As a woman, you have few precious natural resources as important as your muscles. They’re what keep you strong, able, and independent. They’re also frighteningly easy to lose. Around age 30, women begin to lose muscle density. Lean muscle mass slips away to the tune of about 3 percent per decade between the ages of 30 and 80, while strength declines 30 percent between the ages of 50 and 70 and takes a major nosedive after that.

And all the cardio in the world won’t cut it. Fact: strength training beats cardio. Research on women, especially past age 40, shows that even high levels of aerobic activity don’t translate into any meaningful changes in lean body mass. The only solution is strength training.

This means high-intensity power training — heavy lifting for pure strength. This kind of training stimulates your neuromuscular system, activating the maximum amount of muscle fibers. It also keeps those high-energy, powerful type II muscle fibers engaged, which is essential because those are needed for speed, and they’re the first to go.

The best part is that the benefits of strength training are nearly immediate. Even before your muscles get bigger and stronger, you wake up sleeping muscle fibers and develop neuromuscular connections that result in strength gains after just a few sessions.

Here’s what you need to know to optimize your strength-training results:

1. Lift heavy

While there are certainly exceptions, far too many women still simply will not lift weight that is heavy enough to stimulate hypertrophy (muscle growth). For this to happen, you need to challenge and stimulate your muscles so they break down and repair bigger and stronger.

2. How heavy is heavy enough?

Pick up a weight and lift it 10 times. How hard are those last two reps? You have chosen the right weight if you are barely able to eke out that final rep while maintaining good form. If you could easily do two or three more, you need to go heavier. That being said, there is an endless stream of videos online of poorly coached weight lifters using far too heavy weight while contorting themselves in awful ways that are bound to lead to injury. Don’t do that either.

Heavy weight plus good form equals great results. Too little weight is a waste of time. Too much is counterproductive. You can also opt for body-weight exercises, which can be extremely effective as long as you reach the same point of fatigue, which is quite easy to do with pushups and single-leg squats. When lifting, always remember to brace yourself, keep a strong neutral spine, and engage your core for maximum efficiency and results.

3. Lift often.

A good rule of thumb is to perform two or three sets of about 10 repetitions or as many reps as you can complete in the suggested time frame, and remember to follow these tips to strength train safely. Try to fit strength training into your schedule two to three days a week. Three is preferable, but you’ll still see benefits from two.

4. Mix it up.

There are countless exercises to choose from, and variety is your friend when it comes to making muscle. Remember, your body adapts to the challenges you present it with, and strength training can burn fat even faster. When you keep doing the same exercises over and over, your body gets bored and you stop making gains, or worse, you backslide. No one wants to do hard work for nothing. So mix up your routine at least every 2 to 3 weeks.

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Adapted from Roar. This story original appeared on Rodale Wellness