Keith Stokes

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.

Two Weeks of Reduced Activity Decreases Leg Lean Mass and Induces “Anabolic Resistance” of Myofibrillar Protein Synthesis in Healthy Elderly

BACKGROUND Alterations in muscle protein metabolism underlie age-related muscle atrophy. During periods of muscle disuse, muscle protein synthesis is blunted, and muscle atrophy occurs in young and old. The impact of a short reduction in physical activity on muscle protein metabolism in older adults is unknown. PURPOSE The aim of this study was to investigate the impact of 14 days of reduced daily steps on fasted and fed-state rates of myofibrillar protein synthesis (MPS) to provide insight into the mechanisms for changes in muscle mass and markers of metabolic health. METHODS Before and after 14 days of reduced daily step-count, 10 healthy older adults (age, 72 ± 1 y) underwent measures of insulin sensitivity, muscle strength, physical function, and body composition. Using a primed constant infusion of L-[ring-(13)C6]phenylalanine with serial muscle biopsies, basal, postabsorptive, and postprandial rates of MPS were determined before and after the 14-day intervention. RESULTS Daily step-count was reduced by approximately 76% to 1413 ± 110 steps per day. Leg fat-free mass was reduced by approximately 3.9% (P < .001). Postabsorptive insulin resistance was increased by approximately 12%, and postprandial insulin sensitivity was reduced by approximately 43% after step reduction (P < .005). Concentrations of TNF-α and C-reactive protein were increased by approximately 12 and 25%, respectively, after step reduction (P < .05). Postprandial rates of MPS were reduced by approximately 26% after the intervention (P = .028), with no difference in postabsorptive rates. CONCLUSION The present study demonstrates that 14 days of reduced steps in older adults induces small but measurable reductions in muscle mass that appear to be underpinned by reductions in postprandial MPS and are accompanied by impairments in insulin sensitivity and systemic inflammatory markers and postprandial MPS.

Dietary nitrate does not enhance running performance in elite cross-country skiers.

PURPOSE The objective of this study is to examine the effects of acute ingestion of dietary nitrate on endurance running performance in highly trained cross-country skiers. Dietary nitrate has been shown to reduce the oxygen cost of submaximal exercise and improve tolerance of high-intensity exercise, but it is not known if this holds true for highly trained endurance athletes. METHODS Ten male junior cross-country skiers (V˙O(2max)) ≈ 70 mL·kg·min) each completed two trials in a randomized, double-blind design. Participants ingested potassium nitrate (614-mg nitrate) or a nitrate-free placebo 2.5 h before two 5-min submaximal tests on a treadmill at 10 km·h (≈55% of V˙O(2max)) and 14 km·h (≈75% of V˙O(2max)), followed by a 5-km running time trial on an indoor track. RESULTS Plasma nitrite concentrations were higher after nitrate supplementation (325 ± 95 nmol·L) compared with placebo (143 ± 59 nmol·L, P < 0.001). There was no significant difference in 5-km time-trial performance between nitrate (1005 ± 53 s) and placebo treatments (996 ± 49 s, P = 0.12). The oxygen cost of submaximal running was not significantly different between placebo and nitrate trials at 10 km·h (both 2.84 ± 0.34 L·min) and 14 km·h (3.89 ± 0.39 vs. 3.77 ± 0.62 L·min). CONCLUSIONS Acute ingestion of dietary nitrate may not represent an effective strategy for reducing the oxygen cost of submaximal exercise or for enhancing endurance exercise performance in highly trained cross-country skiers.

Growth hormone responses to sub-maximal and sprint exercise.

Exercise is a potent stimulus for growth hormone (GH) release and a single bout of exercise can result in marked elevations in circulating GH concentrations. The magnitude of the GH response to exercise will vary according to the type, intensity and duration of exercise as well as factors such as the age, gender, body composition and fitness status of the individual performing the exercise. However, the mechanisms regulating GH release in response to exercise are not fully understood. This review considers the GH responses to sub-maximal and sprint exercise and discusses the factors that might affect GH release along with the mechanisms that have been proposed to regulate exercise-induced GH release.

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.

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.

The time course of the human growth hormone response to a 6 s and a 30 s cycle ergometer sprint.

Exercise is a potent stimulus for the release of human growth hormone (hGH), but the time course of the hGH response to sprint exercise has not been studied. The aim of the present study was to determine the time course of the hGH response to a 6 s and a 30 s maximal sprint on a cycle ergometer. Nine males completed two trials, on one occasion performing a single 6 s sprint and on another a single 30 s sprint. They then rested on a couch for 4 h while blood samples were obtained. Three of the participants completed a further control trial involving no exercise. Metabolic responses were greater after the 30 s sprint than after the 6 s sprint. The highest measured mean serum hGH concentrations after the 30 s sprint were more than 450% greater than after the 6 s sprint (18.5 - 3.1 vs 4.0 - 1.5 w g·l -1 , P ≪ 0.05). Serum hGH also remained elevated for 90-120 min after the 30 s sprint compared with ~ 60 min after the 6 s sprint. There was a large inter-individual variation in the hGH response to the 30 s sprint. In the control trial, serum hGH concentrations were not elevated above baseline at any time. It would appear that the duration of a bout of maximal sprint exercise determines the magnitude of the hGH response, although the mechanism for this is still unclear.

Epidemiology of time-loss injuries in English community-level rugby union

Objectives Using a prospective cohort study design, to establish the incidence and nature of time-loss injuries in English community rugby and to assess the differences between different playing levels. Setting English community rugby clubs. Participants Injury information for 4635 matches was collected during seasons 2009/2010 (46 clubs), 2010/2011(67 clubs) and 2011/2012 (76 clubs). Clubs were subdivided into groups A (semiprofessional), B (amateur) and C (recreational) for analysis. Primary and secondary outcome measures Any injury resulting in 8 days or greater absence from match play was reported by injury management staff at the clubs. The primary outcome measure was injury incidence (per 1000 player match-hours) and the secondary outcome measure was severity (ie, days absence). Results Overall match injury incidence was 16.9 injuries per 1000 player match-hours. Incidence was higher for group A (21.7; 95% CI 19.8 to 23.6) compared with group B (16.6; 95% CI 15.2 to 17.9) and C (14.2; 95% CI 13.0 to 15.5, both p<0.001). The mean time-loss was 7.6 weeks absence, with knee and shoulder injuries the most severe with mean absences of 11.6 and 9.3 weeks, respectively. Half of all injuries occurred to the lower limb, with knee and ankle joint/ligament injuries the most common diagnoses. Shoulder joint/ligament injuries were the most common and severe upper limb injuries. Contact events accounted for 80% of all injuries and tackles accounted for 50%. Running was the most common non-contact injury event, of which 56% were hamstring injuries. Conclusions More time-loss injuries occur at higher levels of community rugby. Injury prevention strategies should focus on good technique in the tackle and conditioning exercises for the knee, ankle, hamstrings and shoulder.