This isn't exactly what I read, but it may have been somewhere along the lines. Regardless, it makes for an interesting theory.
The most consistent reports are effects of premenstrual syndrome (PMS) on exercise performance. Nearly all women are familiar with symptoms of bloating, headaches, fatigue, and cramping during the late luteal phase. Many studies relate an increase in perceived exertion during premenstrual and early menstruation days. As well, several authors reported that effects of PMS could alter performance as the tasks increased in difficulty and complexity. Others note impairments in exercise performance arise from breast tenderness, abdominal constriction, and fatigue.
Also reported in some of the literature is an increase in musculoskeletal and joint injuries during this time of the menstrual cycle. However, there is little definitive research indicating the exact causes. One theory is a relationship of increased relaxin levels and increased flexibility and elasticity of connective tissue, such as in articular joints. Relaxin is a hormone that is thought to be responsible for softening and relaxation of the ligaments in various joints. Although still poorly understood in humans, relaxin levels highly correlate with relaxing of the pubic bones allowing for birth in females of several mammal species. Relaxin is thought to create joint laxity, which allows the pelvis to accommodate the enlarging uterus. This may also weaken the ability of supports in the lumbar spine to withstand shearing forces. In the pelvis, joint laxity is most prominent in the cartilage between the two pubic bones and the sacroiliac joints.
The rest is pretty interesting as well. Not sure how backed it is, and I didn't read the entire thing, so take it for whatever you believe: Planet Estrogen Part III: The Menstrual Cycle and Athletic Performance
I should note, that I don't frequent that site at all, and if my memory serves me correctly, I believe this is a site that I found a bunch of nonsense on there a long time ago. Whether this is it or not, several cases of nonsense doesn't earn them the reputation of unworthy for every article. Just thought I'd throw that in there, but again, I don't remember if this was the site or not.