A Martial Artist’s Guide to the Science of Generating Power

By Christopher J. Hasson

Top mixed martial artists like Randy Couture (left) and Chuck Liddell know that the key to generating power in their strikes lies in sequentially moving their body and limbs to maximize their momentum.

Photos by Rick Hustead

Momentum for Traditional Martial Artists and MMA Fighters

You don’t often hear martial artists talk about the role momentum plays in striking. However, it’s an integral part of any attack, and success in a street fight or sparring match often depends on your ability to maximize it.

Simply put, momentum is a measure of the “amount of motion” an object has. An object with a lot of momentum is difficult to stop. Momentum depends on the object’s mass (how heavy it is or, more accurately, how much matter it contains) and its velocity. The more mass and/or velocity, the greater its momentum.

The formula is: Momentum = mass x velocity

From that equation, it’s clear that a massive freight train moving very slowly has a lot of momentum and that a less massive motorcycle moving very quickly has a lot of momentum. In other words, you don’t want to be hit by massive objects moving slowly or small objects moving quickly. Of course, you definitely don’t want to be hit by something that’s massive and fast.

Right now, you’re probably thinking: “That’s enough physics talk about trains and motorcycles. How will a knowledge of momentum help me unleash more devastating attacks?”

Conceptually, all you have to do is replace the mass of the freight train with the mass of your body, and the speed of the motorcycle with the speed of your attack. To increase the momentum of your strike, you must increase the effective mass behind it, increase its velocity or, ideally, increase both. The more momentum your attack has, the more forceful it will be and the harder it will be to block.

Using Rotation

Most martial arts strikes involve rotation of the body. That’s obvious for some attacks, like the hook punch and roundhouse kick, but it’s also true for straight-line attacks such as the jab, cross and sidekick. The reason is physiological: Your body segments are linked by joints, which for the most part allow only two neighboring segments to move relative to each other. In straight-line attacks, you must coordinate the rotations of your body segments to make your hand or foot move along a straight path. Proper timing of these rotations is crucial for maximizing the velocity and, thus, the Momentum.

Studies in biomechanics have shown that movements such as striking, throwing, kicking and swinging are performed by rotating body segments in a sequential order, which facilitates an efficient transfer of momentum from one segment to the next. This is referred to by many names, including the “kinetic link” and “summation of speed” principles. The basic idea is that you begin by rotating massive body segments such as your hips, then sequentially rotating progressively smaller segments such as your upper arm, lower arm and hand.

Consider a straight punch like the jab or cross. To understand it, think of your body as consisting of four segments: your legs, hips, shoulders and arm. You first push against the ground with your legs, which causes your body mass to surge forward (this is important and will be discussed in the next section). Next, you begin rotating your hips, allowing the powerful muscles in your legs and pelvis to contribute to the motion.

Pushing off with the rear foot causes the body and hand to accelerate forward (1). The hips

begin to rotate, causing the hand speed to increase (2). As the rotational velocity of the

hips reaches a maximum, the shoulders begin to rotate (about a vertical axis), and hand

speed continues to increase (3). As the shoulders attain maximum rotational velocity, the

arm starts to extend, causing the hand speed to reach its maximum (4). (images courtesy of Christopher J. Hasson)

As the hip rotation progresses, a peak rotational velocity is reached, which is followed by a decrease in velocity as the hip movement approaches the limit of its range of motion. When your hips are rotating most quickly and before they slow down, your shoulders should begin to rotate. However, the rotational velocity of your hips increases the velocity of your shoulders, which makes your shoulders rotate more quickly than your hips. When your shoulders reach their maximum rotational velocity, your arm should begin rotating around your shoulder joint, extending out for the punch.

Once again, the velocities created during the hip and shoulder rotation combine so that your arm is faster still. However, because your arm weighs much less than your hips and shoulders, it increases its velocity dramatically—much more than if the arm rotation was performed in isolation and more than if your hip and shoulder rotation occurred simultaneously. The key is that each segment must begin rotating when the previous segment reaches peak velocity. Although this example uses an upper body attack, the methodology also works for kicks. The sequence of rotations, however, needs to be reversed. In other words, you should move your shoulders, then your hips, then your leg.

This description of the movement sequence probably makes it seem like you must initiate large rotations for each body segment. That, however, would be a bad thing. Making large, conspicuous movements can clue your opponent into your impending attack. It’s much better to make the rotations very small yet very rapid. Remember that momentum is the product of mass and velocity, so the degree of rotation isn’t what’s important; it’s the velocity.

Another good thing about the sequence of body rotations is that the very last thing to move is your arm, which is one of the more conspicuous body parts from your opponent’s perspective. If the initial movements of your legs and hips can be kept relatively small and rapid, he may not be able to detect your attack until it’s too late to react.

Until now, I’ve focused on the mechanical aspects of body rotation. However the sequential order has many other advantages based on muscle physiology. An important consideration is that muscles cannot generate force instantly.

If you try to move all your joints at the same time by contracting all your muscles simultaneously, your muscles may not have time to reach full activation and will consequently be unable to develop maximum force. By performing the rotations sequentially, you buy more time for your muscles to reach their maximum force generating potential. Musclesthat generate more force are able to impart greater acceleration to body segments, which translates into higher rotational velocities and thus more momentum. And that means more damage to your opponent.

The roundhouse kick uses body rotation and sequential muscle activation in much the same way as the reverse punch. (For illustrative purposes, Cung Le is shown kicking.)

Using Your Body

By using your body appropriately, your attack can gain even more momentum. Again, the straight punch will be used as an example, although the principles will work for any strike. The secret is to shift your weight forward during the punch. If done correctly, that increases the mass and velocity of your attack, which increases the momentum. Let’s investigate how this occurs.

If you stand still and throw a punch as hard as you can without shifting your weight, the effective mass behind the attack is the mass of your arm. However, if you shift your weight forward so your entire body is moving toward your opponent when you make contact, the effective mass includes the mass of your body, which is about 20 times more than your arm. If you really want to make an impact on your opponent—forgivethe pun—step forward as you shift your weight. The weight shift causes your effective mass to increase, which increases the momentum of the strike.

Another bonus is that if your body moves forward, the speed of your hand increases, which boosts the momentum. That’s because the speed of your body and hand are additive. For example, when throwing a straight punch with your body standing still, your hand moves relative to your body. Let’s say that the maximum rate at which your hand travels during a punch is 20 miles per hour—the average for Olympic boxers throwing straight punches. 

Now, if you perform the same punch while stepping forward and your body moves forward at 5 mph, your hand is moving at 25 mph. 

This is described by the formula: Hand velocity = velocity of body + velocity of hand relative to body

This relationship is also known as “relative motion,” a concept made famous by Albert Einstein. You can take this scenario one step further and include the motion of your opponent. Your fist moves even more quickly if you strike when your opponent approaches you. Let’s say, as in the previous example, your fist is moving at 25 mph because you’re stepping forward as you punch. If you strike while your opponent steps toward you and he’s moving at 5 mph, your fist will be moving at 30 mph relative

to him. Therefore, by performing a rapid weight shift and timing your attack during his advance, you can maximize your speed.

Although the straight punch served as the example, the same principles apply to most strikes, including the hook punch, front kick, side kick and hook kick. Applying the concepts outlined here will enable you to improve and refine your technique—and help you make the most of momentum.

About the author: Christopher J. Hasson is a doctoral student in the Biomechanics

and Motor Control Laboratories at the University of Massachusetts, Amherst. His research focuses on human motor learning, muscle mechanics and coordination, and computer simulation of human movement.

This article originally appeared in a 2007 edition of Black Belt Magazine.

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