The Hamstrings are a muscle group comprised of three muscles- Biceps Femoris, Semimembranousus and Semitendinosus. While they all originate on the same place on your pelvis, Biceps Femoris travels down the outside of your thigh. Semimembranousus and Semitendinosus are closer to the inside of your thigh. Their main purpose is to aid in bending your knee and they also contribute to your ability to straighten your leg from your hip, and this is called hip extension.
Do you have tight hamstrings? There could be many reasons for this.
One reason that your hamstrings may be tight is related to your hip alignment. Since your hamstrings are attached to your pelvis, if one side is raised higher than the other it can cause one side to be lengthened and the other side to be shortened. The lengthened side will try to resist the constant stretch by contracting against the pull. This causes the muscles to become constantly stiff. Over time the muscles on the shortened side will also become tight as the muscles physically shortens. Our bodies do not like to have muscles that we are not using and as such, it will get rid of the excess length.
Constantly standing or sitting without stretching throughout the day also contributes to tension in this muscle group. The static poses put the muscles in positions that are shorter than their full lengths for extended periods of time. As I mentioned earlier, your body will get rid of the excess length. To avoid this unfortunate side effect, all muscles within our body should be taken through all their movements and their full ranges of motion at least once a day. This can be done through many different strategies such as stretching, strengthening or even simple things like general housework or other light forms of physical activity.
Many people think that the hamstrings are the primary hip extensor, however two other muscles play a bigger role. Gluteus maximus should begin the movement, although it is common for people to use their hamstrings first. This dysfunctional movement pattern can create instability in the pelvis which will contribute to back pain. Additionally, when the hamstrings begin firing before the glutes, it puts an excessive load on to them. The added work is something that the hamstrings were not meant to do and will cause an added stress to them, thus increasing the tension within them.
Rarely do the three separate muscles have the exact same amount of tension on them. When the biceps femoris becomes tighter than the semis, it can turn your toe out from the knee and vis versa. This may be contributing to your toed out or toed in riding!