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Interaction between concurrent strength

and endurance training

D. G. SALE, J.

D.

MA~DOUGALL, I. JACOBS, AND S. GARNER

Departments of Physical Education and Medicine, McMaster University, Hamilton L8S 4Kl;

and Defence and Civil Institute of Environmental Medicine, Downsview, Ontario M3M 3B9, Canada

SALE,

D. G., J. D.

MACDOUGALL, I. JACOBS, AND

S.

GARNER.

Interaction between concurrent strength and endurance truin-

ing. J. Appl. Physiol. 68(l): 260470, 1990.-To assesshe

effects of concurrent strength (S) and endurance (E) training

on S and E development, one group (4 young men and 4 young

women) trained one leg for S and the other leg for S and E

(S+E). A secondgroup (4 men, 4 women) trained one eg for E

and the other leg for E and S (E+S). E training consistedof

five 3-min bouts on a cycle ergometer at a power output

corresponding to that requiring 90400 of oxygen uptake

during maximal exercise (VO

2&. S training consistedof six

setsof 15-20 repetitions with the heaviest possibleweight on a

leg press combined hip and knee extension) weight machine.

Training wasdone3 days/wk for 22 wk. Needlebiopsy samples

from

vastus lateralis were taken before and after training and

were examined for histochemical,biochemical, and ultrastruc-

tural adaptations.The nominal S and E training programswere

“hybrids,” having more similarities as training stimuli than

differences; thus S made ncreases P < 0.05) similar to those

of S+E in E-related measuresof VOW max S, S+E: 8 , 8 ),

repetitions with the pretraining maximal single eg press ift [l

repetition maximum (RM)] (27%, 24%), and percent of slow-

twitch fibers (15 , 8 ); and S made significant, although

smaller, ncreases n repetitions with 80 1 RM (81 , 152 )

and citrate synthase (CS) activity (22%, 51 ). Similarly, E

increased knee extensor area [computed tomography (CT)

scans] as much as E+S (14%, 21%) and made significant,

although smaller, ncreasesn leg press1 RM (20%, 34%) and

thigh girth

(3.4%, 4.8%).

When a presumablystronger stimulus

for an adaptation was added to a weaker one, someadditive

effects occurred (i.e., increases n 1 RM and thigh girth that

were greater in E+S than E; increases n CS activity and

repetitions with 80 1 RM that were greater in S+E than S).

When a weaker, although effective, stimulus was added to a

stronger one, addition generally did not occur. Concurrent S

and E training did not interfere with S or E development in

comparison o S or E training alone.

skeletal muscle;adaptation; aerobic power; enzyme activity

STRENGTH AND ENDURANCE training represent,intheir

extremes, opposite forms of training. Strength training

consists of a relatively small number of contractions of

maximal or near-maximal force. Endurance training con-

sists of a large number of submaximal contractions.

Accordingly, the adaptive responses in skeletal muscle

to strength and endurance training are different and

sometimes opposite. Strength training causes muscle

fiber hypertrophy (26) associated with an increase in

contractile protein

(28),

which contributes to an increase

in maximal contraction force. In contrast, endurance

training usually causes little or no muscle fiber hypertro-

phy (2,7,12,20,23), but it does cause an increase in the

following adaptations expected to enhance endurance

performance: capillary density (2, 7, 20, 37, 39), mito-

chondrial volume density (17), and oxidative enzyme

activity (12, 37).

Strength and endurance training are often done con-

currently by fitness enthusiasts and athletes. However,

since the adaptive responses to strength and endurance

training are different and some may even be opposite, it

is conceivable that skeletal muscle cannot adapt opti-

mally to the two contradictory training stimuli when

they are simultaneously imposed. For example, strength

training may cause a decrease in capillary density (36,

41) and mitochondrial volume density (29), which would

undermine the increase in these measures induced by

endurance training. Endurance training has been asso-

ciated with a loss of strength (5, 31, 33) and decreased

muscle fiber size (Z&39), changes obviously antagonistic

to strength development.

On the other hand, concurrent strength and endurance

training may interact to enhance rather than hinder

strength and endurance development. Some forms of

endurance training have increased strength (31, 34) and

muscle fiber size (2, 12). Strength training has increased

short- (4-6 min) and long- (60-90 min) term endurance

(14.16), maximal aerobic power (14), and oxidative en-

zyme activity (6).

Whether the interaction between concurrent strength

and endurance training results in “antagonism” or mu-

tual enhancement of the training response probably de-

pends on several factors, including the initial state of

training of the trainees; the training modes; the intensity,

volume, and frequency of training; and the way the two

forms of training are integrated. In previously untrained

subjects, a combination of moderate-to-high intensity

and volume endurance and strength training impeded

strength development but not increases in maximal aero-

bic power or short-term endurance (9, 14, 19). In previ-

ously endurance-trained subjects, the addition of

strength training does not cause the impaired strength

development seen in untrained subjects (19), and it im-

proves endurance without increasing aerobic power

(15).

In the present study, the interaction between concur-

rent high intensity, moderate volume strength and en-

durance training wa s examined in previously untrained

subjects.

A

unique aspect of the study w as that several

260 O161-7567/90 $1.50 Copyright 0 1990 the American Physiological Society

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STRENGTH AND ENDURANCE TRAINING INTERACTION

261

measures related to skeletal muscle adaptation were

made to help explain any evidence of antagonism or

mutual enhancement that might be found.

METHODS

Subjects

The subjects were eight young women and eight young

men without previous experience in intense strength or

endurance training. In accordance with the Ethical

Guidelines for Research on Human Subjects at Mc-

Master University, we clearly apprised the subjects of

the purpose of the study and the physical, psychological,

and/or social risks involved in the research, and the

students signed an informed consent form. The project

carried the approval of McMaster University’s Ethics

Committee.

Design

Half (4 women, 4 men) of the subjects (group A) were

randomly assigned to train both lower limbs for strength

and one limb for endurance. The other half of the sub-

jects (group B) trained both limbs for endurance and

one limb for strength. Thus group A assessed the inter-

action between strength and endurance training (S+E)

compared with strength training alone (S), while group

B assessed the interaction between endurance and

strength training (E+S) compared with endurance train-

ing alone (E). The characteristics of the subjects in the

two groups are presented in Table 1.

Training

Training consisted of two ll-wk periods divided by a

3-wk break period, the latter to accommodate a Christ-

mas recess. There were three training sessions per week

during the training periods. For each subject a training

session lasted -1 h, i.e., the time taken to train both

strength and endurance in one leg and strength (group

A) or endurance (group B) in the other leg. In legs that

did combine strength and endurance training, endurance

training preceded strength training in each training ses-

sion.

Strength training. Strength training wa s done on a

“Universal”-type leg press weight training machine

(Global Gym, Downsview, Ontario). The training move-

ment (concentric contraction phase) included simulta-

neous hip and knee extension and ankle plantar flexion.

Each repetition of the exercise included a concentric and

eccentric contraction phase. Subjects in

group A

per-

formed six sets of E-20 repetitions maximum (RM); i.e.,

TABLE

1.

Age, height, and body muss

of

subjects

Group Experiment

Age,

Height,

Mass, kg

Yr

cm

Pre Post

A S vs. S + E 20.9zkO.5 169.2k4.7 65.7+5.1 66.9k4.8

B E vs. E + S 20.6t0.3 168.1k2.4 62.2t3.3 63.8&3.3*

Values are means k SE; each group consisted of 4 females and 4

males . S, strength training; E, endurance training. * P < 0.05 for main

effect in body mass, pre-post training.

the heaviest possible weight was used for the designated

number of repetitions of the leg press movement with

each leg. Sets were alternated between legs, with 1-min

rest periods, until each leg completed the six sets. Sub-

jects in

group B

performed six sets of 15-20 RM with the

randomly designated leg. There were 2-min rest periods

between successive sets.

Endurance training. Endurance training was per-

formed on a cycle ergometer (Monark). The training

consisted of five 3-m+ bouts at a power output corre-

sponding to 90-100% VOWmax.n group A, which trained

only one randomly assigned leg for endurance, 3-min rest

periods intervened between successive bouts. Group B

performed the 3-min bouts alternately with both legs,

with l-min rest periods between successive bouts.

The training program is summarized in Table 2.

Measurements

All measurements were made before and after the 22

wk of training.

Aerobic power.

Aerobic power

(VOW

max)defined here as

the peak 02 consumption attained during the single leg

test) was measured for each leg separately. The test was

performed on an electrically braked cycle ergometer (Jae-

ger) using a standard continuous progressive loading

protocol. The test began at a power output of 30 or 45

W, and the load was increased by 15 W every 2 min until

volitional exhaustion. Electrocardiogram monitoring and

an open-circuit computerized gas analysis system pro-

vided a display of heart rate, expired flow, O2 consump-

tion, COa production, and respiratory exchange ratio

every 20 s during the test.

Voluntary strength. Voluntary strength of each leg was

measured as the maximum weight that could be lifted

for one repetition

(1

RM) on the weight training appa-

ratus. Measurements were made to the nearest 0.5 kg by

means of adapter plates that could be placed on the

apparatus weight stacks. Subjects used the same appa-

ratus and body positioning (apparatus seat position) for

all tests and training. The test was done twice on separate

days before training, and the highest value attained was

taken as the pretraining measure.

Relative endurance. Relative endurance wa s measured

for each leg on the weight training apparatus as the

number of repetitions that could be done with 80% of

the 1 RM.

Absolute endurance.

At the conclusion of the training

program, absolute endurance, the number of repetitions

done with the pretraining 1 RM, was measured for each

leg on the weight lifting apparatus. For both endurance

tests, a metronome controlled the rate of repetitions at

lO/min.

Muscle cross-sectional urea. We measured the cross-

sectional area of the right and left knee extensors and

flexors with a computerized digitizer from photographs

of computed tomography (CT) scans obtained with a CT

scanner (model 20-30, Ohio-Nuclear). CT scans were

made at the mid-thigh level (between the greater tro-

chanter and lateral epicondyle of the femur).

Thigh girth and skinfolds. The thigh girth of the right

and left legs was measured with a steel tape at the

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TABLE 2. Training program

Group A

Leg I

Five 3-min bouts at 90-100%

VO

2 max

6 sets, 15-20 RM

Group B

Jk ?2

Leg 1

kf2

Endurance

Five 3-min bouts at 90-100% Five 3-min bouts at 90-100%

VO

2 max

VO

2 max

Strength

6 sets, 15-20 RM

6 sets, 15-20 RM

Each group consisted o f four females and four males. Endurance training was on a cycle ergometer at a power output corresponding to that

requiring 90-100% maximum oxygen output

(i0 2max).Strength training required 6 sets of 15-20 repetitions with heaviest possible weight on a

leg press weight machine (RM). Each training session lasted 1 h; 3 training sessions were conducted each week on nonconsecutive days; and two

11-wk training periods were divided by a 3-wk rest period.

midthigh level. At this same level, anterior, posterior,

lateral,

and medial skinfold measurements were made

with Harpenden-type skinfold calipers.

Muscle fiber areas, composition, and cupillurizution.

Needle biopsy samples were taken from the vastus later-

alis of right and left legs. Part of one sample was mounted

in an embedding medium and frozen

in

isopentane cooled

with liquid nitrogen for subsequent histochemicaf anal-

yses, and the remaining portion was used for electron

microscopy. Muscle fibers were classified as slow twitch

(ST or type I) or fast twitch (FT or type II) after staining

for myofibrillar adenosine triphosphatase (ATPase) ac-

tivity at a pH of 9.4, after preincubation at pH 10.3 (13).

Muscle fiber composition (%ST) was determined from

fields containing a minimum of 218 (max = 1,392) fibers.

Photographs of serial sections stained for NADH-tetra-

zolium reductase (32) were used to determine the mean

cross-sectional area of each fiber type using computerized

planimetry. The means t SD number of fibers per sam-

ple used to calculate fiber area ranged from 50 t 23 to

83

t

25

for ST and from 49 t

21

to 96 t 60 for FT

fibers. Capillaries were visualized with an amylase-

periodic acid-Schiff stain (1). Capillaries per fiber and

capillaries per square millimeter were determined from

fields of 50 fibers.

Muscle enzyme activities. A second biopsy sample was

frozen directly in liquid nitrogen and stored at -70°C

until analyzed. At analysis, the tissue was freeze-dried,

and then visible impurities, connective tissue, and blood

clots were dissected out before the tissue was weighed on

an electrobalance (Cahn). The tissue was then homoge-

nized by sonication in an ice-cooled medium of 0.1 M

phosphate buffer, pH 7.7, and supernatant extracts were

assayed for the activities of phosphofructokinase (PFK),

lactate dehydrogenase (LDH), and citrate synthase (CS)

with NADH-coupled enzymatic methods (11, 25).

Morphometric analysis. Tissue for electron microscopy

was immediately fixed in glutarafdehyde, dried in

ethanol, and embedded in Epon, using standard tech-

niques. Slightly oblique sections were then photographed

at -~50,000 magnification under a Phillips EM200. An

average of 52 fibers (range, 37-60) were randomly se-

lected per biopsy, and for each biopsy a photographic

field for the interior of each fiber was randomly selected

and photographed. Stereological analysis was performed

on each micrograph by means of a 1680point short-line

test system (42) according to the method described by

Hoppeler et al. (18). Volume densities were calculated

for myofibrils

(V

vmYOf),nterior mitochondria (Vvmit) 3 ipid

(vvlip) 9 and cytoplasm (L,).

Statistical Analysis

Data were analyzed with a two-factor (pre-post-train-

ing, training condition) analysis of variance with re-

peated measures on one factor (pre-post-training). The

analysis would indicate antagonism or “addition” in con-

current strength and endurance training as a significant

interaction between the two factors (pre-post-training

x

training condition). When a significant interaction was

found, a post hoc test (Tukey A) was done to identify

significant differences among mean values. Statistical

significance was accepted at P 5 0.05. Descriptive statis-

tics included means t SE.

RESULTS

The same pattern of results was found in the small

number of males and females in each group; therefore,

the results from both males and females were pooled for

analysis.

Effect of Concurrent Strength and Endurance Training

on Strength Development (Group A)

Voluntary strength. Leg press 1 RM increased (P =

0.006) in both the strength-trained leg (S) and the

strength- and endurance-trained leg (S+E) (Fig. 1). Al-

though the S leg made a greater increase (30.5 kg, 30.2%)

than the S+E leg (21.2 kg, 20.4%), the interaction be-

tween pre-post-training and training condition was not

significant (P = 0.18).

MwxZe cross-sectional urea. Extensor cross-sectional

area increased (P c 0.001) similarly in S (12.9 ) and

S+E (11.2%) legs (Fig. 2). Flexor cross-sectional area

and the ratio of extensor to flexor area did not change

after training.

Thigh girth, skinfolds, and body muss. Thigh girth

increased slightly but significantly (P = 0.008) overall

(Fig. 3). The S+E leg did not make a significantly greater

increase than the S leg (interaction P = 0.171). The sum

of four skinfolds did not change significantly after train-

ing (Fig. 3). Body mass did not change significantly after

training (Table 1).

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263

E+S

S S+E E

E+S

FIG. 1. Leg press results for one repetition on the

weight training apparatus (1 RM) in group A (top left),

which strengbh trained one leg (S) and strength and

endurance trained the other leg (S+E), and group B (top

right) , which endurance trained one leg (E) and endur-

ance and strength trained the other leg (E+S). Top:

before (open bars) and after (stippled bars) training

values. Bottom: increases after training. Values are

means & SE. Main eff ect before vs. after training: * P =

0.006, ** P < 0.001; interaction (E+S > E): T P < 0.001.

lMuscZe fiber area. There were no significant changes

in ST (S, 3,946 & 538 to 4,675 A 537; S+E, 4,481 t 491

to 5,412 $- 1,196) or FT (S, 4,693 t 619 to 5,378 t 783;

S+E, 4,884 t 685 to 5,738 & 1,209) fiber area (means t

SE, pm2). The FT-to-ST area ratio did not change (S,

1.22 $- 0.12 to 1.15 t 0.10; S+E, 1.09 $- 0.09 to 1.08 t

0.08).

Maximal aerobic power (VU~ maw).S (7.9%) and S+E

(8.3%) legs made similar increases in VOWmax (P = 0.006,

Fig. 4).

(S, 260 t 15 to 247 t 37; S+E, 256 t 32 to 245 t 39) did

not change significantly after training.

Muscle enzyme activities. PFK (S, 0.095 t 0.015 to

0.098 t 0.014; S+E, 0.087 t 0.013 to 0.091 t 0.012) and

LDH (S, 5.03 t 0.46 to 5.12 t 0.61; S+E, 4.54 $- 0.41 to

4.59 t 0.33) activities (mkatal/kg dry wt ) did not change

significantly after training. In contrast, CS activity in-

creased significantly (P < 0.001, Fig. 8). There was also

a significant (P = 0.005) interaction for this enzyme.

The S+E leg (51.2%) showed a larger increase than the

S leg (22.1%).

Weight lifting endurance. Relative endurance (repeti-

tions with 80% 1 RM) increased after training (P =

lk&chondrial and lipid volume density. Mitochondrial

volume density appeared slightly higher in the S+E leg

0.013, Fig. 5). There was a significant interaction (P = after training, but the change was not statistically sig-

0.013), indicating that the S+E leg (152 ) improved

n&ant (Fig. 9), In addition, there were large increases

moreonthismeasureaftertrainingthantheSleg (81%).

6, 194%; S+E, 70%) in lipid volume density; these

S (26.8) and S+E (24.4) were similar in the number of

increases also failed to reach statistical significance (P

repetitions that could be done with the pretraining 1 RM = 0.085~ Fig. 9).

after training (absolute endurance, Fig. 6).

%ST and cupillarization. There w as a significant (P =

Effect

of

Concurrent Endurance and Strength Training

0.007)

increase in %ST fibers in both S (31.8-46.5) and

on Endurance Development (Group B)

S+E (39.2-47.0) legs (Fig. 7). Capillaries per fiber (S,

Maximal aerobic power (Voz W). E (6.9%) and E+S

1.92 t 0.27 to 1.76 z z 0.26;

S+E,

2.15 + 0.32 to 2.26 & (7.2%) legs made similar increases in

VOW

maxafter train-

0.39) and capillaries per square millimeter muscle area ing (P

C

0.001, Fig. 4).

7/17/2019 260


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Weight lifting endurance. Relative endurance (repeti-

tions with 80%

1

RM) increased after training (P =

0.022, Fig. 5). There was a significant interaction (P =

0.030). The E+S leg (157%), but not the E leg (60%),

increased relative endurance significantly. After training,

the E+S leg (51) could do more

(P

= 0,032) repetitions

with the pretraining 1 RM (absolute endurance) than

the E leg (16) (Fig. 6).

ST and capillarization.

There was a significant

(P c

0.001) increase in %ST fibers in both E (49.9-56.3) and

E+S (41.6-58.8) legs (Fig. 7). Capillaries per fiber (E,

2.38 z z 0.22 to 2.19 t 0.22; E+S, 2.48 t 0.26 to 2.49 -I-

0.26) and capillaries per square millimeter muscle area

(E, 308 k 16 to 267 t 13; E+S, 309 t 22 to 265 t 24)

did not change significantly after training.

Muscle enzyme actiuities. PFK (E, 0.096 t 0.011 to

0.101 t 0,012; E-G, 0.093 t 0.005 to 0.098 t 0.007) and

LDH (E, 4.46 t 0.77 to 5.09 t 0.77; E+S, 5.28 t 0.77 to

5.28 k 0.63) activity did not change significantly after

training. In contrast, CS activity increased significantly

(P

= 0.003) and similarly in E (38.1%) and E+S (36.3%)

legs (Fig. 8).

t+3

FIG. 2. Knee extensor (top) and flexor (bottom) mus-

cle cross-sectional area in group A (left) for S and S+E

and group B (right) for E and E+S. Values are means

t SE for before (open bars) and after (stippled bars)

training. Main ef fect before vs . after training: * P =

1

0.012, ** P c 0.001.

Mituchondrial and lipid volume density. After training,

mitochondrial volume density wa s -9% higher in the E

leg and 15% higher in the E+S leg, but the changes were

not statistically significant (Fig. 9). The large increases

(E, 120%; E+S, 169%) in lipid volume density also failed

to reach statistical significance (P = 0.063) (Fig. 9).

Voluntary strength. Leg press 1 RM increased signifi-

cantly (P < 0.001) after training (Fig. 1). There wa s a

significant interaction

(P

< 0.001). Although both E

(20.3%) and E+S (34.1%) legs increased the 1 RM sig-

nificantly, the increase in the E+S leg was significantly

greater.

Muscle cross-sectional area. Extensor cross-sectional

area increased (P < 0.001) in both E (14.3%) and E+S

(20.9%) legs (Fig. 2). The greater increase in the E+S

leg was not significant (interaction

P

= 0.13). Flexor

cross-sectional area increased (P = 0.012) in both E

(8.8%) and E+S legs (12.4%). The greater increase in

the E+S leg wa s not significant (interaction

P =

0.126).

The ratio of extensor to flexor cross-sectional area did

not change significantly after training.

Thigh girth, skinfolds, and body mass.

Thigh girth

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265

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FIG.

3. Thigh girth (tr>p) and sum of 4 (anterior, pos-

terior, medial, lateral) thigh skinfolds

(bottom)

in group

A (left) for S and S+E and group B (right) for E and

E+S. Values are means -t SE for before (open bars) and

after (stippled bars) training. Main eff ec t before vs . after

1

raining: * P C 0.01, * P < 0.001; interaction (E+S > E):

t P c 0.05.

S

S+E

80

f

f

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2

70

iz

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iii

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w 60

z

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co

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m m .

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S+E

E

increased slightly but significantly (P <

0.001)

after

training. The increase in the E+S leg (4.8%) was signif-

icantly (interaction P = 0.037) greater than the increase

1

.V.‘.

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skinfolds did not change significantly after training (Fig.

3). There was a small (2.6%) but significant (P < 0.05)

increase in body mass after training (Table 1).

Muscle

fiber area. There were no significant changes

n the E leg

(3.4%) (Fig. 3). -The sum of four thigh

3.2

1

FIG.

4. Maximum aerobic power in group A

(left)

for S and S+E and

group

B (right) for E and

_ E+S. Values are means k SE for before (open bars)

and after (stippled bars) training. Main eff ect be-

i

fore vs, after training: * P = 0.006, ** P < 0,001.

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7/17/2019 260


266

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co

2

0

20

i=

i=

UJ

CL

10

W

a

0

E

a

30

7

8

0

co

Q 20

cn

/

0

F

E 10

CL

w

a

d

0


*

+

T

T 4

T

T

S+E

t

S

S+E

E E+S

FI G. 5. Repetitions with

80%

1 RM in

group A (left)

for S and S+E andgroup B (right) for E and E+S. Top:

before (open bars) and after (stippled bars) training

values. Bottom: increase in repetitions after training.

Values are means k SE. Main ef fect before vs . after

training: * P < 0.05; interaction: t P = 0.013 (S+E >

S), tJ- P < 0.001 (E+S > E).

E E+S

in ST (E, 4,864 t 1,318 to 4,786 t 375; E+S, 5,274 t

695 to 5,347 t 367) or FT (E, 5,590 t 687 to

5,543 t

291; E+S, 5,690 $- 555 to 6,299 & 457) fiber area. The

FT-to-ST area ratio did not change (E,

1.14 t 0.08

to

1.17 k 0.07;

E+S,

1.12 t 0.06

to

1.18 -t 0.05).

DISCUSSION

The nominally designated strength (S) and endurance

(E) training used in the present study had more in

common as training stimuli than differences; thus in

group A, the S leg made increases similar to the S+E leg

in endurance-related measures of VOW max, repetitions

with the pretraining leg press 1 RM, and %ST fibers;

and S made significant, although smaller (vs. S+E),

increases in repetitions with 80 -1RM, and CS activity.

Similarly, in g?vup B, the

E

leg increased knee extensor

CSA as much as the EN leg and made significant,

although smaller, increases in leg press 1 RM and thigh

girth. Therefore the S and E training used in the present

study might be considered hybrids rather than extreme

or “pure” forms of S and E training.

The hybrid nature of the E training was probably due

in part to the high intensity bouts (3 min at 90.100

.

vo 2 max) employed; such bouts might ensure endurance

adaptations in fast- and slow-twitch motor units (8, 27),

but they also induced increases in muscle size and

strength. In addition, E training by cycling (necessitated

in the present study because of the one leg training

model) may be more likely to increase strength (31, 34)

and muscle size (2, 12; see, however, 39) than, for ex-

ample, by running. The S training consisted of sets of

15-20 repetitions with a weight ranging from 75-80% 1

RM at the start of training to 85-90% 1 RM by the end

of training [by comparison only

-5-10

repetitions can

be done with 75-90% 1 RM in upper body exercises such

7/17/2019 260



267

>

u 3o

l--

W

u

a.

Q 20

cJ3

z

0

i=

6 lo

Q

k

0

>

a: 6o

7

W

E

k 40

co

z

0

F 20

i=

W

CL

ii?

0

E E+S

FIG. 6. Repetitions done, after training, with the heaviest weight

that could be lifted for

1

repetition before training in group

A (top)

for

S and S+E and group B (bottom) for E and E+S. Values are means k

SE. Interaction (E+S > E): 7 P < 0.05,

as the bench press (35) and arm curl (30)]. Although the

intensity (%l RM) was appropriate for effective strength

training, the number of repetitions per set (15-20) and

per training session (90-120) might be considered high

(there were -900 contractions in each endurance training

session). The S program was successful in inc:easing

strength and muscle size, but it also increased Voz max

(perhaps due in part to a “central” effect from endurance

training of the other leg), weight lifting endurance, and

CS activity.

When S and E training are done concurrently they

may not interact at all; i.e., the concurrent training would

cause the same strength and endurance adaptations as S

and E training done alone. They may interact to cause

antagonism; i.e., strength and/or endurance adaptations

would be less than in response to S or E training alone.

Or they may interact to cause “addition”; i.e., strength

and endurance adaptations would be greater than in

response to S and E training alone. Whether interaction

occurs and the form it takes probably depend on several

factors: the intensity, volume, and frequency of the two

types of training; the training modes; the training status

-

60 -

3 50-

CT

m

LL

&j 40-

o\o

30 -

20 -

c

60 -

cJ2

I% 5o

m

LL

)-

co

40-

8

30 -

20 -

N=5

N=4

1

E

T

E+S

FIG.

7. Percent slow-twitch (ST) o f vastus lateralis in

group A (top)

for S and S+E and group B (bottom) for E and E+S. Values are means

+ SE for before (open bars) and after (stippled bars) training. Main

ef fec t before vs . after training: * P = 0.007, ** P < 0.001.

of the subjects; and the way the two forms of training

are integrated. Furthermore, the results and conclusions

drawn will be affected by the selected criterion measures

of strength and endurance development. These factors

must be considered in the interpretation of the present

and previous studies (3, 9, 10, 14, 15, 19).

Antagonism did not occur in the present study, prob-

ably because of the hybrid nature of the S and E training

involved and the moderate total volume of training.

However, previous studies have shown antagonism in the

form of impaired strength development (9, 14, 19). An-

tagonism may have occurred in these studies because of

the greater volume of training used (14) or the criterion

measure of adaptation used [e.g., impaired high- but not

low-velocity isokinetic strength development (9)]. Gen-

erally, antagonism may be more likely to occur when

large volume extreme forms of S and E training are done

concurrently (e.g., marathon run training and competi-

tive weight lifting).

In regard to a possible additive effect of combined

strength and endurance training, an interesting pattern

was found. When a presumably stronger stimulus for a

7/17/2019 260



t

**

S S+E E

FIG. 8. Citrate synthase (CS) act ivi ty in group A

(lef t) for S and S+E and group B (right) for E and

E+S. Top: before (open bars) and after (stippled bars)

-

training-values. Bottom: increases after training. Val-

ues are means k SE. Main effect before vs. after

training: * P = 0.003, ** P c 0.001; interaction (S+E

1 >S):P=0.005.

given adaptation was added to a weaker stimulus, addi-

tion sometimes occurred, but when a weaker stimulus

wa s added to a stronger one, addition did not occur. Thus

in group A (S vs. S+E) the addition of E training wa s

additive for increases in endurance (repetitions at 80% 1

RM) and CS activity, although S training alone caused

significant increases in these measures. Similarly, in

group B (E vs. E+S) the addition of S training wa s

additive for increases in strength and one measure of

muscle size (thigh girth), although E training alone

caused significant increases in these measures. On the

other hand, E training wa s not additive for increases in

strength and muscle size (S vs. S+E), although E training

alone caused increases in these measures, nor was S

training additive for increases in VOW max and CS (E vs.

E+S), although S training alone caused increases in these

measures. An exception was that S training was additive

for short-term endurance. The endurance tests were done

on the S training device; therefore, the increased endur-

ance was probably partly related to improved strength,

skill, and efficiency in the exercise movement in the

course of S training.

E+S

The training status of the subjects may determine

whether antagonism or addition occurs in concurrent

strength and endurance training. In previously untrained

subjects, endurance development is not impaired (9, 14,

19, present study) and may be enhanced (present study);

strength development may (9,14,19) or may not (present

study) be impaired. In previously endurance-trained sub-

jects who continue endurance training but add strength

training, strength (19) and endurance (15) development

may be enhanced.

We chose for the present study a training model that

provided a within-subject control and evaluation of in-

teraction between concurrent strength and endurance

training. Thus group A trained for both strength and

endurance in one leg and strength only in the other leg,

whereas group B trained for both strength and endurance

in one leg and endurance only in the other leg. This

model avoided the variability in training response be-

tween separate groups containing a small number of

subjects. For example, a particular group, despite random

assignment of subjects, might by chance contain more

trainable subjects. This group would make a greater

7/17/2019 260



269

- T

S S+E

E E+S

T

l- T

T

S SE

E E+S

-

FIG. 9. Mitochondrial (V, *it) (top) and lipid (V, lip) (bottom) volume

density of vastus lateralis in group A &jQ for S and S+E and group B

(right) for E and E+S. Values are means +: SE for before (open bars)

and after (stippled bars) training.

response to training, regardless of the method of training.

This problem would be minimized with larger groups.

The within-subject model used in the present study had

at least one limitation. The model wa s chosen on the

assumption that a major part of any interaction (antag-

onism or addition) caused by concurrent strength and

endurance training would be expressed at the peripheral

muscle level in measures such as muscle cross-sectional

area and enzyme activity. If antagonism or addition

occurred but were expressed entirely as a “central” phe-

nomenon, then in our subjects even the legs that did only

strength or endurance training would have been affected

in the same way as the legs that did combined strength

and endurance training. Antagonism or addition would

not have been revealed. In the study by Hickson (14),

there was evidence that antagonism may in some in-

stances be entirely central (e.g., central nervous system

fatigue); voluntary strength development was impaired

by concurrent strength and endurance training, but in-

creases in muscle size (indicated by thigh girth measure-

ments) were not impaired. In comparison we found no

impairment of strength or muscle size development, but

we cannot exclude the possibility that some entirely

centrally mediated antagonism occurred in our study. It

can be concluded, however, that no peripherally (muscle)

mediated antagonism occurred.

In conclusion, one finding of the present study that

does not bear directly on the main purpose nevertheless

deserves comment. The percent of ST fibers in vastus

lateralis increased after -5 mo of training. An increase

or any change in %ST fibers after strength or endurance

training in humans is unusual but not unprecedented

(21, 38, 40). Detraining has been associated with a de-

crease in %ST fibers (23). Any observed change in fiber

type composition raises the issue of the methodological

errors associated with determining %ST fibers from sin-

gle biopsy samples from a large muscle. These errors

(e.g., Ref.

4, 24)

and their bearing on the interpretation

of findings of changes in %ST fibers have been discussed

recently elsewhere (23,38). In the present study the pre-

and posttraining biopsy samples were not analyzed in a

single batch but rather 5 mo apart, raising the possibility

that a difference in the pH or temperature of the prein-

cubation medium in the two analyses caused a systematic

error in the staining and subsequent determination of

%ST fibers. However, this possibility is diminished by

the consideration that a difference of at least several

tenths of a pH unit would be necessary to affect the

differentiation of the main fiber types (ST vs. FT).

Nevertheless, our observed change in %ST fibers should

be viewed with caution.

The authors thank J. Moroz for general assistance; J. Laufer, T.

Brown, and D. Kerrigan-Brown for technical assistance; A. Brown and

D. Moroz for coordinating the study; and L. Diskin for secretarial

assistance.

This study was supported by the Dept. o f National Defence, Canada

(DCIEM Contract 8SE85-00082) and the Natural Sciences and Engi-

neering Research Council of Canada.

Address for reprint requests: D. G. Sale, Dept. of Physical Education,

McMaster Universi ty, Hamilton, Ontario L8S 4Kl, Canada.

Received 14 September 1988; accepted in final form 28 August 1989.

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