March 2019

How Mountain Biking Is Reshaping the Landscape of Cycling Injury

Differences in equipment, terrain, riding style, and other risk factors mean different types and prevalence of injuries when riding a mountain bike, compared to a road bike. Be prepared to see those differences in your practice.

By Michael Reeder, Do, And Brent Alumbaugh, MS

Over the past several decades, mountain biking has become remarkably popular as a competitive and recreational activity. Mountain biking is popular internationally and can be observed in numerous competitive events; the most popular are the annual World Cup Series, Olympic Games, and World Championships. The largest increase in number of participants, however, has been in recreational mountain biking. The Outdoor Foundation1 recently reported mountain biking as one of the most popular outdoor activities in the United States, with approximately 8.32 million mountain bikers in 2015.

Equipment and Technology Has Changed

Recently, there has been a change in bike sales in the United States: More mountain bikes are now sold than road bikes.2 More recently, electrical bikes, or e-bikes, have become popular, including electrical-assist mountain bikes, which might make mountain biking a feasible option for more of the population. The price of mountain bikes ranges from a few hundred dollars for an entry-level bike to more than $10,000 for high-end bikes.

“The risk of injury to all parts of the body is ever-present in mountain biking”

Bicycle manufacturers have improved mountain bike technology since the first models appeared on the market in the early 1970’s. There are now different types of mountain bikes that vary significantly, depending on the inclination of rider and the intended use. As the technology of mountain bikes has improved, it’s become easier for riders to attempt more technical terrain and ride at higher speeds. Compared to road bikes, mountain bikes are designed for stability and maneuverability in technical terrain; they generally have larger tires, lower bottom brackets, shorter chain stays, and lower head-tube angles.

Furthermore, improvements in protective apparel have made mountain biking safer; however, these improvements have likely led to greater rider confidence—leading, somewhat paradoxically, to higher speeds and more risk-taking behavior. Despite remarkable improvements in bike technology and the use of protective equipment and clothing, the risk of injury to all parts of the body is ever-present in mountain biking, as we describe in detail in this article.

Getting a Handle on Injury in Mountain Biking

The nature of injury rates in mountain biking is not well-defined. Mountain bikers include competitive and recreational riders, ranging from adolescents to older adults—all of whom have different preferences in riding style. Most older studies of mountain biking injuries are limited to competition and mountain bike parks, making the injury rate outside of those settings hard to define, especially when injuries go unreported.

A study by Gaulrapp et al3 of more than 3800 mountain bikers, most of whom were noncompetitive recreational bikers, cited a very low rate of significant injury: 1 injury for every 1000 hours of riding, with 75% of injuries considered minor. In contrast, Kronisch et al4 looked at competitive mountain bikers and cited an injury rate of 3.7 injuries for every 1000 hours of racing in cross-country biking and 43.4 injuries for every 1000 hours in downhill racing. Similarly, a prospective study by Becker et al5 of downhill mountain biking injuries seen in competition is in agreement with Kronisch’s findings,4 showing an increased incidence of injuries: 16.8 injuries for every 1000 hours of downhill racing cycling.

Nelson and Mckenzie6 illustrated the importance of the age of the rider as it relates to traumatic brain injury. Reporting on more than 200,000 patients who suffered a mountain-biking injury and were treated in an emergency department between 1994 and 2007, the researchers showed that patients 14 to 19 years of age sustained the greatest percentage of traumatic brain injuries. Similarly, 2 studies7,8 from Canada illustrated the preponderance of head and neck injury in young male recreational riders.

What’s behind this preponderance of adolescent male victims? The popularity and continued development of mountain bike parks at ski resorts likely has contributed to the demographic phenomenon. As resorts expand ski-lift access and develop terrain that is more technical, riders are able to spend more time riding downhill at high speed. During competitive downhill races, mountain bikers attain speeds approaching 60 mph over uneven, often rocky, terrain.

There is more: In the United States, competitive high school mountain bike leagues are increasingly popular, drawing more and more participants. These leagues are overseen by the National Interscholastic Cycling Association (NICA; www.nationalmtb.org/), which has developed appropriate rider safety guidelines. In response to concerns over safety, NICA, in conjunction with the University of Utah, recently initiated a study comparing injury reports among various high school sports and cycling (www.nationalmtb.org/nica-safety-study/).

A Look at the Scope of Mountain Biking Injury

Table: Lower-extremity overuse and accidental injuries in mountain biking

Foot numbness

Foot pain

  • Metatarsalgia
  • Morton’s neuroma
  • Plantar fasciitis
  • Sesamoiditis

Iliotibial band syndrome

Knee pain Other

  • Bilateral tarsal tunnel syndrome
  • Lisfranc fracture

As the number of off-road cyclists increases, so has the number of cycling-related injuries.9 Surveys of mountain bikers demonstrate that injury is common, but most are minor and involve soft tissue. The nature of mountain biking lends itself to injuries to skin, with the most common types being soft-tissue abrasion, laceration, and contusion.3,5 After soft-tissue injury, mountain bikers experience the following injuries in order of prevalence: fracture of the clavicle, fracture of the ribs, fracture of the distal radius, and fracture of the scaphoid.5 What follows is a review of mountain biking injury by body region.

Head and face. Along with soft-tissue injury and fractures, older literature suggested that mountain bike riders have a relatively higher associated rate of maxillofacial trauma compared to road cyclists.10 Gassner10 and Chow11 proposed that conventional cycling helmets were inadequate for mountain bikers; they recommended adding face guards to mountain bike helmets secondary to the high rate of maxillofacial trauma.11 Perhaps in response to this recommendation, there has been an increase in helmets that provide greater protection, as shown in a study by Becker et al,5 which demonstrated that the great majority of competitive downhill mountain bikers wear a full-face helmet.

Spine. High speeds and technical terrain associated with downhill racing increase the risk of acute spinal injury. As noted, the greatest occurrence of spinal injury is observed among younger male riders. Similarly, McLean et al12 reported on spinal injury in mountain bikers and showed that, principally, young males are at risk. They recommended mandatory universal use of protective equipment and appropriate rider training.

With regard to overuse injury of the spine, the nature of riding leads to cyclists remaining in a flexed position on the bike, which can lead to neck and back pain; such complaints are frequent in road cyclists. However, the geometry of a mountain bike allows a more upright riding position and changes in riding terrain often require different body positions, which may decrease the incidence of chronic neck and back pain in mountain biking, compared to what is seen in road cycling.

Abdomen. Spleen and liver injuries are the most frequently reported abdominal injuries;9 some have been associated with using bar ends on handlebars that allow for additional riding positions. Nehoda13 reported the relationship between an increase in liver injury and bar ends on handlebars in the late 1990’s, which led to a decrease in the use of bar ends. Recently, however, there has been a resurgence of shorter attachments to the handlebars because of perceived improved comfort.

Skin and soft tissue. Skin and soft-tissue injury is common in mountain biking. Traumatic lacerations and abrasions are common and, likely, underreported. It is probable that many soft-tissue injuries from mountain biking are taken care of at home and, therefore, not reported. For injuries requiring evaluation by a medical provider, initial management includes copious irrigation and tetanus immunization if needed. Proper anesthesia is essential to allow full wound assessment for foreign bodies and deeper injuries (to tendons and joints) as well as appropriate irrigation and debridement.

The anterior lower leg of mountain bikers frequently sustains soft-tissue trauma, including injuries from plant undergrowth, teeth of the chain ring, and sharp edges of flat pedals. Most such injuries heal well with appropriate wound care, which might include aggressive irrigation and debridement. However, these injuries might also require more significant intervention, as noted by Patel,14 who reported significant pretibial lacerations from the chain ring when using quick-release pedals—lacerations that required debridement under anesthesia and delayed wound closure or skin grafting.

Trauma in mountain biking can result in injury to the soft-tissue bursa from a direct blow, resulting in fluid collection and swelling. A similar injury to the bursa involves a shearing force that separates superficial fascia from deep fascia, resulting in a collection of fluid, known as a Morel-Lavallée lesion.15 This lesion is most often seen at the olecranon bursa, the greater trochanter of the hip, or one of the knee bursa. Although many of these injuries are treated with ice and compression, management for a small percentage of patients includes timely aspiration.15

The upper extremity. Ulnar and median neuropathies are the most common overuse problems of the upper extremity in all cyclists. This problem is related to direct pressure on nerves at the wrist on the handlebar. Ulnar neuropathy, or cyclist’s palsy, causes injury to the ulnar nerve at Guyon’s canal and can produce numbness and tingling of the fourth and fifth fingers. Median nerve injury or irritation also occurs and can present with numbness or tingling of the thumb, index finger, and middle finger or with other signs and symptoms of carpal tunnel syndrome. Initial treatment of ulnar neuropathy and median nerve injury includes padded gloves and handlebars, improving rider posture, proper bike fit, night splints, and other appropriate strength and stretching therapy for these specific nerve-compression syndromes.

After such soft-tissue injuries as abrasion and laceration, fractures of the upper extremity are the most common reported injuries among mountain bikers, with fracture of the clavicle most common. Bush16 performed a study in the area of the Whistler Mountain Bike Park in British Columbia, Canada, and reported that scaphoid, distal radius, and metacarpal fractures were the most common fractures of the hand, particularly from landing on an outstretched arm.

The lower extremity. The 3 principal areas of contact between cyclist and bike are the handlebars, saddle, and foot–pedal interface. That foot–pedal link, which is the connection to the drive train of the bike and relates to the kinematics of cycling, is one of the contributors to overuse injury in cycling (Table, page 37). Although there is an abundance of literature related to shoe wear and orthoses in running and walking, information about shoes and orthoses in cycling is limited. Specific to mountain biking, it is more challenging to make observations or give general recommendations about footwear because riders use different types of shoes and flat or clipless pedals.

Knee pain is a common complaint among cyclists, reported by 20% to 27% of mountain bikers.17 During an average weekend ride, a cyclist can flex and extend the knee 15,000 times. With that amount of repetitive motion, even small inefficiencies can contribute to knee pain—particularly, anterior pain. The cycling literature on knee pain generally suggests that pain occurs due to:

  • a sudden increase in mileage and intensity
  • impaired hip gluteal and hip abductor function
  • seat position too low or too far forward
  • poor patellar mechanics.18

In a systematic review of the literature regarding knee pain in cyclists, Bini and Bini19 attempted to synthesize previous studies, suggesting that cyclists with knee pain have increased medial projection of the knee and abnormal muscular activation. They noted, however, that research in this area is limited and true biomechanical understanding of this injury is lacking. Interestingly, they concluded that there is little evidence, based on their review of studies, for a relationship between saddle height and knee pain, which conflicts with the theory that decreasing saddle height might increase patellofemoral pain and pressure, causing anterior knee pain.

Why so much interest in mountain biking?

The increase in popularity of mountain biking is likely due to a number of contributing factors, including:

  • improvements in mountain bike technology
  • accessibility to more and more trails
  • growing knowledge of associated benefits of cardiovascular exercise with cycling.

Although mountain bikers may have similar reasons for participating in the activity, they are still a highly heterogeneous group, with a wide range of disciplines—ranging from recreational cross-country riding to extreme downhill and free-riding.

Medical providers often encourage mountain biking as a lifetime activity that can improve health. There are potential health benefits to mountain biking compared to road biking because of augmented use of the upper body and increased cognitive effort and decision-making. Although there are clearly health benefits, risk exists for acute and chronic overuse injury in this sport, as this article describes, given the nature of the terrain and the technical nature of the sport. It has been challenging to weigh the risks versus the benefits of mountain biking, however, because, first, there are likely many unreported injuries and, second, it is difficult to study the heterogeneous population that participates in this sport.

Iliotibial band syndrome (ITBS) is a common overuse injury at the knee in cycling. Although forces at the iliotibial band at the knee in a cyclist are markedly less than forces seen in runners, bike fit and the high amount of repetition of cycling in the impingement zone likely play a role in ITBS in cycling. It has been suggested that a seat set too high and training errors are the main causes of ITBS in cycling.20

Mountain bikers may present with foot pain or numbness (or both); this can be related to type of shoe or pedal, location of the cleats, and a high amount of repetitive movement. Traditional cycling shoes with cleats might be too narrow in the forefoot for mountain biking, causing compression of the metatarsal phalangeal joints and interdigital nerves. Common diagnoses of foot pain in this group include metatarsalgia, plantar fasciitis, sesamoiditis, and Morton’s neuroma (i.e., of an intermetatarsal plantar nerve).

Initial treatment of foot pain and numbness in a cyclist can include adjustment of shoe wear, modifying the cleat position (often, positioning is too far forward), and adding appropriate footbeds. If the rider uses clipless pedals, adjusting the cleat might help because a cleat that is too far forward can increase 1) pressure on the forefoot and sesamoids of the first metatarsal phalangeal joint and 2) stress on the plantar fascia.

Introduction of newer carbon-soled shoes, which are stiffer than older plastic models, might decrease some of these foot problems by distributing forces differently. Conventional solutions, such as footbeds or orthoses, can be challenging with many traditional (i.e., narrow) cycling shoes, where there is a need to be space-conscious. In addition, there is less research and guidance available to clinicians and therapists about appropriate use of orthoses and wedges in mountain biking. Older studies that looked at performance have evaluated wedges and orthoses in cycling and have reported improvements in power, kinematics, and changes in forces at the knee;21 however, those studies are limited and there is a general lack of direction for providers concerning footwear solutions for foot and ankle pain in mountain biking.

Making a decision to improve comfort and, perhaps, safety, many recreational cyclists prefer flat pedals. They have adopted a stiffer, mountain bike-specific shoe with a wider toe box and sturdy construction, which might offer improved protection of the foot from direct trauma.

Last, unusual foot injuries can occur in mountain biking:

  • Lisfranc fracture. A case report described a fracture dislocation of the tarsometatarsal joint in a mountain biker. The mechanism of injury was axial loading of the foot while attempting to prevent a fall at a high rate of speed.22
  • Bilateral tarsal tunnel syndrome. This uncommon problem was reported in a cyclist, caused by a marked increase in cycling intensity, leading to symptoms of nerve impingement.23

Risk of Injury Is Inherent

Mountain biking has evolved into a popular outdoor activity with health benefits. However, given the nature of the terrain and the demographics of mountain bikers, there remains associated risk to this sport. Medical providers should be aware of common associated injuries and some of the distinctive differences in mountain biking, compared to other cycling activities.

Michael Reeder, DO, board-certified in emergency medicine, is Director of the Monfort Family Human Performance Lab, Colorado Mesa University, Grand Junction, Colorado. He is Director of Medical Education for Cycling CME, a provider of continuing medical education for physicians, PAs, and other health-care providers (see page 62). Dr. Reeder holds a Certificate of Added Qualifications Fellowship in Primary Care Sports Medicine

Brent Alumbaugh, MS, is Clinical Coordinator and Exercise Physiologist at Monfort Family Human Performance Lab, Colorado Mesa University.

REFERENCES
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