Sex- and Age-Specific Analysis of Mountain Biking Injuries: A 10-Year Review of National Injury Data

Abstract

Background:

Mountain biking (MTB) is a quickly growing sport, with many athletes sustaining high-impact injuries. Current literature has not analyzed the most recent MTB-related national emergency department (ED) injury data.

Hypothesis:

It was hypothesized that (1) the total number of injuries presenting to US EDs would significantly increase over the study period, (2) male patients would experience higher rates of shoulder injuries and airborne injury mechanisms than female patients, and (3) youths would present more frequently with injuries of the head and face than adults.

Study Design:

Descriptive epidemiology study.

Methods:

All data were extracted from the National Electronic Injury Surveillance System (NEISS), a public database representing approximately 100 US EDs. The NEISS was queried for MTB-related injuries between January 1, 2013, and December 31, 2022.

Results:

A total of 2543 MTB-related cases presented to US EDs between 2013 and 2022, which extrapolated to a national estimate (NE) of 109,558 injuries using NEISS sample weights. MTB-related injuries increased significantly between 2013 and 2022 (P = .009), including a 64% increase between 2019 and 2020. The most common injury mechanism was falling off the bike (62.6%; NE = 68,536), and the upper extremity was the most frequently injured body region (22.4%; NE = 24,511). Male patients presented with significantly more shoulder (21.1% vs 7.4%, respectively; P < .001) and trunk (21.4% vs 19.8%, respectively; P < .001) injuries than female patients as well as more airborne injury mechanisms (15.7% vs 10.8%, respectively; P < .001). Female patients sustained significantly more concussions (7.2% vs 3.5%, respectively; P < .001) than male patients. Children presented with higher rates of head/face injuries (34.1%), concussions (6.0%), and airborne mechanisms of injury (19.4%) than any other age group.

Conclusion:

MTB injuries increased significantly between 2013 and 2022 likely because of the popularity of outdoor sports during COVID-19. The upper extremity was the most frequently injured body region, and falling off the bike was the most common mechanism. Leading injuries and mechanisms varied significantly by sex and age. This study recommends additional MTB safety measures such as shoulder support for male riders, better coaching on front brake control for youth riders, and an increased emphasis on concussion protocols for female riders.

Cycling is a popular sport worldwide and contributes significantly to emergency department (ED) visits in the United States primarily because of its high-velocity nature.^17,28 Within the cycling world, mountain biking (MTB) presents with certain high-risk mechanisms of injury due to the unpredictability of mountainous terrain and has been characterized as an extreme sport.^23,24 Despite its dangerous reputation, MTB is increasing in popularity and reached nearly 9 million riders in the United States in 2022. ³ As an indicator of future participation, mountain bike sales are estimated to increase 3.61% annually, resulting in a total market volume of US$10.28 billion by 2028. ³

Contemporary literature on MTB injuries tends to focus on youth athletes^4,10,11,29 and is limited to certain body regions^8,13,15,16 or case reports.^1,25,26 Additionally, these studies rarely include sex- and age-specific analyses and how these factors may impact injuries and outcomes. Furthermore, there has been no national study evaluating MTB injuries presenting to EDs across the country since 2007. ²⁰ Conducting research on the cause of MTB injuries on a national scale should be aimed toward informing appropriate prevention protocols and awareness initiatives surrounding the growing sport of MTB.

As members of the SCORE (Scientific Collaborative for Orthopaedic Research and Education) Group, a multi-institutional orthopaedic research and mentorship group of faculty/attending physicians, residents, medical students, and other students, we aimed in this study to evaluate the frequency and distribution of MTB injuries presenting to EDs in the United States between 2013 and 2022 by age and sex. Furthermore, we aimed to identify major contributing mechanisms to MTB injuries. We hypothesized that the total number of injuries presenting to US EDs would significantly increase over the study period. In a sex-specific analysis, we hypothesized that injury types and mechanisms would differ significantly between male and female athletes, with male athletes experiencing greater rates of shoulder injuries and airborne injury mechanisms. In an age-specific analysis, we hypothesized that youth riders would present more frequently with injuries of the head and face and that adult riders would sustain a higher rate of fractures than their younger counterparts.

Methods

Data Collection

All data were extracted from the National Electronic Injury Surveillance System (NEISS). The NEISS is a public deidentified database that collects data from approximately 100 EDs across the United States and serves as a representative probability sample of EDs across the country. National estimates (NEs) of injuries across the United States can be calculated using the statistical sample weight assigned to each patient case at a given hospital by the NEISS. The NEISS was queried for all MTB-related injuries between January 1, 2013, and December 31, 2022, using product code 5033 (mountain or all-terrain bicycles and accessories). All patient characteristics (age, sex, etc) were included as well as injuries for all body parts, diagnoses, and dispositions.

Exclusion Criteria

Injuries that did not occur while participating in MTB were excluded, such as a pedestrian getting struck by a mountain biker. Injuries that were caused by factors unrelated to biking were also excluded, such as an allergic reaction to a plant.

Variables of Interest

For each case, the treatment date along with the patient’s age, sex, body region injured, injury diagnosis, and discharge disposition were available and extracted. A narrative was also provided for each patient case describing the injury. Categories were defined for age, body region injured, diagnosis, and disposition based on NEISS injury codes. Age categories included child (1-13 years), adolescent (14-19 years), young adult (20-39 years), and adult (≥40 years). Categories of body region injured included head/face (face, mouth, ears, eyes), shoulder, upper extremity (upper arm, elbow, lower arm, wrist, hand, finger), lower extremity (upper leg, knee, lower leg, ankle, foot, toe), trunk (upper trunk, lower trunk, neck, pubic region), and other (25% body, 50% body, all body, internal, not specified). Shoulder and upper extremity categories were kept separate to follow the precedence of this distinction in existing MTB literature ²⁰ and to highlight the high prevalence of shoulder injuries. Diagnosis categories included soft tissue (contusion, abrasion, hematoma), laceration (laceration, puncture, avulsion), fracture, dislocation, sprain/strain, concussion, and other (crushing, foreign body, dental injury, nerve damage, internal organ, poisoning, dermatitis, conjunctivitis, hemorrhage, and other). Disposition categories included hospitalized (admitted, transferred, held for observation) and not hospitalized (treated and released, left without being treated).

Each provided narrative was used to code the mechanism of injury based on the action that most directly caused the primary injury. Mechanisms were assigned by author N.H.K. and verified by authors A.R.L. and A.Y. “Falling off the bike” designated narratives that described the rider moving directly from the bike to the ground without gaining altitude or interacting with any objects. “Being thrown from the bike” encompassed all narratives in which the rider flew into the air, while “flipping over the handlebars” described narratives in which the rider flipped forward over the handlebars (direction specific). Together, “being thrown from the bike” and “flipping over the handlebars” comprised airborne mechanisms of injury in which riders launched into the air before injuring themselves on impact. “Hitting an object” designated injuries that were caused by the rider or the bike hitting an object, such as a rock or tree. “Foot slipping off the pedal” described injuries that were caused by riders losing their grip on the pedals, either resulting in them striking the bike with their body or hitting the ground. “Mechanical issue with the bike” referred to injuries that were caused by a malfunction with the bike, such as a flat tire or broken chain. Finally, narratives that described an incident that did not fit into one of these categories were designated as “other,” and narratives with no information describing the injury incident were labeled “not specified.”

Statistical Analysis

Data were assessed using SPSS Statistics (Version 28.0; IBM). The distribution of injuries by age, sex, diagnosis, body region, and primary mechanism of injury was summarized using descriptive statistics and was reported as the NE and percentage. Sex-specific analysis was conducted using the chi-square test with associated P values. Linear regression analysis assessed injury trends over time and included a P value, regression coefficient (β), and 95% confidence interval (CI). Injury frequency was the outcome of interest, and the year of injury was used as the independent variable for simple linear regression analysis of trends over time.

Results

A total of 2614 MTB cases were found via the NEISS. Overall, 71 cases were not caused by MTB and were excluded, yielding 2543 cases for analysis. When weighted, these cases resulted in an NE of 109,558 ED admissions between 2013 and 2022 (Table 1). The mean age at the time of injury was 35.0 ± 15.9 years, with most injuries in the adult age group (42.1%; NE = 46,126). Additionally, 11.5% of all injuries resulted in hospitalization.

Table 1.

Characteristics of MTB Cases ^a

	No. of Cases	NE	Percentage
Sex
Male	2211	93,126	85.0
Female	332	16,432	15.0
Total	2543	109,558	100.0
Age group
Child (1-13 y)	230	6425	5.9
Adolescent (14-19 y)	336	11,819	10.8
Young adult (20-39 y)	986	45,188	41.2
Adult (≥40 y)	991	46,126	42.1
Total	2543	109,558	100.0

^aMTB, mountain biking; NE, national estimate.

MTB-related injuries significantly increased between 2013 and 2022 (2013-2022: P = .009; β = 860.5 [95% CI, 279.6 to 1442.0]) (2013-2019: P = .92; β = 12.3 [95% CI, –294.8 to 319.4]), including a 64% uptick in injuries between 2019 and 2020 (Figure 1). Furthermore, 42.3% of all injuries across the study period occurred between 2020 and 2022.

Figure 1.

National estimates of mountain biking–related injuries that presented to United States emergency departments (EDs) between January 1, 2013, and December 31, 2022.

The most injured body region was the upper extremity (22.4%; NE = 24,511), followed by the trunk (21.2%; NE = 23,210) and the shoulder (19.1%; NE = 20,899). Trunk injuries were responsible for the most hospitalizations among body regions (50.7%; NE = 6387). Among age groups, children presented most often with head/face injuries (34.1%), adolescents most often with upper extremity injuries (30.4%), young adults most often with lower extremity injuries (21.5%), and adults most often with trunk injuries (28.5%) (Figure 2).

Figure 2.

Body region injuries characterized by age.

Fractures were the most common diagnosis (32.2%; NE = 35,260) and accounted for 56.5% of all hospitalizations (NE = 7137). Fractures were also the most common diagnosis for male (33.2%) and female (25.9%) patients. Among age groups, children were diagnosed most with lacerations (32.0%), while fractures were most common in adolescents (29.0%), young adults (28.0%), and adults (37.3%). Concussions were more prevalent among children and adolescents than among young adults and adults (Figure 3).

Figure 3.

Concussions characterized by age.

The most common injury mechanism was falling off the bike (62.6%; NE = 68,536), and the mechanism with the highest rate of hospitalization was being thrown from the bike (23.0%; NE = 1256). Most falls resulted in fractures (30.5%) and upper extremity injuries (23.9%). Being thrown from the bike most commonly led to fracture (39.6%) and trunk injuries (26.8%), and had the highest concussion rate (6.2%), while feet slipping off of the pedal had the highest rate of lower extremity injury (92.0%). Flipping over the handlebars also had a high rate of hospitalization (13.8%), most commonly leading to fractures (36.6%) and trunk injuries (27.0%). Both mechanisms were more common among children and adolescents, accounting for 19.4% of injuries in children, 18.3% of injuries in adolescents, 14.3% of injuries in young adults, and 14.1% of injuries in adults. Falls were the most common mechanism in both male patients (61.9%) and female patients (66.2%).

In a sex-specific analysis, male patients were hospitalized more frequently (12.1%) than female patients (8.5%) (P < .001). Male patients most often sustained trunk injuries (21.4%), while female patients most often sustained upper extremity injuries (29.2%) (Table 2). Furthermore, female patients presented with a significantly lower proportion (7.4%) of shoulder injuries than male patients (21.1%) (P < .001). Males presented with a greater proportion of being thrown from the bike (5.3%; P < .001), flipping over the handlebars (10.4%; P < .001), and a greater total number of airborne injuries (15.7% vs. 10.8%; P < .001) than females. Finally, female patients presented with a higher rate of concussions (7.2%) than male patients (3.5%) (P < .001).

Table 2.

Rates of Body Region Injuries

	Male, %	Female, %	P
Head/face	17.9	22.2	<.001
Shoulder	21.1	7.4	<.001
Upper extremity	21.1	29.2	<.001
Lower extremity	17.8	21.4	<.001
Trunk	21.4	19.8	<.001
Other	0.5	0.03	<.001

Discussion

This study assessed the frequency, distribution, and mechanisms of MTB injuries presenting to US EDs between 2013 and 2022. MTB-related injuries increased significantly across the study period in large part because of a 64% uptick between 2019 and 2020. The most common body regions injured were the upper extremity, trunk, and shoulder, all of which increased in prevalence over the study period. Fractures were the most common diagnosis and the diagnosis most likely to lead to hospitalization. Falling off the bike was the most common mechanism of injury, while being thrown from the bike resulted in the greatest rate of hospitalization and the greatest rate of fractures. Previous literature has also reported falls as the most common injury mechanism, fractures as the most common diagnosis, and airborne mechanisms as the most likely to lead to hospitalization. ²⁰

The increasing trend in MTB injuries between 2013 and 2022 is unprecedented in previous literature evaluating NEISS MTB injuries before 2013. ²⁰ This recent increase may be largely attributable to the increasing popularity of MTB, given that trends in MTB participation mirror injury trends observed within the NEISS. ³ The COVID-19 pandemic saw increased visitation rates to outdoor parks and may have been the primary cause of MTB’s popularity spike observed between 2019 and 2020. ²² The recent popularization of electric MTB (eMTB) has also increased the accessibility of MTB by lowering fitness and skill level requirements, thereby bringing more riders to the sport. ⁶ Furthermore, eMTB has been shown to have a greater rate of hospitalization compared to traditional MTB, accounting for 33% of all MTB injuries in an 82-patient cohort. ² The high injury rate in eMTB may be because of the increased weight and faster maximum speed of electric bikes compared to regular mountain bikes. ¹² Ultimately, an increase in MTB popularity and rising injury rates per rider may both be playing a role in the upward trend of MTB-related ED admissions observed in this study. As the technological landscape of MTB changes, research detailing injury mechanisms in relation to new equipment will be important in minimizing the contribution of new technologies to rising injury rates.

Falling off the bike was the most common mechanism of injury and primarily resulted in trunk injuries. The high prevalence of falls presenting to EDs may therefore be mitigated by increasing protective wear for the trunk, such as chest and torso protectors (Table 3). These measures may be especially effective, given that the trunk was also the body region injured with the greatest rate of hospitalization in this study. Being thrown from the bike had the highest rate of hospitalization, followed by flipping over the handlebars. Flipping over the handlebars also had the greatest rates of shoulder and head/face injuries among mechanisms, a pattern seen in prior literature.^5,7 These 2 injury mechanisms illustrate that the energy of impact (an airborne nature) and direction of fall (forward over the handlebars) play a central role in injury severity and location. Feet slipping off the pedals had the highest rate of lower extremity injuries (92.0%), indicating that a high-impact mechanism is not always necessary in causing serious injuries. The use of shin guards or clipless pedals may be useful in protecting the lower limb from injuries and securing the rider’s feet to the bike (Table 3). ⁵

Table 3.

Summary of Key Mechanisms, Injuries, and Prevention Strategies ^a

Mechanism	Primary Result	Prevention Recommendation
Falling off the bike	Trunk injuries	Chest and torso padding/protectors
Airborne mechanism of injury	Hospitalization, shoulder injuries, concussions	Weight balance, front brake control, shoulder padding, shoulder strength and mobility exercises, MTB-specific concussion protocols
Foot slipping off the pedal	Lower extremity injuries	Shin guard and clipless pedal use

^aMTB, mountain biking.

In regard to sex differences, male patients had a significantly greater rate of hospitalization compared to female patients and accounted for 85% of all injuries. Previous literature has observed similar rates of injured male riders (75%-85%) but reported female riders as more likely to be injured.^5,15,20 This study also found that male patients sustained significantly higher rates of being thrown from the bike and flipping over the handlebars. Because these 2 mechanisms were the leaders in hospitalization rates, these mechanistic differences likely contribute to the dissimilar hospitalization rates observed between the sexes in this study. This statistic also counters previous claims that female riders are lighter and therefore may more easily flip off the bike.^5,15 Male and female patients also had significant differences in body regions injured. Notably, the shoulder was one of the leading body regions injured among male riders, but shoulder injuries were significantly less frequent in female riders, a difference also observed in past literature on MTB and other sports.^20,30 Because being thrown from the bike and flipping over the handlebars had the greatest rates of shoulder injuries, the prevalence of these mechanisms among male riders may also be responsible for the difference in shoulder injuries between sexes. Emphasizing shoulder strength and mobility exercises, as well as protective equipment designed to support the shoulder girdle, may help to minimize the burden of male shoulder injuries (Table 3).^16,27 Conversely, female riders had a significantly greater rate of concussions, a trend that has also been reported in other sports such as soccer and basketball. ¹⁹ The rate of sports-related concussions in female athletes has increased significantly over the past 2 decades, but research on the topic remains limited.^9,21 Because airborne mechanisms had the greatest rates of concussions but were most frequent in male athletes, this suggests that there may be contributors to female concussion rates independent of injury mechanisms. Given that sparse data on concussion rates in MTB have made it challenging to design MTB-specific concussion assessments, this study aimed to help inform new safety protocols by emphasizing the additional dangers that female MTB riders may be facing (Table 3). ¹⁸

The most common body regions injured also varied by age group. Children presented most often with head/face injuries, adolescents most often with upper extremity injuries, young adults most often with lower extremity injuries, and adults most often with trunk injuries. Higher concussion rates were also seen in children and adolescents than in young adults and adults. Previous literature has demonstrated more frequent head/face injuries among pediatric patients, which has been attributed to lower rates of helmet use among younger riders.^10,14,29 However, Jewett et al ¹⁴ demonstrated that helmet use among children surpassed adult compliance, suggesting that there may be other factors leading to higher rates of head/face injuries among children. Kshirsagar et al ¹⁵ suggested that younger riders are more inclined to partake in risky behavior and therefore are more likely to suffer from high-velocity mechanisms of injury. Although our study disagrees with claims suggesting that the lighter weight of female patients makes them more susceptible to injuries, the weight differential between children and adults may be significant enough to cause the disproportionate airborne mechanisms observed in children, further contributing to head/face injuries in youth riders. The prevalence of flipping over the handlebars and its hospitalization rate call for the importance of educating younger riders on weight balance and front brake control while riding their mountain bikes (Table 3).

To our knowledge, this study is the first to examine the last decade of data on MTB injuries presenting to US EDs using the NEISS dataset and demonstrates a significant recent increase in MTB injuries not evaluated in existing literature. By characterizing injury locations, outcomes, and mechanisms, this study helps to guide injury prevention and safety initiatives to protect a growing MTB community.

Limitations

This study is not without limitations. The NEISS dataset is only a cross-sectional probability sample and thus does not represent all national cases that presented to US EDs over the study period. Furthermore, the dataset only assesses injuries severe enough for patients to report to the ED for diagnosis and management, potentially omitting patients who managed injuries on their own or presented to urgent care clinics or orthopaedic/pediatric offices. Characterizing injury mechanisms relied on limited details available in the NEISS case narratives, which may have led to inaccuracies in characterization. Specific information about equipment used, such as helmets, pads, and electric mountain bikes, is not included in the NEISS; thus, this study was unable to quantitatively assess the efficacy of safety practices, such as helmet use on concussion rates, or the risks of specific technologies entering the world of cycling, such as electric bikes. Geographic variation across the country may also have impacted MTB injuries by region and decreased the accuracy of NEISS NEs.

Conclusion

This study demonstrated a significant increase in MTB injuries over the past decade. The upper extremity, trunk, and shoulder were most often injured; however, leading injuries varied significantly by sex and age. Being thrown from the bike led to the greatest rate of hospitalization most likely because of high-energy impacts. Given the findings reported in this study, we suggest additional MTB safety measures such as shoulder support for male riders, better coaching on front brake control for youth riders, and an increased emphasis on concussion protocols for female riders.