Aikido training is for all-around physical fitness, flexibility, and relaxation. The human body in general can exert power in two ways: contractive and expansive. Many fitness activities, for example weight-lifting, emphasise the former, which means that specific muscles or muscle groups are isolated and worked to improve tone, mass, and power. The disadvantage of this, however, is that whole body movement and coordination are rarely stressed. Thus, while muscle size and power may increase, there is no emphasis on the ways in which those muscles can work together most efficiently. Also, this sort of training tends to increase tension, decrease flexibility, and stress the joints. The result may be aesthetically pleasing, but when done to excess may actually be detrimental to overall health.
The second type of power, expansive, is mostly stressed in activities such as dance or gymnastics. In these activities, the body must learn to move in a coordinated manner and with relaxation. Aikido also mostly stresses this sort of training. While both types of power are important, it is interesting to note that a person who masters the second type of power can, in a martial context, often overcome a person who is much bigger or stronger. The reason for this is that the contractive power is only as great as the mass and power of your individual muscles. Expansive power, however, as used in Aikido, can be much greater than your size may lead you to believe. This is because you move with your whole body. Rather than stressing and tensing only a few muscles, you learn to relax and move from the centre of your body, where you are most powerful. Power is then extended out naturally through the relaxed limbs, which become almost whip-like in their motion. Needless to say, the power behind an entire person's body will be more than that of someone's arm or leg alone.
Hence, Aikido develops the body in a unique manner. Aerobic fitness is obtained through vigorous training. Flexibility of the joints and connective tissues is developed through various stretching exercises and through the techniques themselves. Relaxation is learned automatically, since without it the techniques will not function. A balanced use of contractive and expansive power is mastered, enabling even a small person to pit his entire body's energy against their opponent.
With this, different masters stress different aspects of training. Some masters stress importance of body posture while executing the technique in order to coordinate different parts of the body, while others deal with the physical aspects of it. With each way, comes a different means of interpretation of the same basic principles of the art.
