Experts Explain How Pre-Workout Affects Your Body

To pre-workout or not to pre-workout.

Oversized young Caucasian woman drinking water after running in a public park.
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It can be hard to overcome that post-workday slump to power through a sweat session. Enter pre-workout, an exercise supplement popular for it’s energy- and performance-enhancing effects. And if that sounds like the energy boost you’ve been looking for, understanding how pre-workout affects your body can help you determine if it’s the supplement for you.

Pre-workout supplements are intended to increase your stamina and exercise performance, and are often powders that you mix into water. You take it about half an hour before your workout so that common ingredients like caffeine or extra vitamins can kick in just in time for your gym sesh. Though many people swear by its energy-boosting effects, pre-workout formulas vary widely and everyone responds differently to them, so it can have mixed results, says Christina Jax, a registered dietitian and nutritionist and health advisor for Lifesum and Gympass.

To help you decide if the supplement is right for you, nutrition experts explain how pre-workout affects your body and whether or not you should use it.

How Pre-Workout Affects Your Body

It can be hard to summon the strength to slay a workout, and pre-workout can be just the boost you need to get your sweat on, says health and wellness coach Emma Middlebrook, owner of REP Movement gym. Pre-workout typically promises increased strength, stamina, endurance, focus, and blood flow, and there’s research to show that certain ingredients can provide these benefits. For instance, ingredients like L-arginine and L-citrulline can help your body produce nitric oxide, says Dr. Mark Farber, an internal medicine doctor and chief scientific officer of OFFFIELD plant-based hydration company. Nitric oxide helps boost circulation, and that extra blood flow to your brain and muscles can help you think clearly and perform better while you exercise.

Other common ingredients like caffeine and creatine are responsible for giving you that jolt of energy and strength you need to carry you through your fitness routine. Even better, research shows that creatine can help speed your post-workout recovery and improve overall muscle mass.

But you can have too much of a good thing, cautions Jax. While some amount of caffeine can help you stay alert and active throughout your workout, too much of it can cause shakiness, anxiety, and increased heart rate and blood pressure, all of which can actually decrease performance. This is especially true for people with caffeine sensitivities, she says, who may feel jittery or sick after ingesting the stimulant even in small doses. The same goes for consuming too much creatine (that’s around 10 g or more in a single serving, according to 2008 research in the journal Research in Sports Medicine), which can cause digestive symptoms like upset stomach or bloating.

And watch out for added sugars, says Farber. Many pre-workouts include artificial sweeteners or flavors like aspartame or sucralose, and although they make the supplement taste good, they can actually do more harm than help. Too much sweetener can cause unpleasant digestive symptoms like gas or bloating, which make for an uncomfortable workout.

Should You Try Pre-Workout?

Well, it depends, says Jax. “Nutrition is not a one-size-fits-all approach,” she tells Bustle. “Give your body whole foods and hydration and see how it performs. But if time is not on your side and you cannot get these nutrients through food prior to a workout, look for a supplement that has some of those elements.”

Snacks like oranges, rice cakes with peanut butter, or a cup of coffee about an hour before your workout are a more reliable first line of defense against an energy slump, she explains.

If you have a heart disease or high blood pressure, Jax says to steer clear of pre-workouts that include caffeine to avoid aggravating your condition. And if you’re pregnant, have diabetes, or a kidney- or liver-related issue, she advises checking in with your doctor before trying pre-workout to avoid stressing out your body with unnecessary side effects.

That said, if you don’t have any pre-existing conditions, Middlebrook says that pre-workout is a solid option to squeeze in some energy in time to hit the gym, especially when prepping a full snack isn’t in the cards. Just make sure to check the ingredients list before you pick a supplement to ensure that there’s limited sweeteners or ingredients that don’t sit well with you, like caffeine, says Jax.

How To Take Pre-Workout

Just how much pre-workout you consume depends on your supplement of choice, so follow the instructions on the label to make sure you’re taking the right amount. Middlebrook recommends easing in with a lower dose to allow your body time to adjust (she suggests starting with about half the recommended serving), then gradually increasing your dosage until you get the effects you’re looking for.

Jax also cautions against taking pre-workout before every single sweat sesh since food is a healthier, more trustworthy source of energy to rely on in the long term. And if you’re an evening exerciser, she recommends avoiding pre-workout formulas that contain caffeine, since that can mess with your sleep and affect your performance the next day.

Bottom line? Go for food first, but if you must use pre-workout, pick a product that’s best suited to your needs and sensitivities. “Pre-workout supplements have different impacts depending on the each athlete’s experience, metabolism, and type of exercise,” Farber tells Bustle. “Every body is different, and every workout is too.”

Studies referenced:

Bescos, R. (2012). The effect of nitric-oxide-related supplements on human performance. Sports Medicine, https://pubmed.ncbi.nlm.nih.gov/22260513/

Jagim, A. (2019). Common Ingredient Profiles of Multi-Ingredient Pre-Workout Supplements. Nutrients, https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6413194/

Kreider, R. (2017). International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition, https://pubmed.ncbi.nlm.nih.gov/28615996/

Makinen, K. (2016). Gastrointestinal Disturbances Associated with the Consumption of Sugar Alcohols with Special Consideration of Xylitol: Scientific Review and Instructions for Dentists and Other Health-Care Professionals. International Journal of Dentistry, https://pubmed.ncbi.nlm.nih.gov/27840639/

Ostojic, S. (2008). Gastrointestinal distress after creatine supplementation in athletes: are side effects dose dependent? Research in Sports Medicine, https://pubmed.ncbi.nlm.nih.gov/18373286/

Pickering, C. (2019). Caffeine and Exercise: What Next? Sports Medicine, https://pubmed.ncbi.nlm.nih.gov/30977054/

Temple, J. (2017). The Safety of Ingested Caffeine: A Comprehensive Review. Frontiers in Psychiatry, https://pubmed.ncbi.nlm.nih.gov/28603504/


Mark Farber, MD, PhD, an internal medicine doctor and chief scientific officer of OFFFIELD plant-based hydration company

Christina Jax, RDN, LDN, CLT, RYT, a registered dietitian and nutritionist and health advisor for Lifesum and Gympass

Emma Middlebrook, a certified personal trainer, certified health and wellness coach, and owner of REP Movement in Portland, Oregon