Hamstrings

The hamstrings are the muscles at the rear of the thigh. They oppose the quadriceps, the muscles at the front of the thigh. And like the quads, the hamstrings are evolved for both strength and endurance, so to develop them you should do high reps (12-15) with heavy weights. But always start your hamstring exercises with light weights and very high reps (15-20) to thoroughly warm them up. You don't want to pull this muscle, or you'll be hobbling around for days.

Hamstrings require more stretching at the end of a workout than most, as they have a tendancy to become over-tight. Make sure you always stretch at the end of a workout, or a run, or any sport. Hold each hamstring stretch for a full minute, to really stretch them thoroughly.

As well as flexing the leg at the knee and extending the thigh at the hip joint, the hamstrings also act as a braking system to slow down the leg at the end of its forward swing in walking and running. This is why runners are prone to pulled hamstrings, particularly sprinters.

The 3 muscles of the hamstrings are the biceps femoris, semitendinosus, and semimembranosus.

Biceps Femoris

The origin of the 'long head' of this muscle is the ischial tuberosity. The ischium is commonly known as the 'sitting bone', at the base of your pelvis. There is also a 'short head' which originates a quarter of the way down the rear of the femur (the bone of the upper leg). Both heads insert at the lateral side of the head of the fibula and tibia, the bones of the lower leg.

Semitendinosus

This muscle also originates at the ischial tuberosity. It inserts at the medial surface of the shaft of the tibia.

Semimembranosus

Like the other two, this muscle also originates at the ischial tuberosity. It inserts at the rear of the head of the tibia.

Best exercises for the Hamstrings

Leg Curls - The number one exercise for hamstrings, this can be done lying face down on a leg curl machine, or on a seated version (seated is preferrable if you have lower back problems). Some gyms even have a standing leg curl machine.

Barbell stiff leg Deadlifts - make sure you don't round your back when performing this movement.

Squats - this also works the quads.

Leg Press Machine - also works the quads.

Reminder - don't forget to stretch!

I know a personal trainer in London who can do the splits, his hamstrings are so flexible. You don't need to be that flexible, but it's worth devoting plenty of time to stretching out your hamstrings after a leg workout or any activity that has worked the leg muscles (tennis, running etc). Tight hamstrings will set you up for a nasty injury if you're not careful, so stretch this stubborn muscle more than any other.

You can stretch your hamstrings alone, but for an extra-effective stretch it's worth having a personal fitness trainer to assist you.