You don’t have to go for walks or runs. You don’t have to be healthy. You are free to do these things or not do these things. Your innate worth never changes because of being healthy or otherwise. Recognize that you can be as you are and still be happy and peaceful.
To be able to experience this innate self worth, happiness and peace and more conscious control of our actions, we need to learn to live as our true self. Practicing meditation teaches this. This article gives information on how to practice meditation. Practices for people who have difficulty on starting meditation is also given in another sub-article. The sub-article (What if meditation is too difficult?), will give more effort based techniques that can build up peace and the ability to concentrate. Then, a person can begin awareness based meditations with more ease. Self awareness is the key to self control. With greater self control you can better direct your life towards exercise and healthy living. The wording of the question indicates it is for people who do not know exactly how to do this, and also with a mind/emotions which make it difficult to go towards the result desired by the questioner. The solution is to learn to bring the mind to ease, and then practice self awareness (by practicing awareness based meditations and maintaining the state of meditativeness throughout the day) to create the experience of greater self control to be able to go towards the desired result.
As you keep advancing in meditation, your awareness of the pure creative life force energy within you will increase and you will learn to stay focused on this energy. This will in time purify your mind/emotions, reprogram them in a way that you are less dependent on things from outside for your happiness and more centered on this innately available energy. You will be able to create peace in your mind and from this state, you will be naturally able to see what you truly want and be already engaging in that.
As an example, if you are dependent on certain foods that create lethargy and sluggishness in your body and too much activity in your mind and your emotions, your meditation practice will in time transform your dependency in these foods into more healthy ones, by your own freewill choice, and then you will have more peace of mind and energy to exercise.
Another example is, if you have some energy but your depression is holding you down, just practicing some breath exercises given in the sub-article can possibly give you some inner space/peace to go for a walk. Or you may need to take some more time to practice and do some other changes in your life, but you will definitely notice the changes from the beginning.