The human resting muscle tone (HRMT) system provides structural and functional support to skeletal muscle and associated myofascial structures (tendons, fascia) in normal life. Little information is available on changes to the HRMT in bed rest. A set of dynamic oscillation mechanosignals ([Hz], [N/m], log decrement, [ms]) collected and computed by a hand-held digital palpation device (MyotonPRO) were used to study changes in tone and in key biomechanical and viscoelastic properties in global and postural skeletal muscle tendons and fascia from a non-exercise control (CTR) and an exercise (JUMP) group performing reactive jumps on a customized sledge system during a 60 days head-down tilt bed rest (RSL Study 2015-2016). A set of baseline and differential natural oscillation signal patterns were identified as key determinants in resting muscle and myofascial structures from back, thigh, calf, patellar and Achilles tendon, and plantar fascia. The greatest changes were found in thigh and calf muscle and tendon, with little change in the shoulder muscles. Functional tests (one leg jumps, electromyography) showed only trends in relevant leg muscle groups. Increased anti-Collagen-I immunoreactivity found in CTR soleus biopsy cryosections was absent from JUMP. Results allow for a muscle health status definition after chronic disuse in bed rest without and with countermeasure, and following reconditioning. Findings improve our understanding of structural and functional responses of the HRMT to disuse and exercise, may help to guide treatment in various clinical settings (e.g., muscle tone disorders, neuro-rehabilitation), and promote monitoring of muscle health and training status in personalized sport and space medicine.

Abstract The aim of this study was to determine the hemodynamic and neuroendocrinological responses to different levels and protocols of artificial gravity, especially in comparison to what is expected during a moderate bout of exercise. Ten male participants were exposed to artificial gravity using two different protocols: the first was a centrifugation protocol that consisted of a constant phase of 2 Gz for 30 minutes, and the second consisted of an intermittent phase of 2 Gz for two minutes, separated by resting periods for three minutes in successive order. Near infrared spectroscopy (oxyhemoglobin and deoxyhemoglobin) at the prefrontal cortex, Musculus biceps brachii, and Musculus gastrocnemius, as well as heart rate and blood pressure were recorded before, during, and after exposure to artificial gravity. In order to determine effects of artificial gravity on neuroendocrinological parameters (brain-derived neurotrophic factor, vascular endothelial growth factor, and insulin-like growth factor 1), blood samples were taken before and after centrifugation. During the application of artificial gravity the concentration of oxyhemoglobin decreased significantly and the concentration of deoxyhemoglobin increased significantly in the prefrontal cortex and the Musculus biceps brachii muscle. Participants exposed to the continuous artificial gravity profile experienced peripheral pooling of blood. No changes were observed for brain-derived neurotrophic factor, vascular endothelial growth factor, or insulin-like growth factor 1. Intermittent application of artificial gravity may represent a better-tolerated presentation for participants as hemodynamic values normalize during resting periods. During both protocols, heart rate and arterial blood pressure remained far below what is experienced during moderate physical activity.

Direct object selection in an Augmented Reality environment that is coded outside of human body frame of reference is deteriorated under short-term altered gravity. As countermeasures we developed a gravity-adapted resizing technique based on the Hooke’s law that resulted in two techniques of target and interface deformation (compression, elongation). To prove the concept of this resizing approach we initially conducted two experiments under simulated hypergravity conditions. While during the first study hypergravity was induced by a long-arm human centrifuge, in the second study hypergravity was simulated by additional arm weightings that were balanced and attached to the participants’ pointing arm. We investigated the difference of the task performance with respect to the pointing frequency, response time, pointing speed and accuracy, when participants performed a visuomotor task under the resizing conditions compared to the unchanged condition. During the second study we additionally evaluated the speed-accuracy tradeoff of the resizing techniques according to Fitts’ law and the physiological workload by cardiac responses analyzing the heart rate variability. Both experiments showed that the online adaption of the present gravity load to targets’ size and distance influences the performance of direct AR direct pointing. The results revealed that the pointing performance benefits from elongation target deformation by increased target sizes and distances, while pointing towards compressed targets mostly decreases the physiological workload under increased gravity conditions.

PURPOSE: Short radius centrifuge (SRC) devices have been amongst the most important facilities for astronauts for several decades, requiring a high relative velocity in order to generate adequate g-loads for experiments and training. SRCs caught the attention of space agencies due to ongoing plans for interplanetary missions to Mars and the Moon. This study aimed to assess changes in haemodynamics induced by artificial gravity (AG) during centrifugation on a SRC. METHODS: Eleven healthy subjects (29.57 ± 6.61 years, 183.21 ± 5.11 cm, 82.14 ± 7.24 kg) participated, none of them showing any history of vasovagal syncope. Two different AG-protocols were conducted with at least a 48h time lag in between. The continuous AG-protocol included an acceleration phase of 1g, 2g and 3g for 120 s each, followed by a continuous acceleration of 2g for 30 min and a final acceleration phase of 1g, 2g and 3g for 120 s each. In contrast, the intermittent protocol included a phase of intermittent g-load of 2g for 180 s interrupted by a pause of 180 s (baseline rotation of 5RPM). This sequence of acceleration was repeated four times. Changes in oxygenated blood (O2Hb) and deoxygenated blood (HHb) in the underlying tissue were recorded using a 4-channel Near Infrared Spectroscopy (NIRS) system on the prefrontal cortex (PFC), musculus biceps brachii (MBB) and musculus gastrocnemius (MG). RESULTS: Concentration in O2Hb decreased (F(13, 130) = 26,356, p < .05) and in HHb increased (F(13, 130) = 11.119, p < .05) during acceleration phases 1 and 2 in the PFC in both AG profiles. Similarly, concentration in O2Hb decreased (F(13, 130) = 16,478, p < .05) and in HHb increased (F(13, 130) = 11,178, p < .05) during same phases in the MBB. Peripheral venous pooling was indicated by increased concentration in both, O2Hb (F(13, 117) = 11,830, p < .05) and HHb (F(13, 117) = 5,3686, p < .05) during acceleration phases in the MG. Continuous acceleration induced peripheral accumulation of both O2Hb and HHb, whereas intermittent acceleration kept concentration in both parameters stable. CONCLUSION: NIRS is an appropriate method for assessing cranial blood oxygenation and venous pooling in the peripheral extremities during application of AG. Haemodynamics and the regulation of the cardiovascular system appear to be affected by the g-load applied by an SRC.

The performance of Augmented Reality direct object selection coded outside of the human egocentric body frame of reference decreases under short-term altered gravity. Therefore adequate countermeasures are required. This paper presents the results of a proof-of-concept (POC) study to investigate the impact of simulated hypergravity on the size and distance of a given target. The POC study is divided in a case study and a user study, whereby hypergravity was induced by a long-arm human centrifuge and additional arm weighting. For gravity-dependent resizing and –positioning we used the Hooke’s law that resulted in two techniques of target deformation (compression, elongation) and compared both methods with normal sized targets. Besides common metrics to measure the performance, we additionally evaluated the physiological strain by the heart rate variability and the speed-accuracy tradeoff of the resizing techniques according to Fitts’ law. The study showed that the online adaption of the present gravity load to targets' size and distance influences the performance of direct AR direct pointing. The results revealed that the pointing performance benefits from elongation target deformation by increased target sizes and distances.

The performance of Augmented Reality (AR) direct object selection coded outside of the human egocentric body frame of reference is decreased under short-term altered gravity. Therefore an adequate countermeasure is required. This paper presents the results of a proof-of-concept (POC) study to investigate the impact of simulated hypergravity on target's size and distance. For gravity-dependent resizing and -positioning we used Hooke's law for the target deformation. The POC study was divided in two experiments, whereby hypergravity was induced by a long-arm human centrifuge and by weights attached to subjects' dominant arm. The study showed that at higher gravity levels larger target size and larger distance between the targets led to increased performance.

We investigated new interface technologies to ease astronaut's work under altered gravity. By bridging the gap between the physical reality and digital information, Augmented Reality keeps the focus on the task to fulfill. It is important that the operation of such Augmented Reality supported assistant systems is adequate preserved in weightlessness. By distinguishing the interface alignment to the body and outside of the body this paper presents a user study conducted to quantify and qualify the impact of altered gravity on sensorimotor hand-eye coordination related to the human body frame of reference. Taking the advantages of parabolic flights, we compared the performance of this alignment methods under normo- and altered gravity. Beside of verified effects of altered gravity on aimed pointing movements, the study showed a higher efficiency and decreased workload for the body aligned condition.

The application of AG generated by short diameter centrifuges has been proposed by a number of scientists and space agencies as a countermeasure against microgravity induced physiological degradation during long-term space missions, e.g. to Mars. The major objective of :enviFuge is to obtain extensive knowledge of hypergravity effects on the cardiovascular system, the cardio-vegetative regulation, the orthostatic regulation and other physiological systems. Therefore a unique research and training device, the :enviFuge, has been defined by DLR and developed by AMST Systemtechnik GmbH, and is located at DLR’s brand-new :envihab in Cologne. Operation of this multi-purpose research and training centrifuge started in the middle of 2013. :enviFuge features multiple research capabilities, including passive spinning, several kinds of locomotion exercises and ergometric training. Up to four subjects may be tested in parallel – each of them may perform different research relevant tasks and may be additionally and individually exposed to g-loads during a run. Scientists and physicians will have the unique opportunity to perform remotely controlled medical ultrasonics and highly advanced motion capturing, including precise body kinematics and kinetics tracking, during centrifugation. The outstanding modular design of :enviFuge provides easy and highly flexible possibilities for adaptation in future research applications. An important issue that will be considered during assessments on :enviFuge is the significant gravity gradient in the head-to-toe axis, which may be the cause for a number of unexpected physiological side effects within the human body during application of AG. Heart Rate Variability (HRV) measurement can be considered as a promising method for medical control and monitoring during centrifugation sessions. Especially the g-load should be adapted to the patterns of HRV, since this method offers a profound insight into cardiovascular and neurovegetative regulation. Besides applications of AG in the field of space exploration, short diameter centrifuges such as :enviFuge will be beneficial in other scientific disciplines, such as sports medicine and rehabilitation or therapy of immobilized patients.

The application of AG generated by short diameter centrifuges has been proposed by a number of scientists and space agencies as a countermeasure against microgravity induced physiological degradation during long-term space missions, e.g. to Mars. The major objective of :enviFuge is to obtain extensive knowledge of hypergravity effects on the cardiovascular system, the cardio-vegetative regulation, the orthostatic regulation and other physiological systems. Therefore a unique research and training device, the :enviFuge, has been defined by DLR and developed by AMST Systemtechnik GmbH, and is located at DLR’s brand-new :envihab in Cologne. Operation of this multipurpose research and training centrifuge started in the middle of 2013. :enviFuge features multiple research

A broad variety of countermeasures on the effects of weightlessness on human physiology have been developed and applied in the course of space exploration. Devices like treadmills, stretch ropes etc. have several disadvantages in common: they require a significant amount of crew time and they may not efficiently counteract the degradation of physiological structures and cellular functions. Some methods even include potentially painful or uncomfortable procedures for the astronauts. Thus, the application of Artificial Gravity (AG) generated by short radius centrifuges (they fit into space vessels) has been discussed and proposed by a number of scientists and space agencies as an alternative countermeasure during long-term space missions. Although there is a profound knowledge concerning, e.g., the cardiovascular system and immune responses acquired on long radius centrifuges, there is a remarkable lack of knowledge concerning the same issues on devices operating with short radius. In strict contrast to long radius centrifuges, there is a significant gravity gradient in the head-to-toe axis which comes along with the short radius and higher relative rotation velocity. Thus it is of utmost importance to continue investigating the effects of AG, especially by use of short radius centrifuges. The Short Arm Human Centrifuge (SAHC) at the German Aerospace Center (DLR) in Cologne, Germany, is the most advanced type of short radius centrifuges presently commercially available. Experience gained so far using the SAHC at DLR revealed that future projects on centrifuge devices with short radius should aim at a clear identification of the threshold level of the g-load, which is necessary to efficiently counteract the degradation of physical structures and an efficient support of cellular functions. A satisfying result would be combined countermeasure methods applied at a threshold concerning g-load and exposition time in the course of long-term sojourn in microgravity. Another future control or monitoring method to exactly dose AG training is heart rate variability, which offers an insight into neurovegetative and cardiovascular regulation. Centrifuges like the SAHC are also useful platforms to accommodate small biological experiments, e.g., experiments addressing the response of cultured cells to hypergravity. Here, we briefly review the issue of short radius centrifuges and also address our experience hitherto gained during a number of scientific projects carried out at the SAHC at DLR. Keywords: Centrifuge, hyper-g, cardiovascular system, neurovestibular system, countermeasure, artificial gravity.