Should I lift heavy or light weights to lose weight?

Nikkiey explains that the weight you can lift will shift from day to day with food, sleep, water and your cycle, so chasing a specific number misses the point. What builds muscle, and what gets you toned, is the resistance and tension on the muscle you're working, plus the mind-to-muscle connection that good form gives you. Her test for the right weight: you should have to power through the last two to three reps of the set.

Form is the line she won't cross. If you grab a heavy weight and can only get 8 of your 12 reps, or you start losing form around rep 10, drop the weight. Otherwise other muscles take over, you stop targeting the one you meant to work, and you raise your risk of injury. If the last few reps go up too easily, add 2.5 to 5 pounds on your next set.

When a member asked whether more sets helps with weight loss, Nikkiey said to keep the three or four sets your program calls for and go heavier instead. She thinks most women underestimate themselves, so she suggests ramping up. Start the first set at a weight you know you can do, add about five pounds on the next, go a little higher on the third, then repeat that weight for the fourth. Her challenge is to try five to 10 pounds heavier and watch what you can do with good form.