Super-muscle guys like Dwayne Johnson (51) and Arnold Schwarzenegger (76) have clearly been able to preserve their muscle strength through the decades. But it can be a bit more challenging for normal folks.

It's estimated that on average, people who aren't physically active lose 3% of their muscle tone every year after middle age. Fortunately, all you need to do to overcome that decline is get regular resistance exercise and have a steady supply of the amino acid leucine from the food you eat.

Leucine is found in turkey, sunflower seeds, peanuts, pumpkin seeds, salmon, and egg whites. But it only lasts in your body for four hours, so the smart move is to eat one or more of those proteins as part of your first meal of the day and then every four hours thereafter — especially if you’re on a weight-loss program.

One study found that seniors who eat the most protein were 30% less likely to become functionally impaired than those who ate the least.

Additional protection of muscle strength comes from a molecule called trigonelline that's found in the body, as well as and in coffee and the herb fenugreek. It boosts both muscle function and overall health.

You can also preserve muscle tone with regular strength training using your body weight, stretchy bands, and weight machines. Combine that with heart-loving moderate to vigorous walking and other aerobics.