As we age, fast twitch fibres are the first to decline. “Walking improves endurance, but it doesn’t stop the loss of fast twitch fibres. If you don’t train strength, you become sluggish. We see it in older people, who end up walking in short steps because they have lost those fibres. Strength training is the only way to keep them,” Isidro points out. “We gain muscle until the age of 25, maintain it until the age of 35 and, from then on, we start to lose it slowly, accelerating from the age of 50, and even more at the age of 65. There are cases of people in their 70s who maintain the strength of someone sedentary in their 40s or 50s thanks to daily training, proving that this habit can subtract up to 20 years from biological age.”

After all, what you don’t use, you lose. That goes for muscle — but also for bones, the respiratory system, and the pelvic floor. Regular exercise also improves the non-REM phase (deep sleep in which the eyes do not move), and that also decreases with age. Having longer non-REM phases is related to 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

While water is essential for our hydration, 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. 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 scenario 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 fibres, so training them is vital.

Prioritise intensity over reps

Do reps at a high intensity (quickly) to work the fast twitch fibres. 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 fibres 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 fibre and continuing to lose fast twitch fibres,” 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 five to 15 minutes. Do them in circuit format, alternating exercises with breaks. “We all have 10 minutes a day if we prioritise. 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, because contact with nature and socialisation have a direct effect on health.