Fluid requirements during exercise in the winter months

We are all aware of our fluid losses during exercise on hot summer days. We often experience sweat dripping from our skin surface, feeling hot, or are even aware of sweat evaporating (leaving salty skin or salty patches on our clothing). This evaporation is what effectively contributes to removing heat from our body allowing us to continue exercising without our body core temperature rising too high. However, we may be less aware of our fluid losses during exercise when it comes to exercising in the winter months. Part of the reason for this reduced awareness is that in cooler environments we are better able to regulate our body temperature (due to less heat stress). So, we sweat less at lower air temperatures. When we sweat less we are not as aware of our losses, although we are still losing fluid through evaporative sweat losses as well as losses of water vapour through our breathing.

Sweat losses

The image below shows sweat rate data when wearing shorts and T-shirt during moderate intensity exercise conducted in different environmental temperatures. It highlights the typical sweat rate response in a group of male recreationally active individuals. We can see that as ambient temperature rises there is also a rise in the sweat rate per hour (no surprises there), but it should be noted that even at cold (4°C) and cool (11°C) ambient temperatures sweat rate can be in the region of 0.5 to 0.6 Litres per hour. These values in the cold (4°C) and cool (11°C) conditions will be higher if more clothing is worn, so with your winter clothing on you could easily reach the sweat rates reported for 21°C or more. It should also be pointed out that these are average data from a group of males. Individuals can have quite different sweat rate responses so it is best to find out your own sweat rate at different temperatures.

Water losses through breathing

Respiratory water losses amount to about 2 to 5 g of water per minute when exercising at a moderate intensity in a dry air environment (equating to 120-300ml per hour). Often in cold damp weather there is greater moisture in the air meaning that respiratory water losses will be lower than this range. However, on clear crisp cold weather days where the air is very dry, respiratory water losses may be nearer the upper end of this range. This water loss of breathing on cold dry days therefore represents a big proportion of total fluid losses when you are sweating less. That is, water loss from breathing could add 50% to your water losses per hour (600ml/h sweat loss plus 300ml respiratory water loss). Therefore, over several hours of outdoor exercise in a cold dry environment respiratory water loss, on top of your sweat loss, means that your total fluid requirements may be greater than you think!

What about sex differences?

Now, you would be right to point out that the observations above were gathered on males and there might be a difference when considering female fluid replacement requirements. Indeed, the majority of research conducted into sweating rates and respiratory water losses has been done on men. However, studies examining women typically report lower whole body sweat rates on average, with women also able to control body core temperature rises equally as well as men. Therefore, this is typically interpreted as women being more efficient at sweating than men. This translates into overall less fluid requirement for exercising women, but again fluid losses / sweat rates should be assessed on an individual basis.

How do I estimate my sweat rate during winter training?

The easiest thing to do to estimate your sweat rate is to weigh yourself in your underwear (or ideally with no clothes on) before and after your exercise sessions. If you also measure how much fluid you have ingested between each weighing time point then you can correct your mass loss to estimate sweat rate and respiratory water losses. For example, if you weighed 68.3kg before going out on your winter bike for 2 hours, you consumed 700ml of fluid from your drinks bottle over that time period, and weighed in at 67.6kg after exercise, then your total water loss (sweat loss plus respiratory water loss) per hour would be: 0.7 Litres per hour

The calculation is: 68.3kg weight before, + 0.7 kg ingested = 69kg. Then subtract weight after exercise (67.6kg) which leaves 1.4kg lost over 2 hours of exercise. Thus, estimated fluid loss is 0.7 L per hour.

You should note that if any urine is passed during the period of time between weighing yourself, this will alter the calculation. In laboratory studies we collect all urine so that the volume can be factored into the estimation of total fluid losses.

References:

Galloway and Maughan (1997) Effects of ambient temperature on the capacity to perform prolonged cycle exercise in man. Med Sci Sports Exerc. 29(9):1240-1249.

Mitchell, Nadel and Stolwijk (1972) Respiratory weight losses during exercise. J Appl Physiol. 32:474-476.

Wickham, McCarthy, Spriet and Cheung (2021) Sex differences in the physiological responses to exercise-induced dehydration: consequences and mechanisms. J Appl Physiol. 131: 504–510

Rodriguez-Giustiniani, Rodriguez-Sanchez and Galloway (2021) Fluid and electrolyte balance considerations for female athletes. Eur J Sort Sci. Jun 17;1-12. doi: 10.1080/17461391.2021.1939428.

M:X is a proud sponsor of Meadows Marathon 2021 and we’re very excited to be entering a team to take part in the virtual Half Marathon on the weekend of 20th/21st March. Each of our runners have chosen a charity to support, and you can find out more about each below. You can sponsor our team or individual runners here – any contribution is hugely appreciated!

 

Katie Wright (@Run_KatieKitten_Run)

Team GB AG Aquathlon Athlete Katie Wright has chosen to support the Royal National Lifeboat Institution (RNLI), the charity that saves lives at sea.

 

Mike James (@The_Endurance_Physio) 

Endurance athlete Mike James  – AKA The Endurance Physio – is fundraising for Edinburgh RAG’s partner charities, Saheliya, When You Wish Upon A Star and The Rainforest Trust.

 

Sarah Booker (@Mia79GBR_)

Team GB AG Triathlon Athlete Sarah Booker is supporting the Birmingham Crisis Centre, which provides a safe haven for female victims of domestic abuse.

 

Andrew Davidson

M:X Founder Andrew has chosen to fundraise for Maggies, a charity providing free cancer support and information in centres across the UK.

 

Cameron Hughes

M:X Marketing Manager is fundraising for Finding Your Feet, which supports families affected by amputation or limb absence.

 

Any donations to any of our chosen charities are hugely appreciated and will go a long way to help people who need it most. You can also show your support online and keep up to date by following us at @MixHydration on Facebook, Instagram and Twitter.

This is a quite common question that I get asked year after year, and it’s actually a difficult one to answer. In fact it’s probably the epitome of the ‘it depends’ answer. The truth is that training over the festive period will look different for everyone based on their individual circumstances: work, family, race plans and other life commitments. Therefore, all you can do is make sure that you spend enough time giving appropriate consideration so that your plans are realistic.

 

Once upon a time, Christmas for me was actually a time to do more training: no work, a chance to build up credit for, and/or burn off the indulgence that lay ahead. I know this is the case for many, particularly those who may not have young children, and it can also be a tradition for some. Until becoming a dad, my Christmas Day pre-lunch run was something I looked forward to and it became a staple part of my Christmas Day itinerary, as did my Christmas Day pudding race, wherever I may have been based at the time. I used to love the peacefulness of a Christmas morning run. The streets were silent, and I found it very cathartic (although once upon a time they were jammed with youngsters riding new bikes, skateboards or kicking new footballs – but that’s a rant for a different blog!). For some, it’s a timely opportunity to back-off a little and recharge for the new year. A chance to take stock midway through winter training and review, revise or simply rest up for what lays ahead. For me, things have changed over the last 8 years.

It’s entirely about the kids these days and I wouldn’t change it for the world. Until they’re old enough to want to join me in creating a new family tradition of Christmas Day runs, I’ll enjoy factoring my training around them. 

So, hopefully you can see that my point is it’s very individual, and there really isn’t a right or wrong way to think about it. What are you training for? Do you have a race early in the year that needs you to train more over Christmas, for example? This unfortunately won’t be the case for many this year, and even those still wishfully training for Spring races may well find it a challenge to keep their training up. What I would suggest is that whatever the volume or frequency of your Christmas training plans, try to factor the other things in your life into the planning. Nothing becomes more stressful than worrying about getting your training in and also making sure you can do all the other things you have planned. So, a bit more time than usual, maybe thinking outside the box a little more than normal and finding novel ways, times and methods of training may help. The mistake I often see is people trying to juggle too much all at the same time, programming a heavy week’s training on the week that they have Christmas commitments. Maybe split up your usual training regime to factor this in, bring a recovery or lighter training week forward, or indeed, push it back if needed. But for others, maybe putting the feet up, enjoying an extra mince pie and making training a lower priority for a week or two is the solution. Remember to factor the New Year’s training into the plan.

You don’t want to start training like a lunatic in January to make up for a relaxing Christmas and then have problems in February or March.

Finally, my other consideration is for those who may train out of guilt. Guilt for the overindulgence that leads to us adding extra training to our sessions, adding extra intensity to our sessions, or possibly training when you didn’t plan on training. Sometimes the easiest way to control this is to control the indulgence. That’s not saying don’t have fun, but be honest with the reasons why you may alter your training and see if you can affect those.

Thanks for reading and have a very Merry Christmas and a Happy New Year!