Billy T. Hulin

Spikes in acute workload are associated with increased injury risk in elite cricket fast bowlers

Objective To determine if the comparison of acute and chronic workload is associated with increased injury risk in elite cricket fast bowlers. Methods Data were collected from 28 fast bowlers who completed a total of 43 individual seasons over a 6-year period. Workloads were estimated by summarising the total number of balls bowled per week (external workload), and by multiplying the session rating of perceived exertion by the session duration (internal workload). One-week data (acute workload), together with 4-week rolling average data (chronic workload), were calculated for external and internal workloads. The size of the acute workload in relation to the chronic workload provided either a negative or positive training-stress balance. Results A negative training-stress balance was associated with an increased risk of injury in the week after exposure, for internal workload (relative risk (RR)=2.2 (CI 1.91 to 2.53), p=0.009), and external workload (RR=2.1 (CI 1.81 to 2.44), p=0.01). Fast bowlers with an internal workload training-stress balance of greater than 200% had a RR of injury of 4.5 (CI 3.43 to 5.90, p=0.009) compared with those with a training-stress balance between 50% and 99%. Fast bowlers with an external workload training-stress balance of more than 200% had a RR of injury of 3.3 (CI 1.50 to 7.25, p=0.033) in comparison to fast bowlers with an external workload training-stress balance between 50% and 99%. Conclusions These findings demonstrate that large increases in acute workload are associated with increased injury risk in elite cricket fast bowlers.

The acute:chronic workload ratio predicts injury: high chronic workload may decrease injury risk in elite rugby league players

Aim Investigate whether acute workload (1 week total distance) and chronic workload (4-week average acute workload) predict injury in elite rugby league players. Methods Data were collected from 53 elite players over two rugby league seasons. The ‘acute:chronic workload ratio’ was calculated by dividing acute workload by chronic workload. A value of greater than 1 represented an acute workload greater than chronic workload. All workload data were classified into discrete ranges by z-scores. Results Compared with all other ratios, a very-high acute:chronic workload ratio (≥2.11) demonstrated the greatest risk of injury in the current week (16.7% injury risk) and subsequent week (11.8% injury risk). High chronic workload (>16 095 m) combined with a very-high 2-week average acute:chronic workload ratio (≥1.54) was associated with the greatest risk of injury (28.6% injury risk). High chronic workload combined with a moderate workload ratio (1.02–1.18) had a smaller risk of injury than low chronic workload combined with several workload ratios (relative risk range from 0.3 to 0.7×/÷1.4 to 4.4; likelihood range=88–94%, likely). Considering acute and chronic workloads in isolation (ie, not as ratios) did not consistently predict injury risk. Conclusions Higher workloads can have either positive or negative influences on injury risk in elite rugby league players. Specifically, compared with players who have a low chronic workload, players with a high chronic workload are more resistant to injury with moderate-low through moderate-high (0.85–1.35) acute:chronic workload ratios and less resistant to injury when subjected to ‘spikes’ in acute workload, that is, very-high acute:chronic workload ratios ∼1.5.

Influence of physical qualities on post-match fatigue in rugby league players.

OBJECTIVES This study examined the influence of physical qualities on markers of fatigue and muscle damage following rugby league match-play. DESIGN Between subjects design. METHODS Twenty-one male youth rugby league players (age 19.2 ± 0.7 years; height 180.7 ± 5.6 cm; body mass 89.9 ± 10.0 kg) participated in the study. Yo-Yo intermittent recovery test (level 1), 3 repetition maximum back squat and bench press were assessed prior to 2 competitive fixtures. Neuromuscular fatigue (countermovement jump [CMJ] and plyometric push-up [PP]), and blood creatine kinase (CK) were assessed before and after match-play. During match-play, movements were recorded using microtechnology. Players were divided into high- and low-groups based on physical qualities. RESULTS High Yo-Yo and squat performance resulted in greater loads during match-play (p<0.05). There were larger reductions in CMJ power in the low Yo-Yo group at both 24 (ES=-1.83), and 48 h post-match (ES=-1.33). Despite greater internal and external match loads, changes in CMJ power were similar between squat groups. There were larger increases in blood CK in the low Yo-Yo group at 24 (73% vs. 176%; ES=1.50) and 48 h post-match (28% vs. 80%; ES=1.22). Despite greater contact loads, the high squat group exhibited smaller changes in blood CK post-match (ES=0.25-0.39). CONCLUSIONS Post-match fatigue is lower in players with well-developed high-intensity running ability, and lower body strength, despite these players having greater internal and external match loads.

Low chronic workload and the acute:chronic workload ratio are more predictive of injury than between-match recovery time: a two-season prospective cohort study in elite rugby league players

Background Between-match recovery time, and acute and chronic workloads likely affect subsequent match-injury risk in elite rugby league players. Methods Workloads of 28 players throughout two seasons were calculated during short (<7 days), and long (≥7 days) between-match recovery times. ‘Acute’ workloads (1 week) greater than ‘chronic’ workloads (4-week rolling average acute workload) resulted in acute:chronic workload ratios above 1. Results No difference was found between the match-injury risk of short and long between-match recovery periods (7.5±2.5% vs 6.8±2.5%). When players had a short recovery between matches, high chronic workloads (18.9–22.0 km) were associated with a smaller risk of match injury than chronic workloads <18.9 km (relative risk (RR) range 0.27–0.32 (CI 0.08 to 0.92); likelihood range 90–95%, likely). Players who had shorter recovery and acute:chronic workload ratios ≥1.6, were 3.4–5.8 times likely to sustain a match injury than players with lower acute:chronic workload ratios (RR range 3.41–5.80 (CI 1.17 to 19.2); likelihood range 96–99%, very likely). Acute:chronic workload ratios between 1.2 and 1.6 during short between-match recovery times demonstrated a greater risk of match injury than ratios between 1.0 and 1.2 (RR=2.88 (CI 0.97 to 8.55); likelihood=92%, likely). Conclusions Contrary to the philosophy that high workloads and shorter recovery equate to increased injury risk, our data suggest that high and very-high chronic workloads may protect against match injury following shorter between-match recovery periods. Acute:chronic workload ratios ∼1.5 are associated with a greater risk of match injury than lower acute:chonic workload ratios. Importantly, workloads can be manipulated to decrease the match-injury risk associated with shorter recovery time between matches.

Individual and combined effects of acute and chronic running loads on injury risk in elite Australian footballers

A model that takes into account the current workload, and the workload the athlete has been prepared for, as an acute:chronic workload ratio has been previously used as a novel way to monitor training load and injury risk. Fifty‐nine elite Australian football players from one club participated in this 2‐year study. Global Positioning System technology was used to provide information on running workloads of players. An injury was defined as any non‐contact “time‐loss” injury. One‐week (acute), along with 4‐week (chronic) workloads were calculated for a range of variables. The size of the acute workload in relation to the chronic workload was calculated as an acute:chronic workload ratio. An acute:chronic workload ratio of >2.0 for total distance during the in‐season was associated with a 5 to 8‐fold greater injury risk in the current [relative risk (RR) = 8.65, P = 0.001] and subsequent week (RR = 5.49, P = 0.016). Players with a high‐speed distance acute:chronic workload ratio of >2.0 were 5–11 times more likely to sustain an injury in the current (RR = 11.62, P = 0.006) and subsequent week (RR = 5.10, P = 0.014). These findings demonstrate that sharp increases in running workload increase the likelihood of injury in both the week the workload is performed, and the subsequent week.

Physical Demands of Match Play in Successful and Less-Successful Elite Rugby League Teams

PURPOSE To quantify activity profiles in approximately 5-min periods to determine if the intensity of rugby league match play changes after the most intense period of play and to determine if the intensity of activity during predefined periods of match play differ between successful and less-successful teams playing at an elite standard. METHODS Movement was recorded using a MinimaxX global positioning system (GPS) unit sampling at 10 Hz during 25 rugby league matches, equating to 200 GPS files. Data for each half of match play were separated into 8 equal periods. These periods represented the most intense phase of match play (peak period), the period after the most intense phase of match play (subsequent period), and the average demands of all other periods in a match (mean period). Two rugby league teams were split into a high-success and a low-success group based on their success rates throughout their season. RESULTS Compared with their less-successful counterparts, adjustables and hit-up forwards from the high-success team covered less total distance (P < .01) and less high-intensity-running distance (P < .01) and were involved in a greater number of collisions (P < .01) during the mean period of match play. CONCLUSIONS Although a greater number of collisions during match play is linked with a greater rate of success, greater amounts of high-intensity running and total distance are not related to competitive success in elite rugby league. These results suggest that technical and tactical differences, rather than activity profiles, may be the distinguishing factor between successful and less-successful rugby league teams.

Wearable microtechnology can accurately identify collision events during professional rugby league match-play

OBJECTIVES Collision frequency during rugby league matches is associated with team success, greater and longer lasting fatigue and increased injury risk. This study researched the sensitivity and specificity of microtechnology to count collision events during rugby league matches. DESIGN Diagnostic accuracy study. METHODS While wearing a microtechnology device (Catapult, S5), eight professional rugby league players were subjected to a total of 380 collision events during matches. Video footage of each match was synchronised with microtechnology data. The occurrence of each collision event was coded in comparison with whether that event was or was not detected by microtechnology. RESULTS Microtechnology detected 371 true-positive collision events (sensitivity=97.6±1.5%). When low-intensity (<1 PlayerLoad AU), short duration (<1s) events were excluded from the analysis, specificity was 91.7±2.5%, accuracy was 92.7±1.3%, positive likelihood ratio was 11.4×/÷1.4 and the typical error of estimate was 7.8%×/÷1.9 (d=0.29×/÷1.9, small). Microtechnology collisions were strongly and positively correlated with video coded collision events (r=0.96). The ability of microtechnology to detect collision events improved as the intensity and duration of the collision increased. CONCLUSIONS Microtechnology can identify 97.6% of collision events during rugby league match-play. The typical error associated with measuring contact events can be reduced to 7.8%, with accuracy (92.7%) and specificity (91.7%) improving, when low-intensity (<1 PlayerLoad AU) and short duration (<1s) collision reports are excluded. This provides practitioners with a measurement of contact workload during professional rugby league matches.

Activity and recovery cycles and skill involvements of successful and unsuccessful elite rugby league teams: A longitudinal analysis of evolutionary changes in National Rugby League match-play

ABSTRACT We investigated changes in activity and recovery cycles and skill involvements: (1) during National Rugby league (NRL) match-play from 2004 to 2014 and (2) among successful and unsuccessful teams over the same period. Teams were divided into 4 tiers according to final ladder position: (A) 1st–4th, (B) 5th–8th, (C) 9th–12th and (D) 13th–16th. Total, mean and maximum ball-in-play time decreased, while recovery time increased from 2004 to 2014. Offensive and defensive skill involvements changed differentially over time with moderate to large reductions in the number of play-the-balls, offloads and missed tackles, and moderate to large increases in the number of passes, tackles made and ineffective tackles. The gap between Tier A and Tier D decreased for mean activity time and the proportion of short (<45 s) ball-in-play periods. Conversely, the gap between Tier A and Tier D increased for skill involvements, with Tier A completing more play-the-balls, and Tier D performing a greater number of offloads, and total, missed and ineffective tackles. Our results demonstrate the decreasing ball-in-play demands of NRL competition over 11 seasons. However, our data also highlight the narrowing gap in ball-in-play demands, and increasing gap in skill involvements between the top tier and bottom tier teams.

Indeed association does not equal prediction: the never-ending search for the perfect acute:chronic workload ratio

We recently demonstrated associations between workload and injury.1 2 Regrettably, in these manuscripts, we used the words ‘ predict ’ and ‘ predictive ’ within the titles. Although we clearly used more appropriate language throughout these manuscripts, the titles of our work have resulted in a misconception that we believe the acute:chronic workload ratio can predict injury with some certainty.3 4 Our purpose for investigating workload–injury relationships in these studies was to identify workloads that practitioners could use (along with other information) to make informed decisions in regards to when injury risk may be increased or decreased—it was not our intention to imply that one variable could predict injury with crystal ball-like accuracy. We discussed at length that other variables will undoubtedly also have associations with injury,1 2 and that good athlete monitoring involves consideration of factors in addition to workload.5 However, we feel that these views may have been dismissed and, consequently, our purpose here is to provide novel perspectives and some clarity and context on the practical applications of the acute:chronic workload ratio. The acute:chronic workload ratio should never be viewed in isolation. The size of an athlete’s chronic workload is …

The never-ending search for the perfect acute:chronic workload ratio: what role injury definition?

The acute:chronic workload ratio is associated with injury risk in rugby league players.1 Researchers and practitioners have discussed the most appropriate way in which acute and chronic workloads should be modelled and compared with injury. Menaspa2 suggested that when workloads do not follow weekly patterns in team sport, rolling weekly averages may disregard variations in workload within the week and as such, are not ideal. However, Drew et al 3 highlighted that evidence was required before an alternative method could be considered. Williams et al ,4 suggested an exponentially weighted moving average calculation of acute and chronic workloads. To my knowledge, all this discussion has ignored definition of injury—this could influence the findings of any workload-injury analysis. Relating the findings from multiple injury investigations in team sport can be difficult due to the use of inconsistent definitions of injury.5 Both Hulin …