Not saying I can always block every punch or kick that's thrown against me in sparring but why is it that you sometimes cannot block, parry or dodge an attack? Is it because I haven't trained the technique enough?
One thing to realize is that you have two factors that affect blocking a strike: 1) reaction time, and 2) tracking.
Reaction time is the time taken by your brain to notice the strike coming towards you, to calculate an appropriate response, and to begin to move to counter it. (Notice I said "begin" to move, not the complete movement.)
If a strike has a large distance to travel before getting to you, you have more time to react. That means that strikes that begin close to you or strikes that change course when they are close to you are going to be more difficult to react to.
You can actually measure reaction times, by the way. Typical reaction times will be on the order of a half a second, plus or minus 300 milliseconds.
Okay then, what that means is that if someone's strike takes only a half a second to perform from start to completion, your chances of reacting to it are nearly zero. And we haven't even started moving yet. It takes more time to go from reaction to actually moving your limbs to block the strike.
It stands to reason, then, that strikers that initiate attacks closer to their opponent will have a greater chance of it getting through without being blocked. It also stands to reason that the one that starts the fight is often going to be the one who wins it, because the other guy is not able to react in time and will take the first hit.
This old saying applies here: "It's faster to act than to react."
Reaction times are also affected negatively by age and acquired knowledge. Age is obvious. The older you become, the longer your brain takes to react to things. But acquired knowledge is also a detriment to reaction time. Why?
Reaction time is more than just the time needed to realize something is coming towards you. It's also the time needed to come up with an appropriate response (a plan of action). The more you know, the longer your brain takes to consider the variables and decide on the right response. It's strange, but true.
The second factor is tracking. That is your brain's ability to lock onto the object approaching you.
If you can't track the position of your opponent's strike, then you can't block it. You need the correct direction and speed of the strike in order to know where the strike will hit you and when. Your brain has to do some extrapolation (guessing) based on that calculation so that your block will be at the right place and time. It has to plot a path both of the strike and of your block, and they need to intersect at the exact same time and place. It's hard!
One problem is that human eyes and brains aren't good at tracking fast moving objects in general. You can calculate the speed and direction incorrectly. So it requires constant visual feedback to reduce error.
But there's another problem. Certain trajectories (changes in speeds and paths) aren't tracked very well by the brain. So it's hard or even impossible to lock on to the path that some strikes take.
For example, it's been shown in studies that objects traveling diagonally in the field of vision are harder for the brain to track than objects that are traveling horizontally or vertically. So, it's not a coincidence that a lot of attacks in martial arts are diagonal. You can see this in the UFC a lot. The strikes that happen diagonally often get through defenses more reliably.
Strikes that are accelerating are harder to track than strikes that are traveling at a constant velocity. (This is especially true if the acceleration occurs whereby the terms of its mathematical expression have exponents greater than 1 - in other words, non-linear acceleration.)
The other problem is that the brain must calculate the expected path of the strike based on the continuous feedback it gets from tracking it in order to know where and when to block. This takes time, though. You have to actually sit there watching the strike, observing it. That's going to take time. The brain has to look at how the strike is moving to know what the expected path is going to be.
Since strikes are coming so fast, the brain doesn't generally have time to wait for a lock on the strike before beginning to block. It would be too late. So it isn't going to be able to come up with a definitive expected path for the strike. At least not initially. Bummer!
So what defenders do to make up for the lack of tracking, initially, is to use other clues to let them know the general target area of the attack. That way, they can begin to move their arms to block that general area before tracking information is available. As their brains begin to get more information about the path of the strike, they can fine tune their movement so that the block is successful.
In other words, defenders guess at the target of the strike, at least initially.
Good strikers know how to trick their opponents into guessing a different target than they're actually going to take. That causes the defender to block at a different place and time than needed. By the time the defender's brain realizes that the strike is on a different path than expected, it's too late.
For example, the striker may alter the rhythm of their attack so that the defender blocks too soon or not soon enough. Or the striker may look (on purpose) at a different target than they're actually targeting, and so the defender guesses the wrong target based on the striker's eyes. Or the striker begins to strike at one target but then changes course and strikes another target before the defender can react in time to the course change.
It's not all bad news for the defender, though. These two factors (reaction time and tracking) can work in the defender's favor as well. When the defender begins to react to a strike, he can move his body. Just moving the target will cause the striker to have to do the same mental math as the defender: He has to first react to it, and then he has to track it.
Body movement is a hugely important topic in martial arts. The more sophisticated ones body movement is, the better they can defend themselves. Body movement is crucial for self-defense.
And by the way, remember when I mentioned that diagonal strikes were harder for the brain to track and defend against? The same is true about body movement. That's why most martial arts teach you to move diagonally across the floor instead of straight forward and backward, left and right. It's harder for your opponent to track.
Well, this is a lengthy subject, and I think I've only scratched the surface. But you get the idea.
Hope that helps.
Sometimes your opponent is faster than you. Sometimes they can read your body language and your tells, and fake you out, or feint. Sometimes you might have patterns that leave you open in predictable ways, and they take advantage of that. Sometimes you think you are dodging to safety and you're walking right into the attack.
"More training" could help, but mostly it's about "right training". Doing the technique is the easy part, then you have to learn when is it a good idea to use the technique in general, and when is it a good idea to use the specific technique against this opponent, specifically. Range, timing, angles, body language, your own endurance, how fast you can shift your weight and facing, all of this, will be part of what you're learning.
Even then, you will probably not block or avoid every attack. No amount of training makes you invincible. A good teacher, or coach, should be looking at your common patterns that leave you open, and teaching you how to minimize them so you take fewer hits, and how to set it up so the hits you do take are less damaging.
The ability to defend successfully is governed by the following time relationship:
reaction_time + decision_time + defend_time(defend_distance) < telegraph_time + attack_time(attack_distance)
Covering greater distances requires more time.
Here are some defensive principles:
- Control distance - If you simply want to defend yourself, keep others outside of engagement distance where they cannot reach you before you can react. If you want to attack, you need to close distance first.
- Impede direct attacks - If you cover your face, your opponent has to maneuver around your guard to hit it. This has the effect of increasing attack_distance.
- Minimize motion - If your hands are down, your defend_distance will be high. Use a guard position that minimizes the movement distance required to defend yourself.
- Use all of your limbs - The defend_distance for using your leg to block a kick may be shorter than that for you hand to block the same kick.
- Retain mobility - It is often easier to dodge than block or parry.
- It's much easier to defend against attacks that are telegraphed. If you want to attack more effectively, don't telegraph.
Human decision_time can be improved substantially through training. Most people need to train to do something useful immediately upon detecting an attack rather than flinching or simply freezing.
There are fundamental human limits to reaction_time. The human visual system requires tenths of seconds before it react to anything. If you are reacting based on vision, you cannot defend anything that is under this limit.
Humans react more slowly to vision than to touch. So even though you are closer to an attacker when in contact (shorter attack_distance), you can actually learn to defend more quickly at touch because of a reduction in reaction_time.
Why can you not dodge every attack? For the following reasons:
- If you dodge every attack (without supplying your own), you're no longer fighting, but running. That generally goes against the martial aspect of martial arts.
- Your opponent can keep giving out attacks faster than you dodge them.
- Your dodge could end up moving you into the way of the next attack.
- Even if you provide an attack, your opponent can still provide an attack. Ideally, you want to provide attacks and deny your opponent's attacks. In armed forms of martial arts, you try to make your attack and defense one and the same (defensively strike, offensively defend).
The other answers are all pretty good and I won't go over any of that, but nobody has mentioned a fundamental physical fact.
Typical time required to throw a punch is about 1/6 of a second.
Average human reaction time is about 1/4 of a second, so if you're relying on your reactions to defend yourself, you are at an enormous physical disadvantage.
Practised sporting martial artists learn to read their opponent's body language and begin defending before the punch has been thrown, and this is why many sporting methods (and indeed traditional methods) don't translate from one environment to another; people behave differently in different environments. Many of course do translate.
Then there's the purely physical fact that the hand is faster than the body, which in turn is faster than the feet.
i.e. Moving your hand is faster than moving your entire body, which is faster still than taking a step.
This is btw, why all karate "blocks" as normally taught, fail. They physically can't work. Having personally timed them, they are closer to half a second to perform, even at speed.