Despite comprising half the population, females are often left out of muscle research due to the impact of changing hormones during the menstrual cycle and when using oral contraceptives. This makes it hard to perform costly and invasive studies involving tracers to study muscle protein metabolism. Consequently, we lack a clear understanding of how these hormonal changes affect muscle growth.

There is a need for less invasive methods to study how sex hormones and oral contraceptives influence muscle protein metabolism. Ex vivo models, where serum from participants is applied to mouse muscle cell cultures, mimic the conditions of human muscle cells and can provide initial insights.

The aim of the study is to develop a non-invasive model using serum from both oral contraceptive users and non-users at various stages of their cycles, to understand if different cycle or pill stages affect how muscles process proteins.

Inclusion Criteria:

• BMI between 18.5-29.9 kg/m2 (I.e., non-obese).
• For OC users: on monophasic OCs for > 3 months prior to study enrollment
• For non-OC users: regular menstrual cycles length (25-35 days) for at least 3 months prior to study and at least 6 months off of OCs.

Exclusion Criteria:

• Chronic disease diagnosis (cardiovascular, thyroid, diabetes)
• Current or recent remission of cancer
• Regular use of NSAID (except low-dose aspirin), anticoagulants
• Use of prescription drugs that would impact metabolism, e.g. Statins, Lithium, Attention-Deficit/Hyperactivity Disorder (ADHD) medication.
• Insertion of intrauterine device (IUD) - exception: copper
• Use of ergogenic aids such as creatine
• Regular Tabacco use
• Use of illicit drugs (growth hormones, testosterone)
• For non-OC users: Use of oral contraceptives for > 6 months prior to study enrollment - to ensure return to regular menstrual cycle.