The main purpose of the third manned Skylab mission, Skylab 4, was to extend the knowledge of human physiological adaptation to space flight and readaptation to Earth's gravity by continuing the comprehensive a medical research program begun on the Skylab 2 and 3 missions. Since Skylab 4 lasted 84 days, it extended the astronauts' stay in space to almost three months.
In addition to the core biomedical investigations started on Skylab 2, additional inflight tests performed on Skylab 4 included blood flow measurements by an occlusive cuff, facial photographs taken before flight and during flight to study the puffy face syndrome venous compliance, hemoglobin, urine specific gravity, anthropometric measurements, treadmill exercise, center of mass, infrared (IR) anatomical photography, taste and aroma evaluation, measurement of atmospheric volatile chemical concentrations in the spacecraft, light flash phenomenon, and stereophotogrammetry.
High school students from across the United States participated in the Skylab missions as the primary investigators of experiments that studied astronomy, physics and fundamental biology. The student experiments performed on Skylab 4 included the study of x-ray stellar classes, sensorimotor performance, plant growth, plant phototropism, capillary study and neutron analysis.
The crew's health was assessed on Skylab by collecting data on dental health, environmental and crew microbiology, radiation, and toxicological aspects of the Skylab orbital workshop. Other assessments were made of the habitability of the crew quarters in Skylab, astronaut maneuvering equipment, and crew activities/maintenance experiments were examined on Skylab 2 through 4 to better understand the living and working aspects of life in space.