Familiarization, Reliability, and Evaluation of a Multiple Sprint Running Test Using Self-Selected Recovery Periods

The aims of the present study were to investigate the process of self-selected recovery in a multiple sprint test with a view to using self-selected recovery time as a means of reliably quantifying an individual's ability to resist fatigue in this type of exercise. Twenty physically active exercise science students (means ± SD for age, height, body mass, body fat, and V̇O2max of the subjects were 21 ± 2 yr, 1.79 ± 0.09 m, 83.7 ± 10.8 kg, 16.6 ± 3.9%, and 52.7 ± 7.2 ml·kg−1·min−1, respectively) completed 4 trials of a 12 × 30 m multiple sprint running test under the instruction that they should allow sufficient recovery time between sprints to enable maximal sprint performance to be maintained throughout each trial. Mean recovery times across the 4 trials were 73.9 ± 24.7, 82.3 ± 23.8, 77.6 ± 19.1, and 77.5 ± 13.9 seconds, respectively, with variability across the first 3 trials considered evidence of learning effects. Test-retest reliability across trials 3 to 4 revealed a good level of reliability as evidenced by a coefficient of variation of 11.1% (95% likely range: 8.0-18.1%) and an intraclass correlation coefficient of 0.76 (95% likely range: 0.40-0.91). Despite no change in sprint performance throughout the trials, ratings of perceived exertion increased progressively and significantly (p < 0.001) from a value of 10 ± 2 after sprint 3 to 14 ± 2 after sprint 12. The correlation between relative V̇O2max and mean recovery time was 0.14 (95% likely range: −0.37-0.58). The results of the present study show that after the completion of 2 familiarization trials, the ability to maintain sprinting performance in a series of repeated sprints can be self-regulated by an athlete to a high degree of accuracy without the need for external timepieces

Inter-Segmental Coordination during a Unilateral 180° Jump in Elite Rugby Players: Implications for Prospective Identification of Injuries

Musculoskeletal injuries often occur during the execution of dynamic sporting tasks that involve rotation. The prescription of appropriate prevention strategies of musculoskeletal injury relies on assessments to identify risk, but current assessment tools focus on uniplanar movements. The purpose of this paper is to demonstrate the utility of the unilateral 180 • jump as a potential assessment tool for injury risk in the lower body by (1) providing descriptive kinematics of the knee, thigh, and pelvis (2) conducting inter-segmental coordination analysis, and (3) comparing the knee kinematics between the dominant and non-dominant limb (NDL) during the loading (LOP) and landing phase (LAP). Elite rugby players completed one session, performing five 180 • unilateral jumps on each limb while collecting kinematic data. Independent t-tests were used to compare peak angles of DL and NDL. Continuous Relative Phase (CRP) plots were constructed for thorax and pelvis in the transverse plane. At the loading phase, the non-dominant limb had greater peak knee abduction (ABD) (p = 0.01). At the landing phase, the dominant limb had greater peak knee adduction (ADD) (p = 0.05). At the landing phase, the non-dominant limb had greater peak knee ABD (p = 0.01). CRP plots indicate participants can utilize a thorax-led, pelvis-led, or synchronized rotational method. Bilateral asymmetries were observed, indicated by significant differences in the bilateral landing phase peak ADD/ABD, which is of particular interest considering all participants were healthy. Therefore, additional research is needed to determine thresholds for injury risk during rotational tasks

Low-energy Pion-nucleon Scattering

This paper contains the results of an analysis of recent low-energy pion-nucleon scattering experiments. Obtained are phase shifts, the pion-nucleon coupling constant and an estimate of the Sigma term.Comment: 30 pages, 11 figures, LaTe

Diverse Roles and Interactions of the SWI/SNF Chromatin Remodeling Complex Revealed Using Global Approaches

A systems understanding of nuclear organization and events is critical for determining how cells divide, differentiate, and respond to stimuli and for identifying the causes of diseases. Chromatin remodeling complexes such as SWI/SNF have been implicated in a wide variety of cellular processes including gene expression, nuclear organization, centromere function, and chromosomal stability, and mutations in SWI/SNF components have been linked to several types of cancer. To better understand the biological processes in which chromatin remodeling proteins participate, we globally mapped binding regions for several components of the SWI/SNF complex throughout the human genome using ChIP-Seq. SWI/SNF components were found to lie near regulatory elements integral to transcription (e.g. 5′ ends, RNA Polymerases II and III, and enhancers) as well as regions critical for chromosome organization (e.g. CTCF, lamins, and DNA replication origins). Interestingly we also find that certain configurations of SWI/SNF subunits are associated with transcripts that have higher levels of expression, whereas other configurations of SWI/SNF factors are associated with transcripts that have lower levels of expression. To further elucidate the association of SWI/SNF subunits with each other as well as with other nuclear proteins, we also analyzed SWI/SNF immunoprecipitated complexes by mass spectrometry. Individual SWI/SNF factors are associated with their own family members, as well as with cellular constituents such as nuclear matrix proteins, key transcription factors, and centromere components, implying a ubiquitous role in gene regulation and nuclear function. We find an overrepresentation of both SWI/SNF-associated regions and proteins in cell cycle and chromosome organization. Taken together the results from our ChIP and immunoprecipitation experiments suggest that SWI/SNF facilitates gene regulation and genome function more broadly and through a greater diversity of interactions than previously appreciated

Effects of caffeine on time-trial performance and associated physiological responses: a meta-analysis

Background: The aim was to conduct a systematic review and meta-analysis on the effects of caffeine supplementation on time-trial performance and associated physiological responses. Methods: 35 studies met the inclusion criteria of adopting double-blind, randomized, placebo-controlled, crossover designs that included a closed-loop time-trial (≥ 5 mins) performed under a caffeine dose of 3 – 6 mg∙kg-1 administered 30 – 90 minutes beforehand. Meta-analyses were completed using a random-effects model, with effects on time-trial performance presented as standardized mean difference (δ) and with physiological responses presented as raw mean difference (D). 95% confidence limits (CL95) were calculated for all estimates. Results: Relative to placebo, caffeine had a positive effect on time-trial performance (δ = .32; CL95 [.19, .44]). Moreover, the effect of caffeine on time-trial performance corresponded with increases in heart rate (D = 3.3 b∙min-1; CL95 [1.7, 4.8]), oxygen uptake (D = .09 L∙min-1; CL95 [.02, .17]), blood lactate (D = 1.42 mmol∙L-1; CL95 [1.09, 1.74]), and blood glucose (D = .94 mmol∙L-1; CL95 [.58, 1.30]). In contrast, caffeine had no effect on time-trial measures of respiratory exchange ratio (D = .01; CL95 [-.01, .02]), or ratings of perceived exertion (D = .1; CL95 [-.1, .3]). Conclusion: The results reveal a clear effect of caffeine on moderate to high-intensity time-trial performance. When considered in conjunction with research using fixed-intensity exercise, the caffeine-induced increase in time-trial intensity likely explains all of the associated increases in heart rate and oxygen uptake, and part of the increase in blood lactate and blood glucose

The reliability of accelerative sprint performance : does starting position matter ?

Influence de la position de départ debout ou accroupi sur la régularité inter-tests du temps de course de sprint sur 10 et 20 mètres, chez des hommes actifs mais non spécialistes

The Effects of Accentuated Eccentric Loading on Mechanical Variables and Agonist Electromyography during the Bench Press

We compared the effects of accentuated eccentric loading (AEL) on mechanical variables and agonist muscle activation using low (30% 1-repetition maximum (1RM)) and high (80% 1RM) upward-phase loading with AEL (100% 1RM during downward phase) to traditional loading schemes (T) in the bench press. Twelve resistance-trained men (26 &plusmn; 6 years; 1RM: 134 &plusmn; 33 kg) performed sets of two repetitions with three-minute intervals using loading schemes of 30AEL, 30T, 80AEL, and 80T. AEL was applied using weight releasers while force plates and a 3D motion-analysis system were used to measure mechanical variables. Electromyographic activity of the pectoralis major and triceps brachii muscles was also recorded. The greater downward-phase loads experienced during the AEL conditions allowed greater overall mean vertical forces (mean difference ( x &macr; Diff): 118 N, p &lt; 0.001), greater work ( x &macr; Diff: 43 J, p &lt; 0.001), and greater pectoralis major muscle activation ( x &macr; Diff: 27 &micro;V, p = 0.002) compared to the corresponding traditional loading schemes. However, there was little evidence of potentiation of the mechanical variables or muscle activity during the subsequent upward phases caused by the AEL schemes. It is possible that the use of weight releasers may disrupt lifting technique particularly during low AEL schemes thereby diminishing any benefits

THE ACUTE EFFECTS OF BACK SQUATS ON VERTICAL JUMP PERFORMANCE IN MEN AND WOMEN

The aim of the present study was to investigate the acute effects of performing back squats on subsequent performance during a series of vertical jumps in men and women. Twelve men and 12 women were tested on three separate occasions, the first of which was used to determine their 1-repetition maximum (1-RM) parallel back squat. Following this, subjects performed a potentiation and a control treatment in a counterbalanced order. The potentiation treatment culminated with subjects performing parallel back squats with a load equivalent to 70% 1- RM for three repetitions, following which they performed one countermovement vertical jump (CMJ) for maximal height every three minutes for a total of 10 jumps. During the control treatment, subjects performed only the CMJs. Jump height (JH) and vertical stiffness (VStiff) were calculated for each jump from the vertical force signal recorded from a force platform. There were no significant changes in JH or VStiff following the treatments and no significant differences in the responses between men and women (p > 0.05). Correlations between normalized 1-RM back squat load and the absolute change in JH and VStiff were small to moderate for both men and women, with most correlations being negative. Large variations in response to the back squats were noted in both men and women. The use of resistance exercises performed prior to a series of vertical jumps can result in improvements in performance in certain individuals, although the gains tend to be small and dependent upon the mechanical variable measured. There does not seem to be any differences between men and women in the response to dynamic potentiation protocol