Oral contraceptives (OC) are widely used by women. However, their effects on strength training are yet to be resolved. Few studies have directly compared the effects of OC use versus natural menstruation on strength training outcomes, and the results have been mixed. A key limitation in existing studies is the inconsistent and often non-site specific measurement of muscle hypertrophy, even though muscle growth varies across different regions. This highlights the need for more accurate methods to better understand how OC use may influence muscle adaptation. We will be looking at a study that investigated the effects of OC use on muscle hypertrophy and strength adaptation to heavy strength training in young untrained women.
Overview
- What did they test? The authors conducted a cohort study to investigate the effects of OC use on muscle hypertrophy during heavy strength training in young strength-untrained women. A control group of non-OC (NOC) users was included for comparison.
- What did they find? Both OC and NOC groups experienced gains in lean mass and muscle strength, although this was larger for the OC users. The authors suggest that OC use potentiates muscle growth during strength training, although further research is needed.
- What does it mean for you? Despite concerns that hormonal birth control might blunt training adaptations, this study shows that you can still make excellent progress with strength training on an oral contraceptive.
What’s the Problem?
Purpose
Strength training increases muscle growth and maximal strength, supporting health and sports performance 1. However, its effectiveness is influenced by factors like training intensity, nutrition, sleep, and medications 2. For young women, OCs are a common medication that may impact training adaptations 3.
Today, various types of OC are available, with different combinations of synthetic estrogen (ethinyl estradiol) and progestins. Second- and third-generation combined OCs suppress the natural fluctuations in endogenous estradiol and progesterone secretion, thereby preventing ovulation 4.
Both synthetic estrogen (ethinyl estradiol) and progestins in OC can bind to steroid receptors in the body 5. Ethinyl estradiol has a stronger binding affinity for estrogen receptors than natural estrogens 6. These interactions suggest OCs might influence how the body adapts to strength training 7. Mechanistically, OC use can enhance muscle growth to strength training through several pathways, including boosting satellite cell activity, myogenic factor expression, and follistatin levels 8.
Few intervention studies have examined how OC use compares to natural menstruation in affecting strength training outcomes. The findings are mixed with some studies showing OC to have positive, others showing negative effects, and some showing no difference. However, these studies varied widely in how they measured hypertrophy. Most used limited or no localized muscle size assessments, despite known differences in muscle growth across regions. Only one study conducted comprehensive multi-site measurements, suggesting that more precise methods may be needed to detect nuanced effects of OC use on muscle adaptations.
Therefore, in this article we will be looking at a study that aimed to investigate the effects of OC use on muscle strength and hypertrophy during strength training in young untrained women.
Hypothesis
The authors hypothesized that OC would enhance muscle growth during heavy strength training in young adult women compared with eumenorrheic, naturally menstruating women (not using OC).
What Did They Test and How?
Participants
Fifteen OC users and 17 NOC users completed the intervention. Baseline characteristics of the participants are shown in Table 1. The NOC group was slightly older than the OC group, but baseline height and weight were comparable between the groups.
Women aged between 18-40 were eligible if they had either a regular menstrual cycle for at least the past six months, with a cycle length of 28 ± 4 days, or if they had used monophasic second or third-generation OC for at least six months prior to the study. Women had to be untrained, which was defined as participating in less than one strength session per week six months prior to the study.
Table 1
OC (N = 15) | NOC (N = 17) | p | |
---|---|---|---|
Age (years) | 28 ± 3 | 32 ± 5 | 0.01 |
Height (cm) | 171 ± 6 | 170 ± 8 | 0.6 |
Weight (kg) | 70 ± 15 | 69 ± 9 | 0.8 |
Time on current OC (years) | 6 ± 4 | -- | -- |
Time on hormonal contraceptives in general (years) | 8 ± 15 | -- | -- |
Time without OC (years) | -- | 6 ± 6 | -- |
Average cycle length (days) | -- | 28.4 ± 4.0 | -- |
Time from familiariztion to pre-tests (days) | 3 ± 2 | 5 ± 5 | 0.2 |
Time from last ST session to post-tests (days) | 5 ± 2 | 4 ± 1 | 0.5 |
Time from last ST to post-DXA (days) | 5 ± 3 | 5 ± 3 | 0.5 |
Number ST sessions | 24 ± 1 | 24 ± 1 | 0.9 |