PRINCIPAL INVESTIGATOR (S ): Earl V. LaFevers , Arnauld E. Nicogossian, William 



N. Hursta, and Joseph T. Baker 



EXPERIMENT TITLE/NUMBER : Electromyographic Analysis of Skeletal Muscle 



PROGRAM/MISSION : Apollo-Soyuz Test Project 



CLASSIFICATION : Human 



DISCIPLINE(S) : Musculoskeletal, Neurosensory 



OBJECTIVES : To investigate changes in skeletal muscle electrical activity 

 that occur after exposure to short-term weightlessness. 



PROTOCOL : Data were obtained on days F-45, F-30, and F-15. Surface 

 electrodes were placed on the lower leg muscles (gastrocnemius and soleus) and 

 on the arm muscles (biceps brachii and brachioradialis) . Seated in the muscle 

 stress apparatus , the crewman was instructed to exert a series of graded 

 efforts. 



EQUIPMENT : A skeletal muscsle stress apparatus, electromyogram. 



RESULTS : Skeletal muscle disuse attributable to 9 days of space flight 

 weightlessness resulted in increased excitability of the instrumented muscles. 



The ratios of integrated electromyogram (IEMG) to force for both the 

 gastrocnemius and brachioradialis muscles showed a decreased level of 

 electrical efficiency as a result of the 9 days in weightlessness. The data 

 for the biceps and brachioradialis muscles show a tendency for increased 

 electrical efficiency. 



Significant shifting of the power spectra into lower frequencies was 

 considered evidence of muscle fatigability. In the leg muscle, there was a 

 significant difference between preflight and postflight spectral power levels. 

 The postflight data showed a significantly greater progressive power shift 

 into the lower frequencies as a result of the 1 -minute isometric stress. The 

 arm muscles did not exhibit significant differences between conditions. 



CONCLUSIONS : Both upper and lower extremity muscles showed changes in 

 excitability which suggest that skeletal muscles are susceptible to functional 

 changes associated with the reduced muscle activity in weightlessness. Since 

 all changes showed increased sensitivity, the probable site for this effect is 

 the muscle fibers, for the following reason: Previous clinical studies have 

 shown that random loss or reduced activity in muscle fibers, as in myopathy, 

 result in higher firing frequencies of the muscle, whereas dysfunctions of 

 neural loci result in lower firing frequencies. 



Short-term exposure to weightlessness heightens fatigability in skeletal 

 muscle. Greater amounts of spectral power were observed in the lower 



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