Hydration

Yesterday I had a big wake up call: my brother Paul fell at mile 23.5 in the Brighton Marathon and the medical staff on hand insisted that he pull out of the race, before taking him straight to the medical centre. He’d had a perfect 6 months’ training and was physically ready; he had the right race plan and was mentally ready; through half way he was bang on time and was delivering on his plan. So what went wrong?

Dehydration.

He’d had water (exactly how much is hard to say) and gels; it was warm but not super hot (although the sea breeze was deceiving). As we know if the signs of dehydration occur it’s often too late to recover, but he says he felt totally fine until moments before it hit. Many of us have been out of liquids, or under hydrated and know how it feels; despite the logic to the contrary I never take water on training runs and do sometimes see an elevated heart rate in the latter stages and salt residue on my skin afterwards. I take a blended sports drink on the bike, including additional salt to avoid an imbalance of water to electrolytes. In other words: we think we know what we’re doing. But what startled me was just how quickly his race was over and all that hard work was drifting off in the ocean breeze.

Dehydration does not simply mean loss of water. There are three types of dehydration: Hypotonic (primarily loss of electrolytes); Hypertonic (primarily loss of water); Isotonic (loss of water and electrolytes in equal balance). Isotonic is the most common. You may also be aware of Hyponatremia: this occurs when the concentration of sodium in the blood plasma is too low; in sports this can be caused by absorbing too much water without electrolytes.

All this got me thinking about the demands of Ironman. Exactly how much drink and electrolytes will I need? I need to get more scientific.

Fluid mathematics

I usually take 2 x 650ml bottles containing PowerBar Energize (1.5 scoops), Base Amino (1 small scoop) and an electrolyte supplement. I’ve found this gives me good energy levels, even when riding for over 4 hours. But, I need to know whether I am replacing sufficient water and electrolytes.

Today I ran for 2 hours in 15 degrees; pre-run I weighed 11 stone 11 pounds and after 11 stone 8 pounds. Converting the difference – 3 pounds – to ounces is 48, and converting this to millilitres is 1,364ml. That’s 682ml lost per hour; contrast this to 325ml drunk per hour when I ride for 4 hours (less, over longer rides unless I stop for water). By this measure I should be drinking DOUBLE the amount of liquid! Now, with the cooling effect of the wind when cycling my sweat rate might be lower so I will need to test this on the bike and factor in intake as well. But this is an eye opener.

Also, fluid loss (and absorption) can vary depending on heart rate: the higher the heart rate the more the body is having to focus its efforts on getting oxygen to the muscles and cooling itself from the internal heat created in energy production (and the external temperature too). Third in this priority list appears to be actually absorbing liquid and calories. Thus the harder you’re working the more fluid you’ll lose, more calories will be burnt and the less capable you are of replenishing them.

…and Electrolytes?

The average person loses 500ml of sodium per pound of sweat (the range can be 200ml to 1,100ml according to Run the Planet). This means – if average (and I don’t know where I would be on this scale) – I lost 1,500ml of sodium in my run today. If I want to avoid cramp, light-headedness, extreme fatigue and possible collapse I’m going to need to work out how much salt to replace as well!

The Scientist

Upon recommendation, I spoke today to Mike at Infinit Nutrition. They make custom drinks to suit individual needs. He asked a lot of questions about sweat rate, residual salt on skin/clothing, usual nutrition habits – etc – and independently showed great concern at 325ml liquid per hour. He is now on the case to create a more optimal mix using their highly scientific approach to matching concentrated formula to your specific needs.

I could write another entire post on food – and once I have a clearer idea what Infinit’s drink will provide by way of Calories, I’m sure I will. But I guess the message here is that guess work and luck might have got me through 5 marathons and a Half Ironman, but when it comes to 140.6 miles and over 10 hours of exercise it will pay to leave nothing to chance.

————-

27th April: Interesting article tweeted by US elite marathoner Josh Cox relating to core temperature, heart rate and exhaustion. Note the HR of 185bpm at exhaustion; hopefully my brother won’t mind me saying his average HR was generally in the 170s throughout the Brighton Marathon – very impressive in itself, firmly in anaerobic threshold zone – and hit 187bpm in the minutes before he stopped running.

Advertisements

Run Brighton: new marathon launches

My home town became my home city as part of Britain’s millennium celebrations. As a result the city has seen development to public facilities, a redesign of Churchill Square shopping centre, substantial residential property investment and – finally – the approval of work on the controversial new Brighton & Hove Albion football ground and sports complex. And now the city has announced the launch of the inaugral Brighton Marathon, Sunday 18th April 2010.

Brighton marathon_Course map

The route will take in plenty of the charismatic streets of central Brighton and Hove and the panoramic views along the seaside, before finishing on Madeira Drive (the usual finish for the London to Brighton bike ride, amongst other events). The course looks pretty flat – although miles 5 to 8 in Kemp Town might perhaps be undulating (the site doesn’t show a course profile) – so good times should be possible.

The organisers are offering 8000 entries for 2010. Scheduled for just one week before the London Marathon, Brighton will provide a great alternative. Moreover, if you enter Brighton, the event is offering to refund your entry if you are fortunate enough to – subsequently – make it through the ballot for London. This is a great way to ensure early entries into Brighton 2010 whilst avoiding lots of no shows on the day. 

I’m down in Brighton this weekend so I’ll be checking out the route and – more than likely – entering the event. London will still be my preference, but partaking in my home town city marathon would be an equally terrific experience.