Which comes first: shampoo or conditioner? Easy. It's always shampoo. If only exercise were that simple. No matter how good we get at understanding exercise science, there are still some topics that seem forever debatable. One of those topics is whether to do cardio or weights first. Which one comes first? We'd like the answer to be simple, but it’s a bit complicated. The good news? I’ll explain how it can be simple for you. It's only a complicated and difficult question if we are after an answer that applies to everyone. The answer for you is likely simple.

First, if you or someone you know has recently joined the new "Never Do Cardio" cult, that's not the answer and please read this first. Extremism in fitness is a dangerous idea, and vacillating between "always" and "never" on a topic misses the mark every time. From crunches to running shoes to cardio, extremism is for lazy thinkers who dislike nuance.

When seemingly simple questions continue to puzzle us it is often because the "simple" question has a nuanced answer that is dependent on numerous factors. And we run into trouble whenever we take what works for one individual and try to make that the template for all of humanity to follow. The "correct" answer to this question can vary from person to person, but by the end of this article, you should have a better idea of how to answer this question for you.

An ACE-commissioned study found that placing cardio exercise after strength created a heart-rate response that was 12 beats per minute higher for the exact same workout intensity and duration. This would seem to present clear evidence that warrants doing cardio first due to the increase in perceived effort from this shift in heart rate and a potential shifting of the intensity from “moderate” to “vigorous” with no modifications to external intensity. In fact, these were the general conclusions of the study.

However, both the lead researcher in the study, Dr. Lance Dalleck, as well as ACE’s Chief Science Officer Dr. Cedric Bryant mentioned that the results of this study should not be taken as an endorsement of an always cardio-first approach to program design. "When working holistically with a client," explains Dr. Dalleck, "the client's needs and goals should drive the development of the exercise program."

Indeed, you can find other equally well-designed studies that conclude that it’s better to perform strength training first because muscle force-generating capacity (a fancy term for "strength") is reduced when doing cardio first, and because there is a slight increase in the use of fat for fuel because the body's carbohydrate stores are depleted first with strength training.

Furthermore, most previous studies looked at the impact of strength and cardio in a single session. A few more recent studies, however, have investigated what is happening to the body’s response and recovery from exercise as a result of strength and cardio together. Here are some highlights:

Running negatively affects strength training more than cycling.

Endurance-training volume should be limited to 20 to 30 minutes to minimize potentially negative effects.

Moderate- to high-intensity endurance training decreases the efficacy of strength training

You are likely now a little confused. As with most things related to fitness, trying to make gray areas into black and white rules rarely works. In fact, the more deeply you look into the question of whether to do cardio or strength first, the clearer it becomes that the only correct answer is: "It depends."

It depends on…

Goals: Fat loss? Weight loss? Feel better? Have more energy for recreational activities? Get stronger?

Attitude/Mindset: Hate exercise? Love it? Sort of enjoy it, but sometimes struggle? Don’t like it, but you do it consistently because you want the benefits badly enough to do it? Hate cardio? Hate strength training?

To help you make sense of the best choice for you, I'll provide a best answer based on some of the individual factors mentioned above.

Is better endurance performance (i.e., shorter times or better performance when running, competing in triathlons, etc.) your main goal? CARDIO first Is your main goal to get leaner or lose weight? STRENGTH first Are you mostly concerned with improving strength? STRENGTH first Are you doing only upper-body strength training today? EITHER one first Are you doing lower-body strength training today? STRENGTH first (Choose strength alone for serious strength goals.) Do you have general fitness goals with no emphasis on strength or endurance? YOUR CHOICE (Do the one you least enjoy first. You’ll ensure it gets done and you’ll do it when you are less fatigued.)

What is confusing for everyone often gets easier to answer for an individual. And this reflects a certain level of sophistication in one’s understanding of fitness. Sweeping recommendations applied to everyone often end up being correct only for those specific individuals who have individual circumstances that render those recommendations correct. If a shoe store only sold one size, everyone would find a poor fit except for the people whose feet are that one size.

Simple is better, but we sometimes cannot reduce a question to a simple answer for everyone. Sometimes, the simple answer is “it’s complicated,” which then becomes simple again when filtered through the needs of the individual.