hard (external) and soft (internal) martial arts:
http://martialarts.jameshom.com/library/weekly/aa022601.htmOne such distinction is that between internal and external martial arts. External martial arts refer to those that rely on the body's external attributes, such as muscular strength and rigidity, skin and bone toughness, or technique speed and power to be effective. Most striking arts, including karate, muay thai, or tae kwon do, lie within the "external" category. Karate practitioners used to toughen their knuckles by striking a makiwara, or striking post, until heavy calluses formed on their hands. Tae kwon do stylists pride themselves on breaking boards, tiles, and bricks with forceful kicks. Muay thai fighters often lack feeling in their shins, the result of using their lower legs as clubs against their opponents.
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Internal martial arts focus on the martial artist's internal attributes, such as focus, timing, awareness, and precision of technique. The slow movement of a tai chi master's forms might seem inadequate for combat--however, when needed, the master can speed up his movements to match that of his opponent, blending with the attacks and using the attacker's body weight and momentum against himself. Aikido, with its emphasis on blending with the attacker's movement and guiding him or her into the technique, is a classic example of an internal martial art. The following table describes some attributes of both categories:
https://en.wikipedia.org/wiki/Hard_and_soft_%28martial_arts%29#Soft_technique"The goal of the soft technique is deflecting the attacker’s force to his or her disadvantage, with the defender exerting minimal force.[1] With a soft technique, the defender uses the attacker's force and momentum against him or her, by leading the attack(er) in a direction to where the defender will be advantageously positioned (tai sabaki) and the attacker off balance; a seamless movement then affects the appropriate soft technique. In some styles of martial art like Wing Chun, a series of progressively difficult, two-student training drills, such as pushing hands or sticky hands, teach to exercise the soft-technique(s);"
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http://www.nathanielwhitmore.com/budo-blog/hard-and-soft-styles-ofmartial-artsMartial arts are split into two main categories: Yin Styles and Yang Styles. Yin styles are also called Soft Styles or Internal Styles, while Yang are known as Hard Styles or External.
In this sense yin, soft, and internal refer to the receptive, generally slow nature of styles like Tai Chi that focus on the health benefits of the art and on relaxing the body. In contrast, yang, hard, and external refer to the development of combative skill, brute strength, the generation of power, and a stimulating workout.
Often Karate is considered quite different than Tai Chi. However, the differences are not necessarily as pronounced as many think. First of all, it should be pointed out that the full name of Tai Chi is Tai Chi Chuan. Chuan means fist, or fighting style. Clearly Tai Chi evolved from "hard" martial arts and the early practice included "hard" training.
It is also interesting to consider that "Tai Chi" does not mean "soft" and definitely does not mean "yin". In fact, Tai Chi means "Supreme Ultimate", or yin and yang. Likewise, "Goju" means "hard-soft" (Goju Ryu is the karate style I study under Shihan Roger Wehrhahn).
Any style of martial arts, whether hard or soft, will contribute to health problems when imbalanced (too hard or soft). While I agree that karate can be considered a hard style, if the hard is developed while neglecting the soft, it can shorten one's life and contribute to health problems. If tai chi is practices without development of the hard or external practice the circulation will not be properly invigorated. It is a common claim that tai chi benefits the circulatory system, and that it accomplishes this largely throuhg training relaxation in general and during movements and postures. However, if an individual's constitution is already more relaxed (cold) than they might very well benefit more through the practice of karate, which invigorates the blood.
In my opinion the general health benefit of hard styles in the develoment of strength and the invigoration of the blood and chi; while the health benefit of soft styles relates to relaxation of the tendons, connective tissue, circulatory system, and mind and with the sinking of the chi. (Both hard and soft styles develop balance, coordination, and reflex.)
If one were to practice karate excessively without understanding the soft aspects and allowing the body to cool down, imbalance woudl result. Likewise, if one were to only practice tai chi (as presented to the modern public), they may lack the invigoration of harder styles of martial arts, hard work, and exersize like walking. Both hard and soft styles have hard and soft aspects. And as with all things balance is key.