The evaluation of small-sided games as a talent identification tool in highly trained prepubertal soccer players

The aim of this study was to evaluate physiological and technical attributes of prepubertal soccer players during multiple small-sided games (SSGs), and determine if SSGs can act as a talent identification tool. Sixteen highly trained U10 soccer players participated and separated into two groups of eight. Each group played six small-sided (4 vs. 4) matches of 5-min duration. Each player was awarded total points for the match result and goals scored. A game technical scoring chart was used to rate each player’s performance during each game. Time-motion characteristics were measured using micromechanical devices. Total points had a very large significant relationship with game technical scoring chart (r = 0.758, P < 0.001). High-speed running distance had a significantly large correlation with game technical scoring chart (r = 0.547, P < 0.05). Total distance covered had a significant and moderate correlation with game technical scoring chart (r = 0.545, P < 0.05) and total points (r = 0.438, P < 0.05).The results demonstrated a large agreement between the highest-rated players and success in multiple SSGs, possibly due to higher-rated players covering larger distances in total and at high speed.Consequently, multiple SSG could be used to identify the more talented prepubertal soccer players

Influence of oxygen uptake kinetics on physical performance in youth soccer

Purpose: To examine the relationship between oxygen uptake kinetics (VO2 kinetics) and physical measures associated with soccer match-play, within a group of highly trained youth soccer players. Methods: Seventeen highly trained youth soccer players (age: 13.3 ± 0.4 yr, self-assessed Tanner Stage: 3 ± 1) volunteered for the study. Players initially completed an incremental treadmill protocol to exhaustion, to establish gaseous exchange threshold (GET) and VO2max (59.1 ± 5.4 mL.kg-1.min-1). On subsequent visits players completed a step transition protocol from, rest–moderate intensity exercise, followed by an immediate transition from moderate–severe intensity exercise (moderate: 95%GET, severe: 60%∆), during which VO2 kinetics were determined. Physical soccer-based performance was assessed using a maximal Yo-Yo Intermittent Recovery test level 1 (Yo-Yo IR1) and via GPS derived measures of physical soccer performance during soccer match-play, 3 2 x 20min, 11 v 11 matches, to gain measures of physical performance during soccer match-play. Results: Partial correlations revealed significant inverse relationships between the unloaded to moderate transition time constant (tau) and: Yo-Yo IR1 performance (r = -0.58, P = 0.02) and GPS variables (Total distance (TD): r = - 0.64, P = 0.007, High speed running (HSR): r = - 0.64, P = 0.008, High speed running efforts (HSReff): r = - 0.66, P = 0.005). Conclusion: Measures of VO2 kinetics are related to physical measures associated with soccer match-play and could potentially be used to distinguish between those of superior physical performance, within a group of highly-trained youth soccer players

Clinical Potential of Quantum Dots

Advances in nanotechnology have led to the development of novel fluorescent probes called quantum dots. Quantum dots have revolutionalized the processes of tagging molecules within research settings and are improving sentinel lymph node mapping and identification in vivo studies. As the unique physical and chemical properties of these fluorescent probes are being unraveled, new potential methods of early cancer detection, rapid spread and therapeutic management, that is, photodynamic therapy are being explored. Encouraging results of optical and real time identification of sentinel lymph nodes and lymph flow using quantum dots in vivo models are emerging. Quantum dots have also superseded many of the limitations of organic fluorophores and are a promising alternative as a research tool. In this review, we examine the promising clinical potential of quantum dots, their hindrances for clinical use and the current progress in abrogating their inherent toxicity

Reproducibility of an isokinetic eccentric muscle endurance task

Despite the widespread use of isokinetic eccentric muscle endurance protocols, no research has examined the absolute and relative reliability of such tests. The aim of this study was to examine the reliability of an isokinetic eccentric knee muscle endurance task. Fifteen healthy untrained males volunteered to take part in the study and written informed consent was obtained. The procedures received approval from the University Research Ethics Committee. Participants visited the laboratory on three separate occasions: 2 weeks before testing to familiarize them with the experimental procedures, and on two separate occasions, 2 weeks apart and at the same time of day. Isokinetic eccentric knee extension and flexion movements of the dominant limb were performed using a calibrated dynamometer (Biodex System 3). Range of motion during testing was set using voluntary maximal full extension (0 rad) to 1.57 rad of knee flexion and testing was conducted at 1.56 rad . s(-1). Participants performed four maximal efforts to determine maximal peak torque. After 2 min rest, participants completed the all-out endurance test of 50 continuous eccentric repetitions. Data were gravity corrected and windowed to only include constant velocity periods. Repeated-measures analyses of variance were used to examine differences in maximal peak extension and flexion torque and the maximal torque measurement recorded during the endurance test. Absolute and relative reliability of the torque fatigue index, work fatigue index, and total work were assessed through calculation of intra-class correlation coefficients, coefficients of variation, and absolute 95% limits of agreement using the methods described by Bland and Altman (1986). Differences between the strength test and the endurance trial for peak torque were found to be non-significant for both quadriceps (323 vs. 323 N . m) and hamstrings (183 vs. 178 N . m). The intra-class correlation coefficients revealed significant (P<0.05) positive moderate to strong correlations (r=0.44-0.94) across repeated trials for all parameters except hamstring torque fatigue (P=0.11) and hamstring work fatigue index (P=0.08). Coefficients of variation ranged from 6% to 48% and were large for the work fatigue index and torque fatigue index but acceptable for total work for both the extensors and flexors. The 95% limits of agreement indicated systematic bias in repeated trials for both the work fatigue index and torque fatigue index for extensors and flexors, ranging from -3% to -10%, with less fatigue evident in the second test. There was also systematic bias for total work, with more work being performed during the second than the first test for both extensors and flexors. The random error was large for all variables and there was greater random error in the hamstrings compared with the quadriceps. Together with moderate to strong intra-class correlation coefficients and large coefficients of variation, the data suggest that there is small systematic bias in repeated eccentric muscle actions for both the quadriceps and hamstrings, although the random error was large despite habituation procedures. Therefore, data from an isokinetic eccentric muscle endurance task should be viewed with some caution even when participants receive considerable habituation before assessment

THE IMPACT OF CONCURRENT-TRAINING ON THE PHYSIOLOGICAL ADAPTATIONS TO SPORT SPECIFIC EXERCISE IN ELITE FOOTBALLERS

Elite football players are required to train multiple metabolic and physical parameters simultaneously. Due to the nature of the competition schedule and training time available players often perform sports-specific endurance-training and high-load, low repetition resistance-training on the same day (Hoff et al., 2006). Empirical evidence highlights that when two disparate forms of muscular contraction are trained within the same training cycle, adaptations in strength and power related variables can become blunted - a situation most commonly referred to as the ‘interference phenomenon’ (Hickson, 1980). Experimental data suggest the organisation of each training stimulus can modulate the training response and exacerbate the ‘interference phenomenon’. However at present few data exist concerning how elite football teams currently organise their concurrent-training programmes. Furthermore to the authors’ knowledge no practical guidelines exist as to minimise the interference phenomenon within the constraints of the applied football environment. Therefore, the aim of this thesis was to investigate the impact of training organisation on the acute and chronic responses to football-specific concurrent exercise programmes in elite football players. Initially we conducted a pilot study (chapter 3) to observe the concurrent-training strategies currently in place at a professional football club. The study had two aims (1) to describe the training frequency and training load across the first 10 weeks of a competitive season and (2) to characterise the acute organisation of training and nutritional intake around concurrent-training. It was found that training frequency and volume was greatest during the initial three weeks of the observation. Following this training frequency and training load decreased significantly. Although, following the decrease in training load there were no between week fluctuations in training load. Together, these results suggested that the reduced ‘pre-season period’ (i.e. 3 weeks) and the lack of fluctuation in training volume and intensity from weeks 4 to 10 may not be optimal for longer-term muscle performance (Fleck, 1999). The secondary findings from this study demonstrated that when concurrent-training was performed on the same day, the order of aerobic and resistance exercise, the nutritional availability and the recovery period between training sessions was unsystematic. It was thought that this approach to the organisation of concurrent-training may not have been optimal for longer term muscle adaptation. Collectively, this study showed that despite large investment in sports science departments and highly experienced coaches, the application of periodised and well-structured training is not always possible. The lack of systematic training and nutritional intake observed at this football club could have exacerbated the ‘interference phenomenon’ and subsequently been sub-optimal for longer term muscle adaptation and athlete performance. The purpose of study 1 and 2 (chapters 5 & 6) was to investigate if the concurrent exercise protocols previously observed could modulate the ‘interference phenomenon’. In a series of studies we investigated the muscular adaptations following 5 weeks of strength-training performed either before or after football-specific endurance-training (‘S + E’ and ‘E + S’). It was found that improvements in strength and power related variables become blunted in the S + E training group. It was hypothesised that the between group differences could be explained by the differences in muscle architecture adaptation observed in the E + S training group. As both training groups completed similar training loads it was thought that the recovery period and nutrient timing associated with each training group could have either ‘enhanced’ or ‘blunted’ underlying adaptive mechanisms respectively. Although the underpinning molecular or metabolic process responsible for the between group differences in architectural adaptation could not be concluded from this study. Study 3 investigated the hormonal responses to two concurrent-training and nutritional scenarios previously observed at a professional football club. This investigation demonstrated that the sequence of concurrent-training, the recovery period between exercise bouts and the nutritional support provided before, between and after training could influence acute exercise induced hormonal secretion. Whilst the hormonal hypothesis for increasing muscle hypertrophy is questionable (West et al., 2009) the present data in combination with the previous training study suggest that exercise induced hormonal secretion may be involved in other metabolic processes which influence the geometry of the fascicule (i.e. muscle architecture). This thesis has highlighted the need for research to investigate the effect of concurrent-training the applied exercise setting. The lack of studies to investigate the effects of concurrent-training in elite football players has limited our understanding of the physiological effects of concurrent-training in elite football players. Whilst this thesis highlighted that the organisation of the training and nutrition can influence the interference phenomenon, more work is required to confirm these findings. Specifically, our understanding of the effect of manipulating acute training variables on the physiological mechanisms responsible for the effectiveness of concurrent-training programmes require further study. The incorporation of a range of scientific techniques in a controlled setting could lead to a theoretical framework for understanding how to plan and deliver concurrent-training programmes in the applied setting so that the interference phenomenon is minimised

Significant geographical differences in prevalence of mutations associated with Plasmodium falciparum and Plasmodium vivax drug resistance in two regions from Papua New Guinea

Drug resistance remains a major obstacle to malaria treatment and control. It can arise and spread rapidly, and vary substantially even at sub-national level. National malaria programmes require cost-effective and timely ways of characterizing drug-resistance at multiple sites within their countries.; An improved multiplexed post-PCR ligase detection reaction-fluorescent microsphere assay (LDR-FMA) was used to simultaneously determine the presence of mutations in chloroquine resistance transporter (crt), multidrug resistance 1 (mdr1), dihydrofolate reductase (dhfr) and dihydropteroate synthase (dhps) genes in Plasmodium falciparum (n = 727) and Plasmodium vivax (n = 574) isolates collected in 2006 from cross-sectional community population surveys in two geographically distinct regions (Madang and East Sepik) of Papua New Guinea (PNG) where strong regional differences in in vivo aminoquinoline and antifolate therapeutic efficacy had previously been observed. Data were compared to those of a follow-up survey conducted in 2010.; Despite some very low parasite densities, the assay successfully amplified all P. falciparum and P. vivax loci in 77 and 69 % of samples, respectively. In 2006, prevalences of pfdhfr (59R-108 N) double mutation/wild type pfdhps haplotype, pfcrt SVMNT haplotype (72S-76T double mutation), and 86Y pfmdr1 mutation all exceeded 90 %. For P. vivax, 65 % carried at least two pvdhfr mutations, 97 % the 647P pvdhps mutation and 54 % the 976F pvmdr1 mutation. Prevalence of mutant haplotypes was higher in Madang than East Sepik for pfcrt SVMNT (97.4 vs 83.3 %, p = 0.001), pfdhfr (59R-108 N) (100 vs 90.6 %, p = 0.001), pvdhfr haplotypes (75.8 vs 47.6 %, p = 0.001) and pvmdr1 976F (71.2 vs 26.2 %, p &lt; 0.001). Data from a subsequent Madang survey in 2010 showed that the prevalence of pfdhps mutations increased significantly from &lt;5 % to &gt;30 % (p &lt; 0.001) as did the prevalence of pvdhfr mutant haplotypes (from 75.8 to 97.4 %, p = 0.012).; This LDR-FMA multiplex platform shows feasibility for low-cost, high-throughput, rapid characterization of a broad range of drug-resistance markers in low parasitaemia infections. Significant geographical differences in mutation prevalence correlate with previous genotyping surveys and in vivo trials and may reflect variable drug pressure and differences in health-care access in these two PNG populations

Electromechanical delay of the hamstrings during eccentric muscle actions in males and females: Implications for non-contact ACL injuries

Sex differences in neuromuscular functioning has been proposed as one of the factors behind an increased relative risk of non-contact anterior cruciate ligament (ACL) injury in females. The aim of this study was to explore sex differences in electromechanical delay (EMD) of the hamstring muscles during eccentric muscle actions and during a range of movement velocities. This study recruited 110 participants (55 males, 55 females) and electromyography of the semitendinosus, semimembranosus and biceps femoris was determined during eccentric actions at 60, 120 and 240°/s. No significant sex differences were observed irrespective of muscle examined or movement velocity. Irrespective of sex EMD significantly increased with increasing movement velocity (P < 0.01). There was no significant difference in the EMD of the 3 muscles examined. Our findings suggest that during eccentric actions of the hamstrings that there are no sex differences, irrespective of movement velocity. This would suggest that other factors are probably responsible for the increased relative risk of non-contact ACL injury in females compared to males

The impact of joint angle and movement velocity on sex differences in the functional hamstring/quadriceps ratio

Objective: Females are 2-8 times more likely to suffer a non-contact injury compared with males thus the purpose of this study was to explore the influence of joint angle and movement velocity on sex differences in the functional hamstring to quadriceps ratio (H/QFUNC). Methods: Isokinetic concentric and eccentric torque were determined in 110 participants (55 males and 55 females) through a 90° range of movement at 60, 120, 240°/s. Testing was performed with the hip flexed at 10°. The H/QFUNC was determined at 3 specific joint angles (15, 30 and 45° flexion) and where peak torque occurred for concentric knee extension. Results: A significant interaction effect (P <0.01) for sex and joint angle was observed with women demonstrating a lower H/QFUNC than males, especially at more extended knee positions. A significant sex by velocity interaction (P <0.01) indicated a lower H/QFUNC in women as velocity increased. Significant main effects (P < 0.01) indicated that irrespective of sex the H/QFUNC increased as the knee extends and velocity increases. Conclusion: Given the reduced H/QFUNC in females compared to males at more extended knee positions and faster velocities, this may contribute to the observed sex bias in reported injury rates