The effect of ball-carrying technique and experience on sprinting in rugby union

Abstract

There are several ways of carrying the ball in rugby union, which could influence the speed at which a player can run. We assessed 52 rugby players (34 males, 18 females) during a maximum sprint over 30 m without the ball, with the ball under one arm, and with the ball in both hands. Timing gates were used to measure time over the initial 10 m and the last 20 m. It has previously been reported (Grant et al., 2003 Grant, S. J., Oommen, G., McColl, G., Taylor, J., Watkins, L.Friel, N. 2003. The effects of ball carrying method on sprint speed in rugby union football players. Journal of Sports Sciences, 21: 1009–1015. [Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) that running with the ball produces a slower sprinting speed than running without the ball. We hypothesized that the decrease in speed caused by carrying the ball would become less marked with the experience of the player. The male and female players were each divided into two groups: a “beginner” group that consisted of players in their first or second season and an “experienced” group that was composed of players who had played for more than two seasons. A 2 × 3 mixed-model analysis of variance was used to identify differences (P < 0.01) between the beginner and experienced groups in the three sprinting conditions. The times for the males for the first 10 m sprints without the ball, with the ball under one arm, and with the ball in both hands were 1.87 ± 0.08 s, 1.87 ± 0.08 s, and 1.91 ± 0.1 s for the beginners, and 1.87 ± 0.1, 1.88 ± 0.1 and 1.88 ± 0.12 for the more experienced players respectively. The times for the females for the first 10 m without the ball, with the ball under one arm, and with the ball in both hands were 2.13 ± 0.16 s, 2.19 ± 0.17 s, and 2.20 ± 0.16 s for the beginners, and 2.03 ± 0.12 s, 2.03 ± 0.09 s, and 2.04 ± 0.1 s for the more experienced players respectively. For the last 20 m of the 30-m sprint, there were differences between the different sprint conditions (P < 0.001) but no differences that were attributable to experience (P = 0.297). The times for the males over the last 20 m without the ball, with the ball under one arm, and with the ball in both hands were 2.58 ± 0.19 s, 2.61 ± 0.12 s, and 2.65 ± 0.12 s for the beginners, and 2.59 ± 0.12, 2.62 ± 0.23, and 2.65 ± 0.18 s for the more experienced players respectively. The times for the females over the last 20 m without the ball, with the ball under one arm, and with the ball in both hands were 3.25 ± 0.38 s, 3.35 ± 0.42 s, and 3.40 ± 0.46 s for the beginners, and 3.04 ± 0.32 s, 3.06 ± 0.22 s, and 3.13 ± 0.27 s for the more experienced players respectively. No gender-specific differences were detected. The results of this study suggest that practising sprints while carrying a ball benefits the early phase of sprinting while carrying the ball.     

ATP and phosphocreatine utilization in single human muscle fibres during the development of maximal power output at elevated muscle temperatures

Abstract

In this study, we examined the effect of muscle temperature (T _m) on adenosine triphosphate (ATP) and phosphocreatine utilization in single muscle fibres during the development of maximal power output in humans. Six male participants performed a 6-s maximal sprint on a friction-braked cycle ergometer under both normal (T _m = 34.3°C, s = 0.6) and elevated (T _m = 37.3°C, s = 0.2) muscle temperature conditions. During the elevated condition, muscle temperature of the legs was raised, passively, by hot water immersion followed by wrapping in electrically heated blankets. Muscle biopsies were taken from the vastus lateralis before and immediately after exercise. Freeze-dried single fibres were dissected, characterized according to myosin heavy chain composition, and analysed for ATP and phosphocreatine content. Single fibres were classified as: type I, IIA, IIAX25 (1 – 25% IIX isoform), IIAX50 (26 – 50% IIX), IIAX75 (51 – 75% IIX), or IIAX100 (76 – 100% IIX). Maximal power output and pedal rate were both greater (P < 0.05) during the elevated condition by 258 W (s = 110) and 22 rev · min^?1 (s = 6), respectively. In both conditions, phosphocreatine content decreased significantly in all fibre types, with a greater decrease during the elevated condition in type IIA fibres (P < 0.01). Adenosine triphosphate content was also reduced to a greater (P < 0.01) extent in type IIA fibres during the elevated condition. The results of the present study indicate that after passive elevation of muscle temperature, there was a greater decrease in ATP and phosphocreatine content in type IIA fibres than in the normal trial, which contributed to the higher maximal power output.     

Effects of a feint on reactive agility performance

Abstract

This study compared reactive agility between higher-standard (n = 14) and lower-standard (n = 14) Australian footballers using a reactive agility test incorporating a life-size video image of another player changing direction, including and excluding a feint. Mean agility time in the feint trials was 34% (509 ± 243 ms; p < 0.001; effect size 3.06) longer than non-feint trials. In higher-standard players, agility time was shorter than for lower-standard players in both feint (114 ± 140 ms; p = 0.18; effect size 0.52; likely beneficial) and non-feint (32 ± 44 ms; p = 0.22; effect size 0.47; possibly beneficial) trials. Additionally, the inclusion of a feint resulted in movement time increasing over three times more in the lower-standard group (197 ± 91 ms; p = 0.001; effect size 1.07; almost certainly detrimental) than the higher-standard group (62 ± 86 ms; p = 0.23; effect size 0.66; likely detrimental). There were weak correlations between the feint and non-feint trials (r = ?0.13–0.14; p > 0.05), suggesting that reactive agility involving a feint is a unique skill. Also, higher-standard players are more agile than their lower-standard peers, whose movement speed deteriorates more as task complexity increases with the inclusion of a feint. These results support the need for specific training in multi-turn reactive agility tasks.     

The effect of short-duration sprint interval exercise on plasma postprandial triacylglycerol levels in young men

Abstract

It is well established that regular exercise can reduce the risk of cardiovascular disease, although the most time-efficient exercise protocol to confer benefits has yet to be established. The aim of the current study was to determine the effects of short-duration sprint interval exercise on postprandial triacylglycerol. Fifteen healthy male participants completed two 2 day trials. On day 1, participants rested (control) or carried out twenty 6 s sprints, interspersed with 24 s recovery (sprint interval exercise – 14 min for total exercise session). On day 2, participants consumed a high-fat meal for breakfast with blood samples collected at baseline, 2 h and 4 h. Gas exchange was also measured at these time points. On day 2 of control and sprint interval exercise trials, there were no differences (P < 0.05) between trials in plasma glucose, triacylglycerol, insulin or respiratory exchange ratio (RER). The area under the curve for plasma triacylglycerol was 7.67 ± 2.37 mmol · l^–1.4 h^–1 in the control trial and 7.26 ± 2.49 mmol · l^–1.4 h^–1 in the sprint interval exercise trial. Although the sprint exercise protocol employed had no significant effect on postprandial triacylglycerol, there was a clear variability in responses that warrants further investigation.     

Ground reaction forces and osteogenic index of the sport of cyclocross

Abstract

Weight-bearing activity has been shown to increase bone mineral density. Our purpose was to measure vertical ground reaction forces (GRFs) during cyclocross-specific activities and compute their osteogenic index (OI). Twenty-five healthy cyclocross athletes participated. GRF was measured using pressure-sensitive insoles during seated and standing cycling and four cyclocross-specific activities: barrier flat, barrier uphill, uphill run-up, downhill run-up. Peak and mean GRF values, according to bodyweight, were determined for each activity. OI was computed using peak GRF and number of loading cycles. GRF and OI were compared across activities using repeated-measures ANOVA. Number of loading cycles per activity was 6(1) for barrier flat, 8(1) barrier uphill, 7(1) uphill run-up, 12(3) downhill run-up. All activities had significantly (P < 0.01) higher peak GRF, mean GRF values and OI when compared to both seated and standing cycling. The barrier flat condition (P < 0.01) had highest peak (2.9 times bodyweight) and mean GRF values (2.3 times bodyweight). Downhill run-up (P < 0.01) had the highest OI (6.5). GRF generated during the barrier flat activity is similar in magnitude to reported GRFs during running and hopping. Because cyclocross involves weight bearing components, it may be more beneficial to bone health than seated road cycling.     

Using peer effects to explain retention rates in a private university

This study identifies factors associated with freshmen retention rates at a mid‐size private university. A key finding from our analysis is that roommates' academic efforts, residing on an honours floor and membership in co‐curricular groups increase retention. We also confirm many standard results in the literature regarding the impact on retention rates, such as student motivation and ability, and financial aid. We show that a timely housing application, closer proximity to home, a higher number of schools on a student's Free Application for Federal Student Aid and peer effects impact freshman retention. Our results suggest that a more sophisticated dormroom assignment algorithm matching students' abilities and interests could be considered to increase freshman retention rates among private institutions.     

Teaching and tolerance: aversive and divisive pedagogical encounters

This paper takes as its subject the circulation of tolerance discourse within two pedagogical encounters in two Australian educational settings, and draws from the work of Wendy Brown on tolerance as a regulatory force. Brown argues that discourses of tolerance are produced within historical and cultural milieu that enable tolerance and aversion to exist simultaneously. This has significant implications for how we might come to understand the project of working towards a socially just educational system and the various struggles encountered within pedagogical sites. I also examine the pedagogical affects that are produced within different educational moments as we work to teach in or around difference and when we embody the Other in the classroom. I engage with how these experiences speak to the way in which tolerance as national ideal acts to both alleviate and circulate discourses of inequality such as sexism and homophobia.     

“There was Sex but no Sexuality*:” Critical Cataloging and the Classification of Asexuality in LCSH

Abstract

This paper examines the addition of “asexuality” to the Library of Congress Subject Headings as a case study from which to examine the critical cataloging movement. Beginning with a review of some of the theoretical and practical issues around subject access for minoritized and marginalized sexualities, this paper then contextualizes, historicizes, and introduces the critical cataloging movement to the literature, situating it within a larger and longer history of radical cataloging. It will define critical cataloging as a social justice-oriented style of radical cataloging that places an emphasis on radical empathy, outreach work, and recognizes the importance of information maintenance and care. This paper introduces the concept of “catalogic warrant” to characterize the process of “reading” the catalog to examine the harm or benefit of terms on users and the wider library community.