147 research outputs found
The impact of sleeping with reduced glycogen stores on immunity and sleep in triathletes.
PURPOSE: We investigated the effects of a 3-week dietary periodization on immunity and sleep in triathletes. METHODS: 21 triathletes were divided into two groups with different nutritional guidelines during a 3-week endurance training program including nine twice a day sessions with lowered (SL group) or maintained (CON group) glycogen availability during the overnight recovery period. In addition to performance tests, sleep was monitored every night. Systemic and mucosal immune parameters as well as the incidence of URTI were monitored every week of the training/nutrition protocol. Two-ways ANOVA and effect sizes were used to examine differences in dependent variables between groups at each time point. RESULTS: The SL group significantly improved 10 km running performance (-1 min 13 s, P < 0.01, d = 0.38), whereas no improvement was recorded in the CON group (-2 s, NS). No significant changes in white blood cells counts, plasma cortisol and IL-6 were recorded over the protocol in both groups. The vitamin D status decreased in similar proportions between groups, whereas salivary IgA decreased in the SL group only (P < 0.05, d = 0.23). The incidence of URTI was not altered in both groups. All participants in both groups went to bed earlier during the training program (SL -20 min, CON -27 min, P < 0.05, d = 0.28). In the SL group, only sleep efficiency slightly decreased by 1.1 % (P < 0.05, d = 0.25) and the fragmentation index tended to increase at the end of the protocol (P = 0.06). CONCLUSION: Sleeping and training the next morning regularly with reduced glycogen availability has minimal effects on selected markers of immunity, the incidence of URTI and sleeping patterns in trained athletes
Kondo Effect in Electromigrated Gold Break Junctions
We present gate-dependent transport measurements of Kondo impurities in bare
gold break junctions, generated with high yield using an electromigration
process that is actively controlled. Thirty percent of measured devices show
zero-bias conductance peaks. Temperature dependence suggests Kondo temperatures
\~7K. The peak splitting in magnetic field is consistent with theoretical
predictions for g=2, though in many devices the splitting is offset from 2guB
by a fixed energy. The Kondo resonances observed here may be due to
atomic-scale metallic grains formed during electromigration.Comment: 5 pages, 3 figure
Theory of the Fano Resonance in the STM Tunneling Density of States due to a Single Kondo Impurity
The conduction electron density of states nearby single magnetic impurities,
as measured recently by scanning tunneling microscopy (STM), is calculated,
taking into account tunneling into conduction electron states only. The Kondo
effect induces a narrow Fano resonance in the conduction electron density of
states, while scattering off the d-level generates a weakly energy dependent
Friedel oscillation. The line shape varies with the distance between STM tip
and impurity, in qualitative agreement with experiments, but is very sensitive
to details of the band structure. For a Co impurity the experimentally observed
width and shift of the Kondo resonance are in accordance with those obtained
from a combination of band structure and strongly correlated calculations.Comment: 4 pages, ReVTeX + 4 figures (Encapsulated Postscript), submitted to
PR
Crossover from Kondo assisted suppression to co-tunneling enhancement of tunneling magnetoresistance via ferromagnetic nanodots in MgO tunnel barriers
Recently, it has been shown that magnetic tunnel junctions with thin MgO
tunnel barriers exhibit extraordinarily high tunneling magnetoresistance (TMR)
values at room temperature1, 2. However, the physics of spin dependent
tunneling through MgO barriers is only beginning to be unravelled. Using planar
magnetic tunnel junctions in which ultra-thin layers of magnetic metals are
deposited in the middle of a MgO tunnel barrier here we demonstrate that the
TMR is strongly modified when these layers are discontinuous and composed of
small pancake shaped nanodots. At low temperatures, in the Coulomb blockade
regime, for layers less than ~1 nm thick, the conductance of the junction is
increased at low bias consistent with Kondo assisted tunneling. In the same
regime we observe a suppression of the TMR. For slightly thicker layers, and
correspondingly larger nanodots, the TMR is enhanced at low bias, consistent
with co-tunneling.Comment: Nano Letters (in press
The BASES Expert Statement on Exercise, Immunity, and Infection
This article was published in the Journal of Sports Sciences [© Taylor & Francis] and the definitive version is available at: http://dx.doi.org/10.1080/02640414.2011.627371An individual's level of physical activity influences their risk of infection, most likely by affecting immune function. Regular moderate exercise reduces the risk of infection compared with a sedentary lifestyle, but very prolonged bouts of exercise and periods of intensified training are associated with an increased risk of infection. There are several lifestyle, nutritional, and training strategies that can be adopted to limit the extent of exercise-induced immunodepression and minimize the risk of infection. This expert statement provides a background summarizing the evidence together with extensive conclusions and practical guidelines
Hydration and cooling in elite athletes: relationship with performance, body mass loss and body temperatures during the Doha 2019 IAAF World Athletics Championships
Purpose: To characterise hydration, cooling, body
mass loss, and core (Tcore) and skin (Tsk) temperatures
during World Athletics Championships in hot-humid
conditions.
Methods: Marathon and race-walk (20 km and 50
km) athletes (n=83, 36 women) completed a pre-race
questionnaire. Pre-race and post-race body weight
(n=74), Tcore (n=56) and Tsk (n=49; thermography) were
measured.
Results: Most athletes (93%) had a pre-planned
drinking strategy (electrolytes (83%), carbohydrates
(81%)) while ice slurry was less common (11%;
p<0.001). More men than women relied on
electrolytes and carbohydrates (91%–93% vs
67%–72%, p≤0.029). Drinking strategies were based
on personal experience (91%) rather than external
sources (p<0.001). Most athletes (80%) planned
pre-cooling (ice vests (53%), cold towels (45%), neck
collars (21%) and ice slurry (21%)) and/or midcooling (93%; head/face dousing (65%) and cold
water ingestion (52%)). Menthol usage was negligible
(1%–2%). Pre-race Tcore was lower in athletes
using ice vests (37.5°C±0.4°C vs 37.8°C±0.3°C,
p=0.024). Tcore (pre-race 37.7°C±0.3°C, post-race
39.6°C±0.6°C) was independent of event, ranking or
performance (p≥0.225). Pre-race Tsk was correlated
with faster race completion (r=0.32, p=0.046)
and was higher in non-finishers (did not finish
(DNF); 33.8°C±0.9°C vs 32.6°C±1.4°C, p=0.017).
Body mass loss was higher in men than women
(−2.8±1.5% vs −1.3±1.6%, p<0.001), although not
associated with performance.
Conclusion: Most athletes’ hydration strategies
were pre-planned based on personal experience. Ice
vests were the most adopted pre-cooling strategy
and the only one minimising Tcore, suggesting that
event organisers should be cognisant of logistics (ie,
freezers). Dehydration was moderate and unrelated to
performance. Pre-race Tsk was related to performance
and DNF, suggesting that Tsk modulation should be
incorporated into pre-race strategies
Hydration and cooling in elite athletes: relationship with performance, body mass loss and body temperatures during the Doha 2019 IAAF World Athletics Championships.
PURPOSE: To characterise hydration, cooling, body mass loss, and core (Tcore) and skin (Tsk) temperatures during World Athletics Championships in hot-humid conditions. METHODS: Marathon and race-walk (20 km and 50 km) athletes (n=83, 36 women) completed a pre-race questionnaire. Pre-race and post-race body weight (n=74), Tcore (n=56) and Tsk (n=49; thermography) were measured. RESULTS: Most athletes (93%) had a pre-planned drinking strategy (electrolytes (83%), carbohydrates (81%)) while ice slurry was less common (11%; p<0.001). More men than women relied on electrolytes and carbohydrates (91%-93% vs 67%-72%, p≤0.029). Drinking strategies were based on personal experience (91%) rather than external sources (p<0.001). Most athletes (80%) planned pre-cooling (ice vests (53%), cold towels (45%), neck collars (21%) and ice slurry (21%)) and/or mid-cooling (93%; head/face dousing (65%) and cold water ingestion (52%)). Menthol usage was negligible (1%-2%). Pre-race Tcore was lower in athletes using ice vests (37.5°C±0.4°C vs 37.8°C±0.3°C, p=0.024). Tcore (pre-race 37.7°C±0.3°C, post-race 39.6°C±0.6°C) was independent of event, ranking or performance (p≥0.225). Pre-race Tsk was correlated with faster race completion (r=0.32, p=0.046) and was higher in non-finishers (did not finish (DNF); 33.8°C±0.9°C vs 32.6°C±1.4°C, p=0.017). Body mass loss was higher in men than women (-2.8±1.5% vs -1.3±1.6%, p<0.001), although not associated with performance. CONCLUSION: Most athletes' hydration strategies were pre-planned based on personal experience. Ice vests were the most adopted pre-cooling strategy and the only one minimising Tcore, suggesting that event organisers should be cognisant of logistics (ie, freezers). Dehydration was moderate and unrelated to performance. Pre-race Tsk was related to performance and DNF, suggesting that Tsk modulation should be incorporated into pre-race strategies
Position statement part two: maintaining immune health
The physical training undertaken by athletes is one of a set of lifestyle or behavioural
factors that can influence immune function, health and ultimately exercise
performance. Others factors including potential exposure to pathogens, health
status, lifestyle behaviours, sleep and recovery, nutrition and psychosocial issues,
need to be considered alongside the physical demands of an athlete’s training programme.
The general consensus on managing training to maintain immune health is to start
with a programme of low to moderate volume and intensity; employ a gradual and
periodised increase in training volumes and loads; add variety to limit training
monotony and stress; avoid excessively heavy training loads that could lead to
exhaustion, illness or injury; include non-specific cross-training to offset staleness;
ensure sufficient rest and recovery; and instigate a testing programme for
identifying signs of performance deterioration and manifestations of physical
stress. Inter-individual variability in immunocompetence, recovery, exercise
capacity, non-training stress factors, and stress tolerance likely explains the different
vulnerability of athletes to illness. Most athletes should be able to train with
high loads provided their programme includes strategies devised to control the
overall strain and stress. Athletes, coaches and medical personnel should be alert
to periods of increased risk of illness (e.g. intensive training weeks, the taper period
prior to competition, and during competition) and pay particular attention to
recovery and nutritional strategies. [...continues]
The Kondo Effect in Non-Equilibrium Quantum Dots: Perturbative Renormalization Group
While the properties of the Kondo model in equilibrium are very well
understood, much less is known for Kondo systems out of equilibrium. We study
the properties of a quantum dot in the Kondo regime, when a large bias voltage
V and/or a large magnetic field B is applied. Using the perturbative
renormalization group generalized to stationary nonequilibrium situations, we
calculate renormalized couplings, keeping their important energy dependence. We
show that in a magnetic field the spin occupation of the quantum dot is
non-thermal, being controlled by V and B in a complex way to be calculated by
solving a quantum Boltzmann equation. We find that the well-known suppression
of the Kondo effect at finite V>>T_K (Kondo temperature) is caused by inelastic
dephasing processes induced by the current through the dot. We calculate the
corresponding decoherence rate, which serves to cut off the RG flow usually
well inside the perturbative regime (with possible exceptions). As a
consequence, the differential conductance, the local magnetization, the spin
relaxation rates and the local spectral function may be calculated for large
V,B >> T_K in a controlled way.Comment: 9 pages, invited paper for a special edition of JPSJ "Kondo Effect --
40 Years after the Discovery", some typos correcte
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