Grant Trewartha

The physical demands of elite English rugby union

Abstract The aim of this study was to assess the physical demands of elite English rugby union match-play. Player movements were captured by five distributed video cameras and then reconstructed on a two-dimensional plane representing the pitch. Movements based on speeds were categorized as standing, walking, jogging, and medium-intensity running (low-intensity activity), and high-intensity running, sprinting, and static exertion (scrummaging, rucking, mauling, and tackling) (high-intensity activity). Position groups were defined as forwards (tight and loose) and backs (inside and outside). Backs travelled more total distance than forwards (6127 m, s = 724 vs. 5581 m, s = 692; P < 0.05) and greater distances in walking (2351 m, s = 287 vs. 1928 m, s = 2342; P < 0.001) and high-intensity running (448 m, s = 149 vs. 298 m, s = 107; P < 0.05). Forwards performed more high-intensity activity than backs (9:09 min:s, s = 1:39 vs. 3:04 min:s, s = 1:01; P < 0.001), which was attributable to more time spent in static exertion (7:56 min:s, s = 1:56 vs. 1:18 min:s, s = 0:30; P < 0.001), although backs spent more time in high-intensity running (0:52 min:s, s = 0:19 vs. 1:19 min:s, s = 0:26; P = 0.004). Players travelled a greater distance in the first 10 min compared with 50–60 and 70–80 min, but there was no difference in the amount of high-intensity activity performed during consecutive 10-min periods during match-play. These results show the differing physical demands between forwards and backs with no evident deterioration in high-intensity activity performed during match-play.

Choice of sprint start performance measure affects the performance-based ranking within a group of sprinters: which is the most appropriate measure?

Sprint start performance has previously been quantified using several different measures. This study aimed to identify whether different measures could influence the performance-based ranking within a group of 12 sprinters, and if so, to identify the most appropriate measure. None of the 10 performance measures ranked all sprinters in the same order; Spearmans rho correlations between different block phase measures ranged from 0.50 to 0.94, and between block phase measures and those obtained beyond block exit from 0.66 to 0.85. Based on the consideration of what each measure quantifies, normalised average horizontal external power was identified as the most appropriate, incorporating both block velocity and the time spent producing this velocity. The accuracy with which these data could be obtained in an externally valid field setting was assessed against force platform criterion data. For an athlete producing 678 ± 40 W of block power, a carefully set-up manual high-speed video analysis protocol produced systematic and random errors of +5 W and ± 24 W, respectively. Since the choice of performance measure could affect the conclusions drawn from a technique analysis, for example the success of an intervention, it is proposed that external power is used to quantify start performance.

Match injuries in English youth academy and schools rugby union: an epidemiological study.

Background: Numerous injury epidemiology studies have reported injury patterns in senior rugby union, but investigations in youth rugby are limited. Purpose: To describe the nature of injuries resulting from match play within the English youth rugby union, including a comparison between 2 levels of play within the same age group: professional academy versus school rugby. Study Design: Cohort study; Level of evidence, 2. Methods: A 2-season (2006-2007 and 2007-2008) study obtained information on injuries sustained in male youth rugby union players (age, 16-18 years) from 12 English Premiership academies (n = 250) and 7 schools (n = 222). Match exposure (player-hours) and injury details were recorded. Results: Match injury incidence was 47 per 1000 player-hours for the academy and 35 per 1000 player-hours for the school groups; these rates were statistically different (P = .026). The most common injury site was the lower limb and the most common injury type was a ligament sprain, with injuries to the knee and shoulder region resulting in the greatest burden of injury for both groups. The tackle event was the most common cause of match injury for both academy (51% of injuries) and school (57% of injuries) groups. Conclusion: Overall, the incidence of injury for youth rugby was lower than for previous studies in senior rugby, but injury patterns (location, type) and causes were similar. The study confirmed that match injury incidence was significantly greater in elite academy youth rugby union than schools rugby. The results suggest that the specific focus for injury risk management in youth rugby should be on players’ tackle technique and prevention strategies for knee and shoulder injuries.

The Influence of In-Season Training Loads on Injury Risk in Professional Rugby Union.

PURPOSE To explore the association between in-season training-load (TL) measures and injury risk in professional rugby union players. METHODS This was a 1-season prospective cohort study of 173 professional rugby union players from 4 English Premiership teams. TL (duration × session-RPE) and time-loss injuries were recorded for all players for all pitch- and gym-based sessions. Generalized estimating equations were used to model the association between in-season TL measures and injury in the subsequent week. RESULTS Injury risk increased linearly with 1-wk loads and week-to-week changes in loads, with a 2-SD increase in these variables (1245 AU and 1069 AU, respectively) associated with odds ratios of 1.68 (95% CI 1.05-2.68) and 1.58 (95% CI 0.98-2.54). When compared with the reference group (<3684 AU), a significant nonlinear effect was evident for 4-wk cumulative loads, with a likely beneficial reduction in injury risk associated with intermediate loads of 5932-8651 AU (OR 0.55, 95% CI 0.22-1.38) (this range equates to around 4 wk of average in-season TL) and a likely harmful effect evident for higher loads of >8651 AU (OR 1.39, 95% CI 0.98-1.98). CONCLUSIONS Players had an increased risk of injury if they had high 1-wk cumulative loads (1245 AU) or large week-to-week changes in TL (1069 AU). In addition, a U-shaped relationship was observed for 4-wk cumulative loads, with an apparent increase in risk associated with higher loads (>8651 AU). These measures should therefore be monitored to inform injury-risk-reduction strategies.

Effects of carbohydrate and caffeine ingestion on performance during a rugby union simulation protocol.

Abstract In this study, we investigated the effect of ingesting carbohydrate alone or with caffeine on performance of a rugby union-specific shuttle running protocol. On three occasions, at least one week apart in a counterbalanced trial order, eight male rugby union forwards ingested either placebo or carbohydrate (1.2 g · kg−1 body mass · h−1) before and during a rugby union-specific protocol, with pre-exercise caffeine ingestion (4 mg · kg−1) before one of the carbohydrate trials (carbohydrate + caffeine). The intermittent exercise protocol included walking, jogging, and cruising at pre-determined intensities, simulated contact events, a sustained high-intensity test of speed and agility (Performance Test), and a 15-m sprint. Ratings of perceived exertion (RPE) were recorded every 5 min and a motor skills test was performed after each 21-min block. Performance Test times were not significantly different between trials but the likelihood of 2% improvements for carbohydrate + caffeine over placebo and carbohydrate were 98% and 44%, respectively. For carbohydrate + caffeine, 15-m sprints were faster than for placebo (P=0.05) and the motor skills test was performed faster in the carbohydrate + caffeine trial than the carbohydrate and placebo trials (P < 0.05), while RPE was lower in the carbohydrate + caffeine trial than the carbohydrate and placebo trials (P < 0.05). The results indicate a likely benefit to rugby performance following co-ingestion of carbohydrate and caffeine.

Could intra-tendinous hyperthermia during running explain chronic injury of the human Achilles tendon?

Chronic tendinopathy of the human Achilles tendon (AT) is common but its injury mechanism is not fully understood. It has been hypothesised that heat energy losses from the AT during running could explain the degeneration of AT material seen with injury. A mathematical model of AT temperature distribution was used to predict what temperatures the core of the AT could reach during running. This model required input values for mechanical properties of the AT (stiffness, hysteresis, cross-sectional area (CSA), strain during running) which were determined using a combination of ultrasound imaging, kinematic and kinetic data. AT length data were obtained during hopping and treadmill running (12 kmph) using ultrasound images of the medial gastrocnemius (50 Hz) and kinematic data (200 Hz). AT force data were calculated from inverse dynamics during hopping and combined with AT length data to compute AT stiffness and hysteresis. AT strain was computed from AT length data during treadmill running. AT CSA was measured on transverse ultrasound scans of the AT. Mean ± sd tendon properties were: stiffness = 176 ± 41 Nmm(-1), hysteresis =17 ± 12%, strain during running =3.5 ± 1.8% and CSA = 42 ± 8 mm(2). These values were input into the model of AT core temperature and this was predicted to reach at least 41°C during running. Such temperatures were deemed to be conservative estimates but still sufficient for tendon hyperthermia to be a potential cause of tendon injury.

Professional Rugby Union players have a 60% greater risk of time loss injury after concussion: a 2-season prospective study of clinical outcomes

Aim To investigate incidence of concussion, clinical outcomes and subsequent injury risk following concussion. Methods In a two-season (2012/2013, 2013/2014) prospective cohort study, incidence of diagnosed match concussions (injuries/1000 h), median time interval to subsequent injury of any type (survival time) and time spent at each stage of the graduated return to play pathway were determined in 810 professional Rugby Union players (1176 player seasons). Results Match concussion incidence was 8.9/1000 h with over 50% occurring in the tackle. Subsequent incidence of any injury for players who returned to play in the same season following a diagnosed concussion (122/1000 h, 95% CI 106 to 141) was 60% higher (IRR 1.6, 95% CI 1.4 to 1.8) than for those who did not sustain a concussion (76/1000 h, 95% CI 72 to 80). Median time to next injury following return to play was shorter following concussion (53 days, 95% CI 41 to 64) than following non-concussive injuries (114 days, 95% CI 85 to 143). 38% of players reported recurrence of symptoms or failed to match their baseline neurocognitive test during the graduated return to play protocol. Summary and conclusions Players who returned to play in the same season after a diagnosed concussion had a 60% greater risk of time-loss injury than players without concussion. A substantial proportion of players reported recurrence of symptoms or failed to match baseline neurocognitive test scores during graduated return to play. These data pave the way for trials of more conservative and comprehensive graduated return to play protocols, with a greater focus on active rehabilitation.

Differential strain patterns of the human Achilles tendon determined in vivo with freehand three-dimensional ultrasound imaging

SUMMARY The human Achilles tendon (AT) has often been considered to act as a single elastic structure in series with the muscles of the triceps surae. As such it has been commonly modelled as a Hookean spring of uniform stiffness. However, the free AT and the proximal AT have distinctly different structures that lend themselves to different elastic properties. This study aimed to use three-dimensional freehand ultrasound imaging to determine whether the proximal AT and the free AT exhibit different elastic behaviour during sub-maximal, fixed-end contractions of the triceps surae. Six male and five female participants (mean ± s.d. age=27±5 years) performed fixed position contractions of the plantar-flexors on an isokinetic dynamometer at 50% of their maximum voluntary contraction in this position. Freehand three-dimensional ultrasound imaging was used to reconstruct the free-tendon and proximal AT at rest and during contraction. The free-tendon exhibited significantly (P=0.03) greater longitudinal strain (5.2±1.7%) than the proximal AT (2.6±2.0%). The lesser longitudinal strain of the proximal AT was linked to the fact that it exhibited considerable transverse (orthogonal to the longitudinal direction) strains (5.0±4%). The transverse strain of the proximal AT is likely due to the triceps surae muscles bulging upon contraction, and thus the level of bulging may influence the elastic behaviour of the proximal AT. This might have implications for the understanding of triceps surae muscle–tendon interaction during locomotion, tendon injury mechanics and previous measurements of AT elastic properties.

Contributions of the non-kicking-side arm to rugby place-kicking technique

To investigate non-kicking-side arm motion during rugby place kicking, five experienced male kickers performed trials under two conditions, both with an accuracy requirement but one with an additional maximal distance demand. Joint centre coordinates were obtained at 120 Hz during kicking trials and a three-dimensional model was created to enable the determination of segmental contributions to whole-body angular momentum. All kickers possessed minimal non-kicking-side arm angular momentum about the global medio-lateral axis. The more accurate kickers exhibited greater non-kicking-side arm angular momentum about the global antero-posterior axis. This augmented the whole-body antero-posterior angular momentum, and altered the whole-body lateral lean at ball contact. The accurate kickers also exhibited greater non-kicking-side arm angular momentum about the global longitudinal axis, which opposed the kicking leg longitudinal angular momentum and attenuated the whole-body longitudinal angular momentum. All participants increased the longitudinal angular momentum of the non-kicking-side arm in the additional distance demand condition, except for one participant whose accuracy decreased, suggesting that the longitudinal angular momentum of the non-kicking-side arm assists maintenance of accuracy in maximum distance kicking. Goal kickers should be encouraged to produce non-kicking-side arm rotations about both the antero-posterior and longitudinal axes, as these appear important for both the initial achievement of accuracy, and for maintaining accuracy during distance kicking.

Strategies for maintaining a handstand in the anterior-posterior direction.

PURPOSE The purpose of this analysis was to determine the contributions made by wrist, shoulder, and hip joint torques in maintaining a handstand. METHODS Handstand balances (N = 6) executed on a force plate and recorded with two genlocked video cameras were subjected to inverse dynamics analysis to determine anterior-posterior joint torques at the wrists, shoulders, and hips. Multiple regression analyses were conducted to investigate which of the joint torques were influential in accounting for anterior-posterior whole-body mass center (CM) movement. RESULTS Results demonstrated that, in general, all calculated joint torques contributed to CM movement. In a number of trials, wrist torque played a dominant role in accounting for CM variance. Ostensibly, superior handstand balances are characterized by important contributions from wrist torques and shoulder torques with little influence from hip torques. In contrast, hip torques were found to be increasingly influential in less successful balances. CONCLUSIONS It is concluded that multiple joints are utilized in maintaining a handstand balance in the anterior-posterior direction, and there appears to be two joint involvement strategies, which supports similar findings from postural research on normal upright stance.