The Dallas Bed Rest and Training Study, 1966

During the spring of 1966 investigators at the Southwestern Medical School in Dallas recruited six college students for an interesting summer job. Five of the six were from Arlington State University (now the University of Texas at Arlington) and the sixth had already worked two summers as a technician and experimental subject at the medical school.

The six students were asked to participate in a summer-long study of the effects of bed rest and training on cardiovascular and pulmonary function during exercise. The study would proceed in three stages: 1) complete evaluation of cardiovascular and pulmonary function, plus electrolytes and blood work, 2) a three week period of bed rest (when we got to use a real toilet it was in a wheelchair), followed by 3) an eight week training period of mostly running, after which stage one would be repeated.

There are only five of us in this group portrait. The sixth student was a swimmer, a big handsome hunk who drew a crowd of secretaries when it was his turn on the treadmill. However, after seeing the needles stuck in the rest of us he declined further participation in the study. From left to right: Bill Bowman, Kazmer Laszlo, Gregg Hill, James Hulsley, Leo Luebbenhusen.

Most studies of adaptation to exercise prior to the study were cross-sectional. In these studies sedentary people would be compared with active people or athletes. The first studies of energy metabolism were done after the First World War, with a Nobel Prize awarded to A. V. Hill of Great Britain in 1921. The Harvard Fatigue Laboratory was founded in 1927 and many of the scientists who worked there made the first measurements of the body's capacity to consume oxygen. Most of these studies did not follow their subjects over an period of time. The 1966 Dallas report lists four studies of bed rest and training and four review articles about the physiology of training. No study covered the subject to the degree planned for the 1966 project. The picture below shows Dr. Jere Mitchell (left) and Dr. Carlton Chapman planning a summer of activities for five college students.

When muscles contract they consume oxygen. The problem is how to get oxygen from the atmosphere into the muscles, which are well protected from the environment around us. The body solves this problem in five stages:

1. Ventilatory transport with the lungs, which are composed of millions or tiny air sacs, called alveoli, which are surrounded by small arteries that are fed by the right side of the heart
2. Diffusion of oxygen into the blood. This is a passive process in which the barometric pressure pushes oxygen molecules across the extremely thin alveolar membranes and into the lungs arteries
3. The oxygen chemically reacts with hemoglobin in the blood
4. Blood leaving the lungs enters the left side of the heart to be pumped into the arterial system of the body
5. Extraction of oxygen from the blood in the capillaries, the microscopic web of vessels that perfuse the tissues of the body. This process is almost the reverse of stage two.

Once in the muscles, oxygen can be used to help the muscle contract. It has long been established that physical training increased the capacity to consume oxygen. Athletes from the 1930's were tested at the Harvard Fatigue Lab and the oxygen uptakes reported then were similar to the uptakes reported for athletes tested today. The effects of bed rest after prolonged illness or surgery were also noted and naturally the question arose, why the marked drop in physical capacity. Some suggested that changes in blood pressure in the limbs might be important. After watching television on the couch many people experience a brief episode of light-headedness if they quickly stand up to go into the kitchen for another snack. Could long periods of bed rest create a more serious problem?

Our heart rates at rest and increasing levels of treadmill exercise, all the way to voluntary exhaustion, were recorded. The photo shows Dr. Gunnar Blomqvist operating some 1960s vintage EKG equipment. The recordings of our hearts' action was very detailed.

Or, could the cause of reduced exercise capacity after bed rest be a decreased capacity of the cardiovascular or pulmonary systems? Take x-rays of the heart and compare heart volumes before and after bed rest. Measure the capacity of the lungs to move air and diffuse oxygen. Also test cardiovascular function during exercise while in a normal vertical position and in a supine position.

Before the investigators put us to bed for three weeks a number of things were measured. We were weighed under water and that weight was compared with our weight on land. Taking into account the amount of air in our lungs, the under water weight could be adjusted to estimate a percentage of body fat. The picture to the right shows Leo in the stock tank having his residual lung volume measured.

The amount of blood our hearts could pump was estimated by using a green dye, injected into an arm vein. When the dye made it to the heart it was mixed with all the blood returning from the rest of the body and then pumped out through the arteries, where a sample was taken from an artery in our left arm. The dilution of the dye indicated how much mixing had occurred and cardiac output could then be estimated.

Dividing this output by the heart rate at each level of exercise gives the stroke volume, or the amount of blood pumped by the heart with each contraction. The catheter in our right leg allowed blood samples from exercising muscles. The oxygen content of the arterial blood could then be compared with the content from the venous blood coming from our hard working legs. This is called the arterio-venus O2 difference. Our expired air was periodically collected and from that it could be determined how much oxygen we were extracting from the air as we worked at increasing exercise loads. The picture to the left show Bill doing supine cycling. The apparatus to measure the green dye dilution is shown to Bill's left. That's George Vastagh operating the equipment.

The treadmill tests were simple. A first run was done to reach about half the subject's aerobic capacity. Then, after a brief rest a "supermax" run was done. Dr. Bengt Saltin was very good at estimating how much we could do, so he selected a speed and grade that would elicit our maximum oxygen uptake within about 7 minutes. The grade would increase, not the speed, so there would be less danger of the subject flying off the treadmill if he stumbled. The scenes above show Bill Bowman on the treadmill. He's walking at a brisk pace up a grade that increases every minute or so. Periodically blood samples are drawn from the three catheters. The bags for collecting expired air are on Bill's right.

Once all the data was collected, we went to bed. Our diet was controlled so we didn't gain weight, and we restricted to our beds. The picture on the right shows James, Gregg and Kaz confined to bed for three weeks.

We were put to bed on successive days, so we all got the same bed rest period before we were tested again, with one day for each subject. When each subject's turn came to leave bed, a wheelchair was brought for us and we were wheeled into a room across the hall from the treadmill where the catheters were again inserted into our veins and artery and we were allowed to rest about 45 minutes before the first session.

 

After the first tests after bed rest were completed we started training. We ran almost daily. About half of our weekly mileage was continuous running and the other half spent doing interval training. We ran at a pace that would elicit maximum oxygen consumption for three minutes, then we walked for three minutes to recover, then repeated the series for a total of at least five runs. The runners are (L to R) James, Leo, Bengt Saltin, Bill and Kaz. We only used a track for time trials and we did no specific race training (called "speed work" by track runners).

The decrease in cardiac output at rest measured after bed rest was slight and not considered significant. Once we began pedaling a bicycle in the supine position the decrease in cardiac output become more significant the higher the workload (from 50 watts to 100 watts).  The brachial artery pressure during increasing workloads in two of the untrained subjects showed a big drop after bed rest and they fainted during the treadmill tests. After training the arterial pressures all behaved well and no one passed out.

Treadmill tests showed the real culprit. As workloads were increased it became clear that not could we not do as much as before bed rest and the measurements taken showed that our hearts had deconditioned. Heart volumes had dropped and cardiac output had decreased significantly.

After the post bed rest measurements we also ran time trials on a track. The distances were 1, 1.5 or 2 miles, depending on what the subject could do. After three weeks in bed all the work our legs had to do caused a great deal of muscle soreness. My quads were so sore that I had a little difficulty walking and running, and it was even difficult to drive a car, since my sore legs made it hard to depress the break pedal. Our training included continuous running of up to an hour or more and interval training or 3 minutes running followed by three minutes of walking at one mile race pace,  which is close to maximum oxygen uptake pace. We did about as much continuous running as interval running. Most of our running was on grass.

   

The picture above show Kaz on a bicycle ergometer having his skin temperature measured in a climate controlled room and Gregg inhaling a gas mixture that would show how well the lungs functioned in transporting oxygen from the air into the blood. Note the paisley shirt on Gregg.

The untrained subjects made the biggest gains in cardiac output and maximum oxygen uptake. The two trained subjects made less dramatic gains. It all depended on where we started. After three weeks of bed rest the two trained subjects still had a larger maximum oxygen uptake than the untrained subjects before they went to bed, and even after 55 days of training two of the untrained subjects were still below the levels of the two trained subjects after three weeks of bed rest. The great majority of people will respond well to training, but some start at higher levels. Some rare talents appear who start high and make great progress, sometimes in just a few years. The best example of this rare individual in Jim Ryun, who started high school as a 5:30 miler and ended his high school career in 1965 by winning the Kansas state mile title in 3:55, just over the world record.

The Conclusions

Three weeks of bed rest hit everybody pretty hard. Cardiac output and maximum oxygen uptake all dropped significantly. There was some impairment of peripheral circulatory control, indicated by the fainting of two subjects during their first treadmill test after bed rest. The significant decrease in heart size meant that our hearts had to work harder at sub maximal work loads. Our muscles were extracting more oxygen at these work loads in an attempt to make up for the reduced contribution of the heart. Training increased heart volume and cardiac output so that at sub maximal workloads the heart rate was lower and the amount of blood pumped by each contraction increased. Our muscles were extracting more oxygen from the blood in response to training.

The study showed that bed rest after a heart attack is not a good therapy. Any prolonged bed rest would have significant impact on a person's heart. The study showed how previously untrained young men could greatly increase their exercise capacity by strengthening their hearts with physical training which has a large component done at high intensity, as in the interval training sessions.

(L to R) Abe Pringler, Gregg Hill and Dr. Bengt Saltin. This photo was taken at the high altitude chamber at a US Government research facility in Tulsa, Oklahoma. We were on our way to Mt. Evens, Colorado for a three week stay at 14,000 feet. We would have stayed longer but the summer was running out and we had to make arrangements to keep a road open so the doctors could visit us to run tests, and of course we all had to return to college classes. If you visit Colorado you can drive west from Denver on I-70, take the Mt. Evens exit and drive to the top. There's parking, the remains of a burned out restaurant that we visited while we lived at the top, and there is the cabin where we lived, along with the hut for the generator. A recent addition to the summit is an observatory.

It was a very interesting and busy summer for us.

© 2005 by Gregg R. Hill