Altered Gravity Simulated by Parabolic Flight and Water Immersion Leads to Decreased Trunk Motion

RESEARCH ARTICLE Altered Gravity Simulated by Parabolic Flight and Water Immersion Leads to Decreased Trunk Motion Peiliang Wang1☯, Zheng Wang1☯, Dongni Wang1☯, Yu Tian2, Fan Li2, Shaoyao Zhang2, Lin Zhang1, Yaoyu Guo2, Weibo Liu2, Chunhui Wang2, Shanguang Chen2, Jinhu Guo1* 1 Key Laboratory of Gene Engineering of the Ministry of Education, State Key Laboratory of Biocontrol, School of Life Sciences, Sun Yat-sen University, Guangzhou, China, 2 National Key Laboratory of Human Factors Engineering, China Astronaut Research and Training Center, Beijing, China ☯ These authors contributed equally to this work. * Abstract OPEN ACCESS Citation: Wang P, Wang Z, Wang D, Tian Y, Li F, Zhang S, et al. (2015) Altered Gravity Simulated by Parabolic Flight and Water Immersion Leads to Decreased Trunk Motion. PLoS ONE 10(7): e0133398. doi:10.1371/journal.pone.0133398 Editor: Sakamuri V. Reddy, Charles P. Darby Children's Research Institute, UNITED STATES Received: April 7, 2015 Accepted: June 26, 2015 Published: July 24, 2015 Copyright: © 2015 Wang et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Gravity is one of the important environmental factors that influence the physiologies and behaviors of animals and humans, and changes in gravity elicit a variety of physiological and behavioral alterations that include impaired movement coordination, vertigo, spatial disorientation, and perceptual illusions. To elucidate the effects of gravity on human physiology and behavior, we examined changes in wrist and trunk activities and heart rate during parabolic flight and the activity of wrist and trunk in water immersion experiments. Data from 195 person-time parabolas performed by eight subjects revealed that the trunk motion counts decreased by approximately half during ascending legs (hypergravity), relative to the data acquired before the parabolic flights. In contrast, the wrist activity remained unchanged. The results from the water immersion experiments demonstrated that in the underwater condition, both the wrist and trunk activities were significantly decreased but the latter decreased to a much lower level. Together, these data suggest that gravitational alterations can result in differential influences on the motions of the wrist and the trunk. These findings might be important for understanding the degeneration of skeleton and muscular system and performance of astronauts in microgravity. Data Availability Statement: All relevant data are available via Figshare (http://dx.doi.org/10.6084/m9. figshare.1446010). Funding: This work was supported by the National Basic Program of China (2011CB711000, 2012CB947600, http://most.gov.cn/), the National Natural Science Foundation of China (31171119, 71201148, http://www.nsfc.gov.cn/), the New Century Training Program Foundation for the Talents by the State Education Commission (NCET-12-0566, http:// www.moe.edu.cn/). Introduction All lives on the Earth have evolved and developed in the constant presence of 1.0g gravity [1]. To study the changes in physiology and behavior that occur in microgravity, a number of approaches that are applied on the ground have been used to create simulated weightlessness, including head-down bed rest (HDBR), parabolic flight and water immersion [2–4]. Microgravity can be simulated by free-fall during parabolic flights, which follow the ballistic trajectory of a parabola. Parabolic flights produce short successive periods of altered gravity within PLOS ONE | DOI:10.1371/journal.pone.0133398 July 24, 2015 1 / 11 Altered Gravity Causes Decreased Trunk Motion Competing Interests: The authors have declared that no competing interests exist. the range 0 and 1.8g [5]. Water immersion is another approach creating conditions of weight compensation and allows for the study of performance in hypogravity conditions [6, 7]. Changes in gravity have deleterious effects on physiology and behavior that lead to disorientation, muscular atrophy and bone mass loss and deregulation of circadian rhythms and sleep [8–13]. Additionally alterations in gravity influences cognitive performance [1,14]. When exposed to unusual gravity environments, subjects produce exaggerated isometric forces [3,15]. A comparison of muscle activities during walking underwater and on land at a slow speed revealed that activities of the rectus abdominis and paraspinal muscles remained unchanged, but the activities of all of the other tested muscles, including gluteus medius, rectus femoris, vastusmedialis, biceps femoris andtibialis anterior gastrocnemius, decreased underwater [16]. These facts suggest that alterations in gravity affect motion and performance. In a previous study, we found that trunk motions of two orbital astronauts decreased dramatically during a space mission [17], suggesting that microgravity might impose specific effects on trunk motion. Access to space experiments is very expensive and limited, and the number of subjects is typically low. As such, some of the observations obtained from space study require validation in ground-based simulations. In the present work, we analyzed data from parabolic flights and water immersion experiments to further address the influence of simulated gravitational alterations on trunk and wrist motions. The findings of this work may help to facilitate the development of more effective countermeasures for astronauts. Materials and Methods Parabolic flights The 112th parabolic flight campaign was organized by ESA and NOVESPACE at the Société Girondine ďEquipments, de Réparation, et de Maintenance Aéronautique (SOGERMA) center in Bordeaux, France. This study was conducted from Oct. 7 –Oct. 9 in 2014. The AIRBUS A300 ZERO-G aircraft was employed to perform the parabolic flights. Each flight consisted of 31 parabolas. Data from the following five phases (blocks) of each parabola (termed I–V) were sampled and analyzed. I, 1 g, approximately 45 s before the parabolic flights; II, ~1.8 g, during the ascending leg (hypergravity); III, μg at the apex (microgravity); IV, ~1.8 g during the descending leg (hypergravity) and V, 1 g, approximately 30 s before parabolic flights (Fig 1A and 1B). The subjects were trained to assume supine or squatting positions in hypergravity and were free to move during other periods. An Actiwatch was used to record the wrist activity, and an Actiheart to record the heart rate (HR) variables and trunk activity. The Actiheart was worn around the chest with a belt according to the manufacturer’s instruction (Fig 1C). To prevent the Actiheart worn with a chest belt from getting loose owing to movement, it was tightened with a bandage around the chest. These devices were worn before take-off and removed for analysis after landing. Water immersion experiments The water immersion experime (...truncated)