Q: What is your idea of 'heavy' weights (free weights) for a healthy, moderately active slender female? And do you think using free weights to do squats, bicep curls, kickbacks, lunges etc. etc. are as effective at burning fat as working out with machines?

A: For me, a heavy weight for any given person in any given exercise is such a weight that that person can only perform the exercise with it 12 or fewer times in good form before hitting muscular failure. In other words, after s/he performs that exercise with that weight 12 or fewer times, s/he would HAVE to rest for at least a few seconds before being able to lift it once more. This definition is pretty much universal across all exercises for both males and females.

If you look at most of the sample training programs in the Articles section, you'll see that most of the sets are recommended to be to-failure with between 6 and 12 reps, which is basically taking a heavy weight (by the above definition) and pushing yourself to the limit in each set. This is a very demanding training but it also produces the greatest metabolic response. If you are not comfortable with such training, you can still achieve great results by working with heavy weights, but stopping each set a rep or two or three short of failure. Either of these approaches will get you far faster results (whether burning fat or building muscle) than higher rep training where you do 15 or more reps in each set.

If you worry about building too much muscle through this kind of training (which may be aesthetically undesirable for a woman), then be assured that it will not happen AS LONG AS YOU DON'T GAIN WEIGHT! If you overeat to gain weight and perform heavy weight training, then yes, there's a small chance you'll start becoming overly muscular (this, of course, depends on how you define 'overly muscular'). However for a woman, even when overeating and weight training muscle mass comes very slowly. But simply make sure you don't overeat and don't gain weight and then you'll have nothing to worry about at all as far as getting excessively muscular no matter what your training regimen is.

Also keep in mind that heavy weighttraining will make you hungry! This is a side-effect of increased metabolism. So if you don't exercise any diet control, then it is easy to overeat while lifting weights. This is by far the biggest reason why people say that weighttraining made them gain weight! In reality, what actually happened was that weighttraining revved up their metabolism, which led to greater hunger, and they simply ate too much. So, once again, watch what and how much you eat!

As to your second question, freeweights are actually superior to machines in raising your metabolism and burning fat! Machines do all the stabilization work for you and keep your exercise motion the same rep-to-rep. This means that many muscles that could be engaged aren't because the machine is doing the work for them or because machine's mechanics prevent them from ever being used. Because you don't exercise all the muscles you could be exercising, you also don't get metabolic response you could be getting. Still, you can make very good progress with machines only. Machines also provide a good introduction to resistance training for beginners and reduce the risk of injury due to potentially improper use of freeweights (not that freeweights are inherently dangerous -- some people simply don't keep good form on many freeweight exercises).