Effect of eight weeks of strength training on fatigue resistance in men and women

Abstract

The purpose of the present study was to compare the effects of eight weeks of strength training on fatigue resistance in men and women. Thirty-three men and twenty-three women performed eight weeks of strength training in three weekly sessions. Subjects performed four sets using 80% of 1-RM tests on bench press, squat and arm curl. Fatigue index (FI) was used for analysis of decline in motor performance along the sets. The sum of the number of repetitions accomplished in the four sets in each exercise was used to indicate the fatigue resistance. Anova or Ancova two-way (time x gender) was employed for statistical analysis (P < 0.05). Eight weeks of strength training increased significantly 1-RM strength, fatigue resistance and total number of repetitions in both genders. FI decreased significantly in both genders after training (men = 50% vs. women = Time x gender interaction was observed in the total number of repetitions in squat (P = 0.04) and arm curl exercises, regarding gains to women (P = 0.01). In conclusion, eight weeks of ST improved strength, FR, FI and total number of repetitions performed. However, women obtained greater adaptations than men.

Full text

Isokinetics and Exercise Science 17 (2009) 101–106 101
DOI 10.3233/IES-2009-0340
IOS Press
Original Article
Effect of eight weeks of strength training on
fatigue resistance in men and women
Emanuel P´
ericles Salvadora,b,e,∗, Raphael Mendes Ritti Diasc, Andr´
e Luiz Demantova Gurj˜
aoa,e,
Ademar Avelara,e, Luiz Gustavo Pintodand Edilson Serpeloni Cyrinoa,e
aGroup of Study and Research in Metabolism, Nutrition and Exercise, Gepemene, Brazil
bS˜
ao Paulo Support Foundation for Research, FAPESP, Brazil
cSchool of Physical Education, University of Pernambuco, UPE, Brazil
dSchool of Physical Education and Sports, University of S ˜
ao Paulo, Brazil
ePhysical Education and SportCenter, Londrina State University, UEL, Brazil
Abstract. The purpose of the present study was to compare the effects of eight weeks of strength training on fatigue resistance in
men and women. Thirty-three men and twenty-three women performed eight weeks of strength training in three weekly sessions.
Subjects performed four sets using 80% of 1-RM tests on bench press, squat and arm curl. Fatigue index (FI) was used for
analysis of decline in motor performance along the sets. The sum of the number of repetitions accomplished in the four sets in
each exercise was used to indicate the fatigue resistance. Anova or Ancova two-way (time x gender) was employed for statistical
analysis (P<0.05). Eight weeks of strength training increased significantly 1-RM strength, fatigue resistance and total number
of repetitions in both genders. FI decreased significantly in both genders after training (men =50% vs. women =Time x gender
interaction was observed in the total number of repetitions in squat (P=0.04) and arm curl exercises, regarding gains to women
(P=0.01). In conclusion, eight weeks of ST improved strength, FR, FI and total number of repetitions performed. However,
women obtained greater adaptations than men.
Keywords: Weight exercises, resistance training, multiple sets, fatigue, gender
1. Introduction
Strength training (ST) is considered a useful method
to increase strength, power and resistance to fatigue
(FR). Among those adaptations, FR can be defined as
the capacity to resist fatigue in conditions of prolonged
period of strength use [4]. Fatigue resistance is de-
manded in countless sporting modalities, as well as in
common daily activities.
∗Address for correspondence: E.P. Salvador, Grupo de Estudo e
Pesquisa em Metabolismo, Nutric¸˜
aoe Exerc´
ıcio, Centro de Educac¸˜
ao
F´
ısica e Esporte, Universidade Estadual de Londrina, Rod. Celso Gar-
cia Cid, km 380, Campus Universit´
ario, CEP 86051-990, Londrina,
PR, Brasil. E-mail: emanuelps@usp.br.
It is known that the capacity to resist fatigue is mod-
ulated by a series of intrinsic (age, sex, motivation, pre-
vious experience and training level) and extrinsic (vol-
ume, intensity, contraction types and exercises) fac-
tors [12]. Regarding the intrinsic factors, sex is one of
the most studied. The literature suggests that women
present larger FR in comparison with men in differ-
ent contraction types, speed, position, age groups and
exercises performed [2,5–7,10,16].
Howeverthere is lack of information about the post-
training gender variation in FR. Once ST programs are
prescribed according to the specific characteristics of
subjects, possible gender differences in adaptation to
ST must be considered to maximize training adapta-
tions. Thus, attendance studies with interventions can
contribute to the knowledge regarding gender effect of
ISSN 0959-3020/09/$17.00 2009 – IOS Press and the authors. All rights reserved

102 E.P. Salvador et al. / Effect of eight weeks of strength training on fatigue resistance in men and women
training. Therefore, the purpose of the present study
was to compare the effects of eight weeks of ST on FR
in men and women
2. Method
2.1. Subjects
Thirty-three men (21.8 ±2.9 years, 70.5 ±9.4 kg
and 175.4 ±6.7 cm height) and 23 women (20.9 ±
2.1 years, 58.3 ±6.3 kg and 163.3 ±6.5 cm) partic-
ipated voluntarily in this study. As inclusion criteria,
participants should not have taken part in any physical
exerciseprograms duringtheprevioussix months of the
study. All subjects signed a consent term. This study
was approved by the Ethics Committee in Research of
the Londrina State University.
2.2. Muscle strength
Subjects were tested before and after eight weeks of
strength training on bench press, squat and arm curl
exercises, respectively. Each of the three exercises was
preceded by warm up series (6 to 10 repetitions) with
approximately 50% of the load to be used in the first
attempt in the 1-RM test. The test started two minutes
afterwarmingup. Subjectswere asked to complete two
repetitions. The load was gradually increased until the
subjectcouldlift the resistance once but not twice. This
load was therefore defined as 1-RM [3]. Rest interval
between exercises was 3–5 min. For all exercises, the
form and the technique of executionwere standardized
and continually monitored. Besides, the subjects ac-
complished the tests in the same period of the day and
were absent from the physical exercises practice during
the period of the tests. The registered load was the
highest obtained between the different sessions of the
tests.
Allsubjects were submitted to four sessions of 1-RM
tests to become familiarized to strength tests.
2.3. Fatigue resistance
FR test was performed2–3 days after the 1-RM tests.
The exercises and order of exercises used for FR test
were the same as in 1-RM test.
Testprotocolconsistedofthe executionof four series
in each exercise with 80% of 1-RM value, until vol-
untary exhaustion. The subjects were asked to execute
the maximum number of repetitions in each set. Rest
interval between sets was 2 min while 3–5 min was
allowed between exercises. The three exercises were
preceded by warm-up series, with the same equipment
used in the test. Six to 10 repetitions were performed
with approximately 40% of 1-RM for each exercise.
The index of decline strength between the first and
the fourth set of each exercise was used as fatigueindex
(FI) as proposed by Sforzo and Touey [19]:
FI=[(S(1st.series –S
(4th.series))/S(1st.series)] * 100%
–FI =Fatigue Index
–S=Strength (load lifted up X number of repeti-
tions executed during the series).
2.4. Training protocol
The ST program lasted 8 weeks with 3 weekly ses-
sions in alternate days. For all subjects, the frequency
of training sessions was higher than 80% (19 to 24 ses-
sions). The training program consisted of 10 exercises
executed as follows: bench press, leg press at 45◦, lat
pull downs, knee extension, shoulder press, knee flex-
ion, triceps press down,calf extension on legpress, arm
curlandcrunches. All exercises were executed in 3 sets
of 8–12 RM, except for calf extension exercises (three
sets of 15–20 RM) and crunches (three sets of 50 rep-
etitions with body weight). The rest interval between
sets and exercises was 1–2 min. For all exercises, the
load was periodically readjusted using the weight test
by maximum repetitions as proposed by Rodrigues and
Rocha [17].
2.5. Statistical analysis
Normality and homoscedasticity were checked by
Shapiro Wilk’s and Levene test, respectively. The ef-
fectofthe training program on the strengthandFR were
analyzed by two-way ANOVA for repeated measures
(gender x time). For the variables in which there were
differences betweengroups at baseline, ANCOVA two-
waywasused(genderx time), using the baselinevalues
as a covariate. For all ANOVA and ANCOVA analy-
ses that presented significant F value (P0.05), the
Tukey’s post hoc test was used to track the differences.
All values are presented in mean ±SD.

E.P. Salvador et al. / Effect of eight weeks of strength training on fatigue resistance in men and women 103
Table 1
1-RM test (kg) in baseline and after eight weeks of strength training in Bench Press, Squat and
Arm Curl in men and women
Men Women Effects F P
(n=33) (n=23)
Bench Press ANCOVA
Baseline 62.4 ±14.8 31.9 ±5.9 Time 86.6 0.01
Post-training 68.4 ±13.6* 36.7 ±5.6* Gender 10.4 0.01
∆% + 9.6 +15.0 Gender X Time 1.2 0.28
Squat ANCOVA
Baseline 124.0 ±24.8 71.1 ±13.6 Time 85.0 0.01
Post-training 137.7 ±24.5* 80.2 ±14.0* Gender 6.4 <0.01
∆% + 11.0 +12.8 Gender X Time 3.6 0.07
Arm Curl ANCOVA
Baseline 40.0 ±7.4 22.8 ±4.0 Time 47.3 <0.01
Post-training 44.8 ±7.4* 26.9 ±3.5* Gender 8.6 <0.01
∆% + 12.0 +18.0 Gender X Time 0.2 0.62
Total ANCOVA
Baseline 226.4 ±43.3 125.7 ±21.3 Time 123.8 <0.01
Post-training 250.9 ±40.3* 140.7 ±20.4* Gender 11.1 <0.01
∆% + 10.8 +11.9 Gender X Time 2.9 0.09
*P<0.05 vs. baseline.
Table 2
Fatigue index in baseline and after weight training of strength training in Bench Press,
Squat and Arm Curl in men and women
Men Women Effects F P
(n=33) (n=23)
Bench Press ANCOVA
Baseline 75.6 ±10.0 61.6 ±18.5 Time 94.3 <0.01
Post-training 56.7 ±7.7* 39.2 ±8.4* Gender 47.9 <0.01
∆% −25.0 −36.4 Gender X Time 0.8 0.41
Squat ANOVA
Baseline 59.9 ±16.9 64.3 ±14.2 Time 35.9 <0.01
Post-training 46.6 ±13.6* 45.3 ±11.4* Gender 0.4 0.58
∆% −22.2 −29.6 Gender X Time 0.7 0.30
Arm Curl ANCOVA
Baseline 65.1 ±11.3 48.3 ±25.2 Time 12.2 <0.01
Post-training 56.7 ±11.8* 37.1 ±10.9* Gender 29.3 <0.01
∆% −12.9 −23.2 Gender X Time 0.3 0.62
Mean ANCOVA
Baseline 66.8 ±8.1 58.1 ±11.4 Time 117.1 <0.01
Post-training 55.3 ±7.7* 40.5 ±5.5* Gender 31.5 <0.01
∆% −17.3 −31.3 Gender X Time 2.0 0.17
*P<0.05 vs. baseline.
3. Results
Eight weeks of ST increased strength significantly
in both genders (Table 1). The values of intraclass
coefficient correlation for the 1-RM tests at baseline
ranged from 0.97–0.99 indicating a high reliability of
the strength measurements. Before starting the pro-
gram, women presented 51%, 57% and 57% of the
men’s muscular strength in BP, SQ and AC exercises,
respectively. After eight weeks these values increased
to 54%, 58% and 60%. Time x gender interaction
was nonsignificant for any of the tested exercises, indi-
cating a uniform gender-independent improvement of
maximum strength in men and women.
The FI decreased significantly in both genders for
all exercises (Table 2) following the training program.
Again, no time x gender was apparent. There was a
significant increase in total number of repetitions after
the ST in both genders (Table 3). At baseline women
presented better performance in BP and AC exercises
(+11% and +16%, respectively) and a lesser perfor-
mance in the SQ exercise (−24%) compared to men.
Following training, the women presented better perfor-
mance than men in BP, SQ and AC exercises (+13%,
+1% and +27%, respectively). There was time x gen-

104 E.P. Salvador et al. / Effect of eight weeks of strength training on fatigue resistance in men and women
Table 3
Total number of repetitions in the four series with 80% of 1-RM in baseline and after
eight weeks of strength training in Bench Press, Squat and Arm Curl in menand women
Men Women Effects F P
(n=33) (n=23)
Bench Press ANOVA
Baseline 18.3 ±5.3 20.5 ±6.4 Time 87.3 <0.01
Post-training 27.2 ±6.2* 31.2 ±5.6* Gender 6.5 0.01
∆% + 48.6 +52.2 Gender X Time 0.7 0.43
Squat ANCOVA
Baseline 22.3 ±7.9 16.9 ±6.2 Time 62.9 <0.01
Post-training 30.0 ±6.5* 30.3 ±7.0* Gender 0.1 0.80
∆% + 34.5 +79.3 Gender X Time 4.6 0.04
Arm Curl ANCOVA
Baseline 22.1 ±5.2 26.3 ±5.5 Time 12.4 <0.01
Post-training 23.9 ±5.8 32.6 ±8.1* Gender 15.8 <0.01
∆% + 8.1 +23.9 Gender X Time 6.6 0.01
Total ANOVA
Baseline 63.8 ±10.5 63.7 ±12.1 Time 129.6 <0.01
Post-training 81.3 ±13.1* 94.0 ±11.5* Gender 6.7 0.01
∆% + 27.4 +47.6 Gender X Time 9.2 <0.01
*P<0.05 vs. baseline.
der interaction in the total number of repetitions in SQ
(P<0.02 andF =4.6),AC (P<0.01andF =6.6) and
in the total number of repetitions of the three exercises.
A more detailed gender-related performance analy-
sis during the 4 sets is presented in Fig. 1. Except for
the AC in men, there was significant improvement in
the number of repetitions performed at each set of the
three exercises after the training period (P<0.01).
Although the ST program increased the number of rep-
etitions in the all sets of the three exercises, the de-
crease in performance between sets was not different
after eight weeks of ST (P<0.01).
At baseline and post-training, women performed
more repetitions than men in the first, second and third
sets in BP (P<0.01). At baseline and post-training,
women performed more repetitions than men in the
four sets of AC (P<0.01). In SQ at baseline, men
accomplished more repetitions in first and second sets
(P<0.01). In the post-training period those differ-
ences were not apparent.
4. Discussion
Several studies investigated FR gender variations in
isometric,isokinetic and isoinertial contractions. How-
ever,to our knowledge,no other previousstudy investi-
gated the effect of ST program in the fatigue resistance
using isoinertial measurements.
Most of the cross-sectional studies indicate that
women have greater capacity to resist fatigue than
men [2,5–7,10,16]. However, the mechanisms under-
lying the differences between genders are not fully
understood. It has been hypothesized that histolog-
ical, cytological and neural differences may account
for these differences. Previous studies indicated that
women have a greater proportion of type I muscle
fibers [20] and greater amount of muscular creatine
content [14]. Other studies demonstrated that men pre-
sented greater motor unit activation frequency along
the contraction [15,16] that could lead to faster fa-
tigue. Therefore, responses to training programs may
be gender-dependent.
Theresultsofthepresentstudyshowthat eight weeks
ofSTpromotedincreasein1-RMstrengthanddecrease
of FI in both groups. These improvements have been
previously shown in men and women [1,8,9]. Howev-
er, studies comparing gender responses to ST are lim-
ited, indicating greater alteration in the total number of
repetitions in women. In this study we did not analyze
the mechanisms that underlie these responses. Howev-
er, differences between gendersin the neural and mor-
phologic adaptations to the ST program have been pre-
viously indicated. For example, Lemmer et al. [11]
reported that nine weeks of unilateral ST in men and
women induced an increase in the strength of the con-
tralateral limb only in women, indicating differentiat-
ed neural responses between genders. Regarding the
morphologicalterations, Martelet al. [13] havedemon-
strated an exclusive increase in the proportionof type I
fibers with concomitant reduction of type IIx fibers in
women after nine weeks of ST .
Another important finding of the presentstudy refers
to the decrease in performance during the sets in the

E.P. Salvador et al. / Effect of eight weeks of strength training on fatigue resistance in men and women 105
Fig. 1. Number of repetitions performed in four sets in Bench Press, Squat and Arm Curl exercises by men (quadrates) and women (circles) in
baseline (white points) and after eight weeks ofstrength training (black points). a <set 1, b <set2, c <set 3, * vs. baseline (P<0.01).
three exercises. In baseline and post training, there was
a significant decline in the number of repetitions along
setsfor both groups. Thus, the accomplishment of mul-
tiple sets of ST with 80% of 1-RM does not enable the
maintenance of the number of repetitions along sets.
Similar results were observed by Salvador et al. [18],
using multiple sets, also verified significant decline in
the number of repetitions accomplished along the sets.
It seems that the prescription based in percentage of
1-RM is limited in multiple sets of exercises using in-
tensity with 80% of 1-RM.
One limitation of the present study is the absence of
a control group. However, the objective of the present
study was to compare the adaptations after ST between
men and women, and not to analyze the efficacy of ST
to increase strength and FR. Another limitation of the
present study was the inclusion of squat in tests proto-
cols and leg press 45◦in training program. Leg pess
45◦was not used in tests because the weight capacity
of our equipment was limited to 250 kg. On the other
hand, the adaptations occurred in this exercise provide
important indication regarding the transfer of strength
gains suggesting that the increase in the initial period
in novice trainers is not specific for the exercise.
The results of the present study have an important
practical application. Since gender-related responses
due to same ST program aredifferent, ST prescription
for improvement of FR for men and women should
be structured accordingly in order to optimize training
adaptations.

106 E.P. Salvador et al. / Effect of eight weeks of strength training on fatigue resistance in men and women
In conclusion, eight weeks of ST improvedstrength
and the total number of repetitions with concomitant
decrease in FI, in both genders. Women presented
greater adaptation in the total number of repetitions in
the SQ, AC exercises and total number of repetitions
added to the three exercises.
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