As a reader of your book Anatomy of the Moving Body, I am curious to know what role the hamstrings play in standing, walking, etc. In your book and other anatomy books, it is stated that the hamstrings are used to bend the knee, but they seem to have larger role in uprightness. When I lean forward from the ankles, it seems that my hamstrings tighten to keep me from falling. Might these muscles have a dual function?
As an Alexander Technique instructor, I find that often the muscles in the front of the leg are relied on excessively, and that lengthening through the back of the leg seems very helpful. However, when I look at anatomy books it appears that there are few muscles in the back of the leg that help with standing. Any thoughts?
Yes, I think the hamstrings do have a dual function. Acting on the knee joint, they flex the leg at the knee. But they appear to have at least two other functions. First, they help to extend and support the trunk at the hip, which means that in this sense they act as extensors of the trunk at the hip. Second, when the leg is extended at the knee, the hamstrings (which cross the back of the knee joint) seem to act synergistically with the gastrocnemius (which also crosses the back of the knee) to extend the leg at the knee. This action is needed at times, as when we are climbing a steep path and need to forcefully extend the leg at the knee, in which case the hamstrings and gastrocnemius aid the quadriceps in extending the leg. As you point out, however, these muscles are usually shortened and overactive, which causes us to brace, stiffen, and hyperextend the legs. So the hamstrings act as flexors of the leg at the knee but also act as extensors of the hip and knee. This is why, in The Body in Motion, I show the muscles on the back of the leg, and not just the quadriceps, as extensors of the leg. And yes, the hamstrings and the other muscles on the back of the leg are usually overactive and need to release and maintain length in standing and walking.