If Christ dwells in our body, how much care of our body should we take regarding smoking or exercise?
The Bible instructs believers to treat our body with respect knowing that it is the dwelling place of the Spirit:
1Cor. 6:18 Flee immorality. Every other sin that a man commits is outside the body, but the immoral man sins against his own body.
1Cor. 6:19 Or do you not know that your body is a temple of the Holy Spirit who is in you, whom you have from God, and that you are not your own?
1Cor. 6:20 For you have been bought with a price: therefore glorify God in your body.
Paul's principle concern was avoiding sexual immorality, which desecrates our physical body. Instead, we should live in such a way that we glorify the Lord with our body. In matters of food or drink (or by extension, anything else we put in our bodies), we have liberty:
Col. 2:16 Therefore no one is to act as your judge in regard to food or drink or in respect to a festival or a new moon or a Sabbath day —
Col. 2:17 things which are a mere shadow of what is to come; but the substance belongs to Christ.
Nevertheless, if our choices bring discredit on Jesus or call into question our witness, then we should abstain from such things:
Rom. 14:20 Do not tear down the work of God for the sake of food. All things indeed are clean, but they are evil for the man who eats and gives offense.
Rom. 14:21 It is good not to eat meat or to drink wine, or to do anything by which your brother stumbles.
So there are no specific set of rules for how a Christian should care for the physical body other than do not sin with your body nor cause others to sin by your example.