When I did my qualifications many moons ago to become a personal trainer you get taught some basics about resistance training with weights and 'rep ranges' the general consensus is:

• 5 or less for pure strength
• 8-12 muscle building
• 12-15 and above for endurance/tone

What should you be lifting and for how many reps?

We've all heard the old adage muscle weighs more than fat...this is not strictly true, one pound of fat equals the same in weight as one pound of muscle. (Just like a tonne of feathers is the same as a tonne of bricks).

Where muscle and fat differ is the density, muscle is active tissue and a lot denser than body fat, thus taking up less room as the picture clearly demonstrates. 

This means stepping on the scale only gives half a story. To determine healthy body composition, consider your percentage of body fat in proportion to muscle mass.