Quickness is the ability to move in the absence of much external force and without any wind-up. How fast are your hands and feet in simple unloaded movements? Being quick is related to being explosive and vice versa but a person can be very quick but not really fast in a sprinting sense, and vice versa. Someone like Steve Nash is an example of someone who is quick yet not explosive. Guys like Matt Jones or Mario Williams are example of people who are explosive but not as quick as some slower athletes. For more info. on the difference between quickness and explosiveness here is an old article I wrote on the topic:
There's a very strong genetic component when it comes to being quick. Take a group of athletes and see how many times they can stand and tap their feet in place over a given interval. Or see how many punches you can throw in a given time interval. Measurements like those are good measurements of pure quickness.
Real world displays of quickness often involve an additional component called reaction time. Reaction time refers to how long it takes you to react to a stimulus. Examples include how fast you get off the blocks and react to a gun as a sprinter, how quickly you react to an opponents punch as a boxer, or how quickly you recognize and respond to a pitch as a baseball player. Variances in reaction time also go a long way towards explaining variances between predetermined performance and game performance. In the case of a football or basketball player, it's a lot easier to look good and carry out your skills when you know where you're going and what's happening beforehand, but a little more difficult when you have to react and do it in fractions of a second.
Average Reaction Times
The typical reaction time is around .2 to .3 seconds. Audio reaction time is generally 3 to 5 hundredths of a second faster. Someone like a world class sprinter might have a reaction time closer to .1 second. Someone with turtle like reflexes may have a reaction time closer to .4 seconds. One interesting thing is you can take 2 people with the exact same predetermined measurables such as the speed of unloaded movements, tapping tests, sprinting speed, vertical jump, etc. but when you have them react to a stimulus there can be extreme differences. One guy might react in .3 seconds and another guy in .1
Here is a test that measures reaction time:
Anything less than .2 (without getting lucky and guessing), is excellent. Anything closer to .3 is slower than molasses.
Improving Reaction Time
Unfortunately, reaction time is highly genetic and typically can only improve 10 to 20%. Two things that help improve it are stimulants and overspeed training. Stimulants increase adrenaline levels which enhances the speed of your perceptions and mental processes. Try doing the above reaction time test first thing in the morning before you've had anything to get you jacked up. The next day try drinking half a pot of coffee or a couple of red bulls beforehand and note the difference. The positive impact stimulatory neurotransmitters have on reaction time also explains why it tends to improve under competitive situations. The increased arousal naturally boosts adrenaline.
A stimulant free stack you can try may consist of:
acetyl-l-carnitine: 1000 mg
l-tyrosine: 3000 mg
Add 200 mg caffeine for enhanced effectiveness.
You can also improve your reaction time by training yourself to react to things that move faster than the needs of your sport. A baseball player might take batting practice while using a special pitching machine that throws pitches at 130 to 150 miles per hour. His brain would adapt to seeing the faster pitches. In turn, this would improve his ability to react to a 90 to 100 mile an hour pitch. A NASCAR driver might use a special driver simulation device that mimicks driving a race car at 200 plus miles per hour. This makes driving at 130 miles per hour seem slow and easy by comparison. You don't necessarily need a special machine. For example, an offensive tackle who has bad reaction time and continuously gets beat off the ball against defensive ends might practice pass protection drills against speedier linebacker types. Their greater speed would improve his ability to react to the slower defensive end. And what if you're a sprinter with piss poor reaction time? Better learn to jump the gun!
Improving Voluntary Quickness
As for improving voluntary quickness in the absence of reaction time, one good way to do it is to practice being quick. Pick a few movement patterns in your sport and attempt to execute them as quickly as possible as smoothly as possible. A boxer might execute a 5 or 10 punch combo as quickly as possible. A martial artist might execute a kicking combo. A football player might perform a footwork pattern. A basketball player might execute a jab step and crossover move as quickly as possible. General quickness drills applicable to all athletes include things like low line hops and hurdle hops. Draw a line on the ground and hop back and forth over it as quickly as possible for 10 seconds. You oughta eventually be able to get 50 or 60 hops with both legs and 30-40 on one. Various agility related drills also have some value here. The biggest detriment to quickness related drills is excessive muscle tension. Try to be relaxed as possible. Maximum speed at minimum effort is a cue that works well.
Quickness and Personality Type
Also in my observations on personality type (or brain type) and it's influence on motor skills, - superior quickness, agility and reaction time tend to be more a characteristic of right brain perception dominant individuals. It is possible to be left brained judging dominant and still explosive, but I can't think of many left brain dominant individuals I've seen with excellent quickness and reactionary characteristics. If you have a hard time figuring out the difference between right brain perceiving and left brain judging, left brain individuals tend to be regimented overanalyzers and right brain individuals are more carefree and couldn't be bothered to pick up a book. Note how many overanalyzing academic types you see dominating team sports. If you're the overanalyzing type one of the best things you can do is spend as much time as possible actually playing your sport so that you strengthen your ability to perform in unanticipated fashion.
For more info on improving factors related to speed, see my No Bull Speed Development Manual