Dehydration effects on work capacity and aerobic capacities of me

Newton, J. L.

Robinson, S.

Sadowski, B.

English

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4 Fina l  Scient i f ic  Report 6 
National AeronautAxs wpd Snace Administration 
O/December 31, 1966 I @  
3The Effects of Dehydration 
1 on the Aerobic and Anaerobic Capacities of  Men 
9 6 s, Robinson, D. Sadowski and J. L. Newton 
2Departrnent of  Anatoqy and Physiology 
I Indiana University 
Bloomington, Indiana 1, 
3 
https://ntrs.nasa.gov/search.jsp?R=19670018679 2020-03-12T11:36:49+00:00Z
. 1 
.. - 
-The effects of dehydration on the aerobic and anaerobic capacit ies 
S. Robinson, B. Sadowski and J. L. Newton. 
Abstract 
NASA NSG 408, December 
L of menr 
31, 1966. 
The ef fec ts  of dehydration 
temperature regulation of 4 Tnen 
determined. I n  the dehydration 
on f 
i n  exhausting work end recovery were 
experiments the  men were dehydrated by 
max, O2 debt, blood lactate ,  and 
O2 
2 4.2 t o  b.7$ of body weight i n  the  morning by working (MR 190 Cal /m /hr) 
i n  t he  heat (50 C db, 27 C wb) f o r  2 t o  3 hours. 
fo r  about 3 hours i n  a cool room (24 C )  without ingesting any f l u i d  and 
their  responses during an exhausting treadmill  run ( 3  t o  6 min) and 
recovery were determined. 
the  dehydration. 
and b.04 min i n  the control and dehydratlon experiments respectively. 
Body temperature, \to,, m a x ,  O2 debt and the  elevation of blood l ac t a t e  
i n  the  runs were n6t s ign i f icant ly  different  i n  the two experiments. 
The reduced capacity f o r  running i n  dehydration was associated with an 
average increase of 5% i n  the 02 requirement per kg of body weight 
per minute of running time. 
was dependent on more raoid accumulation of the O2 debt during the  
runs. Depletion of carbohydrate reserves was probably not a 
contributing factor  t o  t he  decreased work capacity since the  men's 
metabolic respiratory quotients averaged 0.89 and 0.87 near the  ends of 
t he  50-minute aerobic work recoveries following the control and 
dehydration runs respectively. 
They then rested 
Control experiments were carried out without 
The average tims of running t o  exhaustion were ls.63 
The small increase i n  energy requirement 
~ - 
Dehydration, which is accomanied by a decrease i n  plasma volume, 
has been found t o  in t e r f e re  serimsly with temperature regulation of 
men i n  hot environments, par t icular ly  i f  they a t t e r p t  t o  work i n  the 
heat (1, 5 ) .  Circulating plasma volwre i n  dehydration is decreased 
2.5 t o  4 times as muck! as would be expected if water loss  of the plasma 
were i n  proportion to the loss by the whole body (1, 2, 6,  8), 
under  conditi t ions of work i n  the heat a 10 t o  20% increase i n  
c i rculat ing plasma volume occurs and t h i s  f a c i l i t a t e s  the  circulatory 
adjustments involving large increases i n  blood flow t o  the muscles and 
t o  the skin (2, 6 ) .  Tiken dehydrated men work i n  the heat, c i rculat ion 
f a i l s ' i n  i t s  function of heat transfer fromdeep t issues  t o  skin as 
a r e su l t  of t he  reduction i n  plasma volume, 
Nwmally 
Several investigators have found that dehydration also reduces 
the capacity of m e n  f o r  severe work i n  a cool environment (3 ,  7, 8). 
Buskirk e t  a1 ( 3 )  found a consistent reduction, averaging 0.22 liters/rLn, 
i n  $0, m a x  i n  men dehydrated by an average of 5.7% of body weight. 
On the other hand, S a l t i n  (7,8) found that  dehydration up to 5.2% 
caused no reduction i n  max, or  i n  maximal cardiac output, but 
t ha t  substant ia l  reductions i n  work tolerance and i n  the a b i l i t y  t o  
elevate blood l a c t a t e  i n  exhausting work occurred. 
02 
The present study was designed not only t o  detmnine the e f fec ts  
of dehydration on the work tolerance and aembic c a p c i t i e s  of men, 
but t o  include measurevents of the m a x i m a l  02 debt and the efficiency 
of men performing exhausting work of 3 t o  6 nrinutest duration i n  a 
cool environment , 
PFlO CEDURE 
The same subjects (Table 1) were used, and the same general 
FoclJdure was followed i n  t h i s  study as i n  P a r t  I11 of this report. 
. .  
Table 1. ,Physical character is t ics  and WOT.. ra tes  of the sub jecta. 
i n  the exhausting runs were selected according t o  the yen's ab i l i t i e s .  
Work rates  i n  recovery were individually selected t o  r a i se  V 
ilork ra tes  
to 
about SO$ of maxival rates.  02 
. .  
Each experiment included an exhausting r i m  on the treadroil1 followed i n  
order by a SO-ninate period of aerobic work, and a 3S-minute period of 
rest, a l l  i n  a cool envi.ronment (24 C).  
concentration were determined and r e c t a l  (T,) and skin (T,) temperatures 
were recorded as i n  Part 111. The control exwriments were carried out 
i n  t h e  afternoon i n  a cool env’ronment (24 C) as i n  P a r t  I11 with the 
men normally hydrated. 
a 
02 debt and blood l ac t a t e  
For conmarison w i t h  the responses of t h e  f u l l y  hydrated men i n  
t h e  control experiments they were dehydrated by 4 t o  5% of t h e i r  body 
weights i n  another se r ies  of experiments. 
experiments the men came t o  the laboratory at 8 a.m. a f t e r  a l i g h t  
breakfast, Wearing only slimts, tennis shoes,, and socks, and with 
thermocouples i n  place f o r  r ec t a l  and skin tepperature records they 
walked on the  treadmill ( F I R  190 Cal/m2/hr) i n  the hot room (SO C deb,, 
27 w.b., a i r  movement 55 m/nin) without drinking water u n t i l  they 
reached the planned degree of dehydration. 
balance accurate t o  +& grams before s t a r t i ng  and a t  apwopriate 
intervals  during the walk i n  order t o  follow the course of the 
dehydration and t emina te  t h e  exposure when the proper weight l o s s  was 
reached. 
the Fen. 
(24OC) i n  t h e  laboratory. 
r ich  i n  carbohydrates, bu t  without f l u i d .  
varied f rm none to  230 gram, according t o  individual appetite. 
2 p.m. the thermocouples were replaced on the m e n  and they were neighed 
ap;ain i n  preparation fo r  t h e  exhausting run and recovery i n  a cool 
room (24  C). 
i n  the control expmimnts.  
I n  ?repmation f o r  these 
They w e r e  weighed on a 
It required from 2 to 3 hours work i n  the heat t q  c’ehydrate 
Following the  dehydration period the  rren rested i n  a cool room 
A t  noon they a t e  up t o  230 grams of food, 
The amount of food eaten 
A t  
0 The dehydration experiments were carried out exactly as 
. .  
RESULTS 
0 The men's body temperatures i n  the  experiments a re  given i n  Table 
* 
2, a t  the begin-ing of t h e  exhausting 
runs are  revarkably similm i n  the control and c'ehydration experiments. 
There were considerable individual variations f rorn the  meansj especially 
i n  Ts, but none of the individual temperatures indicated a thermal 
state which would interfere  with performance.5.n t h e  run, according t o  
the  results of the temperature experinents given i n  P a r t  I11 of t h i s  report. 
During the  aerobic work phase o f  recovery the r e c t a l  temperatures of a l l  
men rose t o  s ignif icant ly  higher levels i n  the dehydration than i n  the 
control experi-ments. This is  no t  silrprising since dehydration is known 
t o  reduce blood volume and t h u s  interfere  with cutaneous circulat ion of 
men performing noderate work i n  the heat (1,6). 
i n  r ec t a l  temperature during the resting phase of recovery was about the  
same i n  the two experir?ents. 
The mean values of Tr, Ts and T m 
The m a n  r a t e  of decline 
The metabolic changes i n  the rnen d u r i n g  the 02 debt experiments are 
gilren in Table 3. 
exhausting runs ranged from 4.15 t o  &.7$ of body weight. 
experirents they were normally hydrated a t  the t i r e  of the r ims.  
of the  k men fa i led  t o  coqtinue the runs as long w5en they were dehydrated 
as i n  the control exp>riments, the average time of running being s igni f icant ly  
reduced by dehydration, 9% max values were prac t ica l ly  the same i n  the 
two runs. 
about the same I n  the  2 experiments. 
lower values of 02 debt and blood lac ta te  were observed i n  t h e  dehydration 
experiment thsn i n  the control experiment and these diffsrences were 
related d i rec t ly  t o  a substant ia l  reduction i n  running tire. 
men whose running times were reduced i n  dehydration a l so  had lower blood 
l ac t a t e s  following the  runs. DL who was able  t o  force himself t o  run as 
Dehydration of the men j u s t  before s ta r t ing  the 
In  the control 
Three 
In 3 of the 4 men max;-ral O2 debts foll-owing the runs were 
I n  the other man (DC) considerably 
0 The three 
a m b  
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long i n  the dehydration as i n  the control experinent accumulated a higher 
l a c t a t e  i n  t h e  former. The average @ requirement per  ninute of running 
time was not s ignif icant ly  different i n  the two  runs. 
the  men's body weights were reduced i n  the dehydrgtion experiments, the 
average 
those experiments than i n  the  controls. 
r. 
Hmrever, since 
02 requiremnt/min/kg of body weight was aboL!t 5% higher i n  
DISCUSSION 
Themas'tsignificant e f fec t  of dehydration on wrformance i n  t h e  
exhausting runs was a reduction i n  the time the men could continue the 
runs before they reached exhaustion. "his decrease i n  endurance 
was dependent, E t  l e a s t  i n  part ,  on decreased efficiency as 
-indicated by a small ( 5 % )  increase i n  O2 requirement/kg/min of running 
time. Since the  average 
i n  t h e  runs  was the same, the increased O2 requirements of the men i n  
dehydration expzriments w e r e  dependent on increnents i n  the  r a t e s  of 
accumulating the O2 debt. 
the same 02 debts i n  both runs, but since the averape t i m  af running 
was decrea.sed i n  the dehydration experiments, the b u i l d  up of the 02 
debt was f a s t e r  i n  those experiments than i n  the controls. 
i n  efficiency i n  dehydration was probably nut dependent on depletion 
of the men's carbohydrate reserves i n  the niarni.ng walks preceedipg the 
runs. Evidence f o r  t h i s  is t ha t  the i r  metabolic respiratory quotients 
during steady states near t he  end of the exercise recaveries vere only 
s l i gh t ly  lower i n  dehydration (0.87) than i n  the control experiments (0.89). 
max and the  arilount of 02 debt accumulated 
*02 
On the average the ren accumulated about 
The decrease 
O u r  data showing no reductions of 40, m a x  when t he  men were 
dehydrated confj.rm previous resul ts  of Sa l t i n  (5 ,6) ,  
dehydration d i d  not decrease the r a t e  of elevating the % consumption 
during the first 2 or  3 minutes of the runs (.Fig. 1). 
Furthermore, 
The retent ion of 
! 
1 ~. 
I. . 
, 
'02 L/MIN 
L I 
0 
z 
--I 
;D 
0 r 
P 0 -. 
'd 
P* 
9 . 
the  m a x i m a l  cayacity for  incre3sing 02 consumption i n  exhausting work 
indicates that i n  dehydration the men were able t o  make adequate 
compensatory vasoconstrictor responses i n  the sk-i.n and viscera, and 
thus shunt most of t h e  blood flow t o  the working muscles. Another factor  
which probably helped i n  t h i s  response was the hemoconcentration which 
9 
u 
1 
occurred i n  dehydration; the men's hematocrits a t  the start Df the  runs 
averaged k6.6$ i n  the  control and 49.0$ i n  t he  dehydration experiments. 
This increase i n  02 capacity of. t he  blood could compensate for  a moderate 
reduction i n  m a x i m a l  cardiac output which might be expected t o  occur with 
the reduction of blood volume which occurs i n  dehydration. 
above, Sa l t i n . (6 )  hds found l i t t l e  change i n  rraxirnal cardiac output 
Hmever, as s t a t e d  
of men i n  dehydration. 
Acknowledgment : 
The authors grateful ly  acknowledge t?ie technical assistance of 
They a l s o  wish t o  thank Arthur CarDbell, David Coles, Daniel Haynes. 
George Fj.nley, and David Lloyd for  acting a s  s ~ b j e c t s  i n  these experiments. 
1, .' 
1, Adolnh, E. F. 
Desert. Interscience Publishers . Inc . Chaptgr X. New Ymk, 19b7 . Blood chawes in  dehydration, Physiology of Van i n  the * 
2. Bass, D. E., C. R. Kleeman, 1:. Quin, A. Henschel, and A. H, Hegnauer. 
Mechanism of acclimatization bo heat i n  van, Fedicine 34: 323- 380, 19%. 
Buskirk, E.R., P. 7. Impietro and D. E. 3ass. 
dehydration: effects Df physical condition and heat acclimatieation. 
J, Applied physiol. 12: 
Koelowski, S., and B. Sal t in .  
J. Applied Physiol. 19: 1119-1124, 1964, 
8 
3. Vork prrforrlnance a f t e r  
189-194, 1958, 
4, Effect af sweat loss  on lsody f l u i d s ,  
5.  Pitts, G. C., R. E. Johnson, and  P. C, Consolagio. 
as affected by intake of water, salt, and glucose. 
142: 253- 259, 1944, 
6. Robinson, S,, R. K. Kincaid and R. IC. Rhamey. Effects of desoxycorticosterone 
on acclimatization of men t o  heat. - J. Applied Physiol. 2: 399-406, 1950, 
Salt in ,  B, Aerobic and anaerobic work capacity a f t e r  dehydration. 
J, Applied Physiol. 19: 1114-1118, 1964. 
dehydration. J. Applied Physiol. 19: 1125-1132, 1964, 
Vork i n  the heat 
Am. J. Physiol. 
7. 
8. Sal t in ,  B, Circulatory response t o  submaximal exercise a f t e r  t h e m 1  


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