The Strength and Conditioning Journal, published by the NSCA, did a special issue all about Combat Sports. I'm gonna review most of the articles from that issue.
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Turner, A., Baker, E., Miller, S., (2011). Increasing the Impact Force of the Rear Hand Punch. Strength and Conditioning Journal, volume 33 (number 6), pages 2-9.
The article discusses the kinetics and kinematics of the rear hand punch to show ways of increasing the impact of the punch. Turner indicates that the material is generalizable to other strikes, which I don't doubt. The rear hand punch is used as the basis of the analysis because it is well understood, used in many arts and the most powerful punch.
Five key aspects of the punch are identified to optimize the strike:
1. Rear leg drive
2. Landing with a rigid front leg
3. Stretch-shortening cycle of the trunk
4. Velocity of the strike
5. Effective mass of the strike
These key aspects align with the key elements of the kinetics of the strike
Rear Leg Drive - the rear leg is used to initiate the strike and extended explosively to contribute power. This is done with the front leg in the air and moving forward. The more powerful the rear leg drive the harder the strike.
Rigid Front Leg - the front leg must land rigidly to provide a brake on the forward motion of the body. This focuses the rear leg drive on the upper body. The more rigid the braking action, the more force is transferred to the strike.
SSC of the Trunk - the rear shoulder is pulled back early in the strike coiling the trunk to generate more power. This occurs because of the elastic nature of musculature. Stretch Shortening Cycle (SSC) is the neurologic component that increases the elastic reaction of the muscles. A better trained SSC in the trunk increases the trunks contribution to power.
Velocity of the Strike - the arm can move at tremendous speed and is quite light, so it's primary contribution to force is through velocity. The faster the arm moves the harder the strike.
Increase Effect Mass - the arm actually slows down just before the strike lands. Activation of the muscles in the arm to make it rigid cause this effect. A rigid arm allows more of the mass of the body to be contributed to the power of the strike.
Rear leg drive
Rear leg drive is best increased by exercises that make use of the full extension of the legs. Basic weightlifting exercises for this are the squat and deadlift. Specifically, the traditional bent-leg deadlift should be used for this objective since it includes knee extension as well as the hip extension. Calf raises, especially one-legged calf raises, are a good assistance exercise (not mentioned in the article), since ankle extension (plantarflexion) is not included in the squat and deadlift. The single-leg version is preferable from the viewpoint of specificity to the sport - you never produce rear leg drive with both legs simultaneously.
Similarly, single-leg variants of the squat and deadlift are also useful. However, single-leg versions will reduce max weight, so they should not be the sole version used. Both max weight lifts and more functional/specific lifts together will contribute to maximal performance.
These lifts are best trained at high loads in the 1-8 Rep Max (RM) range. This range will produce the biggest gains in power generation and peak force. Additionally, these high load lifts produce gains primarily through neurologic training not hypertrophy, so athletes who need to make weight are better served in this type of exercise.
Conventional lifts like these will increase peak force or the height of the Force-Time curve. The strike happens very quickly, around 300 milliseconds. Therefore the rate of force development (RFD) is also important i.e. the steepness of the Force-Time curve. Increasing RFD can be trained with very rapid exercises instead of high loads.
Olympic lifts, such as the Clean, are an ideal method of developing rapid force production. However, they are technically demanding and so require training. Squat jumps, with dumbbells in hand to increase load, are a good alternative to these lifts. Squat jumps are less demanding technically and less physically demanding on the back of the athlete.
Plyometric exercises, such as box jumps, are another good method of increasing RFD. Since strikes are normally executed from a fairly stable position, and because the same strike is not normally rapidly repeated, a quick rebound action is not as necessary for lower-body plyometrics. So jumps for height and distance are effective instead of rapid jumps in succession.
The authors note an important part in training lower body power: long, slow, distance running is counter-productive. Long endurance activities shift muscle from peak power type to endurance type, which is not useful in our sports. The legs seldom fatigue in sword arts and combat sports, but peak power generation is a must.
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This article is a big one, so the review of it will be broken up over several posts.