Why do my legs feel heavy and tired when running?

Why are your legs tired after running (or during it)?

There are lots of different reasons why you might have heavy legs after running, from a lack of sleep to overtraining. Let’s take a look at the main factors in more detail.

Overtraining

Yup, that’s right. You might think that you’re doing the right thing by training (and training and training) but if you over train, you can feel super tired. When you’re new to running, you might see lots of improvement quite quickly – and that can be really exciting, spurring you on to run more, or to push harder and faster. But overtraining can see your performance plateau or decrease, rather than making the gains you’d hoped for. When you overtrain, you put too much stress on your body, which – along with heavy legs and decreased performance – can result in physical and mental fatigue, irritability, a higher chance of getting sick, and an increased risk of injuries.

The best way to combat this is to make sure that you don’t do too much too soon – that is, don’t ramp up the intensity and duration too quickly. If you’re new to running, this will help you to build running endurance. And if you’re an experienced runner, it’ll ensure that you stay on track to reach your goals. A training plan can help you to avoid overtraining, whether you’re targeting a 5k or an ultramarathon.

Excessive strength training

Have you been hitting the gym hard? Strength training is beneficial for runners. It can help you to develop your running power and speed and help to prevent injuries. But doing too much can lead to heavy legs, especially if you’ve been doing lots of heavy lower body sessions. If you feel super sore the day after your workout, or even a couple of days later, you’re probably suffering from delayed onset muscle soreness (DOMS). It’s totally normal, but it can make your legs feel like lead when running. It’s a good idea to schedule your strength work into your training plan around your runs.

If you’re training for something specific, then it’s important that your runs are the focus of your plans, with gym sessions supplementing the running. So, if you have a speed session scheduled in, then you probably don’t want to do heavy gym work the day before. Instead, do your speedwork first and then hit the gym. Similarly, avoid too much strength work before your long runs – the long run is key to any training plan, after all, so you want your legs to feel fresh!

Lack of recovery

Do you have rest days scheduled into your plan? Recovery from a run is just as important as the run itself. Both your body and your brain need a break – and without proper rest, you could risk injury, fatigue (both mental and physical), or even burnout. Every training plan should have at least one rest day per week, depending on what you’re training for and how much running experience you have.

As well as rest days, it’s important not to run all of your runs super hard. It might make your Strava stats look good, but you’ll be hurting your progress. Your easy runs should be easy, allowing you to recover from harder runs while maintaining your aerobic fitness. If you keep the pace easy, it’ll help to prevent your legs feeling like lead after running and allow you to put your effort into your long runs and speed sessions.

Not warming up and cooling down

Let’s face it, sometimes we’re all guilty of skipping the warmup and heading straight out the door… But the truth is that both pre- and post-run stretches can really help to reduce runners heavy leg syndrome. Both can help to decrease muscle stiffness, making you feel sprightlier and less like you’ve got dead weights attached to your legs.

You don’t need to devote hours and hours to stretching, but your legs will thank you for taking 5-10 minutes before and after your runs. Your pre-run warm up should be focused on dynamic stretching – think walking lunges, leg swings, walking on your tip toes, bum kicks and high knees. Post-run, you should do dynamic stretches, focusing on all the muscles that have just worked so hard during your run, like your quads, hamstrings, hips, glutes, calves and back. 

Poor running form

Another reason for tired legs could be related to your running form.

Poor running form may cause some muscles to work harder than they should. Overstriding (when your foot lands too far ahead of your body), for example, can put excessive strain on your calves and quads. That means they may tire faster than they otherwise would, which can make them feel tired and heavy. Or, if you heel strike (where you hit the ground with your heel first rather than your forefoot), it can send more impact through your leg which can, again, lead your joints and muscles to fatigue faster. If one leg feels heavy when running but the other is fine, it may mean that one of your legs isn’t as strong as the other, or it could highlight biomechanical differences which are leading to poor form.

Improving your running form will help you to work more efficiently and decrease the risk of tired legs. You may want to get your form checked by a specialist who can check for any issues and advise you on ways to improve.

Alternatively, keep these tips in mind:

• Focus on your posture, keeping upright and avoiding leaning too far forward or backward
• Relax your shoulders
• Drive forward with your arms, swinging them front and back rather than across your body
• Aim for a forefoot strike rather than heel striking
• Keep your core engaged

Dietary deficiencies

As runners, we need to eat enough to fuel our bodies. But it’s not just about how much you eat – it also matters what’s on your plate.

If you eat a low carb diet, it could cause heavy legs. But how can a lack of carbs cause dead legs? Well, carbohydrates are stored in our muscles as glycogen, and when we run, our bodies use these glycogen stores to fuel our muscles. If your glycogen stores are low, your muscles may not have enough energy to perform meaning they’ll feel heavy and fatigued. So, if you’re not eating enough carbohydrates to provide plenty of energy, it’ll be harder for you – and your muscles – to get through a run. Try to eat a healthy, well-balanced diet that includes healthy sources of carbohydrates like fruit, vegetables and whole grains and you should find yourself with plenty of energy – and legs that are less fatigued!

Another dietary deficiency that can lead to tired legs is a lack of iron. Iron plays an important role in transporting oxygen to your muscles – so if you’re deficient in iron, it’s harder for your muscles to get the oxygen they need. That means they can feel tired and heavy, and since you mostly use your legs when you run, this will translate to the dead leg feeling. Iron is also important for muscle repair and recovery after exercise. If you’re not getting enough iron, it can delay the recovery process, meaning your muscles feel sore for longer. Some great dietary sources of iron include red meat, beans, poultry and dark leafy greens like spinach and kale. You can also take iron supplements – but if you suspect you’re iron deficient, it’s always a good idea to check in with your doctor for proper evaluation and guidance.

Dehydration

Are you drinking enough? If you’re dehydrated, it can cause all sorts of problems, from headaches to muscle fatigue. The importance of staying hydrated can’t be overstated, and if you’re not drinking enough – whether before your runs, during your runs, or afterwards – it can cause heavy legs.

Dehydration can decrease blood volume, meaning there’s less blood circulating around your body. That means your muscles may not get enough oxygen and nutrients when you’re running, causing them to feel tired. Being dehydrated can also disrupt the balance of electrolytes in your system, including calcium, magnesium, potassium and sodium – all of which are important for muscle contraction and nerve function. If you don’t get the right mixture of electrolytes, it can cause cramps and tired legs.

Try drinking to thirst throughout the day – but if you need a little extra help, you could set a reminder on your phone telling you to drink every so often. And remember that you’ll need to drink more in warmer weather! You may also want to start using electrolyte drinks to ensure that you’re getting everything you need. If you’re running for an hour or less, plain water should be fine – but for longer runs, electrolyte drinks can be beneficial.

Sleep deprivation

If you’re not getting enough sleep, your body will let you know about it. When you’re tired, your muscles can feel heavy – and you might also find it more challenging to maintain proper running form, which can further contribute to your heavy legs. What’s more, when you sleep, your body releases hormones that support muscle recovery. So, if you’re not getting enough shut eye, you’re doing your recovery a disservice. And inevitably, if your muscles aren’t getting a chance to repair themselves, they’re going to feel heavy and fatigued.

Everyone needs a different amount of sleep. It’s often said that adults need 7-8 hours of sleep a night, but some people function fine on 6 hours and others need 10 hours. Find out what works for you – and then make sleep a priority. You should also try to maintain a consistent sleep schedule, aiming to go to bed and get up at roughly the same time each day, and improve your sleep hygiene by reducing the amount of screen time you have before bed, ensuring your room is at the right temperature and is dark enough for sleep.

When you get into a groove with your sleep, those 6am runs should feel much less painful!