Sustained wet-dry cycling on early Mars.

The presence of perennially wet surface environments on early Mars is well documented1,2, but little is known about short-term episodicity in the early hydroclimate3. Post-depositional processes driven by such short-term fluctuations may produce distinct structures, yet these are rarely preserved in the sedimentary record4. Incomplete geological constraints have led global models of the early Mars water cycle and climate to produce diverging results5,6. Here we report observations by the Curiosity rover at Gale Crater indicating that high-frequency wet-dry cycling occurred in early Martian surface environments. We observe exhumed centimetric polygonal ridges with sulfate enrichments, joined at Y-junctions, that record cracks formed in fresh mud owing to repeated wet-dry cycles of regular intensity. Instead of sporadic hydrological activity induced by impacts or volcanoes5, our findings point to a sustained, cyclic, possibly seasonal, climate on early Mars. Furthermore, as wet-dry cycling can promote prebiotic polymerization7,8, the Gale evaporitic basin may have been particularly conducive to these processes. The observed polygonal patterns are physically and temporally associated with the transition from smectite clays to sulfate-bearing strata, a globally distributed mineral transition1. This indicates that the Noachian-Hesperian transition (3.8-3.6 billion years ago) may have sustained an Earth-like climate regime and surface environments favourable to prebiotic evolution.

Aqueously altered igneous rocks sampled on the floor of Jezero crater, Mars.

The Perseverance rover landed in Jezero crater, Mars, to investigate ancient lake and river deposits. We report observations of the crater floor, below the crater's sedimentary delta, finding that the floor consists of igneous rocks altered by water. The lowest exposed unit, informally named Séítah, is a coarsely crystalline olivine-rich rock, which accumulated at the base of a magma body. Magnesium-iron carbonates along grain boundaries indicate reactions with carbon dioxide-rich water under water-poor conditions. Overlying Séítah is a unit informally named Máaz, which we interpret as lava flows or the chemical complement to Séítah in a layered igneous body. Voids in these rocks contain sulfates and perchlorates, likely introduced by later near-surface brine evaporation. Core samples of these rocks have been stored aboard Perseverance for potential return to Earth.

An olivine cumulate outcrop on the floor of Jezero crater, Mars.

The geological units on the floor of Jezero crater, Mars, are part of a wider regional stratigraphy of olivine-rich rocks, which extends well beyond the crater. We investigated the petrology of olivine and carbonate-bearing rocks of the Séítah formation in the floor of Jezero. Using multispectral images and x-ray fluorescence data, acquired by the Perseverance rover, we performed a petrographic analysis of the Bastide and Brac outcrops within this unit. We found that these outcrops are composed of igneous rock, moderately altered by aqueous fluid. The igneous rocks are mainly made of coarse-grained olivine, similar to some martian meteorites. We interpret them as an olivine cumulate, formed by settling and enrichment of olivine through multistage cooling of a thick magma body.

Recommendations for Reducing Heterogeneity in Handgrip Strength Protocols.

Handgrip dynamometers are widely used to measure handgrip strength (HGS). HGS is a safe and easy to obtain measure of strength capacity, and a reliable assessment of muscle function. Although HGS provides robust prognostic value and utility, several protocol variants exist for HGS in clinical settings and translational research. This lack of methodological consistency could threaten the precision of HGS measurements and limit comparisons between the growing number of studies measuring HGS. Providing awareness of the protocol variants for HGS and making suggestions to reduce the implications of these variants will help to improve methodological consistency. Moreover, leveraging recent advancements in HGS equipment may enable us to use more sophisticated HGS dynamometer technologies to better assess muscle function. This Special Article will 1) highlight differences in HGS protocols and instrumentation, 2) provide recommendations to better specify HGS procedures and equipment, and 3) present future research directions for studies that measure HGS. We also provided a minimum reporting criteria framework to help future research studies avoid underreporting of HGS procedures.

Effects of Three Different Exercise Strategies for Optimizing Aerobic Capacity and Skeletal Muscle Performance in Older Adults: A Pilot Study.

This Brief Report describes a pilot study of the effect of 12 weeks of stationary bicycle high-intensity interval training, stationary bicycle moderate-intensity continuous training, and resistance training on cardiorespiratory, muscular, and physical function measures in insufficiently-active older adults (N=14; 66.4±3.9 years; 3 male, 11 female). After baseline testing, participants were randomly assigned to one of the exercise groups. High-intensity interval training and moderate-intensity continuous training had small-to-large effect sizes on cardiorespiratory/endurance and physical function measures, but very small effect sizes on muscular measures. Resistance training had small-to-large effect sizes on cardiorespiratory, muscular, and physical function measures. This pilot study should be interpreted cautiously, but findings suggest that resistance exercise may be the most effective of the three studied exercise strategies for older adults as it can induce beneficial adaptations across multiple domains. These effect sizes can be used to determine optimal sample sizes for future investigations.

Comparison of a Multi-Component Physical Function Battery to Usual Walking Speed for Assessing Lower Extremity Function and Mobility Limitation in Older Adults.

OBJECTIVES: To compare a composite measure of physical function that comprises locomotor and non-locomotor tests (i.e., the Mobility Battery Assessment (MBA)) with traditional measures of mobility (4-m usual gait speed (UGS), six-minute walk (6MW) gait speed, and short physical performance battery (SPPB) score) for assessing lower extremity function and discriminating community dwelling older adults with and without mobility limitations. DESIGN: Cross-sectional, observational study. SETTING: Laboratory-based. PARTICIPANTS: 89 community-dwelling older adults (74.9±6.7). MEASUREMENTS: Using principal component analysis we derived an MBA score for 89 community-dwelling older adults, and quantified 4-m UGS, 6MW gait speed, and SPPB score. The MBA score was based on five lab-based tests. We also quantified self-reported lower extremity function/mobility using the Neuro-QOL Lower Extremity Function-Mobility instrument. Based on this data a continuous score was derived and subjects were classified as "mobility limited" or "non-mobility limited". Correlations between the mobility measures and the Neuro-QOL score were calculated, and ROC curves were constructed to determine the AUC for the mobility measures ability to predict mobility limitations. RESULTS: The MBA had the largest AUC (0.92) for discriminating mobility limitations and exhibited the strongest correlation (0.73) with the Neuro-QOL Lower Extremity Function-Mobility Scale. The worst performing predictors were the 4-meter UGS and stair climb power both with an AUC of 0.8 for discriminating mobility limitations, and a low correlation with Neuro-QOL Lower Extremity Function Scale of 0.39 and 0.46, respectively. CONCLUSION: The MBA score moderately improves the magnitude of correlation and discrimination of mobility limitation in older adults than singular, standard tests of mobility.

Mars Extant Life: What's Next? Conference Report.

On November 5-8, 2019, the "Mars Extant Life: What's Next?" conference was convened in Carlsbad, New Mexico. The conference gathered a community of actively publishing experts in disciplines related to habitability and astrobiology. Primary conclusions are as follows: A significant subset of conference attendees concluded that there is a realistic possibility that Mars hosts indigenous microbial life. A powerful theme that permeated the conference is that the key to the search for martian extant life lies in identifying and exploring refugia ("oases"), where conditions are either permanently or episodically significantly more hospitable than average. Based on our existing knowledge of Mars, conference participants highlighted four potential martian refugium (not listed in priority order): Caves, Deep Subsurface, Ices, and Salts. The conference group did not attempt to reach a consensus prioritization of these candidate environments, but instead felt that a defensible prioritization would require a future competitive process. Within the context of these candidate environments, we identified a variety of geological search strategies that could narrow the search space. Additionally, we summarized a number of measurement techniques that could be used to detect evidence of extant life (if present). Again, it was not within the scope of the conference to prioritize these measurement techniques-that is best left for the competitive process. We specifically note that the number and sensitivity of detection methods that could be implemented if samples were returned to Earth greatly exceed the methodologies that could be used at Mars. Finally, important lessons to guide extant life search processes can be derived both from experiments carried out in terrestrial laboratories and analog field sites and from theoretical modeling.

Decreased Handgrip Strength is Associated With Impairments in Each Autonomous Living Task for Aging Adults in the United States.

OBJECTIVES: The primary purpose of this study was to determine the time-varying associations between decreased handgrip strength (HGS) and individual instrumental activities of daily living (IADL) impairments for a nationally-representative sample of aging adults in the United States. DESIGN: Longitudinal-Panel. SETTING: Detailed interviews were completed in person and core interviews were typically completed over the telephone. PARTICIPANTS: A total of 15,336 participants aged at least 50 years who participated in the 2006 wave of the Health and Retirement Study were followed biennially for 8-years. MEASUREMENTS: A hand-held dynamometer assessed HGS and performance in IADLs were self-reported. RESULTS: Every 5-kilogram decrease in HGS was associated with an increased odds ratio for the following IADL impairments: 1.11 (95% confidence interval (CI): 1.09, 1.13) for using a map, 1.10 (CI: 1.07, 1.12) for grocery shopping, 1.09 (CI: 1.05, 1.14) for taking medications, 1.07 (CI: 1.05, 1.09) for preparing hot meals, 1.06 (CI: 1.04, 1.08) for managing money, and 1.05 (CI: 1.02, 1.09) for using a telephone. CONCLUSIONS: Decreased HGS was associated with each IADL impairment, and slightly different associations were observed in individual IADL tasks for aging adults in the United States. Our findings suggest that decreased HGS, which is reflective of reduced function of the neuromuscular system, is associated with diminished performance in autonomous living tasks during aging. Losses in HGS may lead to the development of an IADL impairment. Therefore, health-care providers working with aging adults should utilize measures of HGS as a screening tool for identifying future deficits in neuromuscular functioning. Interventions designed to preserve IADLs in aging adults should also include measures of HGS for detecting early changes in IADL capacity, and intervening at the onset of HGS declines may help aging adults retain their ability to live autonomously.

Neuromuscular Changes with Aging and Sarcopenia.

Sarcopenia was originally conceptualized as the age-related loss of skeletal muscle mass. Over the ensuing decades, the conceptual definition of sarcopenia has changed to represent a condition in older adults that is characterized by declining muscle mass and function, with "function" most commonly conceived as muscle weakness and/or impaired physical performance (e.g., slow gait speed). Findings over the past 15-years, however, have demonstrated that changes in grip and leg extensor strength are not primarily due to muscle atrophy per se, and that to a large extent, are reflective of declines in the integrity of the nervous system. This article briefly summarizes findings relating to the complex neuromuscular mechanisms that contribute to reductions in muscle function associated with advancing age, and the implications of these findings on the development of effective therapies.

International Clinical Practice Guidelines for Sarcopenia (ICFSR): Screening, Diagnosis and Management.

OBJECTIVES: Sarcopenia, defined as an age-associated loss of skeletal muscle function and muscle mass, occurs in approximately 6 - 22 % of older adults. This paper presents evidence-based clinical practice guidelines for screening, diagnosis and management of sarcopenia from the task force of the International Conference on Sarcopenia and Frailty Research (ICSFR). METHODS: To develop the guidelines, we drew upon the best available evidence from two systematic reviews paired with consensus statements by international working groups on sarcopenia. Eight topics were selected for the recommendations: (i) defining sarcopenia; (ii) screening and diagnosis; (iii) physical activity prescription; (iv) protein supplementation; (v) vitamin D supplementation; (vi) anabolic hormone prescription; (vii) medications under development; and (viii) research. The ICSFR task force evaluated the evidence behind each topic including the quality of evidence, the benefit-harm balance of treatment, patient preferences/values, and cost-effectiveness. Recommendations were graded as either strong or conditional (weak) as per the GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach. Consensus was achieved via one face-to-face workshop and a modified Delphi process. RECOMMENDATIONS: We make a conditional recommendation for the use of an internationally accepted measurement tool for the diagnosis of sarcopenia including the EWGSOP and FNIH definitions, and advocate for rapid screening using gait speed or the SARC-F. To treat sarcopenia, we strongly recommend the prescription of resistance-based physical activity, and conditionally recommend protein supplementation/a protein-rich diet. No recommendation is given for Vitamin D supplementation or for anabolic hormone prescription. There is a lack of robust evidence to assess the strength of other treatment options.

The Vicious Cycle of Myostatin Signaling in Sarcopenic Obesity: Myostatin Role in Skeletal Muscle Growth, Insulin Signaling and Implications for Clinical Trials.

The age-related loss of skeletal muscle (sarcopenia) is a major health concern as it is associated with physical disability, metabolic impairments, and increased mortality. The coexistence of sarcopenia with obesity, termed 'sarcopenic obesity', contributes to skeletal muscle insulin resistance and the development of type 2 diabetes, a disease prevalent with advancing age. Despite this knowledge, the mechanisms contributing to sarcopenic obesity remain poorly understood, preventing the development of targeted therapeutics. This article will discuss the clinical and physiological consequences of sarcopenic obesity and propose myostatin as a potential candidate contributing to this condition. A special emphasis will be placed on examining the role of myostatin signaling in impairing both skeletal muscle growth and insulin signaling. In addition, the role of myostatin in regulating muscle-to fat cross talk, further exacerbating metabolic dysfunction in the elderly, will be highlighted. Lastly, we discuss how this knowledge has implications for the design of myostatin-inhibitor clinical trials.

OSIRIS-REx Contamination Control Strategy and Implementation.

OSIRIS-REx will return pristine samples of carbonaceous asteroid Bennu. This article describes how pristine was defined based on expectations of Bennu and on a realistic understanding of what is achievable with a constrained schedule and budget, and how that definition flowed to requirements and implementation. To return a pristine sample, the OSIRIS-REx spacecraft sampling hardware was maintained at level 100 A/2 and <180 ng/cm2 of amino acids and hydrazine on the sampler head through precision cleaning, control of materials, and vigilance. Contamination is further characterized via witness material exposed to the spacecraft assembly and testing environment as well as in space. This characterization provided knowledge of the expected background and will be used in conjunction with archived spacecraft components for comparison with the samples when they are delivered to Earth for analysis. Most of all, the cleanliness of the OSIRIS-REx spacecraft was achieved through communication among scientists, engineers, managers, and technicians.

Ancient aqueous environments at Endeavour crater, Mars.

Opportunity has investigated in detail rocks on the rim of the Noachian age Endeavour crater, where orbital spectral reflectance signatures indicate the presence of Fe(+3)-rich smectites. The signatures are associated with fine-grained, layered rocks containing spherules of diagenetic or impact origin. The layered rocks are overlain by breccias, and both units are cut by calcium sulfate veins precipitated from fluids that circulated after the Endeavour impact. Compositional data for fractures in the layered rocks suggest formation of Al-rich smectites by aqueous leaching. Evidence is thus preserved for water-rock interactions before and after the impact, with aqueous environments of slightly acidic to circum-neutral pH that would have been more favorable for prebiotic chemistry and microorganisms than those recorded by younger sulfate-rich rocks at Meridiani Planum.

Elemental geochemistry of sedimentary rocks at Yellowknife Bay, Gale crater, Mars.

Sedimentary rocks examined by the Curiosity rover at Yellowknife Bay, Mars, were derived from sources that evolved from an approximately average martian crustal composition to one influenced by alkaline basalts. No evidence of chemical weathering is preserved, indicating arid, possibly cold, paleoclimates and rapid erosion and deposition. The absence of predicted geochemical variations indicates that magnetite and phyllosilicates formed by diagenesis under low-temperature, circumneutral pH, rock-dominated aqueous conditions. Analyses of diagenetic features (including concretions, raised ridges, and fractures) at high spatial resolution indicate that they are composed of iron- and halogen-rich components, magnesium-iron-chlorine-rich components, and hydrated calcium sulfates, respectively. Composition of a cross-cutting dike-like feature is consistent with sedimentary intrusion. The geochemistry of these sedimentary rocks provides further evidence for diverse depositional and diagenetic sedimentary environments during the early history of Mars.

Soil diversity and hydration as observed by ChemCam at Gale crater, Mars.

The ChemCam instrument, which provides insight into martian soil chemistry at the submillimeter scale, identified two principal soil types along the Curiosity rover traverse: a fine-grained mafic type and a locally derived, coarse-grained felsic type. The mafic soil component is representative of widespread martian soils and is similar in composition to the martian dust. It possesses a ubiquitous hydrogen signature in ChemCam spectra, corresponding to the hydration of the amorphous phases found in the soil by the CheMin instrument. This hydration likely accounts for an important fraction of the global hydration of the surface seen by previous orbital measurements. ChemCam analyses did not reveal any significant exchange of water vapor between the regolith and the atmosphere. These observations provide constraints on the nature of the amorphous phases and their hydration.

WHAT WE HAVE LEARNED FROM EXERCISE AND LIFESTYLE TRIALS TO ALLEVIATE MOBILITY IMPAIRMENT IN OLDER ADULTS.

Enhancement of cardiovascular and muscular fitness through exercise and lifestyle interventions is critical to in alleviating mobility impairment in older adults. In this review article, we discuss the current knowledge-base surrounding mobility improvements in seniors following behavioral interventions that use lifestyle modifications involving physical activity and dietary interventions.

Ancient impact and aqueous processes at Endeavour Crater, Mars.

The rover Opportunity has investigated the rim of Endeavour Crater, a large ancient impact crater on Mars. Basaltic breccias produced by the impact form the rim deposits, with stratigraphy similar to that observed at similar-sized craters on Earth. Highly localized zinc enrichments in some breccia materials suggest hydrothermal alteration of rim deposits. Gypsum-rich veins cut sedimentary rocks adjacent to the crater rim. The gypsum was precipitated from low-temperature aqueous fluids flowing upward from the ancient materials of the rim, leading temporarily to potentially habitable conditions and providing some of the waters involved in formation of the ubiquitous sulfate-rich sandstones of the Meridiani region.

Bacterial growth at the high concentrations of magnesium sulfate found in martian soils.

The martian surface environment exhibits extremes of salinity, temperature, desiccation, and radiation that would make it difficult for terrestrial microbes to survive. Recent evidence suggests that martian soils contain high concentrations of MgSO4 minerals. Through warming of the soils, meltwater derived from subterranean ice-rich regolith may exist for an extended period of time and thus allow the propagation of terrestrial microbes and create significant bioburden at the near surface of Mars. The current report demonstrates that halotolerant bacteria from the Great Salt Plains (GSP) of Oklahoma are capable of growing at high concentrations of MgSO4 in the form of 2 M solutions of epsomite. The epsotolerance of isolates in the GSP bacterial collection was determined, with 35% growing at 2 M MgSO4. There was a complex physiological response to mixtures of MgSO4 and NaCl coupled with other environmental stressors. Growth also was measured at 1 M concentrations of other magnesium and sulfate salts. The complex responses may be partially explained by the pattern of chaotropicity observed for high-salt solutions as measured by agar gelation temperature. Select isolates could grow at the high salt concentrations and low temperatures found on Mars. Survival during repetitive freeze-thaw or drying-rewetting cycles was used as other measures of potential success on the martian surface. Our results indicate that terrestrial microbes might survive under the high-salt, low-temperature, anaerobic conditions on Mars and present significant potential for forward contamination. Stringent planetary protection requirements are needed for future life-detection missions to Mars.

Relative safety of 4 weeks of blood flow-restricted resistance exercise in young, healthy adults.

This study evaluated the effect of 4 weeks of low-load resistance exercise with blood flow restriction (BFRE) on increasing strength in comparison with high-load resistance exercise (HLE), and assessed changes in blood, vascular and neural function. Healthy adults performed leg extension BFRE or HLE 3 days/week at 30% and 80% of strength, respectively. During BFRE, a cuff on the upper leg was inflated to 30% above systolic blood pressure. Strength, pulse-wave velocity (PWV), ankle-brachial index (ABI), prothrombin time (PT) and nerve conduction (NC) were measured before and after training. Markers of coagulation (fibrinogen and D-dimer), fibrinolysis [tissue plasminogen activator (tPA)] and inflammation [high sensitivity C-reactive protein (hsCRP)] were measured in response to the first and last exercise bouts. Strength increased 8% with BFRE and 13% with HLE (P<0.01). No changes in PWV, ABI, PT or NC were observed following training for either group (P>0.05). tPA antigen increased 30-40% immediately following acute bouts of BFRE and HLE (P=0.01). No changes were observed in fibrinogen, D-dimer or hsCRP (P>0.05). These findings indicate that both protocols increase the strength without altering nerve or vascular function, and that a single bout of both protocols increases fibrinolytic activity without altering selected markers of coagulation or inflammation in healthy individuals.