Bartholomew Kay

Physical demands of elite Rugby League referees: Part one — time and motion analysis

The purpose of the present study was to accurately and reliably analyse the nature of movement undertaken by National Rugby League (NRL) referees during matches played in the 2000 season. The movements of NRL referees (n=5) were analysed from videotape footage of ten games. The researchers assigned each movement to one of six defined categories (stationary, walking forwards, jogging forwards, sprinting, sideways, and backwards), and recorded number of repetitions, movement durations, and distances covered during each specific movement category. Distance was estimated using on-field markings as known points. Mean total distance per game was 6.7 km +/- 0.4 km (mean +/- standard deviation), and was made up of approximately 940 movements per game. The data showed 87% of distance was made up of a cyclic activity comprising jogging forwards, then backwards at mean running speeds of 7.2 km x h(-1) and 10.8 km x h(-1) respectively (made up of 9s bursts on average, each separated by 3s breaks). However, this cyclic activity accounted for only 47% of time, as referees were stationary 41% of time. Play was continuous for 90s +/- 71s at each phase of play, and was followed by rest of 45s +/- 36s throughout matches (work to rest ratio was 2:1). These findings suggest Rugby League refereeing is a highly intermittent activity and therefore training and fitness assessments should reflect these specific demands experienced during a game.

Low reproducibility of many lactate markers during incremental cycle exercise

Reports on reproducibility of lactate markers usually considered only two trials. The authors assessed reproducibility of power output at seven markers in 11 fit subjects over at least six trials under tightly controlled conditions. Subjects undertook incremental exercises (50 W start, +50 W every 3 min to exhaustion) on a cycle ergometer. At each trial blood lactate concentration was determined at rest and within the final 30 s of each stage. The Rest+1, 2.0 and 4.0 mmol/l markers were determined by interpolation, the D-max and nadir using a quadratic model and the lactate slope index using an exponential plus constant model, and a visual turnpoint was determined empirically. Intraclass correlations and coefficients of variation assessed reproducibility. Power output at all markers differed significantly between subjects, but not between trials. Intraclass correlation coefficients were respectively 0.799, 0.794, 0.807, 0.903, 0.677, 0.769 and 0.648, and corresponding standard errors of measurement 11.9, 9.2, 9.1, 2.5, 9.2, 10.8 and 24.7 W. Statistical powers of detecting a 30 W increment at these markers were 0.30, 0.43, 0.42, 0.98, 0.58, 0.38 and 0.18 respectively. These results indicate that only the D-max marker has good reproducibility and that it alone can identify small but meaningful changes in training status with sufficient statistical power.

The ongoing discussion regarding standard deviation and standard error

As a nonstatistician, I have watched the discussion on this topic with interest ([1][1]–[8][2]). Dr. Curren-Everett and others make a clear statement that variability of results should always be reported using the standard deviation (SD) and not the standard error (SE). Others cited above

Common misconceptions perpetuated

Morton and others ([15][1]) have recently investigated the prevalence of some common misconceptions in sport exercise science students to assess current teaching strategies. Those authors provided students with 10 multiple-choice questions and indicated the “correct” answers in their article. I