The squat has been named the king of all exercises. Sure there are other leg exercises, but squatting works the entire posterior chain, sends the hips and knees through a full range of motion, activates the stretch-shortening cycle, and is a natural movement. In addition, squats can be effect using barbells, dumbbells, or only your body weight. Squats need to be in every strength training program.
The technique of how to squat will be a topic for a later post. For now, let's determine what is better, the front or back squat?
A perfectly balanced squat has the weighted bar positioned directly over the middle of the foot. A bar either too far forward or backward puts unnecessary stress on the lower back and puts the lifter in an awkward position. The position of the bar is crucial.
The bar position of the front squat is on the front shoulders, ideally in the clean catch position. To keep the bar over the middle of the foot it is necessary to have a more upright posture. As a result, the both the back angle and the hip angle are relatively open. These angles mean the hamstrings are contracted and not able to contribute much to the effort necessary to stand up. The glutes and quads are doing most of the work as you ascend from the bottom of a front squat.
To incorporate more hamstring recruitment it is necessary to decrease both back and hip angle. Putting a weighted bar on your back, and squatting such that the bar is in the middle of the foot, makes these angles more acute. But these angles vary depending on the position of the bar on the back.
Hamstring recruitment occurs when they are stretched out at the bottom of a squat with relatively small back and hip angles. The low bar back squat achieves the smallest angles and the most hamstring recruitment. Bar placement for a low bar squat should be below the traps, resting on the "shelf" made by top of the rear delts when the elbows are held high.
Bar placement higher on the back, up on the traps, is also an option. This is commonly referred to as the high bar squat. At the bottom of the high bar squat, hip and back angles are somewhere between the front and low bar squats. Thus, hamstring recruitment is not optimized.
Adequate shoulder flexibility is necessary achieve proper low and high bar placements. It takes more shoulder flexibility for a low bar position. Wrist and elbow flexibility are necessary to for proper bar placement in the front squat.
There has also been some research concluding that front squats are easier on the knees. It seems that forces produced with greater hamstring recruitment stress the knee. Intuitively this makes sense as the knee supports the base of the hamstrings.
If your goal is to fully develop the posterior chain with one exercise, the low bar squat is a great exercise. The high bar and front squat will still develop leg strength, but further exercises should be done to develop hamstring stength.