You are required to perform ritual ghusl as best as you can. I cannot understand how someone can engage in sexual intercourse and yet is unable to bathe! Ritual ghusl does not require any rigorous exercise. It is a simple procedure. For details, let me cite here one of my earlier answers:

“The proper method of ghusl (ritual bath) involves the following steps:

1- Make the Niyyah (intention) to perform ghusl for purification.

2- Wash your private parts thoroughly with water.

3- Perform wudu’ (ablution) except for washing of your feet, which you can do later while bathing the body.

4- Wash the entire body, starting with your head and the right side, followed by the left.

5- It is preferable to wash the whole body three times. However, the minimum is once, and it would also suffice.

Having completed the above, you are considered eligible to perform the salah (prayer).”

Having said this, I would like to add: If you are not able to follow each of these steps because of your ill health, it is enough to pour water over your body at least once. By doing so, you are eligible to perform salah and other acts of worship.

In conclusion, you ought to perform at least the minimum form of ghusl unless your physician orders you that you cannot use water or water is not available.

Almighty Allah knows best.