Strength training, traditionally favored by body builders seeking to bulk up, has become the go-to regimen for athletes, weekend warriors and exercise enthusiasts determined to slim down.
Fitness experts say metabolic strength training, a high-intensity, full-body interval workout, can add definition to the shape of runners, cyclists and other cardio devotees willing to put some muscle into it.
Florida-based trainer Nick Tumminello believes strength training should be the primary form of exercise for everyone except beginners.
"If you're looking to lose fat, go with strength training," said Tumminello, author of "Strength Training for Fat Loss." "Watch your diet to reveal your shape, and strength train to improve that shape."
It is not your grandfather's body-building program.
While traditional strength training uses free weights or weight machine to build endurance and muscles, metabolic strength training combines high-intensity interval circuits with changing combinations and repetitions using free weights, kettlebells, barbells, dumbbells and resistance bands to increase the metabolic rate after and during the workout.
"The body-building model is great for maximizing body building, but for the average individual looking for fat loss, or to feel better, or to improve general fitness, this creates more of a metabolic disturbance," he said.
Because the combinations are intense, Tumminello recommends starting at once or twice a week and building up gradually to three or four times.
"You do need recovery time," he said, adding that too many beginners tend to take an all-or-nothing approach. "Try to set a realistic goal."
Jenn Burke, a San Francisco-based personal trainer and fitness manager at Crunch, a national chain of gyms, said that steady cardiovascular activity, such as running or cycling, is great for burning lots of calories at a time and increasing heart rate and lung capacity.
But unlike cardio activity, strength training will continue to burn calories up to 72 hours after the exercise is over through a phenomenon called after-burn.
Modern strength training, she said, is less about how much weight you can lift than it is about how to make the body more efficient, lean, toned and strong.
"Strength training is about the quality of life," Burke said. "You can be skinny but not have the ability to lift your suitcase."
Although research has shown people cannot spot reduce, such as targeting just the thighs or arms for slimming, Burke said it is possible to enhance an area of the body with strength training.
"Men are generally drawn to body building seeking size or presence," she said. "Women come