There are two very important, practical, yet extremely underused and misunderstood concepts when training to develop punching and kicking power: the force/velocity curve and the force/power curve. Both curves are extremely important for improving explosive strength and power, and they are far from being the same.
Power (P) is the product of a given force expressed in Newton (N) and the velocity (v) in meters / second) with which that load is moved. In other words we have the typical power equation P = F x v. Power (P) is expressed in Watts or Newton x meters / seconds. The higher the velocity with which you move this load, the higher the power you generate.
In many cases the load is more or less constant, like for example throwing shuriken or a knife, or using a hand-held implement like a katana, a shinai, or a bo. But most important of all, and as applied to karate techniques (karate meaning empty hand), its the weight of our own body and limbs that must be taken into account. Do we want high velocity? Yes indeed!, but with high force!. Do we want high force?, Yes indeed!, but with high velocity.
It becomes quite obvious that a high power output does not sit at both ends of the force/velocity spectrum for two reasons: 1.- at maximum force there is minimum velocity; and 2.- at maximum velocity there is minimum force. This means that maximum or optimum power must lie somewhere in the middle of both polarities. But where? How on earth can we find out exactly the point where the optimum amount of velocity and the optimum amount of force blend in with each other to produce the optimum amount of power?
Knowing all of this, we can say there are only two simple parameters that we must take into account: 1.- the load (which we know); and 2.- the velocity (which we can measure). However, is it as simple as that? Hmmmm, … not quite … but please read on.
During the 1980's Sensei Nishiyama and I spent countless hours testing and retesting all of these parameters, as applied to karate techniques, with highly sophisticated accelerometers and other diagnostic biomechanical equipment. Sometimes both of us would stay at the human performance research center in Los Angeles well passed midnight and we enjoyed every minute of it. Did we finally find that all-elusive point of maximum power development and expression? Yes we did!
However, and at that time, it was definitely not a simple thing indeed. Mainly because force (F) is not a constant and therefore tends to change. Now, what is it that makes force (F) keep changing? Force (F) changes according to the acceleration (a) of the mass or load (m). Why is this so?
Stand on a simple weighing scale while you are in an elevator and you will see yourself (the mass) getting heavier (while going up) or lighter (while going down) depending on the direction and the acceleration of the elevator. This means that the constant force of gravity (g) – which is 9.81 meters per second, every second - is a key factor which always tends to go along with the changing acceleration (a) in terms of gravity (g) plus acceleration (a) – in other words (g + a).
This is extremely important when measuring power with any piece of equipment since some ill-made power measuring devices uses the wrong formula. And they do so because they use: force = mass x g, which does not take into account the acceleration (a); insted of the formula force = mass x g + a, that does take acceleration into account. As Sensei Nishiyama and I clearly saw, there is a HUGE difference in power expression here. A difference that depended upon acceleration and which could be properly and systematically taught in advanced karate classes.
The higher the acceleration and velocity with which you deliver the technique, the more important power becomes and vice versa. This is so because while looking for maximal velocity we have to simultaneously be looking at generating maximal power as well.
Paradoxically, one of the few sports in which power hardly plays a role is …. powerlifting! In powerlifting velocity doesn’t really matter. It doesn’t matter at all if you get the bar up in 1 second, 2 seconds, or 3 seconds, or in 1 minute - as long as you finally get it up. Acceleration is held to a minimum. On the other hand, in Olympic weightlifting it is a completely different concept since power becomes a key factor.
For example, take a barbell that weighs over 60% of your 1 Rmax (1 repetition maximum) and try to lift it overhead in slow motion … it will be impossible for you to do so. You either do it fast or you don't do it at all, and that is why power is such a dominant factor in Olympic weightlifting where the acceleration and speed of the bar is critical. Without acceleration, speed, and power you simply won't be able to lift the bar over your head. Try it and see for yourself …
As for it's application in karate, try to throw a front kick or a front punch with a low velocity and see what you get. Furthermore, try to generate power in your legs and hips for a front punch in slow motion or with a low knee extension velocity and see what you get as well. The faster you execute the technique, the higher will be your acceleration and power output, and the more damage it will cause.
In Los Angeles, and for Sensei Nishiyama and me, it was easy to see that power is an important target in strength training in all karate techniques. Still many instructors and karateka are exclusively looking at the number of kilograms they are able to move. They want to see those numbers go as high as possible, while trying to increase their 1Rmax time after time. Just like in powerlifting, they are only looking to increase their maximal strength, but certainly not their power, and that is not valid in traditional karate training where ability to act in an “instant” is valued over everything else. The difference is between pushing slowly with strength and actually hitting hard and fast … with power.
Thus, power is much more important than strength in karate, and increasing power also becomes much more important than increasing maximum strength. If so, then exactly how do we measure power so we can control it, teach it to our students, and implement it correctly in an instant? This is the main and most basic question that Sensei Nishiyama and I wanted to answer. We found that first of all we have to establish the force/velocity curve from which power is derived. Without determining that curve first, all further implementations circumvented the acquisition of power.
The force/velocity-curve is very easy to understand: the heavier the load you are moving, the slower the movement will be executed and vice versa. Depending on the type of movement, be it via a single joint (knee extension) or via a multi-joint (shoulder and arm extension) a slightly curved or perhaps a straight line will show us the force vs velocity relationship.
Unfortunately we still need a piece of equipment to measure the velocity of the bar because manual timing simply won’t work. Sensei Nishiyama and I used a velocity encoder (a small box that sits on the floor (or a wall) with a thin cable attached to the moving limb. Knowing the weight of the individual limb (arm or leg) this small box measures velocity very accurately and then sends it to the software in the computer. The computer program then creates a crystal clear series of graphs along with other pertinent data. More precisely, it tell us at what velocity you can move a certain load.
For example, Sensei Nishiyama and I wore our respective karate gi's while doing the testing. Quite often we had the stellar assistance of my associate at the research center, Dr. Fred Hatfield (world record squat of 459 kg), to help us with the testing. We started with front punches with just our own body weight and then progressively added small strips of velcro weighing 50g, 75g, 100g, and so on. In order to attain a proper force / velocity curve we had to measure the velocity of our technique as the weight (load) increased.
We executed five front punches with each arm and at each load and at maximum velocity. As always, quality is king. As the load progressively increased speed also progressively decreased, and a slopped line appeared on the graphs for each one of us. Remember: that curve is only telling us at what velocity we could move a certain load – and no more. However, now we had established the essential force / velocity-curve, where each point on the sloped line correlated the maximum velocity achieved by each increasing load.
The next step was to determine exactly at what point along the force / velocity curve – the long and sloped line - we could find the maximum expression of power. In order to do that we had to utilise the force / velocity curve in order to create a force / power curve that would tell us precisely where that elusive point was located. Knowing the force (load) and the related velocity it was relatively easy (for the computer software at least) to calculate the force / power-curve.
If the force / velocity curve is a sloped straight line, the force / power curve is created by bending the first curve and developing an inverted U shaped curve. That U shaped curve shows low power output at both ends of the spectrum (low and high speeds) and high power at its apex – where the optimum amount of velocity blends with the optimum amount of force to create maximum power.
Contrary to our expectations, the apex or top of the force / power curve is not a sharp peak, but rather a small and relatively flat area. This means there is a definitive range in which the power output is close to the maximum. This point is normally found at 30 to 70% of total force. If you were training for this with a barbell and your 1 Rmax was 100 kg, you would be training at maximum speed and acceleration using anywhere from 30 kg to 70 kg.
The core principle of the force / power curve is to train in such a specific way as to increase the amount of power you have to move any load at maximum velocity, it doesn’t matter if it is 30% of 70% of your 1Rmax. Sensei Nishiyama and I found that for karate training it was better to train at the lower end of the 30% to 70% spectrum in order not to alter the technique. Higher loads always tend to alter the technique. And this is precisely why the force / velocity curve always has to be determined before the force / power curve is determined.
Ok, knowing this, a question arises: why should we train power this way? The answer is that the involvement of muscle fibres does not only depend on the load as most of us think, but mainly on the velocity of the movement. Training power this way gives us a way to train the relevant fast twitch muscle fibres! I say this because if you train strength, you simply increase strength and to a certain extent you also increase power. But you will be very lucky if you can, in any possible way, increase the speed of your technique. If you train power, you will also increase power, and you will also increase strength and you increase speed, which means the whole force/velocity-curve shifts to its maximum expression.
In the last analysis, the force / velocity and the force / power curves are perfect tools to monitor your strength and technique development qualities over time. Training without these two simple tools is like having a dashboard in your car which only displays the total mileage driven, not the car's speed nor the motor's RPM. Both curves will allow you to see the shifts created in the velocity, force, and power of your techniques.
Ok, now guess which muscle fibre type generates the highest power output? It is the fast twitch or type II fibre, for the advanced reader its especially the type IIB or IIX fibre. So, if you want to improve the qualities of that fibre type, you have to generate power and lots of it as well.
Furthermore, we always assumed that the biological response of the first rep within a series of front punches (for example 10 reps) will be the same as the last rep in that set. But if you look well, something has changed, and not the load but the velocity of the technique. This always happens in the same direction, the speed of the reps simply slowed down. Ever wondered why this happens?
It's because the powerful fast twitch II fibre runs out of fuel and drops out of the recruitment pattern. Due to its tremendous anaerobic energy consumption, fast twitch II fibres are fast to fatigue. This is the high price that has to be paid for the high power output. After a few reps you solely used slow twitch I fibres and your slow training will only help increase their size.
There is a decrease in velocity, despite the effort to produce maximum velocity in each rep. Fast fibres drop out after about 6 reps, and from that moment on only slow twitch fibres are recruited.
Knowing this allows us to create two training strategies: 1.- determine the optimal intensity for power training; and 2.- determine the optimal repetitions in each set.
A lot of people have something to say about the use of fibre types within movements, but the only way to really figure it out is to use muscle biopsies (long-term) or EMG (real-time) and I know very few people who do this. As I always say: “in God we trust, all others show data.” Following are the most important and practical issues.
If you want to improve explosive strength or power, you have to recruit fast twitch II muscle fibres. If you only recruit slow twitch I muscle fibres, but move too slow and/or do too many reps, you will get chronically slower due to a selective hypertrophy of slow twitch muscle.
For humans it is impossible to selectively recruit fast twitch II muscle fibres, but cats surely can. Just watch how quickly they move when they step into a puddle or when you stick some adhesive tape on one of their rear paws. No matter how fast you move slow twitch I muscle fibres will always be involved. Knowing this, the trick is to try to recruit as many fast twitch II muscle fibres as you can. And that is exactly what power training via the force / velocity and force / power curves do.