ries sustained at a major off-road bicycling race at. Mammoth Mountain, California, July 6 to 10, 1994. A total of 4027 individual starts in five events during the.
Acute
Injuries
in Off-Road
Robert L. Kronisch,*† MD,
From *San Jose State
Tony
University,
K.
Chow,‡ MD, Lauren M. Simon,‡ MD, MPH, and Parthenia F.
Wong,§
MD
University Medical Center, §private practice, Pleasanton, California
San Jose, ‡Loma Linda
Loma Linda, and
cyclists for the last 5 years (United States Cycling Federation, unpublished data, 1995). This year the Olympic Games will feature a full-medal competition in cross-country off-road bicycle racing for the first time. The rise to Olympic competition is unprecedented for a sport so young. Despite this rapid increase in popularity, about 33,000
ABSTRACT A descriptive study was conducted to investigate injuries sustained at a major off-road bicycling race at Mammoth Mountain, California, July 6 to 10, 1994. A total of 4027 individual starts in five events during the race were reported. Overall, the total number of competitors in the 5 events was 3624, with some cyclists participating in multiple events. Injuries were considered significant if they occurred during competition and prevented the rider from completing the event. Sixteen cyclists had injuries that met these criteria for an overall injury rate of 0.40%. These 16 cyclists had 44 injuries. Abrasions were the most common injury, followed by contusions, lacerations, fractures, and concussions. The mean injury severity score was 3.0 (range, 1 to 5) with 81.2% of the injuries resulting from
cyclists going downhill. Injuries
Bicycle Racing
were
little research has been done on injuries in the sport, and our understanding of the risks associated with participation in this sport remains poor. When this study was conducted, prior studies on offroad bicycling injuries consisted of three retrospective surveys published between 1993 and 1994. The Chow et al.’ survey was conducted in 1990 and published in 1993. The survey population was composed primarily of recreational off-road cyclists. Among those surveyed, 51.1% (137 of 268) reported acute injuries from mountain biking during the preceding year, with 74% of the injuries occurring while riding downhill. Excessive speed and unfamiliar terrain were cited as the factors most commonly associated with off-road injuries. In 1992, Kronisch and Rubin’conducted a survey, published in 1994, that was similar to the Chow et al. survey. The population Kronisch and Rubin surveyed was composed primarily of competitive off-road cyclists. Of those surveyed, 85.7% (227 of 265) reported injuries occurring in 1992. Loss of control, high-speed descent, and competitive activity levels were identified as variables significantly associated with traumatic injury in their study. Pfeiffer, 10,11 using the ongoing survey of injuries in the National Off-Road Bicycle Association pro/elite racing category, also found a high injury rate in this highly competitive group, with 90.5% of those surveyed (57 of 63) reporting injuries occurring in 1991 and 88.5% (54 of 61) reporting injuries occurring in 1992. Injuries took place with approximately equal frequency during training and competition in Pfeiffer’s studies. The injury rates reported in all of these studies were based on self-reports using loosely defined inclusion criteria; additionally, these studies are subject to the biases inherent in retrospective surveys. Nonetheless, each study found the majority of injuries to be minor. The study by Kronisch and Rubin introduced further analysis to exclude the minor injuries; they found that 20.4% of those surveyed (54 of 265) sus-
more severe
when the riders were thrown from the bicycles ( P = 0.03). We observed different mechanisms of injury in various events, suggesting that the risk factors for sustaining a traumatic injury may vary according to the type of competition involved.
In recent years, the sport of off-road bicycle (or mountain bike) racing has increased in popularity at an astounding rate. The National Off-Road Bicycle Association, the national governing body for the sport, has grown to more than 32,000 members since its formation in 1983; more than half of this increase has occurred since 1992. In addition, the association issues approximately 35,000 1-day licenses each year to beginners who are competing for the first time (National Off-Road Bicycle Association, unpublished data, 1995). In contrast, membership in the United States Cycling Federation, the governing body for road and track bicycle racing, has remained stable at
tAddress correspondence and repnnt requests to Robert L Kronisch, MD, Student Health Service, San Jose State University, One Washington Square, San Jose, CA 95192-0037 No author or related mstitution has received any financial benefit from research m this study. See &dquo;Acknowledgments&dquo; for funding information.
88
89
tained an injury during the previous year that required medical attention and prevented them from cycling for at least 1 day. Those cyclists who were competing at the time of injury were 4.24 times more likely to sustain such an injury than those who were not competing.
ORGANIZATION OF RACES Each year the National Off-Road Bicycle Association organizes a national championship series that consists of six or seven events taking place throughout the country during the spring and summer. Each national championship series event lasts several days and consists of separate competitions in the cross-country, downhill, and dual slalom races, with cyclists divided into groups according to sex, age, and skill level. Awards are given for each race, with cumulative point standings from each event used to select national champions at the end of the series. The Union Cycliste Internationale, the international governing body for all cycling sports, uses a similar format in its world cup series for elite cross-country and downhill offroad cyclists. Each type of competition (e.g., cross-country versus downhill) differs distinctly in duration and course design. The cross-country race takes place on a loop containing uphill and downhill portions. Typically, the loop is 8 to 10 miles long, with the total race distance varying from 20 to 30 miles, depending on the rider’s sex and skill level. Riding speeds vary with the slope of the terrain. For example, racers may have to walk their bikes up steep uphill sections or they may reach speeds of 40 to 50 mph on downhill portions. Riders start the cross-country race simultaneously, with the winner the first to cross the finish line. The race usually takes 2 to 3 hours to complete. A similar mass-start racing format is used for the hill climb race, a popular competition that is not part of the national championship series. This race tests endurance because riders cycle up hill between 30 and 60 minutes. In contrast, the downhill race is an individual time trial lasting 5 to 10 minutes, with all riders navigating the same downhill course one at a time while competing for the fastest time. Downhill courses are usually 3 to 5 miles long; experienced racers may achieve speeds exceeding 50 mph in straight sections. In the dual slalom, which has multiple runs, two riders race side-by-side on adjacent short downhill courses that contain multiple switchbacks and small jumps. A dual-elimination format is used in this competition, with individual runs lasting 30 to 40 seconds. Men and women compete separately in groups divided by category (skill level) and class (age group). The four skill-level categories are beginner, sport, expert, and pro/ elite. The four age-group classes are junior (12 to 18 years), senior (19 to 34 years), veteran (35 to 44 years), and master (45 years and older).
MATERIALS AND METHODS This study was conducted at the National Off-Road Bicycle Association National Championship Series-Union Cycliste Internationale World Cup Series race held at Mam-
moth Mountain, California, July 6 to 10, 1994. Mammoth Mountain, which is located on the eastern slope of the Sierra Nevada mountains, is elevated approximately 8900 feet above sea level at the base and 11,000 feet at the top
course. Competitive events were the hill climb, cross-country, downhill, and dual slalom races. In addition, the final day featured a special exhibition event, the eliminator, a race in which two riders navigate the downhill course simultaneously. This event followed a dual-elimination format, with the winner of each heat advancing to the next round. The invitation-only elimina-
of the downhill
tor
race was
Injuries
limited to pro riders.
treated at a first-aid station located near the finish line, where at least one physician involved with the study was stationed at all race times. Ski-patrol personnel were stationed along the race course and were available to transport injured riders to the first-aid station if necessary. Cyclists with more serious injuries were taken to the local hospital for treatment and were reexamined later that day by one of the study’s physicians. We defined an injury as any episode of acute trauma sustained during competition that required medical attention and rendered the rider unable to complete the event. Any injured cyclist meeting these criteria was examined by a research team physician who assisted the cyclist in completing a brief questionnaire on the mechanism and circumstances of the injury. All injuries sustained by each injured cyclist were documented, as was the course location where the injury occurred. At the top of the downhill course, cyclists in the downhill and eliminator events were observed and interviewed as necessary to determine what type of protective gear they used. At present, the only safety equipment required is a standard bicycle helmet. However, many riders choose to use additional equipment for downhill racing, much of it borrowed from the sport of off-road motorcycle racing, such as rigid or semirigid chest and shoulder pads; elbow, forearm, knee and shin guards; and helmets that provide facial protection. We identified riders by their race number and recorded their use or nonuse of face guards, chest and shoulder protectors, and upper and lower extremity
pads.
The
were
1-3
was used to quantify the injury severity score severity of each cyclist’s injuries. After calculating the injury severity score for each injured cyclist, individuals were divided into groups based on injury severity as fol-
lows : minor (1 to 3), moderate (4 to 15), and severe (>16). The rationale for this division was that 1) most simple closed fractures are assigned an injury severity score of 4, and these injuries are generally considered moderate rather than minor sports injuries; and 2) injuries with an injury severity score greater than 16 have demonstrated a 10% or greater mortality rate,’ and this level of injury severity has often been used to define major trauma in other studies.’ Denominator data for statistical calculations were obtained from the race officials. Data were already organized by sex, race category, and class. For all calculations, denominator data were expressed as the number of starts in each event, which was not always the same as the number
90 TABLE 1
Injury Rates by Event
Injury rate comparing the number of injuries with the number of starts x 100. The sum of the number of competitors in each individual event. The total number of individuals competed in more than one event. &dquo;
b
of participants because some events involved multiple heats. For the downhill, dual slalom, and eliminator events, the number of starts was the actual count. For the cross-country and hill climb races, which were mass-start events, the number of starts was estimated as the total number of registered cyclists minus the number of preregistered individuals who did not pick up their registration
packets.
Statistical analysis was performed by computer using SAS statistical software (SAS Institute, Cary, North Carolina). Log-likelihood chi-square tests were used to evaluate differences in injury rates by event and sex of the cyclist and to detect associations between predetermined pairs of variables among the injured cyclists. Differences in injury severity scores by event and sex of the participant were tested with nonparametric rank-sum tests.
RESULTS Sixteen injuries in 4027 total starts met the study criteria for an overall injury rate of 0.40%. The injury rates for the individual events are listed in Table 1. There was a statistically significant difference (P 0.01) among the injury rates when all five events were compared with each other. However, when the eliminator event, which is not a standard National Off-Road Bicycle Association or Union Cycliste Internationale race format, was removed from analysis, the differences among the remaining injury rates were no longer significant. No significant difference resulted among the rates of injury to men and women for any of the events. The 16 injured riders had a total of 44 injuries. These injuries are listed in Table 2. Injury severity scores ranged from 1 to 5, with a mean of 3.0. There were no significant differences among these scores for the different events or sexes. The specific injuries and relevant rider data are listed in Table 3. Injured subjects were divided into two injury severity groups, minor and moderate, based on their injury severity scores. This separation of groups enabled us to analyze factors that contributed to the more serious injuries. Eight cyclists were in each of the two groups. Multiple chisquare tests revealed no significant associations between the injury severity and the following factors: the specific event, the rider’s sex, the racing category or class, the slope of the course or type of terrain, and mechanism of =
cyclists
at the
race was
lower, because
some
0.03) resulted beinjury. A significant association (P tween the injury severity and the direction of the injury; that is, those riders who were thrown over their handlebars tended to sustain more serious injuries than those =
who fell off their bikes to the side. All of the moderate injuries were sustained by riders who were thrown over the handlebars of their bikes; minor injuries resulted when riders fell off the bike to one side. Eight of the nine riders who were injured on the downhill course (downhill and eliminator events) were thrown from their bikes; the other rider, who had a mechanical problem that led to his injury, was unsure of the direction of his fall. For the cross-country event only, there was a significant association (P 0.02) between the injury severity and the maneuvers involved in the injury. Specifically, three of the four minor injuries occurred at the start of the race, and both of the moderate injuries resulted during high-speed descents. Thirteen of the 16 injured cyclists (81.2%) at this race sustained their injuries while going downhill, either in one of the downhill events or on a downhill portion of the cross-country course. The only injuries that did not occur while going downhill were the three injuries immediately after the start of the cross-country event, when many riders in this mass-start event vied for position. These three injuries represented half the injuries in the crosscountry event, and all three were minor. Inspection of course maps showing where each injury took place revealed that the only injuries occurring at the =
TABLE 2
Injuries by Type and Body Region in
16
Cyclists
91 TABLE 3 Data
Specific Injuries and
a
b
location
start of the
sulted from
injuries that occurred at the event and the injuries that recollision between two riders in the eliminawere
three
cross-country a
race.
Racers (825 of 834, 98.9%) in the downhill event, and all who started the eliminator event were included in the survey on downhill protective equipment. The results of this survey are shown in Table 4. The nine cyclists who were injured in the downhill and eliminator events used various types of protective gear; the gear is listed in Table 5. racers
TABLE 4 Protective
Equipment Used
in Downhill Events
Amateurs refers to beginner, sport, and expert categories combined. a
16
Cyclists
Dh, downhill; Cc, cross-country; E, eliminator; Ds, dual slalom. ISS, injury severity score.
same
tor
on
DISCUSSION We investigated the incidence of injury in competitive off-road bicycling to gain a better understanding of associated injury mechanisms and related environmental factors. Although the number of injuries sustained during competition does not provide an adequate database to determine risk factors for injury in this sport, a number of observations were made. The most obvious observations were the low overall injury rate of 0.40% and the low mean injury severity score of 3.0. When considering this injury rate, clinicians must remember that this rate applies to only one event, and that National Off-Road Bicycle Association pro/elite category cyclists typically compete in 14 to 17 events per generally spend 10 to year.11 Furthermore, these athletes 12 hours per week in training. 10, 11 Therefore, the overall risk of injury in off-road bicycling is not reflected in our data. When the different types of competition are considered separately, there appear to be numerous differences in the injury patterns among the individual events. For example, all cyclists injured in the downhill event were in the pro/elite category, despite two factors: pro/elite category cyclists represented only 225 (27%) of those starting the downhill race, and they wore more protective gear than cyclists in lower categories. None of the cross-country or dual slalom injuries occurred to pro/elite riders. The explanation for this observation is unclear. Because all in-
92 TABLE 5 Protective
a
Equipment Used by Injured Downhill Riders
Dh, downhill; E, eliminator.
juries, except those at the start of the cross-country event, involved downhill stretches, downhill racing may have some inherent risk of injury. This was suggested earlier by two retrospective surveys. 6,7 In a more recent and larger scale study, Kronisch et al. (unpublished data, 1995) used the same methods of data collection that were used in this study but calculated injury rates based on exposure time for the cross-country and downhill events. This yielded injury rates of 0.37
per 100 hours in the cross-country event and 4.34 per 100 hours in the downhill event, suggesting that the overall risk of injury is higher in downhill than in
injuries
injuries
country off-road bicycling. Biomechanical studies have shown that the forces involved in the transfer of mechanical energy during traumatic injury are proportional to the square of the change in velocity (i.e., doubling the velocity quadruples the forces involved in a crash).12 If that relationship is true in offroad bicycling, then the higher velocities achieved by the pro/elite category downhill riders could increase the risk of injury when compared with slower velocities achieved by cyclists in the lower categories. Another possibility is that these riders were more aggressive and took more chances than their novice counterparts, accelerating, for instance, through areas where a less experienced rider would slow down for safety. The cash prizes awarded to winners in the pro/elite category could have provided additional incentives for achieving higher speeds. Turning, which was the maneuver most commonly associated with injury, was reported as a contributing factor by 7 of the 16 (43.8%) injured participants. All the riders who were injured while turning were going downhill at the time of injury, and six of these seven cyclists cited loss of control or loss of traction as an associated contributing factor. Four of the five injuries in the downhill event involved turning, compared with only one of the six injuries in the cross-country event. The five injuries in the downhill event all occurred either from a mechanical problem with the bicycle or from a loss of control while turning. In contrast, four of the six cross-country injuries were due to collision with another rider; the other two resulted from loss of control in downhill portions. In the eliminator event, two of the four injuries resulted when two riders collided with each other. The other two injuries were caused from a loss of traction cross
while turning. The only injury in the dual slalom race occurred when a beginner came off a jump and crashed into a padded post that supported the finish banner. Thus, in events with more than one rider on the course simultaneously, the presence of other riders may be a risk factor for injury because more than half the injuries in those events resulted from collisions with other riders. The excellent bicycle-handling skills of the pro/elite cross-country cyclists should allow them to maneuver around each other better than the cyclists in the lower categories, which could explain why none of them were injured in competition. The eliminator event, which presumably carries the same risks as the downhill event, poses additional challenges to participants because two cyclists are on the
simultaneously. noteworthy trend is that most of the injuries, particularly the more serious ones, occurred when the rider was thrown off the bicycle while going downhill. If substantiated by further research, this finding could have implications for the development of safety equipment for off-road cyclists. There is currently little protective gear designed specifically for off-road bicycling. Racers and race organizers debate whether additional prolelitetective gear should be made mandatory for downhill competition and whether helmets should be redesigned specifically for off-road riding. We found a wide variety of protective gear used by the downhill racers, although there was no consistent relationship found between the type of protective course
The other
pattern of injury observed. Several potential sources of bias or error exist in this study and should be mentioned. By defining injuries as those episodes of trauma that required medical treatment and prevented completion of the race, we systematically excluded many minor injuries from the study. We did this intentionally because previous studies of off-road cycling and other types of competitive bicycling have demonstrated a preponderance of minor, superficial injuries,4,6,7,9-11 and we believe it would be difficult to accurately document injuries that did not preclude further competition. This may have led us to underestimate the injury rate. Furthermore, we defined rate of injury as the number of injured riders per start, not the number of injuries per start, which could mislead some readers. The number of injuries sustained by each injured rider is reflected in the injury severity score. The denominator data gear used and the
93
(total number of starts per event) may be
more
accurate
for the downhill, eliminator, and dual slalom than for the other races because we had actual starting counts for these events. We had to estimate the total number of starts in the cross-country and hill climb competitions. Additionally, some riders who preregistered may have competed in only some of their registered events, and this discrepancy could have led to errors in the estimate. It also should be pointed out that the race courses at Mammoth Mountain tend to use a great deal of dirt and gravel access roads, which are relatively well maintained, and that the conditions in July 1994 were very dry. Races at other locations often have a higher proportion of singletrack trails that tend to have more ruts, rocks, and other obstacles than the access roads at Mammoth Mountain. Other racing venues often have more muddy sections, particularly during the spring. Because of these variations in environmental conditions, injury patterns could vary at different locations and at different times in the off-road
cycling season. Finally, races
in the national championship and world cup series also differ because higher safety standards are
imposed (e.g., ski patrol personnel
are stationed around and a first-aid station is well staffed). Safety standards and medical support at certain regional level events may not be as comprehensive as those seen at national- or international-level races, which could increase the risks to participants.
the
the downhill course simultaneously appears somewhat riskier. However, the low number of injuries sustained in one event in a long sports season limits the conclusions from this study. The cross-country, downhill, dual slalom, and hill climb events all differ markedly in duration, course design, racing format, and challenges to participants. The different patterns of injury mechanisms seen in this study suggest that the risk factors associated with these events may differ as well. Further research will help determine whether these patterns are influenced by changes in environmental conditions and whether the trends observed in this study represent actual risks associated with the
sport. ACKNOWLEDGMENTS This study was supported by a grant of funds from the National Off-Road Bicycle Association. The authors thank the staff at Mammoth Mountain and the staff at Mammoth Hospital Emergency Department for their assistance.
race courses
REFERENCES The Abbreviated Injury Scale, 1990 Revision, Association for the Advancement of Automotive Medicine, Des Plaines, IL, 1990 2 Baker SP, O’Neill B The injury severity score An update J Trauma 16 1
882-885, 1976
CONCLUSIONS The sport of off-road bicycle racing has grown rapidly in recent years, and the risks associated with participation in it remain poorly understood. Previous retrospective studies have suggested high annual injury rates among participants. The present study investigated injuries at a single event and, as such, cannot be directly compared with previous studies. The majority of injuries at this event occurred while the rider was going downhill. Cyclists who were thrown from their bicycles tended to sustain more serious injuries than those who fell from their bikes to the side. No severe injuries occurred at the event studied, and the injury rates for the standard competitive events were relatively low. The special exhibition event in which two riders maneuver
3 Baker SP, O’Neill B, Haddon W Jr, et al The injury severity score A method for describing patients with multiple injuries and evaluating emergency care J Trauma 14 187-196, 1974 4 Brogger-Jensen T, Hvass I, Bugge S Injuries at the BMX cycling European championship, 1989 Br J Sports Med 24 269-270, 1990 5 Champion HR, Copes WS, Sacco WJ, et al The major trauma outcome study Establishing national norms for trauma care J Trauma 30 1356-
1365, 1990
6 Chow TK, Bracker MD, Patrick K Acute injuries from mountain biking West J Med 159 145-148, 1993 7 Kronisch RL, Rubin AL. Traumatic injuries in off-road bicycling Clin J Sport Med 4 240-244, 1994 8 Maslanka AM Scoring systems and triage from the field Emerg Med Clin North Am 11 15-27, 1993 9 McLennan JG, McLennan JC, Ungersma J Accident prevention in competitive cycling Am J Sports Med 16 266-268, 1988 10 Pfeiffer RP Off-road bicycle racing injuries—the NORBA pro/elite category Clin Sports Med 13 207-218, 1994 11 Pfeiffer RP Injuries in NORBA pro/elite category off-road bicycle competitors Cycling Sci 5 21-24, 1993 12 Withers BF, Baker SP Epidemiology and prevention of injuries Emerg Med Clin North Am 2 . 701-715, 1984
