If you're among the millions who have embraced strength training, you're on the right track for healthy aging. But experts warn that skipping cardio leaves critical health gains on the table.

Dr. Julia Iafrate, a sports medicine physician at NYU Langone Health, says there's been a 'pendulum swing' toward muscle-building workouts because they are time-efficient and produce visible results. While major health organizations recommend two strength sessions and 150 minutes of moderate aerobic activity per week, many people skip the cardio.

Strength training alone does improve key health markers. It can lower blood pressure, improve cholesterol, and reduce the risk of diabetes, heart attack, stroke, and some cancers. On its own, it reduces the risk of death from any cause by about 15 percent.

But to maximize longevity, you need aerobic exercise, says Dr. Christopher Tanayan, a sports cardiologist at Northwell Health in New York. 'By only strength training, you're leaving something on the table,' he says.

Cardio stresses the heart in ways that make it more efficient, keeps blood vessels healthy, and helps grow new blood vessels. Without it, your heart becomes less efficient and blood vessels deteriorate.

Kate Baird, a clinical exercise physiologist at the Hospital for Special Surgery, uses a car analogy: 'You can't forget that there's an engine inside that also needs to be able to drive it down the street at the speed that you'd like.'

Aerobic exercise protects against cardiovascular disease - the leading cause of death for men and women - and many types of cancer. When you combine strength training and cardio, your risk of dying from any cause drops by at least 40 percent compared with doing no exercise. Dr. Iafrate calls that 'astronomical.'

If 150 minutes a week feels impossible, experts recommend sneaking cardio into your strength routine. Spend 10 to 15 minutes on a bike or treadmill before lifting. Add bursts of high-intensity movement like jumping jacks or high knees. Try circuit training, alternating between strength and aerobic exercises with little rest.

The bottom line: Any exercise is better than none, but for maximum benefit, make time for cardio.