6 Unexpected Causes Of Post-Workout Fatigue

Hint: You probs need more water.

Why do I feel tired after working out? Experts weigh in on the culprits behind post-workout fatigue.

It’s one thing to feel out of breath for a few minutes after a workout, but it’s something else entirely if that fatigue lingers long after you’ve left the gym. If you’re still drained hours later and can feel yourself swearing off exercise forever, there may be a few things you need to adjust.

Even though they can be tough, a workout should never feel like a drag, says Dr. Emeka Aludogbu, a sports medicine doctor and founder and CEO of Enovate SportsMed. “You should feel a burst of energy post-workout,” he tells Bustle. That’s how you’ll know you hit the sweet spot where you pushed yourself just hard enough but not so hard that you’re completely burned out.

Of course, some workouts will be harder and more draining than others. You might feel like you need to do some extra recovery after a long run, tough weight training session, or hour-long spin class. But even then, there are a few signs to look out for that indicate your fatigue isn’t normal. Mental fog, feeling like you need a nap, and dizziness are all red flags, says Aludogbu. You may also want to investigate if you feel uncoordinated, have joint pain, or if you still feel sluggish during your next workout, adds Sandra Gail Frayna, PT, a physical therapist and founder of Hudson Premier Physical Therapy & Sports.

The above symptoms are all signs you need to cut back, take a break, or even adjust how you’re eating, drinking, or sleeping so that you can actually enjoy your workouts — and get the most out of them, too. With that in mind, here are a few possible reasons why you feel so tired after working out.

1. You Forgot To Have A Post-Workout Snack


If you feel exhausted after your exercise session, it might be because you didn’t refuel with a post-workout snack. Aludogbu recommends having a meal 45 minutes to an hour after exercising to replenish your body and give it what it needs to recover. “It takes a lot of energy to rebuild the muscle fibers that have been broken down and/or torn in the process [of exercising],” he says, so aim to include all the best building blocks, like carbs and protein, in order to avoid excessive fatigue.

2. You’re Missing Key Nutrients

If you’re dragging hours after your sweat sesh, consider what you ate beforehand, too. “Skipping meals or not eating enough can hinder exercise performance,” says Patricia Kolesa, MS, RDN, a registered dietician nutritionist, so don’t forget to have a carb and/or protein-packed snack before you exercise.

The protein will help your muscles rebuild after your workout, she tells Bustle, and the carbs will fuel you during it. “When we consume carbohydrates as a part of our diet, it gets stored in the form of glycogen,” Kolesa says. “The body uses that glycogen as a source of fuel during exercise.” (That’s why runners are big fans of eating pasta before a race.)

3. You’re Dehydrated


Another common culprit behind post-workout fatigue is dehydration. Water plays a role in helping you maintain the right body temperature, it lubricates your joints, and it naturally invigorates you, says Andrew Lenau, an ISSA-certified personal trainer and sports nutritionist — so if you’re not getting enough of it, your body doesn’t have everything it needs in order to recover optimally. A telltale sign you’re dehydrated is if your urine is dark. Carry a water bottle with you to the gym, and you might still have a spring in your step when you leave.

4. You Didn’t Get Enough Sleep

If you go into a workout tired, it only stands to reason that you’d struggle to get through it. What’s more, lack of sleep can also play a role in how you recover once you set your dumbbells down. “Beginning a workout with fatigue is not an effective way to train as it can increase your risk of injury and poor performance,” Frayna says. “Additionally, sleep deprivation will also lead to quicker and greater fatigue post-workout.”

It’s best to aim for at least seven hours of good sleep a night, says Anthony Maritato, PT, a licensed physical therapist and certified strength and conditioning specialist, in order to wake up refreshed and fully recovered. “Our bodies repair muscle damage and immune function while we sleep,” he tells Bustle. “If we are not sleeping well, we are not repairing our bodies — and as a result, normal workouts result in the accumulation of tissue trauma and excessive fatigue.”

5. You Skipped Rest Days


While it can be tempting to work out every day to reach your goals, rest and recovery — aka taking days off to chill — is the key to feeling great and making progress without feeling exhausted. “Insufficient recovery between workouts may happen when you are exercising too frequently,” Maritato says. “This might mean working out too many days a week or multiple workouts in a day.”

You’ll know you’re in dire need of a rest day if you notice a decline in your performance, increased muscle soreness, or if you start to develop overuse injuries like knee pain, shin splints, tendonitis, or bursitis, Maritato says. Listen to your body to know when to take it easy, but in general, it’s best to take two rest days per week.

6. You Exercised Too Hard

While you might not think it’s possible to exercise too hard — especially if a trainer keeps yelling at you to push it — you actually can overdo it during a workout, which would lead to excessive fatigue afterward. To make sure you aren’t pushing past your limits, keep an eye on your intensity levels, especially if you’re brand new to exercise. It’s also recommended to go easy when starting a different routine until you know what your body is capable of, Frayna says.

It’ll help to aim for the aptly named “Goldilocks zone” where you exercise just hard enough to improve your endurance and muscle strength, but not so hard that you burn through your energy stores and crash afterward, Maritato says. In other words: You don’t want to be crawling off your exercise mat.

You’ll know you’re in the right zone if you leave your workout feeling energized, accomplished, and ready to move on to the next part of your day.

Studies referenced:

Ament, W. (2009). Exercise and fatigue. Sports Med. doi: 10.2165/00007256-200939050-00005.

Beck, KL. (2015). Role of nutrition in performance enhancement and postexercise recovery. Open Access J Sports Med. doi: 10.2147/OAJSM.S33605.

Besedovsky, L. (2011). Sleep and immune function. Pflugers Archiv, 463(1), 121-137.

Charest, J. (2020). Sleep and Athletic Performance: Impacts on Physical Performance, Mental Performance, Injury Risk and Recovery, and Mental Health. Sleep Med Clin. doi: 10.1016/j.jsmc.2019.11.005. PMID: 32005349.

Chennaoui, M. (2021). How does sleep help recovery from exercise-induced muscle injuries? J Sci Med Sport. doi: 10.1016/j.jsams.2021.05.007.

Cote, J. (2008). Effects of fatigue on intermuscular coordination during repetitive hammering. Motor Control. PMID: 18483444 DOI: 10.1123/mcj.12.2.79

Dolezal, B. A. (2016). Interrelationship between Sleep and Exercise: A Systematic Review. Advances in Preventive Medicine, 2017.

Meeusen, R. (2021). Endurance exercise-induced and mental fatigue and the brain. Exp Physiol. doi: 10.1113/EP088186.

Wender, C. L. (2022). The Effect of Chronic Exercise on Energy and Fatigue States: A Systematic Review and Meta-Analysis of Randomized Trials. Frontiers in Psychology, 13.

Yang, D-F. (2019). Sleep deprivation reduces the recovery of muscle injury induced by high-intensity exercise in a mouse model. Life Sci. PMID: 31493480 DOI: 10.1016/j.lfs.2019.116835


Dr. Emeka Aludogbu, sports medicine doctor, founder and CEO of Enovate SportsMed

Sandra Gail Frayna, PT, physical therapist, founder of Hudson Premier Physical Therapy & Sports

Patricia Kolesa, MS, RDN, registered dietician nutritionist

Anthony Maritato, PT, licensed physical therapist, certified strength and conditioning specialist