"As such, female athletes may benefit from systematic determination of their estrogen levels so as to allow their coach/team manager to take extra precautions when deciding on a training plan for those 'at risk females,'" according to the new study, led by Katherine E. Burgess, Ph.D., of University of Salford, Manchester, United Kingdom. However, the study finds no evidence that variations in hormone levels during the menstrual cycle affect tendon properties or injury risk.
The researchers used several techniques to measure the mechanical properties of the patellar (knee) tendon in 23 active young women. The women were studied at different times during the menstrual cycle: from day 1 to 4, day 12 to 14, or day 20 to 23 after menses.
Hormone levels-which vary at different phases of the menstrual cycle-were measured as well. The women in the study were not taking oral contraceptives, which alter hormone levels.
None of the tendon properties measured-such as elongation, torque, strain, or others-varied according to time of the menstrual cycle. This was consistent with previous evidence suggesting "no significant effect of menstrual cycle phase on maximal strength or injury risk."
Nevertheless, the data showed a complex interaction between hormone levels, menstrual cycle phase, and tendon properties. Levels of the hormone estradiol, combined with tendon force, explained nearly one-fifth of the variation in a key measure of tendon stiffness. This suggested that individual differences in hormone levels between women could influence tendon characteristics, and thus potentially affect the risk of injury.
There is a long history of debate over whether variations in hormone levels during the menstrual cycle could affect injury risk in women. Some studies have linked higher hormone levels to decreased tendon stiffness, which might predispose to injury. If this were so, then injury risk might be higher during times of the cycle when hormone levels are higher-especially the days just before menses.
However, the new study does not support this theory. Muscle output, motor control, and injury risk "will remain unchanged over the course of the menstrual cycle," Burgess and co-authors write. "Thus, 'time of the month' does not need to be considered when organising training and competition schedules."
On the other hand, the results do suggest that "intrinsic" or chronic differences in hormone levels between women could be related to tendon properties. Injury risk might be higher for women normally exposed to higher levels of estrogen. The effects of chronic estrogen exposure might also help to explain some of the differences in tendon mechanical properties and injury rates between male and female athletes. Further study would be needed to evaluate this hypothesis-as well as whether targeted training could help to reduce the injury risk for "at risk" women with higher estrogen levels.
Source: The Journal of Strength and Conditioning Research
