View source for Fixing problems in Ultramarathons

The table below lists some of the possible problems you may encounter during an ultramarathon, along with possible causes, treatments and preventions. Continuing a race when you have a problem entails some degree of risk, and these problems can impair your judgment, so use caution. This list is not comprehensive, and is expected to change over time. With all these suggestions, never forget [[The Golden Rule of Racing]], "Never do something in a race you have not practiced in training". <!-- __strippedalt__ __stripped__ -->
=Diagnostic Test=
Try the Jimbo Test. Picture three things in your mind; a cold drink, a cheeseburger, and a slice of cake. 
* If the cold drink appeals, then you're probably thirsty/dehydrated. (Remember, drink to thirst as over-hydration kills.)
* If the cheeseburger appeals, then you're either after fat or salt.
* If the cake appeals, then you'll probably have to some carbohydrate.
You can vary the items to suit your taste. For instance, if a doughnut generally appeals more than cake, then think of a doughnut instead of cake. This test is not foolproof, but it is a good, simple way of evaluating want your body probably wants.
=Nausea or vomiting=
See [[Nausea]].
{| class="wikitable" 
! style="background-color: #8A713B; color:#FEFFF2;" |'''Possible Cause stripped'''
! style="background-color: #8A713B; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #E7E8D8;" |Overheating
| style="background-color: #E7E8D8;" |
* Slow down and cool off. Once you've become overheated, it can be tricky to cool off enough to recover. Slowing down or stopping is normally required to reduce your heat production. Cold fluids pored over your head, neck and body can help, as can ice. Lying down with your feet elevated can also help.
'''Prevention'''
* [[Heat Acclimation Training]].
* [[Running in the Heat]].
|-
| style="background-color: #FEFFF2;" |Overeating
| style="background-color: #FEFFF2;" |
* Reduce calorie intake and only eat what appeals.
* Ginger or mints may help.
'''Prevention'''
* Eat what appeals.
|-
| style="background-color: #E7E8D8;" |Going too fast
| style="background-color: #E7E8D8;" |
* Slow up, possibly dramatically until things improve.
'''Prevention'''
* Better pacing.
|-
| style="background-color: #FEFFF2;" |Too little fluid intake
Even without dehydration, if you're not drinking enough to maintain urine production then you may become nauseated. This is because the hormone that reduces urine output also causes nausea.
| style="background-color: #FEFFF2;" |
* Rehydrate, but try to drink to thirst. Remember that over-hydration kills. 
'''Prevention'''
* [[Practical Hydration]].
|-
| style="background-color: #E7E8D8;" |Excessive fluid intake/too little salt
One of the symptoms of [[Hyponatremia]] is nausea. 
| style="background-color: #E7E8D8;" |
* Reduce fluid intake.
* Increase salt intake.
* If it appeals, a little salty broth may help.
'''Prevention'''
* Drink to thirst.
* Take enough salt to maintain thirst.
|-
| style="background-color: #FEFFF2;" |Too much salt
It's unclear how likely this is to happen in practice.
| style="background-color: #FEFFF2;" |
* Restrict salt intake.
* Be careful with [[Electrolyte Capsules]] to balance them against fluid intake.
'''Prevention'''
* Balance salt intake with fluid intake.
* Avoid [[Electrolyte Capsules]].
|-
| style="background-color: #E7E8D8;" [[NSAIDs and Running| NSAIDs]]
| style="background-color: #E7E8D8;" |
* Avoid NSAIDs
|-
| style="background-color: #FEFFF2;" |Infection
| style="background-color: #FEFFF2;" |
* Sorry, better luck next time
'''Prevention'''
* Careful hygiene, including keeping all your drinking containers sterile
|-
| style="background-color: #E7E8D8;" |Change in intestinal bacteria (due to traveling)
| style="background-color: #E7E8D8;" |
* Sorry, better luck next time
'''Prevention'''
* Travel earlier
* Avoid non-bottled water.
|-
| style="background-color: #FEFFF2;" |Constipation
It's unusual for constipation to cause nausea, but it can happen.
| style="background-color: #FEFFF2;" |
* Higher [[Fiber]] intake.
* Stay hydrated.

|-
| style="background-color: #E7E8D8;" |Tight waist band
| style="background-color: #E7E8D8;" |
* Loosen anything around your waist or pressing on your abdomen. (Waist packs for carrying drinks are a particular problem.)
|}
=Fatigue and sleepiness=
{| class="wikitable" 
! style="background-color: #03476F; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #03476F; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #DFF1F2;" |Low blood sugar
| style="background-color: #DFF1F2;" |
* Take something sweet or a Gel
'''Prevention'''
* Take carbs earlier
|-
| style="background-color: #FEFFF2;" |Low blood fat<ref name="fat"/>
| style="background-color: #FEFFF2;" |
* Consume a high fat food, such as peanut butter
* Combine high fat and high carbs as this will not only boost both, but often these foods are easier to digest
'''Prevention'''
* Eat fat earlier
* Have a higher fat pre-race meal
* Don't consume only fast carbohydrates
|-
| style="background-color: #DFF1F2;" |You're running an ultra (what did you expect?)
| style="background-color: #DFF1F2;" |
* [[Caffeine]]
* Short nap (5-15 min)<ref>Some runners recommend napping in a chair, others lying down with your feet elevated. I like the lying down option as it helps my legs recover more. It can be helpful to have something to eat and/or drink before you take a nap</ref>.
* Pick up the pace<ref>I've consistently found that if I'm moving at a good pace, I don't suffer from sleepiness. Picking up the pace might help with sleepiness, though this is often impractical</ref>.
|-
| style="background-color: #FEFFF2;" |Thinking about the time
| style="background-color: #FEFFF2;" |
* Ignore the time of day and focus on the hours
|}
=Depression=
{| class="wikitable" 
! style="background-color: #8A713B; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #8A713B; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #E7E8D8;" |Low blood sugar
| style="background-color: #E7E8D8;" 
* Take something sweet or a [[Comparison of Energy Gels| Gel]]
'''Prevention'''
* Take carbs earlier
|-
| style="background-color: #FEFFF2;" |You're running an ultra (what did you expect?)
| style="background-color: #FEFFF2;" |
* Music<ref>There's a difference between having music playing in the background and actively focusing on music. Focusing on the music can be more effective than just having it in the background.</ref>.
* Positive thinking.
* Keep moving and wait for it to pass<ref>I've found that in most ultras there are various low spots. Often it's enough to just keep moving and wait for it to pass.</ref>.
* Have a good cry<ref>Sometimes crying can be cathartic and release some of the mental pressure.</ref>.
* Play mental games.
** Don't think about how far you have to go.
** Count the miles down rather than up.
** Mentally hook a runner in front and let them mentally 'pull you along'.
* Join up with another runner or group of runners<ref>Other runners can provide moral support and a well needed distraction. I've had some wonderful experiences running with others on races. Pacers can also help, especially as they'll focus on your race. Company can be especially beneficial at specific times on a race. The latter part of a race is an obvious time, but also sunset is another critical time.</ref>.
|}
=Headache=
{| class="wikitable" 
! style="background-color: #03476F; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #03476F; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #DFF1F2;" |Low blood sugar
| style="background-color: #DFF1F2;" 
* Take something sweet or a [[Comparison of Energy Gels| Gel]].
'''Prevention'''
* Take carbs earlier
|-
| style="background-color: #FEFFF2;" |Tight hat
| style="background-color: #FEFFF2;" |
* Loosen hat.
'''Prevention'''
* [[The Golden Rule of Racing]]
|-
| style="background-color: #DFF1F2;" |Lack of sleep
| style="background-color: #DFF1F2;" |
* Short nap. If you have a sleep deprivation headache, I've found that nothing other than a short nap will help. 
|-
| style="background-color: #FEFFF2;" |[[Caffeine]] withdrawal
| style="background-color: #FEFFF2;" |
* Take [[Caffeine]].
'''Prevention'''
* Monitor [[Caffeine]] intake
* Consider abstaining from [[Caffeine]] for 1-2 weeks before the race
|-
| style="background-color: #DFF1F2;" |Overheating
| style="background-color: #DFF1F2;" |
* Slow down or stop.
* Remove excess clothing.
* See [[Running in the Heat]]

|-
| style="background-color: #FEFFF2;" |Dehydration (only if accompanied by thirst and dry mouth)
| style="background-color: #FEFFF2;" |
* Drink more (but drink to thirst as over-hydration kills).
* Keep salt intake high.
* Slow down or stop.
* See [[Practical Hydration]]
|-
| style="background-color: #DFF1F2;" |Altitude sickness
| style="background-color: #DFF1F2;" 
* [[Viagra, Exercise and Altitude| Viagra for Altitude]].
* Descend.
'''Prevention'''
* [[Altitude Training| Altitude training]]
* [[Viagra, Exercise and Altitude| Viagra for Altitude]]
|}
=Heartburn=
{| class="wikitable" 
! style="background-color: #8A713B; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #8A713B; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #E7E8D8;" |Eating 'wrong' foods
| style="background-color: #E7E8D8;" |
* Antacid tablets
* Eat what appeals
* Avoid what triggered the heartburn
|-
| style="background-color: #FEFFF2;" |Stress
| style="background-color: #FEFFF2;" |
* Try to relax
'''Prevention'''
* Visualization
* Preparation
|}
=Blisters=
See [[Popping Blisters]], [[Taping]], and [[Blister Prevention]].
=Are we there yet?=
In ultras it's common to get the sense of not making progress, or that the miles have become longer. This is because they have, at least in time terms.
{| class="wikitable" 
! style="background-color: #03476F; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #03476F; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #DFF1F2;" |It's an ultra
| style="background-color: #DFF1F2;" |
* Run to the next aid station, not the end and avoid thinking about the overall distance.  
* Run to the next landmark, such as a tree, road sign, rock, etc. (repeat).
* Think about time not distance<ref>If you have 20 miles to go, and you're moving at a 15 min/mile pace, think about the 5 hours rather than the distance.</ref>.  
* Convert to 'effective distance' <ref>If you have 20 miles to go, and you're moving at a 15 min/mile pace rather than your usual 9 min/mile, convert to time (5 hours), then work out how far that would be at your usual pace (about 33 miles). This can be depressing, but it creates a more realistic expectation.</ref>.  
* Listen to music, focusing on it rather than letting it play in the background. 
* Rest your mind, aiming for [[Stillness in Motion]]. Mental energy is a precious thing in an Ultra, so conserve it. 
* Put your head down and keep moving.

|}
=Bloating or gas=
{| class="wikitable" 
! style="background-color: #8A713B; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #8A713B; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #E7E8D8;" |Overeating
| style="background-color: #E7E8D8;" |
* Reduce calorie intake
* Gas-x
'''Prevention'''
* Eat what appeals
|-
| style="background-color: #FEFFF2;" |Eating beans or other gassy foods
| style="background-color: #FEFFF2;" |
* Gas-x
'''Prevention'''
* Change diet before and during the race
|-
| style="background-color: #E7E8D8;" |Antibiotics
| style="background-color: #E7E8D8;" |
* Gas-x
'''Prevention'''
* Take yoghurt to help compensate
|}
=Diarrhea=
See [[Running and Lower GI Problems]].
{| class="wikitable" 
! style="background-color: #03476F; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #03476F; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #DFF1F2;" |Infection
| style="background-color: #DFF1F2;" |
* Consider Imodium<ref name="Imodium"/> 
'''Prevention'''
* Careful hygiene
|-
| style="background-color: #FEFFF2;" |[http://en.wikipedia.org/wiki/Gastrocolic_reflex Gastrocolic reflex]<ref>The Gastrocolic reflex is the urge to defecate after eating. This is not normally diarrhea, but the strong urge to defecate</ref>
| style="background-color: #FEFFF2;" |
* Some foods are a stronger stimulus of this reflex, so avoid those foods
|-
| style="background-color: #DFF1F2;" |Too much [[Fiber]]
| style="background-color: #DFF1F2;" |
* Consider Imodium<ref name="Imodium"/> 
'''Prevention'''
* Carefully reduce [[Fiber]] intake before the race
|-
| style="background-color: #FEFFF2;" |Change in intestinal bacteria (due to traveling)
| style="background-color: #FEFFF2;" |
* Consider Imodium<ref name="Imodium"/> 
'''Prevention'''
* Travel earlier
* Avoid non-bottled water.
|-
| style="background-color: #DFF1F2;" |Too much isolated [[Fructose]] 
| style="background-color: #DFF1F2;" |
* Stop [[Fructose]] intake
|-
| style="background-color: #FEFFF2;" |Dairy (lactose intolerant)
| style="background-color: #FEFFF2;" |
* Stop dairy intake (read the ingredients)
|-
| style="background-color: #DFF1F2;" |[http://en.wikipedia.org/wiki/Ischemic_colitis Ischemic colitis]
| style="background-color: #DFF1F2;" |
* Stay hydrated
|-
| style="background-color: #FEFFF2;" |Antibiotics
| style="background-color: #FEFFF2;" |
* Sorry, better luck next time
'''Prevention'''
* Take yoghurt to help compensate
|-
| style="background-color: #DFF1F2;" |[[Magnesium]] supplements
| style="background-color: #DFF1F2;" |
* Don't take any more during the race 
'''Prevention'''
* Magnesium Oratate does not generally cause diarrhea, unlike other forms of magnesium.
* Limit magnesium in the 24 hours before the race.
|-
| style="background-color: #FEFFF2;" |Excessive fluid intake<ref>Drinking more than your intestines can absorb will produce inevitable diarrhea</ref>
| style="background-color: #FEFFF2;" |
* Drink to thirst (also helps prevent [[Hyponatremia]] and death)
|}
=Weak or painful legs=
Other pain – ITBS, shin splints, cramps
{| class="wikitable" 
! style="background-color: #8A713B; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #8A713B; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #E7E8D8;" [[Delayed Onset Muscle Soreness| DOMS]] 
| style="background-color: #E7E8D8;" |
* [[Caffeine]]
'''Prevention'''
* [[Downhill Running]]
|-
| style="background-color: #FEFFF2;" [[Glycogen| Glycogen depletion]]
| style="background-color: #FEFFF2;" 
* Take something sweet or a [[Comparison of Energy Gels| Gel]]
* Increase carbohydrate intake
* [[Caffeine]] to increase carbohydrate absorption
'''Prevention'''
* [[Carbohydrate Loading]]
|-
| style="background-color: #E7E8D8;" |Muscle spasm
| style="background-color: #E7E8D8;" |
* [[Massage]] can work wonders, even in the middle of a race
|-
| style="background-color: #FEFFF2;" |Low blood fat<ref name="fat"/>
| style="background-color: #FEFFF2;" |
* Consume a high fat food, such as peanut butter
* Combine high fat and high carbs as this will not only boost both, but often these foods are easier to digest
'''Prevention'''
* Eat fat earlier
* Have a higher fat pre-race meal
* Don't consume only fast carbohydrates
|}
=Cramping=
See [[Cramps]]
{| class="wikitable" 
! style="background-color: #03476F; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #03476F; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #DFF1F2;" |[[Sodium Deficiency]]
| style="background-color: #DFF1F2;" |
* Add salt to your drink
* Eat something salty
* Drink pickle juice
* [[Fellrnr's Go Juice]]
* [[DIY Electrolyte Drink]]

|-
| style="background-color: #FEFFF2;" |[[Muscle]] fatigue
| style="background-color: #FEFFF2;" |
* [[Stretching]]
* [[Massage]] (even mid race massage can make a remarkable difference)
* Relaxed [[Running Form]]
|}
=Chafing=
{| class="wikitable" 
! style="background-color: #8A713B; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #8A713B; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #E7E8D8;" |Skin on skin
| style="background-color: #E7E8D8;" |
* Wear something form fitting so the clothing rubs, not the skin
* Tape both surfaces so the tape is rubbing, not the skin
* Lubricants may help if used early enough, but often make things worse
|-
| style="background-color: #FEFFF2;" |Skin on clothing
| style="background-color: #FEFFF2;" |
* Wear something form fitting so the clothing rubs, not the skin
* Tape the skin 
* Lubricants rarely work
|-
| style="background-color: #E7E8D8;" |Monkey butt<ref>Monkey butt is a euphemism for chafing between buttocks. This condition is more serious than you might expect as it can be surprisingly painful. This is also sometimes called "the ring of fire."</ref>.
| style="background-color: #E7E8D8;" 
* Clean the area using moist wipes, making sure it's really clean. Any unwanted residue will act as an abrasive. 
* Diaper (nappy) treatment can help relieve the pain. [http://www.amazon.com/Desitin-Maximum-Strength-Paste-4-Ounce/dp/B003O32P8U Desitin] (or a [http://www.amazon.com/ZINC-OXIDE-OINTMENT-RUG-Size/dp/B000PHZ8W8 generic Zinc Oxide ointment]) is recommended by some runners, but does tend to leave white marks. Smothering the area with Desitin can help if things are bad.  
* Lubricant can help if used early enough, but if the skin is damaged and rough it doesn't help as much. One of the best lubricants for this area is [http://www.amazon.com/2toms-Blister-Shield-SportShield-Roll-On/dp/B00905EBQU 2Toms Sport Shield]. You either need a roll-on dedicated to this area, or preferably use the [http://www.amazon.com/Sport-Shield/dp/B004453IH4 Sport Shield Wipes]. 
'''Prevention'''
* Cleanliness is critical. Make sure the areas is thoroughly clean, using wet wipes if you have to go mid-race.
* Lubricate before the race, clean and lube after you go and periodically through a longer race. 
* [[A review of graduated compression wear| Compression shorts or tights]] that are too tight around the buttocks can hasten the Chafing
|}
=Fainting=
Also near fainting (light headed, dizzy)
{| class="wikitable" 
! style="background-color: #03476F; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #03476F; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #DFF1F2;" |Heart problems
| style="background-color: #DFF1F2;" |
* Fainting or near fainting can be a warning sign of a serious health problem and it may be the only symptom that precedes a sudden cardiac death<ref>See [http://www.aafp.org/afp/1999/1101/p2001.html http://www.aafp.org/afp/1999/1101/p2001.html] and http://www.jfponline.com/Pages.asp?AID=5146</ref>.
|-
| style="background-color: #FEFFF2;" |Dehydration (only if accompanied by thirst and dry mouth)
| style="background-color: #FEFFF2;" |
* Drink more (but drink to thirst as over-hydration kills)
* Keep salt intake high
* Slow down or stop
* See  [[Practical Hydration]]
|-
| style="background-color: #DFF1F2;" |Stopping suddenly<ref>The calf [[Muscle]] helps pump blood, so stopping suddenly can exacerbate low blood pressure. </ref>
| style="background-color: #DFF1F2;" |
* Slow up before coming to a stop
|-
| style="background-color: #FEFFF2;" |Hypothermia
| style="background-color: #FEFFF2;" |
* See [[Hypothermia]].
|-
| style="background-color: #DFF1F2;" |Altitude sickness
| style="background-color: #DFF1F2;" 
* [[Viagra, Exercise and Altitude| Viagra for Altitude]]
* Descend
'''Prevention'''
* [[Altitude Training| Altitude training]]
* [[Viagra, Exercise and Altitude| Viagra for Altitude]]
|}
=Trouble staying warm=
{| class="wikitable" 
! style="background-color: #8A713B; color:#FEFFF2;" |'''Possible Cause'''
! style="background-color: #8A713B; color:#FEFFF2;" |'''Action'''
|-
| style="background-color: #E7E8D8;" |Exhaustion<ref>When you're exhausted, it is much harder to stay warm.</ref>
| style="background-color: #E7E8D8;" |
* Take calories, starting with some fast carbohydrates. 
* Warm soup or other fluids. 
|-
| style="background-color: #FEFFF2;" |Sweating through<ref>If you wear too many clothes you will sweat and once your sweat has soaked your clothes you will become chilled.</ref>
| style="background-color: #FEFFF2;" |
* Change into dry clothes.
* If possible replace all clothes, including underwear.
* If you're not too cold and you don't have the option of dry clothes then remove outer layers to allow inner layers to dry.
'''Prevention'''
* Avoid trying to stay comfortably warm, aiming to be cool enough to avoid excessive sweating while avoiding becoming chilled. (This is as tricky as it sounds.)
* Wear layers with zippers that can be opened and closed to control your temperature.
|-
| style="background-color: #E7E8D8;" |Sunset<ref>Hypothermia is a particular risk at sunset. In most ultras you've been running all days and you're depleted. When the sun goes down you lose the direct warmth of the sun and the air temperature drops. If you also slow up then you have the perfect storm for hypothermia.</ref>.
| style="background-color: #E7E8D8;" |'''Prevention'''
* Be prepared for sunset by carrying some extra layers in the late afternoon.
|-
| style="background-color: #FEFFF2;" |Sunburn<ref>Sunburn prevents the capillaries in the skin from contracting to conserve body heat, making the cold worse.</ref>.
| style="background-color: #FEFFF2;" |
* Make greater allowances for the cold, wearing more clothing than you'd usually need. 
* Don't rely on sunscreen, which does not block all the UV<ref name="VirosSanchez-Laorden2014"/> and their safety is unclear<ref>[http://drmirkin.com/morehealth/sunscreens.html Dr. Gabe Mirkin, Sunscreen]</ref>
'''Prevention'''
* Be careful to avoid sunburn, covering up with UV resistant fabrics.
|}
=Sore feet=
{| class="wikitable" 
! style="background-color: #03476F; color:#FEFFF2;" |
! style="background-color: #03476F; color:#FEFFF2;" |
|-
| style="background-color: #DFF1F2;" |Continual pounding
| style="background-color: #DFF1F2;" |
* Swapping to more cushioned shoes may help.
* Alternatively, going from a highly cushioned shoe like a Hoka to something more moderate can also provide some relief.
'''Prevention'''
* Practice walking in training.
|-
| style="background-color: #FEFFF2;" |Muscular fatigue
| style="background-color: #FEFFF2;" |
* Massaging the feet and calves (focus on the calf muscles that stabilize the foot).
* Try to run more (walking seems to be harder on the feet than running).
'''Prevention'''
* Strengthen the foot muscles by doing balance exercises.
* Massage the feet and calves thoroughly before the race.
|-
| style="background-color: #DFF1F2;" |Stone bruises 
| style="background-color: #DFF1F2;" |
* Swap to shoes with more protection in the midsole
|}
=Notes=
<references>
<ref name="Imodium"> Imodium ([http://en.wikipedia.org/wiki/Loperamide Loperamide]) is an anti-diarrhea mediation, but it works by slowing the progress of material through the digestive tract. Some runners find this makes the problem worse, acting like a cork.</ref>
<ref name="fat">Low fat availability is less well researched than low blood sugar/[[Glycogen]] depletion, but there is some anecdotal evidence that ultrarunning can deplete the available fat sources. This is not to say that you run out of body fat, just that you can't mobilize those fat stores quickly enough, combined with depleted intramuscular triglycerides.</ref>
<ref name="VirosSanchez-Laorden2014">Amaya Viros, Berta Sanchez-Laorden, Malin Pedersen, Simon J. Furney, Joel Rae, Kate Hogan, Sarah Ejiama, Maria Romina Girotti, Martin Cook, Nathalie Dhomen, Richard Marais, Ultraviolet radiation accelerates BRAF-driven melanomagenesis by targeting TP53, Nature, volume 511, issue 7510, 2014, pages 478–482, ISSN [http://www.worldcat.org/issn/0028-0836 0028-0836], doi [http://dx.doi.org/10.1038/nature13298 10.1038/nature13298]</ref>
</references>