Influence of Simulated Microgravity on Mechanical Properties in the Human Triceps Surae Muscle in vivo

Abstract

Abstract. Purpose. The aim of the study was to investigate the effects of a simulated microgravity on the mechanical properties of the human triceps surae (TS) and to assess the effectiveness of physical training (PT) in preventing detrimental effects. Methods. Eight women (aged 26-36 years) underwent 120-d of Bed rest (BR): four underwent Bed rest only (BR group) and four performed PT during this period (BRPT group). The training sessions were conducted for 60 min each day for 6 days a week for 14 weeks, and 30-40 min twice a day for 2 weeks under the experiment conditions. PT was performed over a 4-d cycle: 3-d of training and 1-d of rest. The maximal voluntary contraction (MVC), and isometric twitch contraction (P t ), and electrically evoked tetanic tension at 150 impulses × s -1 (Р о ), time-to-peak tension (TPT) of the twitch were determined. The difference between Р о and MVC expressed as a percentage of Р о and referred to a force deficiency (Р d ). The MTS was determined according to the electromechanical delay (EMD) value during the explosive voluntary contraction. Surface electrodes sensed electromyographic (EMG) activity in the soleus muscle. Electromechanical delay (EMD) was the time interval between the change in EMG and movement muscle force production. Results. In the BR group, Р t , MVC, and Р о had decreased by 12, 36, 24%, respectively, but Р d had increased by 39%. TPT of the twitch had increased by 14%. The rate of increase of voluntary contractions reduced, but in the electrically evoked contraction no changes were observed. The EMD had increased by 27%. In the BREx group, МVС, Р t , and Р о decreased by 3%, and 14%, and 9%, respectively. TPT had decreased by 4%. The P d had decreased significantly by 10%. The rate of rise increase of electrically evoked tetanic did not change significantly, but the rate of rise in isometric voluntary tension development was increased. The EMD had decreased by 12%. Conclusion. Unloading decreased function and EMD muscle and, although the PT did attenuate these effects, they did not completely prevent them. It is suggested that the total loading volume (mainly its intensity) was not sufficient to completely prevent alterations in tendon mechanical properties

Architectural and functional specifics of the human triceps surae muscle in vivo and its adaptation to microgravity

“…A lower ⌰ f observed after a spaceflight (54,57) partly compensates for the loss of force because the force transmission to the tendon becomes more efficient in spite of the decreased stiffness of the MTC (51). Such a decrease in stiffness has been observed, in fact, in subjects after a longterm exposure to G-simulating conditions and in cosmonauts after a long-duration spaceflight (51,52,53).…”