by this means, and also that the question of prac-
tice comes in, and that the quicker result after work is
really due to a better understanding of what was required.

If this suggestion is well-founded—that marked fatigue
is not produced in the first period of work after a prolonged
rest (under the conditions of the experiment)—and it is a
fact that the work is sufficiently heavy to produce fatigue
during the week, an examination of the records for the week
of the individuals concerned should show a gradually increas-
ing lengthening of the evening response compared with that
of the afternoon. This cannot be said to be the case with
No. 1, who shows a ratio of 0-9130 (Monday), 1-2336
(Tuesday), 0-8505 (Wednesday), 1-0550 (Thursday), and
0'7959 (Friday). That is, the diminution of the ratio A/N
(afternoon to night) which should correspond with the
increasing fatigue, is altogether irregular. In No. 2, on
the other hand, after a quicker response after work on the
first day, there is a progressive decrease in the ratio A/N
to the end of the week. No. 3, again, is irregular. No. 4
uniformly longer B/W (before work) than A/W (after work),

for the first three days of the experiment, with a reversal of
the ratio, i.e., B/W less than A/W on the last two days of
the test. No. 5 shows the effect of practice for the first two
days, the results on the second day being considerably lower
than those on the first; on the third day there is a remark-
able increase of A/W over B/W, which is continued on the
fourth day, but which is again reversed on the last day of
the test. No. 6, again, is irregular, though, like three of
the five others, he shows a B/W less than A/W on the
last day.

Taking the averages, it is seen that of the five days, the
first shows no difference between B/W and A/W, the second
shows an actual diminution of time after work, i.e., B/W
greater than A/W, whilst the other three days all show a
distinct increase in the time taken to respond after work as
compared with that taken before the work is commenced.

The figures, therefore, give some indication that practice
has an appreciable effect at the beginning of the series,
and also that the effect of fatigue only becomes obvious
towards the end of the week’s work. These results must be
judged from the averages in'the present state of the enquiry,
and indications afforded that a modified form of the test
should be capable of giving useful results. This suggestion
is supported in a remarkable manner by a chart taken from
another set of experiments, in which the temporary absence
of the manager of the works, and a consequent relaxation of
supervision of the -workers, is accompanied by a very pro-
nounced rise an the curve, indicating a considerable diminu-
tion of the fatigue present.

In the charts the curves show the variations which
occurred (u) reaction time; (b) acuity of vision; (c) blood-
pressure; and (d) acuity of hearing during five successive
days, Monday to Friday, January 4-8.

Sight Tests.

The second experiment (colliers) was made to show the
maximum distance in centimetres at which standard letters

Mon (Noon)

Tues (Noon)

Wed (Noon)

Tburs. (Noon)

*3

I-

--->- TIME HOURS

Chart 1.

can be recognised (chart 2). This—the first test of the
present series based upon an examination of the special
senses—is of great interest.

With two exceptions, every test shows that the distance
at which the standard letters could be seen proved to be
greater before than after work, that is to say, as a result of
the work, the acuity of the sight was diminished. The two
exceptions referred to both occur on the second day of the
test (No. 2, B/W 66, A/W 72, and No. 5, B/W 277, and
A/W 300). The differences are not very considerable,
being but 9 cm.—9 per cent.—in the case of No. 2, and
23 cm.—8’2 per cent.—in the case of No. 5. The differences
in many of the remaining cases are large, and omitting the
results of the first day, when the novelty of the conditions
probably affected the results more than later in the series,
it is seen that the ratio A/N rises consistently during most
of the time of the test—1'118-1'20-1'240-1'190. The existence
of large individual differences will be noticed, the most
marked example being found in No. 1. In explanation of
this it may be mentioned that this man was the oldest
of the examinees, and that a few years ago he suffered from
a bad accident, being imprisoned by a fall in the mine for
a period of 15 hours.

The results of this experiment are distinctly encouraging,
the values appear to be consistent, and the differences suffi-

Mon (Noon)

fri(NvOr)

Tues (Noon) INed.(No'sn) Thurs.(Nocn)

Chart 2.

ciently large to minimise the influence of experimental error.
Moreover, the’test is not one in which the individual is
likely to influence the result wilfully.

Blood Pressure Tests.

In the third experiment (colliers), the blood pressure was
charted in millimetres of mercury (chart 3). A series of
experiments upon the variations in the blood pressure was
carried out in conjunction with the other tests for two dis-
tinct purposes :—(1) To ascertain whether a spell of labour
exerts any definite effect upon the blood pressure; (2) to
ascertain whether there is any definite relation between the
blood pressure and the power of responding to the other tests
employed.

With regard to the first question, an examination of the
records obtained from No. 1 shows that in every case the
period of labour is followed by a definite—in some cases a
considerable—rise of pressure. Nos. 2 and 3, however, do
not bear out this indication, the effect being very variable
from day to day; whilst No. 4, J.W.B., shows a uniformly
lower pressure after work than before it throughout the test
except on the last day, when no difference was shown. No. 5
also shows sometimes a rise—sometimes a fall—as the result
of labour; and No. 6 the same. Obviously, then, as a
direct indication of fatigue produced by labour of the type
here investigated, the blood pressure cannot be relied upon.

With regard to (2), a very interesting point is brought out
in the graphical records plotted on chart 5. Here the line
indicating the ratio A/N of reaction time (equals reciprocal
of daily fatigue) follows very closely the line indicating the
ratio A/N of blood pressure (equals reciprocal of daily rise of
blood pressure), i.e.. the rapidity of response seems to vary
directly with the blood pressure. The magnitudes in the
case of blood pressure are small, yet they are based upon a
considerable number of observations. The magnitudes in

the case of the reaction time are larger. The correspondence
between the tw7o is remarkable, and bears out the observa-
tions made long ago on the influence of the blood pressure
on the nervous system. The line of visual acuity also shows
a marked tendency to vary with or against the blood pressure.

Hearing Tests.

In the fourth experiment (colliers) the test was the maxi-
mum distance at which a standard watch could be heard
(in cms.) (chart 4).

In the great majority of the instances here also, as in the
tests of the sense of sight, the readings at the end of a period
of labour are less than at the beginning, thus indicating that
a distinct lowering of the acuity of the special sense investi-
gated has resulted. The few discrepancies present are alto-
gether swamped in the averages, and the ratio A/N rises

,5° —————"T———————————————————

J_____1^ — _____________________________.

I	Mon.(Noon)	Tues.(Noon)	tNed.(Noon)	Thors (Noon)	Tri. (Noon)

----— TIME HOURS

Chart 3.

from 1-186 on the first day to 1-288 on the third day, falling
to 1-198 on the last day of the test. The special interest
attaching to this series of tests has reference to the fact that
it supports the results obtained in the tests of sight, and
seems to confirm the indication that the special senses are
largely affected by labour prolonged to the point of fatigue,
and that an examination of their condition may be found to
afford a valuable index of such fatigue. The fresh tests
mentioned as having been arranged in connection -with sight
will be combined with further tests on the lines here
indicated.

Experiments with Other Workers.

Chemical Works Men.—The experiments carried out on
workmen employed in other industries may be briefly
summarised. It appears that the results of the “ reaction
time ” tests as at present arranged cannot be taken as
affording a trustworthy index of the grade of fatigue present,
though in view of the figures obtained from the colliers, and
especially in view of the remarkable indication afforded of
a diminution of fatigue corresponding to a less stringent
supervision it appears to be by no means improbable that a
modified test would give results of value. The conclusions
drawn from the sight tests carried out on the colliers are
strengthened by a consideration of the results obtained.
As with the colliers, no constant relation exists between the
blood pressure and the wmrk performed. The results
obtained from the hearing test also support the results
obtained in the examination of the colliers, and are distinctly
encouraging, as indicating a line of investigation to be
pursued in the future. It is of special interest to note that
in one case, whilst the individual was able.to hear the watch
used at a distance of 15'5 cm. on the morning of the first
day, this distance gradually diminished to half that value

Mon.(Noon)

Tues (Noor)

Chart 4,

Wedfttoon)	THurs(N3xi)

-----> TtME HOURS

after the first spell of work, and at the end of the series
was reduced to zero.

Letterpress Printing Workers.—An examination of the
results of this “ reaction time ” test shows that during the
first week the workers were more readily fatigued on
Thursday and Friday than on Monday, Tuesday, or
Wednesday. Such a result might be brought about as a
result of the nightly rest proving insufficient to sweep away
the day’s stock of fatigue, the worker starting next morning
with a small debit balance, to be increased on successive
mornings until the end of the week was reached. The
week’s accumulation would, as a rule, be swept away by the
week-end rest. On the following Monday the curve has
risen to the zero line; it then commences to fall steadily on
Tuesday and Wednesday. On Thursday and Friday, how-
ever, the line, instead of continuing to fall, takes a sharp turn
upwards, indicating a diminution in fatigue production on
these days. The full notes made at the time of all the circum-
stances of the experiment enable one to offer an explanation
of this apparent anomaly. On referring to these notes, the
following entry is found :—“ Manager absent,” and this
absence of the manager coincides in time with the period
during which less fatigue was indicated. Less strict super-
vision, accompanied by a less development of fatigue, has

Chart 5.

been indicated in an unmistakable manner in the records
obtained by the method under discussion, and to this extent
the method may be said to be of value.

A point of some interest brought out by the sight experi-
ment is the difference in acuity of vision existing between
different individuals. With these exceptions, the evening
readings are smaller than the morning readings, indicating
that with the development of fatigue a diminution in the
acuity of vision had occurred.

Under the conditions of the blood pressure experiment, the
blood pressure was as a rule higher in the evening than in
the morning. It is possible, however, that this may have been