Mike Vandeman
2012-02-26 23:26:28 UTC
Wilderness and Environmental Medicine, 6,385-390 (1995)
ORIGINAL ARTICLE
Do conventional bicycle helmets provide
adequate protection in mountain biking?
TONY K. CHOW, MD,* STEPHEN W. CORBETT, MD
and DAVID J. FARSTAD, MD
Department ofEmergency Medicine, Lorna Linda University Medical
Center, Lorna Linda, CA 92354, USA
We present two cases of acute injury to the face and head sustained
from off-road mountain biking
despite the fact that the riders wore bicycle helmets. We reviewed the
literature related to this topic
and suggest that conventional bicycle helmets may be inappropriate for
off-road use. Specifically,
they lack an apparatus to protect the face in falls that involve this
exposed area. In addition, current
standards for bicycle helmets to protect the head were devised for
road use and many presumptions
are incomplete when applied to off-road use. Recommendations for
application toward off-road use
of current helmet design are made.
Key words: bicycle, helmets, standards, facial injury, head injury
Introduction
Since its introduction in the 1970s, the mountain bike (also known as
all-terrain bicycle or
ATB) has continued to grow in popularity. The sport of mountain biking
originated when
riders took conventional bicycles and rode them down dirt roads. These
bicycles have since
been modified in various ways to facilitate travel over a variety of
terrain. Today, the
industry boasts sales in the millions [1] and numerous organizations
promote both
recreational and competitive usage.
Despite the enormous growth of the sport, little is known about the
risks of injury,
particularly to the head and face. A survey of southern California off-
road bicyclists [2]
revealed 15% of all injured riders had injuries to the head and neck,
ranging from
abrasions and contusions to fractures. This was shown despite the fact
that 88% of these
riders were wearing helmets at the time of their crash. Several recent
stl;ldies [3-6] have
demonstrated the effectiveness of helmets in preventing serious head
injuries in standard
bicycling accidents. However, the very nature of mountain biking
differs significantly from
conventional bicycling. It is possible that the degree of safety
provided by conventional
helmets may be inadequate for off-road use.
Two cases of mishaps from off-road mountain biking illustrative of the
incomplete
protection afforded by conventional bicycle helmets are presented. The
literature on the
effectiveness of bicycle helmets and a discussion of the applicability
of the helmet
industry's current testing standards in all-terrain use is reviewed.
'To whom all correspondence should be addressed.
1080-6032 © 1995 Chapman & Hall
Chow, Corbett and Farstad
Cases
Case 1
An 18-year-old male mountain biker was riding downhill at an estimated
speed of 15-20
mph when he hit an obstacle on the dirt trail, causing him to be
pushed forward. He
reportedly went over the handlebars and struck his head and face. The
rider was wearing
an approved standard bicycle helmet at the time and it remained
properly positioned on
the victim's head but was noted to break during the fall. His riding
companions noted him
to be confused but able to ambulate. Paramedics arrived and the victim
was transported
with full cervical spine precautions.
Upon evaluation in the emergency department, the victim was in no
acute distress and
his vital signs were within normal limits. No major injuries were
found in his neck, chest,
abdomen, pelvis, back, or extremities and, neurologically, the patient
was completely
intact. He was noted to have multiple abrasions scattered throughout
his body, but his face
appeared to have absorbed most of the damage from the impact with the
ground. His
upper lip sustained a large, macerated, stellate, full-thickness
laceration. The lower lip was
deeply abraded and there was an avulsion fracture to the upper
incisor. His other teeth
were intact, no facial instability was appreciated, and there was no
malocclusion. Facial
radiographs revealed a nasal fracture.
The patient was stabilized and referred to a plastic surgeon for
repair of his facial
injuries. This consisted of more than 50 sutures and he has
subsequently done well.
Case 2
A 26-year-old male mountain bicyclist sustained an unwitnessed fall.
The area where he
fell was a downhill slope and it was estimated that his speed may have
been as fast as 35
mph based on the speedometer readings of other riders who have
traversed the same path.
When paramedics arrived, the victim was unresponsive and had a
properly fitted helmet
on, which was noted to be "cracked." He appeared to have no obvious
external signs of
trauma but had decorticate posturing and Cheynes-Stokes breathing. He
was intubated
immediately and placed in full cervical spine precautions. The victim
was transported off
the mountain by land ambulance and then transferred to a helicopter
and flown to the
trauma center. He received hyperventilation and, en route, a seizure
was noted and
treated with intravenous diazepam.
In the emergency department, examination revealed a comatose male who
responded
only to painful stimuli with decerebrate posturing. His pupils were 2
mm, equal, and
unreactive. Deep tendon reflexes were symmetric and plantar reflex
yielded down-going
toes. He had palpable hematomas in the right parietal region with no
other deformities
noted and no cerebral spinal fluid otorrhea or rhinorhea was seen. The
remainder of the
physical exam was unremarkable.
Computerized tomography of the head demonstrated multiple
intraparenchymal hemorrhagic
contusions with intraventricular bleeding and a subarachnoid
hemorrhage.
Subsequent hospitalization consisted mainly of supportive care and the
patient's
neurologic status improved little. Electroencephalogram and auditory
brain stem evoked
response study were abnormal and consistent with bilateral cortical
dysfunction. The
patient was eventually discharged from the hospital to a long-term
head injury rehabilitation
program with a guarded prognosis.
Conventional helmets in mountain biking
Discussion
Although the precise origin of the mountain bike is arguable, it has
grown to be the bicycle
industry's most popular product [1]. Large-volume production of
mountain bikes began in
the early 1980s and has enjoyed successful growth. Similarly, bicycle
helmet sales have
increased from a few thousand in 1975 to 5.5 million units in 1991
[7]. Despite their
apparent parallel growth in sales, the design of helmets has remained
relatively unchanged
and focus has been on their use in conventional riding on paved
terrain. In contrast,
mountain biking has evolved a great deal from its modest beginnings in
the late 1970s when
cycling enthusiasts took modified "street bikes" and pedaled them off-
road. The development
of stronger frames, special brakes and components, and a wheel
diameter of 26 in.
with "fat" tires has facilitated its use in off-road conditions.
Today, it has enjoyed
unprecedented growth into a sport that will be a full-medal
competition in the 1996
Summer Olympics. The sport of mountain biking has grown to a level
where it resembles
moto-cross in many ways with the development of front and rear
suspension systems. In
addition, bicycle frames have been modified from the traditional
"double triangle"
configuration to those which incorporate devices borrowed from off-
road motorcycles [8].
Despite this, the riding attire and safety equipment continues to
resemble that used in
conventional road riding. Because of the relative youth of the sport,
no study has
investigated the adequacy of conventional helmets in mountain biking.
Each of the two cases described demonstrate important points regarding
the efficacy of
conventional bicycle safety helmets in off-road cycling. The first
item is the amount of
protection provided by these helmets to the rider's face. Lindqvist et
al. [9] analyzed 93
patients with maxillofacial fractures sustained in bicycle accidents
in Helsinki. Two-thirds
of the fractures were diagnosed in the mandible and, of these, the
majority of them were
condylar and subcondylar fractures (67%). The other one-third of
fractures occurred in
the midface. They observed that "most commercially available helmets
do not protect the
whole facial area and especially not the chin." Thompson et al. [10]
prospectively
examined the effects of safety helmets on the risk of facial trauma.
Their results suggest
that presently designed bicycle safety helmets have little to no
effect on the overall risk to
facial injury but may afford some protection to serious upper facial
injuries (lacerations
and fractures ofthe midface, nose, eye/orbit).
Intuitively, these findings are not surprising because bicycle helmets
as they are
presently designed do not extend to the lower face or ears (Fig. 1)
and helmet standards
for protection of this region are lacking. Worrell [11] recorded the
site of impact in 100
consecutive head injuries in cyclists and observed that only 50% of
the sites of impact
would be covered by a helmet. In another study [12], 64 helmeted
cyclists with head
injuries were noted to have the majority of all impacts occur below
the test lines of the
standards. A modified helmet design which would include a face bar or
chin cover (Fig. 2)
such as that found in other sports may reduce the risks of trauma to
the face [13].
The second point relates to whether or not conventional bicycle
helmets provide enough
protection to the head in off-road riding. Dorsch et al. [14]
estimated that helmeted
bicyclists have reduced risk of death from head injury compared to
unhelmeted cyclists.
Wasserman et al. [4] supported this contention and subsequent studies
by Thompson et al.
[3], McDermott et al. [5], and Maimaris et al. [6] showed helmets to
be highly effective in
reducing risk of head injury. Although these investigations are
convincing that helmets are
efficacious, they provide little information on the extent of injury
to those cyclists who
Chow, Corbett and Farstad
Fig. 1. An example of a conventional bicycle helmet. Note the exposed
facial and temporal area.
sustain serious head injury despite wearing a helmet. Williams [12]
evaluated helmets that
sustained impacts from real crashes and found serious head injuries
occurred when the
helmet came off the rider's head, the helmet collapsed due to a
material defect, or the
head was struck predominantly below the rim. He recommended the test
line of helmet
standards be lowered to provide protection to the forehead, temple,
and ear regions.
The two essential components of a bicycle helmet are its rigid head
covering generally
consisting of polystyrene foam and a retention system composed of
flexible strap. Helmets
are constructed such that the energy from an impact is absorbed by the
helmet material,
causing its partial destruction and thereby protecting the head. Most
helmets manufactured
for bicycling conform to standards set by private, nonprofit
organizations. Shock
absorption standards [15] are based on determining the imparted
acceleration to an
appropriately instrumented test headform. The test headform consists
of a rigid, lowresonance
material and is dropped in a guided fall upon two types of fixed rigid
steel
Fig.2. Diagram of a bicycle helmet with modifications designed to
cover more of the head and lower
face.
Conventional helmets in mountain biking
anvils-one flat and one hemispherical. The test surface attempts to
simulate a flat tarmac
road surface or most parts of a car structure. Therefore, the present
design of helmets is
biased toward protection from impacts with these surfaces but do not
take into consideration
impact with irregular surfaces or deformable objects which are often
found in
off-road use. No standard currently tests protection parameters of
helmets that impact
with a deformable object presumably because ofthe need to replace it
after each test [16].
The importance of test standards with such impact surfaces is
uncertain because presently
available data do not demonstrate what types of surfaces are most
commonly encountered
in off-road crashes.
Even if a helmet meets the standards mentioned above of a certain
minimum level of
protection in the laboratory, how this standard corresponds to a
helmet's performance in a
real-world impact is less certain. One approximation estimates a
helmet which.meets
current standards should protect the cyclists for impacts up to 15 mph
into a flat surface
[17]. Velocities attained in mountain biking have far exceeded this
estimate, as illustrated
in the cases cited and observations from downhill races in which
speeds in excess of 45 mph
are attained [18]. Cyclists, both road riders and mountain bikers,
should be cautioned that
conventional helmets are limited in their capability to protect the
head in a high-velocitY
direct impact.
The cases and discussion indicate further research is needed in this
area. The actual
incidence of such injuries is difficult to estimate because no
surveillance system is currently
available to identify cyclists injured specifically from off-road
riding. Even less known are
the particular mechanisms of injury and the objects struck in crashes.
Investigations are
currently underway to study such items. These details are important
because optimum
design of helmets for off-road use depend on this type of
information.
In summary, it is suggested the helmet industry and standards
organizations should
consider a helmet designed for off-road use and take into
consideration the following
recommendations:
1.
Extending the outer rim of the helmet such that more of the head is
covered,
particularly the ears (Fig. 2).
2.
An additional apparatus to cover the lower face (Fig. 2).
3.
Much of the riding in mountain biking includes steep downhill grades
in which
considerable velocities may be attained; therefore, the material
design would need to
take into account the possibility of greater energy absorption in the
event of a
high-speed crash.
4.
The terrain varies greatly and the presumption of an impact with a
flat, nondeformable
surface may be misleading in the setting of off-road use. Standards
for impact with
irregular surfaces and deformable surfaces also need testing.
References
1.
Bicycle Wholesale Distributors Association. 1993Annual Statistical
Review. Philadelphia: BWDA,
1994.
2.
Chow, T.K., Bracker, M.D. and Patrick, K. Acute injuries from mountain
biking. West J Med
1993; 159: 145-8.
3.
Thompson, R.S., Rivara, F.P. and Thompson, D.C. A case-control study
of the effectiveness of
bicycle safety helmets. N EnglJMed 1989; 320: 1361-7.
4.
Wasserman, R.C., Waller, J.A., Monty, M.J., Emery, A.B. and Robinson,
D.R. Bicyclists,
Chow, Corbett and Farstad
helmets, and head injuries: a rider-based study of helmet use and
effectiveness. Am J Public
Health 1988; 78: 1220-1.
5.
McDermott, F.T., Lane, I.C, Brazenor, G.A and Debney, E.A The
effectiveness of bicyclist
helmets: a study of 1710 casualties. J Trauma 1993; 34: 834-44.
6.
Maimaris, C, Summers, CL., Browning, C and Palmer, CR Injury patterns
in cyclists
attending an accident and emergency department: a comparison of helmet
wearers and
non-wearers. Br Med J 1994; 308: 1537--40.
7.
Fisher, D. History, helmets and standards: 40 years of advancement in
head protection. ASTM
Standardization News, June 1992.
8.
Pfeiffer, RP. and Kronisch, RL. Off-road cycling injuries: an
overview. Sports Med 1995; 19:
311-25.
9.
Lindqvist, C, Sorsa, S. Hyrkas, T. and Santavirta, S. Maxillofacial
fractures sustained in bicycle
accidents. Int J Oral Maxillofac Surg 1986; 15: 12-8.
10.
Thompson, D.C, Thompson, RS., Rivara, F.P. and Wolf, M.E. A case-
control study of the
effectiveness of bicycle safety helmets in preventing facial injury.
Am J Public Health 1990; 80:
1471--4.
11.
Worrell, J. Head injuries in pedal cyclists: how much will protection
help? Injury 1987; 18: 5-6.
12.
Williams, M. The protection performance of bicyclists' helmets in
accidents. Accid Anal Prev
1991; 23: 119-31.
13.
Bjornstig, D., Ostrom, M., Eriksson, A and Sonntag-Ostrom, E. Head and
face injuries in
bicyclists-with special reference to possible effects of helmet use. J
Trauma 1992; 33: 887-93.
14.
Dorsch, M.M., Woodward, AJ. and Somers, RL. Do bicycle safety helmets
reduce severity of
head injury in real crashes? AccidAnal Prev 1987; 19: 183-90.
15.
Snell Memorial Foundation. 1990 Standard for Protective Headgear for
Use in Bicycling. St. James,
NY: Snell Memorial Foundation, Inc., 1990.
16.
Mills, N.J. and Gilchrist, A The effectiveness of foams in bicycle and
motorcycle helmets. Accid
Anal Prev 1991; 23: 153-63.
17.
Mills, N.J. Protective capability of bicycle helmets. BrJ Sports Med
1990; 24: 55-60.
18.
Pfeiffer, RP. Off-road bicycle racing injuries-the NORBA pro/elite
category. Clin Sports Med
1994; 13: 207-18.
ORIGINAL ARTICLE
Do conventional bicycle helmets provide
adequate protection in mountain biking?
TONY K. CHOW, MD,* STEPHEN W. CORBETT, MD
and DAVID J. FARSTAD, MD
Department ofEmergency Medicine, Lorna Linda University Medical
Center, Lorna Linda, CA 92354, USA
We present two cases of acute injury to the face and head sustained
from off-road mountain biking
despite the fact that the riders wore bicycle helmets. We reviewed the
literature related to this topic
and suggest that conventional bicycle helmets may be inappropriate for
off-road use. Specifically,
they lack an apparatus to protect the face in falls that involve this
exposed area. In addition, current
standards for bicycle helmets to protect the head were devised for
road use and many presumptions
are incomplete when applied to off-road use. Recommendations for
application toward off-road use
of current helmet design are made.
Key words: bicycle, helmets, standards, facial injury, head injury
Introduction
Since its introduction in the 1970s, the mountain bike (also known as
all-terrain bicycle or
ATB) has continued to grow in popularity. The sport of mountain biking
originated when
riders took conventional bicycles and rode them down dirt roads. These
bicycles have since
been modified in various ways to facilitate travel over a variety of
terrain. Today, the
industry boasts sales in the millions [1] and numerous organizations
promote both
recreational and competitive usage.
Despite the enormous growth of the sport, little is known about the
risks of injury,
particularly to the head and face. A survey of southern California off-
road bicyclists [2]
revealed 15% of all injured riders had injuries to the head and neck,
ranging from
abrasions and contusions to fractures. This was shown despite the fact
that 88% of these
riders were wearing helmets at the time of their crash. Several recent
stl;ldies [3-6] have
demonstrated the effectiveness of helmets in preventing serious head
injuries in standard
bicycling accidents. However, the very nature of mountain biking
differs significantly from
conventional bicycling. It is possible that the degree of safety
provided by conventional
helmets may be inadequate for off-road use.
Two cases of mishaps from off-road mountain biking illustrative of the
incomplete
protection afforded by conventional bicycle helmets are presented. The
literature on the
effectiveness of bicycle helmets and a discussion of the applicability
of the helmet
industry's current testing standards in all-terrain use is reviewed.
'To whom all correspondence should be addressed.
1080-6032 © 1995 Chapman & Hall
Chow, Corbett and Farstad
Cases
Case 1
An 18-year-old male mountain biker was riding downhill at an estimated
speed of 15-20
mph when he hit an obstacle on the dirt trail, causing him to be
pushed forward. He
reportedly went over the handlebars and struck his head and face. The
rider was wearing
an approved standard bicycle helmet at the time and it remained
properly positioned on
the victim's head but was noted to break during the fall. His riding
companions noted him
to be confused but able to ambulate. Paramedics arrived and the victim
was transported
with full cervical spine precautions.
Upon evaluation in the emergency department, the victim was in no
acute distress and
his vital signs were within normal limits. No major injuries were
found in his neck, chest,
abdomen, pelvis, back, or extremities and, neurologically, the patient
was completely
intact. He was noted to have multiple abrasions scattered throughout
his body, but his face
appeared to have absorbed most of the damage from the impact with the
ground. His
upper lip sustained a large, macerated, stellate, full-thickness
laceration. The lower lip was
deeply abraded and there was an avulsion fracture to the upper
incisor. His other teeth
were intact, no facial instability was appreciated, and there was no
malocclusion. Facial
radiographs revealed a nasal fracture.
The patient was stabilized and referred to a plastic surgeon for
repair of his facial
injuries. This consisted of more than 50 sutures and he has
subsequently done well.
Case 2
A 26-year-old male mountain bicyclist sustained an unwitnessed fall.
The area where he
fell was a downhill slope and it was estimated that his speed may have
been as fast as 35
mph based on the speedometer readings of other riders who have
traversed the same path.
When paramedics arrived, the victim was unresponsive and had a
properly fitted helmet
on, which was noted to be "cracked." He appeared to have no obvious
external signs of
trauma but had decorticate posturing and Cheynes-Stokes breathing. He
was intubated
immediately and placed in full cervical spine precautions. The victim
was transported off
the mountain by land ambulance and then transferred to a helicopter
and flown to the
trauma center. He received hyperventilation and, en route, a seizure
was noted and
treated with intravenous diazepam.
In the emergency department, examination revealed a comatose male who
responded
only to painful stimuli with decerebrate posturing. His pupils were 2
mm, equal, and
unreactive. Deep tendon reflexes were symmetric and plantar reflex
yielded down-going
toes. He had palpable hematomas in the right parietal region with no
other deformities
noted and no cerebral spinal fluid otorrhea or rhinorhea was seen. The
remainder of the
physical exam was unremarkable.
Computerized tomography of the head demonstrated multiple
intraparenchymal hemorrhagic
contusions with intraventricular bleeding and a subarachnoid
hemorrhage.
Subsequent hospitalization consisted mainly of supportive care and the
patient's
neurologic status improved little. Electroencephalogram and auditory
brain stem evoked
response study were abnormal and consistent with bilateral cortical
dysfunction. The
patient was eventually discharged from the hospital to a long-term
head injury rehabilitation
program with a guarded prognosis.
Conventional helmets in mountain biking
Discussion
Although the precise origin of the mountain bike is arguable, it has
grown to be the bicycle
industry's most popular product [1]. Large-volume production of
mountain bikes began in
the early 1980s and has enjoyed successful growth. Similarly, bicycle
helmet sales have
increased from a few thousand in 1975 to 5.5 million units in 1991
[7]. Despite their
apparent parallel growth in sales, the design of helmets has remained
relatively unchanged
and focus has been on their use in conventional riding on paved
terrain. In contrast,
mountain biking has evolved a great deal from its modest beginnings in
the late 1970s when
cycling enthusiasts took modified "street bikes" and pedaled them off-
road. The development
of stronger frames, special brakes and components, and a wheel
diameter of 26 in.
with "fat" tires has facilitated its use in off-road conditions.
Today, it has enjoyed
unprecedented growth into a sport that will be a full-medal
competition in the 1996
Summer Olympics. The sport of mountain biking has grown to a level
where it resembles
moto-cross in many ways with the development of front and rear
suspension systems. In
addition, bicycle frames have been modified from the traditional
"double triangle"
configuration to those which incorporate devices borrowed from off-
road motorcycles [8].
Despite this, the riding attire and safety equipment continues to
resemble that used in
conventional road riding. Because of the relative youth of the sport,
no study has
investigated the adequacy of conventional helmets in mountain biking.
Each of the two cases described demonstrate important points regarding
the efficacy of
conventional bicycle safety helmets in off-road cycling. The first
item is the amount of
protection provided by these helmets to the rider's face. Lindqvist et
al. [9] analyzed 93
patients with maxillofacial fractures sustained in bicycle accidents
in Helsinki. Two-thirds
of the fractures were diagnosed in the mandible and, of these, the
majority of them were
condylar and subcondylar fractures (67%). The other one-third of
fractures occurred in
the midface. They observed that "most commercially available helmets
do not protect the
whole facial area and especially not the chin." Thompson et al. [10]
prospectively
examined the effects of safety helmets on the risk of facial trauma.
Their results suggest
that presently designed bicycle safety helmets have little to no
effect on the overall risk to
facial injury but may afford some protection to serious upper facial
injuries (lacerations
and fractures ofthe midface, nose, eye/orbit).
Intuitively, these findings are not surprising because bicycle helmets
as they are
presently designed do not extend to the lower face or ears (Fig. 1)
and helmet standards
for protection of this region are lacking. Worrell [11] recorded the
site of impact in 100
consecutive head injuries in cyclists and observed that only 50% of
the sites of impact
would be covered by a helmet. In another study [12], 64 helmeted
cyclists with head
injuries were noted to have the majority of all impacts occur below
the test lines of the
standards. A modified helmet design which would include a face bar or
chin cover (Fig. 2)
such as that found in other sports may reduce the risks of trauma to
the face [13].
The second point relates to whether or not conventional bicycle
helmets provide enough
protection to the head in off-road riding. Dorsch et al. [14]
estimated that helmeted
bicyclists have reduced risk of death from head injury compared to
unhelmeted cyclists.
Wasserman et al. [4] supported this contention and subsequent studies
by Thompson et al.
[3], McDermott et al. [5], and Maimaris et al. [6] showed helmets to
be highly effective in
reducing risk of head injury. Although these investigations are
convincing that helmets are
efficacious, they provide little information on the extent of injury
to those cyclists who
Chow, Corbett and Farstad
Fig. 1. An example of a conventional bicycle helmet. Note the exposed
facial and temporal area.
sustain serious head injury despite wearing a helmet. Williams [12]
evaluated helmets that
sustained impacts from real crashes and found serious head injuries
occurred when the
helmet came off the rider's head, the helmet collapsed due to a
material defect, or the
head was struck predominantly below the rim. He recommended the test
line of helmet
standards be lowered to provide protection to the forehead, temple,
and ear regions.
The two essential components of a bicycle helmet are its rigid head
covering generally
consisting of polystyrene foam and a retention system composed of
flexible strap. Helmets
are constructed such that the energy from an impact is absorbed by the
helmet material,
causing its partial destruction and thereby protecting the head. Most
helmets manufactured
for bicycling conform to standards set by private, nonprofit
organizations. Shock
absorption standards [15] are based on determining the imparted
acceleration to an
appropriately instrumented test headform. The test headform consists
of a rigid, lowresonance
material and is dropped in a guided fall upon two types of fixed rigid
steel
Fig.2. Diagram of a bicycle helmet with modifications designed to
cover more of the head and lower
face.
Conventional helmets in mountain biking
anvils-one flat and one hemispherical. The test surface attempts to
simulate a flat tarmac
road surface or most parts of a car structure. Therefore, the present
design of helmets is
biased toward protection from impacts with these surfaces but do not
take into consideration
impact with irregular surfaces or deformable objects which are often
found in
off-road use. No standard currently tests protection parameters of
helmets that impact
with a deformable object presumably because ofthe need to replace it
after each test [16].
The importance of test standards with such impact surfaces is
uncertain because presently
available data do not demonstrate what types of surfaces are most
commonly encountered
in off-road crashes.
Even if a helmet meets the standards mentioned above of a certain
minimum level of
protection in the laboratory, how this standard corresponds to a
helmet's performance in a
real-world impact is less certain. One approximation estimates a
helmet which.meets
current standards should protect the cyclists for impacts up to 15 mph
into a flat surface
[17]. Velocities attained in mountain biking have far exceeded this
estimate, as illustrated
in the cases cited and observations from downhill races in which
speeds in excess of 45 mph
are attained [18]. Cyclists, both road riders and mountain bikers,
should be cautioned that
conventional helmets are limited in their capability to protect the
head in a high-velocitY
direct impact.
The cases and discussion indicate further research is needed in this
area. The actual
incidence of such injuries is difficult to estimate because no
surveillance system is currently
available to identify cyclists injured specifically from off-road
riding. Even less known are
the particular mechanisms of injury and the objects struck in crashes.
Investigations are
currently underway to study such items. These details are important
because optimum
design of helmets for off-road use depend on this type of
information.
In summary, it is suggested the helmet industry and standards
organizations should
consider a helmet designed for off-road use and take into
consideration the following
recommendations:
1.
Extending the outer rim of the helmet such that more of the head is
covered,
particularly the ears (Fig. 2).
2.
An additional apparatus to cover the lower face (Fig. 2).
3.
Much of the riding in mountain biking includes steep downhill grades
in which
considerable velocities may be attained; therefore, the material
design would need to
take into account the possibility of greater energy absorption in the
event of a
high-speed crash.
4.
The terrain varies greatly and the presumption of an impact with a
flat, nondeformable
surface may be misleading in the setting of off-road use. Standards
for impact with
irregular surfaces and deformable surfaces also need testing.
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