63 - On Hydration

I have been having problems with weight loss. When I left Britain I was 74.6 kg pretty regularly – that is, that number was shown on my excellent scales consistently and at the same time of day. [Excellent in this case means that the precision was better than the display, so any number of immediately consecutive measurements gave the same number.] I am currently at 65kg at the end of a run, sometimes even less. I don’t think I can afford to be ten kilos less !!

The move to China and the change of diet, away from dairy products and potatoes, means most westerners lose 4-5kg fairly quickly (5-7% of weight), typically over the first three months. Weight then stabilises at this new lower figure. So, in my case I dropped to below 70kg quite quickly while in Xi’an 2007/8. As the running distances rose from 20 miles per week to 35, so the weight steadied at 69kg. Moving to Nanjing, 2008/9, the distances rose with the immense convenience of Xuan Wu Lake across the road from my apartment, the cooler weather, the stresses at work and the basic enthusiasm to run more. I discovered in the early summer of 2009 that I could lose 2kg across a run, calculating that the losses were in the region of 40g/minute, so a 30 minute run represents a kilo lost. I wrote at the time, to Andrew at Bristol, who runs at a much higher standard than I do:

It is hot and humid here at the moment. I go running to finish before 20:00 and the weekday walk to work at 05:30 has been a sweaty affair of late. The mid-afternoon is conducive to sleep unless you are inside an air-con zone. Chinese do not often siesta here (they do in other parts of the country) and they simply suffer while at work – very Chinese. I have lost over a kilo in weight in 15 minutes running; any model for this needs a delay from the start before sweating takes place, but even so I seem to get 5 minutes for free and then something like 40g per minute.  A vigorous 40 minutes would lose 1.4 kg on this formula – I lost 1.5 in 45 minutes between measurements just two weekends ago.

Sports essays

Running essays include 1723326677142188,

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Allied sports health include  5863112124163188204

Other sport; Rowing

In Nanjing I was for a while running two 9.3 km laps of the lake on a Sunday morning, training for the big race in Xi’an (see City Wall race). This made fluid recovery a bit of a problem. Andrew agreed with the general problem but said that he lost at most 2kg over an hour’s run in Britain. I am finding in ZhaoQing, in the tropics in 2010, that I am losing 2kg in a much shorter time. Indeed my stable weight on rising is around 67kg, but post-run weight is consistently under 66kg, sometimes under 65kg. I am finding that when the weight goes under 65kg I become dysfunctional.
So I am not merely reporting this, I need to do something about it. Running with extra weight such as a drink in a container is awkward. Arranging for a drink supply is making running complicated. So what can one do?

There are several factors to consider. I refer below to a downloadable article from the {US] Journal of Athletic Training, http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1323420/pdf/jathtrain00002-0094.pdf:    I have rewritten the long list of recommendations of the National Athletic Trainers' Association (NATA) from the article found. while keeping their order and numbering:

1  Hydration protocols vary between athletes. They are varied by sweat rate, pattern of exercise, environment, acclimatisation, exercise duration and intensity – and individual preferences
2  Each such protocol considers the unique features of the sport concerned – sometimes the rules of the sport add restrictions to hydration.
3  Fluid replacement should be easily accessible.
4  Athletes should start all exercise well hydrated.
5  To ensure this hydration, athletes should consume 5-600 ml of fluid 2-3 hours before the exercise and 2-300 ml 10 to 20 mins before.
6  Fluid replacement should approximate losses and maintain the weight reduction at less than 2%. This suggests 2-300ml every 10-20 minutes. Hyperhydration is dangerous.
7  Post-exercise hydration aims to correct losses – water, carbohydrates and electrolytes. When rehydration must be rapid, the intake must recover urine losses and exceed sweat losses by 25-50% in the 4-6 hours after the event.
8  Fluid temperature influences the amount consumed. 10-15ºC is recommended.
9  High relative humidity limits evaporative cooling because the air is near saturation for water vapour and so sweating is less effective for heat loss. There is another article from NATA on heat illnesses.
10  Including carbohydrates in the fluid protocol can be beneficial. At about 30 minutes pre-exercise, extra CHOs help. During exercise exceeding 45 minutes, a rate of 1g/min is recommended. This equates to 1litre of a 6% CHO drink per hour of exercise. At 8% the effects are negative if taken during the exercise. Absorption rates are improved by mixed foods ingestion.
11  Recognising the signs of dehydration is an important skill; early action minimises the effects.
12  Including salt (NaCl) in modest amounts should be done with care.
13  Sweat rates should be calculated. Using averaged tables is far from ideal as the rates vary from 0.5 to 2.5 kg/hour.
14  Heat acclimatisation can change the whole pattern. Going from cool to hot increases the overall sweat rate.
15  Sports with weight classes should test for hydration levels at weigh-in.
16  Hyperhydration has equivocal support. This can be achieved by ingesting a mix of water and glycerol.
17  Young people need special treatment, because they tend not to respond to the signs of dehydration.
18  Event management needs to include hydration considerations.
19  Hydration protocols will only succeed when all concerned see the value: education is key. Applying protocols throughout training (not just for special occasions) makes sense.

A long list, much of which applies even in Britain.

I have comment to make, some of which is in the hope of generating argument from readers. I will confine myself to running specifically.

Points 5 & 10 refer to eating and drinking prior to exercise. I spent many years eating lunch and going running within 15 minutes of the last mouthful. I found that being delayed to 25 minutes had a bad effect, as if the stomach had started work on the food and the body was distracted by trying to then, in some way, turn this process off because of the exercise. When the gap was 15±5 minutes, there was no effect – even when doing sprint training. Keeping that gap right meant the difference between enjoying the exercise and being sick. It was something of an issue when running with the Trotters of an evening in Cornwall, where it was sometimes difficult to make the gap between eating and running (for an hour) big enough for the body to have made progress on digestion.

Point 12: I spent many years using ‘slow sodium’ tablets at one per 8 to 10 km to significant positive effect. On an occasion in Henley half marathon where I had forgotten the tablets, I needed to stop and ask (demand) a pint of salty water (a tablespoonful to the pint) drunk in a very few seconds from a lady living on the last three miles of the course. It cost me a minute but saved at least five. Any heavy training or racing under 8km did not justify extra salt – that is, no positives were recognised. Before discovering Slow Sodium I was in the habit of drinking salty water on finishing a run, to avoid the crippling leg cramps common to my soccer experiences.

The research I have done says that taking NaCl is beneficial if part of the rehydration and if fluid intake is less than the sweat losses.

Point 9 is obvious physics but uncomfortable living. I shall experiment with living with less a/c (i.e. higher temperature) and see if that affects the response to heat outside.

The principal way to lose heat is by evaporation of sweat, typically 80% in warm & humid conditions and up to 98% in hot & dry conditions. In this light, anything that limits evaporation will have a serious effect upon the body and performance. The other ways of losing heat are relatively insignificant.

One of the major consequences of dehydration is an increase in core temperature – “with core temperature rising an additional 0.15 to 0.20°C for every 1% of body weight lost (due to sweating) during the activity.” This adds to the strain on the body and is likely to negate the advantages of increased fitness and thermal acclimatisation. So says the NATA and my personal observations agree. What I am calling added strain diverts the body from performance; NATA cites, for example, a rise of heart rate of 3-5 bpm for each 1% of weight loss. I’m looking at a 5% loss at the end of an hour’s running, which means a 20 bpm increase. My ceiling is around 175 bpm these days, so probably I’m running at around 160 bpm; reducing the running to an equivalent of that at 140bpm translates to around a 15-20% reduction in speed at the end of a long run. Which agrees with the overall reduction of 10-15% that I experience. In cooler climates the change in adding distance is much smaller; moving from 8km to 16km [five to ten miles] changes the pace by 5-10%. So the effect of the added heat is exaggerating this difference. It is also making the post-exercise experience unpleasant.

Worse, trying harder exaggerates all the effects. For least effect, going slower early on allows nearer maximal effort at the end of a run with the least degradation of performance. This agrees with the research into hypohydration. In terms of strategy over say 14-15km (an hour), it means that starting off deliberately slowly - in my case sticking to 4:40 per km rather than 4:10 - means that 40 minutes later I can speed up to 4:10 and finish the hour feeling good. Starting at 4:15 means that I break down at the 40 minute mark and finish in 80 minutes, very uncomfortable and not well.


The NATA article, whose background knowledge I really appreciate, goes on to look at rehydration and factors associated with that process. My observed critical temperature is 25ºC; above this figure performance degrades rapidly and this agrees with some of the literature, particularly in the need for better hydration. The general literature on this topics says: learned behaviour is valuable; chilled drinks are more voluntarily drunk; the rehydration stimulus can be psychological; many characteristics of the drink affect how much is drunk; mood affects rehydration, as does concentration (or focus). These collectively suggest that a rehydration system such as a platypus is a good idea – though whether for runners or not, I doubt.

I looked at voluntary over-hydration, hyper-hydration and found conflict over use of glycerol (enough to put one off). The recommendation is to force oneself to drink a half-litre two hours before the exercise and one needs to look at the advantages of increasing this ‘dose’.

Research  - by me and of the work of others – says that athletes tend not to rehydrate to their previous levels, due to combinations of factors. Point 7 above is relevant. I suspect that daily exercise and failing to replace water adequately is contributing to my steady weight loss of recent weeks, I drink until uncomfortable; my preferred drink is rich in glucose and salts (but maybe the wrong salts). Medically inclined readers might research ‘gastric emptying’ at this point. Several sources make the valid point that replacement should be just that, not markedly less that the fluid lost through sweat and urine.

The technically minded might explore their hydration status. Several sources, which I guess are referring to professional behaviour, suggest that frequent recording of body weight, urine colour or specific gravity (USG) and the effects of the current regime upon performance are worthwhile activities. Personally, I am thinking that the Army has it right, that hydration should pass the point where urine is clear, with their ready “double-u” mantra, probably now called a ‘dubya’:  “wee white once a day”.

DJS 20100828       .  
top pic from HK Trail Run, of a lady perspiring freely in the heat.     


Immediate action has been to drink more in advance of running. On 20100828 I finished at 65.6 kg not the previous day’s 64.6 - but it was not a good run, maybe from other reasons. That is one of the general issues; that the differences are small and easily masked by other changes. Since 20100829 (and maintained until departing from Guangdong) I  have added the eating of a sandwich at 15:30 before the run at 17:30. I am measuring weight before and after to show the differences. One of my smaller problems is that my various thermometers disagree what the temperature is, often by six degrees. Right now it is 23º inside and allegedly 32º outside. Two of the three agree, so I’ll use those principally. I have (just) set one of them outside and this one will give humidity too (on a shaded balcony).

Figures collected to 20100920 continue to agree with the idea of 5 minutes free and then 40g/minute sweat loss. That figure is varied by the humidity, the temperature and other factors to do with health. Maximum recent weight loss (with a median start of 67.4) is 3.4kg across 64mins & 14.5km while at 30º and 60% humidity. Minimum for this period is 1.3kg over 15mins at 31º and 50%. An interesting case was 2.2kg over 43mins at 25º and 85%. Of late, no humidity has been lower than 50%, no temperature below 25º, no run below 15mins (I have a cold, so am running to sweat not to tire), and I’ve had 5 days off in the last eight weeks, mainly due to travel issues.

DJS 20100920

Related sport stories and injuries stories are:

A trail run in HK, On HashA different HashA trail run in HK, Sports Day, A bit of PT,    The City Wall Race,    Bumping Races   


© David Scoins 2017