Astronauts conduct experiments during the Neurolab Spacelab mission aboars shuttle Columbia. Photo: NASA

Experiments conducted in space -- in conditions of microgravity -- have contributed to our knowledge about the effects of exercise on the human machine here on earth. Humans undergo many changes when exposed to microgravity; the most studied effects have been on muscle atrophy (shrinking) and decreasing bone density (which can lead to osteoporosis). The decrease in bone mass in space is similar to the decrease on earth, except that it occurs at a drastically accelerated rate. The loss of bone continues throughout space flight and is extremely difficult to reverse upon return to earth.

Without adequate exercise, astronauts may be at increased risk for falls, osteoporosis, and physical incapacitation during emergencies. Astronauts often suffer from poor balance upon return to Earth, and routinely experience lightheadedness, nausea and vertigo upon standing. Experiments conducted by astronaut James A. Pawelczyk, Ph.D., on the STS-90 Neurolab mission examined whether these effects are caused by changes in the brain and nervous system. Ongoing experiments across the country are attempting to determine whether exercise training is effective in combating these and other effects of space flight.

Dr. Pawelczyk, a professor of physiology and kinesiology at the Pennsylvania State University's Noll Physiological Research Center, was the featured speaker at the American Physiological Society's intersociety meeting, "The Integrative Biology of Exercise," held in Portland, ME, last week.

The Dynamic Regulation of Blood Pressure: Problems with moment-to-moment regulation of blood pressure lead to orthostatic intolerance -- an inability to maintain adequate blood flow to the brain -- that affects as many as 500,000 Americans, many of them younger than 35 years of age. More women than men experience this condition, it is thought, because women have lower blood pressure than men, even when healthy.

Among the symptoms patients may experience with this condition are lightheadedness, palpitations, tremulousness, and poor concentration when standing. Other symptoms when standing upright may include visual changes, discomfort in the head or neck, throbbing in the head, poor concentration, fatigue, weakness, and occasionally, fainting. Most patients with orthostatic intolerance have a relatively mild condition that improves over time. Though astronauts are usually free of symptoms a few hours after space flight, orthostatic intolerance can be debilitating for some patients.

Neurolab was the last of NASA's dedicated life sciences missions. In a unique NASA-university partnership, Dr. Pawelczyk and researcher Jay Buckey, M.D. at Dartmouth-Hitchcock Medical Center, joined astronaut-scientists aboard the space shuttle Columbia for 16 days conducting neuroscience experiments to address changes in blood pressure regulation, balance, sleep, the control of movement, and the development of the nervous system. On one of the longest shuttle missions yet flown, Columbia flew 6.4 million miles in space, circling the earth 256 times.

Dr. Pawelczyk received his Bachelor of Arts Degrees in Biology and Psychology from the University of Rochester; a Masters of Science in Physiology from Penn State University; and a Ph.D. in Biology (Physiology) from the University of North Texas. He completed a post-doctoral fellowship at the University of Texas Southwestern Medical Center. He joined the faculty of Pennsylvania State University in 1995. The Noll Physiological Research Center, part of Pennsylvania State's College of Health and Human Development, is one of the nation's oldest research laboratories devoted to the study of human adaptation to exercise and the environment.

The American Physiological Society is devoted to fostering scientific research, education, and the dissemination of scientific information. By providing a spectrum of physiological information, the Society plays a significant role in the progress of science and the advancement of knowledge.