You can’t really change how your muscle grows…when it work out a particular muscle, it will work the whole muscle and grow equally in size in all parts of the muscle. For example, some people can never get that peaked look on their biceps. I can’t and I’ve been trying for awhile. However, while you can’t target parts of a single muscle, you can target individual muscles as a whole. Most women don’t like thick legs. Instead of doing those weird thigh master exercises (which are plain silly since leg muscles consist of the quads and the hamstrings…you can’t target parts of them ) just do light squats or don’t even do leg exercises at all. If you are fairly fit, the definition will show in legs through diet without bulking up.
Drink LOTS of water. Believe me, you ARE thirsty. Don’t believe your brain. Liquify your body and the fat will come off more easily. Then you will see more definition.
Anyone ever hear of the workout technique called “The Hundreds?” That was a routine where you used a very little weight, one set (after a warmup) of 100 reps. I never did it it sounded way too PAINful! It is supposed to make your muscles more dense. The muscles are supposed be stronger than they look with this technique. So if you want a “toned” appearance, use less weight and more reps. Basically you are giving your muscles a “cardiovascular” workout rather than a power workout.
Tee-Bone, are you beefcake or George Castanza? 
If this is happening to you then you need to attack the muscle with different excercises. Many muscles have more than one head. They pull from different directions. For example the triceps have 3. And there are several excercizes to work out the various areas of the bicep. You can lengthen the biceps, or heighten them, depending on how you attack them. To heighten the peak of the biceps, try lying (on your back) dumbell curls. Another example: the best excercize for the pectorals is the dumbell fly, not the bench press, because the muscle is being pulled more directly. One excercize works the muscle, but another works the muscle in a different direction. It goes “with the grain” so it works better.
I would recommend Arnold Schwarzeneggers’s
Encyclopedia of Modern Bodybuilding
This book is more than 2 inches thick and it is only $17.50. And it comes from the workout experience of Arnold. Whether you like him or not, you have to admit, he has the body to prove it. And even if you think he did take steroids, you still have to know how to work out to make the steroids work. So he knows how to work out.
THere is never any reason to do 40 rep curls. The fact that you do this tells me you need to go read a lot more than what people will tell you on this site.
For anyone wanting definition, I would recommend at most 25 reps, then 20, then 15, then 12 then 10. 40 is really too much IMHO. With the (lack of) results you are talking about you probably aren’t working your muscles out enough. I’ll bet you could go to 50, right? That hundreds routine had the muscle FAILING at 100. You HAVE to work to failure. You can’t build up what’s not broken. Break your muscles. Don’t stop because your workout says you do 12 reps this set, or 40. If you still have energy in your muscle then keep going, until you can’t go any more. Then take a breath, and try just one more rep. Then (if you’ve gone over your rep goal a lot) the next time you work out this muscle, up the weight. Whether you want big muscles or tone or the chiseled look, the recipe is the same. I know I’ve had a good workout routine when I can’t lift my pillow at night. Get this kind of determination and you will see results fast.
Of course, there’s this little thing called “overtraining” that gets in the way of a scheme like that…
It’s been said before, but it bears repeating: muscle definition has fuck all to do with how much muscle you have. It is solely a function of how much subcutaneous fat you have. I have a friend who’s about 5’6", 135, and looks absolutely shredded, because he’s got about 8% body fat. He’s also pretty strong. Course, he’s a danseur (male ballerina), so he has to be in pretty good shape.
I, on the other hand, have much more muscle mass, but am kinda fat, so you can’t really tell.
And there is NO evidence that you can “shape” a muscle with any kind of workout. You can place different amounts of stress on the different heads, but muscle shape is determined by the insertion points (where the tendons connect to the bone) and by how much of the length of the muscle is tendons.
Schwarzenegger’s advice may be good, but keep in mind that back when he was competing, you could’ve chopped him up and sold him as steroids. Read the reviews on Amazon before you spend money on his book. I would much more strongly recommend this book, although I don’t agree entirely with the author’s premise (one set to failure didn’t work well for me).
Lifting to failure is not strictly necessary, but some people like it. I don’t, but YMMV.
I concur with this statement. It is almost impossible for someone to gain muscle and lose fat after the first few weeks of working out. You will not see a real 6 pack until your bodyfat % is under 8-9%. If you are already as strong as you want to be, and your muscles are as big as you want them to be, just do a med rep med weight maintenance lifting schedule and focus on your diet and cardio. Do your cardio in the morning to keep your metabolism cooking during the day.
DIET DIET DIET DIET DIET DIET
With a shitty diet you will never be cut no matter how much working out you do.
Yes. Muscle Definition is merely how well defined your muscle is, or how well you can tell where the muscle originates and inserts, how well you can outline the perimeter of the muscle by just looking at it.
However, a more practical way to look at it is: You can’t have muscle defenition if you don’t have (big) muscles! To look more muscular (and arguably have more defenition) you need to lose fat AND build muscle. In the end you will look more “defined”, depending on how you want to use the word.
Definitely not true. I’ve seen scrawny guys with great definition. See my description of my friend above.
True. However it is mostly genetics that allows that. I have seen skinny guys with no fat whatsoever, relatively (3-4%?), and still have no definition. They just look anorexic. If you aren’t born with it, you have to build it. 
ultrafilter,you have to understand where I am coming from. Please, give posters the benefit of the doubt. We all agree here, but you seem to be overlooking my practical point that some dudes are so freaking skinny that no matter how much fat they lose, they are still gonna look like wet blankets. Call that definition if you want, but I’d rather call someone who actually has muscles “defined”.
Try Pilates - you will achieve very nice definition, as well as a long, lean look.
You can always supplement with weights if you want to be a little bulkier.
To Obvious Guy I have to echo what’s already been said here - diet is key. You can have amazing muscle mass, and not be able to see any of it because it’s hidden under a layer of fat.
I would up your protein a little (maybe to 20% protein and 50% carbs). Make sure the carbs are complex - ie - great, honking loaves of white bread aren’t going to do you any good, whatsoever (despite how tasty they are).
Keep up with the cardio. If you are trying to achieve massive size, cardio can be detrimental (to size only - not to health). However, if you just wanna look lean and sculpted, cardio is key.
Al.
Then you’re using the word to mean something different from what everyone else I know of means. That’s fine, but it makes it a bit difficult for us to communicate.
I do agree that if you want to look good, some mass is necessary along with definition, but the two are completely different things. Fair enough?
Anatomically speaking, muscle definition, or tone, is defined as a constant and involuntary contraction of muscle. If you have no muscle tone, then you have atrophied muscles. If this happens, you have a disease or have been bedridden for quite a while. Trust me, you won’t be working out if your muscle tissue has atrophied. Also, the thing about fat is true. Cardio will help you lose weight, with the added benift of getting to see your muscle structure. However, having more muscle will speed up this process. In my opinion, a good mix of cardio and weight training can’t go wrong. You may not get to bodybuilder status, but few do. You’ll look and feel better than you do now if you just work out. It’s really just about pushing yourself. Good luck.
I can boil this down for us: When someone (such as the OP) says they want to have definition, the assumption is that they want to look good, which requires some decent muscle. So you tell them how to gain muscle and lose bodyfat. So, there is an assumption there, but a reasonable one.
I am usually technical like you, but I specifcally stated I was being practical when I said you can’t be defined without some muscle.
You gotta sweat it out!! Watch what you eat, and mix up your workout routines. I love doing a moderate weight workout, then hit the heavy bag and double end for about 45 minutes. Jumping rope, for intervals of 3 minutes, then do a set of pushups or curls…for about five sets.
I’m a reformed runner, I feel better if I don’t do too much of it now, but when I’m in good shape, a 6 mile trail run once a week…I love running intervals up hills, too. Workouts involving pullups and dips have a good reputation for giving you definition, and making you STRONG.
Most important…mix it up, shock your body. Play some basketball or soccer on an “off” day, or a ride on the mountain bike. Don’t get stuck on just doing inertvals of weights, with a schedule cardio day or two in between.
My 2cents
Fair enough. Do remember, I come from a discipline where precise language is absolutely necessary, and that tends to carry over. Don’t think I was ever knocking your advice, cause I wasn’t.