When Bryan Mann talks about weightlifting, he often tells the story of Milo of Croton, a Greek wrestler who lived 2,500 years ago.

Legend has it that Milo started his yearly training by buying a newborn ox calf. Every day, he hoisted the calf onto his shoulders and carried it up the stadium steps. As the calf grew, Milo became stronger, until he was carrying a full-size ox.

While most people can't carry livestock around their neighborhood these days, the formula for getting stronger hasn't changed, said Mann, a clinical associate professor of kinesiology at Texas A&M University. The core of strength training is a concept called progressive overload, in which you gradually increase either the weight, repetitions, difficulty, intensity or some combination thereof.

Strength training, especially as you age, improves cardiovascular health, blood pressure and bone density and reduces the risk of lower back pain. None of that happens without progressive overload.

But overload doesn't mean you have to clean and jerk 200 pounds, said Avery Faigenbaum, a professor of health and exercise science at the College of New Jersey. It doesn't even require lifting heavier weights. You can challenge your muscles by doing a more difficult movement — lunges instead of squats, for instance.

Lifting the same dumbbells the same number of times will lead to a workout plateau. That said, if you are creative, you can get stronger with a pair of dumbbells or even no weights at all, said Elizabeth Wipff, a strength training coach who specializes in working with women over 50.

"You can progress from chair squats, without holding onto anything, to squats holding onto a heavy object," such as a backpack filled with books, Wipff said.

If you already have a strength routine and have been lifting the same weight for months, the simplest change is to add a little more weight. If you don't feel like adding more weight, try a more difficult variation. The exact movements or pounds aren't as important as the increase in difficulty.

For those looking to build muscle, here is a simple 12-week workout cycle to try with dumbbells or a barbell:

Start by lifting twice a week and increase to three or four times a week. Write down your weights and reps as you progress.

Pick three movements total, such as lunge, squat, bench press or shoulder press. You can do the exercises all on one day, or split them up between days. Build in rest days for your muscles to recover.

Weeks 1 to 4: Three sets of 12 to 15 reps. For the first two weeks, use a weight that feels easy and work on your form. For the second two weeks, add a small amount of weight, about 5%.

Weeks 5 to 8: Three sets of 8 to 12 reps. Start with a weight that's 5% to 10% more than what you ended with the previous week. Increase the weight by 5% to 10% every week.

Weeks 9 to 12: Three sets of 5 to 8 reps. Find a weight where your last repetition feels difficult. Increase the weight by 2.5% to 5% every week.

Rest week: Take a week off. Then you can start the program over again, either with new exercises or with heavier weights.