Evidence for data missing at random in youth physical activity monitoring research

This study examined whether or not activity monitor data collected as part of a typical 7-day physical activity (PA) measurement protocol can be expected to be missing at random. A total of 315 participants (9–18 years) each wore a SenseWear Armband monitor for 7 consecutive days. Participants were classified as “compliant” (86 boys and 124 girls) if they had recorded accelerometer data during 70% or more of the predefined awake time (7 AM–10 PM) on four different days; and “non-compliant” (44 boys and 51 girls) when not meeting these criteria. Linear mixed models were used to examine differences in energy expenditure (EE) levels by compliance across 10 different time periods. The results indicated that non-compliant girls were older (13.4 ± 2.9 vs. 12.2 ± 2.5) and taller (156.8 ± 10.3 vs. 152.8 ± 11.3) than their same gender compliant peers (P < .05). Comparisons of EE rates at segmented portions of the day revealed no differences between compliant and non-compliant groups (P ≥ .05). Differences in EE ranged from ?0.32 kcal · kg^?1 · h^?1 (before school time) to 0.62 kcal · kg^?1 · h^?1 (physical education class) in boys and ?0.39 kcal · kg^?1 · h^?1 (transportation from school) to 0.37 kcal · kg^?1 · hour^?1 (recess) in girls. The results showed that compliant and non-compliant individuals differed in a few demographic characteristics but exhibited similar activity patterns. This suggests that data were considered to be missing at random, but additional work is needed to confirm this observation in a representative sample of children using other types of activity monitors and protocols.     

Inter-participant variability in daily physical activity and sedentary time among male youth sport footballers: independent associations with indicators of adiposity and cardiorespiratory fitness

Participation in youth sport is assumed to promote and contribute towards more physically active lifestyles among children and adolescents. The aim of this study was to examine inter-participant variability in objectively measured habitual physical activity (PA) behaviours and sedentary time among youth sport participants and their implications for health. One-hundred-and-eighteen male youth sport footballers (Mean ± s = 11.72 ± 1.60) wore a GT3X accelerometer for 7 days. Average daily PA [min · day^?1, in light (LPA), moderate (MPA), vigorous (VPA) and combined moderate-to-vigorous (MVPA)] and sedentary time were calculated. Participants’ body mass index adjusted for age and sex (BMI–standard deviation score), per cent body fat (BF%), waist circumference and cardiorespiratory fitness were assessed. Results revealed that variability in daily PA behaviours and sedentary time (min · day^?1) was associated with BMI–standard deviation score [VPA (?), MVPA (?)], BF% [sedentary time (+), VPA (?), MVPA (?)], waist circumference [sedentary time (+), LPA (?)] and cardiorespiratory fitness [sedentary time (?), MPA (+), VPA (+), MVPA (+)]. Whilst sedentary time and MVPA were not related to health outcomes independent of one another, associations with markers of adiposity and cardiorespiratory fitness were stronger for sedentary time. Sedentary time was also significantly positively related to waist circumference independent of VPA. Results demonstrate inter-participant variability in habitual PA and sedentary time among youth sport participants which holds implications for their health. Thus, promoting PA and, in particular, reducing sedentary time may contribute towards the prevention of adverse health consequences associated with a physically inactive lifestyle for children and adolescents active in the youth sport context.     

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.     

Achievement in mathematics and language is linked to regular physical activity: a population study in Chilean youth

Abstract

We examined the association between the allocation of time to regular physical activity (PA) and achievement in mathematics and language in Chilean adolescents after controlling for confounders. In a random sample of 620 ninth graders (15.6 ± 0.7 years old), we measured regular PA, including physical education and sports extracurricular activities, and academic performance, using national standardised tests. Bivariate and multivariate regression analyses modelled the relation between academic and health-related behaviours. Sufficiency and proficiency in mathematics and language were used as outcome variables. Only 18% of adolescents had >4 h·week^–1 of regular PA. Devoting >4 h?·?week^–1 to regular PA significantly increased the odds of sufficiency and proficiency in both domains. After full adjustment, the odds of sufficiency and proficiency in mathematics increased by 1.9 (95% CI: 1.1–3.5) and 2.7 (95% CI: 1.7–4.3), respectively. Similarly, the odds of sufficiency and proficiency in language increased by 3.3 (95% CI: 1.7–9.7) and 2.6 (95% CI: 1.6–4.1), respectively. Adolescents with the highest allocation of time to regular PA performed much better in mathematics and language than inactive students. The academic benefits associated with PA can help to promote sustained behaviour changes regarding lifestyles. They can be more easily perceived as gains than health benefits alone.     

Chronic ingestion of a low dose of caffeine induces tolerance to the performance benefits of caffeine

This study examined effects of 4 weeks of caffeine supplementation on endurance performance. Eighteen low-habitual caffeine consumers (<75 mg · day^?1) were randomly assigned to ingest caffeine (1.5–3.0 mg · kg^?1day^?1; titrated) or placebo for 28 days. Groups were matched for age, body mass, V?O_2peak and W_max (P > 0.05). Before supplementation, all participants completed one V?O_2peak test, one practice trial and 2 experimental trials (acute 3 mg · kg^?1 caffeine [precaf] and placebo [testpla]). During the supplementation period a second V?O_2peak test was completed on day 21 before a final, acute 3 mg · kg^?1 caffeine trial (postcaf) on day 29. Trials consisted of 60 min cycle exercise at 60% V?O_2peak followed by a 30 min performance task. All participants produced more external work during the precaf trial than testpla, with increases in the caffeine (383.3 ± 75 kJ vs. 344.9 ± 80.3 kJ; Cohen’s d effect size [ES] = 0.49; P = 0.001) and placebo (354.5 ± 55.2 kJ vs. 333.1 ± 56.4 kJ; ES = 0.38; P = 0.004) supplementation group, respectively. This performance benefit was no longer apparent after 4 weeks of caffeine supplementation (precaf: 383.3 ± 75.0 kJ vs. postcaf: 358.0 ± 89.8 kJ; ES = 0.31; P = 0.025), but was retained in the placebo group (precaf: 354.5 ± 55.2 kJ vs. postcaf: 351.8 ± 49.4 kJ; ES = 0.05; P > 0.05). Circulating caffeine, hormonal concentrations and substrate oxidation did not differ between groups (all P > 0.05). Chronic ingestion of a low dose of caffeine develops tolerance in low-caffeine consumers. Therefore, individuals with low-habitual intakes should refrain from chronic caffeine supplementation to maximise performance benefits from acute caffeine ingestion.     

Urinary creatine and methylamine excretion following 4 × 5 g · day−1 or 20 × 1 g · day−1 of creatine monohydrate for 5 days

Abstract

In this study, we examined the effect of two creatine monohydrate supplementation regimes on 24-h urinary creatine and methylamine excretion. Nine male participants completed two trials, separated by 6 weeks. Participants ingested 4 × 5 g · day^?1 creatine monohydrate for 5 days in one trial and 20 × 1 g · day^?1 for 5 days in the other. We collected 24-h urine samples on 2 baseline days (days 1–2), during 5 days of supplementation (days 3–7), and for 2 days post-supplementation (days 8–9). Urine was assayed for creatine using high-performance liquid chromatography and methylamine using gas chromatography. Less creatine was excreted following the 20 × 1 g · day^?1 regime (49.25 ± 10.53 g) than the 4 × 5 g · day^?1 regime (62.32 ± 9.36 g) (mean ± s; P < 0.05). Mean total excretion of methylamine (n = 6) over days 3–7 was 8.61 ± 7.58 mg and 24.81 ± 25.76 mg on the 20 × 1 g · day^?1 and 4 × 5 g · day^?1 regimes, respectively (P < 0.05). The lower excretion of creatine using 20 × 1 g · day^?1 doses suggests a greater retention in the body and most probably in the muscle. Lower and more frequent doses of creatine monohydrate appear to further attenuate formation of methylamine.     

Movement pattern and physiological response in recreational small-sided football – effect of number of players with a fixed pitch size

Recreational soccer is an effective health-promoting activity, but it is unclear how different game formats influence internal and external load. Thus, to be able to advise how to maximise the outcome of recreational football, we examined movement pattern and physiological response in 11 untrained men (32.6 ± 6.7 yrs, 23.3 ± 4.9 fat%, 43.4 ± 5.3 ml·min^?1·kg^?1) during three football sessions comprising 4 × 12 min of 3v3, 5v5 or 7v7 with a constant pitch size of 20 × 40 m. Movement pattern, heart rate (HR), blood lactate and RPE were measured during and after the 12-min periods. Greater (P < 0.05) total distance and high-speed distance was covered during 3v3 than 5v5 (14 and 30%) and 7v7 (15 and 75%). Mean HR was higher in 3v3 (85.7 ± 5.7%HRmax) and 5v5 (84.2 ± 5.1%HRmax) than in 7v7 (80.7 ± 4.6%HRmax, P < 0.05) and percentage time >90%HR was higher in 3v3 (43 ± 18%, P < 0.05) than in 5v5 (28 ± 21%) and 7v7 (18 ± 14%). Blood lactate was higher in 3v3 (7.4 ± 2.7 mmol·l^?1) than in 7v7 (4.5 ± 2.2 mmol·l^?1, P < 0.001) but not in 5v5 (6.1 ± 2.1 mmol·l^?1, P = 0.061). RPE was higher in 3v3 (6.7 ± 2.3, P < 0.01) than in 5v5 (5.2 ± 2.2) and 7v7 (4.3 ± 2.3). In conclusion, higher external and internal load was found with fewer players, when the pitch size is fixed.     

Effect of the Great Activity Programme on healthy lifestyle behaviours in 7–11 year olds

Abstract

The study investigated the effect of a school-based healthy lifestyles intervention on physical activity and dietary variables. In total 378 children (177 intervention, 201 control; age 9.75 ± 0.82 years (mean ± s)) took part in the 7-month intervention comprising: preparation for and participation in 3 highlight events (a dance festival, a walking event and a running event); an interactive website for pupils, teachers and parents; and vacation activity planners. Primary outcome measures were objectively measured physical activity (pedometers and accelerometers), endurance fitness and dietary variables. Multi-level modelling was employed for data analysis. The increase in physical activity was greater in the intervention group than the control group (steps: 1049 vs 632 daily steps each month; moderate to vigorous physical activity (MVPA) total: 4.6 min · day^?1 · month^?1 vs 1.3 min · day^?1 · month^?1; MVPA bouts: 5.4 min · day^?1 · month^?1 vs 2.6 min · day^?1 · month^?1; all P < 0.05). The increase in multi-stage fitness test distance was greater for intervention participants (46 vs 29 m · month^?1 of intervention, group × month interaction, P < 0.05). There were no differences between groups in dietary variables, body composition, knowledge of healthy lifestyles or psychological variables. Thus an intervention centred around highlight events and including relatively few additional resources can impact positively on the objectively measured physical activity of children.     

Low energy availability in exercising men is associated with reduced leptin and insulin but not with changes in other metabolic hormones

Low energy availability, defined as low caloric intake relative to exercise energy expenditure, has been linked to endocrine alterations frequently observed in chronically energy-deficient exercising women. Our goal was to determine the endocrine effects of low energy availability in exercising men. Six exercising men (VO_2peak: 49.3 ± 2.4 ml · kg^?1 · min^?1) underwent two conditions of low energy availability (15 kcal · kg^?1 fat-free mass [FFM] · day^?1) and two energy-balanced conditions (40 kcal · kg^?1 FFM · day^?1) in randomised order. During one low energy availability and one balanced condition, participants exercised to expend 15 kcal · kg^?1 FFM · day^?1; no exercise was conducted during the other two conditions. Metabolic hormones were assessed before and after each 4-day period. Following both low energy availability conditions, leptin (?53% to ?56%) and insulin (?34% to ?38%) were reduced (P < 0.05). Reductions in leptin and insulin were independent of whether low energy availability was attained with or without exercise (P > 0.80). Low energy availability did not significantly impact ghrelin, triiodothyronine, testosterone and IGF-1 (all P > 0.05). The observed reductions in leptin and insulin were in the same magnitude as changes previously reported in sedentary women. Further research is needed to understand why other metabolic hormones are more robust against low energy availability in exercising men than those in sedentary and exercising women.     

Metabolic power and energy expenditure in an international men’s hockey tournament

The purpose of this study was to ascertain the typical metabolic power characteristics of elite men’s hockey, and whether changes occur within matches and throughout an international tournament. National team players (n = 16), divided into 3 positional groups (strikers, midfielders, defenders), wore Global Positioning System devices in 6 matches. Energetic (metabolic power, energy expenditure) and displacement (distance, speed, acceleration) variables were determined, and intensity was classified utilising speed, acceleration and metabolic power thresholds. Midfielder’s average metabolic power (11.8 ± 1.0 W · kg^?1) was similar to strikers (11.1 ± 1.3 W · kg^?1) and higher than defenders (10.8 ± 1.2 W · kg^?1, P = 0.001). Strikers (29.71 ± 3.39 kJ · kg^?1) expended less energy than midfielders (32.18 ± 2.67 kJ · kg^?1, P = 0.014) and defenders (33.23 ± 3.96 kJ · kg^?1, P < 0.001). Energetic variables did not change between halves or across matches. Across all positions, over 45% of energy expenditure was at high intensity (>20 W · kg^?1). International hockey matches are intense and highly intermittent; however, intensity is maintained throughout matches and over a tournament. In isolation, displacement measures underestimate the amount of high-intensity activity, whereas the integration of instantaneous speed and acceleration provides a more comprehensive assessment of the demands for variable-speed activity typically occurring in hockey matches.     

Parallel assessment of nutrition and activity in athletes: Validation against doubly labelled water, 24-h urea excretion,and indirect calorimetry

Abstract

The assessment of nutrition and activity in athletes requires accurate and precise methods. The aim of this study was to validate a protocol for parallel assessment of diet and exercise against doubly labelled water, 24-h urea excretion, and respiratory gas exchange. The participants were 14 male triathletes under normal training conditions. Energy intake and doubly labelled water were weakly associated with each other (r = 0.69, standard error of estimate [SEE] = 304 kcal · day^?1). Protein intake was strongly correlated with 24-h urea (r = 0.89) but showed considerable individual variation (SEE = 0.34 g · kg^?1 · day^?1). Total energy expenditure based on recorded activities was highly correlated with doubly labelled water (r = 0.95, SEE = 195 kcal · day^?1) but was proportionally biased. During running and cycling, estimated exercise energy expenditure was highly correlated with gas exchange (running: r = 0.89, SEE = 1.6 kcal · min^?1; cycling: r = 0.95, SEE = 1.4 kcal · min^?1). High exercise energy expenditure was slightly underestimated during running. For nutrition data, variations appear too large for precise measurements in individual athletes, which is a common problem of dietary assessment methods. Despite the high correlations of total energy expenditure and exercise energy expenditure with reference methods, a correction for systematic errors is necessary for the valid estimation of energetic requirements in individual athletes.     

Physiological responses and performance in a simulated trampoline gymnastics competition in elite male gymnasts

Abstract

Physiological responses and performance were examined during and after a simulated trampoline competition (STC). Fifteen elite trampoline gymnasts participated, of which eight completed two routines (EX1 and EX2) and a competition final (EX3). Trampoline-specific activities were quantified by video-analysis. Countermovement jump (CMJ) and 20 maximal trampoline jump (20-MTJ) performances were assessed. Heart rate (HR) and quadriceps muscle temperature (T_m) were recorded and venous blood was drawn. A total of 252 ± 16 jumps were performed during the STC. CMJ performance declined (P < 0.05) by 3.8, 5.2 and 4.2% after EX1, EX2 and EX3, respectively, and was 4.8% lower (P < 0.05) than baseline 24 h post-competition. 20-MTJ flight time was ~1% shorter (P < 0.05) for jump 1–10 after EX2 and 24 h post STC. T_m increased (P < 0.05) to ~39°C after the warm-up, but declined (P < 0.05) 1.0 and 0.6ºC before EX2 and EX3, respectively. Peak HR was 95–97% HR_max during EX1-3. Peak blood lactate, plasma K⁺ and NH₃ were 6.5 ± 0.5, 6.0 ± 0.2 mmol · l^?1 and 92 ± 10 µmol · l^?1, respectively. Plasma CK increased (P < 0.05) by ~50 and 65% 0 and 24 h after STC. In conclusion, a trampoline gymnastic competition includes a high number of repeated explosive and energy demanding jumps, which impairs jump performance during and 24 h post-competition.     

Metabolic cost of running is greater on a treadmill with a stiffer running platform

Exercise testing on motorised treadmills provides valuable information about running performance and metabolism; however, the impact of treadmill type on these tests has not been investigated. This study compared the energy demand of running on two laboratory treadmills: an HP Cosmos (C) and a Quinton (Q) model, with the latter having a 4.5 times stiffer running platform. Twelve experienced runners ran identical bouts on these treadmills at a range of four submaximal velocities (reported data is for the velocity that approximated 75–81% VO_2max). The stiffer treadmill elicited higher oxygen consumption (C: 46.7 ± 3.8; Q: 50.1 ± 4.3 ml·kg^?1 · min^?1), energy expenditure (C: 16.0 ± 2.5; Q: 17.7 ± 2.9 kcal · min^?1), carbohydrate oxidation (C: 9.6 ± 3.1; Q: 13.0 ± 3.9 kcal · min^?1), heart rate (C: 155 ± 16; Q: 163 ± 16 beats · min^?1) and rating of perceived exertion (C: 13.8 ± 1.2; Q: 14.7 ± 1.2), but lower fat oxidation (C: 6.4 ± 2.3; Q: 4.6 ± 2.5 kcal · min^?1) (all analysis of variance treadmill comparisons P < 0.01). This study confirms that caution is required when comparing performance and metabolic results between different treadmills and suggests that treadmills will vary in their comparability to over-ground running depending on the running platform stiffness.     

Prospective bi-directional associations between sedentary time and physical activity with cognitive performance: a cohort study

This prospective study determined whether: (1) objective physical activity (PA) and sedentary (SED) time at 9 years was associated with cognition at 15 years, (2) cognition at 9 years was associated with PA and SED at 15 years, and (3) the change in PA and SED from 9 to 15 years was associated with the change in cognition. Cognitive performance was assessed from picture vocabulary, verbal analogy, passage comprehension, and applied problem tasks. Regression models were used to explore each aim while adjusting for covariates. Among the combined sample, SED (min· day^?1) at 9 years was unrelated with cognitive performance at 15 years, whereas participating in ≥ 60 min· day^?1 of moderate-to-vigorous PA (MVPA) at 9 years predicted lower cognitive scores at 15 years. In the reverse direction, cognitive performance at 9 years was unrelated with SED and MVPA (min· day^?1) at 15 years. Over 6 years, increased SED (min· day^?1) predicted lower improvement to verbal analogy scores (B = ?0.01, p = 0.028). In comparison, an increase (or relatively smaller decline) in MVPA (min· day^?1) predicted greater improvement in applied problem scores (B = 0.06, p = 0.007). Contextual information regarding SED and MVPA behavior would help understand bi-directional associations of activity and cognition.     

Quantification of spinning® bike performance during a standard 50-minute class

Abstract

Spinning is a type of indoor fitness activity performed on stationary bikes by participants who pedal together to the rhythm of music and the motivating words of an instructor. Despite worldwide popularity of this type of recreational activity, to date there have been few, mainly non-scientific, studies of the impact of spinning on metabolic, respiratory, and cardiovascular functions. The main aim of this study was to evaluate a number of metabolic and cardiovascular variables during a standard 50-min class performed by Spinning® instructors of both sexes: six males (age 30 ± 4.8 years, body mass index 24 ± 2.5 kg · m^?2; mean ± s) and six females (age 34 ± 6.3 years, body mass index 21 ± 1.9 kg · m^?2). The mean power output, heart rate, and oxygen uptake during the performance were 120 ± 4 W, 136 ± 13 beats · min^?1, and 32.8 ± 5.4 ml · kg^?1 · min^?1 respectively for males, and 73 ± 43 W, 143 ± 25 beats · min^?1, and 30 ± 9.9 ml · kg^?1 · min^?1 respectively for females. Analysis of individual performances showed that they were compatible with physical exercise that ranged from moderate-to-heavy to very heavy, the latter conditions prevailing. The results show that this type of fitness activity has a high impact on cardiovascular function and suggest that it is not suitable for unfit or sedentary individuals, especially the middle aged or elderly, who are willing to begin a recreational physical activity programme.     

Physiological load associated with a Zumba® fitness workout: a comparison pilot study between classes and a DVD

The objectives were to compare the metabolic load elicited by Zumba^® classes and DVD workouts and link the physiological responses to participants’ psychological characteristics. Fifteen women (25.4 ± 4.3 years old; 164.9 ± 5.1 cm; 56.9 ± 5.8 kg; 23.9 ± 4.9% body fat) performed three Zumba^® classes and three Zumba^® DVD workouts using a repeated measure design. Energy expenditure was assessed by extrapolating oxygen cost from heart rate (HR) using regressions from a preliminary incremental running test. Differences between Zumba^® classes and Zumba^® DVD workouts were assessed by Student’s T tests and repeated measures analysis of variance and correlations between physiological and psychological variables by the Pearson’s coefficient. Results showed that Zumba^® classes allowed greater energy expenditure compared to Zumba^® DVD workouts (6.8 ± 0.9 vs 5.6 ± 0.9 kcal · min^?1, 95% confidence interval (CI) limits: 0.3–2.1, P = 0.016), with significant differences in the time spent with a HR above 85% of HR reserve (14.7 vs 1.7%, 95% CI: 5.6–20.4, P = 0.021). Furthermore, women with a greater autonomy score showed a smaller difference between DVD and class (r = 0.511, P = 0.048), while greater differences were shown in women with greater interpersonal skills (r = ?0.563, P = 0.028). The results suggest that while both types of workouts are suitable to maintain fitness Zumba^® classes allow greater energy expenditure.     

Effects of aerobic training on serum omentin-1 and cardiometabolic risk factors in overweight and obese men

Abstract

Omentin-1 is a newly discovered protein expressed and secreted from visceral adipose tissue that increases insulin sensitivity. We examined the effects of 12 weeks of aerobic training on serum omentin-1 concentrations together with cardiovascular risk factors in overweight and obese men. Eighteen overweight and obese participants (age 43.1 ± 4.7 years, BMI ≥25 kg · m^?2) were assigned to exercise training (n = 9) and control (n = 9) groups. A matched control group of normal weight participants (n = 8; age 42.2 ± 3.8 years, BMI <25 kg · m^?2) were also recruited for baseline comparison. The obese exercise group participated in 12 weeks of progressive aerobic training 5 days a week. Measures of serum omentin-1, insulin resistance, lipid profiles, blood pressure, and body composition were obtained before and after the 12 weeks. At baseline, normal weight participants had significantly higher serum omentin-1 concentrations than overweight and obese participants, and there were inverse correlations between omentin-1 and each of waist circumference, fasting glucose, insulin resistance, total cholesterol, triglyceride, and systolic blood pressure (P < 0.05). After the aerobic training, waist circumference, percent body fat, fasting glucose, insulin resistance, triglyceride, total cholesterol, low-density lipoprotein cholesterol, and systolic blood pressure were all significantly decreased (P < 0.05). In contrast, serum omentin-1 concentration was significantly increased after the aerobic programme (P < 0.05), and correlated with changes in insulin resistance (r = ?0.67, P = 0.04), glucose (r = ?0.65, P = 0.05), waist circumference (r = ?0.70, P = 0.03), and aerobic fitness r = ?0.68, P = 0.04). Aerobic training resulted in an improvement in cardiometabolic risk factors in obese participants, and this improvement was accompanied by increased omentin-1 concentrations.     

Biomechanical analysis of dragon boat paddling: A comparison of elite and sub-elite paddlers

Abstract

In this study, video and force analysis techniques were used to distinguish between dragon boat paddlers of different ability. Six elite paddlers (three males, three females) and six sub-elite paddlers (two males, four females) were compared during high-intensity paddling (80–90 strokes · min^?1). Video filming was conducted for two-dimensional kinematic analysis and an instrumented paddle was used to collect force data. Paddling efficiency, paddle force characteristics, and paddler kinematic variables were measured. Elite paddlers achieved higher paddling efficiency than sub-elite paddlers (elite: 76 ± 4%; sub-elite: 67 ± 10%; P = 0.080). Elite paddlers also showed higher peak force (elite: 16.3 ± 4.8 N · kg^?2/3; sub-elite: 11.4 ± 2.6 N · kg^?2/3; P = 0.052), average force (elite: 7.9 ± 2.8 N · kg^?2/3; sub-elite: 5.5 ± 1.4 N · kg^?2/3; P = 0.084), and impulse (elite: 3.0 ± 0.9 (N · s) · kg^?2/3; sub-elite: 1.9 ± 0.4 (N · s) · kg^?2/3; P = 0.026) than sub-elite paddlers, but these three results should be viewed with caution due to the small sample size and the unequal number of males and females in the two groups. Superior technique and greater strength enable the elite paddlers to achieve higher paddling efficiency. Paddlers use different joint movement patterns to develop propulsion, which are reflected in variations in the force–time curve.     

Dribbling determinants in sub-elite youth soccer players

Dribbling speed in soccer is considered critical to the outcome of the game and can assist in the talent identification process. However, little is known about the biomechanics of this skill. By means of a motion capture system, we aimed to quantitatively investigate the determinants of effective dribbling skill in a group of 10 Under-13 sub-elite players, divided by the median-split technique according to their dribbling test time (faster and slower groups). Foot-ball contacts cadence, centre of mass (CoM), ranges of motion (RoM), velocity and acceleration, as well as stride length, cadence and variability were computed. Hip and knee joint RoMs were also considered. Faster players, as compared to slower players, showed a 30% higher foot-ball cadence (3.0 ± 0.1 vs. 2.3 ± 0.2 contacts · s^?1, P < 0.01); reduced CoM mediolateral (0.91 ± 0.05 vs. 1.14 ± 0.16 m, P < 0.05) and vertical (0.19 ± 0.01 vs. 0.25 ± 0.03 m, P < 0.05) RoMs; higher right stride cadence (+20%, P < 0.05) with lower variability (P < 0.05); reduced hip and knee flexion RoMs (P < 0.05). In conclusion, faster players are able to run with the ball through a shorter path in a more economical way. To effectively develop dribbling skill, coaches are encouraged to design specific practices where high stride frequency and narrow run trajectories are required.