Mountain Bike Injuries
by Brendan Anstiss 1997
This is an except from Brendan's thesis which is due to be finished in the next few months. We hope to publish the whole thesis when available. For more information contact firstname.lastname@example.orgCopyright 1997 Brendan Anstiss.
- The Development of Mountain Biking
- Mountain Biking in New Zealand
- Official Statistics for Mountain Bike Morbidity and Mortality
- Summary of New Zealand Injury Statistics
- Academic Research on Mountain Biking Mortality and Morbidity
Mountain biking is a sport involving cycling off the road, over varied terrain, on bikes specifically built to withstand hard knocks and rough treatment. Mountain biking originated in Marin County, California. In 1974 local cycle enthusiasts Gary Fisher and Charles Crow began riding the fire roads of Mount Tamalpias. Ironically Fisher and Crow rode antique Schwinn Excelsior bikes, made in the late 1930ís. Later that same year they built their first hybrid mountain bike, constructed of a reinforced steel frame and fitted with a multitude of salvaged parts. These early innovators yearned to escape the traffic and pollution of San Fransico streets and turned instead to the relative wilderness of Mount Tamalpias. The bikes were rebuilt as they broke, which by all accounts was quite frequently, so the evolutionary process was rapid. Joe Breeze built light weight custom frames, Gary Fisher added gears for uphill riding and Charles Kelly organised the first races.
In a matter of years, Kelly, Fisher and Tom Ritchey had designed and marketed the first custom mountain bike. By 1981 they were joined by the first production mountain bike, the Specialized Stumpjumper. Both Fisher and Ritchey mountain bikes are still produced today, almost a quarter of a century since the originals were first test piloted.
With the explosion of mountain biking as a popular pastime and legitimate sporting pursuit, the conventional mountain bike, as ridden by the pioneers, has since developed into a sophisticated machine with complex suspension, lightweight alloy frame, an effective and reliable braking system, and up to 24 possible gearings suitable for almost every situation.
Mountain biking has enjoyed one of the most spectacular and successful growths of any modern sport (Martin, 1989). In 1996 mountain biking featured as a full medal competition at the Atlanta Olympic Games, unprecedented for a sport so young (Kronisch, Chow, Simon and Wong, 1996). From the humble beginnings of a small group of friends, by 1983 approximately 200 000 American adults regularly rode (Foote, 1987; Coello, 1987), and by 1989 there were an estimated seven and a half million riders, an increase of 3 750 per cent in just six years (Martin, 1989). In 1982 the estimated market share of mountain bikes was less than 1 per cent of the total North American bicycle market, by 1986 it has risen to 20 per cent (Spray, 1986) and by 1990 market share was 42 per cent (Shoa, 1990). This phenomenal increase was not just restricted to North America. The first mountain bike was introduced to England in 1983 (Ruff and Mellors, 1993), by 1987 there were an estimated 20 000 mountain bikes in the country, and by the end of 1990 a phenomenal increase saw the figure mushroom to over one and a half million (Penna, 1990). A similar pattern is reported in Europe. In West Germany for example, in 1990, mountain bikes accounted for 50 per cent of all bicycles sold. This equates to more than one million mountain bikes sold in just one year (Penna, 1990).
Mountain bikes started appearing in small numbers in New Zealand in 1984. Cycle manufacturer Healing imported 15 Shogun mountain bikes and soon after began local production of an almost identical bike, the Mountain Cat (Kennett, Kennett and Kennett, 1993). In 1985 the lowering of import duty on a variety of recreational equipment saw the large scale importation on mountain bikes. Today mountain bikes comprise the majority of the bicycle market in New Zealand. The Bicycle Industry Association of New Zealand (BIANZ) reports than in 1996 159 000 bicycles of all types were imported into the country (BIANZ Unpublished figures, 1997). It is commonly accepted that mountain bikes comprise approximately 80 per cent of the total New Zealand bicycle sales market (Kennett et. al, 1993; Litten, 1992). This compares to slightly over 50 per cent in 1990 (Horne, 1992) and little more than 1 per cent of the total market in 1986 (Litten, 1992). With regard to actual participation figures for the sport of mountain biking, the most comprehensive statistics are provided by the Hillary Commissionís Life in New Zealand Study (1996). Twelve month participation figures reveal that approximately 166 000 persons over the age of 18 years participate in the sport of mountain biking. No distinction is made between the various competitive disciplines of mountain biking. Unfortunately, there are currently no participation figures available that include persons aged below 18 years.
The history of mountain biking as a sport has been well documented by Olsen (1989) and Gaskin and Torr (1988). These sources serve as general introductory manuals, instructing potential consumers on the purchase of a mountain bike, how to improve riding technique and mechanical information on maintenance and repair once you have your mountain bike. However, while these texts are well designed for the recreational market, there is a dearth of qualitative and quantitative academic literature in regards to the subject of mountain biking, particularly with respect to the potential and actual aversive physical consequences of participation. It is this area with which the current study is concerned.
The two major sources of official statistics for sport and recreation injuries in New Zealand are firstly, the Accident Rehabilitation and Compensation Insurance Corporation (ACC) annual injury statistics and secondly, hospital admissions (accident and emergency) as a result of a sporting accident.
ACC Injury Statistics
The most comprehensive collection of morbidity and mortality statistics for New Zealand is contained in the ACC annual injury statistics publication (ACC, 1995). Sport and recreation claims comprise a single section, this is subdivided into 49 separate sporting and recreation activities. This list includes traditional sports such as rugby, netball and jogging and also sports appealing to a more select group of participants, such as bungy jumping, luge riding and motor-cross. Mountain biking does not have its own classification and falls under the broad class of cycling. This presumably includes road cycling, track cycling and BMX, in addition to mountain biking. The gross generalisation of combining diverse cycling activities into a single class is a major fundamental flaw of almost all official statistics. As a result, differences in morbidity and mortality patterns among each distinct cycling discipline are confused or lost altogether.
While it is not possible to accurately determine the extent to which this confounding takes place nor its ultimate effect on official morbidity and mortality rates, descriptions of the various cycling disciplines provide strong support for the potential existence of such an effect. Each discipline presents different challenges and threats to the safety of riders. Road cycling and track cycling pose few natural unexpected hazards but involve consistently high speeds and close bunch riding formation. Protective equipment in these disciplines is normally limited to a lightweight shell helmet. BMX on the other hand involves man made obstacles and jumps designed to spectacularly launch the rider into aerial manoeuvres. Speeds are typically lower than road and track cycling, and riders wear full face hard shell helmets (similar to motorcycle helmets) and protective body armour. Until this point mountain biking has been treated as a single sport, yet beyond the recreational level a number of separate disciplines exist, each differs markedly in racing format, course design and challenges to participants. The most common racing formats typically include cross-country, downhill, hill climb and dual slalom. While it is not pertinent to discuss the various protective and vulnerability factors of each discipline at this stage, it is important to recognise that cycling, and even mountain biking, is not a homogenous sport and therefore variations in frequency and severity of both injury and accident, are likely to be encountered. The present organisation of official statistics does not allow for interpretation of this phenomenon, hence their usefulness in describing mountain biking morbidity and mortality rates is severely limited. Nonetheless the figures may provide an estimate of the morbidity and mortality rates for cycling as a whole (ie. road, track, BMX and mountain biking).
In the year ending June 30th 1995, 427 non-fatal claims and one single fatal claim for the sport of cycling were registered with the ACC. With respect to non-fatal injury claims; in ranked order, this would place cycling 14th out of the 49 sporting categories. This is well behind the leading sports for non-fatal injuries, rugby union, rugby league, netball and skiing, and even sports commonly perceived as safe, such as cricket and tennis.
The second major source of official statistics for cycling morbidity and mortality rates
is hospitalisation figures. An epidemiological study by Hume and Marshall (1994) examined sporting injury admissions to a provincial hospital accident and emergency department. Admissions were coded by the type of sport. As with ACC statistics, no distinction was made between the various cycling disciplines. Results are therefore subject to the same criticisms as ACC figures, hence cycling injury rates should not be interpreted as being accurately representative of mountain bike injury rates.
A total of 4 374 sporting injury admissions were recorded, cycling comprised just 0.6 per cent of these. On a ranked scale, this places cycling far behind the most hazardous sports, with rugby accounting for 35 per cent, and horse-riding with 15.3 per cent of all sporting injury admissions. Cycling has an equivalent hospitalisation rate to the sports of badminton, golf and athletics.
Thus far, the two investigative methods reviewed, ACC statistics and hospitalisation rates, have not proved useful in elucidating accurate objective morbidity and mortality rates for the sport of mountain biking. Without more detailed methodologies and changes to the categorical coding practises of health service providers, the situation within New Zealand is unlikely to change. Furthermore, financial constraints have limited the ability of organisations such as the ACC to provide any more information for research purposes than that contained in their annual report.
Despite the astonishing increase in the popularity of mountain biking, prior to 1993 no published studies had examined the morbidity or mortality rate of this fashionable pastime (Chow, Bracker & Patrick, 1993). Even now, only a handful of retrospective surveys and a similar number of descriptive studies exist on the frequency and nature of mountain biking injuries.
The first comprehensive study of mountain biking, conducted by Chow, Bracker and Patrick (1993), used a postal survey of members of two Southern Californian recreational mountain bike clubs. Cyclists were questioned about their riding and safety habits, the kind(s) of injury sustained with their most recent accident, whether they sought medical treatment, and the circumstances of the accident. Of the 268 mountain bikers questioned, 84 per cent had been injured while riding, 51 per cent in the past year. Twenty-six per cent of those injured required professional medical care and 4.4 per cent were admitted to hospital. The most significant factor contributing to an injury was the grade of terrain on which the accident occurred. Seventy-five per cent of injuries occurred on either moderate or steep downhills, 15 per cent on flat terrain, and the remainder on steep or moderate uphills. This supports the previous suggestion that the competitive mountain biking disciplines of cross-country, downhill and hill climb all differ markedly in their challenges to participants and subsequently each has an individual subset of risk factors contributing to different patterns of injuries.
Kronisch and Rubin (1994) conducted a similar study, using the same methodology, except among a group of competitive mountain bikers. Of the 265 riders surveyed, 86 per cent reported an injury in the preceding year. Further analysis revealed the majority of accidents to be minor. Only 20.4 per cent (54 out of 265) riders sustained an injury severe enough to prevent them from riding for at least one day and requiring medical attention. Likelihood of injury was positively associated with competitive racing at the time. Competing cyclists were 4.24 times more likely to sustain an injury than those not currently competing (Kronisch and Rubin, 1994). Loss of control and high speed descents were also associated with increased injury.
Pfeiffer (1993, 1994), using riders from the National Off-Road Bicycle Association (NORBA) pro/elite racing series, reports a very high injury rate among this competitive sample. In the 1993 study, of 63 riders in the pro/elite category, 57 (90.5 per cent) reported an injury in the previous year. Similarly in the 1994 study, 54 out of 61 (88.5 per cent) of riders reported an injured. Kronisch et. al. (1996) question the accuracy of the retrospective design used in this study. In addition to errors in recall, Kronisch et. al. suggest that this type of study is unlikely to account for any deceased cyclists (either through mountain biking or other cause of death) nor for those who have stopped mountain biking because of the injuries sustained. Consequently Kronisch et. al. (1996) employs a direct observation technique for studying the prevalence of mountain bike injuries.
Kronisch et. al. (1996) provide a report on the injuries sustained at a NORBA sanctioned mountain bike event held at Mammoth Mountain, California. A total of 4027 individual starts in five events; cross-country, downhill, dual slalom, hill climb and eliminator, were recorded. Each of these competitive events differs distinctly in duration and course design. Cross-country racing includes both uphill and downhill portions, with the course length between 30-45km. The race usually takes 2-3 hours to complete. Downhill is an individual time trial lasting 5-10 minutes, with all riders navigating the same course one at a time. The eliminator event uses the same downhill course but racing format places two competitors against each other on the course at the same time. In the dual slalom two riders race side-by-side on adjacent short downhill courses that contain multiple switch backs and small jumps. The hill climb is a test of endurance and fitness with riders cycling uphill for 30-60 minutes.
By individually studying each event, Kronisch et. al. (1996) was able to identify different patterns in the occurrence and frequency of injuries. An injury was defined as "Any episode of trauma sustained during competition that required medical attention and rendered the rider unable to compete the event." (Kronisch et. al., 1996:p90). Just 16 out 4 027 total starters fulfilled this injury criteria. Based on participation, this gives an overall injury rate, for all events, of 0.40 per cent. Due to the small number of injuries, no significant differences between the injury rates for each event were obtained. Of the 16 riders injured, 13 (81.2 per cent) sustained their injuries while going downhill, either in one of the downhill events or on a downhill section of the cross-country course. The other three injured riders all received their injuries from collisions at the start of the cross-country race.
Although the obtained overall injury rate of 0.40 per cent is relatively low compared to other sports (see for example Hume and Marshall, 1994), it needs to be recognised that this observation was made from a single race meeting. Previous studies have shown that competitive mountain bikers typically compete in 14 to 17 such events per year (Pfeiffer, 1993). Furthermore these athletes would be expected to spend up to 20 hours per week on mountain biking training, in addition to other forms of cross-training (Pfeiffer, 1993, 1994).
A more expansive observational study was undertaken by Pfeiffer (Unpublished, 1995). Injury frequency and severity rates from three separate race meetings was compiled. Data was collected on 9 525 riders, from six events (cross-country, downhill, dual slalom, hill climb, eliminator and observed trials).
Using an identical injury definition as to that reported for Kronisch et. al. (1996), Pfeiffer (Unpublished, 1995) reports an overall injury rate of 0.45 per cent - or just 40 out of 8 804 riders. This figure compares similarly to the 0.40 per cent injury rate obtained in the Kronisch et. al. (1996) study. The eliminator event (dual downhill format) proved to be the most hazardous to participants, with injury prevalence rates of 1.61 per cent for males and 2.17 per cent for females. Interestingly no significant differences were found between cross-country and downhill injury rates. Previous studies (Chow et. al., 1993; Kronisch and Rubin, 1994) suggest that the majority of injuries occur when riders are negotiating downhill terrain. The overall infrequency of injuries obtained in the current study may of negated this potential difference in dangerousness between cross-country and downhill events.
Mountain Bike Injuries and Time Exposure
All the studies reviewed thus far have assessed for injury frequency (normally over the previous 12 months) or used observation to determine injury prevalence rates for a defined period. These studies are limited in that no consideration is given to the differences in exposure for the various mountain biking disciplines. Total exposure time in a two hour cross-country event is obviously greater than in a eight minute downhill event. As such, differences in injury rates for the two events should control for, or at the very least, be aware of, length of exposure. The following example serves to illustrate the significance of duration of exposure on injury rate. Pfeiffer (Unpublished, 1995) and Kronisch et. al. (1996) both failed to find significant differences in injury rate between cross-country and downhill events. For example Pfeiffer (Unpublished, 1995) obtained downhill injury rates for both sexes combined of 0.51 as opposed to cross-country injury rates for both sexes combined of 0.49. This result may lead to the erroneous conclusion that both events pose similar injury risks for participants. However when exposure is factored into the equation, the results look drastically different. Using the above figures, and based on average exposure in a cross-country event of 150 minutes and for a downhill event, eight minutes, injuries per hour of exposure for cross-country are 0.20, but for downhill the figure jumps to 3.825 injuries per hour. It is now obvious that based on exposure, the downhill event is almost 20 times more dangerous than the cross-country event. While by no means exact, this method of analysis provides support to the previous finding that the majority of injuries occur when the rider is navigating downhill (Chow et. al., 1993; Kronisch and Rubin, 1994).
In conclusion the research data obtained on the frequency and severity of injury as a result of a mountain biking accident varies widely depending on the population surveyed, the research design and the definitional criteria for injury cases. Using a retrospective design Chow et. al. (1993) found that 84 per cent of recreational mountain bike club members had received an injury in the preceding year. Using a similar methodology Kronisch and Rubin (1994) found a comparable injury rate of 85.7 per cent among competitive mountain bike club members. Among a select sample of competitive racers, Pfeiffer found injury rates of 90.5 per cent (Pfeiffer, 1993) and 88.5 per cent (Pfeiffer, 1994). Among observational studies at particular events and employing a stricter criteria of injury, Kronisch et. al. (1996) and Pfeiffer (Unpublished, 1995) reported injuries (as a percentage of overall race starters) of 0.40 per cent and 0.45 per cent respectively. There is considerable evidence to support the notion that downhill mountain biking is considerably more dangerous than cross-country mountain biking. The vast majority of injuries appear to be sustained when riders are negotiating either a downhill course or a downhill section of a course. It would thus be expected that exponents of the mountain biking discipline of downhill racing will report significantly more injuries than their cross-country counterparts. The current study provides epidemiological research on the prevalence and severity of injuries sustained by both downhill and cross-country mountain bikers. It also investigates the contribution of the personality characteristic of sensation seeking towards involvement in a variety of risky behaviours.