Sunday, 21 September 2014
I have started weighing myself before and after my hour long lunch rides to get a sense of how much weigh I lose through sweat and respiration. The figures are rather alarming. Currently I average a weight loss of 800g over an hour. (Water/weight ratios are 1:1 - 1 litre of water weights 1 kg.) For my typical Magaliesburg rides I don't take any form of hydration apart from a mid-ride bullet coffee at the Wimpy. Those rides typically take 3 hours. So my water losses are probably 2.5 litres and I replenish that with 350 ml. That's a deficit of 2.15 litres. Over 3 hours that's all well and good as a glass or two of water and a pot of tea over the next few hours and it's fixed. Also, as noted in a previous link, there are performance benefits to be gained from running a little dehydrated in training.
Now fast forward to the Karoo in December. Temperatures in the 40's. Hourly hydration losses of ??? I guess a conservative guess would be 1 litre an hour moving at a moderate pace. Over 14 daylight hours that's 14 litres. Then add in the nighttime hours albeit at a lower rate. It's fine to do a 3 hour ride and get slightly dehydrated but over the long haul you will need to retain a good hydration at all times particularly if you intend to cycle 20-22 hours of every day. Research suggests that the max safe oral hydration is 1 litre per hour. Beyond that there is an increased risk of electrolyte imbalance that could lead to hyponatraemia (decreased blood salt levels) in which case you turn into a human sponge and you can absorb plenty of water before you drop down dead. Hyponatraemia is a real risk and this needs to countered through supplemental sodium intake. There are lots of electrolyte replacement options like Rehydrate and the new fizzy pills like High5 and a myriad of other brands that you can pop into your water. Unless informed otherwise it would be safe to assume that you will need to start the race with enough supply to get to the finish as there won't be any at the support stations. Riders in the habit of taking specialised race nutritional supplements would be better served ditching some of that and include more electrolyte additives unless they want to carry everything from the start. Normal food will do the trick from a nutritional standpoint as you pass through support stations but not specifically supplementing electrolytes can lead to disaster.
Lets make some assumptions starting with an average traveling speed of 15km/h. Water points on The Munga are roughly 60 Km's apart. So you only need water for 4 hours. So the simple maths with my current hydration guesstimate makes the requirement 4 litres. That's a 2 litre Camelbak and 3 bottles. Carrying an extra 4kgs is huge. Endurance race experience has highlighted that my hydration requirements are a lot lower than the average rider so for some it could be upwards of 6 litres. It's logistically challenging. Stronger guys will ride a lot faster and might get through water points every 3 hours. Some will be slower and take 5. Add a headwind and it starts to get interesting. Above 35 Celsius normal sweat functions are impaired. Smart clothing choices that maximise evaporative cooling effects become imperative. It is primarily the electrolytic losses through sweating that needs to be replenished. In a 1 hour spin class you can drip out 3 litres of sweat but it takes a few hours for you body to effectively replace that volume. Go for a hike and you sweat a lot less and can easily keep your hydration in balance. I think it's going to be interesting to figure out the right pace to ride at. That pace will be informed more by establishing a hydration balance than how am I doing on the leader board.
Anyway, this is all based on my initial measurements. Will continue to study the losses and see if they improve. Will also ride at different intensities and see how that impacts on losses.
This race format is new and exciting. No one, including the race organisers know how this is actually going to play out. Riding is riding but the extreme endurance and challenging environmental aspects combine to make this one huge science experiment where we are the guinea pigs and the public are the observers. Certainly not going to be boring.