1,727 research outputs found
Assessing the usefulness of acute physiological responses following resistance exercise: sensitivity, magnitude of change and time course of measures
A variety of strategies exist to modulate acute physiological responses following resistance exercise aimed at enhancing recovery and/or adaptation processes. To assess the true impact of these strategies, it is important to know the ability of measures to detect meaningful change. We investigated the sensitivity of measures used to quantify acute physiological responses to resistance exercise and constructed a physiological profile to characterise the magnitude of change and time course of this response. Eight males, accustomed to regular resistance exercise, performed experimental sessions during a âcontrol weekâ, void of an exercise stimulus. Participants repeated this sequence of experimental sessions the following week, termed the âexercise weekâ, except they performed a bout of lower-limb resistance exercise following baseline assessments. Assessments were conducted at baseline, 2, 6, 24, 48, 72 and 96 h post-intervention. Based on the signal-to-noise ratio, the most sensitive measures were maximal voluntary isometric contraction, 20m sprint, countermovement jump peak force, rate of force development (100-200ms), muscle soreness, daily analysis of life demands for athletes Part B, limb girth, matrix metalloproteinase-9, interleukin-6, creatine kinase and high sensitivity C-reactive protein with ratios of >1.5. There were clear changes in these measures following resistance exercise, determined via magnitude-based inferences. These findings highlight measures that can detect real changes in acute physiological responses following resistance exercise in trained individuals. Researchers investigating strategies to manipulate acute physiological responses for recovery and/or adaptation can use these measures, as well as recommended sampling points, to be confident that their interventions are making a worthwhile impact
Ozone Depletion from Nearby Supernovae
Estimates made in the 1970's indicated that a supernova occurring within tens
of parsecs of Earth could have significant effects on the ozone layer. Since
that time, improved tools for detailed modeling of atmospheric chemistry have
been developed to calculate ozone depletion, and advances have been made in
theoretical modeling of supernovae and of the resultant gamma-ray spectra. In
addition, one now has better knowledge of the occurrence rate of supernovae in
the galaxy, and of the spatial distribution of progenitors to core-collapse
supernovae. We report here the results of two-dimensional atmospheric model
calculations that take as input the spectral energy distribution of a
supernova, adopting various distances from Earth and various latitude impact
angles. In separate simulations we calculate the ozone depletion due to both
gamma-rays and cosmic rays. We find that for the combined ozone depletion
roughly to double the ``biologically active'' UV flux received at the surface
of the Earth, the supernova must occur at <8 pc. Based on the latest data, the
time-averaged galactic rate of core-collapse supernovae occurring within 8 pc
is ~1.5/Gyr. In comparing our calculated ozone depletions with those of
previous studies, we find them to be significantly less severe than found by
Ruderman (1974), and consistent with Whitten et al. (1976). In summary, given
the amplitude of the effect, the rate of nearby supernovae, and the ~Gyr time
scale for multicellular organisms on Earth, this particular pathway for mass
extinctions may be less important than previously thought.Comment: 24 pages, 4 Postscript figures, to appear in The Astrophysical
Journal, 2003 March 10, vol. 58
Effect of hot water immersion on acute physiological responses following resistance exercise
Purpose: Hot water immersion (HWI) is a strategy theorised to enhance exercise recovery. However, the acute physiological responses to HWI following resistance exercise are yet to be determined.
Methods: The effect of HWI on intramuscular temperature (IMT), muscle function, muscle soreness and blood markers of muscle cell disruption and inflammatory processes after resistance exercise was assessed. Sixteen resistance trained males performed resistance exercise, followed by either 10 min HWI at 40°C or 10 min passive recovery (PAS).
Results: Post-intervention, the increase in IMT at all depths was greater for HWI compared to PAS, however this difference had disappeared by 1 h post at depths of 1 and 2 cm, and by 2 h post at a depth of 3 cm. There were no differences between groups for muscle function, muscle soreness or any blood markers.
Conclusion: These results suggest that HWI is a viable means of heat therapy to support a greater IMT following resistance exercise. Recovery of muscle function and muscle soreness is independent of acute changes in IMT associated with HWI
OSIRIS-REx Orbit Determination Covariance Studies at Bennu
The Origins Spectral Interpretation Resource Identification Security Regolith Explorer (OSIRIS-REx) mission is a NASA New Frontiers mission launching in 2016 to rendezvous with the small, Earth-crossing asteroid (101955) Bennu in late 2018, ultimately returning a sample of regolith to Earth. Approximately three months before the encounter with Bennu, the asteroid becomes detectable in the narrow field PolyCam imager. The spacecraft's rendezvous with Bennu begins with a series of four Asteroid Approach Maneuvers, slowing the spacecraft's speed relative to Bennu beginning two and a half months prior to closest approach, ultimately delivering the spacecraft to a point 18 km from Bennu in Nov, 2018. An extensive campaign of proximity operations activities to characterize the properties of Bennu and select a suitable sample site will follow. This paper will discuss the challenges of navigating near a small 500-m diameter asteroid. The navigation at close proximity is dependent on the accurate mathematical model or digital terrain map of the asteroid's shape. Predictions of the spacecraft state are very sensitive to spacecraft small forces, solar radiation pressure, and mis-modeling of Bennu's gravity field. Uncertainties in the physical parameters of the central body Bennu create additional challenges. The navigation errors are discussed and their impact on science planning will be presented
Terrestrial Ozone Depletion Due to a Milky Way Gamma-Ray Burst
Based on cosmological rates, it is probable that at least once in the last Gy
the Earth has been irradiated by a gamma-ray burst in our Galaxy from within 2
kpc. Using a two-dimensional atmospheric model we have performed the first
computation of the effects upon the Earth's atmosphere of one such impulsive
event. A ten second burst delivering 100 kJ/m^2 to the Earth penetrates to the
stratosphere and results in globally averaged ozone depletion of 35%, with
depletion reaching 55% at some latitudes. Significant global depletion persists
for over 5 years after the burst. This depletion would have dramatic
implications for life since a 50% decrease in ozone column density results in
approximately three times the normal UVB flux. Widespread extinctions are
likely, based on extrapolation from UVB sensitivity of modern organisms.
Additional effects include a shot of nitrate fertilizer and NO2 opacity in the
visible providing a cooling perturbation to the climate over a similar
timescale. These results lend support to the hypothesis that a GRB may have
initiated the late Ordovician mass extinction (Melott et al. 2004).Comment: 4 color figures; Revised version to be published in Astrophysical
Journal Letters. Moderate revisions, including more detail on atmospheric
processes, on probable climactic and biogeochemical effects, an improved
color scheme for graphics, and an animation of computed DNA damage leve
DawnâDusk Asymmetry in Energetic (>20Â keV) Particles Adjacent to Saturn's Magnetopause
Energetic particles (>âŒ25 keV) have been observed routinely in the terrestrial magnetosheath, but have not been well studied at the magnetosheaths of the outer planets. Here we analyze energetic electrons and ions (mostly protons) in the vicinity (±1 RS) of Saturn's magnetopause, using particle data acquired with the lowâenergy magnetosphere measurements system, one of the three sensors of the magnetosphere imaging instrument on board the Cassini spacecraft, during a period of âŒ14 years (2004â2017). It is found that energetic particles, especially ions, are also common in Saturn's magnetosheath. A clear inward (toward Saturn) gradient in the electron differential flux is identified, suggestive of magnetospheric sources. Such an inward gradient does not appear in some of the ion channels. We conclude that Saturn's magnetopause acts as a porous barrier for energetic electrons and, to a lesser extent, for energetic ions. A dawnâdusk asymmetry in the gradient of particle flux across the magnetopause is also identified, with a gradual decrease at the dawn and a sharp decrease at the dusk magnetopause. It is also found that magnetic reconnection enhanced flux levels just outside of the magnetopause, with evidence suggesting that these particles are from magnetospheric sources. These findings strongly suggest that Saturn's magnetosphere is most likely the main source of energetic particles in Saturn's magnetosheath and magnetosphere leakage is an important process responsible for the presence of the energetic particles in Saturn's magnetosheath
- âŠ