The effects of isometric exercise training on femoral and brachial artery dimension and blood flow in middle-aged men.

Introduction Previous isometric training studies reporting reductions in resting blood pressure have not explored whether there are concomitant changes in resting artery dimensions and blood flow. Furthermore, the influence of isometric training intensity on these adaptations has not been investigated. Therefore, the purpose of this study was to explore whether training-induced reductions in resting blood pressure are associated with concomitant changes in the vasculature of the trained and untrained limbs and to establish if these adaptations were intensity dependent. Methods Subjects undertook an 8 week training programme consisting of 4x2 min bilateral-leg isometric contractions 3 x per week (Wiles et al., 2010). Two groups exercised at intensities equivalent to 70% (n=10) or 85% (n=10) of their peak heart rate (%HRpeak; as established in a prior incremental test), and a third group acted as controls (n=10). Resting systolic (SBP), mean arterial (MAP) and diastolic (DBP) blood pressure was measured at baseline and post-training. Artery diameter and mean blood flow (brachial and femoral) were also measured at rest using Doppler ultrasound. Analysis of variance was used to determine whether post-training measures were significantly different to baseline. Also, baseline values were used as a covariate to account for initial resting blood pressure values. Results There were significant reductions in resting SBP (-10.8±7.9 mmHg) and MAP (-4.7±6.8 mmHg) in the 85%T group post-training and concomitant significant increases in resting femoral mean artery diameter (FMAD; 1.0±0.4 mm) and femoral mean blood velocity (FMBV; 0.68±0.83 cm/s), which resulted in increased femoral artery blood flow (FABF; 82.06±31.92 ml/min). There were no significant changes in brachial artery measures after training. Furthermore, there were no significant changes in any resting measure in the 70%T or control group. Discussion This study shows that the reductions in resting SBP and MAP observed after isometric training are associated with concomitant increases in resting artery dimensions and blood flow, but these changes were restricted to the trained limbs. This suggests that the vascular adaptations were localised. Furthermore, these adaptations seem to be training-intensity dependent, as they were not observed in the 70%T training group. These findings could be explained by reduced resting vascular tone, enhanced endothelium-dependent function or by vascular remodelling. The stimulus for such adaptations may arise from changes in availability/activity of nitric oxide as a result of sheer stresses during isometric exercise (McGowan et al. 2007). Exactly how these sheer stresses occur during isometric exercise and how they might be related to isometric training intensity would be deserving of future study. McGowan CL, Levy AS, McCartney N, MacDonald MJ. (2007). Clin. Sci. 112, 403-409. Wiles JD, Coleman DA, Swaine IL. (2010). Eur. J. Appl. Physiol. 108, 419-428

Is the genetic landscape of the deep subsurface biosphere affected by viruses?

Viruses are powerful manipulators of microbial diversity, biogeochemistry, and evolution in the marine environment. Viruses can directly influence the genetic capabilities and the fitness of their hosts through the use of fitness factors and through horizontal gene transfer. However, the impact of viruses on microbial ecology and evolution is often overlooked in studies of the deep subsurface biosphere. Subsurface habitats connected to hydrothermal vent systems are characterized by constant fluid flux, dynamic environmental variability, and high microbial diversity. In such conditions, high adaptability would be an evolutionary asset, and the potential for frequent host-virus interactions would be high, increasing the likelihood that cellular hosts could acquire novel functions. Here, we review evidence supporting this hypothesis, including data indicating that microbial communities in subsurface hydrothermal fluids are exposed to a high rate of viral infection, as well as viral metagenomic data suggesting that the vent viral assemblage is particularly enriched in genes that facilitate horizontal gene transfer and host adaptability. Therefore, viruses are likely to play a crucial role in facilitating adaptability to the extreme conditions of these regions of the deep subsurface biosphere. We also discuss how these results might apply to other regions of the deep subsurface, where the nature of virus-host interactions would be altered, but possibly no less important, compared to more energetic hydrothermal systems

Exoplanet Atmospheres

At the dawn of the first discovery of exoplanets orbiting sun-like stars in the mid-1990s, few believed that observations of exoplanet atmospheres would ever be possible. After the 2002 Hubble Space Telescope detection of a transiting exoplanet atmosphere, many skeptics discounted it as a one-object, one-method success. Nevertheless, the field is now firmly established, with over two dozen exoplanet atmospheres observed today. Hot Jupiters are the type of exoplanet currently most amenable to study. Highlights include: detection of molecular spectral features; observation of day-night temperature gradients; and constraints on vertical atmospheric structure. Atmospheres of giant planets far from their host stars are also being studied with direct imaging. The ultimate exoplanet goal is to answer the enigmatic and ancient question, "Are we alone?" via detection of atmospheric biosignatures. Two exciting prospects are the immediate focus on transiting super Earths orbiting in the habitable zone of M-dwarfs, and ultimately the spaceborne direct imaging of true Earth analogs.Comment: Annual Reviews of Astronomy and Astrophysics, in press. 47 pages, 16 Figures. This article was completed in January 2010; more recent references are not include

Stretching of active muscle elicits chronic changes in multiple strain risk factors

Introduction: The muscle stretch intensity imposed during 'flexibility' training influences the magnitude of joint range of motion (ROM) adaptation. Thus, stretching whilst the muscle is voluntarily activated was hypothesized to provide a greater stimulus than passive stretching. The effect of a 6-week program of stretch imposed on an isometrically-contracting muscle (i.e. qualitatively similar to isokinetic eccentric training) on muscle-tendon mechanics was therefore studied in 13 healthy human volunteers. Methods: Before and after the training program, dorsiflexion ROM, passive joint moment, and maximal isometric plantar flexor moment were recorded on an isokinetic dynamometer. Simultaneous real-time motion analysis and ultrasound imaging recorded gastrocnemius medialis muscle and Achilles tendon elongation. Training was performed twice weekly and consisted of five sets of 12 maximal isokinetic eccentric contractions at 10[degrees][middle dot]s-1. Results: Significant increases (P0.05), a significant increase in tendon stiffness (31.2%; P<0.01) and decrease in passive muscle stiffness (-14.6%; P<0.05) was observed. Conclusion: The substantial positive adaptation in multiple functional and physiological variables that are cited within the primary aetiology of muscle strain injury, including strength, ROM, muscle stiffness, and maximal energy storage, indicate that the stretching of active muscle might influence injury risk in addition to muscle function. The lack of change in muscle-tendon stiffness simultaneous with significant increases in tendon stiffness and decreases in passive muscle stiffness indicates that tissue-specific effects were elicited

Drake Equation for the Multiverse: From the String Landscape to Complex Life

It is argued that selection criteria usually referred to as "anthropic conditions" for the existence of intelligent (typical) observers widely adopted in cosmology amount only to preconditions for primitive life. The existence of life does not imply in the existence of intelligent life. On the contrary, the transition from single-celled to complex, multi-cellular organisms is far from trivial, requiring stringent additional conditions on planetary platforms. An attempt is made to disentangle the necessary steps leading from a selection of universes out of a hypothetical multiverse to the existence of life and of complex life. It is suggested that what is currently called the "anthropic principle" should instead be named the "prebiotic principle."Comment: 6 pages, RevTeX, in press, Int. J. Mod. Phys.

The relationship between EMG and either heart rate or blood pressure during a single-leg incremental isometric exercise test

Recently Wiles et al. (2008: Journal of Sports Sciences, 24, 155-162) introduced the linear relationship between double-leg EMG and either HR or BP during incremental isometric exercise as a novel method for regulating exercise intensity during training. However, many previous training studies (eg Wiley et al., 1992: Medicine and Science in Sports and Exercise, 24, 749-754) have employed single-leg protocols. The relationship between EMG and HR or BP during an incremental single-leg protocol has not been explored. Therefore, the purpose of this study was to determine whether these relationships were evident in a single-leg protocol. Following ethical approval fifteen healthy, normotensive (mean systolic blood pressure 123.8, s = 6.8 mmHg) and physically active men (age 24.8, s = 6.7 yrs; mass 78.8, s = 9.5 kg) performed a maximum voluntary contraction (MVC) using a seated isometric single-leg extension, from which peak torque (TORpeak) and EMG (EMGpeak) were determined. Subsequently, subjects performed two incremental isometric exercise tests at 10, 15, 20, 25 and 30 %EMGpeak, using dominant and non-dominant legs, during which HR and BP were measured continuously. The slope and elevation (intercept) of the linear regression lines obtained in each leg were compared with the use of analysis of covariance (ANCOVA). The within- and between-subjects variation of the mean HR, SBP, and %EMGpeak values was assessed using a repeated measures multivariate analysis of variance (MANOVA). The group mean data for each leg showed a linear relationship between %EMGpeak and HR (dominant leg r = 0.98; P0.05 and 0.98, P0.05 and 0.99, P< 0.001). The lack of a linear relationship in many individuals was probably due to the accumulation of local metabolites in the single-leg compared to the previously published double-leg isometric exercise. The inter-individual variation in the relationship between EMGpeak and HR or BP during the single-leg protocol, make it difficult to use the single-leg protocol, in the same way as the double-leg protocol, to prescribe isometric exercise intensity during training

Stretching of active muscle evokes greater acute increases in plantarflexor range of motion than static stretching

Introduction Increases in joint range of motion (ROM) in athletic and clinical populations are normally achieved through static stretching. However, substantially greater increases in ROM were recently reported after a 6-week exercise programme when stretch was imposed on active muscle (Kay et al., 2016), although acute effects remain unknown. Therefore, the present study compared the effects of acute and repeated bouts of active muscle stretching and static stretching of the plantarflexors. Methods Using a randomised, crossover design, 18 recreationally active subjects completed four trials under two experimental conditions (static stretch [SS1, SS2]; active muscle stretch [AMS1, AMS2]), with each trial separated by 48-72 h. SS trials comprised 5 sets of 30-s static stretches whilst AMS trials comprised 5 sets of 10 repetitions of 3-s stretches imposed on maximally contracted muscle (total loading in each trial = 150 s). Before and after each set, dorsiflexion ROM and passive plantarflexor moment were recorded on an isokinetic dynamometer, electromyograhic (EMG) activity of the soleus and ultrasound imaging of Achilles tendon and medial gastrocnemius fascicle elongation were simultaneously recorded. Results A significantly (P<0.05) greater increase in ROM was observed in AMS (5.9°-7.7°) than SS (2.2-3.0°) trials, with ROM significantly greater after AMS2 than all other trials (+3.3-5.8°). Furthermore, a significant increase in ROM was already detected after the first set in AMS trials (2.2-3.1°), and this was similar to the magnitude of change after 5 sets of stretches in SS trials. Similar decreases in the passive moment slope occurred after SS (7.3%-11.7%) and AMS (10.1%-15.3%) trials, however significant increases in peak passive moment (30.7-34.7%) and elastic energy storage (54.3-68.2%) occurred only after AMS. A significant reduction in maximal isometric (i.e. active) moment occurred only after SS1 (6.5%). Discussion These data have important practical implications as similar increases in ROM were achieved after a single set of AMS compared with multiple static stretches (i.e. current practice), without a reduction in active muscle force. Furthermore, when time under loading was identical, AMS resulted in a more than twofold greater increase in ROM, indicating that it is more effective and efficient than current stretching practices. The significantly greater ROM after the second AMS trial indicates a repeated bout effect that may explain the previously reported greater long-term adaptations in ROM

Archaea and bacteria with surprising microdiversity show shifts in dominance over 1,000-year time scales in hydrothermal chimneys

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences 107 (2010): 1612-1617, doi:10.1073/pnas.0905369107.The Lost City Hydrothermal Field, an ultramafic-hosted system located 15 km west of the Mid-Atlantic Ridge, has experienced at least 30,000 years of hydrothermal activity. Previous studies have shown that its carbonate chimneys form by mixing of ~90ºC, pH 9-11 hydrothermal fluids and cold seawater. Flow of methane and hydrogen-rich hydrothermal fluids in the porous interior chimney walls supports archaeal biofilm communities dominated by a single phylotype of Methanosarcinales. In this study, we have extensively sampled the carbonate-hosted archaeal and bacterial communities by obtaining sequences of >200,000 amplicons of the 16S rRNA V6 region and correlated the results with isotopic (230Th) ages of the chimneys over a 1200 year period. Rare sequences in young chimneys were often more abundant in older chimneys, indicating that members of the rare biosphere can become dominant members of the ecosystem when environmental conditions change. These results suggest that a long history of selection over many cycles of chimney growth has resulted in numerous closely related species at Lost City, each of which is pre-adapted to a particular set of re-occurring environmental conditions. Due to the unique characteristics of the Lost City Hydrothermal Field, these data offer an unprecedented opportunity to study the dynamics of a microbial ecosystem's rare biosphere over a thousand-year time scale.This research was supported by the W.M. Keck Foundation to MLS, the NASA Astrobiology Institute through the Carnegie Institution for Science to JAB and through the MBL to MLS, NSF Grant OCE0137206 and NOAA Ocean Exploration support to DSK, and grants 96-2116-M002-003 and 97-2752-M004-PAE to C.-C. Shen

Linkages between mineralogy, fluid chemistry, and microbial communities within hydrothermal chimneys from the Endeavor Segment, Juan de Fuca Ridge

Rock and fluid samples were collected from three hydrothermal chimneys at the Endeavour Segment, Juan de Fuca Ridge to evaluate linkages among mineralogy, fluid chemistry, and microbial community composition within the chimneys. Mössbauer, midinfrared thermal emission, and visible-near infrared spectroscopies were utilized for the first time to characterize vent mineralogy, in addition to thin-section petrography, X-ray diffraction, and elemental analyses. A 282°C venting chimney from the Bastille edifice was composed primarily of sulfide minerals such as chalcopyrite, marcasite, and sphalerite. In contrast, samples from a 300°C venting chimney from the Dante edifice and a 321°C venting chimney from the Hot Harold edifice contained a high abundance of the sulfate mineral anhydrite. Geochemical modeling of mixed vent fluids suggested the oxic-anoxic transition zone was above 100°C at all three vents, and that the thermodynamic energy available for autotrophic microbial redox reactions favored aerobic sulfide and methane oxidation. As predicted, microbes within the Dante and Hot Harold chimneys were most closely related to mesophilic and thermophilic aerobes of the Betaproteobacteria and Gammaproteobacteria and sulfide-oxidizing autotrophic Epsilonproteobacteria. However, most of the microbes within the Bastille chimney were most closely related to mesophilic and thermophilic anaerobes of the Deltaproteobacteria, especially sulfate reducers, and anaerobic hyperthermophilic archaea. The predominance of anaerobes in the Bastille chimney indicated that other environmental factors promote anoxic conditions. Possibilities include the maturity or fluid flow characteristics of the chimney, abiotic Fe2+ and S2− oxidation in the vent fluids, or O2 depletion by aerobic respiration on the chimney outer wall

Environmental niches and metabolic diversity in Neoarchean lakes

Financial support for this study came from the NASA postdoctoral program (EES, REA), the NSF-FESD program (RB, TWL), the NASA Astrobiology Institute (TWL, NJP, and RB), and the NASA Exobiology program (grant NNX16AI37G to RB).The diversification of macro-organisms over the last 500 million years often coincided with the development of new environmental niches. Microbial diversification over the last 4 billion years likely followed similar patterns. However, linkages between environmental settings and microbial ecology have so far not been described from the ancient rock record. In this study, we investigated carbon, nitrogen, and molybdenum isotopes, and iron speciation in five non-marine stratigraphic units of the Neoarchean Fortescue Group, Western Australia, that are similar in age (2.78–2.72 Ga) but differ in their hydro-geologic setting. Our data suggest that the felsic-dominated and hydrologically open lakes of the Bellary and Hardey formations were probably dominated by methanogenesis (δ13Corg = −38.7 ± 4.2‰) and biologic N2 fixation (δ15Nbulk =−0.6 ± 1.0‰), whereas the Mt. Roe, Tumbiana and Kylena Formations, with more mafic siliciclastic sediments, preserve evidence of methanotrophy (δ13Corg as low as −57.4‰, δ13Ccarb as low as −9.2‰) and NH3 loss under alkaline conditions. Evidence of oxygenic photosynthesis is recorded only in the closed evaporitic Tumbiana lakes marked by abundant stromatolites, limited evidence of Fe and S cycling, fractionated Mo isotopes (δ98/95Mo = +0.4 ± 0.4‰), and the widest range in δ13Corg (−57‰ to −15‰), suggesting oxidative processes and multiple carbon fixation pathways. Methanotrophy in the three mafic settings was probably coupled to a combination of oxidants, including O2 and SO42-. Overall, our results may indicate that early microbial evolution on the Precambrian Earth was in part influenced by geological parameters. We speculate that expanding habitats, such as those linked to continental growth, may have been an important factor in the evolution of life.PostprintPeer reviewe