Do Sweat the Small Stuff


My dad taught me not to sweat the small stuff – a key to managing anxiety and stress in life. It’s worked for him as he’s still a practicing family doctor at age 82 and as sharp as a tack with few health issues. But what about real sweating – losing fluids in sport! What impact does it have on sports performance? Here is a summary of a very recent review published in the highly-credentialed Nutrition Reviews journal highlighting that we shouldn’t lose anymore than 2-3% of our body weight in fluids before we decrease performance. Moreover, this review throws doubt over many of the long-held beliefs regarding fluid replacement needs in athletes.

Historically, research suggested suggested that fluid loss of anymore than 2% loss of body weight impairs endurance performance under any conditions and that athletes should always drink before feeling thirsty to maximize endurance performance. However, there is recent evidence suggesting that cycling time trial performance is not affected by up to 4% of body weight loss and that drinking when thirsty maximizes endurance performance. Moreover, a 2011 study published in the British Journal of Sports Medicine  showed that the marathon times of 643 runners were inversely correlated to their end-of marathon body weight loss. That is, the greater their body weight loss, the faster they ran!

The Research

This paper rightly questions how well-published and strongly-adghered to fluid replacement guidelines are often based on laboratory-based (vs real world) studies often using fixed power output time trials (vs the real world where pacing and changes of speed are normal) and often using testing methods with poor reliability such as time to exhaustion at a set speed. The review highlights five recent studies that simulate real-world racing conditions. None of these studies showed any difference in performance between being dehydrated less than 2% or greater than 2% in body weight. In fact a couple of studies have suggested that the greater the body weight loss, the better the endurance performance. This has been shown in marathon runners, Ironman triathletes, and 24-hr ultramarathoners. The review also highlighted that Haile Gebrselassie won the 2009 Dubai marathon after a body weight loss of 9.8%. While this information shouldn’t be interpreted as supporting becoming dehydrated to enhance endurance performance, it does question the current guidelines that maintaining body weight loss to no greater than 2% of body weight is critical to endurance performance.

The New Guidelines?

This peer-reviewed and well-researched review provides guidelines to help athletes, coaches and sport health practitioners with guidelines for developing safe hydration plans for endurance athletes. These include:

  1. Be well-hydrated before exercise: It’s been well-documnetd that many athletes start exercise dehydrated and that doing this decreases performance. In the last 2 hours before exercise, athletes should drink fluids when they feel the need but should be around 5-10 mL/kg body weight of sports drink or water. They should drink to the point of having two pees before competition and ensure that the pees are straw yellow or clear that indicates they are hydrated.
  2. Drink according to your thirst: no more, no less: This is an individual sensation but normally means a dry and sticky mouth and throat. Nerves and food intake can sometimes cause this as can very dry weather. Plan ahead and trial a hydration plan in training, ideally in conditions that replicate the conditions of the goal event.
  3. Limit fluid intake in events shorter than one hour: Research consistently shows that fluid intake has no bearing on performance in endurance events shorter than one hour. Gut upsets can occur in some people whan taking in fluids during high intensity endurance events typically shorter than 60  minutes.  As an option, consider mouth rinsing with 20-25 mL of sports drinks for 5-10 seconds every 8-10 minutes.  

Always try before you buy – more father advice! Practice the guidelines above for yourself before doing it in competition. Also remember that these are guidelines and that you as an individual neeed to determine, usually by trial and error, what works best for you.

There are some specific suggestions on hydrating as an older athlete that are discussed in Chapter 11 (Exercising in the heat and cold) of my book The Masters Athlete that is now available as a pdf or as separate chapter pdf’s. Check it out – it’s the most comprehensive book for older athletes that has ever been published.

Goulet, E. (2012). Dehydration and endurance performance in competitive athletes. Nutrition Reviews. 70(Supplement 2): S132-S136.

Fluid Loss in Masters Swimmers – Effects of Water Temperature


Most experienced and competitive masters swimmers have trained or competed in many different pools, lakes, rivers and oceans, and under many different climatic conditions and water temperatures. We’ve learnt that hard sessions in warm water can work up a thirst. While little research has been done on fluid loss in swimmers, here is some recent Italian research that used older open water swimmers as their subjects. The results suggests the level of dehydration, the sweat rate, and the body temperature all increase with increased water temperature as we move from cool to warmer water.

The Research

The purpose of the study was to evaluate the effects of three different water temperatures (23, 27 and 32 ̊C) on physiological responses (dehydration, sweat rate, urine output, rectal temperature, plasma electrolytes and fluid balance) to a “simulated” race of 5 km in competitive athletes in an indoor 25m pool. Nine competitive male master swimmers ranked in the top 5 of category in open water (1.5–10 km) Italian races, were studied (age: 34.6 ± 14.4 years, height: 172.1 ± 9.8 cm, mass: 72.7 ± 8.5 kg, body fat: 12.7 ± 3.5%). The subjects trained five to six times per week (3–8 km per training session) in 25- and 50-meter swimming pools (water temperature about 27 ̊C). Each swimmer completed three experimental trials, separated by 7 days, in a 25-meter indoor swimming pool; they swam 5 km with water at the temperatures of 23, 27 and 32 ̊C. The swimming speed of all athletes in each trial was as close as possible to their personal lactate threshold speed (race pace). No food or fluid was used during the tests. The sport scientists measured body weight, rectal temperature, urine output, and blood electrolytes (sodium, potassium and magnesium before and after each swim.

The Results

Sweat rate increased and body weight loss (%) decreased with increased water temperature (Table 1).


23 ̊C 27 ̊C 32 ̊C

Rectal temperature ( ̊C)

37.2 37.9 38.0
Body weight loss (%) 0.9 1.3


Sweat rate (L/hr) 0.48 0.76


Urine output after each swim was no different between the trails. Body temperature only increased in the 27 and 32 ̊C trials. The sodium level in the blood only increased in the 32 ̊C swim and most probably due to the amount of fluid lost. The researchers concluded that dehydration, sweat rate and body temperatures simultaneously increase with the rise of water temperature during the shortest open water swimming event distance (5 km) performed at race intensity.

So What?

This unique study confirms that as water temperature increases we need to be more cautious about ensuring our hydration status is good. Drink fluids before a pool session and ensure, particularly in hard sessions in warmer water (its 31 ̊C in our Uni pool at present!), that you replace fluids regularly during your session. The hotter the water, the more fluids you need to drink. The harder and longer the session, the more fluids you need to drink. If you are a once a day swimmer doing sessions under an hour, water is all you need. Twice a day and/or doing sessions longer than an hour and/or hard, the more important sports drinks become. For more on temperature regulation and fluid guidelines for masters athletes, see Chapter 11 of my book The Masters Athlete – Exercising in the Heat and Cold.

Source: Macaluso et al. (2011) Effects of three different water temperatures on dehydration in competitive swimmers. Science in Sports, 26: 265-271.

Does dehydration decrease performance? Maybe not!


There has been some robust debate recently in the sport science literature. Some experts are saying a level of dehydration is safe in endurance athletes and that we should rely on thirst to tell us when to drink. In contrast, there are some experts that say drink before we get thirsty and try and maintain your body weight during endurance exercise. This research study on marathon runners suggests marathon performance is better in those that lose more body weight.

The Research

Body weight changes were measured in 643 marathon finishers (560 males and 83 females) before and after the 2009 Mont Saint-Michel Marathon in France.  The runner’s body weight was measured 60-90 minutes before the start of the marathon while they were wearing their running clothing but not shoes. Within 20m of the finish of the event their body weight was measured again by the same researcher on the same scales. Again, no shoes and the same clothing were worn and yep, some sweat may have been in the clothes! Runners were advised to drink 250 mL of fluid (sports drink or water) every 20 minutes during the event. Weather conditions were: 9-16 degrees Celsius, 60-82% humidity and strong winds. For statistical analysis, the runners were divided into three groups – sub 3hr, 3-4 hr, and greater than 4 hour marathoners.

The Results

The average age of the runners was 43±8.8 years and runners lost on average 1.7 kg or 2.3±2.2% of their body weight during the event. Males and females lost similar amounts of fluid (1 kg weight loss equals approximately 1 litre of fluid loss) and their was no effect of age on fluid loss. The weight lost ranging between gaining 5% and losing 8% of pre-race body weight. 55% of runners lost more than 2% of their body weight – the gold standard often mentioned as leading to decreased endurance performance.

Interestingly, and here is the punch line for this research, the runners who finished under 3 hours lost significantly more body weight (3.1±1.9%) and thus fluids than either the 3-4 hr runners (2.5±2.1%) and the 4 hr plus runners (1.8±2.4%). When the scientists plotted the relationship between race time and body weight lost, the relationship was very strong suggesting the greater the weight lost, the faster the run time.

So What?

The bottom line is that these results support a growing body of evidence that questions the laboratory-based findings that a body weight loss of greater than 2% impairs sport performance. In contrast, the results support previous field-based studies that show that successful athletes in marathons, ultra-distance, and triathlon events are those who lose more than 3-4% of body weight during competition. The other intersting observation from this study was that almost 10% of runners gained weight by overdrinking, an observation common in ‘back of the packers’ who read they should drink a lot but often aren’t exercising as hard as faster runners and thus may not lose fluids as much as the books suggest. This overdrinking can lead to potentially fatal condition called hyponatremia (low blood salt levels).

The bottom line again, drink before, during and after training and events and monitor your body by listening to how it responds. For information on the effect of heat (and cold) on masters athletes and, more importantly, how to manage exercising in the heat and cold as an older athlete, see Chapter 11 of my book The Masters Athlete.

Legal Nutritional Supplements for Improving Endurance Performance

Crushed ice before events in hot/humid conditions may help performance

The IntroductionIced slurry drink

Pre-cooling in an ice bath, air conditioning, or wearing an ice vest has consistently been shown to benefit performance in endurance events in the heat. However, these strategies require equipment, logistical problems and make us uncomfortable before events. This recent research has used ice crushed up in a blender as a way to cool the body down. The question was asked, will it also help endurance performance in the heat? The results say yes!

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