Have you recently taken up long distance running?
So with all that's going on at the moment with lockdown and the allowance of exercise once a day, a lot of people have taken up running, which is no bad thing. However make sure you don't dive straight from couch to a long distance run in the space of a few days. It's all about gradual build up and also strength training to ensure you do not damage your joints or cause an unwanted injury.
It's important to have good joint health if you are running some distance, to withstand such a repetitive, high impact exercise. If you are used to sitting at a desk all day and aren't a runner, then you are likely to have reduced joint health and you could end up with an injury. If you are long distance running and have not previously been a runner then it's important to load the joints gradually over time with incremental mileage increases and also resistance training. Start with a proper training program for your running, so you increase gradually, this will help protect your knees from injury and joint trouble. Cardio health improves quicker than your joint health and therefore pushing hard and fast too quickly can cause stress fractures from overuse.
To begin with it can be a good idea to start with walking/running intervals. It's also important to ensure you have rest days to allow your body to recover and do not do long runs back to back every day.
It's also important that you don't just focus on your legs, core strength is equally important and a study has shown that it can help improve your running speed and endurance if you incorporate core exercises into your workout.
You should aim to keep your abs, back and legs strong if you are planning on long distance running. There will be lower impact on your joints the stronger your muscles are. Stretching is also key, before and particularly after a run, focusing on calves, quads, hamstrings and glutes.
Don't forget to also ensure you have the right shoes for the job, this can really make a difference to your run and to the impact on your joints.