Skylab 3 continued a comprehensive medical research program that extended the data on human physiological adaptation and readaptation to space flight collected on the previous Skylab 2 mission. In addition, Skylab 3 extended the astronauts stay in space from approximately one month to two months. Therefore, the effects of flight duration on physiological adaptation and readaptation could be examined.
A set of core medical investigations were performed on all three Skylab manned missions. These core investigations were the same basic investigations that were performed on Skylab 2, except that the Skylab 3 inflight tests were supplemented with extra tests based on what researchers learned from the Skylab 2 science results. For example, only leg volume measurements, and preflight and postflight stereophotogrammetry, and in-flight maximum calf girth measurements were originally scheduled for all three Skylab missions. In-flight photographs from Skylab 2 revealed the puffy face syndrome which prompted the addition of in-flight torso and limb girth measurements to gather more data on the apparent headward fluid shift on Skylab 3. Other additional tests included arterial blood flow measurements by an occlusive cuff placed around the leg, facial photographs taken before flight and during flight to study the puffy face syndrome, venous compliance, hemoglobin, urine specific gravity, and urine mass measurements. These inflight tests gave additional information about fluid distribution and fluid balance to get a better understanding of the fluid shift phenomena.
The Skylab 3 biological experiments studied the effects of microgravity on single cells and cell culture media. Human lung cells were flown to examine the biochemical characteristics of cell cultures in the microgravity environment. Also studied was the stability of the circadian rhythm of a mammalian system during space flight, and the phenomenon of temperature compensation in an insect's circadian rhythm. Because the objectives of the two experiments were similar, they were packaged together as an integrated unit.