Isometric strength and endurance during the menstrual cycle

Area of Science:

• Exercise Physiology
• Reproductive Endocrinology

Background:

• Menstrual cycle phases influence physiological responses.
• Oral contraceptives (OCs) may affect athletic performance and physiological metrics.

Purpose of the Study:

• To investigate the impact of the menstrual cycle on isometric strength and endurance in women.
• To compare these effects between women using and not using oral contraceptives.
• To assess the role of muscle temperature stabilization on these responses.

Main Methods:

• Assessed isometric strength and endurance (40% maximal voluntary contraction) in 7 healthy women over 2 menstrual cycles.
• Measured blood pressure and heart rate during fatiguing contractions.
• Conducted experiments with both ambient and stabilized forearm muscle temperature (37°C water immersion).

Main Results:

• Isometric strength and cardiovascular responses did not significantly vary across the menstrual cycle in ambient conditions.
• Isometric endurance in non-OC users showed sinusoidal variation, peaking mid-ovulatory and lowest mid-luteal.
• Women using OCs exhibited no menstrual cycle variation in isometric endurance under either temperature condition.
• Stabilized muscle temperature revealed hyperbolic endurance in non-OC users (peak at cycle start/end, lowest mid-cycle).

Conclusions:

• Menstrual cycle phase significantly impacts isometric endurance in women not using oral contraceptives.
• Oral contraceptive use abolishes menstrual cycle-related fluctuations in isometric endurance.
• Muscle temperature plays a role in the observed endurance patterns, but OCs override these effects.