The effect of beetroot juice supplementation on repeat-sprint performance in hypoxia     

Georgina L. Kent  Brian Dawson  Lars R. McNaughton  Gregory R. Cox  Louise M. Burke  Peter Peeling 《Journal of sports sciences》2019,37(3):339-346

This investigation assessed the effect of dietary nitrate (NO₃^?) supplementation, in the form of beetroot juice (BR), on repeat-sprint performance in normoxia and normobaric hypoxia. 12 male team-sport athletes (age 22.3 ± 2.6 y, VO_2peak 53.1 ± 8.7 mL.kg^?1.min^?1) completed three exercise trials involving a 10 min submaximal warm-up and 4 sets of cycling repeat-sprint efforts (RSE; 9 × 4 s) at sea level (CON), or at 3000 m simulated altitude following acute supplementation (140 mL) with BR (HYP_BR; 13 mmol NO₃^?) or NO₃^–depleted BR placebo (HYP_PLA). Peak (PPO) and mean (MPO) power output, plus work decrement were recorded during the RSE task, while oxygen consumption (VO₂) was measured during the warm-up. There were no significant differences observed between HYP_BR and HYP_PLA for PPO or MPO; however, work decrement was reduced in the first RSE set in HYP_BR compared with HYP_PLA. There was a moderate effect for VO₂ to be lower following BR at the end of the 10 min warm-up (ES = 0.50 ± 0.51). Dietary NO₃^? may not improve repeat-sprint performance in hypoxia but may reduce VO₂ during submaximal exercise. Therefore, BR supplementation may be more effective for performance improvement during predominantly aerobic exercise.  相似文献   

Systems model and individual simulations of training strategies in elite short-track speed skaters     

Thibaut Méline  Ludovic Mathieu  Fabio Borrani  Robin Candau 《Journal of sports sciences》2019,37(3):347-355

This study aimed to evaluate the effect of simulated training strategies on performance potential in elite short-track speed skaters. Training load and field-based criterion performances from fifteen athletes (10 males, 5 females) were collected over a 3-month training period and the relationship between training loads and performance was computed with a variable dose-response model using a genetic algorithm. Individual simulations of tapers preceded or not preceded by an overload training (OT) were assessed. We obtained a significant correlation between actual and modelled performances (R² = 0.76 ± 0.07). Regarding model parameters, no significant difference was found between males and females but the time to recover performance tended to be lower in females. Simulations in which the taper parameters were free highlighted that an exponential or a step taper were the most effective for increasing performance compared to a linear taper (p < 0.05). Optimal exponential taper duration after OT was 10.7 ± 2.4d and the optimal load reduction was 75.9 ± 3.7%. OT intensity had the greatest influence on the predicted performance, followed by OT duration, taper decay, and to a lesser extent load reduction during taper and taper duration. Thus, a variable dose-response systems model allows the evaluation of different taper strategies and their potential effect on performance changes.  相似文献   

The effects of a calf pump device on second half performance of a simulated soccer match in competitive youth players     

S. Béliard  J. Cassirame  G. Ennequin  G. Coratella  N. Tordi 《Journal of sports sciences》2019,37(6):708-716

During soccer matches, performance decrements have been reported that relate to both physical abilities and technical skills. To investigate the effects of low-frequency electrical stimulation LFES (VeinoplusSport®, Ad Rem Technology, France) administered during half-time recovery on performance alterations during the second half. Twenty-two highly trained young players undertook a soccer-match simulation (SAFT⁹⁰). During half-time, they were randomly assigned to LFES group or Placebo group. Each half was split into 3 bouts of 12 minutes. Following each bout, maximal strike speed (MSS), sprint test (ST), maximal sprint accelerations (MA) and metabolic power (MP) were determined in both groups. Arterial (AF) and venous flows (VF) were measured at rest and at the end of half-time. LEFS group exhibited beneficial effects on performance compared to the Placebo group with a likely effect for MSS, ST, MA, and a possible effect for MP. AF and VF increased statistically more in LEFS group compared to Placebo group. The use of specific calf-pump LFES during half-time of a youth simulated soccer match attenuated the decrease in performance during the second half compared to Placebo group. This effect is most marked at the beginning of the second half with regards to explosive parameters.  相似文献   

Frequent sit-to-stand transitions and several short standing periods measured by hip-worn accelerometer are associated with smaller waist circumference among adults     

Pauliina Husu  Jaana Suni  Kari Tokola  Henri Vähä-Ypyä  Heli Valkeinen  Tomi Mäki-Opas 《Journal of sports sciences》2019,37(16):1840-1848

This cross-sectional study analysed the association of sedentary behaviour (SB) and standing with waist circumference. Finnish adults aged 30-75 years from a sub-sample of population-based Health 2011 Study used a hip-worn tri-axial accelerometer (Hookie AM20, Traxmeet, Ltd, Espoo, Finland) for seven days. Those 1405 participants (57% women) who used accelerometer at least four days, minimum of 10 hours/day, were included. SB and standing were analysed in 6s epochs using validated algorithm. Daily total time, daily number and accumulated time from bouts (30s–5min,30s–10min,30s–15min,30s 30min,>5min,>10min,>15min, >30min) as well as daily number of sit-to-stand transitions were determined. Waist circumference (cm) was measured in standardized way. Participants’ mean age was 52 years (SD 12.2). Mean waist circumference was 97cm (SD 12.3) in men and 87cm (SD 12.7) in women. According to multivariable stepwise linear regression analysis, sit-to-stand transitions [standardised regression coefficient (β)= -0.14, 95%CI -0.20 to -0.09], standing bouts of 30s–5min (β= -0.21, 95%CI -0.26 to -0.15) and number of 30s-30min SB bouts (β=0.12, 95%CI 0.06 to 0.17) were most strongly associated with waist circumference. Besides assessing total SB time, future studies should assess also different bout lengths of SB and sit-to-stand transitions and standing times should be assessed separately.  相似文献   

Effects of periodic carbohydrate ingestion on endurance and cognitive performances during a 40-km cycling time-trial under normobaric hypoxia in well-trained triathletes     

Yi-Hung Liao  Toby Mündel  Yan-Ting Yang  Chen-Chan Wei  Shiow-Chwen Tsai 《Journal of sports sciences》2019,37(16):1805-1815

The purpose of this study was to examine CHO ingestion on a cognitive task using a field-simulated time-trial (TT) under hypoxia in well-trained triathletes. Ten male triathletes (age: 22.1 ± 1.1 years; VO₂max: 59.4 ± 1.4 ml/kg/min) participated in this double-blind/crossover/counter-balanced design study. Participants completed 3 TT trials: 1) normoxic placebo (NPLA; FiO₂ = 20.9%), 2) hypoxic placebo (HPLA; FiO₂ = 16.3%), and 3) hypoxic CHO (HCHO; 6% CHO provided as 2 ml/kg/15 min; FiO₂ = 16.3%). During the TT, physiological responses (SpO₂, HR, RPE, and blood glucose/lactate), cognitive performance, and cerebral haemodynamics were measured. Hypoxia reduced TT performance by ~3.5–4% (p < 0.05), but CHO did not affect TT performance under hypoxia. For the cognitive task, CHO slightly preserved exercise-induced cognitive reaction speed but did not affect response accuracy during hypoxic exercise. However, CHO did not preserve the decreased Hb-Diff (cerebral blood flow, CBF) and increased HHb in the prefrontal lobe (p < 0.05) during hypoxic exercise, and CHO failed to preserve hypoxia-suppressed prefrontal CBF and tissue oxygen saturation. In conclusion, the present study demonstrates that CHO is effective in sustaining reaction speed for a cognitive task but not promoting TT performance during hypoxic exercise, which would be important for strategy-/decision-making when athletes compete at moderate high-altitude.  相似文献   

Reviewing the Variability-Overuse Injury Hypothesis: Does Movement Variability Relate to Landing Injuries?     

Andrew D. Nordin  Janet S. Dufek 《Research quarterly for exercise and sport》2019,90(2):190-205

Purpose: Overuse injuries are common in sport, but complete understanding of injury risk factors remains incomplete. Although biomechanical studies frequently examine musculoskeletal injury mechanisms, human movement variability studies aim to better understand neuromotor functioning, with proposed connections between overuse injury mechanisms and changes in motor variability. Method: In a narrative review, we discuss the variability-overuse injury hypothesis, which suggests repeated load application leads to mechanical tissue breakdown and subsequent injury when exceeding the rate of physiological adaptation. Due to the multidisciplinary nature of this hypothesis, we incorporate concepts from motor control, neurophysiology, biomechanics, as well as research design and data analysis. We therefore summarize multiple perspectives while proposing theoretical relationships between movement variability and lower extremity overuse injuries. Results: Experimental data are presented and summarized from published experiments examining interactions between experimental task demands and movement variability in the context of drop landing movements, along with comparisons to previous movement variability studies. Conclusion: We provide a conceptual framework for sports medicine researchers interested in predicting and preventing sports injuries. Under performance conditions with greater task demands, we predict reduced trial-to-trial movement variability that could increase the likelihood of overuse injuries.  相似文献   

Day care and family dynamics     

Jaipaul L. Roopnarine  Lynn M. Hempel 《Early childhood research quarterly》1988,3(4)

Twenty-one dual-earner families whose preschool-aged children entered day care before 6 months of age and 19 dual-earner families whose preschool-aged children entered day care during the second year of life filled out questionnaires on the nature of their children's caregiving environment; their perceptions of the effects of day care on parent-child interaction and children's development; their overall job satisfaction; social support networks; and personal well-being, marital stress, and companionship. Mothers and fathers reported high levels of satisfaction with the caregiving environment and the effects of day care. Parental perceptions of the effects of day care on parent-child interaction and children's development did not differ as a function of time of entry into day care. Parental perceptions of selected parent-child variables were associated with job satisfaction, social support, and the marital measures. Parental perceptions of parent-child interaction were related to their perceptions of the effects of day care on children's social and cognitive skills. Mothers and fathers differed in these perceptions. There was some support for a conceptual link between marital variables and children's functioning in day care.  相似文献   

Coordination of perspective by sixth graders and teacher trainees     

Gwendolyn N. Kelly  Joseph T. Kelly  Wallace S. Johnson 《Contemporary educational psychology》1988,13(4)

Sixth grade students were compared by sex for their performance on two perspective coordination tasks. Responses were compared with understanding of the principle that still water remains invariantly horizontal. Forty-eight randomly selected sixth grade students (24 girls and 24 boys) and 12 college women were individually shown a standardized three-dimensional scene. While seated in a single position, subjects completed two tasks: (1) selecting from a set of 12 pictures (displayed together) the one which could be seen from each of eight positions marked on the displayed scene and (2) choosing the positions from which could be seen eight of the 12 pictures (shown one at a time). Four of the 12 pictures were mirror images which were impossible views. Males outperformed females on both of the coordination-of-perspective tasks. For both males and females, choosing the place was more difficult than choosing the picture. Strong relationships were found between understanding of horizontality and performance on the perspective tasks. Selection of mirror images (impossible views) indicated more understanding of perspective than other, less systematic errors. Finally, female teacher trainees performed only marginally better than sixth grade students, suggesting possible remediation needs.  相似文献   

Time and Politics: Parliament and the Culture of Modernity in Britain and the British World     

Joseph S. Meisel 《Cultural and Social History》2017,14(5):739-740

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Developing Culturally Competent Preservice Teachers     

Calli Lewis Chiu  Donna Sayman  Kelly M. Carrero  Thomas Gibbon  Staci M. Zolkoski  Mandy E. Lusk 《Multicultural Perspectives》2017,19(1):47-52

An unfortunate, yet persistent, truth in U.S. public schools is the large achievement gap existing between children from culturally and linguistically diverse backgrounds and their White, middle-class counterparts. The potential for cultural dissonance between contemporary teachers and their students necessitates that educators must persistently seek culturally responsive practices. Much has been written regarding strategies for culturally responsive pedagogy; therefore, this article moves beyond a review of culturally responsive pedagogy. Rather than providing teacher candidates with more suggestions for culturally responsive teaching activities, the authors provide teacher educators with specific resources for facilitating the development of cultural competence among preservice teachers.  相似文献