From Ergo Log
Even if you do a couple of hundred reps for each set of your triceps extensions, it won't help the fat on your upper arms to disappear. And you won't get rid of the fat on your hips by doing sets of hundreds of reps on the leg press either. Spot reducing fat through training is impossible, as any good trainer will tell you. But until recently there was no scientific proof for what most people knew from experience. Now Chilean scientists have published the results of a small but convincing study in the Journal of Strength and Conditioning Research.
Admittedly, the idea behind spot reduction of fat sounded quite plausible. A number of studies from the 1960s showed that women who did abdominal exercises managed to whittle down their waist measurement [Res Q. 1965 May;36:168-73.], and men who trained their biceps had less fat on their upper arm. [Res Q. 1968 Oct;39(3):647-52]
But the studies weren't terribly convincing. Genuine spot reduction means that you have to measure fat in specific parts of the body and then observe that subjects only lose fat in these spots.
The Chileans decided to adopt a different approach. They got 11 students to train one of their legs on a leg press machine three times a week for 12 weeks. The load was low, between 10 and30 percent of the weight at which the students could just manage 1 rep.
Each workout consisted of just one set, but it was a set of 960-1200 reps. This took the subjects about 80 minutes to complete. Time to burn off quite a few calories.
Before and after the training period the researchers did scans of the students to measure their bone mass, lean body mass and muscle mass. The table below shows that this training programme had little effect on the bone mass and little effect on the lean body mass of the subjects. Their total fat mass decreased by 700 g however – and that was a statistically significant effect.
The amount of fat reduction on the trained leg was 20 g; the amount lost on the untrained leg was 70 g. The difference between these two was not statistically significant. The students lost most fat from their trunk.
The Chileans conclude that spot reduction of fat is not possible. Strength training with extremely high amounts of reps is a way of losing body fat all over your body. But this form of training doesn't help build muscle mass.
J Strength Cond Res. 2013 Aug;27(8):2219-2224.