Repeated-measures Crossover Design Research Articles

Results From a Controlled Study of the iPad Fractions Game Motion Math

Although fractions knowledge is essential for future success in mathematics, data show that most U.S. students fail to become proficient in fractions. With the advent of mobile technologies such as iPad tablets, new kinds of interactions with subject matter have become possible that have potential for improving learning. The present study used an experimental repeated measures crossover design to investigate whether the iPad fractions game Motion Math would improve fourth graders’ fractions knowledge and attitudes. In results from 122 participants, students’ fractions test scores improved an average of over 15% after playing Motion Math for 20 min daily over a 5-day period, representing a significant increase compared to a control group. In addition, children’s self-efficacy for fractions, as well as their liking of fractions, each improved an average of 10%, representing a statistically significant increase compared to a control group. Implications for the design and study of interactive games are discussed.

No clear effects of acute tryptophan depletion on processing affective prosody in male adults with ADHD

Adults with attention deficit hyperactivity disorder (ADHD) have difficulties processing affective prosody, and research evidence demonstrates the importance of brain serotonin (5-HT) in the neurobiology of ADHD. This study aimed to investigate whether diminished brain 5-HT synthesis, as achieved by acute tryptophan depletion (ATD), can impair the processing of affective prosody in adults with ADHD. Twenty male patients with ADHD and twenty male healthy controls received ATD and a tryptophan-balanced control condition on separate days in a double-blind within-subject repeated measures crossover design. In both conditions, the Tübingen Affect Battery was administered in which subjects had to name the affective prosody of sentences with neutral, congruent, or incongruent semantic content. Participants in the group of patients with ADHD perceived affective prosody less accurately than controls. Participants with ADHD showed compromised processing of sentences, committing more errors than healthy controls when identifying affect in instances of incongruent semantic content (P = 0.031). ATD did not contribute to this effect (all P > 0.5). The difficulties male adults with ADHD have in accurately processing affective prosody may result from impairments in their ability to inhibit unwanted stimuli and impulses. No clear evidence implicates 5-HT as a cause of these impairments.

Dairy snack reduces glycaemia in normal weight children

Increased snacking in children is associated with higher energy and sugar intake, known risk factors for obesity and diabetes. The objective of this study was to determine the effect of dairy and non‐dairy snacks on glycaemia in children.MethodsIn a repeatedmeasures crossover design, normal weight (5th–85th BMI percentile) children (n =11, 5 boys and 6 girls; age: 9–14 y), were randomly assigned to consume one of two treatments: Greek yogurt (171 kcal) and mini sandwich type cookies (175 kcal). Both treatments contained 25 g of available carbohydrates. After an overnight fast, children consumed a standardized breakfast in the morning, two hours before arriving at the lab. Venous blood samples were collected for glucose and insulin at 0 min (immediately before the treatment), and at 30, 60, 90 and 120 min.ResultsThere was an effect of treatment, time and a time by treatment interaction (P<0.0001) on blood glucose and insulin over 120 min. The yogurt treatment resulted in lower glycaemic and higher insulin responses compared to the cookies treatment (P<0.0001). This effect can be explained by the higher content of protein in the yogurt treatment (17 g) compared to the cookies treatment (1.3 g).ConclusionMacronutrient composition of a snack predetermines its glycaemic response and can affect postprandial hyperglycaemia in children.Grant Funding Source: Dairy Farmers of Canada

Video Game–Based Exercise, Latino Children's Physical Health, and Academic Achievement

There is a paucity of research investigating the effects of innovative physical activity programs on physical health and academic performance in the Latino population. To examine the impact of Dance Dance Revolution [DDR]-based exercise on Latino children's physical fitness and academic achievement. A repeated-measures crossover design was used. In Year 1, Grade-4 students were assigned to the intervention group and offered 30 minutes of exercise (DDR, aerobic dance) three times per week. Grade-3 and Grade-5 students made up the comparison group and were offered no structured exercise at school. In Year 2, the Grade-4 students were again assigned to the intervention, whereas Grade-5 and Grade-6 students were in the comparison group. Assessments were conducted with 208 Latino school children. The baseline measures included time to complete a 1-mile run, BMI, and reading and math scores. Data were collected again 9 months later. Overall, data were collected in 2009-2011 and analyzed in 2012. Data yielded significant differences between the intervention and comparison groups in differences in 1-mile run and math scores in Year 1 and Year 2. The results also revealed net differences in the intervention versus comparison group scores on the 1-mile run for Grade 3 (p<0.01). Additionally, children's yearly pre-test and post-test BMI group changes differed (χ(2)((2)) = 6.6, p<0.05) only for the first year of intervention. The DDR-based exercise intervention improved children's cardiorespiratory endurance and math scores over time. Professionals should consider integrating exergaming at schools to achieve the goals of promoting a physically active lifestyle and enhancing academic success among Latino children.

Cold habituation does not improve manual dexterity during rest and exercise in 5 °C

When exposed to a cold environment, a barehanded person experiences pain, cold sensation, and reduced manual dexterity. Both acute (e.g. exercise) and chronic (e.g. cold acclimatization or habituation) processes might lessen these negative effects. The purpose of this experiment was to determine the effect of cold habituation on physiology, perception, and manual dexterity during rest, exercise, and recovery in 5°C. Six cold weather athletes (CWA) and eight non habituated men (NON) volunteered to participate in a repeated measures cross-over design. The protocol was conducted in 5°C and was 90min of resting cold exposure, 30min of cycle ergometry exercise (50% VO2 peak), and 60min of seated recovery. Core and finger skin temperature, metabolic rate, Purdue Pegboard dexterity performance, hand pain, thermal sensation, and mood were quantified. Exercise-induced finger rewarming (EIFRW) was calculated for each hand. During 90min of resting exposure to 5°C, the CWA had a smaller reduction in finger temperature, a lower metabolic rate, less hand pain, and less negative mood. Despite this cold habituation, dexterity performance was not different between groups. In response to cycle ergometry, EIFRW was greater in CWA (~12 versus 7°C) and occurred at lower core temperatures (37.02 versus 37.31°C) relative to NON but dexterity was not greater during post-exercise recovery. The current data indicate that cold habituated men (i.e., CWA) do not perform better on the Purdue Pegboard during acute cold exposure. Furthermore, despite augmented EIFRW in CWA, dexterity during post-exercise recovery was similar between groups.

A randomized trial of a classroom intervention to increase peers' social inclusion of children with attention-deficit/hyperactivity disorder.

Interventions for peer problems among children with attention-deficit/hyperactivity disorder (ADHD) typically focus on improving these children's behaviors. This study tested the proposition that an adjunctive component encouraging the peer group to be socially inclusive of children with ADHD would augment the efficacy of traditional interventions. Two interventions were compared: contingency management training (COMET), a traditional behavioral management treatment to improve socially competent behavior in children with ADHD, and Making Socially Accepting Inclusive Classrooms (MOSAIC), a novel treatment that supplemented behavioral management for children with ADHD with procedures training peers to be socially inclusive. Children ages 6.8-9.8 (24 with ADHD; 113 typically developing [TD]) attended a summer day program grouped into same-age, same-sex classrooms with previously unacquainted peers. Children with ADHD received both COMET and MOSAIC with a repeated measures crossover design. TD children provided sociometric information about the children with ADHD. Whereas the level of behavior problems displayed by children with ADHD did not differ across treatment conditions, children with ADHD displayed improved sociometric preference and more reciprocated friendships, and received more positive messages from peers, when they were in MOSAIC relative to COMET. However, the beneficial effects of MOSAIC over COMET predominantly occurred for boys relative to girls. Data support the concept that adjunctive procedures to increase the inclusiveness of the peer group may ameliorate peer problems among children with ADHD, and suggest the potential utility of modifying MOSAIC to be delivered in regular classroom settings.

The effect of lower body stabilization and different writing tools on writing biomechanics in children with cerebral palsy

A high percentage of children with cerebral palsy (CP) have difficulty keeping up with the handwriting demands at school. Previous studies have addressed the effects of proper sitting and writing tool on writing performance, but less on body biomechanics. The aim of this study was to investigate the influence of lower body stabilization and pencil design on body biomechanics in children with CP. Fourteen children (12.31±4.13 years old) with CP were recruited for this study. A crossover repeated measures design was employed, with two independent variables: lower body stabilization (with/without) and pencil (regular/assigned grip height/biaxial). The writing task was to trace the Archimedean spiral mazes. Electromyography (EMG) of the upper extremity, the wrist flexion/extension movements, and the whole body photography were recorded to quantify the changes in posture and upper extremity biomechanics. Two-way repeated measures ANOVA was used for statistical analysis. No significant main effects were revealed in the EMG and wrist kinematics. The lower body stabilization significantly decreased the trunk lateral and forward deviations, and the visual focus-vertical angle. The biaxial pencil and the assigned grip height design significantly decreased the head, shoulder, trunk, and pelvic deviations compared with the regular design. The results indicated that the lower body positioning was effective in improving the trunk posture. A pencil with an assigned grip height or with a biaxial design could improve head, shoulder, trunk and pelvic alignment, but did not influence the muscle exertion of the upper extremity. This study could provide guidelines for parents, teachers and clinicians regarding the selection of writing tools and the knowledge of proper positioning for the children with handwriting difficulties. Further analyses can focus on the design, modification and clinical application of assitive sitting and writing devices for the use in children with handwriting difficulties.

Cochlear Implant Combined with a Linear Frequency Transposing Hearing Aid

Adults with cochlear implants (CIs) are usually implanted unilaterally. To preserve binaural advantages, a noninvasive method involves maintaining the hearing aid (HA) on the contralateral ear; the choice of HA for this purpose is therefore crucial. In recent years, the use of frequency transposition has gained a renewed interest in clinical practice. This type of processing records information from the high-frequency region and conveys it to a low-frequency region where there is still some residual hearing. To conduct an investigation and examine whether adults with unilateral CI derive benefits from a HA utilizing linear frequency transposition (LFT) on the contralateral ear. A two-period, single-blind, repeated-measures crossover design was conducted to examine the combination of LFT in conjunction with a CI. Speech recognition tests were performed in quiet and in noise with LFT either activated or deactivated. The Speech, Spatial and Qualities of Hearing Questionnaire (SSQ) was used to measure subjective benefit. The participants were nine frequent bimodal users, five males and four females, with a moderate to profound high-frequency sensorineural hearing loss in the nonimplanted ear. The current study was conducted using the Widex Mind440 power (m4-19) behind-the-ear HA. The participants acted as their own control in a total of seven conditions: (1) bimodal with own HA, (2) CI only, (3) own HA alone, (4) bimodal new HA LFT-off, (5) new HA LFT-off, (6) bimodal new HA LFT-on, and (7) new HA LFT-on. Monosyllabic words in quiet and the Swedish version of Hearing in Noise Test (HINT) were used as speech test materials. Stimuli were presented in sound field at a speech level of 65 dB sound pressure level (SPL) via a loudspeaker at a distance of 1 m from the participant in a sound-treated room. The SSQ was administered in each session evaluating the three bimodal conditions. SPSS software was used for statistical analyses. General linear model (GLM) analysis of variance for repeated measures was performed and followed with Bonferroni-adjusted post hoc pairwise comparisons. Participants performed better with CI only than with HA alone, and the bimodal conditions were superior to the CI alone. No significant differences (p > .05) were observed when comparing the LFT-on with LFT-off regardless of whether the use of CI was included in the different listening conditions in objective and subjective measurements. The results suggest an advantage for CI patients with a HA in the opposite ear, and that the LFT neither degraded nor enhanced speech performance in conjunction with a CI in quiet or in noise in comparison to when it was deactivated.

Acute Bone Marker Responses to Whole-Body Vibration and Resistance Exercise in Young Women

Whole-body vibration (WBV) augments the musculoskeletal effects of resistance exercise (RE). However, its acute effects on bone turnover markers (BTM) have not been determined. This study examined BTM responses to acute high-intensity RE and high-intensity RE with WBV (WBV+RE) in young women (n=10) taking oral contraceptives in a randomized, crossover repeated measures design. WBV+RE exposed subjects to 5 one-minute bouts of vibration (20Hz, 3.38 peak-peak displacement, separated by 1min of rest) before RE. Fasting blood samples were obtained before (Pre), immediately after WBV (PostVib), immediately after RE (IP), and 30-min after RE (P30). Bone alkaline phosphatase did not change at any time point. Tartrate-resistant acid phosphatase 5b significantly increased (p<0.05) from the Pre to PostVib, then decreased from IP to P30 for both conditions. C-terminal telopeptide of type I collagen (CTX) significantly decreased (p<0.05) from Pre to PostVib and from Pre to P30 only for WBV+RE. WBV+RE showed a greater decrease in CTX than RE (−12.6%±4.7% vs −1.13%±3.5%). In conclusion, WBV was associated with acute decreases in CTX levels not elicited with RE alone in young women.

DMA Clinical Pilates Directional-Bias Assessment: Reliability and Predictive Validity

Randomized, repeated-measures crossover design. To determine the interrater reliability of directional-bias assessment and to investigate its validity for predicting immediate changes in dynamic postural stability and muscle performance following directionally biased exercises. Directional bias in dynamic postural stability deficits may be associated with outcome following intervention. Two researchers independently assessed 33 participants, each with a history of more than 1 unilateral lower-limb injury, for directional bias. Interrater reliability was evaluated with the kappa coefficient and a prevalence-adjusted and bias-adjusted kappa coefficient. Participants were randomly allocated to perform matched-bias (MB) or unmatched-bias (UB) exercises first, in 2 crossover groups. Two outcome measures, time to stabilization and rebound hopping, were assessed before and following each exercise intervention, using a force plate. Crossover trial data were analyzed by t tests for period, interaction, and treatment effects, and repeated-measures analyses of variance were used to investigate differences between baseline, MB, and UB. Interrater reliability of directional-bias assessment was substantial (κ = 0.75; prevalence-adjusted and bias-adjusted κ = 0.76). Following MB exercises, medial/lateral time to stabilization and time on the ground during rebound hopping were significantly shorter (P = .01 and P = .05, respectively) compared with UB exercises. Compared with baseline, pairwise change in anterior/posterior time to stabilization (P = .008) improved following MB, whereas time in the air decreased following UB (P = .036). Directional-bias assessment demonstrates substantial reliability, and outcomes suggest validity for predicting immediate improvements following matched directionally biased exercises.

No Improvement in Endurance Performance after a Single Dose of Beetroot Juice

Dietary nitrate supplementation has received much attention in the literature due to its proposed ergogenic properties. Recently, the ingestion of a single bolus of nitrate-rich beetroot juice (500 ml, ~6.2 mmol NO3-) was reported to improve subsequent time-trial performance. However, this large volume of ingested beetroot juice does not represent a realistic dietary strategy for athletes to follow in a practical, performance-based setting. Therefore, we investigated the impact of ingesting a single bolus of concentrated nitrate-rich beetroot juice (140 ml, ~8.7 mmol NO3-) on subsequent 1-hr time-trial performance in well-trained cyclists. Using a double-blind, repeated-measures crossover design (1-wk washout period), 20 trained male cyclists (26 ± 1 yr, VO(2peak) 60 ± 1 ml · kg(-1) · min(-1), Wmax 398 ± 7.7 W) ingested 140 ml of concentrated beetroot juice (8.7 mmol NO3-; BEET) or a placebo (nitrate-depleted beetroot juice; PLAC) with breakfast 2.5 hr before an ~1-hr cycling time trial (1,073 ± 21 kJ). Resting blood samples were collected every 30 min after BEET or PLAC ingestion and immediately after the time trial. Plasma nitrite concentration was higher in BEET than PLAC before the onset of the time trial (532 ± 32 vs. 271 ± 13 nM, respectively; p < .001), but subsequent time-trial performance (65.5 ± 1.1 vs. 65 ± 1.1 s), power output (275 ± 7 vs. 278 ± 7 W), and heart rate (170 ± 2 vs. 170 ± 2 beats/min) did not differ between BEET and PLAC treatments (all p > .05). Ingestion of a single bolus of concentrated (140 ml) beetroot juice (8.7 mmol NO3-) does not improve subsequent 1-hr time-trial performance in well-trained cyclists.

The effect of increasing sets (within one treatment session) and different set durations (between treatment sessions) of lumbar spine posteroanterior mobilisations on pressure pain thresholds

Spinal mobilisations are a common form of treatment intervention applied by physiotherapists in clinical practice to manage musculoskeletal pain and/or dysfunction. Previous research has demonstrated that mobilisations cause a hypoalgesic effect. However, there is very little research investigating the optimal treatment dose inducing this effect. AimTo investigate the effect of the number of sets (up to 5) and different durations (30 vs. 60 s) on pressure pain thresholds (PPTs) at different sites. MethodsThis single-blinded, randomised, same subject repeated measures crossover design included 19 asymptomatic healthy volunteers. The participants received 5 sets of either 30 or 60 s of postero-anterior mobilisations to L4 on different days. PPTs were measured immediately before, between and after the intervention at 4 different standardised sites. ResultsA 4-way ANOVA analysis revealed that there was no statistically significant difference between 30 versus 60 s of mobilisations. However, there was a tendency for PPT values to be higher for the 60 s intervention. All PPT measurements after the interventions were significantly higher than the baseline. Only the measurement after the 4th set of mobilisations was significantly higher than the measurement after the 1st set (p = 0.035). ConclusionsThe results suggest that in order to induce the greatest local hypoalgesia, at least 4 sets of mobilisations are required. The different durations of 30 versus 60 s of mobilisation may not change the extent of the hypoalgesic effect.

The effect of school uniform on incidental physical activity among 10-year-old children

The school setting provides a unique opportunity to promote physical activity in children by ensuring adequate time, appropriate facilities and education guidance is offered. However school uniform design could also limit physical activity. A repeated measures crossover design was used to compare school recess and lunchtime physical activity over four weeks in 64 primary school children (M=10.48 yrs) when wearing winter uniform or sports uniform. Pedometers recorded step counts during each school recess and lunch break. Perception of the level of intensity of physical activity was also measured using a self-report log book. Mixed model analyses found that girls, but not boys, were significantly more active at recess (p=.03), lunch (p=.04) and overall (p=.006) when wearing their sports uniform compared to their winter uniform. School uniform did not impact the boy's physical activity levels. Perceived intensity of physical activity increased slightly among both girls and boys. A physically restrictive school uniform has the potential to inhibit physical activity among primary-school-aged girls.

Nitrate Supplementation’s Improvement of 10-km Time-Trial Performance in Trained Cyclists

Six days of dietary nitrate supplementation in the form of beetroot juice (~0.5 L/d) has been reported to reduce pulmonary oxygen uptake (VO₂) during submaximal exercise and increase tolerance of high-intensity work rates, suggesting that nitrate can be a potent ergogenic aid. Limited data are available regarding the effect of nitrate ingestion on athletic performance, and no study has investigated the potential ergogenic effects of a small-volume, concentrated dose of beetroot juice. The authors tested the hypothesis that 6 d of nitrate ingestion would improve time-trial performance in trained cyclists. Using a double-blind, repeated-measures crossover design, 12 male cyclists (31±3 yr, VO2peak=58±2 ml·kg⁻¹·min⁻¹, maximal power [Wmax]=342±10 W) ingested 140 ml/d of concentrated beetroot (~8 mmol/d nitrate) juice (BEET) or a placebo (nitrate-depleted beetroot juice; PLAC) for 6 d, separated by a 14-d washout. After supplementation on Day 6, subjects performed 60 min of submaximal cycling (2×30 min at 45% and 65% Wmax, respectively), followed by a 10-km time trial. Time-trial performance (953±18 vs. 965±18 s, p<.005) and power output (294±12 vs. 288±12 W, p<.05) improved after BEET compared with PLAC supplementation. Submaximal VO₂ was lower after BEET (45% Wmax=1.92±0.06 vs. 2.02±0.09 L/min, 65% Wmax 2.94±0.12 vs. 3.11±0.12 L/min) than with PLAC (main effect, p<.05). Whole-body fuel selection and plasma lactate, glucose, and insulin concentrations did not differ between treatments. Six days of nitrate supplementation reduced VO₂ during submaximal exercise and improved time-trial performance in trained cyclists.

Goal-directed outpatient rehabilitation following TBI: A pilot study of programme effectiveness and comparison of outcomes in home and day hospital settings

Primary objective: To determine (i) the effectiveness of a goal-directed, environment-focused occupational therapy intervention and (ii) to compare rehabilitation gains across a day hospital (outpatient) setting and home setting.Research design: Repeated measures cross-over design with pre–post test measures and a baseline control period, random allocation to a treatment setting sequence and an independent outcome assessor who was blinded to treatment sequence.Methods and procedures: Descriptive and non-parametric comparative analyses employed. Fourteen participants with severe traumatic brain injury completed a 12 week outpatient occupational therapy programme. The programme was directed by the participant's chosen goals, which were established using a client-centred, structured, goal-planning process. Outcome measures included Goal attainment scaling, the Canadian Occupational Performance Measure, the Sydney Psychosocial Reintegration Scale, the Mayo-Portland Adaptability Index, the Craig Hospital Inventory of Environmental Factors and self-rated satisfaction with therapy.Main outcomes and results: The therapy programme resulted in significant improvements in goal attainment, occupational performance, psychosocial reintegration and ability and adjustment levels, compared with baseline. Differences in gains made in home vs day hospital settings were not statistically significant, with the exception of higher levels of patient satisfaction with therapy at home.Conclusions: To assist further with decision-making about where to conduct therapy, further research is needed to compare the outcomes and determine the cost effectiveness of therapy at home and in day hospital settings.

Getting Off the “Gold Standard”: Randomized Controlled Trials and Education Research

While useful in some situations, randomization is not the “gold standard” for medical education research. More important is that decisions regarding methodology precede the intervention, that adequate numbers of subjects and iterations are used, that a comparison group is included, and that limitations are addressed in a thoughtful, thorough manner. In addition, the literature demonstrates quite definitively that medical learners will learn whatever we teach and also may supplement any teaching deficits to meet certification requirements.18 Thus, to increase our understanding of effective educational interventions, a new educational intervention should be compared to another effective intervention. Unlike clinical research, a placebo arm is rarely helpful. Comparing the new educational intervention to “usual” practices is productive as long as students are not “cued” to the novelty of the research arm—which may enhance (or negatively bias) their learning—and the usual practices are well described. Whether randomized or nonrandomized, medical education studies must carefully analyze sources of bias—unforeseen confounding variables—to explain the observed results and ensure that subsequent researchers will find these results reproducible. Rather than an obligatory listing of these potential sources of error in the discussion, researchers will enhance existing knowledge through a careful and detailed analysis of sources of bias that may have affected the results.3 Equally important, research designs must include a control group, concurrent if possible, to ensure equal likelihood of exposure to nonintervention events that could bias the results. If educators begin to work together, more collaborative, multi-institutional projects, perhaps akin to “pragmatic trials,”12 may be produced in the future. This is likely to add substantially to our understanding of effective resident education.

Effects of acute sprint interval cycling and energy replacement on postprandial lipemia

High postprandial blood triglyceride (TG) levels increase cardiovascular disease risk. Exercise interventions may be effective in reducing postprandial blood TG. The purpose of this study was to determine the effects of sprint interval cycling (SIC), with and without replacement of the energy deficit, on postprandial lipemia. In a repeated-measures crossover design, six men and six women participated in three trials, each taking place over 2 days. On the evening of the first day of each trial, the participants either did SIC without replacing the energy deficit (Ex-Def), did SIC and replaced the energy deficit (Ex-Bal), or did not exercise (control). SIC was performed on a cycle ergometer and involved four 30-s all-out sprints with 4-min active recovery. In the morning of day 2, responses to a high-fat meal were measured. Venous blood samples were collected in the fasted state and at 0, 30, 60, 120, and 180 min postprandial. There was a trend toward a reduction with treatment in fasting TG (P = 0.068), but no significant treatment effect for fasting insulin, glucose, nonesterified fatty acids, or betahydroxybutryrate (P > 0.05). The postprandial area under the curve (mmol·l(-1)·3 h(-1)) TG response was significantly lower in Ex-Def (21%, P = 0.006) and Ex-Bal (10%, P = 0.044) than in control, and significantly lower in Ex-Def (12%, P = 0.032) than in Ex-Bal. There was no treatment effect (P > 0.05) observed for area under the curve responses of insulin, glucose, nonesterified fatty acids, or betahydroxybutryrate. SIC reduces postprandial lipemia, but the energy deficit alone does not fully explain the decrease observed.

Simple verbal instruction improves knee biomechanics during landing in female athletes

Knee injuries are highly prevalent in athletic populations, particularly among female athletes. Many of these injuries occur during landing from a jump. Various comprehensive knee injury prevention programs have been developed to date. However, there is a need to determine which components of these programs contribute directly to changes in knee biomechanics. Therefore, the purpose of this study was to investigate the immediate effect of three different simple verbal instructions on knee biomechanics during landing in adult female recreational athletes. Three-dimensional kinematic and kinetic analysis of landing from a countermovement jump was conducted in a counterbalanced cross-over repeated measures design. Results indicated that the instruction to land with equal weight distribution reduced the asymmetry of peak vertical ground reaction force compared to the control condition. The instruction to land softly reduced peak vertical ground reaction force and increased peak knee flexion compared to the control condition. The instruction to land with knees over toes increased peak knee flexion compared to the control condition. These findings indicate that verbal instruction may be a key component of the effects seen in previous research studies that have investigated the benefits of more complex training programs designed to reduce knee injury risk in female athletes.

Persistent Effect of Acute Sprint Interval Cycling and Energy Replacement on Postprandial Lipemia

Increasing sedentary behavior and caloric intake are predisposing Americans to the metabolic syndrome. Aerobic and resistance exercise reduces postprandial blood triglycerides (TG). PURPOSE: To determine the influence of sprint interval cycling (SIC) on postprandial lipemia (PPL) and whether the replacement of the energy deficit created by SIC influences the reduction in PPL. METHODS: In a repeated-measures cross-over design, 12 healthy subjects, 6 men and 6 women, participated in 3 trials, each taking place over 2 days. On the evening of the first day of each trial, the subjects either did SIC without replacing the energy deficit (Ex-Def), did SIC and replaced the energy deficit (Ex-Bal), or did not exercise (Con). SIC was performed on a mechanically braked cycle ergometer and involved four 30-s all-out sprints with 4 min active recovery. In the morning of the second day, subjects ate a high-fat meal composed of 1.2 g fat, 0.9 g carbohydrate, and 0.4 g protein per kg body weight. Venous blood samples were collected in the fasted state and then at 0, 30, 60, 120, and 180 minutes postprandial. RESULTS: There was no significant difference in fasting TG concentrations (Ex-Def: 0.78 ± 0.60 mmol·l-1, Ex-Bal: 0.85 ± 0.54 mmol·l-1, Con: 0.98 ± 0.69 mmol·l-1). The postprandial area under the curve (AUC) (mmol·l-1·3 h-1) TG response was significantly lower in Ex-Def (21% and 12%) compared to Ex-Bal and Con (Ex-Def: 3.31 ± 1.83, Ex-Bal: 3.78 ± 1.83, Con: 4.20 ± 2.09). TG AUC was significantly lower in Ex-Bal (10%) compared to Con. Incremental TG AUC response did not differ among the treatments (Ex-Def: 1.00 ± 0.66, Ex-Bal: 1.26 ± 0.87, Con: 1.28 ± 0.51), suggesting the reduction in TG AUC was associated with lower fasting TG concentrations. CONCLUSION: Sprint interval cycling reduces postprandial lipemia, in part, because of the energy deficit created.

Chewing gum moderates multi-task induced shifts in stress, mood, and alertness. A re-examination

The finding that chewing gum can moderate stress and mood changes following a multi-task cognitive stressor ( Scholey et al., 2009) was re-examined. In a repeated measures cross-over design, thirty participants completed a 20-min multi-tasking stressor on consecutive days, both with and without chewing gum. Both prior to and post stressor, participants provided salivary cortisol samples and self-rated measures of stress, state anxiety, calmness, contentedness, and alertness. Contrary to Scholey et al. (2009), chewing gum failed to attenuate both salivary cortisol levels and the increase in self-rated stress. Self-rated anxiety, calmness, and contentedness were not impacted by chewing gum. This suggests that the stress effects reported by Scholey et al. may be constrained by particular features of that study (e.g. morning testing). However, consistent with Scholey et al. (2009), chewing gum was shown to increase alertness following the stressor. The mechanisms underpinning heightened alertness are unclear; however, such increases may be linked to greater cerebral activity following the chewing of gum ( Fang Li, Lu, Gong, & Yew, 2005).