A novel approach to the application of critical velocity within soccer

The relationship between velocity and time to exhaustion is hyperbolic and is defined by two parameters: critical velocity (CV), which represents the highest sustainable work rate; and the curvature constant (D’), which is the maximum amount of work that can be performed above CV. An important challenge that needs to be addressed however, before more research is conducted on both the importance of, and understanding of the physiology underlying CV and D’, is the protocol implemented for the measurement of these two parameters. At present, the number of exhaustive test bouts required restricts its use in intervention studies and makes its application within team based sports highly impractical. The main aim of the present study was to validate a novel critical velocity field test protocol that would allow the determination of CV in a single testing session. Twelve healthy male soccer players (mean ± SD) (22 ± 3yrs; 179 ± 7 cm; 74 ± 9 Kg; 4.5 ± 0.6 l.min¬-1) participated in this study and were randomly assigned to one of two intervention groups: a high intensity aerobic training group (INT) that completed two sessions per week comprising of 4x4 minute high intensity interval training at 90-95% of maximum heart rate (Hfmax); or alternatively, a controlled training group (CON), wherein habitual training practices were maintained throughout the 6 week training period. As outlined by the investigation testing protocol, both prior to, and following the completion of each respective 6-week intervention, all subjects performed an incremental exercise test for estimation of peak oxygen uptake (VO2peak) and peak treadmill running velocity (Vpeak) respectively. Having established Vpeak, a randomised series of four constant velocity treadmill tests to the limit of tolerance (tlim) were performed for the estimation of CV and D’. Each test was separated by a minimum period of 24 hours and was performed at designated work rates elected to span a tlim range of 3 to 20 minutes. Forming the novel element of this investigation, a field based test was also performed pre- and post-intervention. In contrast to the laboratory protocol however, 3 constant velocity tests to tlim were performed simultaneously, separated only by a 15minute recovery period for the determination of the V-t relationship and CV and D’ respectively. The results indicated that following the 6 week high intensity aerobic intervention, while a mean significant difference in peak oxygen uptake was displayed in the intervention group pre- to post-intervention (4.36 ± 0.67 vs. 4.50 ± 0.58 l.min-1; P = 0.020), this was not supported by a mean significant increase in critical velocity (3.65 ± 0.24 vs. 3.72 ± 0.25 m.sec-1; P = 0.355), post-intervention (lab determined CV values). No significant differences where displayed in either mean peak oxygen uptake (4.65 ± 0.45 vs. 4.56 ± 0.56 l.min-1; P = 0.225) or CV (3.66 ± 0.49 vs. 3.72 ± 0.52 m.sec-1; P = 0.216) (lab determined CV values) following the 6 week control intervention. While both protocol estimates for the determination of critical velocity displayed no significant difference pre- to post-intervention for either study group, (3.65 ± 0.24 vs. 3.72 ± 0.25 m.sec-1; P = 0.355) (INT lab) vs. (3.44 ± 0.10 vs. 3.44 ± 0.22 m.sec-1; P = 0.935) (INT field) and (3.66 ± 0.49 vs. 3.72 ± 0.52 m.sec-1; P = 0.216) (CON lab) vs. (3.42 ± 0.28 vs. 3.44 ± 0.32 m.sec-1; P = 0.640) (CON field) respectively, disparity between laboratory and field derived estimates was evident for both groups, with a significant difference between post-intervention protocol estimates being presented for CV within the INT group (3.72 ± 0.25 vs. 3.44 ± 0.22 m.sec-1; P = 0.018). Closer inspection of the data revealed little to no agreement between lab and novel field protocols estimates, with the field protocol inherently underestimating CV. Overall the lab protocol performed better than the field protocol, displaying a narrower interval (0.35m.sec¬-1) from which to detect a possible intervention effect relative to that of the field protocol (0.42m.sec-1). In concurrence it also provided better reproducibility for CV estimation, exhibiting a higher reproducibility coefficient relative to the field protocol (0.94 vs. 0.81) The key finding from the present study was that little evidence exists to validate the application of the novel field based protocol to determine critical velocity from a single testing session. The current results indicate that little to no agreement was found between laboratory derived and field test estimates of critical velocity, with the field test inherently underestimating critical velocity. Analysis of the results reveal that the novel field test, relative to the laboratory protocol, offers limited sensitivity and reproducibility to accurately estimate and track changes in critical velocity following a high intensity aerobic training intervention. The large disparity displayed between lab and field protocol estimates implies more research is required into the development of a novel field test that facilitates the accurate estimation of critical velocity from a single test sitting before its application within team based sporting environments can be justified

An Investigation of Return to Sport Decision Making in Male Professional Football Following Lower Limb Muscle Injury

Background: Return to sport (RTS) following muscle injury represents an on-going challenge for professional male football teams. While published expert consensus have provided guidance to practitioners, it is currently not clear if, and what criteria are being used by teams, nor what decision-making practices look like in reality.Methods & Results: Study one, a global survey of premier-league professional football teams, found that the RTS practices of surveyed teams closely align with consensus recommendations. The majority of teams (95%) adopted a continuum model. At each phase, a combination of clinical, functional, and psychological criteria was used to inform rehabilitation progression decisions. A shared decisionmaking approach was used by 80% of teams surveyed. Study two, a scoping review of literature (n=68 studies) regarding the criteria used to inform rehabilitation progression and support RTS decision-making in high-level football-code athletes, found that RTPlay was the most consistently studied rehabilitation phase (94% of studies) with injuries involving the hamstring the primary focus of research (78% of studies). Considerable heterogeneity was found regarding the specific criteria and metrics used. Only 9% of studies reported using psychological criteria to inform RTS decisions. Study three, a prospective two-season investigation of the psychometric properties of the Injury-Psychological Readiness to Return to Sport scale (I-PRRS), found that the instrument demonstrated good structural validity and internal consistency and exhibited good longitudinal measurement invariance in professional male football players.Conclusion: Professional male football teams follow basic scientific recommendations during RTS, but there remains a lack of standardised specific criteria and metrics in both practice and in research. While decision-making is recognised as needing to be shared, there are several contradictions in the shared decision-making process within teams. Establishing the internal structure of the IPRRS represents a first step in determining appropriate psychometric properties for use in professional male footballers, however other key psychometric properties are yet to be established to advocate its use in practice

The Complete Star Formation History of the Universe

The determination of the star-formation history of the Universe is a key goal of modern cosmology, as it is crucial to our understanding of how structure in the Universe forms and evolves. A picture has built up over recent years, piece-by-piece, by observing young stars in distant galaxies at different times in the past. These studies indicated that the stellar birthrate peaked some 8 billion years ago, and then declined by a factor of around ten to its present value. Here we report on a new study which obtains the complete star formation history by analysing the fossil record of the stellar populations of 96545 nearby galaxies. Broadly, our results support those derived from high-redshift galaxies elsewhere in the Universe. We find, however, that the peak of star formation was more recent - around 5 billion years ago. Our study also shows that the bigger the stellar mass of the galaxy, the earlier the stars were formed. This striking result indicates a very different formation history for high- and low-mass formation.Comment: Accepted by Nature. Press embargo until publishe

Combined analysis of the integrated Sachs-Wolfe effect and cosmological implications

We present a global measurement of the integrated Sachs-Wolfe (ISW) effect obtained by cross-correlating all relevant large scale galaxy data sets with the cosmic microwave background radiation map provided by the Wilkinson Microwave Anisotropy Probe. With these measurements, the overall ISW signal is detected at the ~ 4.5 sigma level. We also examine the cosmological implications of these measurements, particularly the dark energy equation of state w, its sound speed, and the overall curvature of the Universe. The flat LCDM model is a good fit to the data and, assuming this model, we find that the ISW data constrain Omega_m = 0.20 +0.19 -0.11 at the 95% confidence level. When we combine our ISW results with the latest baryon oscillation and supernovae measurements, we find that the result is still consistent with a flat LCDM model with w = -1 out to redshifts z > 1.Comment: 24 pages, 15 figures. Version accepted by PRD. Improved quasar data, revised parameter constraint

Supermassive Black Hole Mass Regulated by Host Galaxy Morphology

We investigated the relationship between supermassive black hole (SMBH) mass and host starburst luminosity in Seyfert galaxies and Palomar-Green QSOs, focusing on the host galaxy morphology. Host starburst luminosity was derived from the 11.3 micron polycyclic aromatic hydrocarbon luminosity. We found that the SMBH masses of elliptical-dominated host galaxies are more massive than those of disk-dominated host galaxies statistically. We also found that the SMBH masses of disk-dominated host galaxies seem to be suppressed even under increasing starburst luminosity. These findings imply that final SMBH mass is strongly regulated by host galaxy morphology. This can be understood by considering the radiation drag model as the SMBH growth mechanism, taking into account the radiation efficiency of the host galaxy.Comment: 6 pages, 1 figure; accepted for publication in MNRA

Open-porous magnesium-based scaffolds withstand in vitro corrosion under cyclic loading: a mechanistic study

The successful application of magnesium (Mg) alloys as biodegradable bone substitutes for critical-sized defects may be comprised by their high degradation rate resulting in a loss of mechanical integrity. This study investigates the degradation pattern of an open-porous fluoride-coated Mg-based scaffold immersed in circulating Hanks' Balanced Salt Solution (HBSS) with and without in situ cyclic compression (30 N/1 Hz). The changes in morphological and mechanical properties have been studied by combining in situ high-resolution X-ray computed tomography mechanics and digital volume correlation. Although in situ cyclic compression induced acceleration of the corrosion rate, probably due to local disruption of the coating layer where fatigue microcracks were formed, no critical failures in the overall scaffold were observed, indicating that the mechanical integrity of the Mg scaffolds was preserved. Structural changes, due to the accumulation of corrosion debris between the scaffold fibres, resulted in a significant increase (p < 0.05) in the material volume fraction from 0.52 ± 0.07 to 0.47 ± 0.03 after 14 days of corrosion. However, despite an increase in fibre material loss, the accumulated corrosion products appear to have led to an increase in Young's modulus after 14 days as well as lower third principal strain (εp3) accumulation (−91000 ± 6361 με and −60093 ± 2414 με after 2 and 14 days, respectively). Therefore, this innovative Mg scaffold design and composition provide a bone replacement, capable of sustaining mechanical loads in situ during the postoperative phase allowing new bone formation to be initially supported as the scaffold resorbs

Keck Spectroscopy of 3<z<7 Faint Lyman Break Galaxies: The Importance of Nebular Emission in Understanding the Specific Star Formation Rate and Stellar Mass Density

The physical properties inferred from the SEDs of z>3 galaxies have been influential in shaping our understanding of early galaxy formation and the role galaxies may play in cosmic reionization. Of particular importance is the stellar mass density at early times which represents the integral of earlier star formation. An important puzzle arising from the measurements so far reported is that the specific star formation rates (sSFR) evolve far less rapidly than expected in most theoretical models. Yet the observations underpinning these results remain very uncertain, owing in part to the possible contamination of rest-optical broadband light from strong nebular emission lines. To quantify the contribution of nebular emission to broad-band fluxes, we investigate the SEDs of 92 spectroscopically-confirmed galaxies in the redshift range 3.8<z<5.0 chosen because the H-alpha line lies within the Spitzer/IRAC 3.6 um filter. We demonstrate that the 3.6 um flux is systematically in excess of that expected from stellar continuum, which we derive by fitting the SED with population synthesis models. No such excess is seen in a control sample at 3.1<z<3.6 in which there is no nebular contamination in the IRAC filters. From the distribution of our 3.6 um flux excesses, we derive an H-alpha equivalent width (EW) distribution. The mean rest-frame H-alpha EW we infer at 3.8<z<5.0 (270 A) indicates that nebular emission contributes at least 30% of the 3.6 um flux. Via our empirically-derived EW distribution we correct the available stellar mass densities and show that the sSFR evolves more rapidly at z>4 than previously thought, supporting up to a 5x increase between z~2 and 7. Such a trend is much closer to theoretical expectations. Given our findings, we discuss the prospects for verifying quantitatively the nebular emission line strengths prior to the launch of the James Webb Space Telescope.Comment: 16 pages, 9 figures, submitted to Ap

Constraints on Physical Properties of z~6 Galaxies Using Cosmological Hydrodynamic Simulations

We conduct a detailed comparison of broad-band spectral energy distributions of six z >= 5.5 galaxies against galaxies drawn from cosmological hydrodynamic simulations. We employ a new tool called SPOC, which constrains the physical properties of observed galaxies through a Bayesian likelihood comparison with model galaxies. For five out of six observed z>=5.5 objects, our simulated galaxies match the observations at least as well as simple star formation histories such as tau-models, with similar favored values obtained for the intrinsic physical parameters such as stellar mass and star formation rate, but with substantially smaller uncertainties. Our results are broadly insensitive to simulation choices for galactic outflows and dust reddening. Hence the existence of early galaxies as observed is broadly consistent with current hierarchical structure formation models. However, one of the six objects has photometry that is best fit by a bursty SFH unlike anything produced in our simulations, driven primarily by a high K-band flux. These findings illustrate how SPOC provides a robust tool for optimally utilizing hydrodynamic simulations (or any model that predicts galaxy SFHs) to constrain the physical properties of individual galaxies having only photometric data, as well as identify objects that challenge current models. (abridged)Comment: 22 pages, 11 figures, accepted by MNRAS. Added discussions of dust, numerical resolution; clarified conclusion