Tannath J. Scott

The Validity and Reliability of Global Positioning Systems in Team Sport: A Brief Review.

The use of global positioning systems (GPS) has increased dramatically over the last decade. Using signals from orbiting satellites, the GPS receiver calculates the exact position of the device and the speed at which the device is moving. Within team sports GPS devices are used to quantify the external load experienced by an athlete, allowing coaches to better manage trainings loads and potentially identify athletes who are overreaching or overtraining. This review aims to collate all studies that have tested either (or both) the validity or reliability of GPS devices in a team sport setting, with a particular focus on (a) measurements of distance, speed, velocities, and accelerations across all sampling rates and (b) accelerometers, player/body load and impacts in accelerometer-integrated GPS devices. A comprehensive search of the online libraries identified 22 articles that fit search criteria. The literature suggests that all GPS units, regardless of sampling rate, are capable of tracking athletes distance during team sport movements with adequate intraunit reliability. One Hertz and 5Hz GPS units have limitations in their reporting of distance during high-intensity running, velocity measures, and short linear running (particularly those involving changes of direction), although these limitations seem to be overcome during measures recorded during team sport movements. Ten Hertz GPS devices seem the most valid and reliable to date across linear and team sport simulated running, overcoming many limitations of earlier models, whereas the increase to 15Hz GPS devices have had no additional benefit.

Contributing Factors to Change-of-Direction Ability in Professional Rugby League Players.

Abstract Delaney, JA, Scott, TJ, Ballard, DA, Duthie, GM, Hickmans, JA, Lockie, RG, and Dascombe, BJ. Contributing factors to change-of-direction ability in professional rugby league players. J Strength Cond Res 29(10): 2688–2696, 2015—Rugby league is an intermittent team sport in which players are regularly required to accelerate, decelerate, and change direction rapidly. This study aimed to determine the contributing factors to change-of-direction (COD) ability in professional rugby league players and to validate the physical and physiological components of a previously proposed COD ability predictor model. Thirty-one male professional rugby league players (age: 24.3 ± 4.4 years; height: 1.83 ± 0.06 m; body mass: 98.1 ± 9.8 kg) were assessed for anthropometry, linear speed, various leg muscle qualities, and COD ability. Change-of-direction ability was assessed for both the dominant (D) and nondominant (ND) legs using the 505 test. Stepwise multiple regression analyses determined the combined effect of the physical and physiological variables on COD ability. Maximal linear speed (SpMax) and relative squat strength (squat:BM) explained 61% of the variance in 505-D performance, whereas measures of mass, unilateral, and bilateral power contributed 67% to 505-ND performance. These results suggest that the 505-ND task was heavily dependent on relative strength and power, whereas the 505-D task was best predicted by linear sprint speed. Second, the physical component of the COD predictor model demonstrated poor correlations (r = −0.1 to −0.5) between absolute strength and power measures and COD ability. When made relative to body mass, strength and power measures and COD ability shared stronger relationships (r = −0.3 to −0.7). Change-of-direction ability in professional rugby league players would be best improved through increases in an athletes strength and power while maintaining lean muscle mass.

Reliability and Usefulness of the 30-15 Intermittent Fitness Test in Rugby League

Abstract Scott, TJ, Delaney, JA, Duthie, GM, Sanctuary, CE, Ballard, DA, Hickmans, JA, and Dascombe, BJ. Reliability and usefulness of the 30-15 Intermittent Fitness Test in rugby league. J Strength Cond Res 29(7): 1985–1990, 2015—This study examined the reliability and usefulness of the 30-15 Intermittent Fitness Test (30-15IFT) within rugby league. Fifty-five young rugby league players participated in the study. These included representative players from Under 16s (n = 19; 15.6 ± 0.3 years; 78.1 ± 10.9 kg), Under 18s (n = 21; 17.4 ± 0.5 years; 86.9 ± 11.2 kg), and Under 20s (n = 15; 19.4 ± 0.5 years; 95.9 ± 8.7 kg) squads within a professional rugby league club. Players performed the 30-15IFT twice within 9 days of each other. Maximal intermittent running velocity (VIFT) and heart rate at exhaustion (HRpeak) were collected for both tests. Intraclass correlation coefficients (ICCs) for the “Combined” and Under 20s were very large (r > 0.7), whereas the ICCs for Under 16s and Under 18s were almost perfect (r > 0.9). Coefficients of variation were 1.9% (95% confidence interval, 1.6–2.4) for the combined test-retest of the 30-15IFT and 0.6% (0.5–1.0) for HRpeak. As the typical error of measurement (TE) (0.36 km·h−1) was greater than the smallest worthwhile change (SWC) (0.21 km·h−1) value, the usefulness of the VIFT was rated as “marginal.” The TE for HRpeak was similar to the SWC, rating the usefulness of this variable as “OK.” Despite the usefulness of the 30-15IFT being deemed Marginal, a change as small as 0.5 km·h−1 (1 stage) in VIFT could be considered substantial or “real.” As a consequence, the 30-15IFT presents as both a reliable and useful field test in the assessment of intermittent fitness for rugby league players.

Establishing Duration-Specific Running Intensities From Match-Play Analysis in Rugby League

UNLABELLED Rugby league coaches often prescribe training to replicate the demands of competition. The intensities of running drills are often monitored in comparison with absolute match-play measures. Such measures may not be sensitive enough to detect fluctuations in intensity across a match or to differentiate between positions. PURPOSE To determine the position- and duration-specific running intensities of rugby league competition, using a moving-average method, for the prescription and monitoring of training. METHODS Data from a 15-Hz global positioning system (GPS) were collected from 32 professional rugby league players across a season. The velocity-time curve was analyzed using a rolling-average method, where maximum values were calculated for 10 different durations, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10 min, for each player across each match. RESULTS There were large differences between the 1- and 2-min rolling averages and all other rolling-average durations. Smaller differences were observed for rolling averages of greater duration. Fullbacks maintained a greater velocity than outside backs and middle and edge forwards over the 1- and 2-min rolling averages (ES 0.8-1.2, P < .05). For rolling averages 3 min and greater, the running demands of the fullbacks were greater than those of the middle forwards and outside backs (ES 1.1-1.4, P < .05). CONCLUSIONS These findings suggest that the running demands of rugby league fluctuate vastly across a match. Fullbacks were the only position to exhibit a greater running intensity than any other position, and therefore training prescription should reflect this.

Do players and staff sleep more during the pre- or competitive season of elite rugby league?

Abstract This study establishes the sleep behaviour of players and staff during the pre- and competitive seasons of elite rugby league. For seven days during both the pre- and competitive seasons, seven rugby league players and nine full-time staff from one professional Australian rugby league club had their sleep monitored via wrist actigraphy and self-report sleep diaries. Two-way repeated measures analysis of variance determined differences between the pre- and competitive season in players and staff, with effect sizes (ES) used to interpret the practical magnitude of differences. Findings show an earlier bed time and wake time for players (−34 min, ES = 1.5; ±0.5 and −39 min, 2.1; ±0.5 respectively) and staff (−29 min, ES = 0.8; ±0.3 and −35 min, ES = 1.7; ±0.4 respectively) during pre-season when compared to the competitive season. Despite this, no differences were seen when considering the amount of time in bed, sleep duration or sleep efficiency obtained between the pre- and competitive seasons. Our results suggest that early morning training sessions scheduled during pre-season advances wake time in elite rugby league. However, both players and staff can aim to avoid reductions in sleep duration and sleep efficiency with subsequent adjustment of night time sleep patterns. This may be particularly pertinent for staff, who wake earlier than players during both the pre- and competitive seasons.

Validity of Skinfold-Based Measures for Tracking Changes in Body Composition in Professional Rugby League Players

UNLABELLED High levels of lean mass are important in collision-based sports for the development of strength and power, which may also assist during contact situations. While skinfold-based measures have been shown to be appropriate for cross-sectional assessments of body composition, their utility in tracking changes in lean mass is less clear. PURPOSE To determine the most effective method of quantifying changes in lean mass in rugby league athletes. METHODS Body composition of 21 professional rugby league players was assessed on 2 or 3 occasions separated by ≥6 wk, including bioelectrical impedance analysis (BIA), lean-mass index (LMI), and a skinfold-based prediction equation (SkF). Dual-X-ray absorptiometry provided a criterion measure of fat-free mass (FFM). Correlation coefficients (r) and standard errors of the estimate (SEE) were used as measures of validity for the estimates. RESULTS All 3 practical estimates exhibited strong validity for cross-sectional assessments of FFM (r > .9, P < .001). The correlation between change scores was stronger for the LMI (r = .69, SEE 1.3 kg) and the SkF method (r = .66, SEE = 1.4 kg) than for BIA (r = .50, SEE = 1.6 kg). CONCLUSIONS The LMI is probably as accurate in predicting changes in FFM as SkF and very likely to be more appropriate than BIA. The LMI offers an adequate, practical alternative for assessing in FFM among rugby league athletes.

Does self-perceived sleep reflect sleep estimated via activity monitors in professional rugby league athletes?

ABSTRACT This study examined agreement between self-perceived sleep and sleep estimated via activity monitors in professional rugby league athletes. 63 athletes, from three separate teams wore actigraphy monitors for 10.3 ± 3.9 days. During the monitoring period, ratings of perceived sleep quality (on a 1–5 and 1–10 Likert scale), and an estimate of sleep duration were recorded daily. Agreement between sleep estimated via activity monitors and self-perceived sleep was examined using mean bias, Pearson correlation (r) and typical error of the estimate (TEE). 641 nights of sleep were recorded, with a very large, positive correlation observed between sleep duration estimated via activity monitors and subjective sleep duration (r = 0.85), and a TEE of 48 minutes. Mean bias revealed subjective sleep duration overestimated sleep by an average of 19.8 minutes. The relationship between sleep efficiency estimated via activity monitors and self-perceived sleep quality on a 1–5 (r = 0.22) and 1–10 Likert scale (r = 0.28) was limited. The outcomes of this investigation support the use of subjective measures to monitor sleep duration in rugby league athletes when objective means are unavailable. However, practitioners should be aware of the tendency of athletes to overestimate sleep duration.

The validity and contributing physiological factors to 30-15 Intermittent Fitness Test performance in Rugby League.

Abstract Scott, TJ, Duthie, GM, Delaney, JA, Sanctuary, CE, Ballard, DA, Hickmans, JA, and Dascombe, BJ. The validity and contributing physiological factors to 30-15 intermittent fitness test performance in rugby league. J Strength Cond Res 31(9): 2409–2416, 2017—This study examined the validity of the 30-15 Intermittent Fitness Test (30-15IFT) within rugby league. Sixty-three Australian elite and junior-elite rugby league players (22.5 ± 4.5 years, 96.1 ± 9.5 kg, &Sgr;7 skinfolds: 71.0 ± 18.7 mm) from a professional club participated in this study. Players were assessed for anthropometry (body mass, &Sgr;7 skinfolds, lean mass index), prolonged high-intensity intermittent running (PHIR; measured by 30-15IFT), predicted aerobic capacity (MSFT) and power (AAS), speed (40 m sprint), repeated sprint, and change of direction (COD—505 agility test) ability before and after an 11-week preseason training period. Validity of the 30-15IFT was established using Pearsons coefficient correlations. Forward stepwise regression model identified the fewest variables that could predict individual final velocity (V IFT) and change within 30-15IFT performance. Significant correlations between V IFT and &Sgr;7 skinfolds, repeated sprint decrement, V[Combining Dot Above]O2maxMSFT, and average aerobic speed were observed. A total of 71.8% of the adjusted variance in 30-15IFT performance was explained using a 4-step best fit model (V[Combining Dot Above]O2maxMSFT, 61.4%; average aerobic speed, 4.7%; maximal velocity, 4.1%; lean mass index, 1.6%). Across the training period, 25% of the variance was accounted by &Dgr;V[Combining Dot Above]O2maxMSFT (R 2 = 0.25). These relationships suggest that the 30-15IFT is a valid test of PHIR within rugby league. Poor correlations were observed with measures of acceleration, speed, and COD. These findings demonstrate that although the 30-15IFT is a valid measure of PHIR, it also simultaneously examines various physiological capacities that differ between sporting cohorts.

Intra-individual variability in the sleep of senior and junior rugby league athletes during the competitive season

ABSTRACT This study examined the sleep intra-individual variability (IIV) of rugby league athletes across senior and junior levels during one week of the competitive season. Forty-five rugby league athletes across elite senior, sub-elite senior and elite junior levels each wore actigraphy monitors for seven days during the competitive season, and completed a subjective sleep diary each morning upon waking. Linear mixed models were used to assess differences in sleep measures between playing levels. Intra-individual standard deviations for each sleep measure were calculated for each athlete to determine their respective IIV, allowing differences in IIV between groups to be assessed. Elite junior athletes went to bed later (ES = 0.94 ± 0.50, p < 0.05) and woke later than elite senior athletes (ES = 0.94 ± 0.40, p < 0.05), while also displaying greater IIV when considering time in bed (ES = 1.14 ± 0.60, p < 0.05) and sleep duration (ES = 1.53 ± 0.64, p < 0.05) compared with elite senior athletes. Similarly, IIV was more pronounced in elite junior players for time in bed (ES = 0.88 ± 0.60, p < 0.05) and sleep duration (ES = 1.03 ± 0.64, p < 0.05) compared with sub-elite senior athletes. Despite this, elite junior athletes still obtained sufficient sleep duration, efficiency and quality. The outcomes of this investigation show a distinct difference in the habitual sleep-wake patterns of senior and junior rugby league athletes, and show how sleep IIV differs between playing levels in rugby league.

Running momentum: a new method to quantify prolonged high-intensity intermittent running performance in collision sports

ABSTRACT Purpose: This study determined differences in prolonged high-intensity running (PHIR) performance and running momentum (pIFT) between competition levels and positional groups in rugby league. Methods: Elite Australian National Rugby League (NRL), sub-elite [state-based competition (SRL); National Youth Competition (NYC); local league (LL)] and junior-elite (U18; U16) rugby league players completed the 30–15 Intermittent Fitness Test (30–15IFT) to quantify PHIR performance. Final running momentum (pIFT; kg·m∙s−1) was calculated as the product of body mass and final running velocity (VIFT; m∙s−1). Effect sizes (ESs) were used to examine between-group differences. Results: 30–15IFT performance was possibly to likely higher in NRL players (19.5 ± 1.0 km·h−1; mean ± SD) when compared with SRL (ES = 0.6 ± 0.5; ES ± CI), NYC (ES = 0.6 ± 0.5) and U18 (ES = 0.8 ± 0.5) players. NRL players (537 ± 41 kg·m·s−1) possessed possibly to very likely greater pIFT than SRL (ES = 0.7 ± 0.5), NYC (ES = 1.2 ± 0.5), U18 (ES = 2.3 ± 0.6), U16 (ES = 3.0 ± 0.7) and LL players (ES = 2.0 ± 0.7). Middle forwards attained a likely superior pIFT (ES = 0.5 − 1.8) to all other positional groups. Conclusions: This study demonstrated that elite rugby league players possess superior PHIR capacities, whilst highlighting that pIFT can account for the disparities in body mass between groups.