Lifting heavy weights makes you big and bulky — or at least that’s the conventional wisdom. It’s the reason many women (and some men) who want slim and “toned” physiques opt for lighter weights, lifted more times.
But the notion is not supported by science. Producing bulky muscles requires not just heavy weights but heavy calorie consumption as well, typically far above the 2,000 daily calories recommended for many adults.
For people who lift weights to tone up and slim down, experts say, a regimen that includes a combination of challenging weights and fewer repetitions can help significantly. In a 2002 study, for example, scientists looked at what happened when women performed various resistance exercises at different weights and repetitions (85 percent of their maximum ability for 8 reps, versus 45 percent for 15). Subjects lifting more weight fewer times burned more energy and had a greater metabolic boost after exercise.
In another study published last year, scientists followed 122 women for six years. They found that those who were assigned to do resistance exercises three times a week — sets of 8 reps at 70 to 80 percent of their ability — lost the most weight and body fat. A similar two-year study of women who did strength training with challenging weight twice weekly found similar effects on body and “intra-abdominal” fat. 

THE BOTTOM LINE
For better tone, try fewer reps and more challenging weights. 


ANAHAD O’CONNOR scitimes@nytimes.co