You’re tired, and someone tells you to go for a run. It sounds like bad advice, like being told to spend money you don’t have. But exhausted people who start exercising regularly usually end up with more energy, not less. The bigger surprise is how little it takes. In the best-known trial on this question, the gentler workout reduced fatigue more than the harder one.
This article is part of our complete guide on how to increase your energy levels naturally. It covers what the research says about exercise and fatigue, why low intensity is often the better place to start, how to tell if you’re overdoing it, and the one group of people for whom “just exercise more” is the wrong advice. It is general information, not medical advice.
Does Exercise Really Give You More Energy?
Yes, and the evidence is stronger than most people expect. It comes in two forms: what one workout does to how you feel that day, and what weeks of regular exercise do to your baseline.
The long-term effect: regular exercise lowers fatigue
The most up-to-date summary is a 2022 systematic review and meta-analysis by Wender, Manninen and O’Connor in Frontiers in Psychology. They pooled 81 randomized trials with 7,050 participants and found that regular exercise:
- reduced feelings of fatigue by a small amount (effect size g = −0.37),
- increased feelings of energy by a small-to-moderate amount (g = 0.42), and
- increased feelings of vitality by a moderate amount (g = 0.54).
The results held up when the authors re-ran the analysis without outlier or unusually influential studies. “Small to moderate” may not sound like much, but this is the average across thousands of people with very different starting points and programmes, from walking groups to resistance training. It’s a reliable, repeatable effect, not a one-off finding.
This builds on an earlier review by the same research group. Puetz, O’Connor and Dishman’s 2006 meta-analysis in Psychological Bulletin pooled about 70 randomized trials with more than 6,800 people. According to the University of Georgia’s summary of that work, more than 90% of the studies found that people who exercised reported less fatigue than people who didn’t. Many of the participants in those trials were older adults or people living with chronic illness, so the benefit isn’t limited to people who were already fit.
The short-term effect: one session can lift your energy
You don’t have to wait weeks to notice anything. The 2022 review summarises earlier work from the same group showing that a single session of roughly 20–40 minutes reliably raises feelings of energy. The drop in fatigue showed up mainly after at least 20 minutes of low-to-moderate intensity exercise. That’s a brisk walk, not a punishing interval session.
Why Low Intensity Can Beat Pushing Harder
The study that put this on the map is a 2008 randomized controlled trial by Puetz, Flowers and O’Connor, published in Psychotherapy and Psychosomatics. The researchers recruited 36 sedentary young adults who had felt persistently fatigued, with no diagnosed medical condition to explain it. They were split into three groups for six weeks:
- Low intensity: cycling at about 40% of their peak aerobic capacity, 20 minutes, three times a week. This is easy enough to hold a conversation.
- Moderate intensity: the same schedule at about 75% of peak aerobic capacity. This is noticeably harder work.
- Control: no exercise.
Both exercise groups felt more energetic. The university’s summary of the results put the energy increase at about 20% in both. The difference was in fatigue. Fatigue symptoms fell by about 65% in the low-intensity group and about 49% in the moderate-intensity group. In the authors’ words, the more favourable fatigue outcome came from low-intensity exercise.
One more detail matters. The improvements in energy and fatigue were unrelated to changes in aerobic fitness. People didn’t feel better because their hearts and lungs got stronger in six weeks. The authors suggest exercise may act more directly on the brain systems that regulate energy and fatigue, though that explanation is still a hypothesis.
Keep this study in proportion. It was small, it involved young adults, and it was one trial. It doesn’t prove that low intensity is always better. What it does show is that, for a tired person, easy exercise is not a watered-down second choice. It can work at least as well as harder exercise, and it’s far easier to keep doing.
Why that matters in practice
When you’re exhausted, the biggest risk isn’t picking the “wrong” intensity. It’s doing a hard workout, feeling wiped out afterwards, and quitting by week two. Low intensity solves that problem:
- It doesn’t leave you drained for the rest of the day.
- It’s easier to repeat three or more times a week, which is what the trials actually tested.
- It doesn’t eat into the recovery you may already be short on if your sleep is poor.
You can build up intensity later. Harder training has its own well-documented benefits for long-term health. Our articles on VO2 max and exercise intensity and on the best exercise for heart health cover that side. For energy, especially when you’re starting from tired, easy and regular comes first.
How to Start Exercising When You’re Exhausted
Here’s a practical way to put the research into action. It mirrors the low-intensity group in the 2008 trial.
1. Start with 20 minutes, three times a week
That was the dose in the trial. A brisk walk, an easy bike ride, a swim, or a session on a walking pad all count. If 20 minutes feels like too much right now, start with 10 and add a few minutes each week.
2. Use the talk test
At low intensity you should be able to speak in full sentences. You’re breathing a little harder, but you’re not out of breath. If you can only get out a few words at a time, ease off. This is roughly the same zone as Zone 2 cardio, or a bit easier.
3. Pick a time that protects your sleep
Many people find a walk in daylight, in the morning or after lunch, works well. Moving after a meal can also help with the post-lunch dip. If a late-evening workout leaves you wired at bedtime, move it earlier.
4. Judge it by the next day, not the next hour
Feeling pleasantly tired straight after exercise is normal. What matters is how you feel the following day. If you’re more energetic over a couple of weeks, you’re on the right track. If you’re consistently worse the next day, read the next section.
5. Work toward the guidelines, gradually
The World Health Organization’s 2020 guidelines recommend that adults get 150–300 minutes of moderate-intensity activity a week, or 75–150 minutes of vigorous activity, plus muscle-strengthening activity on two or more days. The guidelines also stress that some activity is better than none. Three 20-minute walks is 60 minutes, which is a real start, not a failure to meet the target.
When Exercise Makes Fatigue Worse: Know the Warning Signs
For most tired people, gentle exercise helps. But there are times when it doesn’t, and pushing through is the wrong move.
Post-exertional malaise and ME/CFS
Some people get dramatically worse after physical or mental effort. The crash often comes a day or more later and can last days. This is called post-exertional malaise, and it is the hallmark of myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). It is very different from ordinary tiredness.
For people with ME/CFS, the UK’s National Institute for Health and Care Excellence (NICE) guideline published in 2021 (NG206) says that any programme based on fixed, step-by-step increases in physical activity, such as graded exercise therapy, should not be offered as a treatment. It also says no therapy based on exercise is a cure for ME/CFS. NICE recommends energy management (pacing), led by the person themselves with support from a specialist team.
So if exercise reliably leaves you much worse a day or two later, or your fatigue has lasted for months with symptoms like unrefreshing sleep, brain fog and dizziness on standing, don’t try to train through it. See a doctor first.
Medical causes worth ruling out
Exercise can’t fix tiredness caused by something it doesn’t touch. Two common examples are low iron stores and sleep apnea. Thyroid problems, diabetes and depression are others. The NHS advises seeing a GP if you’ve been tired for a few weeks without an obvious reason, or if the tiredness affects your daily life or comes with other symptoms such as weight loss or low mood.
Also see a doctor before starting a new exercise routine if you have chest pain, breathlessness, dizziness or palpitations with activity, or a known heart condition.
Fatigue during cancer treatment
Exercise also helps with one of the most stubborn kinds of fatigue. A Cochrane review (Cramp and Byron-Daniel, 2012) of 56 studies with 4,068 participants found that exercise reduced cancer-related fatigue compared with usual care, with aerobic exercise showing the clearest benefit. The effect was modest, and most participants had breast cancer. If this applies to you, plan any exercise with your care team.
Frequently Asked Questions
Should I exercise when I’m tired?
Usually, yes, as long as you keep it gentle. A 20–40 minute session of low-to-moderate exercise, like a brisk walk, tends to raise energy and lower fatigue. The exceptions are when you’re ill, badly sleep-deprived, or when exercise reliably makes you much worse the next day.
What is the best exercise for fatigue?
The best exercise is the one you’ll do regularly. Research suggests low-intensity aerobic exercise, at a pace where you can still hold a conversation, works at least as well as harder exercise for reducing fatigue. Walking, easy cycling and swimming are good starting points.
How long does it take for exercise to improve energy levels?
A single session can lift your energy the same day. In trials of regular exercise, people reported meaningful improvements in energy and fatigue within about six weeks of training three times a week.
Why do I feel more tired after exercising?
Feeling pleasantly tired straight after a workout is normal, especially if you’re new to it or went too hard. If you feel much worse a day or two later and it happens every time, scale back and talk to a doctor. Severe crashes after effort can be a sign of post-exertional malaise.
Is walking enough exercise to boost energy?
Yes. Brisk walking is low-to-moderate intensity, which is exactly the range the research links with less fatigue. Three 20-minute walks a week is a solid start, and you can build toward the WHO guideline of 150 minutes a week from there.
This article is for general information and is not medical advice. Talk to a qualified healthcare professional if you have persistent or unexplained fatigue, or before starting exercise if you have a medical condition.
Sources
- Wender CLA, Manninen M, O’Connor PJ. The effect of chronic exercise on energy and fatigue states: a systematic review and meta-analysis of randomized trials. Frontiers in Psychology, 2022;13:907637.
- Puetz TW, O’Connor PJ, Dishman RK. Effects of chronic exercise on feelings of energy and fatigue: a quantitative synthesis. Psychological Bulletin, 2006;132(6):866–876.
- Puetz TW, Flowers SS, O’Connor PJ. A randomized controlled trial of the effect of aerobic exercise training on feelings of energy and fatigue in sedentary young adults with persistent fatigue. Psychotherapy and Psychosomatics, 2008;77(3):167–174.
- Cramp F, Byron-Daniel J. Exercise for the management of cancer-related fatigue in adults. Cochrane Database of Systematic Reviews, 2012;(11):CD006145.
- National Institute for Health and Care Excellence. Myalgic encephalomyelitis (or encephalopathy)/chronic fatigue syndrome: diagnosis and management (NG206), 2021.
- Bull FC, et al. World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine, 2020;54(24):1451–1462.
- NHS. Tiredness and fatigue (nhs.uk).
