Fluid replacement: sports drinks

Are sports drinks suitable for interval workouts as well?

By now, you know the familiar sports-drink story. If you’re going to be exercising continuously for an hour or more, quaffing a sports drink will help you perform better. Ten ounces of the stuff 10 minutes before you start – and then five to six ounces (ie, regular swallows) every 15 minutes as you move along – will keep you well hydrated and push enough carbohydrate to your muscles to help you maintain your pace, even as your leg muscles start to run low on glycogen.

That one-hour threshold has – until now – been a pretty firm one. Exercise for less than one hour and your muscles don’t run low enough on glycogen to be assisted by the carbohydrate in a sports drink. Train or race for over an hour and the sports-drink carbos can be a welcome source of additional fuel. What could be easier to remember?

However, notice that this sports-drink rule does not take into account the type of exercise actually carried out. That has seemed a bit odd to many athletes. After all, running, cycling, or swimming at a hard intensity ‘burns up’ leg-muscle glycogen at a considerably higher rate, compared to exercising easily, yet in both cases you wouldn’t reach for the sports drink bottle unless you were going to be out for 60 minutes or more.

Basically, the 60-minute rule creates a somewhat paradoxical situation: if you were going to exercise fairly modestly for 70 minutes or so, you would take in sports drink along the way, even though your leg muscles might still be richly endowed with glycogen at the end of your effort. On the other hand, if you were going to work intensely for 50 to 55 minutes, you wouldn’t imbibe any sports beverage at all, even though your glycogen gauge might be drawing significantly close to ‘E’ (ie, close enough to slow you down) near the end of your exertion – because of your hard pace, and therefore greater rate of glycogen degradation.

Sports drinks during intervals?
In addition, many exercise scientists have wondered what to do about interval workouts. For example, if you were running a series of 1200- to 1600-metre intervals at breakneck pace (and thus burning up glycogen at high rates), and also jogging between intervals (breaking down even more glycogen), and adding your total carbohydrate consumption during the intervals and recoveries to the glycogen expense of your two- to three-mile warm-up, it’s conceivable that you could become very fatigued in 45 minutes (or less) because of reduced muscle-glycogen concentrations. Would taking in some sports drink increase your ability to make the last intervals of your workout as high-quality as the first ones, simply because more fuel would be available to your leg muscles? Could sports drinks also help you when you carry out high numbers of hill reps? When you sizzle through several speed-strength circuits? Or, are sports drinks just for sustained, fairly prolonged exercise?

Fortunately, some recent research helps to answer these questions. In work carried out at the University of South Carolina, scientists asked seven physically active women and nine physically active men to take part in two rigorous interval workouts – once while ingesting a sports drink and on another occasion while taking in a placebo beverage (flavored water which tasted like sports drink but contained no carbohydrates).

The workout proceeded as follows: subjects warmed up by pedalling easily (at around 70% VO2max) on exercise bikes for five minutes and then begin alternating one-minute work intervals at close to maximal intensity (120 to 130% VO2max) with three-minute recovery intervals. Heart rate rocketed to 175 to 182 beats per minute during the work intervals but mellowed to 120 to 132 bpm during recoveries. Every 20 minutes during the session, the athletes took in seven to nine ounces of Gatorade or (on another occasion) a placebo which was indistinguishable from Gatorade but contained no carbohydrate. The participants were allowed to continue working until they were no longer able to sustain the required intensity of 120-130% VO2max during a one-minute work interval (or until they voluntarily ‘gave up’ because of profound fatigue).

Did Gatorade help?
The Gatorade provided a rather amazing boost to workout quality. With the placebo, men and women were able to complete just 14 one-minute work intervals before falling prey to fatigue, but with Gatorade the men lasted for 22 high-quality intervals and the women hung in for 21! Not surprisingly, the subjects reported lower ratings of perceived exertion when using the sports drink (the intervals, although at the same intensity and heart rate in both cases, felt significantly easier when the sports drink was utilized). To put it simply and accurately, the sports drink helped the athletes get a better workout, one which contained a greater quantity of intense work.

Is this true only for cycling, or would sports drinks also help interval-training runners? In a separate study carried out at the University of Loughborough in the UK, runners who imbibed a sports drink expanded performance by about 33 per cent during an interval workout, compared to using a placebo. One of the scientists involved in this work was the venerable Clyde Williams, who during his career has made a major contribution to our understanding of appropriate sports-drink usage during exercise and optimal carbohydrate intake during heavy-duty training.

A very nice feature of the South Carolina study was the inclusion of women, who are rather rudely and routinely excluded from much training research. Various studies have suggested that women burn more fat and less carbohydrate during workouts, compared to men, in which case one might expect that females would have less need for sports drink during exercise (if they truly were less reliant on carbohydrate, they would clearly benefit less from taking in the carbohydrate in a sports drink, compared to just sipping a placebo or pure water during exertion). However, the female athletes’ improvements in performance with the sports drink were identical to the gains made by male athletes, indicating that women profit from sports-drink usage just as much as men do.

Roller-coaster glucose?
One still routinely hears that sports-drink imbibing will lead to peaks and valleys of blood glucose and insulin during exercise, potentially hurting performance. However, this naysaying ignores the simple fact that such roller-coasting is blunted by the exercise process itself. The truth is that you usually don’t have to worry about peaks and valleys of glucose or insulin if you are going to be running, cycling, or swimming. The only caution is that if you take in a mass of carbohydrate 60 to 75 minutes before exercise begins, you might be at a blood-glucose low point when you begin your exercise. That’s why it’s best to eat your pre-race or pre-workout meal a couple of hours before you start to exercise – and drink your first bolus of sports drink 10 minutes before your exercise starts. If you do so, you won’t have to worry about plunging glucose levels.

One also occasionally hears, particularly from the purveyors of the 40-30-30 ‘Zone’ diet or similar nutritional oddities, that insulin is a bad thing for the endurance athlete (supposedly because of its slow-down effect on fat metabolism). However, insulin levels were highest in the South Carolina research when the athletes took in sports drink, not placebo. And of course, that is exactly when they performed at their very best.

The bottom line? Sports-drink intake can be useful during interval workouts, as well as during prolonged, sustained exercise. Interval sessions can burn glycogen at high rates, and even if they do not wipe out total muscle glycogen to the same extent as more prolonged efforts, they may still wash away much of the glycogen in fast-twitch muscle fibres, leading to a premature ending to a workout (or an inability to complete the last intervals of a workout at planned pace). The idea here is that your overall muscle-glycogen levels might be in pretty good shape, but if your fast-twitchers are low on fuel, you wouldn’t be able to exercise as intensely as you wanted to.

In addition, even if glycogen wipe-out is not a major cause of fatigue during interval sessions, the high blood-glucose levels which result from sports-drink use may allay mental fatigue during such sessions. Sports drinks can also preserve blood volume and delay dehydration, so there are lots of reasons to use sports drinks during your intervals and reps, and few reasons not to (the primary problem would be gastric discomfort associated with sports-beverage intake, but even if this does occur, it will abate over time as you get used to quaffing the sports drink).

I recommend that you take in about five to 10 ounces of a sports drink like Gatorade before your interval workouts, hill reps, and speed-strength circuits, and also about five normal swallows every 15 minutes as you work out. If you do, chances are good that your legs and your logs (your workout logs, that is) will show off a higher level of performance.

Jim Bledsoe

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