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The exercise sex gap and the 
impact of the estrous cycle on 
exercise performance in mice
Aderbal S. Aguiar Jr  1,2, Ana Elisa Speck1,2, Inês M. Amaral1, Paula M. Canas1 & 
Rodrigo A. Cunha  1,3
Exercise physiology is different in males and females. Females are poorly studied due to the complexity of 
the estrous cycle and this bias has created an exercise sex gap. Here, we evaluated the impact of sexual 
dimorphism and of the estrous cycle on muscle strength and running power of C57BL/6 mice. Like men, 
male mice were stronger and more powerful than females. Exercise-induced increase of O2 consumption 
(VO2) and CO2 production (VCO2) were equal between sexes, indicating that running economy was higher 
in males. Thermoregulation was also more efficient in males. In females, proestrus increased exercise VO2 
and VCO2 at low running speeds (30–35% female VO2max) and estrus worsened thermoregulation. These 
differences translated into different absolute and relative workloads on the treadmill, even at equal 
submaximal VO2 and belt speeds. In summary, our results demonstrate the better muscle strength, 
running power and economy, and exercise-induced thermoregulation of males compared to females. 
Proestrus and estrus still undermined the running economy and exercise-induced thermoregulation of 
females, respectively. These results demonstrate an important exercise sex gap in mice.
The importance of differences between sexes/genders is recognized in biology and medicine. Sex describes bio-
logical differences, while gender includes social, cultural and economic aspects1. The historical gender differences 
in motivation/opportunity to practice physical activity (including physical exercise and training) limited the best 
women exercise/sport performance, a phenomenon known as exercise gender gap in humans2. For instance, 
women are more prone to physical inactivity3, a risk factor for many diseases4,5. The historical evolution of exer-
cise gender gap in modern Olympic Games (World Record and 10 best performances) also reveals a systemati-
cally lower sport performance of females compared to males; nowadays, the differences varies between 10.7% for 
running and 36.8% for weightlifting2. The exercise gender gap is greatest in sports that require running economy, 
muscle strength, and exercise power2. Running economy is the energy demand for a submaximal running speed6, 
higher in men7,8 but it is unknown if this sex difference is also present in laboratory animals.
A review of ≈1400 manuscripts involving more than 6 million people revealed an under-representation of 
women in studies of exercise and sports (35–37%)9. However, sex is a major determinant of exercise performance 
through the impact of anthropometry (height, weight, body fat, and muscle mass), aerobic power and anaerobic 
threshold, besides genetic and hormonal factors2–4,10. The minor representation of females also translates into less 
knowledge about the biology of exercise in this sex. So far, the main features of sexual dimorphism important for 
exercise described in rodents are differences in skeletal muscle kinetics and fiber-type composition10 and energy 
metabolism11,12. In fact, the biological mechanisms underlying the benefits of exercise were investigated in 
numerous animal studies in a laboratory setting, with a strong tendency to only use males probably to avoid deal-
ing with the possible influence of the menstrual/estrous cycle9,13. Exercise-induced thermoregulation, submaxi-
mal and maximal VO2 and VCO2, and running economy are gold physiological indexes for exercise, but have 
never been studied in females at different phases of the estrous cycle.
In humans, the exercise sex gap is greatest in sports that require running economy, strength, and power. 
Similarly, we investigated the role of sex and estrous cycle in maximum (and submaximal) muscle strength and 
running power/economy of mice. We also evaluated exercise-induced thermoregulation. This knowledge is 
1Purines at CNC-Center for Neuroscience and Cell Biology, University of Coimbra, 3004-517, Coimbra, Portugal. 
2Research Group on Biology of Exercise, Department of Health Sciences, UFSC-Federal University of Santa Catarina, 
Araranguá, SC, 88905-120, Brazil. 3FMUC – Faculty of Medicine, University of Coimbra, 3004-504, Coimbra, Portugal. 
Correspondence and requests for materials should be addressed to A.S.A. (email: aderbal.aguiar@ufsc.br)
Received: 22 January 2018
Accepted: 21 June 2018
Published: xx xx xxxx
OPEN
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essential to advance the knowledge of exercise physiology in female sex. We will demonstrate that the simple 
extrapolation of male knowledge is not correct.
Results
Mouse morphology and the estrous cycle. 
The body mass of males was 22.7 ± 1.1% higher than females 
(F4,51 = 12.6, P < 0.05, Fig. 1A). Rodent tails are important for regulating body temperature14–16. The length of 
the tail of the males (6.5 ± 0.2 cm) was shorter than females (8.1 ± 0.3 cm, t27 = 4.5, P < 0.05). These parameters 
were independent of the estrous cycle, which was devoid of effects on body weight (F3,43 = 0.1, P > 0.05; Fig. 1A) 
and tail length (F4.51 = 0.4, P > 0.05; data not shown). The prominent estrous cycle was estrus (H2 = 8.1, P < 0.05, 
Fig. 1B), where vaginal smears were marked by clusters of cornified squamous epithelial cells (Fig. 1E). The vag-
inal smears also allowed the morphological identification of diestrus, proestrus and metestrus, as exemplified in 
Fig. 1C,D and F, respectively.
Male are stronger and more powerful than females. 
Figure 2 shows the basal motor behavior and 
ergometric performance of male and female mice. The open field test did not reveal significant differences in 
locomotion (F4,53 = 0.39, P > 0.05; Fig. 2A), average (F4,53 = 0.38, P > 0.05; Fig. 2B) and maximum speed of males 
and females, independently of their estrous cycle (F4,53 = 0.43, P > 0.05; Fig. 2B).
Absolute exercise performance of females was curtailed in relation to males, being 27.2 ± 1.1% (F4,32 = 14.2, 
P < 0.05; Fig. 2C) and 40.5 ± 0.9% lower (F4,32 = 9.9, P < 0.05; Fig. 2F) in the absolute grip strength and treadmill 
power test, respectively. Moreover, the absolute exercise performance of females was independent of the estrous 
cycle in the two tests (grip strength F3,27 = 0.27, P > 0.05; Fig. 2C) (treadmill power test F3,27 = 0.19, P > 0.05; 
Fig. 2F).
Although the absolute exercise performance of males was higher, the submaximal comparisons indicated a 
different conclusion. The ergometric test applied progressive running speeds for males and females through serial 
acceleration (F21,310 = 3.2, P < 0.05; Fig. 2E). The treadmill running power in males and females was statistically 
similar up to 15 m/min (F21,310 = 3.2, P > 0.05; Fig. 2E), when the relative intensity was 50 ± 3.7% of the maximum 
power for females, and 35 ± 3.9%% for males. The lower running power of females appeared at speeds 18 → 30 m/
min (F28,252 = 18.1, P < 0.05; Fig. 2E, gray area). At 30 m/min, the maximum overload of females (100 ± 5.7%) 
corresponded to a relative overload of males (71 ± 2.2% of maximum). Males reached maximum overload at 
speeds 39 → 42 m/min (Fig. 2E).
The normalization of exercise performance by body mass eliminates sexual dimorphism. 
We 
then normalized the exercise performance by the body mass. This transformation eliminated the sex differences 
for muscle strength (F4,32 = 0.78, P > 0.05; Fig. 2D) and running power at speeds 15 → 30 m/min (F4,32 = 0.63, 
P > 0.05; Fig. 2G).
Figure 1. Impact of sexual dimorphism on body mass (A) and analysis of the estrous cycle based on a 
morphological analysis of vaginal smears (C–F) that revealed that the prominent estrous cycle was estrus  
(B). Values are expressed as mean ± standard error of the mean (SEM). N = 8–10 animals/group. *P < 0.05 vs. 
male (ANOVA, Bonferroni post hoc test). @P < 0.05 (Kruskal-Wallis test).
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Males show a better running economy. 
There were no differences in V O2 and V CO2 kinetics between 
sexes. The progressive running speeds of the ergospirometry increased the V O2 (F7,126 = 2.8, P < 0.05; Fig. 3A) 
and VCO2 (F7,126 = 2.4, P < 0.05; Fig. 3E) of males and females at all comparative intensities (9 → 30 m/min, 
Fig. 3A and E). Thus, the higher submaximal running power developed at speeds 18 → 30 m/min, associated to 
the same submaximal V O2, showed a better running economy in males compared to females at (Fig. 3A and E, 
gray area).
Importantly, males ran up to higher speeds (33 → 42 m/min; Fig. 2E), which resulted in a higher V O2 
(F4,33 = 2.7, P < 0.05; Fig. 3D) and V CO2 (F4,33 = 2.7, P < 0.05; Fig. 3G), but not V O2max in relation to females.
Proestrus increases VO2 and VCO2 during submaximal exercise testing. 
The submaximal V O2 
(F18,192 = 2.5, P < 0.05; Fig. 3B) and V CO2 (F18,192 = 2.3, P < 0.05; Fig. 3C) of females during proestrus were signif-
icantly larger at lower exercise intensities (30–35% V O2max females. We also detected these differences in total V
O2 (F3,35 = 3.8, P < 0.05; Fig. 3D) and V CO2 (F3,35 = 3.2, P < 0.05; Fig. 3G) for females at proestrus during these 
low exercise intensities (30–35% V O2max females). The higher intensities (30–100% VO2max females) presented 
similar kinetics for VO2 and VCO2 in the different phases of the estrous cycle.
Exercise-induced thermoregulation is less effective in estrus females. 
Thermoregulation requires 
the dissipation of heat produced during exercise. Exercise increased the heat production of males and females 
(F7,126 = 264, P < 0.05; Fig. 4A), without influence of the estrous cycle (F7,94 = 0.32, P > 0.05; Fig. 4B). Environment 
temperature and humidity did not interfere in the thermography results, since they were similar before and after 
the exercise test session (Fig. 4C). The thermal image (Fig. 4D) shows a female at rest, with the body and tail 
heated after a maximum exercise test (Fig. 4E).
Resting body and tail infrared temperatures did not differ between sexes or in females at different phases of the 
estrous cycle (body, F4,19 = 0.53, P > 0.05; Fig. 4F) (tail, F4,19 = 2.01, P > 0.05; Fig. 4G). The maximum exercise was 
not enough to heat the body of males and females on metestrus, diestrus and proestrus cycle (F4,43 = 3.4, P < 0.05; 
Fig. 4H). Moreover, all males and females (all cycles) presented significant tail warm up after maximal exercise 
(F4,43 = 2.8, P < 0.05).
The temperature scores (Fig. 4H and I) reinforced the prominent exercise-induced hyperthermia of females at 
estrus. Estrus female body heating was larger than that of males and females in other cycles (F4,43 = 3.3, P < 0.05; 
Fig. 4H). The tail warming of estrus females was superior to males and females at metestrus after exercise 
(F4,43 = 2.3, P < 0.05; Fig. 4H).
Figure 2. Motor and ergometric data. Sex and estrous cycle did not influence the basal locomotion (A) and speed 
(B) of mice. Males were stronger (C) and more powerful on the treadmill (E,F) than females, regardless of the 
phase of the estrous cycle. The normalization of the performance per body mass dissipated the sexual dimorphism 
(D and G). Values are expressed as mean ± standard error of the mean (SEM). N = 8–10 animals/group. *P < 0.05 
vs. male (ANOVA, Bonferroni post hoc test).
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Discussion
Sex matters. 
Sexual dimorphism and the estrous cycle influenced exercise performance and metabolism of 
mice implying that these factors should be considered in experimental designs and data interpretation involving 
exercise biology. We showed that males were stronger and more powerful than females at moderate-high intensi-
ties of exercise, when evaluating strength and running. Since submaximal and maximum overloads of exercise 
were different for males and females, but submaximal VO2 and VCO2 were similar, this means that the running 
economy of females was lower than that of males. The estrous cycle did not influence muscle strength, but under-
mined the running economy and exercise-induced thermoregulation.
Size matters. 
The sex-related exercise differences disappeared after normalization of exercise performance 
by size (body mass). This had already been described for muscle strength17–19, but not for running power and 
economy. However, body size and muscle strength are well-known secondary sexual characteristics, influenced 
primarily by the anabolic action of the hormone testosterone, a major determinant of sexual dimorphism20.
Skeletal muscle mass and strength are lower in females19,21. Likewise, normalization of exercise performance 
by specific muscle mass (rather than body mass) makes sexual dimorphism disappear19,21. Male mammals are 
larger, with larger cross-sectional muscle area8,10. Several studies also showed that muscle length (and the length 
of the long bones) is also higher in male mammals, important for greater tetanic strength of the anterior mas-
seter muscle8. Larger levers determine higher torques and muscle strength. Sex is also important for muscle 
fiber-type composition, especially the myosin IIB gene (fast muscle fiber)10. Evidence shows threefold more IIB 
muscle fibers in the masseter of male mice8,22. In addition, testosterone signals hypertrophy in this musculature20. 
Conversely, estrogen decreases muscle contractile force in female mice23,24. Thus, muscle strength and running 
power depends on size and sex: males have large muscles and bones, responsible for great muscle strength; this 
difference is further amplified by the anabolic effects of testosterone, resulting in larger muscle strength, speed 
and power.
The testosterone also seems to influence running endurance, but not the running economy. Castration of 
mouse testicles deplete blood testosterone and impair running wheel endurance (10–30% males with intact 
gonads)25, a model of submaximal physical activity. Testosterone replacement completely reversed this impair-
ment25. The antiandrogen Flutamide decreases the treadmill endurance of rats, but does not change VO2max and 
running economy26. Here, the exercise-induced submaximal VO2 and VCO2 up to V O2max were similar between 
sexes, as previously described11,12,27. Only one study demonstrated increased female submaximal V O2 during 
treadmill test, which further reinforces the hypothesis of females’ worst running economy27. These testosterone 
evidences support the best physical performance (power and endurance) of running male mice, but not the best 
running economy.
Figure 3. Respiratory gases during an incremental test. Running similarly increased general O2 consumption 
(V O2, A,B) and CO2 production ( VCO2, E,F) in males and females at different speeds up to 33 m/min. V O2max 
was similar between the sexes (C) total VO2 (D) and V CO2 (G) was only higher in males due to higher running 
speeds. Proestrus increased submaximal VO2 (B and D) and VCO2 (G) at lighter intensities of ergospirometry 
(30–35% VO2max). Values are expressed as mean ± standard error of mean (SEM). N = 8–10 animals/group. 
*P < 0.05 vs. male, #P < 0.05 vs. females (ANOVA, Bonferroni post hoc test).
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On the other hand, estrogen seems to influence VO2 and possibly the running economy of mouse. Similar to 
our results, submaximal VO2 was higher in female rats during the estrogen-dominant proestrus at low treadmill 
speeds 5–12 m/min (6° grade, without acceleration)17, which may be considered as a low intensity exercise. We 
also found these differences at near speeds 9–12 m/min. A possibility is the effect of estradiol in the lung 
gas-exchange surface area (GSA). VO2 is directly proportional to GSA28,29; which increases during proestrus with 
high estradiol levels28,29. Estradiol also increases lung’s GSA and V O2 in ovariectomized rats29. Our results suggest 
that estrogen can increase V O2 during exercise, and worsen the running economy, especially at proestrus.
Exercise-induced hyperthermia is a biological response due to greater muscle activation, mitochondrial 
uncoupling and proton leak30. We now report that sex and the estrous cycle do not modify the calories consumed 
by exercise, another important variable for running economy; however, our results showed that male thermoreg-
ulation was more efficient, since the infrared dissipation of males was more effective. Literature suggests two 
important points for mouse thermoregulation: body surface area (BSA) and tail dry heat loss. BSA is estimated 
by the Meeh’s formula (BSA = body weight0.667)25. The greater body mass of males assists in better heat dissipation 
during/after exercise. Moreover, tail size seems to be related to thermal stress14–16,31, with animals that live in 
warm environments having longer tails15,32. Female tails, even longer, warmed up more during exercise than that 
of males. The tail length of C57BL/6 female mice was similar to that described in female BALB/c mice15. Thus, a 
longer tail length in female mice is suggestive of a required adaptation to compensate for their lower body mass 
(and area).
Sanchez-Alavez33 demonstrated that body warming during exercise was higher in female mice at estrous. We 
saw it in the tails. Progesterone promotes heat conservation and higher body temperatures at rest34,35. Bilateral 
ovariectomy eliminated this estrous-associated change14,33. We suggest that this may apply to body temperature 
of running female mice during estrus, characterized by high progesterone levels. Thus, sex seems to be a crucial 
factor also for the exercise-induced thermoregulation of mice.
Some of our results are similar to those reported in humans, since the physical performance of women is gen-
erally lower than in men, in accordance with the exercise gender gap2,36,37. The woman’s menstrual cycle is divided 
into three phases: follicular, ovulation and luteal. The follicular phase can be divided into initial and late, corre-
sponding to metestrus and diestrus, respectively. Ovulation corresponds to proestrus, and the luteal phase to 
estrus. The woman’s follicular and luteal menstrual cycle does not seem to influence muscle strength, power, and 
V O2
1,38–40. Human studies still allow evaluating rate of perceived effort (RPE), which also does not differ in the 
different menstrual phases38,41. However, the differences we found are close to ovulation, virtually impossible to 
Figure 4. Exercise heat production and dissipation, or thermoregulation. Upon exercise, male and female mice 
consumed similar calories during the incremental test (A) without any evident impact of the estrous cycle. (B) 
Experiments were conducted in a controlled temperature and humidity environment. (C) The thermal IR image 
shows an evident tail heating after the maximum exercise (or recovery time, REC, E) in relation to rest. (D) The 
body and tail temperature was not different at rest (F and G, respectively). Exercise warmed the body of females 
at estrus (H) and the tails of all groups of mice (I). Again, female tail heating was larger at estrous (I). Values 
are expressed as mean ± standard error of the mean (SEM). N = 8–10 animals/group. *P < 0.05 (ANOVA, 
Bonferroni post hoc test).
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evaluate in women. We demonstrated that the mouse proestrus (or human ovulation) increased VO2 and heat 
production at light exercise.
In summary, our results highlight differences in exercise performance and metabolism between male and 
female mice. Sex influences size, which appear to be the main factor for mice exercise sex gap. Mouse sexual 
dimorphism also influenced exercise workload, but not V O2 and VCO2, implying a finest running economy in 
males. Males also presented better thermoregulation after exercise. The estrous cycle played a subtle role in mouse 
physical performance: proestrus impaired running economy and estrus impaired exercise heat loss. This implies 
that the impact of the estrous cycle on the performance of females should not be considered a limiting factor for 
their use in experimental designs. In fact, size is the main factor that should be considered in the construction of 
experimental designs involving exercising male and female mice. For running, a light-intensity exercise seems 
similar between the sexes (except proestrus), but the performance of females at moderate-intensity running cor-
responded to the performance of males at low-moderate intensity; the performance of females at high-intensity 
running corresponded to the performance of males at moderate-high for males, and male high-intensity running 
was supra-maximal for females. Failure to consider these differences by measuring only the running speed, as 
done in most studies, introduces an error to compare performance between sexes. These results are of particular 
interest to counteract the underrepresentation of females in exercise experimental designs.
Methods
Animals. 
Male and female C57BL/6 mice (10–12 weeks old) were obtained from Charles River (Barcelona, 
Spain). Mice were housed under controlled environment (12 h light-dark cycle, lights on at 7:00 AM, and room 
temperature of 21 ± 1 °C) with ad libitum access to food and water. Animals were housed and handled accord-
ing to European Union guidelines and the study was approved by the Ethical Committee of the Center for 
Neuroscience and Cell Biology (University of Coimbra).
The animals were accustomed to the treadmill for 3 days. The open field or grip strength test was performed 
on the 4th day in independent groups of animals. Ergospirometry was performed on the 5th day. All tests were 
carried out between 9:00 and 17:00 hours in a sound-attenuated and temperature controlled observation room 
under low-intensity light (≈10 lux), where mice had been habituated for at least 1 hour. The apparatuses were 
cleaned with 10% ethanol between animals. Within the time window of the tests, we did not record any significant 
impact of the time of day (morning vs. afternoon) on the treadmill vertical power, VO2max and temperature of the 
tail at rest in either males or females (data not showed).
Vaginal cytology. 
We evaluated the estrous cycle immediately after the behavioral and exercise experiments, 
through 4–5 consecutive vaginal lavages (with 40–50 μL of distillated H2O) then mounted on gelatinized slides 
(76 × 26 mm). These procedures lasted no more than 3–5 minutes, and there were no major temporal delays 
between behavioral experiments and fluid collection for vaginal cytology.
The vaginal smear were desiccated at room temperature and covered with 0.1% crystal violet for 1 min, then 
twice washed with 1 mL H2O and desiccated at room temperature. The slides were mounted with Eukitt medium 
(Sigma-Aldrich) and evaluated under an optical microscope at 1x, 5x and 20x (Zeiss Axio Imager 2). The char-
acterization of the estrous cycle was performed according to literature20,42. Females were categorized for initial 
(metestrus) or late (diestrus) follicular phase, ovulation (proestrus), or luteal phase (estrus)20,42.
Open field. 
The exploration of an open field (38 × 38 cm) was analyzed for 15 min using the ANY-maze™ 
video tracking system (Stoelting Co.)41.
Grip strength. 
The animal was hung with its forepaws to the central position of a 300 g metal grid and the 
grip strength was determined as the weight pushed (in grams)41. The computed result was the average of 3 trials, 
expressed in kgf.
Ergospirometry. 
Mice were accustomed with a single-lane treadmill (Panlab LE8710, Harvard apparatus) 
for 3 consecutive days (speed 15 cm/s, 10 min, slope 8.7%, 0.2 mA), with 24 h interval between each habituation 
session.
The ergospirometry test was carried out on 5th day, 48 hours after the last habituation session. The incremental 
protocol started at 15 cm/s with an increment of 5 cm/s every 2 min, with a constant inclination of 8.7% (5° for the 
LE8710 model). The exercise test lasted until running exhaustion, defined by the inability of the animal to leave 
the electrical grid for 5 seconds43,44. We estimated the power output for treadmill running based on a standard 
conversion of the vertical work, body weight and running speed45,46. Power is the 1st derivative of work relative to 
time (run time at each stage).
Oxygen uptake ( VO2) and carbon dioxide production ( VCO2) were estimated during treadmill running in a 
metabolic chamber47 (Gas Analyzer ML206, 23 × 5 × 5 cm, AD Instruments, Harvard) coupled to treadmill. The 
animals remained in the chamber for 15 min prior to exercise testing. Atmospheric air (≈21% O2, ≈0.03% CO2) 
was renewed at a rate 120 mL/min, using the same sampling rate for the LASER oxygen sensor (Oxigraf X2004, 
resolution 0.01%) and infrared carbon dioxide sensor (Servomex Model 15050, resolution 0.1%). Heat (calories) 
was estimated according to the equations of Lusk48.
Thermal imaging. 
An infrared (IR) camera (FLiR C2, emissivity of 0.95, FLiR Systems) placed overtop 
(25 cm height) of a plastic tube (25 cm diameter) was used to acquire a static dorsal thermal image49. IR images 
were taken immediately before and after exercise tests, namely at rest (Fig. 4D) and recovery (REC, Fig. 4E) peri-
ods, respectively. IR images were analyzed with FLiR Tools software (Flir, Boston).
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Tail length. 
The FLiR C2 camera also captures digital pictures (640 × 480 pixels) that were loaded and cali-
brated (plastic tube, 25 cm diameter) in the ImageJ software (v1.51j8, NIH, USA) for tail length measurement of 
live animals (ImageJ software).
Statistics. 
Data are presented as mean ± Standard Error of the Mean (SEM). A test for normality was per-
formed by Kolmogorov–Smirnov test. For each test, the experimental unit was an individual animal. The fre-
quency of the estrous cycle was assessed using the Kruskal-Wallis test. The role of sex and estrous cycle in the 
dependent variables body mass, open field, grip strength and vertical power, V O2 and VCO2, and body and tail 
temperature was evaluated using on-way ANOVA. The repeated measures of ANOVA were performed to evaluate 
the effect of different treadmill speeds, sex and estrous cycle on the vertical power, V O2 and VCO2, and heat. The 
Bonferroni post hoc test was applied for significant F values. The accepted level of significance was p < 0.05. 
Statistics were performed using Dell Statistica (data analysis software system), version 13.
Data availability. 
The datasets generated and analyzed during the current study are available from the cor-
responding author on reasonable request.
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Acknowledgements
The work was supported by Prémio Maratona da Saúde, CAPES-FCT (039/2014), FCT (PTDC/NEU-NMC/4154) 
and ERDF through Centro 2020 (project CENTRO-01-0145-FEDER-000008:BrainHealth 2020). A.S.A.Jr 
is a CNPq fellow. We would like to acknowledge Flávio N.F. Reis and Frederico C. Pereira (IBILI - Institute 
for Biomedical Imaging and Life Sciences, University of Coimbra) for making available the treadmill and gas 
analyzer.
Author Contributions
A.S.A. Jr. designed and performed the experiments, prepared the figures, and wrote the manuscript. A.E.S. and 
I.A. performed the experiments. P.M.C. designed the experiments and wrote the manuscript. R.A.C. designed the 
experiments and wrote the manuscript. All authors revised the manuscript.
Additional Information
Competing Interests: The authors declare no competing interests.
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© The Author(s) 2018

The exercise sex gap and the impact of the estrous cycle on exercise performance in mice.
Aguiar, Aderbal S,Speck, Ana Elisa,Amaral, Inês M,Canas, Paula M,Cunha, Rodrigo A