Quantifying external load in Australian football matches and training using accelerometers.

PURPOSE: To describe the external load of Australian football matches and training using accelerometers. METHODS: Nineteen elite and 21 subelite Australian footballers wore accelerometers during matches and training. Accelerometer data were expressed in 2 ways: from all 3 axes (player load; PL) and from all axes when velocity was below 2 m/s (PLSLOW). Differences were determined between 4 playing positions (midfielders, nomadics, deeps, and ruckmen), 2 playing levels (elite and subelite), and matches and training using percentage change and effect size with 90% confidence intervals. RESULTS: In the elite group, midfielders recorded higher PL than nomadics and deeps did (8.8%, 0.59 ± 0.24; 34.2%, 1.83 ± 0.39 respectively), and ruckmen were higher than deeps (37.2%, 1.27 ± 0.51). Elite midfielders, nomadics, and ruckmen recorded higher PLSLOW than deeps (13.5%, 0.65 ± 0.37; 11.7%, 0.55 ± 0.36; and 19.5%, 0.83 ± 0.50, respectively). Subelite midfielders were higher than nomadics, deeps, and ruckmen (14.0%, 1.08 ± 0.30; 31.7%, 2.61 ± 0.42; and 19.9%, 0.81 ± 0.55, respectively), and nomadics and ruckmen were higher than deeps for PL (20.6%, 1.45 ± 0.38; and 17.4%, 0.57 ± 0.55, respectively). Elite midfielders, nomadics, and ruckmen recorded higher PL (7.8%, 0.59 ± 0.29; 12.9%, 0.89 ± 0.25; and 18.0%, 0.67 ± 0.59, respectively) and PLSLOW (9.4%, 0.52 ± 0.30; 11.3%, 0.68 ± 0.25; and 14.1%, 0.84 ± 0.61, respectively) than subelite players. Small-sided games recorded the highest PL and PLSLOW and were the only training drill to equal or exceed the load from matches across positions and playing levels. CONCLUSION: PL differed between positions, with midfielders the highest, and between playing levels, with elite higher. Differences between matches and training were also evident, with PL from small-sided games equivalent to or higher than matches.

The reliability of MinimaxX accelerometers for measuring physical activity in Australian football.

PURPOSE: To assess the reliability of triaxial accelerometers as a measure of physical activity in team sports. METHODS: Eight accelerometers (MinimaxX 2.0, Catapult, Australia) were attached to a hydraulic universal testing machine (Instron 8501) and oscillated over two protocols (0.5 g and 3.0 g) to assess within- and between device reliability. A static assessment was also conducted. Secondly, 10 players were instrumented with two accelerometers during Australian football matches. The vector magnitude was calculated, expressed as Player load and assessed for reliability using typical error (TE) ± 90% confidence intervals (CI), and expressed as a coefficient of variation (CV%). The smallest worthwhile difference (SWD) in Player load was calculated to determine if the device was capable of detecting differences in physical activity. RESULTS: Laboratory: Within- (Dynamic: CV 0.91 to 1.05%; Static: CV 1.01%) and between-device (Dynamic: CV 1.02 to 1.04%; Static: CV 1.10%) reliability was acceptable across each test. Field: The between-device reliability of accelerometers during Australian football matches was also acceptable (CV 1.9%). The SWD was 5.88%. CONCLUSIONS: The reliability of the MinimaxX accelerometer is acceptable both within and between devices under controlled laboratory conditions, and between devices during field testing. MinimaxX accelerometers can be confidently utilized as a reliable tool to measure physical activity in team sports across multiple players and repeated bouts of activity. The noise (CV%) of Player load was lower than the signal (SWD), suggesting that accelerometers can detect changes or differences in physical activity during Australian football.

The validity and reliability of GPS units for measuring distance in team sport specific running patterns.

PURPOSE: To assess the validity and reliability of distance data measured by global positioning system (GPS) units sampling at 1 and 5 Hz during movement patterns common to team sports. METHODS: Twenty elite Australian Football players each wearing two GPS devices (MinimaxX, Catapult, Australia) completed straight line movements (10, 20, 40 m) at various speeds (walk, jog, stride, sprint), changes of direction (COD) courses of two different frequencies (gradual and tight), and a team sport running simulation circuit. Position and speed data were collected by the GPS devices at 1 and 5 Hz. Distance validity was assessed using the standard error of the estimate (±90% confidence intervals [CI]). Reliability was estimated using typical error (TE) ± 90% CI (expressed as coefficient of variation [CV]). RESULTS: Measurement accuracy decreased as speed of locomotion increased in both straight line and the COD courses. Difference between criterion and GPS measured distance ranged from 9.0% to 32.4%. A higher sampling rate improved validity regardless of distance and locomotion in the straight line, COD and simulated running circuit trials. The reliability improved as distance traveled increased but decreased as speed increased. Total distance over the simulated running circuit exhibited the lowest variation (CV 3.6%) while sprinting over 10 m demonstrated the highest (CV 77.2% at 1 Hz). CONCLUSION: Current GPS systems maybe limited for assessment of short, high speed straight line running and efforts involving change of direction. An increased sample rate improves validity and reliability of GPS devices.

Variability of GPS units for measuring distance in team sport movements.

PURPOSE: To examine the difference in distance measured by two global positioning system (GPS) units of the same model worn by the same player while performing movements common to team sports. METHODS: Twenty elite Australian football players completed two trials of the straight line movement (10, 20, 40 m) at four speeds (walk, jog, stride, sprint), two trials of the changes of direction (COD) courses of two different frequencies (gradual and tight), and five trials of a team sport running simulation circuit. To assess inter-unit variability for total and high intensity running (HIR) distance measured in matches, data from eight field players were collected in three Australian Hockey League (AHL) matches during the 2009 season. Each subject wore two GPS devices (MinimaxX v2.5, Catapult, Australia) that collected position data at 5 Hz for each movement and match trial. The percentage difference ±90% confidence interval (CI) was used to determine differences between units. RESULTS: Differences (±90% CI) between the units ranged from 9.9 ± 4.7% to 11.9 ± 19.5% for straight line running movements and from 9.5 ± 7.2% to 10.7 ± 7.9% in the COD courses. Similar results were exhibited in the team sport circuit (11.1 ± 4.2%). Total distance (10.3 ± 6.2%) and HIR distance (10.3 ± 15.6) measured during the match play displayed similar variability. CONCLUSION: It is recommended that players wear the same GPS unit for each exercise session to reduce measurement error. The level of between-unit measurement error should be considered when comparing results from players wearing different GPS units.

Cytogenetic analysis of a hemosiderotic fibrolipomatous tumor.

Hemosiderotic fibrolipomatous tumor is an extremely rare, nonencapsulated, fatty lesion with a consistent histologic appearance that was originally considered reactive in nature. To our knowledge, there are no previous reports on the cytogenetics of this lesion. Reported here is a case of hemosiderotic fibrolipomatous tumor arising within the subcutaneous tissue of the right foot, dorsal aspect, of an otherwise healthy 35-year-old woman. Subsequent cytogenetic analysis revealed a clonal reciprocal translocation between chromosomes 1 and 10, with a further rearrangement involving this derivative chromosome 1 and chromosome 3. This, in addition to its characteristic morphology and immunophenotype, supports the neoplastic nature of this tumor and may aid in its diagnosis.

Meiotic exchange event within the stalk region of an inverted chromosome 22 results in a recombinant chromosome with duplication of the distal long arm.

Meiotic recombination occurs between homologous euchromatic regions of human chromosomes in early meiosis. However, such exchanges have been thought not to occur in the stalk regions of acrocentric chromosomes. We describe a child whose chromosome analysis suggests that crossovers do occur in homologous stalk regions. The proband, initially seen as a term female infant, was born to a 28-year-old mother. Dysmorphic features included wide metopic sutures, low anterior hairline, hypertelorism, external ear malformations, and cleft lip and palate. Blood chromosomes of the proband and parents were studied by G-banding, Q-banding, R-banding, and silver staining. The infant karyotype showed a sub-metacentric chromosome 22; that of the mother showed a pericentric inversion of chromosome 22. Chromosomes of the father were normal. In the infant, the abnormal chromosome 22 long arm appeared normal, but with additional long arm material attached to the distal short arm. In the mother, the distal long arm of the abnormal chromosome 22 was translocated to the distal short arm. The abnormal chromosome stalk in the child was intermediate in size to the stalk size of the abnormal and normal chromosomes 22 in the mother. Fluorescent in situ hybridization (FISH) analysis using chromosome 22 paint and ARSA gene probe confirmed that the duplicated material in the proband was of chromosome 22 origin; the karyotype interpretation is: 46,XX,rec(22)dup(22q)inv(22)(p13q13.1)mat. This abnormal karyotype is most likely due to a crossover event within the inversion loop during meiosis. The stalk length discrepancy suggests that the crossover site occurred in the stalk region.

Y chromosome heterochromatin of differing lengths in two cell populations of the same individual.

OBJECTIVE: To present a prenatal diagnosis report on a case where G-banding analysis of fetal metaphase chromosomes showed populations of cells with two different Y chromosomes; one with a short block of heterochromatin (Yqh-) and one with a longer block of heterochromatin (Yqh+). METHODS: These two populations of the Y chromosome were studied using fluorescent quinacrine banding and fluorescent in situ hybridization (FISH). A chromosome paint corresponding to the euchromatic region of the Y chromosome, and probes corresponding to the SRY, DYZ1, and DYZ3 regions were used for this study. RESULTS: Both Y chromosomes appeared to be structurally normal by these analyses. Subsequent ultrasound examination at 20 weeks' gestation revealed normal male genitalia. Follow-up with a neonatal blood sample analysis confirmed the above findings. CONCLUSIONS: This study reports a direct prenatal diagnosis case of two populations of the Y chromosome in the same individual. This apparent mosaicism may be explained by a postzygotic simple deletion or unequal crossover event between sister chromatids in the DYZ region.