“The movement that’s going to require the most attention, effort, technique, and energy—you want to do that first, so you can put all your effort into it,” she says. “If you’re doing the hardest part last, you risk injury or not reaping the benefits of why you’re doing that exercise.”

For many people, the most technically tough part is going to be the lift—that’s why in most cases, Dr. Olenick says she prefers weights before cardio. “Running or cardio can be very demanding on our central nervous system and deplete our muscles’ carbs stores a bit more than our lifting sessions,” she says. This means that when you strength train first, you might have an easier time recruiting the muscles you’re trying to target, and more fuel in them to power stronger contractions (and thus heavier lifts), than if you log a few miles beforehand. Besides, being tired when you pick up heavy things—say, from a run or bike ride first—can lead to injury and burnout, Johnson says.

But make sure you consider your goals.

The calculus may change a bit if you’re working toward a specific longer-term goal—for example, training for a race or a weightlifting PR. In those cases, you may want to begin with what’s going to get you closer to that objective. “Prioritize the training that is most important to you for that day,” Johnson says.

If you’re primarily looking to get stronger, pick up the weights first. Meanwhile, if you’re in the thick of training for a race and doing speedwork—intervals of fast running or biking—you’ll probably want to do that before lifting, Dr. Olenick says. According to research by the American Council on Exercise, doing strength training first increased exercisers’ heart rates in a subsequent cardio session. That means if you start with lifting, you might find it harder to hit the quick paces you’re aiming for—and you might feel more fatigued afterward. (Quick note: If you’re a runner newer to lifting, Johnson often recommends against doing speedwork and strength workouts in the same session, since both will be pretty taxing on your body. So when you want to do strength and cardio together, it’s probably best to save that for days when your scheduled cardio is of a lower intensity—more on how to structure your routines below.)

Also note that you don’t have to go in the same order every day. After all, your goals can shift over time. That’s why Dr. Olenick cycles between “seasons,” where she focuses on one type of workout more than the other. When she’s in a strength-focused training cycle, she’s even more likely to put weights first. When she’s training for a race, she’ll prioritize running more.

Even if you don’t have a longer-term plan that’s quite so structured, you might still have an idea of what you most want to accomplish that day, and that can guide your choices. “Maybe I’m going to push my speed faster on cardio, and therefore, I’m going to do it first—or I’m going to try to hit a heavier weight this session, therefore, I should do that first,” Rountree says.

Sometimes, logistics makes the decision for you—and that’s okay.

Of course, physiology is one thing—real life is another. There are all sorts of reasons why it might make sense for you to structure your workout in a specific way, despite everything we’ve said above.