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Objective: 31 magnetic resonance spectroscopy (MRS) was used to document long lasting losses in muscle oxidative capacity after bouts of intense endurance exercise. Methods: The subject was a 34 year old highly fit female cyclist (Vo2MAX = 53.3 mI/kg/min). Over a five month period, she participated in three separate intense bouts of acute unaccustomed exercise. 31P MRS measurements were performed seven weeks after the first bout and every Iwo weeks for 14 more weeks. In all cases, 31P MRS measurements followed three days after each bout. Results: The subject showed a decreased ability to generate ATP from oxidative phosphorylation and an increased reliance on anaerobic ATP production during the 70% and 100% maximal voluntary contractions after the exercise bouts. Increased rates of fatigue and increased indicators of exercise difficulty also accompanied these reductions in muscle oxidative capacity. Increased oxidative and anaerobic ATP production were needed to maintain the work level during a submaximal 45% maximal voluntary contraction exercise. Conclusions: Acute increases in intensity accompanied by a change in exercise mode can influence the ability of muscle to generate ATP. The muscles were less economical and required more ATP to generate force during the submaximal exercises. During the maximal exercises, the muscle's mitochondria showed a reduced oxidative capacity. However, these reductions in oxidative capacity at the muscle level were not associated with changes in whole body maximal oxygen uptake. Finally, these reductions in muscular oxidative capacity were accompanied by increased rates of anaerobic ATP production, fatigue, and indicators of exercise difficulty. [ABSTRACT FROM AUTHOR]

Football is a global game which is constantly evolving, showing substantial increases in physical and technical demands. Nutrition plays a valuable integrated role in optimising performance of elite players during training and match-play, and maintaining their overall health throughout the season. An evidence-based approach to nutrition emphasising, a 'food first' philosophy (ie, food over supplements), is fundamental to ensure effective player support. This requires relevant scientific evidence to be applied according to the constraints of what is practical and feasible in the football setting. The science underpinning sports nutrition is evolving fast, and practitioners must be alert to new developments. In response to these developments, the Union of European Football Associations (UEFA) has gathered experts in applied sports nutrition research as well as practitioners working with elite football clubs and national associations/federations to issue an expert statement on a range of topics relevant to elite football nutrition: (1) match day nutrition, (2) training day nutrition, (3) body composition, (4) stressful environments and travel, (5) cultural diversity and dietary considerations, (6) dietary supplements, (7) rehabilitation, (8) referees and (9) junior high-level players. The expert group provide a narrative synthesis of the scientific background relating to these topics based on their knowledge and experience of the scientific research literature, as well as practical experience of applying knowledge within an elite sports setting. Our intention is to provide readers with content to help drive their own practical recommendations. In addition, to provide guidance to applied researchers where to focus future efforts., Competing Interests: Competing interests: JC has received payment for sports nutrition consultancy work with Arsenal Football Club, England Football Association and France Football Federation. Through his consultancy he also receives payment for nutrition services with individuals and corporate organisations. He is author of a book (The Energy Plan) for which he receives payment from Penguin Random House. He has written articles for BBC Good Food for which he has received payment. He co-authored an article in 2014 and presented at European College of Sports Sciences in 2019 for The Gatorade Sports Science Institute, for which he received honoraria. He has received travel and accommodation expenses to speak at conferences over the past 5 years including; UEFA Medical Symposium, Isokinetic Football Medicine Strategies, Swedish Sports Medicine Congress and International Sport & Exercise Nutrition Conference. He is a council member and past president of The Royal Society of Medicine’s Food & Health Forum. He received from UEFA the cost of flight and accommodation to attend an Expert Group Meeting with the UEFA Medical Committee in Brussels, Belgium, to discuss preparation of this manuscript.” He did not receive any other form of financial support directly related to this manuscript. RM holds an honorary (unpaid) professorship at the School of Medicine, St Andrews University, Scotland. He holds visiting (unpaid) professorships at Stirling University and at the Chinese University of Hong Kong. He is co-author of two books published by Oxford University Press (Biochemistry of Exercise and Training; The Biochemical Basis of Sports Performance) for which he receives royalties. He is Program Director on the IOC Diploma programs in Sports Medicine, Sports Nutrition and Sports Physical Therapies, for which he receives honoraria and additionally contributes lectures to those programs, for which he has received honoraria. He was a member of the Expert Scientific Committee of the IOC Medical and Scientific Commission. This position was unpaid, but travel to meetings and accommodation were provided. He contributed a scientific review to a meeting of the Gatorade Sports Science Institute in Texas in March 2019: travel and accommodation were paid and an honorarium was received for participation in the meeting and for preparation of a summary paper for publication in the SSI Sports Science Exchange. He participated in an ACSM online podcast in 2019 for which an honorarium was received. He participated in a sports medicine education meeting organised by the Medical Committee of the German Football Federation in Frankfurt in January 2020: travel expenses and an honorarium were paid. He has participated in numerous other international sports nutrition symposia between 2015 and the present for which travel and accommodation were provided. He received from UEFA the cost of flight and accommodation to attend an Expert Group Meeting with the UEFA Medical Committee in Brussels, Belgium, to discuss preparation of this manuscript.” He did not receive any other form of financial support directly related to this manuscript. MG is co-author of two books published by Oxford University Press (Biochemistry of Exercise and Training; The Biochemical Basis of Sports Performance) for which he receives royalties. He is also co-author of 3 other books; one published by Human Kinetics (Sport Nutrition), one published by Routledge (Exercise Immunology) and the other by Meyer & Meyer Sport (Eat, Move, Sleep, Repeat; Beating Type 2 Diabetes) all of which he receives royalties for. He has contributed to several recorded lectures for which he received honoraniums for; 2020 to the IOC Diploma program Sports Nutrition, 2020 to the Nutrition Society Training Academy, 2020 to the My Sport Science Academy. He was a member of the IOC Expert Scientific Group on training load and illness/injury in 2015. This position was unpaid, but travel to a meeting and accommodation were provided. Other international symposia were attended as speaker where honorarium was paid plus travel and accommodation; Japan, 2016, London 2015, Barcelona 2015, Vienna, 2015. Mike also contributed a scientific review on nutrition, exercise and immune function for a sport nutrition company, NutritionX, in 2020 for which an honorarium was received. He has received complimentary tickets for Leicester City FC football matches for occasional nutrition consultancy advice but no honoraria were received. He has spoken at a number of other conferences, symposia and other events within the last five years: travel and accommodation were provided for most of these, but no record has been kept. He did not receive any form of financial support directly related to this manuscript. JB has presented at the Arsenal Sports & Exercise Medicine conference in London, UK, where travel and accommodation were paid by Arsenal FC. He has co-authored two chapters in the book, ‘The Science and Application of High-intensity interval training (HIIT) with no honorarium nor any royalties received. He did not receive any form of financial support directly related to this manuscript. AJ holds a visiting professorship at the Loughborough University, UK and is director of mysportscience. He is also co-founder and CEO of CORE Nutrition planning. He is author of a book sport nutrition by Human Kinetics for which he receives royalties. He is board member of the IOC Diploma programs in Sports Medicine. Asker worked as a consultant for the Dutch Olympic Committee NOC*NSF, Red Bull Leipzig, FC Barcelona, PSV Eindhoven, Athletic Club de Bilbao, US Soccer, Red Bull Athlete Performance Center, Jumbo Visma Pro cycling, Universidad d’Europea de Madrid, University of Barcelona, CAR, VIC University, Hiddit, SinSeb, Enervit, Volanthen, Friesland Campina, Nutrition Society, Clif, Snelle Jelle, Jumbo Supermarkten, PepsiCo, Unit Nutrition, BF Eventos, Mexican sports nutrition federation and the Turkish sports nutrition federation. Travel expenses and an honorarium were paid. He has participated in numerous other international sports nutrition symposia between 2015 and the present for which travel and accommodation were provided. He did not receive any form of financial support directly related to this manuscript. JM has received research grants from UEFA, Science in Sport, Lucozade Ribena Suntory, GlaxoSmithKline, Liverpool Football Club, Everton Football Club, British Horseracing Authority, Racing Welfare Foundation, Port Adelaide FC, English Institute of Sport and MuscleSound. He has received paid consultancy for Liverpool Football Club, Team Sky, Healthspan Elite, FA Premier League, Irish Football Association, The Football Association, Rangers FC and Science in Sport. He is the current Director of Performance Solutions for Science in Sport. He is the co-author of the textbook Biochemistry for Sport and Exercise Metabolism and receives annula royalties form Wiley. He has received travel and accommodation costs to speak at over 50 conferences in the last 5 years. He did not receive any form of financial support directly related to this manuscript. SP reports personal fees from Enhanced Recovery (donated to charity), equity from Exerkine (donated to charity), grants from Canadian Institutes of Health Research, grants from National Science and Engineering Council, personal fees (Travel and Honorarium, 2018) from US National Dairy Council, personal fees from US Dairy Export Council (Traval and Honorarium, 2019), personal fees from Leprino Foods (2017), personal fees from Agropur (2018), grants from Alliance for Potato Research and Education, grants from US National Dairy Council, outside the submitted work; In addition, Dr. Phillips has a patent 3052324 (Canadian) issued to Exerkine, a patent 16/182891 (US) pending to Exerkine, and a patent 2018157258 (Worldwide) pending to Exerkine. He did not receive any form of financial support directly related to this manuscript. LA received honoraria as an occasional consultant and reimbursement for travel expenses from the Drinking Water Research Foundation, Alexandria, VA, USA and from Danone Nutricia Research, France. He previously received research grant funding from both organizations. He formerly served as the elected President of the American College of Sports Medicine (unpaid), 2015-2016. He received honoraria and reimbursement of travel expenses from five universities and the Texas Regional Chapter of the American College of Sports Medicine during a speaking tour in 2018. He presently serves as a member of the Medical & Science Advisory Board, Korey Stringer Institute, University of Connecticut, USA (unpaid). Professor Armstrong received no financial support for participating in this manuscript. LB is an author or editor of textbooks on sports nutrition for which she receives royalties. She is a Program Director and contributor to the IOC Diploma programs in Sports Nutrition for which she receives honoraria. Prior to June 2020 she was Head of Sports Nutrition and Chief of Nutrition Strategy at the Australian Institute of Sport, where her representation at numerous international sports nutrition symposia and workshops was generally undertaken within her job description and any travel reimbursements and honoria were provided to the AIS. Presentations during the period of 2015-2020 in which the activity and its support were undertaken as private consultancy include: 2015 Berlin Marathon powerbar conference; 2019 ACSM meeting and pre-conference GSSI workshop (supported by the International Association of Athletics Federation and Gatorade); 2019 Northern Ireland Workshop on Sports Nutrition (supported by Dairy Council Northern Ireland) and the 2016 SCAN conference and 2019 FNCE conference (supported by the Academy of Nutrition and Dietetics). She has received a research grant from the Alliance of Potato Research and Education. She did not receive any form of financial support directly related to this manuscript. GC has previously received payment for nutrition consultancy at Everton, Nottingham Forest and West Bromwich Albion and Aston Villa Football clubs, Munster Rugby, England Rugby The Lawn Tennis Association The Football Association, The English Institute of Sport and The Saudi Arabian Olympic Association and The European Tour Golf. He currently advises HealthSpan Elite and NutritionX for which he receives an honorarium and in the past has advised GetBuzzing bars. GC has spoken on several occasions for GSSI and produced articles for their exchange series for which he received an honorarium. He has spoken at a number of other conferences, symposia and other events within the last five years: travel and accommodation were provided for most of these, but no record has been kept. GC currently or has previous received research grants from the MRC, BSSRC, GSK, Sirtris, Research into Ageing, Aliment Nutrition, Naturecan, HH Sheikh Mansour Bin Zayad Al Nahyan Global Arabian Horse Flat Racing Festival, The Racing Foundation, The British Horse Racing Association, The Rugby Football Union, The Lawn Tennis Association, Newport Gwent Dragons, Gloucester Rugby, Everton FC, Aston Villa FC. GC has delivered guest lectures for the IOC diploma in Sport Nutrition and The Football Science Institute for which he received an honorarium. GC has previously performed consultancy work for Callaway Golf and Quooker Taps. He did not receive any form of financial support directly related to this manuscript. RD receives is Joint Head of Research & Development at Football Federation Australia and is paid for this role. He has received travel and accommodation funding to speak / present at several international congress, including; the Football Science Institute, Football Federation Australia, Tennis Australia, Brazil National Football Federation, UFSC Brazil, Canadian Institute of Sport, Bristol City FC and UdS Germany. He is not affiliated or received any travel, accommodation, funding from any nutrition company in the last 10 years. He did not receive any form of financial support directly related to this manuscript. EL-M is author of a book published by Human Kinetics (Plant-Based Sports Nutrition: Expert Fueling Strategies for Training, Recovery, and Performance) for which she receives royalties. She was a member of the Dietary Supplements and the High-Performance Athlete Expert Scientific Committee of the IOC Medical and Scientific Commission in 2017; this committee assignment was unpaid, but travel to the group meeting and accommodation were provided. She contributed scientific presentations to a meeting of the Gatorade Sports Science Institute in Florida in Oct 2017 and Gatorade at NFL Combine in Feb 2020: travel and accommodation were paid and an honorarium was received for participations at both meetings and for preparation of a summary paper for publication in the SSI Sports Science Exchange in 2018. She presented at a Danone Essential Dairy and Plant-Based Proteins Board Meeting in New York in July in 2019 for which travel, accommodations and an honorarium were paid. She has participated in numerous other national nutrition and medical conferences between 2015 and the present for which travel and accommodation and typically an honorarium were received. She did not receive any form of financial support directly related to this manuscript. JL has received payment for sport nutrition consultancy work with French Football Federation, Liverpool Football Club, Lille Football Club, Paris-Dakar association. He has received travel/accommodation funding and honorariums to speak / present at several national/international conferences between 2015 to present) including: Research day of the Dairy Council UK; European College of Sport and Exercise Physicians, Paris, France; International conference of Sports Physiotherapy, Kuala Lumpur, Malaysia; French Football Federation congress for S&C coaches, Paris; congress of the Mexican Nutrition Society, Guadalajara; and congress of the Swiss Nutrition society, Nottwil. He has contributed to several recorded lectures for which he received honorariums for the IOPN Diploma, London, UK. He co-supervised a PhD project funded by a nutrition company (Lactalis, Laval, France). He did not receive any form of financial support directly related to this manuscript. DM has no conflicts to disclose. He did not receive any form of financial support directly related to this manuscript. FM is the main editor of a book published by CRC Press, Taylor & Francis Group (Fluid Balance, Hydration and Athletic Performance) for which she receives royalties. She hold a visiting professor position at the Human Movement Graduate Program from 2018 to 2020 (unpaid) at the Federal University of Rio Grande do Sul. She did not receive any form of financial support directly related to this manuscript. IR is an employee of the Gatorade Sports Science Institute (GSSI), a division of PepsiCo, Incorporated. The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of PepsiCo, Incorporated. Ian leads the FC Barcelona, innovation hub certificate in sports nutrition, he is co-author on the FC Barcelona Sports Nutrition guide for Football and co-organises the FCB conference in Sports nutrition, all as part of his role with GSSI. Ian co-authored a chapter on nutrition in the book “Elite Soccer Players” with no honorarium nor any royalties received. He not receive any form of financial support directly related to this manuscript. JSB holds a professorship at the Norwegian School of Sports Science in Oslo Norway. She receives research grants from The Norwegian Woman's Public Health Association, the Norwegian Extra Foundation for Health and Rehabilitation, The Norwegian Association of Youth Mental Health, and the Dam Foundation and TINE SA. She has contributed with lectures for the IOC Diploma programs in Sports Medicine and Sports Nutrition and receives honoraria for about one lecture per year. She was a member of the Expert Scientific Committee of the IOC Medical and Scientific Commission. She has also been a member in IOC working group (position papers). These positions were unpaid, but travel to meetings and accommodation were provided. She is also an International trustee (ACSM) and Vice president in Nordic Eating Disorder Society. These positions are unpaid, but travel to meetings and accommodation are provided. BW Received honorarium for consultancy with Nutricia. BW is the editor of one book (carnitine metabolism and human nutrition) published by CRC press for which he receives royalties. He has made lecture contributions to the International Society for Sports and Exercise Conference (ISENC), Nutrition Society, European Society for Parenteral and Enteral Nutrition (ESPEN) and Physiological Society which were unpaid for which he received expenses. He has received travel and expenses for an organised symposium (by Ketchum PR, US) at American Society for Nutrition (ASN) and the Reducetarian Conference. He has received payments from various UK universities for external examining with the last 5 years. He did not receive any form of financial support directly related to this manuscript. BB is co-author of two books, one published by McGrawHill (Nutrición Deportiva) for which she receives royalties and another one published by Organización Panamericana de la Salud (La Receta de los Campeones) for which she received royalties in the past. She is Program Director on the FMND-Nutrinfo Curse in Sports Nutrition, for which she receives honoraria and additionally contributes with one lectures to these program, for which she has received honoraria. She has participated in numerous international sports nutrition symposia between 2011 and the present for which travel and accommodation were paid by The Mexican Football Federation. She advises The Coca Cola Company for issues related to their Sport Beverage Powerade since 2012 for which she receives honoraria. She did not receive any form of financial support directly related to this manuscript. GD is head of performance for CF Real Madrid. He holds visiting (unpaid) professorships at Liverpool John Moores University He previously worked for the French Football Federation, Lille FC and the universities of Artois and Lille. He is co-author of a book on training methodology and performance (2007, three chapters (monitoring fatigue and recovery, Thieme eds, 2017; Targeted Systems of the Body for Training in Football Science, Human Kinetics, 2016; Boosting Aerobic Performance in High-Performance training for Sports, Human Kinetics, 2016), for which he received royalties. He has lectured for Aspetar twice (2013, 2016) recovery and nutrition courses for which he has received travel expenses, accommodation and an honorarium. He has spoken at 33 international conferences on sports science and football for which he has received travel expenses and accommodation, no honorariums have been received. He did not receive any form of financial support directly related to this manuscript. MAL: Toña is Professor of the Human Nutrition and Dietetics degree at the University of Barcelona and Nutritional Advisor of FCB. She is involved in clinical consultation and advice to competitive athletes and she did not receive any form of financial support directly related to this manuscript. PR is currently employed by the Dutch Olympic Team. He was formerly employed by AFC Ajax Amsterdam. He is owner of PR Sportvoedingsadvies. Through his consultancy he also receives payment for nutrition services with individuals and corporate organisations. He co-authored an article for The Gatorade Sports Science Institute, for which he received honoraria. He received honoraria as an invited speaker for the Barça Sport Nutrition Conference and FrieslandCampina Institute congress “sport en voeding”. He did not receive any form of financial support directly related to this manuscript. MB has received travel and accommodation funding (from the organizers and/or the Schulthess Clinic) to speak/present at several international congress between 2015 to present, including: the Isokinetic Football Medicine Strategies Conferences (2015-2019, London & Barcelona), Team Concept Conference 2016 (Las Vegas), the IOC World Conference 2017, the World Conference of Sports Physical Therapy (Belfast 2017, Vancouver 2019), the Salzburg Sports PT Congress 2019, the ACL Consensus Meeting (Pittsburgh 2019), the International Conference on Football Refereeing (Lisbon 2019), the International Society of Hip Arthroscopy Physiotherapy Meeting (Madrid 2019). As a member of F-MARC (2002- 2016) he received compensation from FIFA for his work during this time, but no other compensations or grants have been received. Between 2015 and 2019 he has authored/co-authored nine book chapters (football medicine, sports medicine) with no honorarium nor any royalties received. He did not receive any form of financial support directly related to this manuscript. CC: Since 2007 I have been invited in international conference/seminar by FIFA and UEFA for lectures on refereeing receiving no honorary but having paid travels, accommodation and daily expenses. I did not receive any form of payment for the contribution to this manuscript. CC has not received any honorarium from any company in the last 5 years. She is employed by the Football Association and has a private medical practice. She is member of the UEFA medical committee and have paid expenses (travel & accommodation) for UEFA medical committee meetings. She received from UEFA the cost of flight and accommodation to attend an Expert Group Meeting with the UEFA Medical Committee in Brussels, Belgium, to discuss preparation of this manuscript.” She did not receive any other form of financial support directly related to this manuscript. MD: The travel to attend an Expert Group Meeting with the UEFA Medical Committee in Brussels, Belgium, to discuss preparation of this manuscript was paid by UEFA. No other conflicts to declare. He did not receive any other form of financial support directly related to this manuscript. HG has received honorarium and reimbursement of travel and accommodation expenses for expert statements in doping cases in connection with nutritional supplements for several federations and anti-doping organisations, including UEFA and FIFA and several National Anti-Doping Agencies. He has received daily fees and reimbursement of travel and accommodation expenses for his participation in WADA expert groups for the athlete biological passport. He has received honorarium and reimbursement of travel and accommodation expenses for lectures about doping risks of nutritional supplements in congresses of several medical societies. He has received reimbursement of travel and accommodation expenses for his participation at the IOC consensus conference about nutritional supplements. The travel to attend an Expert Group Meeting with the UEFA Medical Committee in Brussels, Belgium, to discuss preparation of this manuscript was paid by UEFA. No other conflicts to declare. He did not receive any other form of financial support directly related to this manuscript. TM has never received any royalties or fees from nutritional companies or other relevant sources. For none of his publications has he ever received any financial compensation except for one article about the management of infectious diseases in the Aspetar Sports Medicine Journal. He received from UEFA the cost of flight and accommodation to attend an Expert Group Meeting with the UEFA Medical Committee in Brussels, Belgium, to discuss preparation of this manuscript.” He did not receive any other form of financial support directly related to this manuscript. NP: The travel to attend an Expert Group Meeting with the UEFA Medical Committee in Brussels, Belgium, to discuss preparation of this manuscript was paid by UEFA. No other conflicts to declare. She did not receive any other form of financial support directly related to this manuscript. MV: The travel to attend an Expert Group Meeting with the UEFA Medical Committee in Brussels, Belgium, to discuss preparation of this manuscript was paid by UEFA. No other conflicts to declare. He did not receive any other form of financial support directly related to this manuscript. AM has received a grant from FIFA to investigate health and performance of footballers during the transition from club to national teams. He has received travel and accommodation funding to speak / present at several international congress between 2015 to present), including; the Isokinetic Football Medicine Strategies Conference (London and Barcelona), KNVB national federation, Danish SportsKongress, Denmark, Sportsfisio congress, Switzerland, The Barça Innovation Hub, Barcelona, Spain. Oslo Sports Trauma Research Group, Oslo, Norway. Mapei Research Centre, Bergamo, Italy. Brazil National Football Federation, Rio, Brazil, French Football Federation, Paris, France. He is not affiliated or received any travel, accommodation, funding from any nutrition company. He also received consultancy fee from the French Football Federation for injury prevention recommendations for the 2018 FIFA World Cup. He received from UEFA the cost of flight and accommodation to attend an Expert Group Meeting with the UEFA Medical Committee in Brussels, Belgium, to discuss preparation of this manuscript.” He did not receive any other form of financial support directly related to this manuscript., (© Author(s) (or their employer(s)) 2021. No commercial re-use. See rights and permissions. Published by BMJ.)

Competing Interests: Competing interests: See COI document linked to the main paper (too large to copy paste in here).