Why exercise intensity MATTERS!

Why exercise intensity MATTERS!

Feb 2022
Why exercise intensity MATTERS!

<text-size-medium>Your legs and lungs are on fire, sweat is pouring down you and there are just a few seconds left of this effort......and DONE! Phew. Then the realisation kicks in, that was only the first(!) interval and you have 5 more to go, aaah sh*t! We have all been here, we didn’t get enough fuel into our bodies today, and now we’re going to pay the price for the rest of the session.<text-size-medium>

So, how come underfueling high intensity exercise really makes you pay the price? There are a LOT of reasons to go into here, so we have picked out some of the key ones that really impact how our body responds to different levels of exercise intensity and why they make us feel the way they do.

During high intensity exercise the first and most obvious change we see (and feel) is our heart rate increasing as we start to work pretty hard. We start to feel hot (blood coming to the surface of the skin aka red face) and sweating to help our bodies get rid of the heat that is being generated by the muscles as they turn fuel into energy approximately 100 times faster than they do when you’re sitting still.

To generate energy this quickly the muscles use carbohydrates that are already stored in the muscle as glycogen, and there are a couple of simple bits of biology that make carbs the most effective fuel for high intensity exercise. Firstly, most of the body's store of carbs is in the muscles (if you’ve eaten correctly, we’ll get to that later), glycogen is stored in between and around the muscle fibers themself, which means that when needed for fuel it is literally right there and ready to go! Second, carbs (glycogen) can be turned into energy with (aerobic), and importantly, without (anaerobic) oxygen fully   available. This is vitally important because in the early stages of high intensity exercise, and if we are working super hard, our body can not get the oxygen into our muscles quick enough to produce energy aerobically at the same rate as we are burning it during exercise. That is also the reason that fat only provides a small amount of energy for high intensity exercise, as fat can only be burned aerobically as a fuel for the muscles. There is always a mix of fats and carbs used to produce energy, but as we crank up the intensity we also crank up the percentage of energy that is generated from carbs, and turn down the contribution from fat.

Smart Fuelling

Because carbs are so important for our workouts, when we don’t have enough to keep us going there can be big problems! As you start to run low on carbs the exercise we are doing begins to feel much harder, this can make it a challenge to hit our goals for a workout, and if we get really low on carbs in the muscle then it can mean that we don’t finish the workout at all! Here is where smart fuelling comes in!

Because different workouts have different demands (type of exercise, intensity, and durations) this means we need different amounts of carbs in our bodies and muscles to match the training we want to do. On days where the workouts are going to be long and hard then topping up our stores of glycogen will help improve our performance and give us the best chance of hitting our training goals. And consistent training leads to better performances.

How can hexis help?

Hexis uses carb coding to match the demands of your life and training to the carbs and energy you are putting in. The goal of carb coding is to deliver the correct amount of fuel to your muscles before a workout so you can achieve your training goals, then to replenish the glycogen stores in time for you to be ready to go again. By doing this we give you the edge your training needs to push to the next level, and feel great doing it too!

Dr. Sam Impey

Performance Scientist

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Dr. Sam Impey