Why am I so tired after working out?

title of article in front of picture of dumbells, phone, and water bottle

If you’ve recently started a new exercise routine and thought you’d be benefiting from a runner’s high but instead have been met with fatigue after your workout, you’re not alone. There are many reasons why you might be left feeling more tired after working out than you did prior. 

Boosting your energy with exercise is key to maintaining your new routine. In this article you’ll read about the top reasons why you might feel tired after working out and how to fix this issue. 

Common causes of fatigue after a workout:

  • Underfueling
  • Dehydration
  • Lack of sleep

Avoid under fueling

Underfueling means that you either aren’t getting enough to eat before and/or after exercise or you aren’t getting enough nutrients in your diet. Here are some tips to avoid underfueling.

Pre-workout nutrition

You should eat 1-2 hours before exercise. If eating a larger meal, give yourself closer to two hours to digest the meal before exercising, but if you’re having a snack before exercise then you might be fine with just one hour prior. Aim to include easy-to-digest carbohydrates plus a small amount of protein. 

Snack ideas:

  • Peanut butter on toast
  • Small bowl of plain cheerios with milk (dairy or soy for the protein)
  • Banana with peanut butter spread on it
  • Whole milk greek yogurt with honey

Post-workout nutrition

Eat within an hour of completing a workout for the best muscle repair benefits. Again, this can be a full meal or a snack. Aim to include carbohydrates, protein, and water or an electrolyte drink if you were sweating a lot or exercising for more than an hour. 

Snack ideas:

  • Trail mix cookies + milk 
  • Hummus and crackers
  • Shredded wheat with milk
  • Whole milk Greek yogurt with granola and berries
  • Avocado toast with ground flax seeds and eggs

A nutrient-dense diet

Although pre- and post-workout nutrition is important, it’s even more critical to be getting enough nutrients from the food you’re eating throughout the day. 

A well-balanced diet includes food from all of the food groups so avoid diets that exclude entire groups like low carb diets, or fat free diets. Your body needs nutrients from carbs, fat, and protein plus micronutrients (aka vitamins and minerals) from each food group. 

Sample meal plan:

  • Breakfast: grain + protein + fruit (e.g. overnight oats with berries and walnuts)
  • AM snack: fruit + dairy (e.g. yogurt and an apple)
  • Lunch: vegetable + protein + starch (e.g. tuna salad, crackers, cheese stick, salad with dressing)
  • PM snack: grain + protein (½ or full peanut butter sandwich)
  • Supper: starch + protein + vegetable (e.g. grilled chicken, sauteed peppers, mushrooms and potatoes in olive oil)
  • PM snack: dairy + grain (e.g. trail mix cookie, milk) 

Prevent dehydration

Dehydration can be a sneaky culprit. It’s a slow onset of fatigue that happens so gradually it can be easy to miss. Although many people, when asked, will admit they probably aren’t drinking enough water. 

Drink at least 64 oz of water/day

Herbal teas, plain water, and sparkling water can all count toward this goal. 

Drink all day, don’t just wait until right before a workout to start hydrating. This will help you avoid needing to stop your exercise for a bathroom break and help you feel more energy throughout the day. 

Limit caffeine

The FDA states that most adults should not consume more than 400 mg of caffeine in a day. This is about 4 cups of brewed coffee. However, some studies show that a cup of coffee before a workout can help with energy and stamina while exercising so you might want to use your limited caffeine intake wisely. Caffeine too close to bedtime can also disrupt sleep which we’ll get to in a bit. 

Electrolyte drinks

Drinks like Gatorade, LMNT, or Liquid IV probably aren’t needed unless you’re sweating a lot during your workout or if you’re exercising for more than an hour. If your workout is less than an hour and you aren’t very sweaty then water is likely enough to keep you hydrated.

Prioritize sleep

It may seem obvious, but getting enough sleep can help prevent you from being tired after working out. Most adults need 7-9 hours of sleep each night. This scientific review showed that not getting enough high quality sleep can increase risk of injury, impair cognition, harm mental well-being, interfere with growth and repair of cells and metabolism of glucose, and lower immune response. 

Tips to improve sleep:

  • Set a bedtime routine to sleep and wake at the same time every day
  • Try meditation or light yoga before bed
  • Limit water intake in the hour or two before bedtime
  • Reduce screen time and light in the room
  • Use white noise if random sounds bother you

It’s ok to sleep and exercise with your natural patterns. If you’re a morning person, go to bed early and exercise in the morning. If you’re a night owl, exercise in the evening. In this study, they found that moderate-intensity exercise in the evening may not impair sleep. 

Other considerations

There are many other reasons you may be tired after working out. Avoid under fueling at meals, aim to eat 3 meals per day with a snack between each meal if you’re hungry. Listen to hunger cues to help guide portions at meals. Include a carbohydrate, protein, fat, and fiber with each meal. 

You can talk to a registered dietitian to get personalized recommendations based on your activity level and individual needs. A dietitian can also help recommend vitamin or mineral supplements based on your food intake, symptoms, and lab work. 

If you are exercising for more than an hour, you may also need to fuel during your workout with gels, gummies, applesauce, or other snacks to refill your glycogen stores (aka the sugar your liver keeps on hand to keep you going during exercise). 

Extreme fatigue may not be normal and could require a visit to the doctor to rule out underlying conditions. 

This information is for educational purposes only and is not meant to be a substitute for medical treatment or diagnosis. You should consult with your doctor before changing your diet or starting supplements for any health condition.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top