A runner loses heat via sweating. This sweat evaporates on the skin which dissipates heat by convection, assuming that humidity is low enough. Heat stroke will occur when the bodies thermoregulation is overwhelmed.
Overwhelming the body (in simplistic terms) may come from excessive environmental heat (running in a hot climate), running too fast or too hard, being dehydrated, a lack of free flowing air that will help cool the body or a lack of water to splash on the body to cool down.
Read the full article on RUNULTRA HERE
This week we’re starting a series of articles titled ‘environmental physiology’. We’re going to open with a 2 part series relating to exercise in the heat (I say 2 parts, but who knows what could happen by next week). Following that, we’ll take a look at altitude training and potential benefits.
But before we go on, why not catch up on our seven part series of posts on RACE DAY NUTRITION HERE
Too Hot? Call The Police & Fireman…
Exercise in the heat can place a lot of strain upon your body, if you’re used to cooler climates. For this reason, many elite athletes will spend time acclimatising to the higher temperature. Acclimatisation can require up to 14 days, so what if you’re an amateur athlete travelling abroad for an endurance event, who can’t afford to travel 3 weeks before the event? Well this blog is quite timely for me, as I’m off to Lanzarote in less than 4 weeks for the Ironman triathlon and potentially, it could be very hot. There’s probably quite a few people reading this blog who are traveling abroad this year to take part in triathlon or running events in hot places. The purpose of this blog is to explain simple ways, which you can acclimate your body beforehand and explain the physiological changes, which take place to improve your performance.
Too hot? You Make A Dragon Want To Retire Man…
In a nutshell, when you exercise in hot climates, your core temperature rises and your performance suffers. If your core temperature rises too much, it could potentially be lethal, so your brain is pretty quick to try and stop that happening, by persuading you to stop!
How do we reduce core temperature?
There 2 main ways, the first is ‘convection’ and the second is ‘sweat evaporation’.
Think about a car radiator, it’s positioned right at the front of the car as that’s where the wind hits it when you’re driving. Heat is generated in the engine, this in turn heats the water which is then pumped to the radiator. The wind hits the radiator, cools the water and the cool water goes back into the engine to pick up more heat. This cycle continues, to keep removing heat from the engine, which is why it’s important to keep the fluid topped up or your car will overheat! The human body works the same way, heat is generated in the engine and your blood then picks up the heat. The blood is pumped to the coolest part of the body (the skin), where the wind hits it and cools the blood. It then returns back into the engine to pick up more heat and the cycle continues.
If the wind is blowing against your skin whilst you exercise, convection may well be enough to keep you cool and maintain a normal body temperature. It’s easier to do this when cycling, compared to running, as your speed is generally higher, so the wind chill is greater. Runners will notice that treadmill running leads to more sweating than running outside as the air temperature is generally warmer, but also you’re not moving, so there’s no air flow past the skin and therefore no wind chill or convection. The same can be said about indoor cycling or using a turbo trainer, especially if you don’t have a fan blowing.
Let’s use the treadmill running or turbo cycling scenarios as an example. If there’s no air flow past your skin to cool the blood, then in effect, you pump hot blood to the skin surface, it doesn’t get cooled, so the hot blood goes back into the engine / core. That’s a sure fire way to overheat. This is the same as leaving your car engine running on a hot day, whilst stuck in a traffic jam. If you’re not moving, there’s no wind hitting the radiator, so convection cooling can’t happen.
Sweating is based on ‘evaporation’. Water from your body cells makes it’s way to the skin and as the hot blood arrives, the heat is passed from the blood into the water droplets (leaving the blood cool). The heated water on your skin, evaporates into the air like water from a boiling pan and takes the heat with it. If you’re running on a treadmill and there’s no convection, you need another method of getting rid of heat, so the sweating and evaporation will kick in.
It’s important to recognise that ‘evaporation’ removes the heat, so any sweat on your skin, clothing or floor, serves no purpose other than to lead to dehydration.
Convection and sweating don’t compliment each other too well
If you’re racing in hot weather, convection isn’t enough so you’ll also sweat to keep your temperature down. As you sweat, you lose fluid from your body and this leads to a drop in blood plasma (plasma is the fluid/water component of blood). The problem is that you need a lot of blood for convection to work well. When you’re exercising, blood is pumped to the exercising muscles and what’s left is pumped to the vital organs. So what happens when you then need to pump extra blood to the skin to cool down? Do you reduce blood flow to the muscles and vital organs? It sounds like a great idea to keep you cool, but where is this extra blood coming from? As if that wasn’t bad enough, you’re now sweating and the amount of blood you have is dropping. So not only do you have to supply muscles, organs and the skin, you’ve got less and less blood available as sweating continues.
Blood is made up of plasma (fluid) and cells (red/white/platelets). When you sweat, you lose plasma, but not cells. This means that the total amount of blood is reduced and it also gets thicker (same number of cells but less fluid).
What does this mean in terms of performance?
As you’ve probably guessed already, this isn’t good for performance. Heart rate is generally higher for any level of exercise. This is due to the fact that you’re trying to pump blood to all areas of your body and your total blood volume is dropping. Your cardiovascular system is therefore working overtime, trying to match the demand with a struggling supply. Due to fluid and salt losses, your body becomes dehydrated and cells cannot function correctly. We’ve mentioned previously that salt is required for transporting fluid throughout the body and as high amount of salt can be lost in sweating, this mechanism is impaired.
Something of great importance, which is less frequently discussed, is the change in substrate utilisation. Whilst the exact mechanism is still under question, it’s pretty clear that you use more carbohydrates and therefore empty your glycogen stores more quickly when exercising in the heat. The simple explanation is that that there’s a lack of ‘spare blood’ going to the muscles, due to the fact it’s going to the skin for cooling. Fat metabolism requires more oxygen than carbohydrate metabolism so there’s a switch from fat to carbohydrate. This may also be explained by a switch from ‘slow twitch’ to ‘fast twitch’ fibres, which use less oxygen.
All in all, this isn’t looking too good. We’ve got an ever-decreasing blood volume, which is being pulled in several different directions. We’ve got decreasing salt levels and an onset of dehydration. We’ve got a heart rate which is significantly higher than it should be for the intensity we’re exercising at and to cap it all off, we’re running out of carbohydrates at a faster rate than normal.
Don’t worry help is at hand. Next week we’ll discuss how acclimatisation helps you to deal with the issues and explain the physiological changes responsible.
Until then, stay cool.
Sports Science lecturer for 10 years at St Helens HE College.
2004 established The Endurance Coach LTD sports science and coaching business. Worked with British Cycling as physiology support 2008-2008. Previous Triathlon England Regional Academy Head Coach, North West.
In 2006 established Epic Events Management LTD. Now one of the largest event companies in the NW, organising a range of triathlon, swimming and cycling events. EPIC EVENTS also encompasses Montane Trail 26 and Petzl Night Runner events.
In 2010 established Montane Lakeland 50 & 100 LTD. This has now become the UKs leading ultra distance trail running event.
In 2010 established The Endurance Store triathlon, trail running and open water swimming store. Based in Appley Bridge, Wigan, we are the North West’s community store, organising and supporting local athletes and local events.
Check out the endurance store HERE
Okay, lets start as we mean to go on! Do you you prefer it on your back, in your hand or maybe you need both hands or maybe you prefer it all centered around your waist… of course I am talking about your method of hydration.
With temperatures rising, the UK in a heat wave and longer lighter days, we can hopefully all get out and run more. But as we all know, or maybe we don’t. We need to consider several things when running in the heat;
- It’s harder
- You sweat more
- You need more fluid
We need to adapt. So what happens when the mercury rises?
Well, the body’s core temperature rises with exercise. In simple terms the more we exercise, or the harder we exercise and this core temperature rises. Unchecked this internal core would exceed boiling point; not a good idea. So, our clever body reduces this core temperature by evaporation (sweat). This process helps cool the body, maintain a manageable core temperature and hopefully allow us to continue exercise.
I say hopefully because the process of evaporation means that we loose liquid (hydration). So the trade off of a cooler core is potentially dehydration.
Dehydration as we all should know is something that does not go well with any sport. It increases heart rate and also adds to core temperature rises. It therefore can become a vicious circle. Initially running will feel much harder, the supply of oxygen to the brain will become impeded as blood is forced to the skins surface to help reduce the internal pressure. Your muscles will start to fail, become heavy and cramp. You may start to have blurred vision in extreme cases and in severe cases you will just stop, potentially collapse and black out. If you need clarification, this is NOT GOOD.
Depending on external temperatures, your ability to withstand heat, your own personal sweat rate and your adaptation to heat it is possible to loose 3-4 litres of fluid in an hour when running. I know, 3-4 litres! Loose more than 2% of body weight and this will impair performance and your mental ability. So, if your looking to perform or if you just want an enjoyable stress free run in the heat, you need to keep on top of hydration.
Hydration is NOT just fluid. Sweating means that we loose key minerals. These minerals keep our body in balance. Therefore you must replace electrolytes (salt) to keep your body in balance. Like your own personal fluid requirements, you salt requirements will also differ to that of your run friends. So take your time to work out what works for you. At the end of a hot run do you have salt marks on your clothes, do you have dried salt on your face? If so, you are more than likely a heavy sweater and your salt needs may very well be double or triple. Plenty of products are now available on the market and they all offer different methods and tastes. For example, Saltstick offer a really handy tablet which works well with bladders or bottles as it means you can keep your electrolyte supply separate and it also means that you can adjust your needs on the fly. However, Nuun offer a very popular flavoured tablet that comes in a handy tube that again can be taken with you on training or racing. This product must be added to your liquid though. Of course other products are available and I use these two reference points as purely as demonstration of what is on offer. It is fair to say that all sports drinks manufacturers now offer a form of electrolyte replacement.
How do you avoid the dreaded dehydration?
First and foremost assess yourself and your abilities. If you live in a hot climate with all year sun and heat you are going to be well adjusted. If you live in the UK and then we suddenly get a heat wave, you are not going to be adjusted. It’s a simple fact that many fail to acknowledge. Running 7 min miles in 10 degrees is much easier than running 7 min miles in 25 deg. As I said previously, you try to run the same pace in much hotter temperatures and only one thing will happen; your core will rise, you will sweat more, you will start to suffer and eventually you will come to a stand still.
Slow down. Accept that the warmer temperatures will mean a slower pace. This will allow you to regulate your temperature and keep on top of your hydration. The longer you spend in the heat, the more you will adjust and eventually you will start to be able to lift the pace for the same effort and sweat rate. In simple terms this is what pro athletes do when they ‘acclimatize’.
- Start a run hydrated. Your urine colour is a great indicator of how hydrated you are. A light straw colour is best.
- Keep the sun off your head when running by wearing a white hat with a peak.
- Wear sunglasses.
- Wear light clothing that is loose and that will reflect the suns rays.
- Use waterproof sun cream and be careful around your eyes.
- Drink regular and often.
- When possible, pour water on your head to reduce your core temperature.
- Plan your runs and make allowances for refilling bottles or bladders on long runs using streams or shops (as applicable). You may want to carry some water purification tablets if you are in extreme places.
- Take some money, mobile phone and ID.
Do a self-check when running:
- Do you feel cool? (and I don’t mean in a ‘rap’ way)
- Do you feel clammy?
- Have you stopped sweating?
- Do you feel sick?
- Are you dizzy?
- Are you fatigued?
- Is your heart rate pounding?
Any of the above and you are starting to show signs of dehydration. Don’t wait to be thirsty… it will be too late. Depending on how bad your symptoms are you will need to do one of the following:
- Reduce your pace to a walk, let your temperature drop and slowly rehydrate – don’t gulp.
- Stop. Sit down in the shade. Recover and let your temperature drop while drinking slowly to rehydrate.
- Stop and basically STOP. If you have all or a combination of the above symptoms your best option may well be to stop and recover. Come back another day with lessons learnt
Recovery is key and it is important to rehydrate post training and racing. For every 1kg of weight loss drink 1ltr of water. When your urine has returned to a light straw colour, stop drinking and resume normal drinking… do not over drink.
Drink sensibly, don’t force yourself with water. Research into Hyponatremia has shown that it’s not a lack of salt, which leads to hyponatremia, it’s drinking too much fluid. If you urine regularly and it is clear, you are drinking too much. A bloated stomach is a sign of the onset of the problem, headaches and nausea. During an event just sip and understand your sweat rate and needs. You can always test yourself by wiggling yourself naked pre run, run for 1 hour without drink and then re weigh yourself. The difference will give you an idea of your sweat rate; 1kg = 1ltr. Of course please keep in mind external conditions. Your sweat rate will differ for hot/cold days and depending on how hard or easy you run.
Drinking methods when running?
Do you you prefer it on your back, in your hand or maybe you need both hands or maybe you prefer it all centered around your waist…
How we carry our fluid is very personal and it also does depend on the demands of the training or the race. If you are racing you may need to carry compulsory equipment and this will almost certainly mean waist pack or rucksac is required.
But how we carry the liquid is what counts. The fluid needs to be accessible at all times as this will promote drinking.
Bladder v Bottle
Bladders come in varying sizes. 1ltr to 3ltr, with different methods of distributing the liquid to the runner, ultimately this is a pipe with a mouth valve. Bladders sit on your back or around the waist and offer an easy slurp system that is easy to use. The main issues with them are that they are difficult to clean, you are never quite sure how much you have left and they are more awkward to fill when racing.
Like bladders they come in varying sizes but 500ml to 1ltr is normal. The size of the bottle may very well depend on your carrying system. For example – handheld bottles, bottles in a waist pack, bottles on a rucksac (at the back) or bottles on a rucksac (at the front). Bottles are easy to fill on the go, easy to clean, cheap to replace.
Manufacturers realize now that runners needs are increasing and runners are becoming more demanding. Therefore packs such as the S-Lab 12 has allowances for a bladder, bottles on the front and even two large ‘dump’ pockets on the side of the pack that will take bottles. The advantages here are excellent as you can customize your needs for each run.
Putting it into practice
I personally use all of the above.
When it is really hot and I am just going for a training run I love just having two hand held bottles (Dakota Style) and running free. It allows for no restriction on my waist it also allows my back to be free and ultimately enables me to remain cooler.
If I need to carry some essentials then I will add a waist pack that will hold just a light jacket, phone, money etc and keep the bottles in my hand.
When the demands are greater I shift to a rucksac allowing me to use a bladder and or bottles with the option to carry other equipment.
I am not a fan of waist bottle belts as they usually become uncomfortable, bounce and rub the skin – but that is my personal feedback.
It’s not rocket science but not putting it into practice is the difference between a great run and a lousy run. More importantly, when racing, it is the difference between potentially winning and not even finishing.
Choose your method and keep hydrated on your next run!
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