JOURNAL
OF APPLIED
PHYSIOLOGY
Vol. 26, No. 6,June 1969.
Printed
in U.S.A.
Energy utilization
in intermittent
of supramaximal
intensit
exercise
R. M
ARIA,
R. D. OLIVA,
AND
P. CERRETELLI
Debartment of Physiology, University
A
MARCARIA,
K., R. II. OLIVA, P. E. DI PRAMPERO, AND
Pm CERRETELLI.
Energy utili<ation in intermittent exercise of supamaximal intensity. J. Appl. Physiol. 26(6) : 752-756.
1969.~In
supramaximal
exercise the extra energy which is not met by
oxidation
is drawn
from splitting
of high-energy
phosphate,
and only when this source is exhausted
is energy drawn
from
the other anaerobic
source, the splitting of
acid. In strenuous intermittent
exercise, no lactic acid is formed
if the oxygen debt contracted
during the working
period can be
met completely
by the alactic phosphagen-splitting
mechanism;
the oxygen debt contracted
during the working
period must
then be completely
paid during the rest period. If these conditions are met, very heavy intermittent
exercise can be carried
out indefinitely,
leading to a total amount of work much greater
than would
have been possible were the exercise protracted
continuously
until exhaustion.
The payment
of the alactic
oxygen debt fraction is confirmed
to be a fast process, the halfreaction
time being about 20-25
set; the capacity
of this
mechanism
in young fit nonathletic
subjects is about 20 ml/kg
body wt.
muscular
exercise,
intermittent;
oxygen
debt,
lactic acid, formation
in intermittent
exercise
P. E. DI
of Milan,
PRAMPERQ,
Milan,
Italy
exercise could be repeated
indefinitely,
thus summing
up
to a total amount
of work much greater than would have
been possible
had the work been carried
out uninterrupted until exhaustion.
On this hypothesis
the following
experiments
were
lanned.
METHODS
Three
subjects,
whose vital
statistics
are given
in
Table
1, came to the laboratory
a few hours after the last
meal, and, after 30-40 min of rest, a sample of blood was
drawn from the arm vein for lactic acid determination
( enzymatic
method)
( 1) .
It was known
from previous
experiments
that when
running
on a treadmill
at 18 km/hr
and at + 15
cline, these subjects reached
exhaustion
after 30-40 set,
and that at the end of the run the maximal
lactic acid
concentration
in blood amounted
to 50-60 mg/ 100 ml.
The experiments
consisted
of a run at the rate indicated for only 10 set, after which
the subjects
were
allowed
a. period of
t lasting,
in three different
series,
10, 20 and 30 set, r
ectively.
After the rest period the
0 see, and so on, until exhaustion
subjects ran again fo
or a steady state was reached.
For each series of experiments
the subjects came to a
stop after a predetermined
number
of runs, after which
blood was withdrawn
3 and 5 min from the end of the
exercise. The maximal
lactic acid value reached at these
times was assumed to represent
an equilibrium
condition
of lactic acid concentration
in the body fluids, and the
total
lactic
acid produced
could
then be calculated.
This was considered
to be produced
during
the exercise,
since the amount
of lactic acid that disappeared
in the
interval
between the end of the exercise and the collection of blood was considered
negligible;
the disappearance of LA from the blood is in fact a very slow process
(8) .
On different
days the subjects performed
successively
) 15, and 20 runs for the different
series of experirnents, and at the end of each period lactic acid was determined
as described.
With
this technique
the concentration of lactic acid in blood or the amount
of lactic acid
alactic-lactic;
I
T HAS BEEN SHOWN
in previous
work that when a subject is involved
in very strenuous
exercise leading
to
exhaustion
in about 30-40 set (running
on a treadmill
at
kmjhr
at an incline
of + 15 %) lactic acid
produced
only after lo-15 see from the beginning
of the
exercise, presumably
when the anaerobic
energy stores,
as given
by the high-energy
phosphate
compou
(phosphagen
= ATP
+ CP) are exhausted,
or h
reached a critical
level (7).
It may then be reasonably
assumed that if this exercis
is sustained
only 10 set, only an alactic
oxygen debt is
contracted.
Since the speed of payment
of this fraction
of
the oxygen debt is very high, the half-time
being about
20--30 see: (4, 8j, a very short period of recovery
may be
suficient
to refill the phosphagen
stores to enable
the
subject to perform
the exercise again on the same energy
source. No appreciable
lactic
acid formation
and accumulation
in the blood would then take place and the
752
ENERGY
BALANCE
Subj
GR
AC
AR
IN
INTERMITTENT
EXERCISE
Age, yr
Weight, kg
Height, cm
Total Vozmsx.
ml/kg per min
--
25
18
22
70
71
65
180
176
179
57.5
58.0
55.0
753
terrupted
run), 10, 20, and 30 set, respectively,
is shown
in Table
2 for all subjects. When the rest period was 10
set, the total running
time could
be increased
about
three times and when the rest period
was 20 set, six
times. In the case of the 30-set pause the exercise could
be carried out indefinitely.
Lactic acid formation.
The concentration
of lactic acid in
blood increases at a high rate in the first few runs in all
subjects and for all series of experiments
to attain a steady
rate after about the fifth run (Fig. 2). The lactic acid
formation
in milligrams
per 100 ml per run or its 02
equivalent
(44 ml OS/g lactic
acid produced
(6)), is
given for all subjects in Fig. 3. From this graph it appears
that at steady state u) no lactic acid production
takes
place if the period of rest is 30 set; and b) the increase of
lactic acid concentration
in blood due to a lo-set run
period increases with decreasing
the duration
of the rest
period, from 3 mg/lOO
ml for a 20-set rest to 11 mg/lOO
ml for a lo-set
rest period.
With a plot of the lactic acid produced
(or the lactacid
oxygen debt built)
as a function
of the length of the rest
period,
the minimal
time of rest at which no lactic acid
formation
takes place can be appreciated
graphically
by
extrapolation
of this function
to LA = 0 (Fig. 4). This
appears
to be on the average
about
25 set, which
is,
2. Total time of performance of a supramaximal
intermittent
work of 10 set duration (running on a + 15 9%
incline at 18 km/hr) with change in duration
of rest periods as indicated
TABLE
FIG.
1. Record of PCOZ at the mouth, VE and PEO% in expired
air measured during the intermittent
work. Working
period is indicated on time line.
formed
as an effect of work could be related
with the
duration
of the intermittent
exercise, or with the number
of runs.
In some experiments,
the oxygen
consumption
was
measured
continuously
during
the whole period of intermittent
exercise.
The expired
air was sampled
from a
mixing
chamber
placed on the expiratory
line and analyzed by a fast-response
02 electrode
(90 % of the response in 0.5 set), whereas the ventilation
was measured
on a breath-by-breath
basis from a spirograph
tracing.
A correction
was made for the time lag in the response of
the Polarograph
depending
on the gas flow and on the
dead space of the system,
in order
to align
the VE
with the PEAR. A typical
record is shown in Fig. 1. In all
other experiments
the 02 uptake
of the subjects
was
measured
by collecting
in a 150-liter
Tissot spirometer
the
air expired
in a given number
of cycles, not including
the
first five, and by analyzing
it for 02 and CO2 by means of
a Scholander
apparatus
(“steady-state
02 consumption”).
Subj
GR
AC
AR
Uninterrupted,
xc
IO&x Pause,
set
20&c Pause,
set
38
32
33
100
90
200
210
200
30.Set Pause,
set
Indefinite
Time for the 20-see pause series of experiments
is actually a
little higher then indicated as the subjects were nearly, but not
completely, exhausted at the end of the experiment.
L. A.
b mg%
100
r
I
I
10-10
'O-lo cy
"
/I
I
1
Subj. A.C.
c
runs
RESULTS
AND
The total
the interval
DISCUSSION
time of the run leading
to exhaustion
when
between
the running
periods were 0 (unin-
2. Blood LA concentration
above resting level in intermittent work (10 set) as a function of number of runs for three
series of performances,
with resting periods of 10, 20, and 30 set,
respectively
(subject AC).
FIG.
7
734
MARGARIA,
therefore,
the minimal
time necessary to pay the oxygen
debt
contracted
during
the lO-set
exercise
on pure
alactacid
( phosphagen)
sources only, without
involving
the glycolytic
mechanism.
In this case, at the end of the
10-set exercise period
the alactic
energy
sources must
be reduced
to a minimum
if the assumption
that LA is
d LA.
d run
20
( 1
mgz
run
15
x)
5
0
10
.
15
+
OLIVA,
DI
PRAMPERO,
,4ND
CERRETELLI
built only when the alactic
mechanism
is exhausted,
or
when it has reached a critical
level, is valid.
Since the half-reaction
time for the alactic
oxygen
debt payment
is about 25 set (4, 8>, and since 25 set is
the minimal
time of the interval
between runs that allows
the exercise to be carried out with no lactic acid formation, at steady state each run must involve
an alactic
oxygen
debt contracted
which
amounts
to half the
alactic
capacity.
The alactic
oxygen
debt pool then
oscillates
during
this kind of exercise between
0 at the
end of the run and 50 70 at the end of the 25-set recovery
period as indicated
schematically
in Fig. 5.
0 xygen consump hon. In Fig. 6, VOW on a breath-bvbreath basis from tracings such as in Fig. 1 is shown for’a
10 bursts of exercise with a
subject
AC) p er f orming
20-set pause. VOW appears
to increase very fast at the
beginning
of the exercise and in the first pause it is not
appreciably
different
from the first running
period.
At
steady state, van is sensibly less during
the pause than
20
runs
ml and per run, or in
FZG. 3. Rate of LA production
in mg/lO
its 02 equivalent
in ml/kg
body wt, as a function
of the number
of
runs. 8 subject AC; l subject AR ; -i- subject GR.
10
20
30
pause (set)
40
pool
5. Contribution
of the alactic
Voz al and lactacid
in percent
of the total alactic
capacity
to the energy requirement.
Working
period
lasts 10 set, the pause 25 set as indicated by vertical
thin lines (schematic).
FIG.
4. Rate of LA production
at steady state (avg of all subects) expressed
as its O:! equivalent
(ml Oz/kg
body wt and per
un) as a function
of the duration
of the pause period.
PIG.
vo 2
1act
5
%,
I/min
4
3 0
2
1
0
0’
00
4 0
l-
O
0
1
0
30
60
90
120
FIG.
6. Breath-by-breath
02 uptake as a function
of time during
intermittent
exercise (18 km/hr
-l- 157& lo-set exercise followed
by
210
270
240
2O-set pause). Some data at about
were not collected
(subject AC).
the middle
set
300
of the res .ing periods
ENERGY
BALANCE
IN
INTERMITTENT
EXERCISE
TABLE 3. Average 0, consumjhon after jifth
together with LA production expressed in O2
“4 uivalents *for subj’ect AC
Type
____--____
of Exp
l__l-_____-
lo-Set
lo-Set
Run,
Pause
I
-
lo-Set
20-Set
755
rUn (steady
State)
Run,
Pause
Run,
Pause
lo-Set
JO-Sect
-______-__)
Net &Q, ml/kg per min
~‘o~LA, ml kg per min
an average Tjoz value however
can be
during
running;
obtained
graphically
without
incurring
in an appreciable error.
Since the energy cost of the exercise is known (5) and
the average
oxygen
consumption
in these experiments
has been measured
(see Table
3), the oxygen consumed
during
the run, the oxygen debt contracted,
and the 02
debt paid during
the pause can be calculated.
Running
at 18 km/‘hr
on an incline
of + 15 % involves
a net energy expenditure
of 1.8 Cal/m per kg equivalent
to an oxygen consumption
of 108 ml/kg
per min, or 18
ml:/kg
per run (5). Since the maximal
net oxygen consumption
for these subjects was 54 ml/kg
per min, the
oxygen consumption
during the IO-set run at steady state
could not be higher than 5416 = 9 ml. This figure however should be reduced,
because when the pause amounts
to 25 set the average oxygen consumption
is appreciably
lower than the maximum
(see Table 3 and Fig. 6)? and
the average oxygen consumption
for the lo-set exercise
period cannot be expected
to be higher
than 7 or 8 ml.
If we assume that during
the run 8 ml/kg
of oxygen are
actually
used up, then about 10 ml are to be accounted
for bv the alactic oxygen debt. As this is paid in 25 set,
this should
therefore
be half the total alactic
02 debt,
which is supposed to have reached its maximal
value at
the end of the lo-set run. The alactic
capacity
of the
subject should therefore
amount
to about 20 ml oxygen
100 Cal/kg.
This is a figure of the same
kg, i.e., about
order of magnitude
as that found previously
(6, 7 j.
GENERAL
DISCUSSION
Because the oxidative
mechanism
is rather
sluggish,
and it takes about 1 min to reach full level, during
the
first run the subject is in a state of relative
anoxia (4, 9).
More energy is then drawn from anaerobic
mechanisms
and less from the oxidative
ones, and since the capacity of
the alactic mechanism
is limited
the body has to rely on
the lactacid
mechanism
to fulfill
its metabolic
reuuiremerits. Only after 1 min or more from the beginning
o
the exercise
does the oxygen
consumption
reach its
maximum,
and less energy is therefore
drawn from the
anaerobic
rnecha.nisms.
If the rest period is longer tha
25 set the phosphagen
source is then adequate
and no
call is made on the lactic mechanism.
Figure 5 shows schematically
the energy drawn from
the pools of the alactic and lactacid
energy as a function
of time in a performance
consisting
of 10 set of exercise
alternated
with 25 set of rest. The first run takes place
almost
exclusively
(90 %) at the expense of the alactic
oxygen debt, and the availability
of this source is reduced
at the end of the run to only 10 %. During
the following
25 set of rest, the alactic pool is restored to about 45 % by
the oxygen debt payment.
On the second run period
a
greater amount
of energy is paid by the oxidative
mechanism during
the run, and consequently
the oxygen debt
contracted
is less than in the first run, i.e., about
75 %
of the total energy requirement.
However,
this amount
is too high to be sustained
by the alactic mechanism
only,
since the alactic pool at the beginning
of the second run
is only 45 CT0of the initial
resting value; an appreciable
amount
of lactic acid is then. formed.
During
the next
25 set the alactic
oxygen debt is paid at a higher
rate
than in the first interval,
because the alactic energy pool
is practically
exhausted
and because the oxygen
consumption
is higher
than at the end of the first run. On
the third cycle the actual
oxygen
consumption
during
the running
period is still higher than during
the second
run, and therefore
a lesser oxygen debt needs to be built
while a higher amount
of the debt is paid in the restin
period.
In the following
cycles a progressively
higher
amount
of the oxygen
debt is paid during
the 25-set
pause and a lesser amount
is contracted
during
the
running
periods,
until
after 4-5 runs a steady state is
reached.
The payment
of the lactacid
oxygen debt is not shown
in Fig. 5 because it is negligible,
the rate of lactic acid
disappearance
from blood in recovery being very low (8).
In the experiment
in which the pause was only 10 set,
the oxygen consumption
during
the lo-set work period
is nearly maximal
when a steady state is reached.
It can
then be assumed that in this condition,
for example,
from
the 6th to the 10th run, 9 of the 18 ml of oxygen necessary to cover the cost of the lo-sec. run are actually
used
during
the run, and 9 ml are drawn from the anaerobic
energy sources. If we assume, as before, that the rate of
the alactic
oxygen debt payment
is such that the halfreaction
time is 25 set, in lo-set recovery
only about
25 % of the oxygen
debt
is paid,
corresponding
to
0.25 x 20 = 5 ml oxygen/kg
body wt and per run. The
remaining
amount
(4 ml) of the energy required
for the
run is then to be charged
on the lactacid
fraction
of the
oxygen debt. This amounts
to 20 cal, equivalent
to 0.09 g
lactic acid (6) which corresponds
to an increase of about
12 mg/ 100 ml of the lactic acid concentration
in blood
per run, approximately
the figure actually
found
and
given in Fig. 1.
In the experiments
in which the pause was 20 set, at
the end of this time 43 %I of the alactic
oxygen debt is
paid, corresponding
to 8.6 ml. Since in this condition
when a steady state is reached,
i.e., after the fifth run,
the oxygen consumption
during
the IO-set run can be
assumed to be about 8 ml (Fig. 61, only 18 - 8.6 - 8 =
1.4 ml oxygen/kg
and per run arc left on charge of the
glycolitic
mechanism.
This corresponds
to an increase of
lactic acid in blood of about 4 mg/lOO
ml and per run,
as actually
found.
Experiments
on intermittent
exercise were performed
756
recently
by Keul et al. (2, 3) on subjects exercising
on a
bicycle ergometer.
The intensity
of the exercise was 350 w
and it lasted in two series of experiments
30 see or 1 min,
the rest period being 1 min in both series. In the 30-set
exercise series a very limited
increase
of blood lactate
(about 26 mg/ 100 ml) took place at the beginning
of the
exercise, but no increase of lactic acid was observed when
was reached.
In the I-min
a steady-state
condition
exercise series, the lactic acid increased
progressively
to
the end of the experiment
( 10 runs) up to about 100 mg/
100 ml. Evidently
in this case a steady state in oxygen
consumption
could not be reached
and lactic acid was
An exercise
of 350 w correcontinuously
produced.
sponds to about 5 kcal/min
of mechanical
work, or, if
we assume an efficiency
of 20 % for this type of exercise,
to an energy expenditure
of 25 kcal/min,
or of 5 liters/
min of oxygen consumption.
The maximal
oxygen consumption
of the subjects is not given, and therefore
it is
not possible
to calculate
exactly
the role played
by the
alactic
and the lactacid
mechanisms.
Evidently
the intensity of the exercise did not exceed greatly the maximal
aerobic
power of the subjects and the oxygen debt built
in the 0.5-min
exercise period could be paid completely
in the I-min
pause, whereas the debt contracted
in the
1-min
period
of exercise was presumably
greater
than
the alactic
fraction.
We calculated
the excess from the
increase of lactic acid in blood at the end of this exercise.
It amounted
to 4 mg/lOO
ml lactic acid per run, corresponding
to 1.4 ml/kg
02 or to about
100 ml for the
whole
body.
If we assume that the maximal
alactic
oxygen
debt in these subjects was about
1,400 ml, the
oxygen
needed to fill up the 5,000 ml 02 requirement
during
the 1-min exercise amounts
to 5,000 100 of the
1,400 = 3,500 ml, a value which is presumably
order of magnitude
of the maximal
02 consumption
for
In the 0.5-min
run, the oxygen requirethese subjects.
ment being only 2.5 liters and the oxygen actually
con-
MARGARIA,
OLIVA,
DI
PRAMPERO,
AND
CERRETELLI
sumed during the run about 1.75 liters, only an additional
0.75 liter oxygen
is required,
and obviously
this can
be met completely
by the alactic fraction
only of the 02
debt.
In conclusion,
the behavior
of the lactic acid production, as observed in very heavy intermittent
exercise, is in
substantial
agreement
with the predictions
made on the
basis of previous
findings
which are therefore
supported
by the present experiments.
Particularly,
the following
points are confirmed.
a) In supramaximal
exercise, the
energy for the contraction
is not drawn from the glycolitic mechanism
until
the high-energy
phosphate
(phosphagen)
sources are exhausted
or they reach a critical
level. This alactic
mechanism
for providing
energy in
muscular
contraction
always precedes chronologically
the
lactacid
mechanism.
b) Payment
of the alactic
oxygen
debt takes place during recovery at a very fast pace. It is
an exponential
process with a half-reaction
time of the
order of 20-25 sec. c) The capacity
of this mechanism
is
about 20 ml oxygen/kg
body wt. d) Very heavy intermittent
exercise can be carried
out indefinitely
if the intensity of the exercise and its duration
are such as to involve an energy expenditure,
besides that sustained
by
the actual 02 consumption,
not greater than that corresponding
to the alactic fraction
of the oxygen debt, and
if the rest periods are long enough to allow the payment
of the oxygen
debt during
the exercise period.
If the
recovery
period
is too short, and the oxygen debt contracted
during
the working
period cannot be paid completely,
the energy balance
is filled up by an energetically
equivalent
amount
of lactic
acid built
in the
muscles.
This work has been supported by a grant from the Italian
tional Research Council (CNR).
R. D. Oliva is a Fellow of the World Health Organization.
Received
for publication
3 December
Na-
1968.
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enzymatische
Dehydrierung
von
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Spot-tar&
Sportmed.
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AND E. MANGILI.
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MARGARIA, R., H. T. EDWARDS, AND D. B. DILL.
mechanism of contracting
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Am. J. Physiol.
106:
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