Muscle building

Training the quadriceps muscles is an integral part of most sports strength programmes. The quadriceps are important for cycling, swimming, running, jumping, sprinting, throwing - in fact, virtually every full-body athletic movement. Three of the most common quadriceps exercises are the squat, the leg press and the knee extension. But although all three exercises target the quads, they all vary in terms of knee joint forces, muscle activity and functionality. There are even variations within an exercise through changes in technique or equipment

The squat and the leg press are considered to be a different type of exercise from the knee extension. The squat and the leg press are known as closed kinetic chain exercises (CKC), whereas the knee extension is considered an open chain kinetic exercise (OKC). CKC exercises are distinguished by the foot being fixed and the knee joint moving in conjunction with the hip and ankle in a predictable manner. With the squat, for example, the foot is on the floor. and ankle, knee and hip all flex and then extend in sync. OKC exercises, on the other hand, are distinguished by the foot being free to move and the knee joint working independently of any other joints. With the knee extension, the hip joint is fixed and the knee flexes and extends with the foot freely rotating. (Recently, researchers have argued that this classification system of exercises is too simplistic, but for the purposes of this article, the simple distinction is sufficient.)

researchers say

Researchers and physiotherapists seem to be agreed that CKC exercises are superior to OKC ones. CKC knee exercises are considered safer and more effective since they place less strain on the anterior cruciate ligament (ACL) and elicit a hamstrings co-contraction together with the quadriceps. Researchers from the Mayo Clinic (New York) showed that leg press placed no strain on the ACL and elicited significant hamstring co-contraction, whereas the knee extension placed strain on the ACL at 30° of flexion. The decreased ACL strain makes CKC knee exercises important for ACL rehabilitation programmes.The Mayo Clinic team also argue that CKC exercises are superior because they are more functional than OKC exercises. Walking, jumping and running movements all involve the kinetic chain of ankle, knee and hip. Thus it is advantageous to strengthen the quadriceps in a similar manner to real movements - specificity of training is an accepted principle in sports science. During the squat and leg press, the knee and hip extend together. While the knee extends, the rectus femoris shortens and the hamstrings lengthen, but while the hip extends, the rectus femoris lengthens and the hamstrings shorten. The result is a simultaneous concentric and eccentric contraction at the opposite ends of each muscle. This is known as the 'concurrent shift', and is a specific neuromuscular pattern which occurs during all multi-joint leg movements. This concurrent shift does not take place in OKC exercises. Theoretically, training the quadriceps in isolation, without normal muscular recruitment patterns, could lead to inefficient neuromuscular coordination in athletic movements. Training movements that involve the concurrent shift are very important, so CKC knee exercises are recommended.Other studies have compared the muscle electromyographic (EMG) activity during the squat, leg press and knee extension exercises. EMG activity is an objective measure of the amount of muscle activity during the exercise. This allows exercises to be compared. Joseph Signorile and a team from the University of Miami investigated the EMG activity of the quadriceps during the squat and knee extension. They used experienced lifters and determined the 10-repetition maximum weight for each exercise. This guaranteed that both exercises required the same relative effort. The team found that the squat elicited significantly more quadriceps EMG activity compared to the knee extension. Signorile et al concluded that because of this the squat should be seen as the superior quadriceps exercise, especially as it is a more functional movement.