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

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 (Pt), and electrically evoked tetanic tension at 150 impulses × s–1 (Ро), time-to-peak tension (TPT) of the twitch were determined. The difference between Ро and MVC expressed as a percentage of Ро and referred to a force deficiency (Рd). 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, Рt, MVC, and Ро had decreased by 12, 36, 24%, respectively, but Рd 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, Рt, and Ро decreased by 3%, and 14%, and 9%, respectively. TPT had decreased by 4%. The Pd 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 propertie

Real-world experience of feasibility and efficacy of electrical muscle stimulation in elderly patients with acute heart failure: A randomized controlled study.

BACKGROUND Reduced aerobic capacity and deconditioning contributes to morbidity and mortality in elderly acute heart failure (AHF) patients. Electrical muscle stimulation (EMS) has shown to be a suitable alternative to exercise in AHF. However, feasibility and efficacy are unknown in a real-world setting. METHODS This is a prospective, open label blinded, randomized, controlled study, investigating feasibility and efficacy of high-intensity versus low-intensity EMS versus controls in elderly AHF patients. Patients and investigators were blinded to the intervention. EMS was offered to >60 years old AHF patients, initiated during hospitalization and continued at home. Outcome measures included changes in 6-min walk distance (6-MWTD), functional capacity and quality-of-life at 3 and 6 weeks. RESULTS Among 97 consecutive AHF patients (78.1 ± 9.4 years, 42.3% females), 60 (61.9%) were eligible for EMS. Of these, 27 provided written informed consent and were randomly assigned to high-intensity (n = 10), low-intensity EMS (n = 9) and controls (n = 8). 13/27 completed the intervention. Main reason for dropouts was intolerance of the overall intervention burden. MACE occurred in 5 and were not associated with the study. EMS groups showed significant improvement of 6-MWTD (controls vs low-intensity p = 0.018) and of independence in daily living (for both p < 0.05). CONCLUSIONS Changes in 6-MWDT suggest efficacy of EMS. Whereas all tolerated EMS well, the burden of study intervention was too high and resulted in a consent rate of <50% and high dropouts, which limit the interpretability of our data. Less demanding EMS protocols are required to evaluate the full potential of EMS in elderly AHF patients

NEUROMUSCULAR AND MYOTENDINOUS ALTERATIONS IN-FLIGHT IN PLANTAR FLEXOR MUSCLES

BACKGROUND Despite extensive exercise countermeasures, astronauts still experience sizable deficits in calf muscle mass and strength. Recent muscle biopsy data suggest deficits are associated with metabolic deviations [1]. Many studies have tested astronaut strength before and after spaceflight. The one study that tested in-flight reported a significant reduction in isometric and isokinetic knee extensor strength that was pronounced from the very beginning of the space sojourn [2]. This is in stark contrast to bed rest studies, where a gradual and continuous loss of muscle mass and strength has been repeatedly reported. METHODS The Sarcolab3 study attempted to describe the time course of changes in isometric and isokinetic muscle strength and in muscle mass. Crew members were tested on board the ISS after 8.9 (SD 3.0), 49.1 (10.1) and 131.5 (SD 27.7) days in-flight, as well as pre-and post-flight, using the Muscle Atrophy Research and Exercise System (MARES). Specifically, maximal voluntary torques in plantar flexion and knee extension were measured at various angles in order to establish the torque-angle relationship. Simultaneously, activation capacity was assessed by supra-maximal myo-electrical stimulation superimposed to a maximum voluntary contraction. Calf muscle volume was assessed by magnetic resonance imaging pre-and post-flight. RESULTS Results demonstrate early declines in muscle strength at flight days 9 and 49, and a tendency for the decaying time course to level off at flight day 131. Activation capacity of plantar flexor, as elicited by myo-electrical stimulation, was maintained during in-flight and post-flight testing. At 4 days post-flight, soleus muscle volume had declined by 15-20% as compared to pre-flight. CONCLUSIONS Results suggest that existing exercise countermeasures are still not fully effective for preventing weakness and wasting of the calf musculature. The observed time course of in-flight muscle loss seems more compatible with results from bed rest. Potentially, the rate of muscle wasting may decline during the second half of 6-month missions with the current countermeasure exercise regimens. REFERENCES 1. Rittweger, J., et al., Sarcolab pilot study into skeletal muscle's adaptation to long-term spaceflight. NPJ Microgravity, 2018. 4: p. 18. 2. Tschan, H., et al., Resistance training - a strategy proposed to coutneract muscular deconditioning in microgravity, in 10 Years Space Biomedical Research and Development in Austria, H. Hinghofer-Szalkay, Editor. 2001, Facultas: Wien. p. 95-108