Hamstrings

The hamstrings originate from the ischial tuberosity (the lower part of the pelvis, the part you sit on) and insert on the tibia and the fibula. The biceps femoris has a long head and a short head; the long head, the semitendinosus, and the semimembranosus all cross both the hip and the knee. This biarticular nature has direct training implications: to fully stimulate them you need exercises that work them in both functions.

Hamstring exercises fall into two categories: those dominated by hip extension (Romanian deadlift, stiff-leg deadlift, good morning) and those dominated by knee flexion (lying leg curl, seated leg curl, Nordic curl). Both categories are necessary for complete development. The seated leg curl puts the hamstrings in greater stretch at the hip compared to the lying leg curl, producing more hypertrophic stimulus. The Romanian deadlift is probably the single most effective exercise for the hamstrings.

Weak hamstrings are one of the most common causes of knee injury and ACL tears. A balanced strength ratio between quadriceps and hamstrings is essential for knee health and athletic performance. If you only do squats and leg extensions and never work the posterior chain, you're creating a dangerous imbalance. Dedicate at least one third of your leg volume to the hamstrings.