Effect of postactivation potentiation on fifty-meter freestyle in national swimmers

Effect of postactivation potentiation (PAP) on fifty meters freestyle in national swimmers. 2013.- The purpose of this study was to examine the effect of PAP on 50m freestyle in national-level swimmers. Four warm-ups were compared: A traditional race-specific warm-up (RSWU), upper body PAP (UBPAP), lower body PAP (LBPAP) and combined PAP warm-up (CPAP). Eighteen (10 men, 8 women) national-level swimmers participated in this study, which included seven separate testing sessions. Participants' 3 repetition maximum (3RM) of the pull-up (PU) was established in session 1. In session 2, rest periods for muscle enhancement of the upper body were determined using a medicine-ballthrow test 4, 8 and 12 minutes post UBPAP stimulus (1 x 3RM of the PU). In session 3, swimmers performed a counter movement jump 4, 8 and 12 minutes post LBPAP stimulus (1x5 jumps to a box whilst carrying 10% of the participants' body weight). The 50m freestyle tests were performed on sessions 4 to 7, preceded by each warm-up protocol and corresponding rest periods. A repeated measures ANOVA (p<0.05) and Bonferroni post hoc test revealed that RSWU elicited faster swimming times than UBPAP (29.00 ± 2.05 vs. 29.36 ± 1.88s p=0.046). Additionally, when data were split into gender, in the male group the UBPAP elicited significantly slower times than RSWU (27.51 ± 1.06 vs. 28.01 ± 1.17s p=0.047) and CPAP (27.49 ± 1.12 vs. 28.01 ± 1.17s p=0.02). These findings suggest individualized PAP warm-up may be a valuable tool to enhance performance in sprint events, particularly in male swimmers. However, the PU may not be an appropriate PAP stimulus on its own

Observational Constraints on the Angular and Spectral Distributions of Photons in Gamma-Ray Burst Sources

The typical spectra of gamma-ray bursts (GRBs) are discussed in the context of the compactness problem for GRB sources and how it is resolved in the popular fireball model. In particular, observational (model-independent) constraints on the collimation of the gamma-rays and the dependence of the collimation angle on the photon energy are considered. The fact that the threshold for the creation of $e^{-}e^{+}$ pairs depends on the angle between the momenta of the annihilating photons in the GRB source provides an alternative solution to the compactness problem. A new approach to explaining GRBs, taking into account the angular dependence for pair creation, is proposed, and the main features of a scenario describing a GRB source with a total (photon) energy smaller or of the order of $10^{49}$ erg are laid out. Thus, we are dealing with an alternative to an ultra-relativistic fireball, if it turns out (as follows from observations) that all "long" GRBs are associated with normal (not peculiar) core-collapse supernovae. The effects of radiation pressure and the formation of jets as a consequence of even a small amount of anisotropy in the total radiation field in a (compact) GRB source are examined in this alternative model. Possible energy release mechanisms acting in regions smaller or of the order of $10^{8}$ cm in size (a compact model for a GRB) are discussed. New observational evidence for such compact energy release in the burst source is considered.Comment: 15 pages, no figures, no table

Gender differences in the use of cardiovascular interventions in HIV-positive persons; the D:A:D Study

Peer reviewe

Combining QTL and gene expression studies to identify important genes and genetic pathways underlying resistance to mastitis in Danish Holstein cattle

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