Do the two rak’ahs of Duha suffice for one’s physical well-being, and does the Duha prayer extend to eight rak’ahs?

There is no hadith stating that the two rak'ahs of Duha prayer are a cause for physical health. However, it is mentioned in a hadith that for every joint in one's body, there is a charity due, and that the two rak'ahs of Duha prayer suffice for that. It is understood from both hadiths that the two rak'ahs of Duha prayer are sufficient as charity for every single joint.