In my opinion, the best way to accomplish this is with two incubators. Grow cells in the standard conditions. At the time of experiment, transfer cells to temperature and gas pre-equilibrated media in secondary incubator. Simple!
In my opinion I don't think this is an easy question to answer and would depend on the objective of the study. If you want to simulate what happens in an animal under heat stress then you would need to know what type of heat fluctuations there really are in the muscles themselves - the body's temperature as you would know is a tightly regulated mechanism and it may be that heat stress at the muscle level manifests in ways other than temperature.