Back foot influence on dorsiflexion using three different positions of the weight bearing lunge test.

OBJECTIVES: To determine whether back foot (BF) position influences dorsiflexion range of motion (DFROM) during three different positions of the weight bearing lunge test (WBLT). DESIGN: Randomised, repeated measures design. SETTING: Sports clubs. PARTICIPANTS: 52 athletes participating in cutting and pivoting sports. MAIN OUTCOME MEASURES: DFROM was obtained using a WBLT in three different BF positions: BF heel in full contact with the floor, BF heel raised off the floor and BF was non weight bearing (NWB). All measurements were obtained using three methods: inclinometer at the tibial tuberosity, toe to wall distance and goniometer angle from the lateral malleolus to the fibula head. Differences between testing positions were determined using a repeated measures one-way ANOVA and reliability analysis was performed using the Intraclass Correlation Coefficient (ICC). RESULTS: DFROM was statistically significantly different for all three positions of the WBLT for each measurement technique (P < .001). These results were associated with large effect sizes for all BF positions and measurement techniques. Reliability ICC values were excellent for all measurements (ICC 0.94-0.99). CONCLUSIONS: Results show that DFROM differs depending upon the position of the BF during the WBLT. Further research is needed to establish the reproducibility of these three BF positions due to the variability observed.

Phase variation in pneumococcal populations during carriage in the human nasopharynx.

Streptococcus pneumoniae is one of the world's leading bacterial pathogens, responsible for pneumonia, septicaemia and meningitis. Asymptomatic colonisation of the nasopharynx is considered to be a prerequisite for these severe infections, however little is understood about the biological changes that permit the pneumococcus to switch from asymptomatic coloniser to invasive pathogen. A phase variable type I restriction-modification (R-M) system (SpnIII) has been linked to a change in capsule expression and to the ability to successfully colonise the murine nasopharynx. Using our laboratory data, we have developed a Markov change model that allows prediction of the expected level of phase variation within a population, and as a result measures when populations deviate from those expected at random. Using this model, we have analysed samples from the Experimental Human Pneumococcal Carriage (EHPC) project. Here we show, through mathematical modelling, that the patterns of dominant SpnIII alleles expressed in the human nasopharynx are significantly different than those predicted by stochastic switching alone. Our inter-disciplinary work demonstrates that the expression of alternative methylation patterns should be an important consideration in studies of pneumococcal colonisation.

Recombination of the Phase-Variable spnIII Locus Is Independent of All Known Pneumococcal Site-Specific Recombinases.

Streptococcus pneumoniae is one of the world's leading bacterial pathogens, causing pneumonia, septicemia, and meningitis. In recent years, it has been shown that genetic rearrangements in a type I restriction-modification system (SpnIII) can impact colony morphology and gene expression. By generating a large panel of mutant strains, we have confirmed a previously reported result that the CreX (also known as IvrR and PsrA) recombinase found within the locus is not essential for hsdS inversions. In addition, mutants of homologous recombination pathways also undergo hsdS inversions. In this work, we have shown that these genetic rearrangements, which result in different patterns of genome methylation, occur across a wide variety of serotypes and sequence types, including two strains (a 19F and a 6B strain) naturally lacking CreX. Our gene expression analysis, by transcriptome sequencing (RNAseq), confirms that the level of creX expression is impacted by these genomic rearrangements. In addition, we have shown that the frequency of hsdS recombination is temperature dependent. Most importantly, we have demonstrated that the other known pneumococcal site-specific recombinases XerD, XerS, and SPD_0921 are not involved in spnIII recombination, suggesting that a currently unknown mechanism is responsible for the recombination of these phase-variable type I systems.IMPORTANCEStreptococcus pneumoniae is a leading cause of pneumonia, septicemia, and meningitis. The discovery that genetic rearrangements in a type I restriction-modification locus can impact gene regulation and colony morphology led to a new understanding of how this pathogen switches from harmless colonizer to invasive pathogen. These rearrangements, which alter the DNA specificity of the type I restriction-modification enzyme, occur across many different pneumococcal serotypes and sequence types and in the absence of all known pneumococcal site-specific recombinases. This finding suggests that this is a truly global mechanism of pneumococcal gene regulation and the need for further investigation of mechanisms of site-specific recombination.

Different neuromuscular parameters influence dynamic balance in male and female football players.

PURPOSE: To analyse the relationship between several parameters of neuromuscular performance with unilateral dynamic balance measured through the Y-Balance test, as well as to determine the possible sex-related differences. METHODS: The Y-Balance test, isokinetic (concentric and eccentric) knee flexion and extension strength, isometric hip abduction and adduction strength, lower extremity joint range of motion (ROM) (hip, knee and ankle) and core stability were assessed in male (n = 88) and female (n = 44) professional football players. A stepwise multivariate linear least square regression with backward elimination analysis was carried out to identify a group of factors that were independently associated with balance performance in both sexes. RESULTS: Passive hip flexion and ankle dorsiflexion with knee flexed ROM were the main factors that retained a significant association to dominant (R2 = 23.1) and non-dominant (R2 = 33.5) balance scores for males. For females, core stability, hip abduction isometric peak torque, passive hip abduction and ankle dorsiflexion with knee flexed ROM variables retained a significant association with balance scores for both, dominant (R2 = 38.2) and non-dominant (R2 = 46.9) legs. CONCLUSIONS: Training interventions aimed at improving or maintaining unilateral dynamic balance in male football players should include, among other things, stretching exercises for the posterior chain of the lower extremity. However, females should also include exercises for strength and mobility of the hip abductors and core stability (especially in the frontal plane). This knowledge would allow clinicians and sport practitioners to develop more effective and tailored unilateral dynamic balance training interventions in male and female football players, possibly improving performance and reducing the risk of injury. LEVEL OF EVIDENCE: III.

A prospective investigation to evaluate risk factors for lower extremity injury risk in male youth soccer players.

There is an inherent risk of injury in male youth football; however, pertinent risk factors for injury have yet to be examined. This study used a prospective cohort design with 357 elite male youth football players (aged 10-18 years) assessed during the preseason period and then monitored during the season recording all non-contact lower extremity injuries. Screening tests included single leg hop for distance (SLHD); 75% of maximum hop and stick (75%Hop); single leg countermovement jump (SLCMJ); and the tuck jump assessment (TJ). Players were divided into subgroups based on chronological age. SLCMJ peak landing vertical ground reaction force (pVGRF) asymmetry was the most prominent risk factor (U11-U12s, OR 0.90, P = .04; and U15-U16s, OR 0.91, P < .001). Maturational offset (OR 0.58, P = .04), lower right leg SLCMJ pVGRF relative to body weight (OR 0.36, P = .03), and advanced chronological age (OR 3.62, P = .04) were also significantly associated with heightened injury risk in the U13-U14s, U15-U16s, and U18s, respectively. Univariate analyses showed combinations of anthropometric and movement screening risk factors were associated with heightened risk of lower extremity injury; however, there was variability across the different chronological age groups. Greater SLCMJ pVGRF asymmetry, lower right leg SLCMJ pVGRF %BW, later maturation, and advanced chronological age are potential risk factors for injury in elite male youth football players, although the strength of these relationships was often low to moderate. In addition, risk factors are likely to change at different stages of development.

Muscular and neuromuscular control following soccer-specific exercise in male youth: Changes in injury risk mechanisms.

Poor neuromuscular control has been proposed as a risk factor for non-contact injuries, thus this study aimed to explore the effects of soccer-specific fatigue on leg muscle activation, reactive strength, leg stiffness, and functional hamstring/quadriceps ratio (H/QFUNC ) in elite male youth soccer players. Outcome measures were determined in 18 youth players (age 14.4 ± 0.5 years; stature 169.4 ± 9.9 cm; mass 59.3 ± 8.9 kg; maturity offset 0.86 ± 0.88 years) pre and post simulated soccer match play (SAFT90 ). There was no fatigue-related change in the H/QFUNC ; however, reactive strength and leg stiffness were both compromised (P < 0.001) after soccer-specific fatigue. Muscle activation was also locally compromised (P < 0.001) in the medial hamstring and quadriceps but not in the lateral muscles. Where statistically significant changes were observed, the effect sizes ranged from small to large (0.33-0.97). Compromised stiffness when fatigue is present suggests an increased yielding action, greater ground contact times, greater center of mass displacement, and less efficient movement when the limb comes into contact with the ground. This combined with a reduction in medial quadriceps muscle activation may reflect poor kinetic chain control at the hip and an increase in knee injury risk.

Within-day and between-day Reproducibility of Baroreflex Sensitivity in Healthy Adult Males.

Within-day and between-day reproducibility of supine and tilt baroreflex sensitivity were investigated utilising sequence and spectral indices in 46 healthy adult males employing 3 repeat measures; baseline, +60 min and +24 h. Reproducibility was assessed via the 95% limits of agreement and by the technical error of the measurement. For spectral parameters, the limits of agreement indicated same day was marginally better than between-day reproducibility. For sequence parameters, between-day had marginally better agreement than same-day reproducibility. Tilt markedly improved reproducibility across all outcome measures. Precision expressed by the technical error of the measurement for all spectral outcomes was good in both supine and tilt baroreflex sensitivity (<6%). Precision was lower, but acceptable, for sequence baroreflex sensitivity outcomes in both positions (<11%). Baroreflex sensitivity transfer gain provided the best agreement and reproducibility during supine and tilt conditions. These findings suggest time and spectral techniques may be employed to assess within-day and between-day baroreflex sensitivity changes in healthy individuals. The inclusion of a tilt manoeuvre may improve the reproducibility of the outcome measure, which may aid in the detection of modest baroreflex sensitivity changes in studies employing limited sample sizes.

ACL injury risk in elite female youth soccer: Changes in neuromuscular control of the knee following soccer-specific fatigue.

Fatigue is known to influence dynamic knee joint stability from a neuromuscular perspective, and electromechanical delay (EMD) plays an important role as the feedback activation mechanism that stabilizes the joint. The aim of this study was to investigate the influence of soccer-specific fatigue on EMD in U13-, U15-, and U17-year-old female soccer players. Thirty-six youth soccer players performed eccentric actions of the hamstrings in a prone position at 60, 120, and 180°/s before and after a soccer-specific fatigue trial. Surface electromyography was used to determine EMD from the semitendinosus, biceps femoris and gastrocnemius. A time × age × muscle × velocity repeated measures analysis of variance was used to explore the influence of fatigue on EMD. A significant main effect for time (P = 0.001) indicated that EMD was significantly longer post- compared with pre-fatigue (58.4% increase). A significant time × group interaction effect (P = 0.046) indicated EMD was significantly longer in the U13 age group compared with the U15 (P = 0.011) and U17 (P = 0.021) groups and greater post-fatigue. Soccer-specific fatigue compromised neuromuscular feedback mechanisms and the age-related effects may represent a more compliant muscle-tendon system in younger compared with older girls, increasing risk of injury.

Physical activity and screen time in adolescents transitioning out of compulsory education: a prospective longitudinal study.

BACKGROUND: Within the UK context, it is unclear whether physical activity and screen time changes between completing compulsory education and the period afterwards, and the factors associated with any change. METHODS: A prospective population-based longitudinal design among adolescents (n = 2204 at baseline) was adopted. A self-report questionnaire was administered at baseline (final year of compulsory education) and follow-up (i.e. post compulsory education) to measure physical activity over the previous 7 days and screen time (weekday and weekend) in relation to recommended guidelines. Magnitude of change in physical activity and screen time and key influencing variables associated with changes were analysed. RESULTS: For physical activity, there was a significant change in participants meeting guidelines at baseline but not meeting guidelines at follow-up with 81.0% not meeting guidelines at baseline and follow-up. For screen time, there was no significant change between baseline and follow-up, with 70.6% not meeting guidelines at baseline and follow-up. Gender was associated with the change in physical activity with a decline less likely in females. CONCLUSIONS: Findings reinforce the importance of reducing physical inactivity and sedentary behaviour during this transition. Factors associated with changes in physical inactivity and sedentary behaviour need further investigation.

Comparison of active stretching technique in males with normal and limited hamstring flexibility.

OBJECTIVE: (1) to analyse the accumulative effects of a 12-week active stretching program on hip flexion passive range of motion (HF-PROM), and (2) to compare whether participants with different PROM baseline scores (normal and limited hamstring flexibility) respond in the same way to stretching. DESIGN: Repeated measures design. SETTING: Controlled laboratory environment. PARTICIPANTS: 138 males were categorized according to hamstring flexibility in the unilateral passive straight-leg raise test (PSLR) and assigned to one of two groups: normal hamstring flexibility (≥80°) or limited hamstring flexibility (<80°). In each group, participants were randomly distributed into one of two treatment subgroups: (a) control or (b) active stretching. The active stretching subgroups performed 12 weeks of flexibility training, the control subgroups did not stretch. MAIN OUTCOME MEASURES: HF-PROM was determined through the PSLR test. RESULTS: Both stretching subgroups significantly improved (p < 0.01) their HF-PROM from baseline. The control subgroups did not. CONCLUSIONS: 12 weeks of an active stretching program performed 3 days per week with a daily stretch dose of 180 s improved HF-PROM in both populations (normal and limited hamstring flexibility). The stretching program was equally effective in terms of absolute improvement values for males with normal and limited hamstring flexibility.

Absolute reliability of isokinetic knee flexion and extension measurements adopting a prone position.

The main purpose of this study was to determine the absolute and relative reliability of isokinetic peak torque (PT), angle of peak torque (APT), average power (PW) and total work (TW) for knee flexion and extension during concentric and eccentric actions measured in a prone position at 60, 180 and 240° s(-1). A total of 50 recreational athletes completed the study. PT, APT, PW and TW for concentric and eccentric knee extension and flexion were recorded at three different angular velocities (60, 180 and 240° s(-1)) on three different occasions with a 72- to 96-h rest interval between consecutive testing sessions. Absolute reliability was examined through typical percentage error (CV(TE)), percentage change in the mean (ChM) and relative reliability with intraclass correlations (ICC(3,1)). For both the knee extensor and flexor muscle groups, all strength data (except APT during knee flexion movements) demonstrated moderate absolute reliability (ChM < 3%; ICCs > 0·70; and CV(TE) < 20%) independent of the knee movement (flexion and extension), type of muscle action (concentric and eccentric) and angular velocity (60, 180 and 240° s(-1)). Therefore, the current study suggests that the CV(TE) values reported for PT (8-20%), APT (8-18%) (only during knee extension movements), PW (14-20%) and TW (12-28%) may be acceptable to detect the large changes usually observed after rehabilitation programmes, but not acceptable to examine the effect of preventative training programmes in healthy individuals.

Efecto agudo del estiramiento activo sobre la fuerza y potencia de la flexión y extensión de rodilla / Acute effect of active stretching on knee flexion and extension strength and power output

Objetivo. Analizar el efecto agudo de un protocolo de estiramientos estáticos activos de corta duración sobre la potencia y máxima fuerza isocinética concéntrica y excéntrica de la flexión y extensión de rodilla en deportistas recreativos. Método. Un total de 27 hombres y 25 mujeres completaron tres sesiones de evaluación, una inicial de familiarización y dos experimentales (control y estiramientos en orden aleatorio), con un intervalo de 72-96 horas entre sesiones consecutivas. El protocolo de estiramientos estáticos activos consistió en cinco ejercicios unilaterales diseñados para estirar los principales grupos musculares de la extremidad inferior. Cada ejercicio de estiramiento fue realizado dos veces, manteniendo la posición de estiramiento durante 30 s (2 x 30 s), con un periodo de descanso entre serie, pierna contralateral y/o ejercicio de 20 s. En la sesión de control no se realizó el programa de estiramientos. Inmediatamente después de ambos tratamientos (control y estiramientos), se valoraron los índices isocinéticos pico de fuerza máximo (PFM) y potencia media (PM) durante los movimientos de flexión y extensión de rodilla concéntrica y excéntrica. Resultados. El análisis ANOVA llevado a cabo reveló la no existencia de un efecto de interacción significativo entre las sesiones de evaluación (control y estiramiento) para las variables PFM y PM (concéntrica y excéntrica) de la flexión y extensión de rodilla. Conclusiones. Un protocolo de estiramientos estáticos activos de corta duración (2 x 30 s por grupo muscular) del miembro inferior no causó una alteración negativa en la potencia y máxima fuerza isocinética concéntrica y excéntrica de la flexión y extensión de rodilla(AU)

Aim. To analyze the acute effect of a short duration active-static stretching protocol on maximal isokinetic strength and power output during concentric and eccentric flexion and extension knee movements in recreational athletes. Method. A total of 27 males and 25 females completed three measurement sessions, an initial session of familiarization and two experimental session (control and active stretching in randomized order) with 72-96 hours interval among consecutive sessions. The active stretching protocol consisted in 5 different unilateral exercises designed to stretch the major lower limb muscle groups. Each stretching exercise was performed twice, holding the position during 30s (2 x 30s), with a rest-interval among series, contra-lateral leg and /or exercises of 20s. In the control session no stretching exercises were performed. Immediately after performed both treatments (control and stretching), the isokinetic indexes of peak torque (PT) and average power (AP) were tested during concentric and eccentric flexion and extension knee movements. Results. The ANOVA analysis carried out revealed no significant interaction effect between testing sessions (control and stretching) for knee flexion and knee extension peak torque and mean power in both concentric and eccentric muscle contractions. Conclusions. Short (2 x 30s per muscle group) pre-exercise active-static lower-limb stretching routine did not elicit stretching-induce reductions in knee flexor and knee extensor isokinetic concentric and eccentric strength(AU)

Reproducibility and criterion-related validity of the sit and reach test and toe touch test for estimating hamstring flexibility in recreationally active young adults.

OBJECTIVE: 1) to examine the test-retest reproducibility and criterion-related validity of the sit and reach test (SRT) and the toe touch test (TT) for estimating hamstring flexibility measured through the passive straight leg raise test (PSLR); and 2) to determine whether the SRT cut-off scores may be used for the TT test to identify participants in this sample of young healthy adults as having short hamstring flexibility. DESIGN: Test-retest design. SETTING: Controlled laboratory environment. PARTICIPANTS: 243 active recreationally young adults. MAIN OUTCOME MEASURES: Participants performed the SRT, the TT test and PSLR twice in a randomized order with a 4-week interval between trials. Reproducibility was examined using typical percentage error (coefficient of variation [CV]) and intraclass correlation coefficient (ICC) as well as their respective confidence limits. Regression and Kappa correlation statistical analyses were performed to study the association of the SRT and TT test with the PSLR test and the 95% limits of agreement (LoA) between SRT and TT test were calculated to explore differences in the mean differences between these measurements. RESULTS: The finding showed acceptable reproducibility measures for SRT (8.74% CV; 0.92 ICC), TT test (9.86% CV; 0.89 ICC) and PSLR (5.46% CV; 0.85 ICC). The SRT (R² = 0.63) and TT test (R² = 0.49) were significantly associated with PSLR. The 95% LoA between SRT and TT test reported systematic bias (2.84 cm) and wide 95% random error (±9.72 cm). CONCLUSIONS: Reproducibility of SRT, TT test and PSLR is acceptable and the criterion-related validity of SRT and TT test is moderate. Furthermore, the SRT cut-off scores should not be used for TT test for the detection of short hamstring muscles.

Absolute reliability of hamstring to quadriceps strength imbalance ratios calculated using peak torque, joint angle-specific torque and joint ROM-specific torque values.

The main purpose of this study was to determine the absolute reliability of conventional (H/Q(CONV)) and functional (H/Q(FUNC)) hamstring to quadriceps strength imbalance ratios calculated using peak torque values, 3 different joint angle-specific torque values (10°, 20° and 30° of knee flexion) and 4 different joint ROM-specific average torque values (0-10°, 11-20°, 21-30° and 0-30° of knee flexion) adopting a prone position in recreational athletes. A total of 50 recreational athletes completed the study. H/Q(CONV) and H/Q(FUNC) ratios were recorded at 3 different angular velocities (60, 180 and 240°/s) on 3 different occasions with a 72-96 h rest interval between consecutive testing sessions. Absolute reliability was examined through typical percentage error (CVTE), percentage change in the mean (CM) and intraclass correlations (ICC) as well as their respective confidence limits. H/Q(CONV) and H/Q(FUNC) ratios calculated using peak torque values showed moderate reliability values, with CM scores lower than 2.5%, CV(TE) values ranging from 16 to 20% and ICC values ranging from 0.3 to 0.7. However, poor absolute reliability scores were shown for H/Q(CONV) and H/Q(FUNC) ratios calculated using joint angle-specific torque values and joint ROM-specific average torque values, especially for H/Q(FUNC) ratios (CM: 1-23%; CV(TE): 22-94%; ICC: 0.1-0.7). Therefore, the present study suggests that the CV(TE) values reported for H/Q(CONV) and H/Q(FUNC) (≈18%) calculated using peak torque values may be sensitive enough to detect large changes usually observed after rehabilitation programmes but not acceptable to examine the effect of preventitive training programmes in healthy individuals. The clinical reliability of hamstring to quadriceps strength ratios calculated using joint angle-specific torque values and joint ROM-specific average torque values are questioned and should be re-evaluated in future research studies.

Criterion-related validity of four clinical tests used to measure hamstring flexibility in professional futsal players.

OBJECTIVE: To examine the criterion related validity of the sit-and-reach test (SR), toe touch test (TT), modified sit-and-reach test (MSR) and back-saver sit-and-reach test (BSSR) for estimating hamstring flexibility measured through the passive straight leg raise test (PSLR) in professional futsal players. DESIGN: Correlation laboratory study. SETTING: Controlled laboratory environment. PARTICIPANTS: One hundred and three futsal players (55 males age 26 ± 4 years, 48 females age 23 ± 5 years). MAIN OUTCOME MEASURES: Two trials of SR, TT, MSR, BSSR (left and right) and PSLR right and left (hamstring criterion measure) in a randomized order. RESULTS: Regression analysis was performed to examine the association of SR, TT, MSR and BSSR with PSLR in both males and females separately. In males, only MSR test had moderate association criterion with PSLR (R(2) = 0.57). In females, SR (R(2) = 0.86), TT (R(2) = 0.85), MSR (R(2) = 0.53) and average BSSR (R(2) = 0.82) were associated with PSLR. CONCLUSIONS: SR, TT, MSR and BSSR had moderate criterion related validity for estimating hamstring flexibility in female but not male professional futsal players. The authors recommend that researchers, clinicians, and physical therapists adopt one angular test as a measure of hamstring muscle length in futsal players.

Effect of active stretch on hip flexion range of motion in female professional futsal players.

AIM: The purpose of this study was to determine the hamstring flexibility progression through hip flexion passive range of motion before (baseline hip flexion PROM, lasting 6 weeks), during (effect of stretching program, lasting 8 weeks) and after (flexibility retention, lasting 4 weeks) an 8-week active stretching program in female professional futsal players. METHODS: Eighteen young adult professional female futsal players completed this study. An uninterrupted, longitudinal repeated-measures design was employed with participants randomly assigned into two groups: control and stretching group. The stretching group performed an 8-week active stretching program. The unilateral passive straight leg raise test was used to assess hip flexion PROM (hamstring extensibility) at 2, 4, and 6 weeks before the stretching program, at 2, 4, 6, and 8 weeks during the stretching program and at 2 and 4 weeks after the stretching program. RESULTS: The analysis of the initial phase revealed that baseline hip flexion PROM had an irregular tendency with positive and negative peak hamstring ROM. An 8-week active stretching program improved hip flexion ROM 26.0±8.8% (P<0.05). Four weeks after the stretching program ended, hip flexion PROM retention showed a significant decrease (P<0.05). CONCLUSION: The effect of acute stretching prior to intensive physical activities should be considered by strength and conditioning specialists before using this active stretching program as part of a pre-exercise warm up routine.

Functional eccentric-concentric ratio of knee extensors and flexors in pre-pubertal children, teenagers and adult males and females.

The purpose of this study was to examine the age and sex associated differences in the eccentric/concentric functional ratio for the knee. Isokinetic concentric and eccentric knee extension and flexion was measured at 0.52 rad x s (-1) and 3.14 rad x s (-1) in 121 subjects. Other than mass there were no significant age-by-sex interaction effects for all variables examined. A significant velocity-by-age group effect was demonstrated for ECC (KF)/CON (KE) with higher ratios at 3.14 compared to 0.52 rad x s (-1). Females' CON (KF)/ECC (KE) was significantly lower than males at both velocities. Adults demonstrated significantly lower CON (KF)/ECC (KE) than the teenagers at 0.52 rad x s (-1) and lower than the prepubertal and teenager groups at 3.14 rad x s (-1). However, for ECC (KF)/CON (KE) at 3.14 rad x s (-1), prepubertal ratios were significantly lower than teenagers and adults. The results of the current study suggest that functional rather than conventional ratio should be used when examining knee stability. During fast velocity movements, prepubertal children have a lower capacity for generating eccentric compared to concentric torque. The lower CON (KF)/ECC (KE) ratio in adults appears to be due to a greater ability to generate large eccentric torques at all slow and fast movement velocities. The lower CON (KF)/ECC (KE) ratio in females is a product of lower concentric torque as opposed to high eccentric torque producing capability as previously thought.

Measurement of maximal muscle cross-sectional area of the elbow extensors and flexors in children, teenagers and adults.

The aims of this study were to examine age and sex differences in elbow extensor and flexor anatomical muscle cross-sectional area (mCSA) measured by magnetic resonance imaging (MRI) and the location of maximal mCSA as a percentage of the distance from the distal to the proximal end of the humerus. Ninety-five individuals spread across the age groups 9 - 10 years, 16 - 17 years and ?21 years participated in the study. Muscle cross-sectional area derived from the manual MRI tracing proved to be highly reliable in terms of limits of agreement (-2.5 to 1.5 cm(2)) and the intraclass correlation coefficient (ICC = 0.998). A sex-by-age group analysis of variance revealed significant effects (P < 0.01) of sex, group and a sex-by-group interaction, the latter reflecting a greater increase in males than females of upper arm mCSA from childhood to adulthood. Extensor mCSA was more proximal (55 +/- 6%) than that of the flexors (28 +/- 6%). A significant effect (P < 0.01) of group was found for location of maximal extensor mCSA, reflecting its more distal position with increasing age. Measurements of muscle size should be made at the individually determined position of maximal mCSA if interpreting data collected during growth and maturation, especially if the muscle group of interest is the elbow extensors and if different age groups are being monitored.

Longitudinal changes in isokinetic leg strength in 10-14-year-olds.

This study used multilevel regression modelling to longitudinally investigate the influences of age, sex, body size, skinfold thicknesses and maturity on the development of isokinetic knee extension and flexion on eight occasions over a 4-year period. Forty-one subjects (20 boys and 21 girls) were measured and 295 isokinetic leg strength tests and associated measures were successfully completed. Subjects were aged 10.0 +/- 0.3 years at the onset of the study. Stature, body mass, triceps and subscapular skinfold thicknesses, and sexual maturation (according to pubic hair development) were assessed at each test occasion. Isokinetic concentric knee extension and flexion of the dominant leg were determined to elicit maximal peak extension (PET) and flexion torque (PFT). Statistical significance was accepted at p < 0.05. Multilevel regression modelling indicated that stature and mass were significant predictors of both PET and PFT. Age and maturity were non-significant explanatory variables once stature and mass had been accounted for. Skinfold thickness exerted a significant negative effect independent of mass and stature on PFT but not PET. At test occasion 8, cross-sectional areas (CSAs) of the knee extensors (ExCSA) and flexors (FlexCSA) were determined using magnetic resonance imaging on 23 boys and 14 girls and examined as predictors of isokinetic leg strength. There were no significant sex-related differences in PET or PFT. Pearson product moment correlation coefficients indicated a significant relationship between ExCSA and PET and FlexCSA and PFT for both boys and girls. Analysis of covariance (ANCOVA) demonstrated that ExCSA and FlexCSA were significant explanatory variables for PET and PFT, respectively, but became non-significant once stature and mass had been introduced into the analysis. To conclude, there were no significant sex differences in PET or PFT between the ages of 10 and 14 years and the development of PET and PFT could be accounted for by the increase in stature and mass. Age, maturity and thigh muscle CSA were all non-explanatory variables in the production of PET and PFT once body size had been controlled for.

Changes in short-term power output in 10- to 12-year-olds.

In this study, we used multi-level regression modelling to assess the influence of age, sex, body size, skinfold thicknesses, maturity, thigh muscle volume and isokinetic leg strength on the development of load- and inertia-adjusted peak (1 s) and mean power (30 s) determined using the Wingate anaerobic test. Fifteen males and 19 females were measured twice, first aged 10.0 +/- 0.3 years and then aged 11.8 +/- 0.3 years. Initial models identified body mass and height as significant explanatory variables (P < 0.05) for peak power and mean power, with an additional age effect for the former. No significant differences between the sexes or maturity effects were observed for either peak or mean power (P > 0.05). The introduction of sum of skinfolds improved the fit of the model and rendered the height term non-significant for both peak and mean power (P> 0.05). An age effect became apparent for mean power. When isokinetic leg strength and thigh muscle volume were entered into the model, the latter exerted a significant effect on both peak and mean power (P< 0.05), whereas isokinetic leg strength was not a significant explanatory variable for either (P> 0.05). In conclusion, thigh muscle volume exerts a positive influence on young people's short-term power output, which is additional to the effects of body mass, sum of skinfolds and age.