Does Exercise Make You Feel More Tired?

Exercise has the potential to boost your energy levels as well as your mental and physical health, but this doesn’t always happen. In fact, depending on how you approach exercise, it may have the opposite effect. This blog looks at how exercise can leave you feeling more tired or give you more energy, depending on how you approach it, plus tips on how to avoid feeling lethargic during and after a workout.

What happens to our bodies when we exercise?

When you work out, your muscles use sugar and burn glycogen for energy. This creates lactic acid as a by-product. As lactic acid is carried in your blood, exercising causes fatigue because of its mild acidity. However, other factors like dehydration and low oxygen levels can also cause post-exercise fatigue and even muscle soreness. The good news is that those effects usually go away after a few hours or days.

How to avoid tiredness during a workout

Start off with a light warm-up, like jogging in place for five minutes or pedalling on a stationary bike at an easy pace. End your workout on a positive note. As you approach your final exercise routine, go all out, working up to your hardest set of exercises (like sprinting or lifting weights). During each exercise session, make sure to increase the intensity when possible. The more intensely you can work out without feeling exhausted, the less likely you are to feel drained later in the day.

Post exercise soreness can also be due to Blood Pooling- where lack of cool down causes blood to store “or pool” in the muscles (usually in the legs/feet/ankles) and can lead to swelling and discomfort- a 10 minute light cool down and static stretching (stationary) will allow venous return, essentially the blood will return to the heart evenly distributed and reduce the likelihood or sore muscles.

DOMS (delayed onset muscle soreness) is common in people new to exercise- as their muscles have torn and will feel sore as they rebuild- this is perfectly normal, however can be reduced by “taking it easy” for the first few workouts- and not lifting too heavy early on (even if it feels fine on the day!)

It is also important to remember that after warming up (jogging etc) “Dynamic” stretching is important- this is stretching with movement- e.g. lunges- squats, leg swings- so Warming up= Dynamic, Cooling down = Static

How does exercise increase energy levels?

As a general rule, exercise will not make you feel more tired. In fact, it is likely to make you feel more energised and full of life. This is because when we work out our body produces endorphins which make us feel better and healthier. Also, when we exercise on a regular basis our metabolism speeds up and we burn fat which also improves our energy levels.

If you don’t have time for a proper workout, it’s crucial to make sure that at least some small amount of movement fits into your schedule every day. Even if it’s just walking around while you work or catching an extra flight of stairs at lunch, doing something every day will pay off in terms of improving your overall fitness and your ability to fight fatigue later on.

Other chemicals released in exercise are Dopamine + Serotonin (feel good chemicals) as well as Endorphins- which are natural painkillers and mood elevators- which is why many people feel better after a workout and generally less tired.

Exercise can also reduce Cortisol levels- which is the body`s main stress hormones- thus alleviating anxiety and improving mental health.

What type of exercise give us more energy?

The best way to get energy from exercise is a combination of high-intensity and high-duration activities. When we exercise intensely, our heart rate increases dramatically. That increases our metabolic rate so that we burn more calories, even after we stop exercising. We have all experienced after exercise what is called a runner’s high, which is caused by the rush of chemicals in our brain.

Increasing intensity each workout is known as “Progressive overload”- and this does depend on the target- for general fitness- this can be an extra minute running/cycling- or one more set of squats, one more exercise in a circuit.

For weight training, tracking sets and reps is the best way to manage progress- and it is important to vary workouts to maintain motivation and prevent a plateau- increasing weight and reducing reps can promote muscular strength- whilst reducing weight and increasing reps/sets promotes muscular endurance. The key is to modify the workout each week (if comfortable) to push the body a little more- thus creating more microtears in the muscles- which will (with adequate protein intake) repair quicker and stronger. For more information on weight training, you can refer to our strength training guide for beginners.

Likewise, in running/aerobic activity, the heart will strengthen and become more efficient in pumping blood (and oxygen) to the muscles with regular cardiovascular training. For more information on running, you can refer to our ‘how to start running’ guide.


This was written with the collaboration of personal trainer Marcus Bird.