Title: Effects of oral contraceptive use on muscle strength, muscle thickness, and fiber size and
composition in young women undergoing 12 weeks of strength training: A cohort study
Version: 3 Date: 01 Mar 2022
Reviewer:  Mikkel Oxfeldt
Reviewer's report:
Comments to the author:
This is an interesting and highly relevant study in the growing body of literature investigating
the influence of female hormones on skeletal muscle.
The present study elucidated whether oral contraceptive (OC) users and non-OC users responded
differentially to 12 weeks of resistance training. The main finding of the study was that both
groups increased muscle strength and mass, with no significant difference between groups.
The data and overall methodology look good and provide valuable insights to a growing body
of literature. However, the paper is unclear due to the author’s use of imprecise language. Thus,
the whole manuscript needs editing for readability and grammar, preferably by a professional.
Furthermore, the paper does not sufficiently introduce or discuss new literature in this area of
research. This is specifically evident in the introduction and discussion where claims are made
without proper citation.
Overall, the authors need to increase the readability of the manuscript and improve the
introductions and discussions structure and summary/discussion of existing literature.
Specific Comments:
Title:
Please change the title so it includes muscle strength, muscle diameter, and fiber size and
composition.
Abstract:
Trainability of strength? Or response to strength training? Please clarify.
Line 35: please move “leg-press machine with a combined force and load cell” so it is mentioned
when you mention the outcome measure: Fmax. You should also mention that muscle diameter
was measured with ultrasound.
Line 42: change groups to group
The use of macroscopic and microscopic sounds awkward. Please write the outcome measures
instead.
Conclusion: you only mention strength. What about all other outcomes? Please change the
conclusion, so it answers the aim of the study: Do OC-users vs. non-OC users respond differently
to strength training?
Introduction – Overall, the introduction presents knowledge on OC use and basal physiology in
terms of sex steroid hormones. However, it does not present any longitudinal data from previous
studies comparing strength training adaptations between OC-users and non-users. Instead, it
focuses on cross-sectional data comparing muscle strength between OC-users and non-users.
Line 57: some studies suggest a reduced risk of musculoskeletal injuries. However, the evidence
is still conflicting. I suggest you either delete this statement or cite original studies supporting
this statement.
Line 69: please changes Estrogen to Ethinylestradiol
Line 73: The statement that OC use may lead to differences in training adaptation comes with
no connection to paragraph. Please make a proper introduction, before making this statement.
Line 85: insert “use” after OC
Line 96-101: This section needs to cite previous literature. Please cite previous longitudinal
studies investigating if OC-use influences skeletal muscle adaptations to resistance/strength
training. There have been published a handful of studies in recent years.
Line 103: Your hypothesis is vague. You need to make it more clear throughout the paper that
you investigate strength training adaptations and NOT cross-sectional measures of strength and
size.
Methods
Line 112: I think the use of “untrained or moderately trained” is confusing. I suggest you
instead state clearly that the participants were unaccustomed to resistance training (name specific
inclusion criteria) but otherwise active (performed less than 2h per week of exercise….).
Line 117: Regular menstrual cycle – please clarify your definition here and state if you had a
time range (3-6 months before enrolment into the study?)
Line 120: Could you provide a list of the OCs used? It would be relevant to know if they used
the same generation (ie. 2nd generation, 3rd generation?).
Line 130: Really nice job monitoring the non-OC users MC! However, you don’t clarify what
you use this information for? When did the non-OC users start the intervention in their MC?
Line 146-148: I just mentioned in the previous paragraph that body temperature was used to
measure the MC. Please don’t repeat yourself.
Line 148-152: “In the second control and each training cycle”. I am not sure what you mean
here and the experimental design is not described sufficiently. Please rewrite the sentence.
Line 160: thrice
Line 164: Please clarify the volume and intensity of the home program.
Line 167: I find it confusing that you increased weights by 10kg for all participants instead of
using percentages or individual progressions.
Line 178: Were the participants familiarized on the day of testing or before?
Line 176: You state that each participant's Fmax was measured on the 25th day of the menstrual
cycle. Menstrual cycle length normally varies between 25-35 days. How did you control this? I
am concerned that some participants may have trained one more week than others?
Line 187: Was the MD measurements made before or after the leg press testing?
Line 197-199: Static muscle tension? Please describe this in more detail.
Line 212-214: please change the wording or the sentence.
Line 231: Due to the large variability, it is recommended to count at least 150 fibers per sample
(doi: 10.1152/jappl.1985.59.4.1228.). This is a large limitation to your MFD analysis.
Line 235: did you count muscle cell nuclei on all samples you measured MFD on?
Results – Please include unit in all the results you present
Line 271: You state that there were differences in post-training Fmax and Fmax/Mdm. However,
you don’t present a group x time interaction. Please clarify.
Line 285-307: This paragraph is written confusingly, mentioning the results from non-OC group
first and then OC-group afterward. I would prefer that you presented the actual training effect
first and then highlighting the differences between groups afterward. You did this in the previous
paragraph.
Table 3: Change “by young women” to “In young women”
Discussion – The discussion needs structure and a comprehensive revision of the literature
included in it.
Line 315-316: please cite previous studies.
Line 316-320: This statement is incorrect. In recent years, a number of studies have been
published comparing strength training adaptations in OC-users and non-OC users (Such as
Dalgaard 2020, Oxfeldt 2020, and others….)
Line 325: Please delete “Also”
Line 339: This statement is incorrect. Please cite original studies supporting this statement. The
literature is very limited and possibly inconclusive. Please change the wording of the sentence.
Line 341-343: Again, this statement is not supported by proper literature.
Line 343-345: Please cite the literature you refer to. Also, you should focus on previous strength
training studies, rather than aerobic training studies.
Line 350-367: Please cite new studies published in this area of research. Preferably
investigations of 2nd and 3rd generation OC users.
Line 371: please cite the previous studies you are referring to.
Line 392: Postmenopausal women do not use OCs? Please rewrite this sentence
Conclusion
Line 438-441: Your data does not support this statement. Please delete.