What is the relationship between health and prayer?

All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.

What we have understood from your question is that you are inquiring about the health benefits of prayer. In fact, the Islamic prayer has many, significant health benefits, which Allaah, the Exalted, confers upon His obedient slaves who observe the prayer. Indeed, Muslims perform prayer in adherence to the commands of Allaah, the Exalted, seeking His satisfaction and hoping to draw closer to Him. However, when a worshipper performs prayer, he is actually performing physical exercises for all his body parts from head to toe. Each movement in prayer is an excellent physical exercise for the muscles, joints, tendons and ligaments of the entire body. This brings most of the muscles of the body, if not all, in active motion, serves to give them some exercise and helps strengthen them.

If a worshipper is told that he is performing at least fifty different movements during prayer every day, he will be astonished. In fact, as will be clarified later, a worshiper is actually doing much more than this. Prayer is just a simple and gentle, yet regular, exercise and few movements that are done five times a day. Were we to calculate the number of such movements (performed during the daily prayers) precisely, we would have been in awe of such a great number. 

Dr. F. Azure, a specialist in nerve and joint disorders in American universities said:

The prayer of the Muslims, altogether with the bowing (or genuflection) and prostration, strengthens the back muscles, softens vertebrae and fosters the maintenance of the mobility of vertebral joints), especially if the prayer is performed from an early age. Moreover, it materializes immunity from the diseases of muscles surrounding the spine. Different sorts of nerve disorders cause tense pains as well as muscular spasms and cramps.

Such great health benefits of prayer can be underlined by any fair-minded doctor. In fact, there are numerous physical benefits in the Islamic prayer. Allaah, the Exalted, says (what means): {And seek help through patience and prayer, and indeed, it is difficult except for the humbly submissive [to Allaah], who are certain that they will meet their Lord and that they will return to Him.} [Quran 2:45-46]

Therefore, Islam urges Muslims to observe the prayer and hold on to this great obligation. Even sick people are asked to perform the due prayers while standing, sitting down or even lying down on their sides, each according to his ability. All these great benefits of prayer are reaped by those who observe this great obligation and not by Allaah, the Exalted. In fact, Allaah, the Exalted, did not prescribe the prayer except for the benefit of people. The wrath of Allaah Almighty that those who neglect the obligation of observing the prayer incur is not because they are causing harm to Him in any way. Rather, it is because they have wronged themselves.

Allaah Knows best.