The eccentric torque maximum was 400 foot pounds. Subjects abstained from food for 2 hours before testing, from caffeine 4 hours before, and from exercise 12 hours before. The dynamometers were calibrated externally and internally (electronically) before each test session. Joint configurations and ranges of motion were recorded for each subject and reproduced for each test session. Testing of the limbs was unilateral with the dominant limb, unless contraindicated. Verbal instructions were consistent and given before each joint test. No verbal encouragement was given during the tests.
Mean results from tests conducted approximately 1, 2, and 3 weeks before launch were compared to results from landing day and from 7 days after landing. Only 17 subjects were tested on landing day. Losses greater than about 9% were considered to be operationally relevant.
Four of the astronauts also performed in flight exercise as part of DSO 476, using a treadmill with a tether system to simulate gravity. They followed continuous or interval exercise protocols with target heart rates intended to correspond to 60% to 85% of preflight maximum oxygen consumption. The percentages of change in their strength and endurance test results were compared with those of 5 astronauts who did not exercise during the flight.
From before the flight to landing day, large decreases in the strength of the back and abdomen occurred. Strength had decreased by 23% in the concentric tests of the back, 14% in the eccentric tests of the back, and 10% in the concentric tests of the abdomen. The loss in back strength was greater after flights of 9 to 11 days (concentric, 28%; eccentric, 17%) than after flights of 5 days (concentric, 18%; eccentric, 11%). Eccentric abdominal and concentric back strength had recovered significantly 7 days after landing. A significant (12%) decrease in concentric strength of the quadriceps muscle of the thigh was also seen on landing day. No significant loss of strength was seen in the hamstring muscles or in the tests at the ankle, shoulder or elbow, except for a few minor losses that were not considered operationally relevant.
The four astronauts who exercised during flight actually gained eccentric strength of the gastrocnemius muscle of the calf. Although the exercising astronauts lost concentric strength in the quadriceps, the percent change was significantly less than for the four nonexercising astronauts. For the other results of the knee and ankle tests, decreases in strength were generally smaller in those who exercised; although, the differences between exercisers and nonexercisers were not statistically significant. Treadmill exercise did not prevent losses of strength in the back or abdomen. Decrements exhibited by muscles of the five astronauts who did not exercise during flight indicated that muscles are less able to maintain endurance and resist fatigue after space flight. The astronauts who exercised had no loss of endurance.
There was no change in endurance after 5-day flights, but the endurance of the quadriceps decreased after flights of 9 to 11 days. Endurance recovered within 7 days of landing.
These results showed that space flight results in losses of skeletal muscle strength and endurance, and that the losses are greater after flights of longer duration. Strength was lost primarily in the antigravity muscles of the legs and torso. Exercise may prevent losses of muscle strength and endurance.