I need things to be kept as simply as possible. And I am not ashamed of it.


In my dealings with the world of nutrition this often becomes a problem for me. As Beth Mansfield, one of Canada’s leading sports nutrition dietitian, has been known to quip: “Nutrition is not rocket science… it’s much more complicated”. That’s why I’m relatively proud of myself (if I may say so) for coming up with the following table whose purpose is to answer the question as to whether or not a person needs to be concerned about nutrition during his/her physical activity:


Is my physical activity…                >1 Hour in Length?              <1 Hour in Length?

Performance based?                                 YES!!!                                        No

Not Performance based?                         Possibly                                   NO!!!


One question in this table asks you about time i.e. how long will you be physically active? I’ve used the cut-off of greater or less than 1 hour but of course in reality time exists on a continuum i.e. nutrition will play a far bigger role if your activity is 5 hours than if it is just 70 minutes. Nevertheless 1 hour represents a fairly reasonable marker where the evidence shows us nutrition begins to become more relevant in optimizing exercise performance. Which brings us to the second question in my table: Is this particular bout of physical activity performance based or not? In other words, are you competing to try and post a best-ever time, or even win some event? Or is the nature of this particular bout of physical activity to simply elicit a training effect i.e. will you be happy just for getting this particular workout in?


Here’s a little more insight into each of the four scenarios, starting with those with the most definitive answers:


#1) Activity that is >1 Hour in Length and Performance Based:

This is the quintessential situation where nutrition plays an important role optimizing exercise performance. Examples include competing in a marathon or triathlon. The 2009 position joint position stand of the American College of Sports Medicine, American Dietetics Association and Dietitians of Canada tells us that there are three key nutrients that may be limiting in exercise of this nature: carbohydrates, fluid and electrolytes (most specifically sodium).


#2) Activity that is <1 Hour in Length and Not Performance Based:

The classic example here is the average gym-goer trying to squeeze a workout into his/her busy day. Maybe he is going to run on the treadmill for an hour before work. Or maybe she’s booked a session with a personal trainer. In these situations the exerciser is less concerned with “performing” and really more concerned with just getting in a bout of exercise for the day. There’s absolutely no reason to think any kind of nutrition will be necessary during such workouts. On the contrary, in a world with an obesity epidemic, a message promoting intaking extra nutrition during such activities might even do more harm than good.


#3) Activity that is <1 Hour in Length and Performance Based:

The best example I can give you is a personal one: every year I do the Toronto Zoo 10K run. Last year I ran it in 43 minutes and 21 seconds. My goal this year is to better that mark. So when the gun goes off on September 21, 2013, will nutrition be something I need to worry about? Probably not. There simply isn’t enough time for it to become a factor. The chances of me becoming dehydrated or losing too much muscle glycogen are extremely small during an event of this type. Of course, that assumes my nutrition was good in the days and weeks leading up to the race. But that’s a whole other enormous topic!


#4) Activity that is >1 Hour in Length and Not Performance Based:

In the table I’ve answered that nutrition will “possibly” become important in this scenario. Quite frankly it depends on how long you’ll be exercising. Say someone is in training for a marathon or a half marathon. The cornerstone of such training is the “long run” which will likely exceed the one hour mark. But what if the workout takes exactly 90 minutes or even 2 hours? I might suggest there are possible beneficial training adaptations to be gained by doing such workouts without any nutritional aid. Of course this is a general statement and I might give more personalized advice depending on the situation i.e. particularly if it was a hot day and dehydration was a concern then taking along a bottle of water might be a good idea. Another example that falls into this category is going out into the country for a lengthy hike or mountain bike ride. Some dedicated souls do this for 3-4 hours on a weekend! Even though there is no performance aspect to such activity, the sheer length of time means you’ll probably need to consider nutrition to make the most of your day. Fluids and trail mix are a great option.


When Does Nutrition During Activity Become Important?

by Denis Collier, RD

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