After all, what you don’t use, you lose. That goes for muscle—but also for bone, the respiratory system, and the pelvic floor. Regular exercise also improves the non-REM phase (deep sleep in which the eyes do not move), which also decreases with age. Having longer non-REM phases is related to a gradual and healthy aging. “Strength training is an investment in health for the future,” Isidro says. “It reduces anxiety and it makes us feel better at all levels. In reality, a healthy body is a perfect body.”

The right amount of strength training

Just as water hydrates, too much of it can cause us to drown. Strength training is similar: the proper dosage is key. It’s not about doing it in excess; it’s about doing it right. The right dose, says Isidro, means few repetitions, lots of recovery time, and, above all, not looking to fatigue. “Many people think that if they don’t get tired they haven’t trained properly, and it’s actually just the opposite: in strength we’re not looking to exhaust ourselves, we’re looking for quality.” To that end, here are seven points to keep in mind in order to strength train properly, no matter your age or fitness level.

Increase the frequency slowly

The minimum for adaptation is two days a week, although the ideal would be to progress to three or four with breaks in between—one day on, one day off. You should also do strength before endurance; if you do both on the same day, it’s best to finish with cardio.

Start with the legs

If you’re new to working out, it’s best to focus on the legs. They are the largest reservoir of muscle mass in the body and also the quickest to deteriorate. In addition, the legs contain a lot of fast twitch fibers, so training them is vital.

Prioritize intensity over reps

Do reps at high intensity (quickly) to work the fast twitch fibers. It is recommended to do a few repetitions—half or less of the maximum you can do—to avoid fatigue. “The key is speed and intensity, because that’s what activates the fast fibers through the nervous system,” says Isidro.

Incorporate rest

Give yourself plenty of time to rest between sets. At minimum, rest time should be one minute, but two or three minutes between exercises is even better. “You’re fully recovered when you can speak and sing, not just utter and grunt monosyllables,” says Isidro.

Avoid fatigue

“It is essential that the exercise be non-exhausting or fatiguing. When you fatigue, you’re working the slow twitch fiber and continuing to lose fast twitch fibers,” says Isidro. “It’s better to do a few exercises well and repeat them a couple of times. Stop before fatigue sets in.”

Start small

Start with short workout sessions that last 5 to 15 minutes. Do them in circuit format, alternating exercises with breaks. “We all have ten minutes a day if we prioritize. Forget your previous experience—many of us think that exercise should be tiring and painful to work. If we do less, we enjoy it more and see the benefits, creating a positive ripple effect.”

Breathe right

Working the respiratory muscles is also essential, because it improves recovery and endurance. Take long, full breaths, breathing into the diaphragm.

When, where, and how

According to Isidro, the best time to exercise is in the morning. “This stimulates the sympathetic system early, which makes it easier for the parasympathetic system to be stimulated in the evening, improving sleep.” If possible, exercise outdoors: contact with nature and socialization have a direct effect on health.