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1.
Abstract

The aim of this study was to compare selected physiological variables and performance markers of soldiers from two “elite” units of the British Army. Ten soldiers from each of the two units were recruited for this study (n = 20). All participants completed three tests while carrying a 20 kg backpack load: (1) a maximal treadmill test using the Bruce protocol; (2) a 2 mile backpack run test specific to Unit A on a consistently flat tarmac road; and (3) a 29 km time-trial over hilly terrain typical of a mountainous area used by Unit B for performance assessment. Heart rate, maximal blood lactate concentration and performance (run time) were assessed during all three tests, with peak oxygen uptake also being measured during the maximal treadmill test. Measurements of anthropometry, isokinetic strength and mental toughness (MT48) were also recorded. There were no significant differences in terms of performance markers between the units (P > 0.05). Performance on the maximal treadmill test correlated with performance on the 2 mile backpack run test (r = ?0.57) and 29 km time-trial (r = ?0.66). Performance on the 2 mile backpack run test in turn correlated with 29 km time-trial performance (r = ?0.77), accounting for 59% of the variance. In conclusion, the maximal treadmill test and the 2 mile backpack run test are useful indicators of performance on the arduous hill march and could be employed in the screening and selection of potential recruits.  相似文献   

2.
Abstract

We examined the effects of instructional and motivational self-talk on centre of mass displacement and hip kinematics during the vertical jump. Twenty-four male rugby union players (age 21.1 years, s = 3.5; body mass 81.0 kg, s = 8.9; height 1.80 m, s = 0.06) performed three vertical jump tests, with a 2 min rest between jumps. Before each jump, participants engaged in one of three counterbalanced interventions (motivational self-talk, instructional self-talk or no-intervention). Motivational self-talk led to greater centre of mass displacement (0.602 m, s = 0.076; P = 0.012) than the no-intervention control (0.583 m, s = 0.085). Centre of mass displacement did not differ between instructional self-talk and the control condition or between motivational and instructional self-talk. Motivational (100.75°, s = 16.05; P = 0.001) and instructional self-talk (106.14°, s = 17.04; P = 0.001) led to greater hip displacement than the no-intervention control (94.11°, s = 17.14). There was also a significant difference in hip displacement between motivational and instructional self-talk (P = 0.014), although there was no difference between instructional self-talk and the control condition. Motivational (451.69 °/s, s = 74.34; P = 0.008) and instructional self-talk (462.01 °/s, s = 74.37; P = 0.001) led to greater hip rotation velocity than the no-intervention control (434.37 °/s, s = 75.37), although there was no difference between the two self-talk interventions. These results indicate that self-talk may influence performance and technique during the vertical jump in male rugby players.  相似文献   

3.
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.  相似文献   

4.
Abstract

Following fixed-duration exercise of submaximal intensity, caffeine ingestion is associated with an attenuation of the exercise-induced decline in N-formyl-methionyl-phenyl-alanine (f-MLP) stimulated neutrophil oxidative burst. However, the response following high-intensity exhaustive exercise is unknown. Nine endurance-trained male cyclists ingested 6 mg caffeine or placebo per kilogram of body mass 60 min before cycling for 90 min at 70% of maximal oxygen consumption ([Vdot]O2max) and then performing a time-trial requiring an energy expenditure equivalent to 30 min cycling at 70% maximum power output. Time-trial performance was 4% faster in the caffeine than in the placebo trial (P = 0.043). Caffeine was associated with an increased plasma adrenaline concentration after 90 min of exercise (P = 0.046) and immediately after the time-trial (P = 0.02). Caffeine was also associated with an increased serum caffeine concentration (P < 0.01) after 90 min of exercise and immediately after the time-trial, as well as 1 h after the time-trial. However, the f-MLP-stimulated neutrophil oxidative burst response fell after exercise in both trials (P = 0.002). There was no effect of caffeine on circulating leukocyte or neutrophil counts, but the lymphocyte count was significantly lower on caffeine (20%) after the time-trial (P = 0.003). Our results suggest that high-intensity exhaustive exercise negates the attenuation of the exercise-induced decrease in neutrophil oxidative burst responses previously observed when caffeine is ingested before exercise of fixed duration and intensity. This may be associated with the greater increase in adrenaline concentration observed in the present study.  相似文献   

5.
Abstract

The aim of the present study was to determine the effect of a carbohydrate mouthwash on running time-trial performance. On two separate occasions, seven recreationally active males ([Vdot]O2max 57.8 ml · kg?1 · min?1, s = 3.7) completed a preloaded (15 min at 65%[Vdot]O2max) time-trial of 45 min in duration on a motorized treadmill. At 6-min intervals during the preload and time-trial, participants were given either a 6% maltodextrin, 3% lemon juice solution (carbohydrate trial) or a 3% lemon juice placebo mouthwash (placebo trial) in a double-blind, randomized crossover design. Heart rate, oxygen consumption ([Vdot]O2), respiratory exchange ratio (RER), and ratings of perceived exertion (RPE) were measured during the preload, and blood glucose and lactate were measured before and after the preload and time-trial. There were no significant differences in distance covered between trials (carbohydrate: 9333 m, s = 988; placebo: 9309 m, s = 993). Furthermore, there were no significant between-trial differences in heart rate and running speed during the time-trial, or [Vdot]O2, RER or RPE during the preload. Blood lactate and glucose increased as a result of the exercise protocol, with no between-trial differences. In conclusion, there was no positive effect of a carbohydrate mouthwash on running performance of ～1 h duration.  相似文献   

6.
This study adopted a multidimensional approach to performance prediction within Olympic distance cross-country mountain biking (XCO-MTB). Twelve competitive XCO-MTB cyclists (VO2max 60.8 ± 6.7 ml · kg?1 · min?1) completed an incremental cycling test, maximal hand grip strength test, cycling power profile (maximal efforts lasting 6–600 s), decision-making test and an individual XCO-MTB time-trial (34.25 km). A hierarchical approach using multiple linear regression analyses was used to develop predictive models of performance across 10 circuit subsections and the total time-trial. The strongest model to predict overall time-trial performance achieved prediction accuracy of 127.1 s across 6246.8 ± 452.0 s (adjusted R2 = 0.92; P < 0.01). This model included VO2max relative to total cycling mass, maximal mean power across 5 and 30 s, peak left hand grip strength, and response time for correct decisions in the decision-making task. A range of factors contributed to the models for each individual subsection of the circuit with varying predictive strength (adjusted R2: 0.62–0.97; P < 0.05). The high prediction accuracy for the total time-trial supports that a multidimensional approach should be taken to develop XCO-MTB performance. Additionally, individual models for circuit subsections may help guide training practices relative to the specific trail characteristics of various XCO-MTB circuits.  相似文献   

7.
Abstract

In this study, we examined the effects of a pre-acclimatization programme on endurance performance at moderate altitude using a resting intermittent hypoxia protocol. The time-trial performance of 11 cyclists was determined at low altitude (600 m). Athletes were randomly assigned in a double-blind fashion to the hypoxia or the control group. The pre-acclimatization programme consisted of seven sessions each lasting 1 h in normobaric hypoxia (inspired fraction of oxygen of 12.5%, equivalent to approximately 4500 m) for the hypoxia group (n = 6) and in normoxia (inspired fraction of oxygen of 20.9%) for the control group (n = 5). The time-trials were repeated at moderate altitude (1970 m). Mean power output during the time-trial at moderate altitude was decreased in the hypoxia group (?0.26 ± 0.11 W · kg?1) and in the control group (?0.13 ± 0.04 W · kg?1) compared with at low altitude but did not differ between groups (P = 0.13). Our results suggest that the applied protocol of intermittent hypoxia had no positive effect on endurance performance at moderate altitude. Whether different intermittent hypoxia protocols are advantageous remains to be determined.  相似文献   

8.
ABSTRACT

Purpose: This study aimed (1) to compare physical activity (PA) indicators, metabolic biomarkers, and comorbidity, (2) to investigate the relationship between PA indicators and metabolic biomarkers, comorbidity and (3) to identify barriers to PA in patients with type 2 diabetes (T2DM) who are using oral hypoglycaemic agent (OHA) or combined OHA and insulin (OHAiN). Methods: Sixty-one patients were classified as patients using only OHA or combined OHAiN. Metabolic biomarkers (waist-to-hip ratio, body mass index (BMI), lipid profile, glycosylated haemoglobin (HbA1c), fasting blood glucose, comorbidity and PA indicators (self-reported PA, number of steps (NOS), 6-minute walking distance (6MWD)) were assessed. PA perceptions and reasons for inactivity were questioned. Results: The comorbidity (p = .013), low-density lipoprotein-cholesterol (p = .026), total cholesterol (p = .008) and HbA1c (p = .020) were higher and PA level was lower (p = .007) in the OHAiN group. NOS was positively correlated with high-density lipoprotein-cholesterol (p = .037) and negatively correlated with BMI (p = .007). 6MWD was negatively correlated with BMI (p = .014) and comorbidity (p = .004) in the OHA group. BMI was a significant predictor of NOS (adjusted R2 = 0.242) and comorbidity for 6MWD (adjusted R2 = 0.250) in the OHA group. The majority of the patients (OHA = 34.3%, OHAiN = 42.3%) reported “lack of time” as the most common barrier to PA. Conclusions: This study showed that patients on OHAiN have lower PA levels, poorer metabolic profiles, and higher comorbidity rates than OHA users. PA indicators were related with some metabolic biomarkers and comorbidity in only OHA users. The most common reason for inactivity was “the lack of time” in both groups.  相似文献   

9.
Purpose: To determine the accuracy of critical power (CP) and W? (the curvature constant of the power-duration relationship) derived from self-paced time-trial (TT) prediction trials using mobile power meters to predict 16.1-km road cycling TT performance. This study also aimed to assess the agreement between functional threshold power (FTP) and CP.

Methods: Twelve competitive male cyclists completed an incremental test to exhaustion, a FTP test and 4–5 self-paced TT bouts on a stationary bike within the lab, and a 16.1 km road TT, using mobile power meters.

Results: CP and W? derived from the power-duration relationship closely predicted TT performance. The 16.1-km road TT completion time (26.7 ± 2.2 min) was not significantly different from and was significantly correlated with the predicted time-to-completion (27.5 ± 3.3 min, r = 0.89, P < 0.01). CP and FTP were not significantly different (275 ± 40 W vs. 278 ± 42 W, P > 0.05); however, the limits of agreement between CP and FTP were 30 to -36 W.

Discussion: The findings of this study indicate that CP and W? determined using mobile power meters during maximal, self-paced TT prediction trials can be used to accurately predict 16.1-km cycling performance, supporting the application of the CP and W? for performance prediction. However, the limits of agreement were too large to consider FTP and CP interchangeable.  相似文献   


10.
Purpose: The purpose of this study was to compare the kicking performance of young soccer players in the U9 to U20 age groups. Method: Three hundred and sixty-six Brazilian players were evaluated on an official pitch using three-dimensional kinematics to measure (300 Hz) ball velocity (Vball), foot velocity (Vfoot), Vball/Vfoot ratio, last stride length, and distance between the support foot and the ball. Simultaneously, a two-dimensional procedure was also conducted to compute (60 Hz) the mean radial error, bivariate variable error, and accuracy. Possible age-related differences were assessed through one-way analysis of variance and magnitude-based inferences. Results: Ball velocity increased by 103% (p < .001, η2 = .39) from the U11 age group (48.54 ± 8.31 km/hr) to the U20 age group (98.74 ± 16.35 km/hr). Foot velocity presented a 59% increase (p < .001, η2 = .32) from the U11 age group (49.08 ± 5.16 km/hr) to U20 (78.24 ± 9.49 km/hr). This finding was due to improvement in the quality of foot–ball impact (Vball/Vfoot ratio) from U11 (0.99 ± 0.13 a.u.) to U20 (1.26 ± 0.11 a.u.; p < .001, η2 = .25). Parameters such as mean radial error and accuracy appeared to be impaired during the growth spurt (U13–U15). Last stride length was correlated, low to moderately high, with Vball in all age groups (r = .36–.79). Conclusions: In summary, we concluded that simple biomechanical parameters of kicking performance presented distinct development. These results suggest that different training strategies specific for each age group could be applied. We provide predictive equations to aid coaches in the long-term monitoring process to develop the kick in soccer or search for talented young players.  相似文献   

11.
Purpose: Correlations between fatigue-induced changes in exercise performance and maximal rate of heart rate (HR) increase (rHRI) may be affected by exercise intensity during assessment. This study evaluated the sensitivity of rHRI for tracking performance when assessed at varying exercise intensities. Method: Performance (time to complete a 5-km treadmill time-trial [5TTT]) and rHRI were assessed in 15 male runners following 1 week of light training, 2 weeks of heavy training (HT), and a 10-day taper (T). Maximal rate of HR increase (measured in bpm·s?1) was the first derivative maximum of a sigmoidal curve fit to HR data recorded during 5 min of running at 8 km·h?1 (rHRI8km·h?1), and during subsequent transition to 13 km·h?1 (rHRI8–13km·h?1) for a further 5 min. Results: Time to complete a 5-km treadmill time-trial was likely slower following HT (effect size ± 90% confidence interval = 0.16 ± 0.06), and almost certainly faster following T (–0.34 ± 0.08). Maximal rate of HR increase during 5 min of running at 8 km·h?1 and rHRI8–13km·h?1 were unchanged following HT and likely increased following T (0.77 ± 0.45 and 0.66 ± 0.62, respectively). A moderate within-individual correlation was found between 5TTT and rHRI8km·h?1 (r value ± 90% confidence interval = –.35 ± .32). However, in a subgroup of athletes (n = 7) who were almost certainly slower to complete the 5TTT (4.22 ± 0.88), larger correlations were found between the 5TTT and rHRI8km·h?1 (r = –.84 ± .22) and rHRI8–13km·h?1 (r = –.52 ± .41). Steady-state HR during rHRI assessment in this group was very likely greater than in the faster subgroup (≥ 1.34 ± 0.86). Conclusion(s): The 5TTT performance was tracked by both rHRI8km·h?1 and rHRI8–13km·h?1. Correlations between rHRI and performance were stronger in a subgroup of athletes who exhibited a slower 5TTT. Individualized workloads during rHRI assessment may be required to account for varying levels of physical conditioning.  相似文献   

12.
Purpose: The purposes of this study were to (a) investigate the effect of physical effort (cycling for 60 min at 60 ± 5% of individually computed reserve heart-rate capacity), combined with 2 different levels of cognitive demand (2-back, oddball), on intraocular pressure (IOP) and subjective judgments of perceived exertion (ratings of perceived exertion [RPE]), affect (Affective Valence subscale of the Self-Assessment Manikin [SAM]), and mental workload (National Aeronautics and Space Administration Task Load Index [NASA-TLX]); and (b) ascertain whether baseline IOP, measured before exercise, is associated with individual differences in subjective assessments of effort and affective response during exercise. Method: Seventeen participants (Mage = 23.28 ± 2.37 years) performed 2 physical/cognitive dual tasks, matched in physical demand but with different mental requirements (2-back, oddball). We assessed IOP before exercise, after 2 min of active recovery, and after 15 min of passive recovery, and we also collected RPE and SAM measures during the sessions (28 measurement points). We used NASA-TLX and cognitive performance as checks of the mental manipulation. Results: (a) Intraocular pressure increased after concomitant physical/mental effort, with the effect reaching statistical significance after the 2-back task (p = .002, d = 0.35) but not after the oddball condition (p = .092, d = 0.29). (b) Baseline IOP was associated with subjective sensitivity to effort and showed statistical significance for the oddball condition (p = .03, ?p2 = .622) but not for the 2-back task (F < 1). Conclusions: Results suggest a relationship between IOP and physical/cognitive effort, which could have implications for the management of glaucoma. Additionally, a rapid measure of IOP could be used as a marker of individual effort sensitivity in applied settings.  相似文献   

13.
Purpose: The purpose of this investigation was to examine the effects of a submaximal running warm-up on running performance in male endurance athletes (n = 16, Mage = 21 ± 2 years, MVO2max = 69.3 ± 5.1 mL/kg/min). Method: Endurance performance was determined by a 30-min distance trial after control and submaximal running warm-up conditions in a randomized crossover fashion. The warm-up began with 5 min of quiet sitting, followed by 6 min of submaximal running split into 2-min intervals at speeds corresponding to 45%, 55%, and 65% maximal oxygen consumption (VO2max). A 2-min walk at 3.2 km/hr concluded the 13-min warm-up protocol. For the control condition, participants sat quietly for 13 min. VO2 and heart rate (HR) were determined at Minutes 0, 5, and 13 of the pre-exercise protocol in each condition. Results: At the end of 13 min prior to the distance trial, mean VO2 (warm-up = 14.1 ± 2.2 mL/kg/min vs. control = 5.5 ± 1.7 mL/kg/min) and mean HR (warm-up = 105 ± 11 bpm vs. control = 67 ± 11 bpm) were statistically greater (p < .001) in the warm-up condition compared with the control condition. The distance run did not statistically differ (p = .37) between the warm-up (7.8 ± 0.5 km) and control (7.7 ± 0.6 km) conditions; however, effect size calculation revealed a small effect (d = 0.2) in favor of the warm-up condition. Thus, the warm-up employed may have important and practical implications to determine placing among high-level athletes in close races. Conclusions: These findings suggest a submaximal running warm-up may have a small but critical effect on a 30-min distance trial in competitive endurance athletes. Further, the warm-up elicited increases in physiological variables VO2 and HR prior to performance; thus, a submaximal specific warm-up should warrant consideration.  相似文献   

14.
Purpose: The purpose of this study was to examine whether white blood cell (WBC) level mediated the relationship between physical activity and prostate-specific antigen (PSA) levels. Method: Data from the 2003–2006 National Health and Nutrition Examination Survey were used; 1,726 U.S. adult men (aged 40 years or older) provided complete data on the study variables. Participants wore an ActiGraph 7164 accelerometer for a 7-day period to measure their physical activity behavior, and PSA and WBC levels were obtained from a blood sample. Results: After adjustments, results showed that moderate-to-vigorous physical activity (MVPA) was inversely associated with WBC count (b = ? .03; 95% CI [ ? 0.04, ? 0.006; p = .01), and WBC count (b = .10; 95% CI [0.009, 0.18; p = .04) was positively associated with PSA. Both the Sobel (coef. = ? .004, SE = .002; z = ? 2.0; p = .03) and the Aroian (coef. = ? .004, SE = .002; z = ? 1.9; p = .03) tests demonstrated that WBC mediated the relationship between physical activity and PSA. Additionally, among 107 participants with prostate cancer, survivors engaging in more MVPA had lower levels of WBC (b = ? .04; 95% CI [ ? 0.09, ? 0.0009; p = .04). Conclusion Physical activity may influence PSA levels through WBC modulation; however, future research is needed to determine the direction of causality. Additionally, prostate cancer survivors engaging in higher levels of MVPA had lower levels of WBC, underscoring the importance of promoting physical activity among prostate cancer survivors.  相似文献   

15.

Purpose: The purpose of the meta-analysis was to examine the effectiveness of physical activity interventions on physical activity participation among preschoolers. A secondary purpose was to investigate the influence of several possible moderator variables (e.g., intervention length, location, leadership, type) on moderate-to-vigorous physical activity (MVPA). Method: Nine databases were systematically searched for physical activity interventions. Studies were included if they contained statistics necessary to compute an effect size (ES), were written in or translated into English, examined physical activity in preschoolers, incorporated a physical activity intervention, and targeted preschool-aged children. Fifteen studies satisfied these criteria. ESs were calculated using a random-effects model. Results: Results indicated that overall, interventions had a small-to-moderate effect on general physical activity (Hedges g = 0.44, p < .05, n = 73 ESs) and a moderate effect on MVPA (Hedges g = 0.51, p < .05, n = 39 ESs). The greatest effects for MVPA were identified for interventions that were less than 4 weeks in duration, were offered in an early-learning environment, were led by teachers, involved outdoor activity, and incorporated unstructured activity. Conclusions: This meta-analysis provides an overview and synthesis of physical activity interventions and highlights effective strategies for future interventions aimed at increasing physical activity levels among preschoolers.  相似文献   

16.
Abstract

Glutamine enhances the exercise-induced expansion of the tricarboxylic acid intermediate pool. The aim of the present study was to determine whether oral glutamine, alone or in combination with hyperoxia, influenced oxidative metabolism and cycle time-trial performance. Eight participants consumed either placebo or 0.125 g · kg body mass?1 of glutamine in 5 ml · kg body mass?1 placebo 1 h before exercise in normoxic (control and glutamine respectively) or hyperoxic (FiO2 = 50%; hyperoxia and hyperoxia + glutamine respectively) conditions. Participants then cycled for 6 min at 70% maximal oxygen uptake ([Vdot]O2max) immediately before completing a brief high-intensity time-trial (～4 min) during which a pre-determined volume of work was completed as fast as possible. The increment in pulmonary oxygen uptake during the performance test (Δ[Vdot]O2max, P = 0.02) and exercise performance (control: 243 s, s x  = 7; glutamine: 242 s, s x  = 3; hyperoxia: 231 s, s x  = 3; hyperoxia + glutamine: 228 s, s x  = 5; P < 0.01) were significantly improved in hyperoxic conditions. There was some evidence that glutamine ingestion increased Δ[Vdot]O2max in normoxia, but not hyperoxia (interaction drink/FiO2, P = 0.04), but there was no main effect or impact on performance. Overall, the data show no effect of glutamine ingestion either alone or in combination with hyperoxia, and thus no limiting effect of the tricarboxylic acid intermediate pool size, on oxidative metabolism and performance during maximal exercise.  相似文献   

17.
Purpose: Several studies have demonstrated that physiological variables predict cycling endurance performance. However, it is still unclear whether the predictors will change over different performance durations. The aim of this study was to assess the correlations between physiological variables and cycling time trials with different durations. Methods: Twenty trained male cyclists (maximal oxygen uptake [VO2max] = 60.5 ± 5.6 mL/kg/min) performed 4 separate experimental trials during a 2-week period. Cyclists initially completed an incremental exercise test until volitional exhaustion followed by 3 maximal cycling time trials on separate days. Each time trial consisted of 3 different durations: 5 min, 20 min, and 60 min performed in a randomized order. Results: The main results showed that the physiological measures strongly correlated with long cycling performances rather than short and medium time trials. The time-trial mean power output was moderately high to highly correlated with peak power output and VO2max (r = .61–.87, r = .72–.89, respectively), and was moderately to highly correlated with the lactate threshold Dmax method and second ventilatory threshold (r = .52–.75, r = .55–.82, respectively). Conclusions: Therefore, trained cyclists should develop maximal aerobic power irrespective of the duration of time trial, as well as enhancements in metabolic thresholds for long-duration time trials.  相似文献   

18.
Low-cost physical activity monitors may provide a more accurate measure of physical activity than subjective methods (e.g., self-report) while being less costly than research-grade accelerometers. The present study assessed the validity of a low-cost monitor (Movband 2) to estimate physical activity behavior/intensity. Participants (N = 23, n = 16 female, BMI = 22.9 ± 4.0 kg/m2, age = 21.9 ± 1.6 years) completed four, five-minute treadmill stages (2.0, 3.0, 4.0, 5.0 MPH) while wearing both the Movband and the previously-validated Actigraph monitor. Oxygen consumption (VO2) was recorded during each stage (Laboratory assessment). A subset (n = 15, n = 10 female, BMI = 22.2 ± 3.2 kg/m2, age = 21.5 ± 0.8 years) of these participants then wore the two accelerometers for three days (Free-living assessment). During the Laboratory assessment there were strong, significant (r = 0.94, p ≤ 0.001) relationships between Movband and Actigraph counts and VO2. During Free-living assessment there was also a strong, significant (r = 0.97, p < 0.001) correlation between Movband and Actigraph counts. The low-cost, Movband accelerometer appears to provide a valid assessment of physical activity behavior/intensity.  相似文献   

19.
ABSTRACT

The aim of the present study was to determine the factors affecting sports involvement in a school-based adolescent population. The cross-sectional cohort study assessed anthropometry, physical capacities and motor competence in 501 boys (aged 10–16 y), from junior (10–12 y) and senior (13–16 y) cohorts. Sports participation data was collected from junior participants. Multivariate analysis of covariance revealed moderate maturity, anthropometry, physical capacity and motor competence differences between sports in the senior cohort (F = 2.616, p < 0.001, η2 = .08), but not in the junior cohort. Furthermore, differences in physical fitness were revealed between playing levels (F = 2.616, p < 0.001, η2 = .08), with a discriminant analysis correctly classifying 73% of participants using aerobic fitness and vertical jump measures. Representative level participants engaged in more structured training and commenced organised competition at a later age (F = 4.332, p < 0.001, η2 = .21). This study’s findings are twofold: 1) physical and motor competence profiles differ more between sports with increasing age, and 2) participants at a higher level of competition report delayed engagement in their main sport. As a result, schools may be the ideal environment in which to provide children and adolescents with the opportunity to sample different sports.  相似文献   

20.
Abstract

Mechanical models of cycling time-trial performance have indicated adverse effects of variations in external power output on overall performance times. Nevertheless, the precise influences of the magnitude and number of these variations over different distances of time trial are unclear. A hypothetical cyclist (body mass 70 kg, bicycle mass 10 kg) was studied using a mathematical model of cycling, which included the effects of acceleration. Performance times were modelled over distances of 4–40 km, mean power outputs of 200–600 W, power variation amplitudes of 5–15% and variation frequencies of 2–32 per time-trial. Effects of a “fast-start” strategy were compared with those of a constant-power strategy. Varying power improved 4-km performance at all power outputs, with the greatest improvement being 0.90 s for ± 15% power variation. For distances of 16.1, 20 and 40 km, varying power by ± 15% increased times by 3.29, 4.46 and 10.43 s respectively, suggesting that in long-duration cycling in constant environmental conditions, cyclists should strive to reduce power variation to maximise performance. The novel finding of the present study is that these effects are augmented with increasing event distance, amplitude and period of variation. These two latter factors reflect a poor adherence to a constant speed.  相似文献   

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