Influence of Menstrual Cycle and Oral Contraceptive Phase on Spinal Excitability.
Ellen Casey, Maria Reese, Ezi Okafor and 4 others
PMID 26872589WHAT IT FOUND
Spinal reflex excitability did not change across menstrual or oral contraceptive phases in 30 women, even though hormone levels changed.
The study offers no support for expecting this reflex measure to shift with cycle phase.
Key findings
01The spinal excitability measure, Hmax/Mmax, did not show a significant change across cycle phases or a significant difference between oral contraceptive users and nonusers.
02Estradiol and progesterone levels changed across phases: users had an estradiol increase at the ovulatory session, and nonusers had higher estradiol in ovulatory and luteal phases and higher progesterone in the luteal phase.
03The spinal excitability measure was not statistically related to estradiol or progesterone levels.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
Only 30 women were studied, and the power calculation was based on the first 5 participants in each group. Testing occurred at only 3 broad cycle phases, so a true hormone peak or a delayed reflex change could have been missed. The H-reflex is an indirect measure of spinal excitability, not a direct motor neuron measurement, and may not be sensitive enough for small changes. The participants were not the same women as in the authors' earlier muscle stretch reflex study, so the two sets of results cannot be directly linked. Oral contraceptive users were exposed to exogenous hormones that were not measured in the blood assays, and pill type was not balanced or fully evaluated. The sample excluded competitive athletes and women exercising more than 7 hours per week, so active athletes may be underrepresented.
The easy way to misread this
Do not conclude that menstrual or oral contraceptive phase has no effect on neuromuscular control or injury risk. This study only found that one spinal reflex measure did not change across 3 cycle phases in 30 women, and the method may miss small or delayed changes.