Eur J Appl Physiol 44, 25-34 (1980) European Journal of

Applied Physiology and Occupational Physiology �9 Springer-Verlag 1980

Transfer Effects of Endurance Training to Exercise with Untrained Limbs*

Steven Lewis 1, Paul Thompson/, Nils-Holger Areskog 3, Paul Vodak, Marian Marconyak, Robert DeBusk, Susan Mellen, and William Haskell

Cardiology Division, Stanford University School of Medicine, Stanford, CA 94305, USA

Summary. There has been a controversy over whether the increases in maximal oxygen uptake (P'O 2 max) and reductions in heart rate at a given submaximal workload after endurance training are limited to exercise with trained limbs or also may be observed during exercise with untrained limbs. In the present study five ini- tially very sedentary young men trained by leg cycling (LT) and five by arm cranking (AT) 30 min per day on 4 days a week for 11 weeks at an intensity _> 75 -80% VO z max" Before and after training the subjects performed submaximal and maximal arm cranking and leg cycling tests. Leg cycling and arm cranking VO2 max increased 15% and 9% after LT and 12% and 35% after AT, respectively. Heart rate at a given submaximal workload was lower (p < 0.05) during trained and untrained limb exercise following LT and AT. However, subjective ratings of perceived exertion (RPE) at a given submaximal workload were lower (p < 0.01) only during exercise with trained limbs after LT and AT. In light of previous findings, the present increases in VO 2 max and reductions in submaximal exercise heart rate with untrained limbs suggest that the initial fitness of the subjects as well as the intensity, frequency, and duration of training may be important factors in de- termining the extent to which transfer effects of endurance training can be ob- served. Although the present data suggest that reductions in RPE after endurance training may be the result of local changes in trained muscles, the possible contribution of central nervous adaptations cannot be excluded.

Key words: Maximal oxygen uptake - Heart r a t e - Subjective ratings of perceived exertion - Arm vs. leg training - Exercise

* Supported in part by Grant HL 18907 from The National Heart, Lung, and Blood Institute 1 Present address: Division of Cardiology, University of Texas, Southwestern Medical School, Dallas, TX 75235, USA 2 Present address: Division of Cardiology, Brown University School of Medicine, The Memorial Hospital, Pawtucket, RI, USA 3 Present address: Department of Clinical Physiology, LinkSping University, Regionsjukhuset, Link6ping, Sweden Offprint requests to: Steven Lewis, Ph.D., Southwestern Medical School, Division of Cardiology, 5323 Harry Hines Blvd. (H8.116), Dallas, TX 75235, USA

0301-5548/80/0044/0025/$ 02.00

26 S. Lewis et al.

Increases in maximal oxygen uptake (~/rO 2 max) and reductions in submaximal exercise heart rate have been demonstrated repeatedly after endurance training [4]. In nearly all studies both exercise testing and training have been performed with the same limbs. After endurance training of one limb or set of limbs several investigators have reported increases in fzO 2 m,x or reductions in heart rate during submaximal exercise with trained but not untrained limbs [6, 9, 16, 24, 26, 29]. These "limb specific" training ef- fects may result from peripheral adaptations, such as enhanced activity of oxidative en- zymes in trained skeletal muscle [25], rather than from changes in the heart itself, the central circulation, or the central nervous system [4]. In contrast, there have been a few reports of "transfer effects", i.e., increased VO z max or lowered submaximal exercise heart rate also with untrained limbs [5, 23]. Improvements in the exercise capacity of untrained limbs have been considered evidence for central circulatory adaptations to endurance training [4].

The conditions under which transfer effects of training may occur are controver- sial. An absence of improvement with untrained limbs in some recent studies might have resulted from the fact that the subjects initially were physically active with those limbs or from training programs which may have been unlikely to elicit central circulatory adaptations because of inadequate intensity, frequency, or duration [6, 16, 24, 29]. In the present study we sought to determine whether increases in VO 2 max and reductions in submaximal heart rate would occur during exercise with untrained limbs after a period of arm or leg training in initially very sedentary men.

Another aim of this study was to obtain subjective ratings of perceived exertion (RPE) [3] in connection with exercise performed with trained and untrained limbs. RPE have been demonstrated to be valid and reliable indicators of the physiological strain produced by exercise [27, 28]. It was observed previously [ 12, 22] that RPE were lower when exercise was performed at a given submaximal workload with endurance trained limbs. Both central cardiorespiratory and local muscle, tendon and joint factors appear to influence RPE in acute exercise [ 12, 21]. However, the relative contributions of central and local factors in the response of RPE to endurance training have not been clarified [21].

Methods

Subjects

Ten healthy male college students volunteered to participate as subjects. None had performed regular stre- nuous physical activity with their arms or legs for at least 6 months prior to entering the study. Only one subject, who had been a college junior varsity basketball player two years before, had ever been trained previously. At random, five subjects were assigned to perform arm training (mean _+ SD for age, height and weight: 20 + 3 yr, 175 _+ 2 cm and 73 _+ 12 kg) and five to perform leg training (22 _+ 2 yr, 186 _+ 10 cm and 79 _+ 13 kg). Body weight remained essentially constant for each group during the study period.

Procedures

Subjects underwent evaluation before and within 5 days after 11 weeks of training. In each evaluation sub- maximal and maximal exercise tests were performed in the sitting position on each of two separate days. On each testing day the subjects performed two submaximal exercise tests with the same set of limbs, either

Cross-transfer of Training of Arms or Legs 27

arm cranking or leg cycling, followed by one maximal test with the other set of limbs. Alternate subjects in each group were assigned to perform arm or leg testing first and the order of tests performed by each sub- ject was the same before and after training. Testing was conducted at approximately the same time each day for each subject. On two separate days prior to the pre-training evaluations all subjects performed sub- maximal and maximal arm cranking and leg cycling to become familiar with the experimental procedures and apparatus.

Submaximal exercise tests lasted 10 rain and were performed at a cranking or pedalling rate of 60 �9 min -1. On each testing day the first submaximai test was performed at a constant workload which was the same pre- and post-training for each set of limbs and which had an energy requirement approximately equal to 70% of individual pre-training fzO z max with the respective limbs. The second submaximal test was performed after a rest period of 15 rain. Before and after training the workload of this test was adjusted to maintain heart rate approximately at the average of that achieved during the last 3 rain of the first pre- training submaximal test with that set of limbs. The second submaximal test was designed to examine the effects of training on systolic time intervals, the results of which will be reported elsewhere. The maximal test began 10 rain after the second submaximal test ended. The initial workload for maximalleg testing was 50 W and the load was increased by 33 W/rain. For maximal arm testing the initial workload was 25 W and was increased by 17 W/rain. In maximal testing a cranking or pedalling rate of approximately 70 �9 rain was maintained and the subjects exercised to exhaustion.

Exercise testing was performed on a Collins ergometer (model PE) which had been modified to accommodate both arm cranking and leg cycling [ 11]. The ergometer crankshaft housing was mounted on a steel cylinder rod which was part of a counterweighted pulley system mounted on a floor-to-ceiling shaft. For arm cranking the crankshaft was positioned so that when the cranks were ~r the upper crank han- dle was horizontal with the subject's acromioclavicular joint. The subject sat erect in a chair with his back against the chair back and feet fiat on the floor. The chair was positioned so that nearly full arm extension would be achieved when the cranks were horizontal. The distances from the center of the ergometer crank- shaft to the floor and from the chair to the base of the floor-to-ceiling shaft were individually adjusted on the first day of measurement and maintained throughout the study. Considerable care was taken to center the subject in the chair so the work could be divided as equally as possible between each arm. The subject was cued frequently to minimize upper body movement other than that required of his arms and shoulders to perform the work and to maintain a loose handgrip on the cranks. Excessive movement of the trunk and lower body was prohibited. A carpeted floor permitted only slight motion of the chair even during maximal exercise. The subjects breathed through a low resistance Daniels type valve [8]. Expired air volume (fZEL �9 min -1 BTPS) was measured with a Vertek 400 pneumotachograph and fractions o fO z and CO 2 in expired air were determined with a Beckman model OM-11 02 analyzer and a Godart C apnograph CO z analyzer. The accuracy of the gas analyzers was checked regularly with the Scholander technique, leO 2 (L . min -1 STPD) was calculated from the percentage of O z and CO 2 in expired air according to standard formulas. Heart rate was determined from a single-lead E C G tracing. RPE were determined immediately postexercise using the Borg 15 point scale [3].

During submaximal exercise testing heart rate was recorded during the last 15 s of each rain and ex- pired air was collected during rain 8, 9, and 10. In maximal testing expired air was collected during the last 2 - 3 rain and heart rate was recorded continuously during the last 1--2 rain.

Training Program

Leg training consisted of pedalling a bicycle ergometer; arm training consisted of arm cranking a similar ergometer. For arm training the ergometer pedals were modified to permit comfortable gripping and the er- gometers were clamped on top of heavy tables. The arm trainers sat in chairs with their feet flat on the floor and cranked as they did during the arm tests in the laboratory. No restrictions were placed upon the use of the handlebars during leg training. However, the leg training group pedalled without gripping the handlebars approximately 50% of the time.

The arm training and leg training groups trained 30 min per day on 4 days a week for 11 weeks at an intensity corresponding to approximately 7 5 - 8 0 % fzO 2 max with the respective exercise mode. All training sessions were supervised by one of the authors. Training intensity was monitored by frequently checking the subjects' pulse rates and by recording the workload settings on the ergometers. In both the arm training

28 S. Lewis et al.

and leg training groups training pulse rates ranged from 150-170 �9 min -1. During the last 2 min of each session the subjects exercised to exhaustion achieving maximal pulse rates.

Attendance at the training sessions was excellent; only two subjects missed as many as three sessions over 11 weeks without making them up. For the duration of the study the subjects did not perform stren- uous exercise with the limbs not designated for training.

Data Analysis

The reported submaximal and maximal exercise data represent averages of the values obtained in the last 3 rain of the submaximal tests and the highest values recorded during the maximal tests, respectively.

Paired t-tests were used for within group statistical comparisons of pre- versus post-training results. To compare the magnitude of reduction in submaximal exercise heart rate among the two modes &testing and two modes of training, an analysis ofcovariance with repeated measures [30] was used. This analysis enables removal of the effects of one or more concomitant variables (covariables) on the dependent variable effect [30]. The magnitude of reduction in submaximal exercise heart rate depends to a certain ex- tent upon the pretraining heart rate and in the present study pre-training heart rate varied among the two training groups and modes of exercise (Table 1). For this reason pre-training heart rate was used as the co- variable.

Results

Submaximal Exercise

After arm training and leg training heart rate during exercise with trained and untrained limbs was lower at the same absolute workload (a l lp < 0.05) (Table 1). After arm train- ing, heart rate was reduced from 137 to 111 ( - 2 6 ) . min -1 during exercise with trained arms and after leg training, it dropped from 140 to 118 ( - 2 2 ) �9 min -1 during exercise

with trained legs. After arm training, it fell from 154 to 137 ( - 1 7 ) �9 min ~ during exercise with untrained legs and after leg training, it fell from 125 to 108 ( - 17) �9 rain during exercise with untrained arms. When pre-training heart rate was adjusted for us- ing the analysis of covariance, the mean reductions in heart rate became - 2 8 �9 min- with trained arms, - 2 2 . min -1 with trained legs, - 9 �9 min -a with untrained legs, and - 2 4 �9 min -1 with untrained arms. The analysis of covariance showed that the in- teraction between mode of training and mode of exercise was not significant (F = 5.09, 1,7 d . f . ;p < 0.06). Thus, when the effects of pre-training heart rate were removed there were statistically similar reductions in heart rate at a given workload with trained and untrained limbs after both modes of training.

There were reductions in feO 2, fe E, and feE/feO2 (a l lp < 0.01) during submaximal arm exercise after arm training (Table 1). Reduct ions in feO2, feE' and feE/feO2 during leg exercise after leg training were not significant. There was a small reduction in leg ex- ercise feO z after arm training (p < 0.05). A mean reduction of similar magnitude in arm exercise feO z after leg training was not significant (Table 1). To determine if the reductions in submaximal exercise heart rate might have been influenced by these significant and non-significant changes in feO 2, another analysis of covariance was run on the heart rate data using pre-training heart rate together with A feO 2 as covariables. This analysis gave essentially the same results as those obtained with the analysis using pre-training heart rate alone as the covariable.

After arm training and leg training, R P E were lower (p < 0.01) in response to exer- cise with trained but not with untrained limbs (Table 1).

Tab

le

1. S

ubm

axim

al e

xerc

ise

data

pre

- an

d po

st-t

rain

ing

('1

Stu

dy

Hea

rt r

ate

VO

2 gr

oup

(min

-')

(L.

rain

~)

(N

= 5

) (L

. m

in -L

) ~/

r

pre

post

pr

e po

st

pre

post

pr

e po

st

pre

RP

E

post

r~

,#

p~

r~ o~

Arm

A

T

137

I 11

a 1.

24

1.08

a 41

.2

31.2

a 33

.4

28.8

a E

xerc

ise

_+

19.8

•

15.3

•

• •

3.9

+ 5.

3 +

1.9

_+

3.5

LT

12

5 10

8"~

1.37

1.

28

41.9

39

.8

30.5

31

.2

• 17

.1

• 8.

8 +

0.2

0

• +

6.9

• 5.

3 •

1.8

• 2.

0 L

eg

AT

15

4 13

7j ~

1.82

1.

74t

48.1

49

.1

26.5

28

.3

Exe

rcis

e •

14.5

•

11.7

•

_+0.

20

_+

6.5

• 8.

5 •

2.9

_+

3.1

LT

14

0 11

81"

2.10

1.

88

54.7

45

.8

26.0

24

.4

• 10

.2

• 8.

2 •

0.21

•

0.20

•

10.6

•

4.9

• 3.

8 •

1.7

13.8

•

0.8

12.8

+

1.6

13.4

•

1.7

14.4

•

1.5

11

.0 ~

• 0.

7 12

.6

• 0.

9 14

.0

+ 3.

2 11

.4 a

• 1.

1

3 r~

Val

ues

are

mea

ns _

+ S

D

AT

=

arm

tra

inin

g; L

T

leg

trai

ning

a

Pre

- vs

. po

st-t

rain

ing

mea

n v

alue

s si

gnif

ican

tly

diff

eren

t: p

<

0.01

, t

p <

0.05

Tab

le

2. M

axim

al e

xerc

ise

data

pre

- an

d po

st-t

rain

ing

Stu

dy

Hea

rt r

ate

VO

2 gr

oup

(min

-1)

(L.

min

-1)

(N =

5)

(L

. m

in -l

) R

R

PE

pre

post

pr

e po

st

pre

post

pr

e po

st

pre

post

Arm

A

T

177

180

1.64

2.

22 a

72.8

10

8.0"

E

xerc

ise

_+

7.3

• 6.

4 +

0.22

•

0.30

•

14.4

_•

21

.1

LT

16

5 16

8 1.

97

2.1

5t

87.9

98

.9

• 10

.1

• 9.

2 +

0.32

_+

0.3

6 _+

31.

5 •

29.2

L

eg

AT

18

3 17

6t

2.69

3.

02

114.

2 13

1.5t

E

xerc

ise

+ 6.

5 •

5.4

• 0.

40

• 0.

54

• 14

.2

+_

20.2

L

T

178

176

3.09

3.

60"

113.

3 13

7.04

" _+

8.

0 •

10.2

•

0.41

•

0.26

•

19.5

•

29.2

1.28

1.

26

18.2

•

0.09

+

0.07

_+

1.

3 1.

27

1.33

18

.4

• 0.

06

_+ 0

.12

• 1.

5 1.

28

1.32

18

.4

_+ 0

.08

_+ 0

.10

• 1.

1 1.

28

1.27

18

.3

• 0.

12

• 0.

08

+_ 2

.1

18.2

_+

1.

0 18

.5

• 2.

4 19

.2

_+ 0

.5

18.2

+

2.1

Val

ues

are

mea

ns +

S

D

AT

=

arm

tra

inin

g; L

T =

le

g tr

aini

ng

a P

re-

vs.

post

-tra

inin

g m

ean

val

ues

sign

ific

antl

y di

ffer

ent:

p

< 0.

01,

t p

< 0.

05

30 S. Lewis et al.

Maximal Exercise

The R values > 1.20 achieved during each type of maximal exercise are indicative of the exhaustive effort put forth (Table 2). Training had no effect on maximal heart rate ex- cept for a reduction of 7 �9 min -~ (p < 0.05) during leg exercise after arm training. RPE determined after maximal exercise were in all cases similar before and after training (Table 2).

After leg training, leg VO 2 max increased from 3.09 to 3.60 L- rain ~ (15%, p < 0.01) and a r m J/ tO 2 max increased from 1.97 to 2.15 L . min -x (9%,p < 0.05) (Table 2). After arm training, arm ~'O 2 max increased from 1.64 to 2.22 L . min -1 (35%,p < 0.01), and leg [zO 2 max increased from 2.69 to 3.02 L . min -a (12%), but the latter change was not significant (p < 0.06). Maximal l~" E increased significantly (p < 0.05) in all cases ex- cept during arm exercise after leg training.

Discussion

Generally, ~'O 2 m a x during arm cranking is 60-75% of that which can be achieved with leg cycling [2, 5, 10]. In the present subjects the pretraining ratios of arm/leg f / tO 2 max

were 0.61 in the arm training group and 0.64 in the leg training group. Thus, although the initial relative arm vs leg exercise capacities of the present arm training and leg train- ing groups were similar to each other and to subjects in previous studies, both groups were initially rather deconditioned for arm and leg exercise (Table 3).

The main findings of the present study were increases in [zO 2 max and reductions in submaximal exercise heart rate with untrained as well as trained limbs. Although the mean increase of 330 ml. min -1 in leg VO 2 max after arm training (Table 2) was not sta- tistically significant, each subject in the arm training group increased leg [gO 2 m a x

(increases ranging from 99 to 711 ml. rain-l). Thus, the lack of statistical significance in this case was probably due to the small number of subjects studied. Table 3, which summarizes the changes in trained and untrained limb VO 2 max after arm or leg training in previous studies and the present study, suggests that the degree of transfer effect probably depends on factors such as the initial fitness of the subjects for each type of ex- ercise, the training intensity and frequency, and the duration of each training session and of the total training program. For example, in one study [ 16] no improvement was found in treadmill running [zO 2 max after arm training in subjects who had been initially trained with their legs. The very low initial capacities for arm and leg exercise in the pre- sent subjects may have provided the potential for transfer effects to exercise with untrained limbs.

When the differences in pre-training heart rate were removed by analysis of covariance, a statistically similar magnitude of reduction in submaximal exercise heart rate with trained and untrained limbs was found after leg training and arm training. However, after arm training there was a strong tendency for the fall in heart rate to be greater for arm exercise ( -28 �9 min-1), than for leg exercise ( - 9 �9 rain-l). In contrast, several previous studies [6, 24, 29] have not found lower submaximal heart rates with untrained limbs. However, Clausen et al. [5] and McKenzie et al. [17] found a heart rate reduction pattern similar to that of the present study: a similar magnitude of fall in heart rate with trained and untrained limbs after leg training but a greater drop with trained arms than untrained legs after arm training. Taken together the present heart

Tab

le

3. A

rm o

r le

g ~7

02 i

nax

chan

ges

aft

er t

rain

ing:

pri

or

stud

ies

and

the

pre

sen

t st

ud

y

Stu

dy

N

Ag

e M

od

e a

Tra

inin

g p

rog

ram

Inte

nsi

ty

Day

s/W

k

(hea

rt r

ate)

Ses

sion

d

ura

tio

n

(mm

)

Pro

gra

m

du

rati

on

(w

k)

Max

imal

tes

ting

Ty

pe

test

a ~

70

2

max

(ml/

kg

/min

) p

re

zX%

r~

3 C

lau

sen

et

al.

[5]

3 2

1-3

0

B

>

170

�9 m

in

1 5

Mag

el e

t al

. [1

6]

7 "~

A

>

85

%

max

3

Pol

lock

et

al.

[23]

11

22

--55

A

15

0--1

65

�9 m

in -1

3

Rid

ge e

t al

. [2

4]

5 23

K

8

5--

90

%

max

4

5 22

B

8

5--

90

%

max

4

Sta

mfo

rd e

t al

. [2

9]

8 20

A

_>

18

0 �9

min

-1

3

9 19

B

1

80

--1

90

. ra

in

1 3

Pre

sent

5

20

A

>_

150-

-170

�9

min

i

4

5 22

B

_>

150

--17

0 -

min

-I

4

35

5 B

46

.4

17

A

36.5

10

20

10

A

33

.9

16

T

56.4

1

30

20

A

23.3

39

T

37

.9

7 30

4

K

31.9

8

30

4 K

30

.7

1 10

10

A

36

.9

19

B

42.7

1

15

10

B

42.1

15

A

37

.0

0 30

11

A

22

.8

35

B

37.2

12

30

11

B

39

.2

15

A

25.0

9

0~

r~

a B

=

bicy

cle,

A

arm

cra

nk,

K

=

kay

ak,

T

=

trea

dmil

l;

t m

ale

coll

ege

stud

ents

32 S. Lewis et al.

rate and ~'rO 2 max data are suggestive of somewhat greater transfer effects to untrained limbs after leg training than after arm training. Although our small sample sizes may preclude a more discriminative statement, it does appear that transfer effects can occur after training of the legs or the arms.

One question which might be raised is whether any muscular overlap between arm and leg training could be responsible for the magnitude of transfer effect to untrained limbs observed in the present study. All available evidence suggests this is very unlikely. Any use of the legs during arm training and the handlebars during leg cycling was mere- ly for stabilization and thus represents at most moderate static work. The presence or absence of transfer effects to untrained limb exercise does not appear to be dependent on whether stabilization work with untrained limbs has or has not been permitted during the testing and training procedures [5, 24, 29]. Furthermore, it is well known that even very intense static or heavy resistance dynamic training has essentially no ef- fect on the cardiovascular response and endurance in dynamic arm or leg exercise [ 1, 19, 20]. Our RPE data strongly confirm the notion that there was no unintended training of untrained limbs. In agreement with previous findings [12, 22] we observed a lower RPE at a given submaximal workload after training. However, after each type of training we found reductions in RPE only during trained limb exercise. Had the un- trained limbs actually been trained, a lower RPE probably also would have been observed during exercise with these limbs.

Even though heart rate dropped during untrained limb submaximal exercise, RPE remained the same in this case. Thus, in spite of the close relationship reported between reductions in ratings of perceived exertion and drops in heart rate in response to a given workload after endurance training [ 12, 22], the present data suggest that reductions in heart rate and perceived exertion are not necessarily linked. One explanation for the lower RPE only during exercise with trained limbs may be that the perception of exertion is linked to metabolic conditions in the exercising muscles which can be altered by training. Ratings of perceived exertion and lactic acid concentrations in muscle and in blood have been shown to be reduced after training [ 12, 13]. However, a lower blood lactate concentration has been found during exercise with trained but not with un- trained limbs [15, 24].

It should be noted that the contribution of central factors to the reduced RPE dur- ing submaximal exercise only with trained limbs cannot be excluded. Training may cause a selective hypertrophy of trained muscle fibers [25] and a more synchronous pattern of motor unit recruitment in trained muscles [18]. Thus, after training fewer centrally activated motor units may need to be recruited to perform the same sub- maximal workload [26] and a reduced "central nervous command" may be perceived. The finding that the greatest reductions in submaximal VO 2 after training occurred dur- ing trained limb exercise appears to support this hypothesis.

In conclusion, the present results demonstrate that transfer effects of endurance training to untrained limb exercise can occur in initially very sedentary young men. These findings appear to be consistent with the central circulatory changes observed af- ter short periods of endurance training in initially sedentary women [7, 14]. Our data also demonstrate that endurance training reduces perceived exertion at a given sub- maximal workload during trained limb exercise only. Although the drop in perceived exertion may have been the result of metabolic alterations in trained muscles, the possible role of a reduced central nervous command may not be ruled out.

Cross-transfer of Training of Arms or Legs 33

A eknowledgement. We appreciate the assistance of Carolyn Donahue in the preparation of the typescript. At the time of this study Steven Lewis was a Pre-doetoral Fellow of the Bay Area Heart Research Committee.

References

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2. Bergh U, Kanstrup I-L, Ekblom B (1976) Maximal oxygen uptake during exercise with various combinations of arm or leg work. J Appl. Physiol 41:191--196

3. Borg G (1973) Perceived exertion: A note on "history" and methods. Med Sci Sports 5 :90-93

4. Clausen JP (1976) Circulatory adjustments to dynamic exercise and effect of physical training in nor- mal subjects and patients with coronary artery disease. Prog Cardiovasc Dis 18:459--495

5. Clausen JP, Klausen K, Rasmussen B, Trap-Jensen J (1973) Central and peripheral circulatory changes after training of the arms or the legs. Am J Physiol 225:675-682

6. Clausen JP, Trap-Jensen J, Lassen NA (1970) The effects of training on the heart rate during arm and leg exercise. Seand J Clin Lab Invest 26:295-301

7. Cunningham DA, Hill JS (1975) Effect oftralning on cardiovascular response to exercise in women. J Appl Physiol 39 : 891-895

8. Daniels J (1971) Portable respiratory gas collection equipment. J Appl Physiol 31:164-167 9. Davies CTM, Sargeant AJ (1975) Effects of training on the physiological responses to one and two-

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Accepted February 6, 1980