Latest research in football - week 38 - 2017

As previous literature updates, I have performed a PubCrawler search looking for football articles in NCBI Medline (PubMed) and GenBank databases.

Following studies were retrieved for this week:

#1 Elite Youth Soccer Players' Physiological Responses, Time-Motion Characteristics, and Game Performance in 4 vs. 4 Small-Sided Games: The Influence of Coach Feedback
Reference: J Strength Cond Res. 2017 Oct;31(10):2652-2658. doi: 10.1519/JSC.0000000000001717.
Authors: Brandes M, Elvers S
Summary: The purpose of this study was to determine the impact of mild vs. strongly pushed coach feedback on the physiological response, ratio of perceived exertion (RPE), and time-motion characteristics in soccer training with small-sided games (SSGs). Sixteen elite youth soccer players (aged 17.2 ± 0.7 years, V[Combining Dot Above]O2max 62.1 ± 3.8 ml·kg·min) played two 4 vs. 4 small-sided games each. In random order, the coach provided a mild, unobtrusive, or a strongly pushed feedback throughout the game. Physiological measurements included heart rate expressed in mean values and intensity zones, blood lactate concentration, and RPE. The distance traveled, number of sprints, and work:rest ratio were captured by global positioning systems at 5 Hz. Game performance, such as volume of play and efficacy index, was estimated using the Team Sports Assessment Procedure. No differences were found for the physiological response and time-motion characteristics, but effect sizes demonstrated an increase in RPE (+0.4, p = 0.27) and a decrease in game performance (e.g., volume of play, -2.5, p = 0.08) under pushed feedback. Although a pushed feedback raises RPE, it negatively affected the players' game performance, without necessarily provoking higher physiological responses. These results should help coaches to understand that modifying the type of feedback provided during SSG does not impact the physiological response if SSG are already played with high intensity but that the feedback affects RPE and game performance. To keep a better game performance, soccer coaches are encouraged to provide smooth feedback during SSG.

#2 Hopping and Landing Performance in Male Youth Soccer Players: Effects of Age and Maturation
Reference: Int J Sports Med. 2017 Sep 20. doi: 10.1055/s-0043-114009. [Epub ahead of print]
Authors: Read PJ, Oliver JL, Myer G, De Ste Croix M, Lloyd R
Summary: Quantifying hopping and landing performances can assist coaches in identifying young male soccer players who may be at increased risk of injury. The influence of chronological age and maturation on these measures in this population is unknown. Single leg hop for distance (SLHD) and 75% horizontal hop and stick landing force (75%Hop) were examined in a cross-sectional sample (N=400) of elite male youth soccer players. Between-group differences for both chronological age (U11-U18) and stage of maturation (pre-, circa- or post-peak height velocity (PHV)) were analyzed. Absolute 75%Hop increased with both age and maturation. Apart from the U18s, pre-PHV and U11-U12 players displayed the greatest relative landing forces compared to all other groups (p<0.001; d=0.56-0.93). Absolute and relative SLHD were greatest in the U18s and post-PHV players (p<0.001; d=0.35-2.04). A trend showed increased SLHD with each consecutive age group although a reduction in performance was identified in the U13s (d=0.50-0.59). High volumes of accumulated soccer participation in the U18s may lead to altered landing strategies indicative of high injury risk. A temporary reduction in hop performance in the U13s may also be linked to a period of adolescent awkwardness.

#3 Case study: sleep and injury in elite soccer. A mixed method approach
Reference: J Strength Cond Res. 2017 Sep 11. doi: 10.1519/JSC.0000000000002251. [Epub ahead of print]
Authors: Nedelec M, Leduc C, Dawson B, Guilhem G, Dupont G.
Summary: The present case study allowed an examination of the link between sleep and injury occurrence in an elite male soccer player competing in French League 1 and Union of European Football Associations matches. During 4 months, a mixed method approach was used, combining actigraphic sleep assessment with qualitative interviews on a daily basis. Three injuries were reported over the study period. Sleep onset latency, both in the single night (117±43 min) and in the week (78±50 min) before injury occurrence, was longer than pre-season baseline values (18±13 min; effect size (ES): 3.1 and 1.6, respectively). Similarly, sleep efficiency in the single night (73±7%) and the week (75±7%) before injury occurrence, was lower than baseline (90±3%; ES: 3.2 and 2.8, respectively). In the present case-study, sleep onset latency and efficiency were altered on the night and in the week before injury occurrence. Individualized assessment of sleep during congested playing schedules may be useful to aid in preventing injury occurrence.

#4 A comparison of isomaltulose versus maltodextrin ingestion during soccer-specific exercise
Reference: Eur J Appl Physiol. 2017 Sep 19. doi: 10.1007/s00421-017-3719-5. [Epub ahead of print]
Authors: Stevenson EJ, Watson A, Theis S, Holz A, Harper LD, Russell M
Summary: The performance and physiological effects of isomaltulose and maltodextrin consumed intermittently during prolonged soccer-specific exercise were investigated. University soccer players (n = 22) performed 120 min of intermittent exercise while consuming 8% carbohydrate-electrolyte drinks (equivalent to ~ 20 g h-1) containing maltodextrin (Glycaemic Index: 90-100), isomaltulose (Glycaemic Index: 32) or a carbohydrate-energy-free placebo in a manner replicating the practices of soccer players (i.e., during warm-up and half-time). Physical (sprinting, jumping) and technical (shooting, dribbling) performance was assessed. Blood glucose and plasma insulin (both P < 0.001) concentrations varied by trial with isomaltulose maintaining > 13% higher blood glucose concentrations between 75 and 90 min versus maltodextrin (P < 0.05). A decline in glycaemia at 60 min in maltodextrin was attenuated with isomaltulose (-19 versus -4%; P = 0.015). Carbohydrates attenuated elevations in plasma epinephrine concentrations (P < 0.05), but isomaltulose proved most effective at 90 and 120 min. Carbohydrates did not attenuate IL-6 increases or reductions in physical or technical performances (all P > 0.05). Ratings of abdominal discomfort were influenced by trial (P < 0.05) with lower values for both carbohydrates compared to PLA from 60 min onwards. Although carbohydrates (~ 20 g h-1) did not attenuate performance reductions throughout prolonged soccer-specific exercise, isomaltulose maintained higher blood glucose at 75-90 min, lessened the magnitude of the exercise-induced rebound glycaemic response and attenuated epinephrine increases whilst maintaining similar abdominal discomfort values relative to maltodextrin. When limited opportunities exist to consume carbohydrates on competition-day, low-glycaemic isomaltulose may offer an alternative nutritional strategy for exercising soccer players.

#5 The Energy Cost of Running with the Ball in Soccer
Reference: Int J Sports Med. 2017 Sep 18. doi: 10.1055/s-0043-118340. [Epub ahead of print]
Authors: Piras A, Raffi M, Atmatzidis C, Merni F, Di Michele R
Summary: Running with the ball is a soccer-specific activity frequently used by players during match play and training drills. Nevertheless, the energy cost (EC) of on-grass running with the ball has not yet been determined. The purpose of this study was therefore to assess the EC of constant-speed running with the ball, and to compare it with the EC of normal running. Eight amateur soccer players performed two 6- min runs at 10 km/h on artificial turf, respectively with and without the ball. EC was measured with indirect calorimetry and, furthermore, estimated with a method based on players' accelerations measured with a GPS receiver. The EC measured with indirect calorimetry was higher in running with the ball (4.60±0.42 J/kg/m) than in normal running (4.19±0.33 J/kg/m), with a very likely moderate difference between conditions. Instead, a likely small difference was observed between conditions for EC estimated from GPS data (4.87±0.07 vs. 4.83±0.08 J/kg/m). This study sheds light on the energy expenditure of playing soccer, providing relevant data about the EC of a typical soccer-specific activity. These findings may be a reference for coaches to precisely determine the training load in drills with the ball, such as soccer-specific circuits or small-sided games.

#6 Practical nutritional recovery strategies for elite soccer players when limited time separates repeated matches
Reference: J Int Soc Sports Nutr. 2017 Sep 12;14:35. doi: 10.1186/s12970-017-0193-8. eCollection 2017.
Authors: Ranchordas MK, Dawson JT, Russell M
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Summary: Specific guidelines that aim to facilitate the recovery of soccer players from the demands of training and a congested fixture schedule are lacking; especially in relation to evidence-based nutritional recommendations. The importance of repeated high level performance and injury avoidance while addressing the challenges of fixture scheduling, travel to away venues, and training commitments requires a strategic and practically feasible method of implementing specific nutritional strategies. Here we present evidence-based guidelines regarding nutritional recovery strategies within the context of soccer. An emphasis is placed on providing practically applicable guidelines for facilitation of recovery when multiple matches are played within a short period of time (i.e. 48 h). Following match-play, the restoration of liver and muscle glycogen stores (via consumption of ~1.2 g⋅kg-1⋅h-1 of carbohydrate) and augmentation of protein synthesis (via ~40 g of protein) should be prioritised in the first 20 min of recovery. Daily intakes of 6-10 g⋅kg-1 body mass of carbohydrate are recommended when limited time separates repeated matches while daily protein intakes of >1.5 g⋅kg-1 body mass should be targeted; possibly in the form of multiple smaller feedings (e.g., 6 × 20-40 g). At least 150% of the body mass lost during exercise should be consumed within 1 h and electrolytes added such that fluid losses are ameliorated. Strategic use of protein, leucine, creatine, polyphenols and omega-3 supplements could also offer practical means of enhancing post-match recovery.

#7 Risk factors for football injuries in young players aged 7 to 12 years
Reference: Scand J Med Sci Sports. 2017 Sep 18. doi: 10.1111/sms.12981. [Epub ahead of print]
Authors: Rossler R, Junge A, Chomiak J, Nemec K, Dvorak J, Lichtenstein E, Faude O
Summary: Football (soccer) is very popular amongst children. Little is known about risk factors for football injuries in children. The aim was to analyse potential injury risk factors in 7 to 12 year old players. We collected prospective data in Switzerland and the Czech Republic over two seasons. Coaches reported exposure of players (in hours), absence, and injury data via an internet-based registration system. We analysed time-to-injury data with extended Cox models accounting for correlations on team- and intra-person-level. We analysed injury risk in relation to age, sex, playing position, preferred foot, and regarding age-independent body height, body mass, and BMI. Further, we analysed injury risk in relation to playing surface. In total, 6,038 player seasons with 395,295 hours of football exposure were recorded and 417 injuries occurred. Injury risk increased by 46% (Hazard Ratio 1.46 [1.35; 1.58]; P<0.001) per year of life. Left-footed players had a higher injury risk (Hazard Ratio 1.53 [1.07; 2.19]; P=0.02) for training injuries compared to right-footed players. Injury risk was increased in age-adjusted taller players (higher percentile-rank). Higher match-training-ratios were associated with a lower risk of match injuries. Injury risk was increased on artificial turf (Rate Ratio 1.39 [1.12; 1.73]; P<0.001) and lower during indoor sessions (Rate Ratio 0.68 [0.52; 0.88]; P<0.001) compared to natural grass. Age is known as a risk factor in older players and was confirmed to be a risk factor in children's football. Playing surface and leg dominance have also been discussed previously as risk factors. Differences in injury risks in relation to sex should be investigated in the future.

American Football
#1 The Latarjet Procedure at the National Football League Scouting Combine: An Imaging and Performance Analysis
Reference: Orthop J Sports Med. 2017 Sep 1;5(9):2325967117726045. doi: 10.1177/2325967117726045. eCollection 2017 Sep.
Authors: LeBus GF, Chahla J, Sanchez G, Akamefula R, Moatshe G, Phocas A, Price MD, Whalen JM, LaPrade RF, Provencher MT
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Summary: The Latarjet procedure is commonly performed in the setting of glenoid bone loss for treatment of recurrent anterior shoulder instability; however, little is known regarding the outcomes of this procedure in elite American football players. The purpose was to (1) Determine the prevalence, clinical features, and imaging findings of elite college football athletes who present to the National Football League (NFL) Combine with a previous Latarjet procedure and (2) describe these athletes' performance in the NFL in terms of draft status and initial playing time. After review of all football players who participated in the NFL Combine from 2009 to 2016, any player with a previous Latarjet procedure was included in this study. Medical records, position on the field, and draft position were recorded for each player. In addition, imaging studies were reviewed to determine fixation type, hardware complications, and status of the bone block. For those players who were ultimately drafted, performance was assessed based on games played and started, total snaps, and percentage of eligible snaps in which the player participated during his rookie season. Overall, 13 of 2617 (<1%) players at the combine were identified with a previous Latarjet procedure. Radiographically, 8 of 13 (61%) showed 2-screw fixation, while 5 of 13 (39%) had 1 screw. Of the 13 players, 6 (46%) players demonstrated hardware complications. All players had evidence of degenerative changes on plain radiographs, with 10 (77%) graded as mild, 1 (8%) as moderate, and 2 (15%) as severe according to the Samilson Prieto classification. Six of the 13 (46%) players went undrafted, while the remaining 7 (54%) were drafted; however, no player participated in more than half of the plays for which he was eligible during his rookie season. Only a small percentage of players at the NFL Combine (<1%) had undergone a Latarjet procedure. High rates of postoperative complications and radiographically confirmed degenerative change were observed. Athletes who had undergone a Latarjet procedure demonstrated a variable amount of playing time, but none participated in more than half of their eligible plays during their rookie season.

#2 A Case Series of Pectoralis Major Injuries on One Collegiate Football Team
Reference: Curr Sports Med Rep. 2017 Sep/Oct;16(5):346-350. doi: 10.1249/JSR.0000000000000400.
Authors: Baker HP, Tjong VK, Varelas A, Wonais M, Terry MA.

#3 American football and other sports injuries may cause migraine/persistent pain decades later and can be treated successfully with electrical twitch-obtaining intramuscular stimulation (ETOIMS)
Reference: BMJ Innov. 2017 Apr;3(2):104-114. doi: 10.1136/bmjinnov-2016-000151. Epub 2017 Mar 24.
Authors: Chu J, McNally S, Bruyninckx F, Neuhauser D
Summary: Autonomous twitch elicitation at myofascial trigger points from spondylotic radiculopathies-induced denervation supersensitivity can provide favourable pain relief using electrical twitch-obtaining intramuscular stimulation (ETOIMS). The aim was to provide objective evidence that ETOIMS is safe and efficacious in migraine and persistent pain management due to decades-old injuries to head and spine from paediatric American football. An 83-year-old mildly hypertensive patient with 25-year history of refractory migraine and persistent pain self-selected to regularly receive fee-for-service ETOIMS 2/week over 20 months. He had 180 sessions of ETOIMS. Pain levels, blood pressure (BP) and heart rate/pulse were recorded before and immediately after each treatment alongside highest level of clinically elicitable twitch forces/session, session duration and intervals between treatments. Twitch force grades recorded were from 1 to 5, grade 5 twitch force being strongest. Initially, there was hypersensitivity to electrical stimulation with low stimulus parameters (500 µs pulse-width, 30 mA stimulus intensity, frequency 1.3 Hz). This resolved with gradual stimulus increments as tolerated during successive treatments. By treatment 27, autonomous twitches were noted. Spearman's correlation coefficients showed that pain levels are negatively related to twitch force, number of treatments, treatment session duration and directly related to BP and heart rate/pulse. Treatment numbers and session durations directly influence twitch force. At end of study, headaches and quality of life improved, hypertension resolved and antihypertensive medication had been discontinued. Using statistical process control methodology in an individual patient, we showed long-term safety and effectiveness of ETOIMS in simultaneous diagnosis, treatment, prognosis and prevention of migraine and persistent pain in real time obviating necessity for randomised controlled studies.

#4 Severe Exercise-Associated Hyponatremia in a Collegiate American Football Player
Reference: Curr Sports Med Rep. 2017 Sep/Oct;16(5):343-345. doi: 10.1249/JSR.0000000000000399.
Authors: Changstrom B, Brill J, Hecht S

#5 Mild Traumatic Brain Injury in a High School Football Player with Familial Hemiplegic Migraine: A Case Report
Reference: PM R. 2017 Sep 13. pii: S1934-1482(16)31114-5. doi: 10.1016/j.pmrj.2017.07.081. [Epub ahead of print]
Authors: Chand MR, Kanwar S, Peck E
Summary: Mild traumatic brain injury is a major concern in young athletes, with an estimated 1.6 to 3.8 million reported concussions in the US annually. Familial hemiplegic migraine is a rare autosomal-dominant condition characterized by sporadic episodes of transient unilateral motor weakness which may begin at any age. We present a case of a 17-year-old male with a history of familial hemiplegic migraine who suffered prolonged symptoms following a mild traumatic brain injury during sports participation.

#6 Erratum to: Editorial: Do Orthopaedic Surgeons Belong on the Sidelines at American Football Games?
Reference: Clin Orthop Relat Res. 2017 Sep 18. doi: 10.1007/s11999-017-5508-1. [Epub ahead of print]
Authors: Leopold SS, Dobbs MB, Gebhardt MC, Gioe TJ, Rimnac CM, Wongworawat MD
Summary: In the November Editorial, "Editorial: Do Orthopaedic Surgeons Belong on the Sidelines at American Football Games?" a statistic was attributed to a JAMA study (Ref. 10) that should have been attributed to an article from the New York Times (Ref. 16). The sentence in question should read: "We accept that critique, provided that the skeptics acknowledge that the best-case estimate in support of the safety of football would result in a CTE prevalence estimate of 9%, since only another 1200 ex-NFL players have died [16] since this research group [10] began studying football players' brains."

#7 Age of first exposure to American football and long-term neuropsychiatric and cognitive outcomes
Reference: Transl Psychiatry. 2017 Sep 19;7(9):e1236. doi: 10.1038/tp.2017.197.
Authors: Alosco ML, Kasimis AB, Stamm JM, Chua AS, Baugh CM, Daneshvar DH, Robbins CA, Mariani M, Hayden J, Conneely S, Au R, Torres A, McClean MD, McKee AC, Cantu RC, Mez J, Nowinski CJ, Martin BM, Chaisson CE, Tripodis Y, Stern RA
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Summary: Previous research suggests that age of first exposure (AFE) to football before age 12 may have long-term clinical implications; however, this relationship has only been examined in small samples of former professional football players. We examined the association between AFE to football and behavior, mood and cognition in a large cohort of former amateur and professional football players. The sample included 214 former football players without other contact sport history. Participants completed the Brief Test of Adult Cognition by Telephone (BTACT), and self-reported measures of executive function and behavioral regulation (Behavior Rating Inventory of Executive Function-Adult Version Metacognition Index (MI), Behavioral Regulation Index (BRI)), depression (Center for Epidemiologic Studies Depression Scale (CES-D)) and apathy (Apathy Evaluation Scale (AES)). Outcomes were continuous and dichotomized as clinically impaired. AFE was dichotomized into <12 and ⩾12, and examined continuously. Multivariate mixed-effect regressions controlling for age, education and duration of play showed AFE to football before age 12 corresponded with >2 × increased odds for clinically impaired scores on all measures but BTACT: (odds ratio (OR), 95% confidence interval (CI): BRI, 2.16,1.19-3.91; MI, 2.10,1.17-3.76; CES-D, 3.08,1.65-5.76; AES, 2.39,1.32-4.32). Younger AFE predicted increased odds for clinical impairment on the AES (OR, 95% CI: 0.86, 0.76-0.97) and CES-D (OR, 95% CI: 0.85, 0.74-0.97). There was no interaction between AFE and highest level of play. Younger AFE to football, before age 12 in particular, was associated with increased odds for impairment in self-reported neuropsychiatric and executive function in 214 former American football players. Longitudinal studies will inform youth football policy and safety decisions.

#8 Cold-Water Immersion Cooling Rates in Football Linemen and Cross-Country Runners With Exercise-Induced Hyperthermia
Reference: J Athl Train. 2017 Sep 22. doi: 10.4085/1062-6050-52.7.08. [Epub ahead of print]
Authors: Godek SF, Morrison KE, Scullin G
Summary: Ideal and acceptable cooling rates in hyperthermic athletes have been established in average-sized participants. Football linemen (FBs) have a small body surface area (BSA) to mass ratio compared with smaller athletes, which hinders heat dissipation. The purpose was to determine cooling rates using cold-water immersion in hyperthermic FBs and cross-country runners (CCs). Nine FBs (age = 21.7 ± 1.7 years, height = 188.7 ± 4 cm, mass = 128.1 ± 18 kg, body fat = 28.9% ± 7.1%, lean body mass [LBM] = 86.9 ± 19 kg, BSA = 2.54 ± 0.13 m2, BSA/mass = 201 ± 21.3 cm2/kg, and BSA/LBM = 276.4 ± 19.7 cm2/kg) and 7 CCs (age = 20 ± 1.8 years, height = 176 ± 4.1 cm, mass = 68.7 ± 6.5 kg, body fat = 10.2% ± 1.6%, LBM = 61.7 ± 5.3 kg, BSA = 1.84 ± 0.1 m2, BSA/mass = 268.3 ± 11.7 cm2/kg, and BSA/LBM = 298.4 ± 11.7 cm2/kg). Participants ingested an intestinal sensor, exercised in a climatic chamber (39°C, 40% relative humidity) until either target core temperature (Tgi) was 39.5°C or volitional exhaustion was reached, and were immediately immersed in a 10°C circulated bath until Tgi declined to 37.5°C. A general linear model repeated-measures analysis of variance and independent t tests were calculated, with P < .05. Physical characteristics were different between groups. No differences existed in environmental measures or maximal Tgi (FBs = 39.12°C ± 0.39°C, CCs = 39.38°C ± 0.19°C; P = .12). Cooling times required to reach 37.5°C (FBs = 11.4 ± 4 minutes, CCs = 7.7 ± 0.06 minutes; P < .002) and therefore cooling rates (FBs = 0.156°C ± 0.06°C·min-1, CCs = .255°C ± 0.05°C·min-1; P < .002) were different. Strong correlations were found between cooling rate and body mass (r = -0.76, P < .001), total BSA (r = -0.74, P < .001), BSA/mass (r = 0.73, P < .001), LBM/mass (r = 0.72, P < .002), and LBM (r = -0.72, P < .002). Using cold-water immersion, the cooling rate in CCs (0.255°C·min-1) was greater than in FBs (0.156°C·min-1); however, both were considered ideal (≥0.155°C·min-1). Athletic trainers should realize that it likely takes considerably longer to cool large hyperthermic American-football players (>11 minutes) than smaller, leaner athletes (7.7 minutes). Cooling rates varied widely from 0.332°C·min-1 in a small runner to only 0.101°C·min-1 in a lineman, supporting the use of rectal temperature for monitoring during cooling.

#9 Head impact exposure measured in a single youth football team during practice drills
Reference: J Neurosurg Pediatr. 2017 Sep 12:1-9. doi: 10.3171/2017.5.PEDS16627. [Epub ahead of print]
Authors: Kelley ME, Kane JM, Espeland MA, Miller LE, Powers AK, Stitzel JD, Urban JE
Summary: This study evaluated the frequency, magnitude, and location of head impacts in practice drills within a youth football team to determine how head impact exposure varies among different types of drills. On-field head impact data were collected from athletes participating in a youth football team for a single season. Each athlete wore a helmet instrumented with a Head Impact Telemetry (HIT) System head acceleration measurement device during all preseason, regular season, and playoff practices. Video was recorded for all practices, and video analysis was performed to verify head impacts and assign each head impact to a specific drill. Eleven drills were identified: dummy/sled tackling, install, special teams, Oklahoma, one-on-one, open-field tackling, passing, position skill work, multiplayer tackle, scrimmage, and tackling drill stations. Generalized linear models were fitted to log-transformed data, and Wald tests were used to assess differences in head accelerations and impact rates. A total of 2125 impacts were measured during 30 contact practices in 9 athletes (mean age 11.1 ± 0.6 years, mean mass 44.9 ± 4.1 kg). Open-field tackling had the highest median and 95th percentile linear accelerations (24.7 g and 97.8 g, respectively) and resulted in significantly higher mean head accelerations than several other drills. The multiplayer tackle drill resulted in the highest head impact frequency, with an average of 0.59 impacts per minute per athlete, but the lowest 95th percentile linear accelerations of all drills. The front of the head was the most common impact location for all drills except dummy/sled tackling. Head impact exposure varies significantly in youth football practice drills, with several drills exposing athletes to high-magnitude and/or high-frequency head impacts. These data suggest that further study of practice drills is an important step in developing evidence-based recommendations for modifying or eliminating certain high-intensity drills to reduce head impact exposure and injury risk for all levels of play.

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