Frequently Asked Questions about Mountain Biking
Michael Vandeman, Ph.D.
Last Updated May 17, 2013
1. Why do people mountain bike?
a. They say that using a bike allows them to get much farther, in the same amount of time, than they can by walking. They also maintain constant pressure on land managers, to open more and more trails to bikes. Of course, all of these trails are already open to them, if they choose to walk. They also frequently claim that closing trails to bikes "excludes" them from the parks. This could only be true if they were unable to walk. Of course, they are able to walk. There's nothing inherently wrong with bicycling instead of walking; we all like to save energy, when it's appropriate. Use of a bicycle to replace automobile use is obviously beneficial. However, by the same token, replacing hiking with mountain biking is obviously not beneficial.
b. They are interested in the quantity of nature they can see, rather than the quality of their experience. While riding a bike, especially over terrain as rough as a trail, one has to be constantly paying attention to not crashing. That makes it almost impossible to notice much else. (IMBA confirmed that in their "Rules of the Trail": "Control Your Bicycle: Inattention for even a moment could put yourself and others at risk": http://www.imba.com/about/rules-trail. Or: http://bikemagic.com/news/guest-blog/craig-bowles-3rd-at-world-24-hour-solo-mountain-bike-championships.html: "The rest of the lap dazzled us with stunning views of the azure waters below, although fast rocky descending and even more steep loose climbing meant you had to pay attention to the tricky trail.") By contrast, a hiker feels the ground, hears all the sounds and smells all the odors of nature and can stop instantly, if he/she finds something interesting. The brain thrives on stimulation. A biker has to travel several times as far as a hiker, to get the same stimulation as a hiker. (And, by the same token, motorcyclists have to travel several times as far as a bicyclist, and an auto user several times as far as a motorcyclist, since they are enclosed in a metal box.)
c. They are interested in thrills. Riding a bike on a trail, especially a trail containing many obstacles, or a trail one is not familiar with, is very challenging. (But if mountain biking is the high point of your week, as it seems to be for many mountain bikers, you must be leading a pretty dull life, off of the bike!)
d. They are interested in building mountain biking skills and competing with other mountain bikers. The thrill of racing drives people to spend more money on their bike, and ride it harder and more often. Racing, up to and including the Olympics, drives a lot of mountain biking. Of course, it is also extremely harmful to the parks and natural areas that are used for practice! It is hard to think of any other (legal) use of public lands, other than hunting, that is as harmful as mountain biking.
e. They want to get to their destination faster (not considering that the process of getting there is a major part of the enjoyment). Once, when much younger, I was hiking along a very boring trail. The thought came to me that if I had a bike, I could get past the boring section of the trail, and to the interesting part much faster. But about 2 seconds later I realized that if I could do that, so could everyone else, and the place would be full of people and ruined. That was the end of my (2-second) mountain biking career.
f. Example: "What do you enjoy most about mountain
biking?" "Just the experience of being out in a forest on a trail,
just flowing down it and enjoying the scenery. I know it sounds cheesy, but you
really become one with nature. At the same time, there's the adrenaline rush
you get from downhills and runner's high from climbing. It's a lot of stuff
that's hard to put into words." Steve Ray, mountain biker
2. What is driving the sport of mountain biking? Besides the attraction for participants, manufacturers and retailers of mountain bikes and mountain biking accessories, as well as "adventure" travel guides, make a lot of money from promoting mountain biking. Even some auto manufacturers (e.g. Subaru) promote and sponsor mountain biking, and try to use its popularity to sell more cars. The tourism industry also promotes mountain biking, among other attractions.
3. What harm does mountain biking do?
a. Most obvious is the acceleration of erosion. Knobby tires rip into the soil, loosening it and allowing rain to wash it away. They also create V-shaped grooves that make walking difficult or even dangerous. The mechanical advantage given by the gears and ball bearings allow a mountain biker to travel several times as fast as a hiker. Given their increased weight (rider plus bike), this results in vastly increased momentum, and hence much greater horizontal (shearing) forces on the soil. (Witness the skid marks from stops, starts, and turns.) According to Newton, every action has an equal and opposite reaction. Mountain bikes were built much stronger than other bikes, so that they could withstand the greater forces they were subject to on rough trails. These same forces, therefore, are being applied to the trails! To give a definite number, the winner of a 20-mile race here in Briones Regional Park averaged 13 MPH (the speed limit is 15 MPH -- where were the park rangers?). Mountain bikers themselves use the expression "shred trails" for mountain biking. That is not an accident. That is exactly what knobby tires are designed to do! (http://blogs.bikemag.com/news/diamondback-welcomes-billy-lewis/: "Northwest shredder Billy Lewis is now riding for Diamondback. ... Filmed at Duthie Hill and NWSOF.com(windells) as well as a couple secret spots.")
b. Mountain bikers love to race on singletrack (narrow) trails. But it makes absolutely no sense to "race" on a singletrack trail, where, by definition, everyone must travel single-file, and you can't pass anyone (or risk widening the trail)!
c. A hiker must be very careful not to accidentally step on small animals and plants on the trail. For a mountain biker, it is almost impossible to avoid killing countless animals and plants on and under the trail. They have to pay attention to controlling the bike, and can't afford to look carefully at what is on the trail, especially when travelling fast. And even if they happen to see, for example, a snake, it is hard for them to stop in time to avoid killing it (e.g. see http://bb.nsmb.com/showthread.php?t=128889). A hiker, when crossing a creek, will try to avoid getting wet, by crossing on stepping stones or logs. Mountain bikers, on the other hand, simply ride right through the creek bed, crushing any animals or plants that happen to be there. Mountain biking magazines are full of photos of mountain bikers throwing up spray, as they barrel through creeks. Not only do bikes destroy animals and plants as they ride across streams, they ride through streams stirring up sediment. The sediment in the water interferes with the oxygen uptake by aquatic life, for example, killing fish- and frog eggs. Young fish, insects, amphibians, and aquatic microorganisms are extremely sensitive to sediment in water.
d. Bikes also allow people to travel several times as far as a hiker. This translates into several times the impacts, both on the trail and on the wildlife (to say nothing of the other trail users). Existing parklands are already inadequate to protect the wildlife that live there. When they are crisscrossed by mountain bikers and legal or illegal trails, their habitat becomes even more inadequate. Mountain bikers frequently advertise rides of 20-50 miles or more. Have you ever tried to walk that far in a day? In other words, allowing bikes in a park greatly increases human presence in that park and drives wildlife further from the resources that they need to survive, including water, food, and mates.
e. Due to their width and speed, bikes can't safely pass each other on narrow trails. Therefore, policies that permit mountain biking also result in more habitat destruction, as trails are widened by bikers (or by hikers and equestrians jumping out of their way).
f. Knobby mountain bike tires are ideal for carrying mud, and consequently exotic plants, fungi, and other organisms from place to place, resulting in the spread of exotic invasive species, such as weeds and Sudden Oak Death.
g. Mountain biking is driving the very young and old off of the trails and hence out of the parks. Even able-bodied hikers and equestrians fear for their safety, and don’t enjoy sharing the trails with bikes. (The mountain bikers claim that they are simply being selfish and "unwilling to share", but actually they have no problem sharing trails with mountain bikers; it is only their bikes that are a problem!)
h. Mountain bikes, which are obviously built to go anywhere, teach children and anyone else who sees them that the rough treatment of nature is acceptable. This undoubtedly has a negative effect on people's treatment of nature.
i. In order to mitigate bike-caused erosion, park managers have been resorting to extreme measures -- even in some cases putting a plastic matrix or other exotic material under the trail (e.g. in Pleasanton Ridge Regional Preserve, near Pleasanton, California)! It's hard to imagine that this will have a beneficial effect on the park and its wildlife….
j. Allowing mountain bikes in a park greatly increases the damage to the trails, damage from "bootleg" (illegally created) trails, and the problems of conflicts between trail users, and hence the cost of maintaining the park. Considering how tight park budgets are, we can't afford the extra costs of policing, and repairing the damage from, mountain biking.
k. For the science on mountain biking and its impacts on wildlife and people, see http://mjvande.nfshost.com/scb7.htm.
4. Mountain bikers claim that their sport has no greater environmental impact than hiking. Is that true?
a. If you read the "studies" that make that claim, you find that they don't really compare the impacts of hiking and mountain biking, but only the impacts per foot. If, for a moment, we assume that the studies are correct in their having equivalent impacts per foot, it would still follow that mountain biking has far greater impact per person, since mountain bikers typically travel so much farther than hikers. Besides overlooking distances travelled, those "studies" almost all ignore impacts on wildlife. And they don't study mountain biking under normal conditions -- only at a very slow speed. Actually, the comparison with hiking is irrelevant. It would only be relevant if we planned to allow only one of the two, and were considering which of the two is more harmful. In fact, no one is considering banning hiking. We are only considering adding mountain biking. Therefore, the only relevant question is, "Is mountain biking harmful"? (Of course, it is!) There is only one truly scientific study that I know of that compares the impacts of hiking and mountain biking. It found that mountain biking has a greater impact on elk than hiking (Wisdom, M. J., H. K. Preisler, N. J. Cimon, B. K. Johnson. 2004. Effects of Off-Road Recreation on Mule Deer and Elk. Transactions of the North American Wildlife and Natural Resource Conference 69, 2004, pp.531-550.) See http://mjvande.nfshost.com/scb7.htm.
b. On its web site, IMBA mentions recent research on mountain biking by Dave White et al and Jeff Marion, both of whom claim that mountain biking and hiking have "similar" impacts. Is that true? First, "similar" is not a scientific term and really has no clear meaning. That term is being used only to obfuscate. Second, these are survey studies, not experimental studies. By its very nature, a survey study cannot be used to compare the impacts from two activities, because it doesn't control all the variables. For example, we don't know if the differences in erosion between two trails are due to the mountain biking vs. hiking use, or due to differences in the weather, terrain, steepness, soil type, management practices, amount of use, hikers on the "mountain biking trail", mountain bikers on the "hiking trail", etc. White et al only measured their trails once, and didn't even collect any data on hiking impacts! See http://mjvande.nfshost.com/white.htm and http://mjvande.nfshost.com/marion.htm.
c. Why would a researcher risk his/her reputation by doing such shoddy work? For money! And to ensure the continuance of their sport. If land managers think that mountain biking is more harmful than hiking, they will be more likely to close trails to bikes. Bike parts manufacturer Shimano paid Professor White to do his study. Research funds are difficult to obtain. A researcher who can be relied upon to produce research favorable to mountain biking will be able to obtain funding from the mountain biking industry. A researcher who tells the truth about mountain biking won't be able to obtain research funds and will risk stunting his/her career.
5. Where should mountain biking allowed? A couple of role models for wildlife protection are Yosemite National Park and East Bay Municipal Utility District (in Alameda and Contra Costa counties, California). They both restrict bicycles to paved roads, where they can't do much harm. Somehow bicyclists have managed to enjoy their sport for over a hundred years, without riding off-road.
6. What should the policy be on trails? Closed to bikes, unless marked open. Signs that say "No Bikes" are quickly and repeatedly ripped out of the ground by mountain bikers.
7. Isn't it discriminatory to allow hikers and equestrians on trails, but not mountain bikers? Mountain bikers love to say this, apparently because they think it will gain them some sympathy. The truth is that mountain bikers have exactly the same access to trails that everyone else has! It is only their bikes that are banned. If mountain bikers were really being discriminated against, they could easily go to court to gain access. However … they already have access to every trail in the world!
8. Don't I have a right to mountain bike on all public lands? I am a taxpayer! The public has the right, through its elected representatives, to restrict how land is used. A federal court has already ruled that there is no right to mountain bike. It is a privilege, and any land manager who gives a good reason (such as safety or protecting the environment) can keep bikes off of trails (see http://mjvande.nfshost.com/mtb10.htm).
9. Don't mountain bikers do some good things, like trail construction and trail maintenance? Trail construction destroys wildlife habitat both directly (by killing plants and animals) and indirectly (by reducing the size of the intervening "islands" of habitat). Moreover, mountain bikers favor trails that are "twisty" (sinuous), bumpy, and full of obstacles that provide thrills for mountain bikers. Such designs increase habitat destruction (by lengthening the trail) and make the trails less useful for hikers and equestrians. Trail maintenance sounds good, until you realize that it would hardly be necessary, if bikes weren't allowed there. The mountain bikers are the main reason why trail maintenance is necessary! Trails used only by hikers require hardly any maintenance. Therefore, admitting bicycles to a park greatly increases its cost of maintenance. Nothing is really "free", including trail construction and maintenance. (How does the saying go? "Beware of Trojans bearing gifts"?) Not many mountain bikers volunteer for trail maintenance: "We had 20 people, mostly NON-MOUNTAIN BIKERS, turn out for the IMBA Trail Care Crew this weekend at Newberry Heritage Park. ... Would have been nice to see other riders there helping out, but it's average for only 1-2% of mountain bikers (nationally) to donate time to building or maintenance." Mountain bikers claim that they perform a valuable service by maintaining trails. But if not properly trained and managed, they can easily cause millions of dollars in damage and death to wildlife and people: there are hidden costs associated with it down the road that will cost substantial money (e.g. erosion, fire). For example, two mountain bikers doing unauthorized "trail maintenance" started a fire that destroyed 80 homes!: http://www.independent.com/news/jesusita-fire.
"Mother Nature was being her cantankerous old self and
decided to drop a couple of mature Monterey pines next to one of our trails at
Joaquin Miller Park in the Oakland hills. As such, we'll be restoring some of
the trail that was damaged by the roots of the tree and doing some additional
This illustrates why bikes should not be allowed on trails. Hikers can step over tree roots; bikers always ride over them and damage them -- they are too lazy to dismount and step over them. There is no good reason to cut the roots away, just to please mountain bikers. Wildlife, including trees, should get top priority in parks, because wildlife is what makes a place a park! Mountain bikers should not be doing "trail maintenance". They obviously don't know how to do it properly.
10. But don't mountain bikers provide added safety, by being able to quickly summon help in the event of an emergency? I would rather trust in a cell phone, than a speeding mountain biker. Besides, natural areas are already one of the safest places you can be. In over 50 years of hiking and backpacking, I have never witnessed any situation requiring emergency aid. Most people go to natural areas partly for solitude. If we wanted to be around large, fast-moving pieces of machinery, we would stay in the city!
11. Can't mountain biking help get our overweight kids off the couch? Hiking can already do that, without causing extra harm to wildlife and people. Mountain biking downhill provides zero exercise benefit. Mountain biking on level ground provides minimal exercise benefit, much less than walking. Since it's impossible to pay any attention to your surroundings while mountain biking (or you will crash), there's no reason to promote mountain biking. It benefits only those who stand to make money off of it, such as bike manufacturers, retailers, and tour companies. Mountain biking is also inappropriate for young people because it's very expensive!
"Fri, Aug 10 2007:
From: Ride-A-Lot <firstname.lastname@example.org>
Date: Fri, 10 Aug 2007
Subject: Re: need suggestions on mountain bike, thanks a lot
Any bike you buy from a big box store (i.e. Target, Wal-Mart, Dicks, Sports Authority, etc.) is going to be JUNK. If you ware going to do any actual mountain biking, you will very very disappointed with the performance. For a new mountain bike, the low-end entry level bike Specialized Rockhopper is one) will cost around $500."
(Mountain bikes are built tough because street bikes can't take the pounding that they would get on trails. They would fall apart.)
12. But isn't mountain biking healthful exercise? No! Mountain biking is inherently dangerous, and cannot be made safe. Hiking trails are not designed for bicycling. They are unpredictable. There is a reason why departments of transportation have standards for bicycle trails that require a smooth surface, not too steep a grade, a no-skid surface, a minimum width, a long sight distance (no blind turns), etc. Mountain bikers regularly fall off their bikes, resulting in paraplegia, quadriplegia, or even death. This obviously cancels out any possible health benefit. See http://mjvande.nfshost.com/mtb_death.htm and http://mjvande.nfshost.com/mtb_dangerous.htm. In 2010, a 12-year-old girl died during her very first mountain biking lesson!: http://www.nbc11news.com/home/headlines/98876339.html. Bicycling also reduces bone density: http://www.latimes.com/features/health/la-he-cycling16-2009feb16,0,1785648.story. A bicycle is an energy-saving device. In fact, according to a "Scientific American" article, it is the most energy-efficient of all forms of transportation. For healthful exercise, nothing can beat walking.
Mountain bikers are a danger to themselves: http://www.youtube.com/watch?feature=endscreen&v=5EAcljh4cxw&NR=1
Mountain bikers are a danger to others: http://www.globaltvedmonton.com/woman+injured+by+bike+on+river+valley+trail+speaks+out/6442701011/story.html
13. Won't a helmet protect me from serious injury? Don't bet on it!:
Man injured in Brown County mountain biking accident
Staff Reports email@example.com
First Posted: May 21, 2012 - 11:19 am
1:17 p.m. update
Alan Keeling, 48, of Crestwood, Ky., is in good condition today at IU Health Methodist Hospital in Indianapolis.
NASHVILLE, Ind. A Kentucky man was critically injured in a mountain biking accident at Brown County State Park.
Alan Keeling, 48, of Crestwood, Ky., was slammed face first into a fallen log after he was thrown from his mountain bike at about 4 p.m. Sunday while riding the trails at the state park, according to Indiana conservation officers.
Keeling was wearing a helmet, but he struck the log lower on his head. He suffered face and skull fractures and was flown to IU Health Methodist Hospital in Indianapolis for treatment.
Indiana Conservation Officer Brent Bohbrink investigated the accident. Nashville Volunteer Fire Department, Columbus Regional Hospital EMS and state park personnel assisted at the scene.
14. Doesn't mountain biking get people out of their cars? So do walking, road cycling, and transit use, without harm to the natural environment. Since very few mountain biking opportunities are within easy bicycling distance, the vast majority of mountain bike trips require transporting the bike in a truck, SUV, or car. If mountain bikers cared about the environment, they would bicycle to the park, lock their bike at the trailhead, and hike. Or simply bicycle on paved roads, as bicyclists have for the past century.
15. Doesn't the threat from mountain biking pale, in comparison to other sources of environmental damage, such as logging? Maybe, and maybe not. Mountain biking teaches people that the rough treatment of nature is acceptable, so it may lead to many other abuses. In parks, where most mountain biking is done, it is probably the most harmful activity allowed. But even if mountain biking is less damaging than another activity, such as logging, it is still additional damage. If an area is already messed up (e.g. by logging), how does that make it okay to do additional damage? It doesn't!
16. What's wrong with night riding? Humans have been destroying wildlife habitat for centuries, so that very little remains. Our presence in parks prevents wildlife from using a large part of their habitat, at least during the daytime. Now that night riding is becoming popular, wildlife and being denied that habitat even at night, or incur an increased risk getting run over, if they attempt to use it. There is very little law enforcement even during the day in these days of tight budgets. There is no patrolling of parks at night! This gives mountain bikers free rein to do whatever they want, including riding trails that are closed to bikes or even building their own illegal trails. No wonder night riding is so popular! And, of course, night riding makes an activity that is already very dangerous, much more dangerous.
17. Don't the vast majority of mountain bikers ride responsibly? Actually, just the opposite is true. In a scientific study that IMBA had on their website for a while, then quietly removed, 83.1% of mountain bikers broke the law (see http://mjvande.nfshost.com/mtb76.htm).
18. Aren't the problems with mountain biking just caused by "a few bad apples"? There aren't just a few! There are enough to put some in just about every park in the world. The same problems appear everywhere: riding off-trail, riding where prohibited, illegal trail construction, excessive speed, accelerating erosion, killing plants and animals on and next to the trail, driving other trail users off the trails, etc.
19. Isn't mountain biking good for the economy? Nearly all mountain bicycles are made by foreign companies. The profit from bicycle sales goes abroad! The small shops and bike mechanics find it hard to make a living. So, IMBA isn't supporting much USA business; IMBA is supporting foreign companies and their renegade sport. Mountain biking destroys wildlife habitat and drives non-mountain bikers off of the trails, so there is a net loss in recreation. This can't be good for the economy. As David Brower used to say, "There's no economy on a dead planet".
20. Why is mountain biking so addicting? It seems that once someone starts mountain biking, they feel a need to do it as often as possible – at least weekly. And they become impervious to information about the harm that mountain biking does. (That's why it is extremely unfortunate when land managers or their staff start mountain biking.) Apparently, some people have an especially strong desire or "need" for danger and thrills, and it seems to be accompanied by an unusually low concern for the welfare of wildlife, the environment, non-bikers, or anything else that gets in the way of their thrill-seeking. A phenomenon that may be related is the existence of psychopaths -- people who seem to be genetically devoid of moral feeling. See Without Conscience: The Disturbing World of the Psychopaths Among Us, by the brilliant scientist Dr. Robert Hare. I highly recommend his book. As far as I know, in Hare's terminology, mountain bikers are sociopaths, not psychopaths.
21. Aren't mountain bikers just
hikers with wheels, and don't they care about protecting the land as much as
conservationists? I am going to quote a friend, who said it much better
than I ever could: "What comes across very strongly to me is that this is
like the Biblical fable of Solomon trying to decide which woman is the real
mother to a baby. Sick of their bickering, he threatens to cut the baby in half
and give half to each. The true mother cries out in objection, saying she would
rather he gave the baby to the other woman than killed. That's how Solomon knew
who the real mother was. What does this have to do with mountain bikers and the
wilderness? It seems to me that the mountain bikers commenting in this thread
really don't care about the land unless they can use it. They would just as
soon the land not be protected as 'wilderness' at all, than be declared
off-limits to them. If they really cared about the wilderness, they would say,
please preserve the land, even if we cannot use it. And in fact, as Mike
correctly states, the land would still open to their use. Just without the
22. How can I see first-hand the harm that mountain biking does? Easy! Just watch their own videos: http://mjvande.nfshost.com/mtbvideo.htm.
23. IMBA has rules designed to minimize the impacts of mountain biking, such as not riding under wet conditions. Don't they protect the parks from damage?
IMBA's "rules" are just for show, and are universally ignored. So much for IMBA's rule about not riding under wet conditions! They could stick to pavement, but they are too selfish to do so:
"Date: Sat, 23 Jan 2010 21:15:01 -0800
From: Ross Finlayson <firstname.lastname@example.org>
Subject: Your favorite 'midst of the wet season' rides?
At this time of the year (especially during an 'El Nino' winter like this one), we often find ourselves wanting to ride just a couple of days after a major rainy spell. Most of the trails are too muddy to ride, but there are a few trails (mostly fireroads) that hold up OK even after heavy rain.
In the past, my favorite 'midst of the wet season' ride was the main (Aptos Creek) fireroad in Nisene Marks - from Aptos up to Sand Point overlook and back. But even that fireroad often gets very wet.
My new favorite 'midst of the wet season' ride - which I did again today - is at Butano State Park: Up the Butano Fireroad, past the abandoned airstrip, then down Olmo Fireroad, and back along the paved road. This is a 12-mile loop with 2000' of total climbing , and holds up well (especially the Butano Fireroad) even after a long period of heavy rain, such as we had this past week.
So lets hear your favorite 'midst of the wet season' rides?
24. Aren't most mountain bikers responsible? Mountain biking organizations always say that they oppose illegal trail-building and illegal mountain biking. Those statements are just empty words. They are always followed by excuses that exonerate the outlaws. For example, when three people were arrested for building an illegal trail in Marin County across four different jurisdictions, IMBA said that it was caused by a lack of sufficient singletrack opportunities! Is it any wonder that these activities never stop?! Here is just one of the many examples on the following website: http://forums.mtbr.com/showthread.php?t=595571: "As much as I disrespect vigilante trail building, sometimes its [sic] the swift kick in the butt needed to get the powers that be to recognize a problem. I know many will disagree, but you should check out the Freedom Riders movie and see how that turned out." Mountain bikers have never lifted a finger to actually stop illegal trail-building or illegal mountain biking. IMBA co-founder Michael Kelley once asked me where the illegal mountain biking is going on, and promised to do something about it. He has never shown up.
25. Can't horses be taught to tolerate the presence of bikes on the trail, so that mountain bikers can safely share trails with equestrians? No: "The other advantage for an equestrian, sometimes, is that if the horse is trying to avoid an obstacle/collision, the rider may be already out of the way of impact due to the horse's reflexes in avoiding the obstacle. Horses have reflexes 10 times faster than humans, so I'm told. So the injured rider usually has injuries not due to collision with the biker but instead with trees, rocks, falling, or other trail issues. Falling on her back and hitting her head are the main culprits for women riders. I now ride with a helmet to protect at least one part of me. Hopefully I will not land on my back if I go off; and if I have a choice, I'll try to roll. Another helpful piece, try to ride a horse that has some sense and some training rather than a green one or a colt, if possible. No matter how well trained, however, that is not a guarantee that the rider will be safe in an emergency." "The other problem with horse reflexes is that should they wheel and try to gallop out of danger, often the rider is already thrown half out of the saddle and is off balance due to the spin. Then the rider can hit the ground with great force, or worse yet, hit their head on a rock. Also, a panicked, otherwise completely sensible horse can back you off a cliff, fall with you and roll over on you, saddle, horse and all. I have very well trained, level headed horses that can meet many challenges that would frighten another horse. I am a very experienced rider who was riding with a friend who is a horse trainer. Both horses were frightened by the sudden, silent appearance of some speeding bikes. One horse spun so hard that my trainer friend was laid out flat on his neck, but didn't come off. My horse, a nearly bomb proof mare, freaked out and started backing up toward a cliff. I got her stopped just as her hind legs went off the edge of the cliff. I've had this mare for 14 years, she's never tried to back off a cliff before. Another variation is that once off balance on a spinning horse, the horse remains on the cliff, but the rider is thrown over the side, rolling and bouncing all the way to the bottom. … You can get a horse trail ready, but you can NEVER train the flight response out of a horse." "I and 2 other gals were all injured in an accident precipitated by a mountain biker who was wearing ear buds, and bombing down a narrow mountain trail. MB Websites have posts & pictures from mountain bikers bragging about AVERAGING 20 mph on that same trail. The mountain biker hit the first horse and they all spun and ran. We all had concussions, one gal suffered a compression fracture of her spine, the second such injury in ONE WEEK, due to an equestrian mountain bike accident. I was wearing a helmet and still got a concussion and back injuries. My horse suffered abrasions down to her tendon sheath on her hind fetlocks. If her injuries had gotten infected, that would have been it for her. The 2 gals I was riding with had been riding all their lives and one is a breeder and trainer. I was the rookie having been riding and owning horses for only 20 yrs. All the horses were well accustomed to bikes on the trail. You can't train them to be non reactive zombies when their life is threatened and a biker never stops."
Note: I was the Chair of the Wildlife Committee of the Sierra Club's San Francisco Bay Area Chapter for a decade. During the same period, I studied conservation biology and the environmental impacts of mountain biking, which are summarized in my paper "The Impacts of Mountain Biking on Wildlife and People -- A Review of the Literature": http://mjvande.nfshost.com/scb7.htm.