Here are a couple of points on how to do seated leg curl for the hamstrings muscles. Although the tightness of hamies is a very common postural issue, the weakness of this muscle can also cause many other problems. People with hyperlordosis (excessive lumbar curvature) usually suffer from a weak hamstrings. On the other side, people with hypolordosis condition(flat back) have a tight hamstrings muscle. It's good to note that a tight muscle doesn't necessarily mean a strong muscle. I've noticed a combination of weakness and tightness in the hamstrings muscles of many of my clients during these years. So, stretching and strengthening this muscle needs a lot of attention. In this video I explain a couple of points which can help you isolate the hamstrings to have an effective exercise for it with a focus on its knee flexion function.