Influence of body position when considering the ecological validity of laboratory time-trial cycling performance

Abstract

The aims of this study were to compare the physiological demands of laboratory- and road-based time-trial cycling and to examine the importance of body position during laboratory cycling. Nine male competitive but non-elite cyclists completed two 40.23-km time-trials on an air-braked ergometer (Kingcycle) in the laboratory and one 40.23-km time-trial (RD) on a local road course. One laboratory time-trial was conducted in an aerodynamic position (AP), while the second was conducted in an upright position (UP). Mean performance speed was significantly higher during laboratory trials (UP and AP) compared with the RD trial (P < 0.001). Although there was no difference in power output between the RD and UP trials (P > 0.05), power output was significantly lower during the AP trial than during both the RD (P = 0.013) and UP trials (P = 0.003). Similar correlations were found between AP power output and RD power output (r = 0.85, P = 0.003) and between UP power output and RD power output (r = 0.87, P = 0.003). Despite a significantly lower power output in the laboratory AP condition, these results suggest that body position does not affect the ecological validity of laboratory-based time-trial cycling.     

Reliability and validity of field-based measures of leg stiffness and reactive strength index in youths

Abstract

The aim of the study was to assess the reliability of a mobile contact mat in measuring a range of stretch–shortening cycle parameters in young adolescents. Additionally, vertical leg stiffness using contact mat data was validated against a criterion method using force–time data. The reliability study involved 18 youths completing a habituation and three separate test sessions, while 20 youths completed a single test session for the validity study. Participants completed three trials of a squat jump, countermovement jump, and maximal hopping test and a single trial of repeated sub-maximal hopping at 2.0 Hz and 2.5 Hz. All tests were performed on the contact mat. Reliability statistics included repeated-measures analysis of variance, intraclass correlation coefficient, and coefficient of variation (CV), while the correlation coefficient (r) and typical error of estimate (TEE) were reported for the validity study. Squat jump height was the most reliable measure (CV = 8.64%), while leg stiffness during sub-maximal hopping, and reactive strength index produced moderate reliability (CV = 10.17–13.93% and 13.98% respectively). Measures of leg stiffness obtained from contact mat data during sub-maximal hopping were in agreement with the criterion measure (r = 0.92–0.95; TEE = 6.5–7.5%), but not during maximal hopping (r = 0.59; TEE = 41.9%). The contact mat was deemed a valid tool for measuring stretch–shortening cycle ability in sub-maximal but not maximal hopping. Although reliability of performance was generally moderate, the tests offer a replicable assessment method for use with paediatric populations.     

Optimization of insulin-mediated creatine retention during creatine feeding in humans

Abstract

The aim of this study was to determine whether creatine ingested in combination with relatively small quantities of essential amino acids, simple sugars, and protein would stimulate insulin release and augment whole-body creatine retention to the same extent as a large bolus of simple sugars. Seven young, healthy males underwent three randomized, 3-day experimental trials. Each day, 24-h urine collections were made, and on the second day participants received 5 g creatine + water (creatine trial), 5 g creatine + ～95 g dextrose (creatine + carbohydrate) or 5 g creatine + 14 g protein hydrolysate, 7 g leucine, 7 g phenylalanine, and 57 g dextrose (creatine + protein, amino acids, and carbohydrate) via naso-gastric tube at three equally spaced intervals. Blood samples were collected at predetermined intervals after the first and third naso-gastric bolus. After administration of the first and third bolus, serum insulin concentration was increased by 15 min (P < 0.05) in the creatine + carbohydrate and creatine + protein, amino acids, and carbohydrate trials compared with creatine alone, and plasma creatine increased more following creatine alone (15 min, P < 0.05) than in the creatine + carbohydrate and creatine + protein, amino acids, and carbohydrate trials. Urinary creatine excretion was greater with creatine alone (P < 0.05) than with creatine + carbohydrate and creatine + protein, amino acids, and carbohydrate. Administration of creatine + protein, amino acids, and carbohydrate can stimulate insulin release and augment whole-body creatine retention to the same extent as when larger quantities of simple sugars are ingested.     

High-intensity interval running is perceived to be more enjoyable than moderate-intensity continuous exercise: Implications for exercise adherence

Abstract

The aim of this study was to objectively quantify ratings of perceived enjoyment using the Physical Activity Enjoyment Scale following high-intensity interval running versus moderate-intensity continuous running. Eight recreationally active men performed two running protocols consisting of high-intensity interval running (6×3 min at 90% [Vdot]O_2max interspersed with 6×3 min active recovery at 50% [Vdot]O_2max with a 7-min warm-up and cool down at 70% [Vdot]O_2max) or 50 min moderate-intensity continuous running at 70% [Vdot]O_2max. Ratings of perceived enjoyment after exercise were higher (P < 0.05) following interval running compared with continuous running (88 ± 6 vs. 61 ± 12) despite higher (P < 0.05) ratings of perceived exertion (14 ± 1 vs. 13 ± 1). There was no difference (P < 0.05) in average heart rate (88 ± 3 vs. 87 ± 3% maximum heart rate), average [Vdot]O₂ (71 ± 6 vs. 73 ± 4%[Vdot]O_2max), total [Vdot]O₂ (162 ± 16 vs. 166 ± 27 L) or energy expenditure (811 ± 83 vs. 832 ± 136 kcal) between protocols. The greater enjoyment associated with high-intensity interval running may be relevant for improving exercise adherence, since running is a low-cost exercise intervention requiring no exercise equipment and similar relative exercise intensities have previously induced health benefits in patient populations.     

Changes in energy availability across the season in Division I female soccer players

Abstract

Low energy availability [(energy intake – exercise expenditure)/kg lean body mass], a component of the Female Athlete Triad, has been associated with menstrual disturbances and low bone mass. No studies have examined the energy availability of athletes across a season. The purpose of this study was to assess the prevalence of, and what contributes to, low energy availability in Division I female soccer players across a season. Nineteen participants aged 18–21 years (mean [Vdot]O_2max: 57.0 ± 1.0 mL · kg^?1 · min^?1) were studied during the pre, mid, and post season. Mean energy availability was overall lowest at mid season, and lower at mid than post season (35.2 ± 3.7 vs. 44.5 ± 3.7 kcal · kg^?1 lean body mass, P = 0.009). Low energy availability (<30 kcal · kg^?1 lean body mass) was observed in 5/19 (26.3%), 5/15 (33.3%), and 2/17 (11.8%) of participants during the pre, mid, and post season. Dietary energy intake was lower mid (P = 0.008) and post season (P = 0.022) than it was pre season (pre: 2794 ± 233 kcal · day^?1; mid: 2208 ± 156 kcal · day^?1; post: 2161 ± 143 kcal · day^?1). Exercise energy expenditure decreased significantly (P ≤ 0.001) over time (pre: 819 ± 57 kcal · day^?1; mid: 642 ± 26 kcal · day^?1; post: 159 ± 28 kcal · day^?1). Low energy availability was due to lower dietary energy intake at lunch during pre season (P = 0.014) and during lunch and dinner during mid season (P ≤ 0.030). Energy availability was inversely related to body dissatisfaction (r = ?0.62, P = 0.017) and drive for thinness (r = ?0.55, P = 0.041) during mid season. Although most Division I female soccer players are not at risk for low energy availability, a concerning proportion exhibited low energy availability at pre or mid season. Further studies are needed to explore strategies to prevent and monitor low energy availability in these athletes.     

Effect of the 3-Point Line Change on the Game Dynamics in Girls' Minibasketball

We examined the game dynamics in minibasketball when comparing two different forms of the 3-point line. During the first competition, participants used a 3-point line delimited by the free-throw lane, and 1,642 ball possessions were recorded. During the second competition, participants played with a 3-point line delimited by a rectangular area, and 1,669 ball possessions were recorded. Results from the Mann-Whitney U Test show that when playing with a 3-point line delimited by the free-throw lane, higher average values were achieved in terms of points scored, number of players taking part in the ball possessions, number of passes, and one-on-one situations.     

Interleukin-6 and Delayed Onset Muscle Soreness Do Not Vary During the Menstrual Cycle

The purpose of this study was to determine if a difference in interleukin-6 (IL-6) and delayed onset muscles soreness (DOMS) exists in two different phases of the menstrual cycle. Nine runners performed one 75-min high-intensity interval running session during the early follicular (EF) phase and once during the midluteal (ML) phase of the menstrual cycle. Estrogen and progesterone levels were significantly reduced in the EF phase when compared to the ML phase. IL-6 levels increased from pre- to postexercise in the EF and ML phases (p < .001). There was no relationship between the IL-6 level and DOMS. The results suggest that menstruating female runners need not vary training throughout the month to reduce DOMS.     

Guiding Attention Aids the Acquisition of Anticipatory Skill in Novice Soccer Goalkeepers

Purpose: The ability to anticipate the actions of opponents can be enhanced through perceptual-skill training, though there is doubt regarding the most effective form of doing so. We sought to evaluate whether perceptual-skill learning would be enhanced when supplemented with guiding visual information. Method: Twenty-eight participants without soccer-playing experience were assigned to a guided perceptual-training group (n = 9), an unguided perceptual-training group (n = 10), or a control group (n = 9). The guided perceptual-training group received half of their trials with color cueing that highlighted either the key kinematic changes in the kicker's action or the known visual search strategy of expert goalkeepers. The unguided perceptual-training group undertook an equal number of trials of practice, but all trials were without guidance. The control group undertook no training intervention. All participants completed an anticipation test immediately before and after the 7-day training intervention, as well as a 24-hr retention test. Results: The guided perceptual-training group significantly improved their response accuracy for anticipating the direction of soccer penalty kicks from preintervention to postintervention, whereas no change in performance was evident at posttest for either the unguided perceptual-training group or the control group. The superior performance of the guided perceptual-training group was preserved in the retention test and was confirmed when relative changes in response time were controlled using a covariate analysis. Conclusions: Perceptual training supplemented with guiding information provides a level of improvement in perceptual anticipatory skill that is not seen without guidance.     

JROTC as a Substitute for PE: Really?

Purpose: Even though physical education (PE) is an evidence-based strategy for providing and promoting physical activity, alternative programs such as the Junior Reserve Officer Training Corps (JROTC) are commonly substituted for PE in many states. The purpose of this study was to compare student physical activity and lesson contexts during high school PE and JROTC sessions. Method: The System for Observing Fitness Instruction Time was used to assess PE and JROTC sessions (N = 38 each) in 4 high schools that provided both programs. Data were analyzed using t tests, negative binomial regression, and logistic regression. Results: Students engaged in significantly more moderate-to-vigorous physical activity during PE than during JROTC sessions and they were significantly less sedentary. Significant differences between the 2 program types were also found among lesson contexts. Conclusions: PE and JROTC provide substantially different content and contexts, and students in these programs engage in substantially different amounts of moderate-to-vigorous physical activity. Students in JROTC, and perhaps other alternative programs, are less likely to accrue health-supporting physical activity and engage in fewer opportunities to be physically fit and motorically skilled. Policies and practices for providing substitutions for PE should be carefully examined.