Overview

The goal of this observational study is to learn how the menstrual cycle affects immune cell activation, recruitment, and recovery responses after resistance exercise in healthy, resistance-trained women aged 18-40. The main questions it aims to answer are:

Does the menstrual cycle influence neutrophil recruitment and adhesion after resistance exercise? Does the menstrual cycle affect markers of muscle damage and functional recovery? Researchers will compare three menstrual phases (early follicular, late follicular, and mid-luteal) to see if immune responses and recovery outcomes differ across these phases.

Participants will:

Complete resistance exercise protocols across three different menstrual cycle phases.

Provide blood samples to assess immune cell activation and muscle damage markers.

Track sleep, mood, and recovery with questionnaires and wear an accelerometer.

Eligibility

Inclusion Criteria:

• Women between the ages of 18 and 40.
• Must weigh at least 110 pounds.
• Healthy as determined by medical history, physical activity readiness, and menstrual cycle questionnaires.
• Actively resistance training for at least 6 months (minimum of 3 resistance training sessions per week, with at least one lower body session).
• Pre-menopausal and have a regular menstrual cycle (eumenorrheic), with a clear start of menses (early follicular phase).
• Not currently pregnant or planning to become pregnant during the study.
• Have not used hormonal birth control or intrauterine devices in the past 3 months (or three full menstrual cycles).
• Able to recall approximate start dates of their last 6 menstrual cycles.
• Willing to follow study instructions, including avoiding exercise, alcohol, and caffeine before testing visits.
• Free from previous or current lower body injuries that could limit performance.
• Not regularly taking any medications that could interfere with the study.
• Determined to have a high likelihood of successful blood draws by a certified phlebotomist.

Exclusion Criteria:

• Do not give consent to participate.
• Have been determined unfit to participate based on medical or activity history (using health questionnaires).
• Currently take prescription or over-the-counter medication that could affect the study results.
• Have a chronic illness requiring medical care.
• Not currently resistance-trained (don't meet the exercise requirement).
• Pregnant or planning to become pregnant during the study.
• Do not have regular periods or have been diagnosed as amenorrhoeic (absence of menstruation).
• Currently taking any performance-enhancing drugs.
• Currently using hormonal birth control or intrauterine devices (IUDs), or have used them in the past three months (or three full menstrual cycles).
• Determined unlikely to have a successful blood draw by a trained phlebotomist.
• Weigh less than 110 pounds.