Here's the answer, in case you were wondering.
Every day the question pops up in gyms across the country: "I already run/bike/swim/[insert your favorite cardio here]. Do I need to strength train?" Meanwhile, with the growing popularity of boot camp and CrossFit, women who have clicked with lifting are wondering if they still need cardio. While there are benefits to both types of exercise, the latest science suggests there's a clear winner—it just depends on your goals.
This article originally appeared in the October 2015 issue of SELF. For more like this, subscribe to SELF and download the digital edition.
Which is better for weight loss?
Strength training. While you burn only up to 10 calories per minute lifting weights, compared with as many as 12 for cardio, you continue torching calories after you put those dumbbells down.
"When you jog or hit the elliptical, your body is actually pretty comfortable," says exercise physiologist Mike Bracko of Calgary, Alberta. "But when you strength train, your body is like, 'Whoa, this is a lot different!'" And that "whoa" takes you about an hour to recover from—burning an extra 25 percent on top of the calories you torched during your workout. That means if you burn 160 calories doing a 20-minute strength circuit, you'll actually burn 200 by the time you've gone on with your day.
Bonus: Your metabolism stays elevated by up to 10 percent for three days after you lift as your body repairs the microtrauma in muscles, says Wayne Westcott, Ph.D., an exercise-science professor at Quincy College in Massachusetts.
Which should I do first?
Whichever you prefer, because they both have benefits, says Westcott. On one hand, moderate-intensity cardio makes a great warm-up, priming your muscles for strength training. On the flip side, cardio also makes a great cooldown, helping flush out the soreness-inducing lactate that builds up in your muscles during tough training and turning it back into energy you can use. The one exception: If you're training for an event like a triathlon or 10K, you want to tackle that type of exercise first, when you're fresh.
Does one give a bigger endorphin boost?
Cardio. It's been shown to change brain chemistry enough to improve mood, anxiety and depression. And in a new study in the Journal of Experimental Biology, volunteers who ran on a treadmill increased their levels of endocannabinoids—marijuanalike chemicals created in the body that make you feel good and even have a slight pain-relieving effect.
You can still enjoy an endorphin boost from strength training, but you'll need to rev your heart rate. Do that by lifting heavy weights or moving quickly between sets and strength exercises instead of taking long rest breaks.
Should I lift heavy or light weights?
Both. Light weights—light enough that you can do 15 to 20 reps before fatigue sets in—tend to activate slow-twitch muscle fibers. Heavy weights—so heavy that you can eke out only 8 to 10 reps—activate a higher percentage of fast-twitch ones. Combining the two lifting styles will give you the best results, says Brad Schoenfeld, Ph.D., an assistant professor in exercise science at CUNY Lehman College in Bronx, New York. Ideally, you'd do one light lifting day and one or two heavy days in a week, or mix it up in a single session.
What if I have time to do only one?
Strength train, for one simple reason: "It's possible to get your cardio from strength alone," says Westcott. If you keep moving between sets, either by inserting plyometric moves that leave you breathless (think jump squats) or going straight from one exercise to the next, you'll strengthen your heart and lungs along with your other muscles. Studies show that you can get better results—both aerobic and strength gains—from three 20-minute strength circuits a week than you can from 60 minutes of cardio five days a week.