There are two kinds of attacks: linear and circular. A linear attack follows the path of a straight line, such as a reverse punch. A circular attack follows an arched path, such as a roundhouse kick.
Traditional Taekwondo stresses re-chambering as a way to add additional powerful strikes. This implies the use of linear attacks. Circular attacks do not re-chamber between strikes, thus time, power, and momentum are preserved. At the end of a linear strike, the momentum stops and is reversed creating wasted time. When a boxer throws two jabs in a row, the time between jabs is spent re-chambering and therefore is wasted time. Yet, when a boxer uses a speed bag, he/she uses circular strikes and retains the same amount of power with increased speed and efficiency.
Linear techniques limited to the length of the arm or leg while linear techniques have a large range of motion. During linear movement, maximum velocity is achieved just before the end of the movement. During circular movement, maximum speed is reached at approximately one half of the movement, and does not appreciably diminish in speed thereafter.
To get maximum impact effect from linear movement, the technique should be focused. That is, after gaining maximum velocity, at the moment of impact, the body must be suddenly tensed to transfer energy to the target and then relaxed to stop transfer of the rebound energy. If this is not done, some of the force generated will be dissipated. Since a circular movement's maximum speed is achieved at approximately ½ of a circle, with no appreciable loss of velocity thereafter, then focus needed in linear movements becomes unnecessary and maximum force nay be generated by striking through the target.
Circular movements, allow a natural continuation of successive techniques as well as a continuous flow from technique to technique in combination. Circular movements typically necessitate the use of both hands.
Most attack movements travel along a relatively horizontal plane; the arm or leg is going to be at a relatively horizontal position relative to the target surface. Thus, blocks and parries are going to travel along a relatively vertical plane so as to gain the greatest surface area (and the greatest advantage) against the attacking appendage. If both the attack and the block traveled along a horizontal plane, the block would have a greater chance of missing and being ineffective.
The quickest way to engage a blocking arm with force against an attack is to use a circular movement, but this is not the quickest movement. The quickest movement would be simply to bend the arm. However, this would merely place the arm between the attack and the intended target. If we wish to deflect the blow, we would need to move the arm at some angle to the attack. This is where the circular movement allows for a quick response.
It is not practical to use circular movements in one direction only, and, if we stop the movement to reverse direction, we would lose continuity and speed. Therefore, to change directions without losing speed, the arm needs to travel in a figure eight. With this movement, blocking and attacking may be continuous and the arm maintains its speed and power. In contrast, a linear block would require a change of direction which takes time.
Linear movements have a range advantage. Normally, during linear movements, the arms or legs are relatively straight, while in circular movements, the arms or legs make contact when the appendage is bent. Thu, linear movements have greater reach and circular movements have greater continuity.