If the above sounds all too familiar, you've fallen prey to a common but mistaken misconception.
The myth of training with light weight, high repetition toning, encourages people to use weights so light, they don't have any appreciable effect. Women do not naturally have enough of the hormone, testosterone to get the big muscles they are often afraid of developing.
You have two basic options to make your muscles stand out and look more defined:
You can make your muscles bigger or you can shrink the layer of fat covering them. . Reducing fat is a whole body problem; you can't just target the fat on your arms, legs, etc.
A simple rule for building muscle: whatever weight you use, you should be unable to lift it again upon completion of the set; be it 6, 8, 10, or 15 reps. Workouts with light weights and a high number of repetition do have a place in building muscular endurance but even then, the weight should be heavy enough to complete the final set of each exercise, no matter how many repetitions you're doing.
For shaping and building muscle/lean tissue, your best bet is to choose routines that build muscle size by lifting heavy weights with multiple sets - I.e. Up to 6 sets of each exercise, with 6-12 repetitions in each set - or else focus on mixing strength, cardio, and diet for overall weight loss.
Strength training guidelines often refer to your one rep max. or "1RM" - The heaviest weight that you can lift once for any given exercise. The American College of Sports Medicine suggests that beginners work with weights that are 60-70% of 1RM for 8-12 repetitions; using less than 50% of 1RM may not stimulate any muscle growth.
Use trial and error to find a weight that has you reaching "failure" near the end of your final set. If you plan three sets of 10 reps and you successfully complete them, increase the weight slightly next time so that you're unable to complete the final 1 or 2 reps.
New research by Stuart Phillips at McMaster University suggests that reaching failure is the most important factor in building muscle - even more important than how heavy the weights are or how many reps you do. Don't get caught up on the amount of weight you're lifting, but instead, focus on how it feels.
Source - Alex Hutchinson, Ph.D. - Author of Which Comes First, Cardio Or Weights