If you're looking to run high mileage at a 24 hour race, then these suggestions are for you. A 24 hour race can be used in many ways, but aiming for 100 miles or more creates some unique opportunities and problems. Much of this advice may apply to those running shorter distances.

The usual rules apply. All of the usual rules of ultrarunning still apply to 24 hour races, so have a read of Essential Ultrarunning Tips, Sleep Deprivation in Overnight Events, and Your First 100 Mile Race. Remember to drink to thirst and eat what appeals.
Loop Size. 24 hour races are typically run on a short loop. Ideally, you want a loop of around 1 to 1.5 miles (1.6 to 2.4 Km). Loops longer than these are not conducive to running extreme distances, as the logistics change. These short loops mean that you never have to carry much with you, and fuel and fluids are never far away.
Details matter. Because you are running the same loop so many times, it becomes critical to optimize the fine details.
Terrain. Relatively small elevation changes can add up over the course of 24 hours on a small loop course. Even the difference between gravel and asphalt can make quite a difference to your total mileage, as your feet slip very slightly on gravel.
Pacing. The key for the vast majority of runners is to find a pace you can maintain without slowing up too much for the entire 24 hours. There are a few elites runners like Mike Morton that can go out at a suicide pace and hang on for the duration, but that approach does not generally work well, even amongst the elites. A capital mistake is to run until you can't run anymore and then walk the rest of the race. This is a recipe for a slow and generally miserable race.
Walk early, walk often. Unless you believe you can run the entire 24 hour period, Walking Breaks become critical. My general recommendation is to walk for part of each lap, finding a routine and rhythm that works for you. I generally run the first few laps to pull clear of the crowd, then start my walking breaks after 5 to 10 miles. I aim to begin each walking break at my aid table, so that I use the walking break to eat and drink. Tweaking the time you're walking can allow for changing your overall lap time without altering your walking or running pace. Occasionally you may want to walk an entire lap, to eat more food or to cool off, but keep these to a minimum if you want to achieve high mileage.
Find a Rhythm. I find it helpful to get into a rhythm I can keep up for the duration of the race. Depending on the length of the loop, I will grab something from my aid station on every lap, or every other lap, and then walk while I consume it. It's important not to over hydrate, but I find taking a sip of drink can sometimes wake up my thirst.
Planning. It can be hard to estimate what mileage you can achieve in 24 hours, even if you are an experienced at racing 100 mile races. My approach has been to run at my most efficient pace, walk at my most efficient pace, time my walking breaks to give me a reasonable break on each lap and then see what happens. My goal is to set a pace and routine that I think I can manage for the full 24 hours, though in reality I tend to slow down as time passes.
Run the tangents. As a much as is possible, run the tangents, taking the shortest path possible. Even small deviations from the shortest path can add up over the course of 24 hours.
Transitions. Going from running to walking or from walking to running is something that few people practice, but these transitions can create unusual and sometimes dramatic stresses on the body. The worst example is the transition from running to walking where the feet slap hard on the ground as the runner relaxes rather than controls the transition. The transitions should be gradual and controlled, aiming to use the minimum effort and the minimum strain.
Walk carefully. Unless you practiced race walking extensively, keep your walking pace natural and smooth. While rapid race walking can improve your overall pace, it does present significant stress on your body, and of the stresses are quite different from running. Walking faster than about a 14:00 min/mile pace uses more energy than running at the same speed, so race walking is generally not a strategy for high mileage.
The 100 mile barrier. For many runners, there seems to be a barrier at hundred miles or just after. This may be worse for people used to running a fast hundred mile race. Psychologically it can be tough to realize that you just covered hundred miles and there are now many hours left in the race. Visualizing how you will feel at this point in the race can help, but the most important thing is to pace yourself for 24 hours, not 100 miles.
Just one more lap. When things become tough on a 24 hour race, it can help to focus on doing just one more lap.
Fixing problems. Knowing how to quickly and effectively fix the type of problems that are likely to occur is obviously important. See Fixing problems in Ultramarathons for details.
Don't Panic. When something goes wrong, focus on dealing with the problem if possible, or accepting the consequences. Any type of stress reaction will burn through your physical and mental reserves remarkably quickly, and can ruin a race.
Be Prepared. A loop course makes it easy to have access to a wide variety of gear. I will often bring gear for more extreme conditions than I expect, as things could easily turn unusually hot or cold. It's better to have something and not need it than to need it and not have it. Use a Race Checklist to make sure you've not forgotten something.
Don't stop. While walking breaks don't slow you up as much is you expect, being stationary has to be avoided as much as possible. You should set up your aid so that you can grab nearly everything you need as you walk past, rather than having to stop. Obviously there are some situations where you have to stop, such as using the toilet or changing shoes, etc., but these should be relatively infrequent. The time you spend stationary goes past much faster, and it's easy to burn chunks of time without realizing.
No sleep. To achieve big miles in a 24 hour race you have to avoid sleeping. If you're having serious sleep deprivation problems, then a 15 minute nap may be required, but try short periods (100 yards/meters) of picking up the pace to see if that helps first.
BYOA. While most 24 hour races provide aid, I would recommend that anybody wanting to achieve big miles brings their own aid. I have a small folding table that I use to support my drinks and anything I expect to grab during the race. Some things like shoes and extra clothing goes under the table, and I have a chair to sit on for changing shoes. You want to avoid picking things up off of the ground if at all possible. There are several advantages to BYOA:
- You ensure you have familiar food and drink that you've practiced with. You can still use the main aid station for variety if something different appeals. Sometimes the urge for something unusual does occur in an ultra, and I believe in consuming what appeals as I think the subconscious is far better at knowing what I need than my conscious mind.
- There is no delay in getting to the aid as you negotiate other runners. This is rarely a significant problem, but even minor delays add up.
- You can mix up your drink ahead of time in disposable bottles that are the right size. That way you can grab a drink, consume it on your walking break, and then throw it in the trash bag. (24 hour races typically have trash receptacles at appropriate places. Make sure you place your aid table far enough ahead of the last trash to have time to consume your drink or eat anything that might leave trash.)
Be organized. The gear you expect to use can probably be laid out on your aid table so you can grab it as you go by. Of course, not everything will fit this way, so it's useful to have an organization system. You could use Ziploc bags, or hard plastic containers. Label each container and put related items together. The number and size of containers is a trade-off; if you have a few large containers you can end up rummaging through them to find what you need, but if you have too many containers you just end up rummaging for the right container. Try to think through how likely you are to need stuff and put common items closer to hand then emergency gear. Remember that during the race it will be dark, and you are likely to be "cognitively impaired", so to list all the contents on the containers.
Don't carry stuff. Because your aid is always close, don't carry anything you don't need to. This is especially true of hydration as water is heavy. Avoid carrying a water bottle and use disposable bottles or cups that hold about the right amount of drink. Don't use a hydration pack!
Using a crew. While it's quite possible to run big miles in a 24 hour race without a crew, some support can be useful. A crew can do things like getting lights or MP3 players ready for you, changing batteries, getting your shoes out, etc. You could even have your crew hand you your drinks rather than pick them up from the table, but that is not really necessary. Some elite runners will work out hand signals to let that crew know what they're after as they approach, but typically it's easy enough to tell your crew what you need on the next lap.
Lights. Some races will be illuminated, and you won't need to carry a light, which is really nice. However, it's best to be prepared in case the illumination is not working. I would also recommend a small colored flashing light to put on your aid table to make it easier to locate it in the dark. Make sure you don't blind or annoy other runners. I've found I can point a flashing light down to the table and still see it well enough to be functional.
Lap recording. Different races have different techniques for recording your lap count, from a human making a note on paper through to electronic timing systems. Regardless of the system the race uses, I would suggest that you keep your own tally using a good sports watch that will record each lap, along with the lap time and ideally some idea of the lap distance. GPS watches do not have the battery life to record the GPS data at sufficiently high resolution to be much use. I would recommend disabling GPS and using a Footpod. This data will help if there is any problem with the timing system or lap count. If this does happen (and it's happened twice to me), politely mention it to the volunteers and ask them to look into it. They may be able to find the problem, but if not, you have a record you can use to discuss the issue with the race organizers after the race.
Staying on pace. In addition to recording your lap count and times, you can also get most sports watches to display your previous lap time and your average lap time. It's a simple matter to create a chart of total distance against the average lap time needed to hit that distance in 24 hours. This is a far easier system than trying to calculate using your lap count. For instance, if you know that to hit your target of 120 miles requires an average lap time of 12:34 then just looking at your watch will tell you how many seconds ahead or behind your target you are. I generally check my lap time on most laps, so that I'm aware of what's happening to my pace. It's easy to slow up without realizing it, and I like to know if that's happening as soon as possible. Sometimes the slow up will be due to a lack of concentration, or the wrong music, in which case I just focus on picking up the pace back up to where it needs to be. However, sometimes a slow up is indicative of an underlying problem, such as a lack of calories. If that's the case, then I can take steps to correct the problem before it gets out of hand. If I've not had enough of calories, then I will look at the aid station a little more carefully to see what appeals, but I won't force myself to eat anything.
Be nice. I believe that it's better to be nice to everybody in the race, and encourage everyone. I try to take time to thank the volunteers, and to encourage other runners regardless of their pace. In addition to general encouragement, I also like to check that other runners are doing okay. With practice, you can tell a lot about a runner's state just by their initial response, and sometimes just the look in their eyes tells you if they're really in trouble. I believe we're morally obligated to help people in need, and I'll stop to help a struggling runner, or seek out support staff to help them. While I do this because it's what I believe is the right thing to do, there are also some psychological benefits to encouraging others. It helps you realize you are not alone in your misery, and changes your focus from to be more outward.
Use psychology? If you are aiming to win a race, then out psyching your competition can be a powerful tool. Overtaking your competition while looking strong and moving faster than your average pace can demoralize and help defeat your opponents. It's up to you to decide if you wish to use these techniques. Personally I would rather encourage my competition and be beaten than to win using that approach. However, you need to decide your own ethics. (I will go past a runner faster than usual if I want to be left alone rather than talk, but that seems different to me.)
Weather. You want cool, windless conditions for a good race, but you don't always get what you want. If the weather is warm then your performance will suffer. However, ignoring the heat and trying to run as if it were cooler will result in more dramatic problems. The best approach is to slow up during the warmer part of the day and save your energy for the night. Your walking breaks can help you cool off a little, but also use the usual techniques for running in the heat.
You'll see (nearly) everyone. A 24 hour race is rather different from a social standpoint as you will see nearly everyone else in the race. It's not often the fastest and slowest runners get to run together in a race. However, the people you won't see are those doing the same pace as you, and they are your nearest competition. Don't assume that because you are passing every runner and no one seems to be passing you that you don't have competition.
Downhill training. Even for a flat 24 hour race, Downhill Training is important as it builds up the ability of your muscles to withstand the long distances.
Morton Stretch. When I saw Mike Morton run 172 miles in 24 hours, he used what I call the Morton Stretch and I've found that it gives my legs new life when I do it. I've found that about every 5-10 miles is about right between Morton Stretches.
Don't drive. After a 24 hour race you will be sleep deprived and driving is dangerous. Get a designated driver to take you back.
Boredom. There is a general expectation that running a short loop course would be boring, but I've found that a loop course has a continual change in view, and I always feel like I'm making progress. By comparison, I've done long point to point races where I've felt like I've not moved in the last few hours.
Non-linearity. In a distance race, if you go faster you're finished sooner, but in a timed race you have to go further. This means that to increase your distance by 10% you have to run 10% further and 10% faster, a non-linear increase in difficulty.
Where to stay. Getting a good night's sleep the night before the race can help get you through the later stages of the race.

Gallery

Aid Stations at 24 Hour Races
This is the aid station I set up at Hinson Lake, with callouts for some of the items. Click for a larger version.
My aid station from the other side.
Some of the treats at the Hinson Lake 24 hour aid station.
Another part of the Hinson Lake 24 hour aid station.
A view along the Hinson Lake 24 hour aid station, with people's personal aid areas behind.
The US aid station at the world 24 hour championships. Notice that each runner only has a space about 18 inches wide.
A little of the chaos of the world 24 hour championships.
The aid station while the runners are all out on the course. There is a tape marker every 18 inches to divide up each runner's space.
Mike Morton on his way to setting the US record with 172 miles, just getting up from the Morton Stretch.

24 Hour Races

Gallery

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