Background: Muscle stretching has been practiced by people for thousands of years. Its effectiveness is well-proven, but the diversity of the obtained results should prompt a search for causative factors. One of the possible explanations can be hormonal fluctuations, which occur during the menstrual cycle.
Objectives: To assess the influence of menstrual cycle on the efficiency of static stretching of hamstrings with special reference to changes in their length.
Material and methods: A total of 534 young women were recruited for the study, but after applying the inclusion criteria, only 48 of them have been accepted. The inclusion criteria for the study comprised a reduced length of the hamstring muscles and a regular menstrual cycle. The whole study included a twofold examination of hamstring length before and after the stretching (3 × 45 s), performed by a physiotherapist. All the measurements were carried out 3 times in individual phases of the menstrual cycle.
Results: Statistically significant influence of static stretching upon the length of hamstring muscle was revealed. A change in the passive knee extension (PKE) test was 13.34% (standard deviation (SD) = 10.97), and in active knee extension (AKE) test it was 8.46% (SD = 9.26). Hamstrings length demonstrated no differences in various phases of the menstrual cycle.
Conclusions: Static stretching is an effective tool for the improvement of the length of the hamstring muscle in young women. However, the effectiveness of stretching in healthy women is not influenced by the menstrual cycle phases.
Keywords: elasticity; hamstring muscle; menstrual cycle; muscle stretching exercises.