T.E EFFECT OF TWO YEARS TRAINING ON AEROBIC POWER AND MUSCLE ST--ETC(U
APR 00 0IL.DANIELS, I E WRIGHT, 0 S SHARP
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J.E. Wright, D.S. Sharp, D.M. Kowal
**R.S. Stauffer
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USA Med Rsch and Dev Cmd, Ft. Detrick
Frederick, MD 21701
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Cadiets
C*W.L.Daniels,
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S. TYPE OF REPORT & PERIOD COVERED
The Effect of Two Years Training on Aercbic
.. .Power and Muscle Strength of Male and Female
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To be published in Medicine and Science in Sports and Exercise.
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Co
Long-term
treadmill.exercise, sex differences, cardiorespiratory fitness, lean body mass,
LUJ
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*
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sids i ne.esary mid Id--i- by block num ber) Eighteen cadets (11 males,
7 females) were studied on five occasions during their first tqo years of training at the U.S. Military Academy. Studies began during their first week at the
SAcademy and continued until the end of the second academic year. During the
study, the.regimented lifestyle imposed comparable environmental and dietary
factors. V02 (i/min) lean body mass and body weight increased significantly in
both groups. Per cent body fat was significantly reduced.only after the first
summer of training and then returned to initial values. VO2 max (ml/kg.min) did
not change in males during the sdy- Hcw-ver.
20. AUSrhACrcoti ,e.revers
DD,,A
1473
DITIONOF.6
IS OBSOLETE
~301
SECURITY CLASSIFICATION OF THIS PAOEOFham Date Entered)
it
after the initial 6 weeks of training (44.2 to 48.8 mlAcg.min). They remained
at this level through the second summer of training. However, by the end of
their second academic year, females, values dropped to 45.9 inlAg.min. Maximal
isometric strength measured 30-40% higher in males than in females. awiing the
last year of training, arm and shoulder strength increased (9.3%) in males but
was undianged in females. Our results suggest that even extended military tan
ing did not enable females to significantly narrow the difference with male
cadets in terms of nuiscle strength and aercobic power. <,-
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The Effect of Two Years Training on Aerobic Power and Muscle Strength
of Male and Female Cadets.
William L. Daniels, 3ames E. Wright, Dan S. Sharp,
Dennis M. Kowal, Robert P. Mello and Robert S. Stauffer
U.S. Army Research Institute of Environmental Medicine, Natick, MA 01760
and
U.S. Military Academy, West Point, NY 10996.
Address for correspondence and mailing proofs:
William L. Daniels, Ph.D., CPT, MSC
Exercise Physiology Division
U.S.A.R.I.E.M.
Natick, MA 01760
Running Head: Training of Male and Female Cadets.
Eighteen cadets (II males, 7 females) were studied on five occasions during
their first two years of training at the U.S. Military Academy.
Studies began
during their first week at the Academy and continued until the end of the second
academic year. During the study, the regimented lifestyle imposed comparable
environmental and dietary factors.
/O 2 (1/min), lean body mass and body weight
increased significantly in both groups.
Per cent body fat was significantly
reduced only after the first summer of training and then returned to initial
values.
O2 max (ml/kg.min) did not change in males during the study.
However, females increased significantly after the initial 6 weeks of training
(44.2 to 48.8 ml/kg.min). They remained at this level through the second summer
of training. However, by the end of their second academic year, females' values
dropped to 45.9 ml/kg.min. Maximal isometric strength measured 30-40% higher
in males than in females.
During the last year of training, arm and shoulder
strength increased (9.3%) in males but was unchanged in females. Our results
suggest that even extended military training did not enable females to
significantly narrow the difference with male cadets in terms of muscle strength
and aerobic power.
Long-term exercise, sex differences, cardiorespiratory fitness, lean body mass,
treadmill.
_
D__/y
/
Recently, there has been considerable interest in the military concerning
the physical fitness levels of females, their responses to physical training, and
comparisons of males and females in terms of physical fitness.
Much of this
interest has been generated by the large increase in the number of women in the
services and their entrance into job specialities which have been traditionally
held by males. While there have been many reports of the effects of training on
females (4,7) and even reports comparing males and females in the same training
program (2,3), these studies involved training of relatively short duration (6-9
weeks).
It
is not known how extended military training will affect the
differences in the levels of fitness which have been reported between genders.
The purpose of this study was to compare the responses of male and female
cadets to extended military training at the U.S. Military Academy.
During the
course of the study, the training program of both male and female cadets was
similar and in some respects identical.
At all times the regimented life style
imposed comparable environmental and dietary factors.
METHODS
Eighteen cadets (11 males, 7 females) completed all phases of this study.
These volunteers were part of a group of 60 cadets who were studied before and
after the initial summer training program which all cadets undergo and has been
described elsewhere (3).
For this study subjects were evaluated on five separate
dates listed in Table 1. These dates were selected so that they coincided with
the beginning and the end of the training programs which all cadets undergo
during their first two summers.
The final test date was at the end of their
second academic year.
The training during the first summer was six weeks long and similar to an
enlisted, initial entry, basic training program.
Physical
training consisted of
calisthentics, grass drills and a 30-minute run 5-6 times per week.
For the
running, cadets were divided into three groups based upon their performance in a
1.5 mile run.
Therefore, duration and frequency were identical while intensity
was adjusted to meet an individual's capability.
The second summer's training
program was designed to give cadets seven weeks of military field training. It
included infantry patrolling, hand to hand combat, wilderness survival, as well as
daily calisthenics and running.
During the academic year, all cadets were
required to participate in either an intramural, club or varsity sport and to
attend physical education classes. The first year of physical education consisted
of boxing and wrestling for males while females were given a course in selfdefense. Although the training was not identical during the entire study, it was
similar. All cadets led a very active life style and were required to participate
in demanding physical activities regularly. The regimented life style which was
in effect constantly assured similar dietary, sleeping and recreational habits
throughout the study.
Subjects underwent height, weight and skinfold measurements.
SkinLolds
(bicep, tricep, subscapular and suprailiac) were used to estimate body fat using
the formula of Durnin and Wormesley (5). All skinfold and weight measures were
performed by the same individual in order to maximize the reliability of the
comparisons.
On the last three test dates, subject's muscular strength was assessed with
maximal voluntary isometric contractions.
Three muscle groups were tested:
upper torso (arm and shoulder) flexors, leg extensors and trunk extensors with
equipment and procedures previously described (8).
Strength of the upper torso
was assessed with the subject securely fastened with a lap belt in a sitting
position. the upper arms were parallel to the floor with the arms forming a 900
2
_ _ _ _
I'
_ _
angle when an overhead bar was grasped. This bar was secured with a stationary
cable and the force exerted was measured with a strain gauge transducer.
Strength of the leg extensors was determined by testing the quadriceps
femoris muscle. The subject sat securely fastened in a chair with knees bent at
900 and grasped handles on the seat edge for additional stability. The subject
exerted outward force on a bar placed against the arch of the feet and connected
to a transducer.
Strength of the trunk extensors was assessed with the subject in a standing
position with the shoulders strapped to the bar which was connected to the
transducer.
The subject flexed back against the shoulder harness while driving
the pelvic girdle forward against a stabilizing plate.
Another isometric measure involving the arms, shoulders and upper back
muscles was also made. For this test, the subject was in a standing position and
pulled upward on a bar fixed at a height of 132 cm, which was attached by cable
to a force transducer.
subject stood.
The transducer was mounted on a plate on which the
For all the strength measures, two maximal contractions were
performed and averaged.
During each session, subjects peformed a running maximal oxygen uptake
(ftO2 max) determination. The test used was a modification of the test used by
Mitchell et al (10).
The test began with a warm-up run for 6 minutes, followed
by a 5-10 minute rest period. Two to four additional runs were performed, each
3-4 minutes long and interrupted by rest periods. Workloads were increased by
raising speed and/or grade. During the last minute of each run, expired air was
collected in plastic Douglas bags through a mouthpiece and Kogel y-valve.
A
plateau in 02 comsumption with increasing workload was considered indicative
of
VO 2
max.
A plateau was defined as an increase of less than 2.0 ml/kg.min
3
with an increase of 2.5% grade.
Expired air was analyzed with a Beckman LB-2
CO 2 analyzer and a Model 53-A oxygen analyzer from Applied Electrochemistry,
Incorporated.
Volumes were measured with a Tissot spirometer.
Ratings of
perceived exertion were recorded during the last minute of each run using a Borg
scale (1).
Heart rate was monitored using a modified V, electrocardiograph
recording.
Statistical comparisons were made using an analysis of variance for
repeated measures.
Tukey's HSD test was used for post-hoc comparisons.
For
statistical significance, we used p < 0.05.
RESULTS
Table 2 lists the physiological data collected on males during the testing
period.
O02 max (ml/kg.min) and HR max did not change significantly during
the entire study.
In contrast,
O2 max (liter/min) did increase significantly
along with body weight over the two year period. This weight increase in males
was due exclusively to an increase in lean body mass (LBM) since body fat was
reduced only after the first summer's training.
Minute ventilation (BTPS)
increased at the end of each summer's training and remained elevated throughout
the second academic year.
Table 3 lists the physiological data that was collected from female cadets
during this study.
In contrast to the male cadets, females underwent
a
significant increase in VO 2 max (ml/kg.min), however there was a decrease over
the course of the second academic year.
cadets in 'O2 max (1/min) and LBM.
A similar trend is seen in the female
Like the males, females showed a decrease
in % body fat after the first summer's training.
However, by the beginning of
the second summer both groups had % body fat values similar to that at which
they started. HR max and minute ventilation (BTPS) changed significantly in the
females and was associated with the summer training programs.
4
The results of the maximal isometric strength testing are listed in Table 4.
This testing was performed before and after the second summer's training and
after the second academic year. No data was available for the leg extensors at
the end of the second academic year due to technical problems with that
measure.
Over the summer of 1978, both males and females showed increased
leg extensor strength (6.9 and 8.3% respectively).
This increase was statistically
significant for males (p<0.01) but not for females.
Males showed larger
increases in both measures of upper body strength than females between June,
1978 and May, 1979.
females by 4.6% (NS).
On the upright pull, males increased by 6.7% (NS) and
Upper torso strength for males increased by 9.7%
(p<0.01) while females had a 3.7% increase (NS) in strength.
On all strength
measures the values for female cadets averaged approximately 30-40% lower
than their male counterparts.
Trunk extensor maximal isometric strength declined over the summer of
1978 but returned to their initial levels when measured in May, 1979.
While
unsure of the actual cause for this phenomenon, it seems much likelier to be due
to fatigue resulting from some aspect of the summer training program rather
than an actual decrease in muscle strength.
DISCUSSION
The results of this study indicated that even after two years training,
female cadets did not narrow the gap between them and their male counterparts
in terms of aerobic power and muscle strength. Both males and females started
this study in a fairly high state of fitness. Initial aerobic power measurements in
both male and female cadets are comparable to values reported for college aged
athletes (4,6). The high level of fitness is probably responsible for the lack of an
increase in aerobic power (ml/kg.min) in males.
5
However, the effect of the
training on the males is apparent when one examines changes in
(liter/min), lean body mass (LBM) and upper torso strength.
O max
2
It is interesting to
note that males were able to retain their high /O2 max while they increased
body weight.
Females, on the other hand, had significant increases in aerobic
power and lean body mass but not in any of the muscle strength measures.
Females showed a characteristic response to an aerobic training program during
the first summer.
They maintained this level of fitness through the second
summer but had a drop in aerobic power when tested at the end of their second
academic year.
This decrease in aerobic power was associated with a decrease
in minute ventilation, body weight and lean body mass. It appears as though the
females underwent a period of detraining over the course of the second academic
year.
However, it must be pointed out that both males and females were in
excellent physical condition when compared to a similar aged group (6,11).
In an effort to determine the cause for the decrease in aerobic power we
evaluated questionnaires given to each cadet, regarding injury and illness.
During the course of the second academic year, 5 of the 7 female cadets were
restricted for some period of time (4 days to 6 weeks) from performing physical
training for medical reasons. On the other hand, only 2 of the I
restrictions, both for three weeks (Table 5).
males had such
This difference betwen males and
females in loss time in training is characteristic of the pattern that is seen in all
cadets (personal communication, Louis Tomasi, A.T.C., USMA, West Point, NY).
It therefore appears that women are more susceptible to injury/illness as a result
of this type of lifestyle and that this may contribute to the detraining affect
seen in this study.
Even though the length of restriction was fairly short in all
the cases listed above, the fact that the injury rate was so much higher in
females than in males may mean that, because of untreated, minor injuries or
6
___
__
__i
discomforts, they were unable to train at the frequency, duration and intensity
required to maintain an exceptionally high level of fitness.
However, further
studies are required in order to substantiate this hypothesis.
Unlike males, females did not show any significant changes in upper torso
strength.
Studies in animals indicate that males have greater capacity for
improving muscle strength and mass than females (9). The results of the present
study agree with those findings and indicate that the training stimulus did not
cause significant changes in muscle strength of female cadets.
However, it
should be noted that most of the strength gains occurred during the summer
program when training was virtually identical.
Therefore, females may not be
physiologically able to respond to the training in the same manner as males as
regards muscle strength.
Both male and female cadets had greater aerobic power and muscle
strength when compared with enlisted military counterparts.
A group of males
and females were recently tested at the end of the 6-week basic training
program ( 1). Males had a
at 39.3 + 3.5.
O2 max (ml/kg*min) of 52.3 + 3.8 and females were
The male and female cadets had values for aerobic power that
were approximately 15% and 20% higher, respectively.
had lower % body fat levels, also.
Male and female cadets
At the end of basic training the males
averaged 14.5 + 3.8% body fat and females averaged 26.2 + 3.8% body fat.
:" terms of muscle strength, male and female cadets were stronger than
basic trainees in upper torso and leg extensor measures. There was no difference
in trunk extensor measurements (unpublished data from this laboratory).
The results of this study demonstrate that male and female cadets have
greater aerobic power, less body fat and are stronger than a similar aged
military enlisted group who performed the same tests.
7
The female cadets did
not significantly narrow the discrepancies with male cadets in terms of muscle
strength and aerobic power, even after two years of similar training.
These
results support the theory that most of the difference observed between males
and females in aerobic power
and muscle strength is due to genetically
determined physiological differences rather than social, cultural and environmental differences in state of training.
8
References
1.
Borg, G. A. V. and B. 3. Noble. Perceived Exertion. In: Exercise and
Sports Sciences Reviews, Vol. 2, Jack H. Wilmore (ed.) Academic
Press, New York, N.Y. pp. 131-153, 1974.
2.
Burke, E. 3. Physiological effects of similar training on males and females.
Res. Q. Am. Assoc. Health Phys. Edu. 48: 510-517, 1977.
3.
Daniels, W. L., D. M. Kowal, J. A. Vogel and R. M. Stauffer. Physiological
effects of a military training program on male and female cadets.
Avia. Space Environ. Med. 50(6): 562-566, 1979.
4.
Drinkwater, B. L. Physiological responses of women to exercise. In:
Exercise and Sports Sciences Reviews, Vol. 1, Jack H. Wilmore (ed.)
Academic Press, New York, N.Y. pp. 126-153, 1973.
5.
Durnin, 3. U. G. A. and J. M. Wormesley. Body fat assessed from total
body density and its estimation from skinfold thickness, measurements on 481 men and women from 16 to 72 years. Brit. 3. Nutr. 32:
77-92, 1974.
6.
Kamon, E. and K. B. Pandolf. Maximal aerobic power during laddermill
climbing, uphill running and cycling. 3. Appl. Physiol. 32: 467-473,
1972.
7.
Kearney, 3. T., G. A. Stull, 3. L. Ewing, Jr. and J. T. Atrein. Cardiorespiratory responses of sedentary college women as a function of training
intensity. J. Appl. Physio. 41: 822-825, 1976.
8.
Knapik, J. 3., D. M. Kowal, P. Riley, M. Sacco and J. E. Wright.
Development and description of a device for static strength measurement in Armed Forces Examination and Entrance Stations. USARIEM
Technical Report No. T-2/79, 1979.
9.
Kochakian, C. D. Body and Organ Weights and Composition. In: Anabolic
-Androgenic Steroids, C. D. Kochakian (ed.), Springer-Verlog, New
York, N.Y. pp. 73-154, 1976.
10.
Mitchell, 3. H., J. Sproule and C. B. Chapman. The physiological meaning
of maximal oxygen uptake test. J. Clin. Invest. 37: 538--547, 1957.
11.
Patton, j. F., W. L. Daniels and J. A. Vogel. Aerobic power and body fat of
men and women during Army basic training.
Accepted for
publication. Aviat. Space Environ. Med.
9
Table t
le
S..Ibdul-e
Tfo lnr
Aerobic Power
1. June 1977
1st Summer c1 Training
2. August 1977 Aerobic
1st Acdmkc Year
Fower
Aerobic Fower &Muscle Sfrenglh
3. June 1978
2nd Summer of Training
Aerobic Fower • Muscle Sfrengfh
4. Augusf 1978
2nd Academic Year
Aerobic Power & Muscle Strenth
5.May 1979
- .
Table2.
Physioloical
Collcted
Data
Tesing
"xerise
Dring Maximal
Of Mle.
..
June 1977
N 11
977 June 1978
August
August 1978
May 1979
Tukey's
HSD
58.5
3.5
60.1
3.9
60.8
4.2
59.9
3.4
60.3
2.8
"S
v0 2 max(L/rmin)
4.13
A6
A
4.21
4.41
.34
4.3
4.54
.21
HRmax(bfs/min)
190
6
185
6
190
7
189
16
140.1
19.3
70.5
150.5
29.3
69.9
141.4
19.3
72.2
157.6
16.9
156.6
22.2
7.7
8.0
7S.0
8.4
1.6
8.1
74.1
8.0
% Body Fat
12.1
2.3
9.7
3.0
12.1
2.3
12.1
2.3
12.1
2.8
1.3
LBM (kg)
62.4
63.5
63.9
65.3
66.0
1.1
rO
2 max
(mI/ kg.mil)
VE BTPS (L/min)
Wt (kg)
6.5
Values
S.
..
,...
.31
6.3
6.4
expressed as
;.
i
i S.D.
"Al
6.5
188
7
6.6
HS
13.3
Table 3. Physiological Dat. Collected
Lf 7
90 maxn(ml/kg.min)
2
June 1977
44.2
4.6
Amu, 1977
48.8
3.7
June 1978
48.1
4.4
August 1978
49.0
4.4
Tukoh 's
HSD
3.11
Mal1979
45.9
2.8
902 max(L/min)
2.47
.26
2.74
.24
2.78
.29
2.91
.28
2.67
.14
HRmxx(bls/min)
193
7
186
9
193
6
186
7
192
5
VE BTPS(L/A in)
90.8
17.4
105.1
14.5
93.6
17.6
107.4
19.1
100.7
10.8
16.6
Wt(kg)
56.1
3.9
56.2
3.0
57.9
4.0
59.4
3.2
58.3
3.2
2.0
% Body Fat
22A
3.3
19.3
2.4
21.3
2.6
21.9
2.8
21.0
1.8
L3M (kg)
43.5
1.9
45.2
1.6
45.5
2.1
46.3
1.4
45.9
1.7
1.3
Values expressed as
• ....
Exercise Testing Of Females.
Maxinmal
During
.
. ...
:.':--.....
..
.*................................................
.
7
3.1
f
!S.D.
...: :
.,. ..
.26
..
.
*
- i:11,
. ..
.
i..
.
.. ...
.
i° .... ::
:
Table 4. Masimal Isomel_ StregiaL.
Jon
Au.,igg1978
1978
May 1979
L6iald Pull
Males
Females
134.3
6.4
140.9
59
143.3
6.3
38.1
3.9
87.8
4.1
92.0
.
6.6
. ..
Us~p~ Tares
Mles
Females
106.6
4.7
113.9
3.7
11S.8"
SA
"A
1 .9
70.5
1.
6.3
1.5
Tail, Eiillep~u
Males
87.1
3.5
79.7"
B.
86.2
3.8
Females
59.2
26
55.0
2i
58.1
3.4
Le
Males
181.0
9.7
124.2
Females
_alems.orf
193.6
8.4
134.5
14
Values espressed as
.
Subie
ime Lost Due T. lllnss/Tn.,
!liess/Tmniuryi
Time Lost
Data
Females
NO Dale
9.4
6.7
- .
Table S.
1612
pelvic
1628
nane
1626
1
SA
.pa 0.0S
pain
lower back pain
1 wk
2 wks
1629
endmnilis
2 wks
1638
fig
4 days
1650
none
1659
stress fracture
6 wks
Males
1614
lone
1616
sprained
1620
me
1624
nMae
• o.
I
.
.
.
...
.
.
..
.
3 wks
1640
em"
1654
no"e
1656
strelched ligemtns(soulder) 3 wks
1657
W
ankle
"no
1662
none
1665
mem
1668
noe
The views, opinions, and/or findings contained in this report are those
of the author(s) and should not be construed as an official department
of the Army position, policy, or decision, unless so designated by other
official documentation.
Human subjects participated in these studies after giving their free and
informed voluntary consent. Investigators adhered to AR 70-25 and
USAMRDC Regulation 70-25 on Use of Volunteers in Research.