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There was a time, not too long ago, where it seemed like everyone was advocating the use of sports drinks to aid fluid balance, electrolyte replenishment and overall sporting performance. As a performance coach in an academy setting, I would travel the junior circuit, going from tournament to tournament. Youngsters would be gulping down neon coloured Gatorades yet could barely see over the net.
But then, a wave of anti-sugar marketing ads began coming to light. And all of a sudden, sugar-free sports drinks became the norm (if you were seen with a ‘regular’ Gatorade, you’d receive a long, evil stare - from coaches, parents and other players).
Today, there’s confusion. Which camp should we listen to? Sugar-free or sugar-full? Perhaps there’s a time when one is warranted over the other? Or maybe we should simply stick to water?
This post will try to answer these prevailing questions while tackling other topics related to hydration during tennis - including hydration and skill, physical performance and whether a predetermined fluid plan is necessary. While the evidence on the topic can at times be misleading (and contrasting), when it comes to replacing fluid, electrolyte and glycogen stores, there are some definite guidelines that every player should follow.
The Current State of Play
A recent study (Fleming et al 2018) looking at the nutritional interventions of competitive tennis players (from Europe and North America) found that the most common nutritional aids during training/matchplay were water (94%), bananas (86%) and sports drinks (50%).
Furthermore, from the 70 total players that took part in the study, only 23% of them had a specific target for how much fluid they would consume during their match (with half of those aiming for 500mL and the other half for >2L) - the other 77% didn’t have any fluid intake objectives at all! Considering fluid losses through sweat can reach 1-2 L (or more) per hour AND sodium losses can be as high as 1.5g/h, it might be worth it to have a plan in place (but more on that below).
As for post-match recovery, 39% of players said they had ‘nothing specific’ planned for replenishment of fluids/carbohydrates. That’s a concern.
There’s an overwhelming amount of evidence indicating the importance of fluid + nutrient replacement strategies for competitive athletes - not only for health reasons but to increase both physical & cognitive performance, delay fatigue and aid in recovery.
Let’s explore this topic further.
Duration and Intensity of Training/Competition
Before we get into the nitty gritty details, let’s get the basics out of the way. If you train less than 2 hours AND you’ve had a balanced meal prior to playing (about 2-3 hours beforehand) AND the intensity is moderate, you probably don’t need to add any carbohydrates or electrolytes to your water. The research on this is pretty strong - with a recent review (Kenefick et al 2018) stating that there was no difference in performance when athletes replaced fluid loss with either an electrolyte/carb mixture or a placebo (water + other substances to mimic the sports drink taste).
If, however, you’re training hard or in the midst of a tough match - in other words, the intensity is definitely high - AND the duration is longer than 2 hours, according to research, water simply isn’t enough. Further to that, I’d say that in extreme heat, any practice or match over 1 hour, using a electrolyte/carb mix is warranted (given the intensity is still very high...not the case if it's a basket feeding session). While the research clearly states that it isn’t necessary to supplement unless an athlete has met the aforementioned duration criteria, in my experiences (both as a player and coach), when the weather is +30 C or greater, humidity is a factor and you’re working hard, water alone just doesn’t cut it (believe me I’ve been there).
How much of a carbohydrate solution should we add? Probably less than what you’re used to...but let’s find out.
Combining low intensity sessions with high doses of sports drinks is where most players (and their parents) get it wrong. The reality is, most juniors aren’t able to reach intensities that are high enough to warrant a sports drink supplement. Yet we’ve all seen it before, young players chugging down blue Gatorade after barely breaking a sweat.
The research suggests that a ~6% carbohydrate solution is adequate in terms of blood glucose needs during exercise. In practice, here’s what that looks like - in a 500mL water, you’ll need about 25-30g of carbohydrate solution. Most sports drink powders have 30g of glucose per 1 scoop.
From personal experience, I suggest a less concentrated mix for pre-pubescents (3-5%) because as we mentioned, they just can’t reach the same intensities as teens and adults.
4 Side Notes on Water vs Sugary Drinks for Tennis Kids
Unless your child is playing in a highly-competitive/intense tennis program or academy (i.e. recreational tennis), water is more than enough during pretty much all conditions.
Kids and teens of all ages should limit the amount of sugary drinks they consume (including fruit juice) to almost nothing (unless training/competing within the criteria we mentioned above)! Especially if that juice is from concentrate - freshly squeezed juice, on occasion, is ok. And don’t get me started on soda!
While you may be able to make your own homemade electrolyte/carb drink, it likely won’t have the same effect if you use fruit juice. Fruits contain the sugar fructose which compared to sugars found in sports drinks (glucose, sucrose, malactose etc.) are oxidized at a slower rate - in other words, they won’t be as readily available in the blood stream. Baker et al (2015) do suggest that ultra endurance sports (which a 5-set tennis match might qualify for OR multiple matches in 1 day), may require a 2:1 ratio of glucose:fructose - i.e. a mix of fast and slow oxidizing carbohydrates.
You’ll get enough fructose from real fruit - either in-match or between matches. Again, no juice required.
How Much Fluid do I Need?
While supplementing with a glucose sports drink is dependant on many factors we’ve outlined above, consuming fluid itself (i.e. fresh, clean water) is an absolute MUST.
Currently, there’s a debate in the scientific literature as to what strategy works best, replenishing fluids based on the thirst mechanism (aka drinking ‘ad libitum’) or using a predetermined fluid replacement program. Here’s a look at the 2 strategies and why a predetermined program is advised.
Drinking Ad Libitum (I.e. 'when thirsty')
Here’s my initial problem with ‘I drink when I’m thirsty’ angle. Firstly, the evidence has repeatedly shown that aerobic and anaerobic performance is impaired with as little as a 2% drop in body mass due to fluid loss (1.5kg for a 75kg person). Skill and cognitive performance aren’t far behind - both also decrease as a result of dehydration (interestingly, strength & power activities, according to the research, don’t seem to be as affected; but based on anecdotal experience, I would disagree here).
Let’s go back to our problem. Greenleaf et al (1996) reported that during exercise, when drinking ad libitum, subjects only replenished on average about half of their fluid loss. This occured in both hot and cool environments - i.e. the temperature wasn’t a factor. Basically, during intense activity, our thirst mechanism isn’t very good. During periods of low/no activity, it’ll keep us within an acceptable range of hydration, but during exercise, it’s another story. According to Kenefick (2018), here’s why:
“...the mechanisms that stimulate the sensation of thirst are subject to numerous influences and sensitivity to these signals during exercise is likely different given the physiological state during activity (elevated heart rate and respiration; decrease in renal blood flow and plasma volume; elevation in anti-diuretic and other fluid regulatory hormones, etc.) compared to rest.”
In other words, our physiological state changes during intense activity vs rest (kind of a no-brainer). Oh and another thing - children and elderly are MORE at risk - both populations seem to have reduced sensitivity to thirst during exercising conditions compared to 'healthy' adults.
Another issue here is that the feeling of thirst is generally alleviated before fluid replenishment is achieved. We’ve all been there on the tennis court - drink a bit on change-overs because we’re thirsty from long and challenging points - but have we done an adequate job of rehydrating? Is our performance still being optimized?
Predetermined Fluid Intake
The other option players have is to consume a set amount of fluids on a regular basis. According to research, this is more effective than simply drinking when thirsty (because of the various reasons we mentioned above).
Remember, there’s no time clock in tennis - meaning that certain games can last longer than others. A range rather than a concrete amount is likely best when determining a fluid replacement plan.
The folks at Precision Nutrition (PN) recommend consuming ~250mL every 15 minutes - which may account for 2 change-overs (4 games). As an example, if a set goes 7-5 (12 total games), players will need about 750mL of fluids. This is just a suggestion as many factors can influence this number - from age, height/weight of the athlete, sweat rate, absorption rate etc. But it’s a good place to start. So it looks like you’ll need over 2 L of fluids for a 3 set match. This of course is based on the notion that you’re well hydrated before hitting the courts to begin with...our next point of discussion.
Hydration Doesn’t Start and End with Activity
It’s imperative that elite players have hydration strategies in place beyond the time they spend on court or in the gym. It’s funny how many players ask me about supplements and other advanced performance strategies but they don’t even have a handle on their hydration! It’s like the beginner who wants to play like a pro without learning the basics of hitting the ball in the centre of the racquet!
In any case, outside of intense activity, the recommended water intake is about 3 L per day - 1 of those coming from food sources and the other 2 from liquids. This again is a generalization and will be higher or lower depending on each individual (but a good frame of reference nonetheless). Further to that, before sport, PN advises athletes to consume around 500 mL of water at least 30min prior to starting.
As for replenishing fluids post-match. This can be a tricky situation given the large discrepancies in fluid loss from one athlete to the next. PN suggests that athletes consume between 500mL and 1L every hour after training/competing. But if you’ve been out in the heat and need to rapidly rehydrate, this intake can increase to as much as 1.5 L per hour.
Post-training/matchplay; you’ll have to do more than replenish water if you want to absorb your fluids. Have you ever finished playing, chugged water and had the urge to urinate (badly)? This is a sign that you’ve depleted both your sodium and carbohydrate stores. Both must be replenished, otherwise recovery will be delayed. In terms of a carbohydrate solution, the concentration can be higher immediately post-training (as long as the intensity was high...this is always key!) - about 10-12% is sufficient. This can either be in the form of a sports drink or a supershake - I prefer that latter as it aids in protein re-synthesis and adds a number of other nutrients (but more on optimizing post-match recovery in another post).
Lastly, a simple and effective way to gauge hydration is to monitor urine colour. Below is a table that can be helpful (this method has been proven in research studies to be both valid and reliable).
Beyond Health, Why are Fluid Needs so Vital?
Hydration Status and Physical Performance
A 2014 study by Brink et al reported that when a match does not exceed 2 hours in length, balanced meals are taken between matches and when hydration during matches is adequate, there’s no significant decreases in physical performance of the lower-limbs (measured via a variety of performance tests; 20m sprint, vertical jump etc.).
I do have a number of issues with this study, however. First, the matches were simulated - in other words, the subjects weren’t involved in an actual tennis tournament. We know that competition intensity is ALWAYS higher than practice intensity - and thus guaranteed to be higher than an ‘artificial’ condition. The question I bear to ask is...were these players giving it their absolute all on every point?
Second, matches were played on an indoor court. Most tennis tournaments are played outdoors in rather hot conditions. Heat increases sweat rates, perceived exertion levels and has been reported to augment muscle damage to greater degrees compared to normal temperatures. This may seem obvious but it has to be accounted for.
Lastly, how many matches are longer than 2 hours? In competitive scenarios, many extend beyond this number.
As an interesting side note, the same results were not true of the upper-limbs. According to the authors, the triceps brachii had a higher index of fatigue rating in the placebo group compared to the control group. This was an indication that the upper-limbs were more inclined to fatigue when sports drink supplementation pre, during and post match were NOT administered. Strange but intriguing...
If you take a close look at the literature on intermittent sports and hydration, you’ll see an overwhelming benefit to carb ingestion when compared to a placebo (this isn’t always the case in tennis specific research...likely due to testing procedures).
For instance, a recent review (Baker et al 2015) revealed that soccer players performing a treadmill test that simulated a match, who ingested carbs before and during half-time, had a significantly longer time to exhaustion (49% to be exact) and covered more distance (+1.12km). In youth athletes, the story is quite similar - with pre and during exercise ingestion allowing for greater time to exhaustion and greater running distance.
While there are studies that don't agree with this research, when it comes to the intermittent (repeat sprint) sports, they are few and far between.
Does Hydration Influence Skill Performance?
What about skill? This topic is a bit more controversial (and debatable). For instance, in a review by Russell and Kingsley (2014), 6 of 8 studies on soccer found an association with skill improvement (at least one aspect of skill), when a fast-oxidizing carb solution was taken. Another study found that soccer shot speed decreased by only 5% vs 10% when carbs were ingested compared to a placebo.
That said, many others have found no difference in skill when comparing a placebo to a carb solution. In tennis, there was no impact on shot quality between carbs and no carbs. But, during the final stages of a match (post the 2 hour mark), there was a 3-7% improvement in defensive rallies, stroke quality and serves when 50g/h of carbs were taken (according to the review).
The problem with these tennis studies is the there isn’t a consistent measuring procedure. Some studies use ball machines, others simulate matchplay, while some look at retrospective results to determine associations. A more standardized protocol is warranted.
Furthermore, when it comes to skill, is the decrease in performance due to the muscle not firing well (peripheral fatigue) or something to do with cognition (central fatigue)? Or perhaps a combination of the two? We don’t have the means to make these conclusions...yet. I do believe, however, that there’s an interplay between the muscles ability to clear metabolites AND some sort of decrease in reaction/response time (due to fatigue). In either case, supplementation, in my earnest opinion, should improve both aspects. At minimum, the degradation in both physical and skill perfomance should be slower and less abrupt.
Conclusions and Recommendations
I’d like to talk more about these strategies in future posts, but just to be clear, if your diet isn’t covering the basics well to begin with, advanced strategies won’t help much. And hydration is one of those basics. Did you know that the majority of the american population is in a constant state of mild dehydration? I hope that’s not you.
So before we hark on a kid because of his ‘effort’ or that he doesn’t have any ‘jump’ or he’s not listening to instructions and must have attentional problems - perhaps we should look into his drinking habits. It’s not enough to simply drink during tennis. Hydration is an around the clock process.
If you’re someone who only trains/exercises at a moderate intensity, for a relatively short period of time (less than 90 min) and in normal/cool conditions (like an indoor court or AC regulated gym), drinking when you feel thirsty is likely enough. But at the elite levels you're looking for that extra edge in performance. So if you train hard, for more than 90 minutes at a time, under a variety of unpredictable conditions, you'll have to take your fluid needs just as seriously as your training needs.
One small note, ALWAYS test products and fluid replacement strategies during training sessions first! The last thing you want during a competitive event are surprises (indigestion, low blood sugar, allergies, cramping etc).
Below are some general recommendations for players based on the info that was presented in this post (especially for those training/competing in hot environments):
- ~2L of water a day (not including food sources, which provide about 1L, for a total of 3L)
- 500mL of fluid 30min before
- A balanced meal - including appropriate portions of carbs, proteins and fats - 2-3h prior to play
- Fluid AND electrolyte replacement is key
- Consume 250mL every 15min (depends on body size, temperature, environment and training intensity)
- ~6% carbohydrate + electrolyte; if intensity and duration criteria are met
- If playing more than 3 hours per day, a 2:1 glucose:fructose mix is warranted (adding additional fruits between training sessions and/or matches should be sufficient)
- ~1L of fluid intake combined with a 10-12% carbohydrate + electrolyte solution
- Add a mix of nutrients - proteins, fats - to get the most out of your recovery
- Within the first 15-30min is ideal, especially if you’re playing another match on the same day (even on a subsequent day)
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