Abstract
Lower body negative pressure (LBNP) is an established method of simulating the gravitational effects of orthostasis on the cardiovascular system during space flight or at supine body position on Earth. We hypothesized that LBNP added onto leg press exercise would promote leg muscle perfusion, stimulate oxygen consumption, and modify acute molecular responses. Eighteen subjects performed fifteen slow-paced concentric (4 s) and eccentric contractions (4 s) without or with 40 mmHg LBNP. Force corresponding to 6% of the one-repetition maximum (1-RM) at knee flexion gradually increased to 60% 1-RM within the first half of the range of motion, thereafter remaining constant. AMPK and P-AMPK protein expression was determined in biopsies of vastus lateralis. Venous blood samples were used to measure angiogenic factors. Physiological responses to LBNP included an elevated EMG amplitude, higher heart rate and doubling of the cardiac output compared to control (p < 0.001). Muscle total hemoglobin was increased by around 20 μmol/l vs. control (p < 0.001), accompanied by decreasing tissue oxygen saturation and elevated oxygen uptake (p < 0.05). MMP-2 levels were reduced, and the ratio of P-AMPK to AMPK elevated after exercise with LBNP (p < 0.05). MMP-9 similarly increased in both groups, whereas endostatin was only elevated in the control group (p < 0.05). Our results indicate facilitated peripheral blood supply and higher oxygen exploitation leading to activation of the energy sensor AMPK and differential regulation of angiogenic factors involved in muscle tissue remodeling and capillary growth. Simulating orthostasis with LBNP might promote beneficial structural adaptations of skeletal muscles during resistance exercise and contribute to future exercise countermeasures achieving increased muscle strength and endurance during space flight.
Highlights
One of the prevalent issues astronauts face during space flight is the redistribution of fluids toward their upper body, a phenomenon that occurs due to the lack of gravity in space (Hargens and Richardson, 2009; Hargens et al, 2013)
At 120 min after exercise, the matrix metalloproteinase (MMP)-9 levels of both groups were elevated by approximately 100 ng/ml compared to respective baseline
Subsequent to the main exercise set, the AMP-activated protein kinase (AMPK) level was initially decreased in the control group by approximately 40% compared to baseline, as determined 10 min after exercise (d = 1.3, p < 0.01) and 30 min after exercise (d = 1.2, p < 0.01), and recovered to baseline values at 60 min following the exercise (Figure 9 and Supplementary Figure S4)
Summary
One of the prevalent issues astronauts face during space flight is the redistribution of fluids toward their upper body, a phenomenon that occurs due to the lack of gravity in space (Hargens and Richardson, 2009; Hargens et al, 2013). Considering an additional difficulty of providing adequate loading, skeletal muscles are presented with a difficult challenge that leads to structural alterations and loss of muscle mass through prolonged exposure to microgravity This challenge is yet to be fully tackled by countermeasures and represents a particular difficulty when considering long duration space missions, such as traveling to a different planet (Narici and De Boer, 2011; Thornton and Bonato, 2017; Dillon et al, 2018). Lower body negative pressure (LBNP) is a well-known method of simulating the cardiovascular and physiological effects of gravity and has been used to assess the function of the cardiovascular system before and after space flight (Baisch et al, 2000; Hargens and Richardson, 2009; Hargens et al, 2013). Molecular responses to LBNP have so far been investigated, among others, for catecholamines, volume regulating hormones, markers of renal function and blood coagulation
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
