Cycling is an increasingly popular sport and is used as both a recreational activity and a form of transport globally (1). Cycling is made up of two main categories, ‘road’ (or street) and ‘mountain’ (or off-road) biking. Mountain biking is further described by the Union Cycliste Internationale (UCI) as cross-country, cross-country marathon, downhill and four-cross (2). Cross-country is exclusively an elite competition for professional riders, while cross-country marathon includes both amateur and professional riders in the same races on the same routes. These routes are usually between 60 and 120 km (2). Mountain biking can include highly technical riding through rough terrain and with steep downhills, while the challenges of road cycling include negotiating other vehicles and pedestrians in traffic (3,4). Competitive races are becoming more demanding and have evolved into multi-stage races in both road and mountain cycling categories (5).
As participation in cycling has increased, conflicting evidence on the incidence of injury has emerged (6,7). Both Denmark and the United States report a national decrease in injury incidence, while Australia has reported an increase in cycling injuries presenting to emergency departments (6,8,9). In Denmark in 2015, commuter cycling resulted in 26 cycling related deaths, 297 light injuries and 512 severe injuries in a population of 5.7 mil (8). In the United States, cycling injuries account for 12.7% of all sports- or exercise-related injuries, and of these injuries, only 9.5% occurred during ‘sporting activity’ (7). The majority (56%) occurred while commuting on the streets, with 70% of street injuries involving a motor vehicle (7).
Fifty percent of mountain bikers have reported at least one serious acute injury related to mountain biking and in professional mountain bikers this number increases to 80% (6). The incidence of injury among cross-country marathon riders is 7.5 and 3.1 injuries per 1000 hours in males and females respectively. Downhill riding is associated with a significantly greater incidence of injury (males; 46.8 injuries per 1000 hours, and females; 42.7 injuries per 1000 hours) (6). Most data on cycling injuries report cases presenting to emergency departments; these data may underestimate the incidence, particularly of the less serious injuries. Many race events have onsite medical care, and these riders may never be admitted to hospital (10). Care must be taken in extrapolating national cycling injury data to competitive cycling events as the mechanisms, incidence and management of these injuries may differ between commuting and race events.
Acute injuries in competitive cycling may result from falls and collisions, or rapid and forceful contractions resulting in musculotendinous injuries, contusions or bony fractures (11). Falls related to collisions with other riders accounted for 17% and mechanical failures accounted for a further 16%. The remaining 68% were caused by loss of control (32%), loss of traction (14%), collisions with stationary objects (7%) and other or unknown causes (14%) (11). There are more spinal injuries in mountain biking than in road cycling due to the the rider falling over the handlebars onto the top of the head (12). Injuries in mountain biking events present a unique challenge to event organisers. Riders may present with a combination of muscle strains, joint injury, overuse injury and trauma related to falling, and there may be a lack of access to injured athletes related to the environment/terrain (13).
Illness in mountain biking is not well reported. Most of the data are from a limited number of race events (14,15). Gastrointestinal illness, allergies, respiratory illness, dehydration, headaches and skin irritations are the most commonly reported illnesses in cycling events (14,16,17). In the 2016 Olympic Games, approximately 5% of mountain bikers were treated for a variety of illnesses by their medical teams (14).
The reporting of injury and illness in events varies depending on the definitions used by the researchers. The International Olympic Committee uses a medical attention definition for both injury and illness, and includes all occurrences of injury or illness reported to the medical teams regardless of the effect on the athlete’s ability to continue training or to compete (14). Severity of the injury or illness is determined by the number of days absence from training or competition, and more than one week is defined as ‘severe’ (14).
The Consensus Statement of Epidemiological Studies in Athletics defines injury ‘a physical complaint or observable damage to the body produced by a transfer of energy of the athlete’ (15). Illness is defined as a ‘physical or psychological complaint or manifestation by an athlete not related to injury’ (15). This consensus statement is explicit that injuries and illness have occurred regardless of the impact on training or competition and whether or not medical attention was sought. This definition has been adapted for use in a previous cycling study, but injuries and illness were reported based only on medical attention following interactions with medical staff in spite of the definition (16). When only including medical attention injuries, it is possible to underestimate the incidence as riders who are able to continue without medical intervention, or are self-treating would not be considered injured.
Significance of this systematic review
Injury and illness prevention programmes require knowledge of the aetiology and magnitude of the injury or illness problem within the context of the sport (18,19). The current available knowledge in cycling is largely based on commuter cycling and hospital admissions. This systematic review will provide a comprehensive review of the available injury and illness statistics and reporting in mountain biking events of different lengths. Differences in injury reporting methods will be identified and may assist in the development of a more appropriate injury definition specific to mountain biking. The magnitude of the injury and illness problem in mountain biking races will be identified. Existing gaps in the literature will be also be identified for further investigation.