Roald Bahr

Norwegian School of Sport Sciences · Department of Sports Medicine

The International Olympic Committee’s (IOC) consensus statement on ‘methods for recording and reporting of epidemiological data on injury and illness in sport’ recommended standardising methods to advance data collection and reporting consistency. However, additional aspects need to be considered when these methods are applied to specific sports se...

Background The long-term prognosis of jumper's knee and whether structural changes in the patellar tendon persist is unknown. Purpose To investigate whether limitations in knee function and structural changes persisted beyond the athletic career of young elite volleyball players. Study Design Cohort study; Level of evidence, 2. Methods Volleybal...

Background Current injury prevention programmes in football are limited by a one-size-fits-all approach, which predominantly focuses on preventive exercise programmes while ignoring differences in risk profiles between individuals and teams. Objective To address this gap, we developed a new data-driven, customisable approach based on the principle...

Knowledge of how to treat chronic tendinopathy has advanced in recent years, but the treatment of early tendinopathy is not well understood. The main purpose of this prospective observational study was to investigate if changes occur in clinical and imaging outcomes over 12 weeks in elite athletes with recent debut of tendinopathy. Sixty‐five elite...

Objective To describe and categorise the injury-inciting circumstances of sudden-onset hamstring match injuries in professional football players using systematic video analysis. Methods Using a prospective injury surveillance database, all sudden-onset hamstring match injuries in male football players (18 years and older) from the Qatar Stars Leag...

Objective A periodic health evaluation (PHE) is a comprehensive and multidisciplinary investigation of athlete health widely used in elite sport, but its contents and benefits can be questioned. This study aimed to determine the prevalence of conditions identified by a PHE among Paralympic and Olympic athletes over four consecutive Games cycles fro...

The aim was to determine how jump load affects knee complaints in elite men's volleyball. We collected data from four men's premier league volleyball teams through three seasons in a prospective cohort study (65 players, 102 player‐seasons). Vert inertial measurement devices captured the jump load (jump frequency and jump height) from 21 088 daily...

Objective To describe the prevalence, incidence, and burden of groin injuries in the Norwegian women's premier football league and to describe their clinical and imaging characteristics. Methods During the 2020 and 2021 seasons, players in the Norwegian women's premier league reported groin injuries weekly, using the Oslo Sports Trauma Research Ce...

Background In male football, adductor injuries have been reported to account for two thirds of all groin injuries, and therefore, been the focus for prevention. This classification of groin injuries into clinical entities has not yet been utilized in epidemiological studies in professional women’s football. Objective To record all groin injuries i...

Background The efficacy of injury prevention programs is clear, but their causal mechanisms are not. Better knowledge about why injury prevention programs work will improve implementation and guide further research. Objective To describe the proposed biomedical effect mechanisms in research on injury prevention programs in football and handball....

Background Jumper’s knee is difficult to treat; athletes may suffer persistent problems during their career, and some even retire. However, the long-term prognosis is unknown. Objective To investigate whether young athletes with jumper’s knee suffer persistent problems post-career or retire from sport. Design Prospective cohort study. Setting &...

Rapid somatic growth and biological maturity status may affect injury patterns in youth football, yet firm conclusions cannot be drawn from the existing research. We aimed to explore growth velocity, maturity and age as injury risk factors in 95 academy players (11.9-15.0 years), using anthropometric (height and body mass), maturity (skeletal age),...

Objective To describe the patterns of health problems among Norwegian Olympic candidates during their preparations for five consecutive Olympic Games (London 2012, Sochi 2014, Rio de Janeiro 2016, PyeongChang 2018 and Tokyo 2020). Methods This was a descriptive epidemiological study using the Oslo Sports Trauma Research Center Questionnaire on Hea...

Objectives To describe the prevalence, incidence and burden of all health problems in the Norwegian women’s premier league. Methods During the 2020 and 2021 seasons, players in the Norwegian women’s premier league reported all health problems (sudden-onset injuries, gradual-onset injuries and illnesses) weekly, using the Oslo Sports Trauma Researc...

Background Nordic hamstring test devices are commonly used to measure maximal eccentric hamstring force. The ability to control the final phase of the exercise has been adopted as a criterion to add weight when testing, without substantial evidence. We investigated if adding weight affected the maximal force measured, and if there were differences...

Background Athletes are at risk for developing exercise-induced lower airway narrowing. The diagnostic assessment of such lower airway dysfunction (LAD) requires an objective bronchial provocation test (BPT). Objectives Our primary aim was to assess if unsupervised field-based exercise challenge tests (ECTs) could confirm LAD by using app-based sp...

ABSTRACT Objective Vertical jump tests are more sensitive in revealing asymmetries in performance metrics at the time of return to sport after anterior cruciate ligament (ACL) reconstruction (ACLR) than horizontal hop tests. However, it remains unclear which vertical tests (bilateral or unilateral) and which metrics (kinetics or performance) are mo...

Introduction Regular exercise is associated with reduced risk of cardiovascular disease. Paradoxically, an increased risk of sudden cardiac arrest (SCA) is documented during or immediately after exercise and in athletes compared to the nonathletic population. Our objective was to identify, through multiple sources, the total number of exercise‐rela...

Context: The knee, low back, and shoulder account for the majority of overuse injuries in volleyball; unfortunately, previous studies utilized methodology that failed to examine the extent of their injury burden and impact on performance. Objective: To develop a more accurate and complete understanding regarding the weekly prevalence and burden...

Background Research focusing on reducing the risk of injuries has increased over the last two decades showing that prevention implementation in real life is challenging. Objective To explore the experience and opinions of professional football stakeholders regarding injuries, their prevention and the implementation of preventive measures. Design...

Epidemiological studies on fractures in European professional football (soccer) are in abundance. However, such data are lacking in Middle Eastern professional footballers and information on fracture treatment is scarce. The aim of this study is to describe the epidemiology of fractures across seven seasons in Qatar Stars League (QSL) footballers....

Objectives: We studied associations between the burden of health problems and athlete burnout in a population of athletes from Norwegian Sport Academy High Schools. Methods: This is a mixed prospective/retrospective cohort study. We included 210 athletes, 135 boys and 75 girls, from endurance, technical and team sports. We used the Oslo Sports T...

Introduction The primary aim of this study was to describe the clinical entities and imaging characteristics of groin injuries in women’s football. Materials and Methods During the 2020 and 2021 seasons, players in the Norwegian women’s premier football league reported groin injuries weekly, using the Oslo Sports Trauma Research Center Questionnai...

Introduction Previous epidemiological studies in women’s football have used methods inappropriate to capture overuse injuries and illnesses. The aim of this study was to describe the injury and illness patterns in women’s premier league football. Materials and Methods During the 2020 and 2021 seasons players in the women’s premier football league...

Several sports have published consensus statements on methods and reporting of epidemiological studies concerning injuries and illnesses with football (soccer) producing one of the first guidelines. This football-specific consensus statement was published in 2006 and required an update to align with scientific developments in the field. The Interna...

Objectives At present, there is no cure for osteoarthritis (OA), but severe hip joint degeneration can require total hip arthroplasty (THA). The literature on OA after elite sport is limited. We hypothesise that elite athletic activity increases the risk of receiving a THA later in life. Methods We linked a cohort of former Norwegian world-class a...

Introduction: Neurological soft signs (NSS) are minor deviations from the norm in motor performance that are commonly assessed using neurological examinations. NSS may be of clinical relevance for evaluating the developmental status of adolescents. Here we investigate whether quantitative force plate measures may add relevant information to observe...

Neurological soft signs (NSS) are minor deviations in motor performance. During childhood and adolescence, NSS are examined for functional motor phenotyping to describe development, to screen for comorbidities, and to identify developmental vulnerabilities. Here, we investigate underlying brain structure alterations in association with NSS in physi...

Background Training and game loads are potential risk factors of injury in junior elite ice hockey, but the association of training and game loads to injuries is unknown. Purpose To investigate the association of chronic training and game loads to injury risk in junior male elite ice hockey players. Study Design Cohort study; Level of evidence, 2...

The evidence-based hamstring strengthening programme for prevention of hamstring injuries is not adopted by football teams because of its high training volume. This study on female football players investigated if high-volume training with the Nordic hamstring exercise is more effective on hamstring strength, jump height, and sprint performance tha...

Background Injury risk prediction is an emerging field in which more research is needed to recognize the best practices for accurate injury risk assessment. Important issues related to predictive machine learning need to be considered, for example, to avoid overinterpreting the observed prediction performance. Purpose To carefully investigate the...

Hamstring injuries constitute the single largest cause of lost playing time in professional football. While restoring high‐speed running ability is paramount for rehabilitation from these injuries, little evidence exists regarding the extent of return to sport running performance after hamstring injury in football. We examined medical and match per...

To assess the mechanisms of ACL injury in male professional football players in Qatar across multiple seasons using systematic video analysis. 15 ACL injuries occurred in competition among the professional football teams that participated in an injury Surveillance Programme during 6 seasons (2013/2014 to 2018/2019). High-definition broadcast videos...

Quantification methods based on the acquisition of diffusion magnetic resonance imaging (dMRI) with multiple diffusion weightings (e.g., multi-shell) are becoming increasingly applied to study the in-vivo brain. Compared to single-shell data for diffusion tensor imaging (DTI), multi-shell data allows to apply more complex models such as diffusion k...

Introduction Most epidemiological studies in the field of military medicine have been based on data from medical records and registries. The aims of this study were to test a self-reporting injury surveillance system commonly used in sports medicine in a military setting, and to describe the injury pattern among Norwegian army conscripts during a p...

Background Current return-to-sport (RTS) criteria after anterior cruciate ligament (ACL) reconstruction (ACLR) include demonstrating symmetry in functional and strength tests. It remains unknown if at the time that athletes are cleared to RTS, they exhibit between-limb symmetry in ACL and tibiofemoral contact forces or if these forces are comparabl...

Background To evaluate the efficacy of early versus delayed introduction of lengthening (ie, eccentric strengthening) exercises in addition to an established rehabilitation programme on return to sport duration for acute hamstring injuries in a randomised controlled superiority trial. Methods 90 male participants (age: 18–36 years, median 26 years...

Aim: To explore the short-term effects of accidental head impacts and repetitive headers on circulating microRNAs, accounting for the effects of high-intensity exercise alone. Methods: Blood samples were collected from professional soccer players at rest. Repeat samples were drawn 1 h and 12 h after three conditions: (1) accidental head impacts...

Background After anterior cruciate ligament reconstruction (ACLR), a battery of strength and hop tests is frequently used to determine the readiness of an athlete to successfully return to sports. However, the anterior cruciate ligament reinjury rate remains alarmingly high. Purpose To evaluate the lower limb function of athletes after ACLR at the...

Objectives: Vertical jump performance (height) is a more representative metric for knee function than horizontal hop performance (distance) in healthy individuals. It is not known what the biomechanical status of athletes after anterior cruciate ligament (ACL) reconstruction (ACLR) is at the time they are cleared to return to sport (RTS) or whether...

Repetitive head impacts (RHI) are common in youth athletes participating in contact sports. RHI differ from concussions; they are considered hits to the head that usually do not result in acute symptoms and are therefore also referred to as “subconcussive” head impacts. RHI occur e.g., when heading the ball or during contact with another player. Ev...

Background Little is known about the association between physical fitness and the risk of injury or illness in ice hockey. The least-fit players may be more prone to injury and illness. Purpose To examine the association between preseason fitness level and injury or illness risk among elite ice hockey players during the regular season. Study Desi...

The objective of this study was to examine the effect of a neuromuscular training (NMT) warm-up on the prevalence of overuse lower extremity (LE) injuries in children’s football. Twenty Finnish U11-U14 youth football clubs (n=1409 players; females 280, males 1129; age range 9-14) were randomised into intervention and control groups containing 10 cl...

Background Shoulder problems are common in handball, but preventable. However, player compliance remains a challenge, as the existing prevention program is time consuming. Objective To assess the effect of the Oslo Sports Trauma Research Center shoulder injury prevention program on external rotation (ER) strength and internal rotation (IR) range o...

Background While effective programmes to prevent anterior cruciate ligament (ACL) injury have been established, it is important that programme design, consistent with the van Mechelen model, is based on the specific injury mechanisms, representative of the region and playing conditions. Presently, no such data exist for professional football player...

Background Studies addressing risk factors for injuries in youth athletics are scarce and although growth and maturation represent potential risk factors for adolescent athletes, the available literature is inconclusive. Objective The aim of this study was to examine if growth rate, maturity status and maturity tempo are associated with injury ris...

Background Little is known about the association between physical fitness and the risk of injury or illness in ice hockey. Objective The aim of this study was to examine the association between pre-season fitness level and injury or illness risk among elite ice hockey players during the subsequent season. Design Prospective cohort study. Setting...

Background The link between head-impact exposure in football and neurological sequelae remains controversial. Blood-based biomarkers can provide valuable information in traumatic brain injuries, reflecting e.g. axonal damage. Objective To investigate if repetitive headers or accidental head impacts in football could cause structural damage to the...

Background Little is known about the burden of overuse injuries and illnesses in junior elite ice hockey. Objective The aim of this study was to describe the prevalence and burden of all health problems in junior elite ice hockey in Norway during one school year. Design Prospective cohort study. Setting Elite Sport Academy High Schools in Norway...

Background As previous epidemiological studies in elite ice hockey have focused on acute time-loss injuries, little is known about the burden of overuse injuries and illnesses in ice hockey. Objective The aim of this study was to report the prevalence and burden of all health problems in male senior elite ice hockey during one competitive season....

Background Wearable sensor systems have the potential to quantify head kinematic responses of head impacts in football. However, on-field use of sensors (e.g. accelerometers) remains challenging due to factors such as poor coupling to the head. Objective To test the validity of a novel in-ear sensor for quantifying head-impact exposure in youth fo...

Background Previous research indicates that psychological factors is associated with injury incidence. The associations between health burden, psychological health and coaching style have, to our best knowledge not been investigated. Objective Explore associations between health burden, need-supportive coaching and athlete burnout after three year...

Background Restrictions on heading in youth football have been implemented in the U.S. to limit head-impact exposure up until the age of 13. However, current interventions remain poorly guided by evidence, and providing more accurate data on heading exposure is key to assess risk. Objective To quantify heading exposure in youth football, assessing...

Introduction Physeal injuries have been overlooked in epidemiological research in youth sports. Our prospective study investigated the incidence, severity, and burden of physeal injuries in a youth elite football academy. Methods 551 youth male football players from Under-9 to Under-19 were included and observed over four consecutive seasons. Inju...

Objective To describe the illness and injury pattern of Norwegian Para athletes over five consecutive Paralympic Summer and Winter Games cycles and to identify which health problems should be targeted in risk management plans with respect to impairment types. Methods We monitored athletes from 12 to 18 months prior to each Game using a weekly onli...

Background Little is known about the burden of overuse injuries and illnesses in junior elite ice hockey. Purpose To describe the prevalence and burden of all health problems in junior male elite ice hockey players in Norway during 1 school year. Study Design Descriptive epidemiological study. Methods A total of 206 junior male ice hockey player...

Classification algorithms determine the similarity of an observation to defined classes, e.g., injured or healthy athletes, and can highlight treatment targets or assess progress of a treatment. The primary aim was to cross-validate a previously developed classification algorithm using a different sample, while a secondary aim was to examine its ab...

Objective: To determine whether visually assessed performances of the single-leg squat (SLS) and vertical drop jump (VDJ) were associated with future noncontact anterior cruciate ligament (ACL) injury. Design: Prognostic accuracy cohort study. Methods: Elite female handball and football (soccer) athletes (n = 880) were tested from 2007 to 2014...

Background Despite being the most commonly incurred sports injury with a high recurrence rate, there are no guidelines to inform return to sport (RTS) decisions following acute lateral ankle sprain injuries. We aimed to develop a list of assessment items to address this gap. Methods We used a three-round Delphi survey approach to develop consensus...

Background: We assessed SARS CoV2 contamination of random surfaces in football training facilities in an environment with a high prevalence of infections. Methods: In six clubs of the Qatar Stars League, surfaces of random locations (high touch areas, ventilation systems, toilets, cleaning tools, freezers, pantries) in routinely cleaned training fa...

Objective To describe the implementation of a health monitoring programme for Norwegian Paralympic and Olympic candidates over five consecutive Olympic and Paralympic Games cycles (London 2012, Sochi 2014, Rio de Janeiro 2016, PyeongChang 2018 and Tokyo 2020). Methods Athletes were monitored for 12–18 months preparing for the games using a weekly...

The aim of this study was to investigate if frontal plane knee and hip control in single-leg squats or vertical drop jumps with an overhead target were associated with future non-contact anterior cruciate ligament (ACL) injury in elite female athletes. Of the 429 handball and 451 football athletes (age 21.5 ± 4.0 years, height 169.6 ± 6.4 cm, body...

Background We evaluated the lower limb status of athletes after anterior cruciate ligament reconstruction (ACLR) during the propulsion and landing phases of a single leg hop for distance (SLHD) task after they had been cleared to return to sport. We wanted to evaluate the biomechanical components of the involved (operated) and uninvolved legs of at...

Many handball studies have reported injuries that cause absence from participation. In this prospective cohort study on elite Icelandic male players, the aim was to examine the prevalence of overuse problems in low back, knee and shoulder. Sixteen Icelandic teams were invited. Thirteen teams agreed to participate. The OSTRC overuse questionnaire wa...

Background The association between injury risk and skeletal maturity in youth soccer has received little attention. Purpose To prospectively investigate injury patterns and incidence in relation to skeletal maturity in elite youth academy soccer players and to determine the injury risks associated with the skeletal maturity status, both overall an...

Objectives The risk of viral transmission associated with contact sports such as football (soccer) during the COVID-19 pandemic is unknown. The aim of this study was to describe the infective and immune status of professional football players, team staff and league officials over a truncated football season resumed at the height of the COVID-19 pan...

Background: The UEFA Elite Club Injury Study is the largest and longest running injury surveillance programme in football. Objective: To analyse the 18-season time trends in injury rates among male professional football players. Methods: 3302 players comprising 49 teams (19 countries) were followed from 2000-2001 through 2018-2019. Team medica...