High-intensity interval training has taken the fitness world by storm – and why not? If you’re looking for a time expedient way to boost your heart rate and improve your body composition, high-intensity interval training (HIIT) is your answer. Because HIIT routines are shorter in duration and you can vary the exercises you do during a HIIT workout, they’re anything but boring and monotonous. Plus, there’s little doubt that HIIT training offers substantial health and fitness benefits.
Health Benefits of High-Intensity Interval Training
Just recently, a new study further highlighted the benefits of HIIT training. This research, a meta-analysis of a number of studies, showed high-intensity interval training may be better for weight loss and controlling blood sugar levels in diabetics than moderate-intensity cardio. This adds to a growing body of research extolling the health benefits of high-intensity interval training.
Research even suggests HIIT training, being a vigorous type of exercise, is more beneficial for heart health than moderate-intensity exercise. In one study, high-intensity exercise led to greater improvements in aerobic capacity, diastolic blood pressure, and better blood glucose control compared to moderate-intensity exercise.
Now you know why HIIT training should be part of your routine, as long as you’re healthy and have built up a certain degree of fitness, but how should you fuel up beforehand?
The Role Nutrition Plays in High-Intensity Exercise
Optimizing nutrition is super important if you plan on getting the most out of high-intensity interval training. You’ve probably heard people talk about “training low,” doing cardiovascular exercise in a low-glycogen state. The idea is to enter a cardio workout with low glycogen stores so your body will be forced to burn primarily fat as fuel. To do this, you train first thing in the morning before eating breakfast.
Although the idea of training low is controversial and not all studies show it leads to greater fat loss, it’s NOT the way you want to approach a high-intensity workout. You can sustain moderate intensity exercise for a long period of time using stored fat as fuel. You’re not as dependent on stored glycogen to fuel your workout.
Not so with high-intensity exercise. As the intensity of exercise increases, your body becomes more reliant on stored glycogen, primarily in muscles, but also liver glycogen, for fuel. That’s because fat oxidation (breakdown of fat to make ATP) is a slow process whereas glycogen can be turned into ATP quickly, making it the preferential, if not necessary, fuel source for muscles contracting vigorously.
How do you keep enough glycogen stored in your muscles and liver to meet the demands of high-intensity exercise? By consuming enough carbohydrates, of course. If you don’t have glycogen stores to tap into during a HIIT workout, your performance will suffer as your muscles don’t have the substrate (glycogen) they need to make ATP quickly enough. Instead, they’re forced to use fat, which means you have to slow the pace of your exercise – and that defeats the purpose, doesn’t it? The pathways that break down carbohydrates for exercise fuel are more efficient and don’t need oxygen whereas pathways that use fat need oxygen, making them much slower.
Does research support the idea that a low carbohydrate diet limits high-intensity exercise performance? In a study published in French National Institute of Sport, trained athletes who reduced the number of carbohydrates they consumed prior to training experienced a bump-up in markers for fat oxidation, suggesting their body was using fat stores for energy, BUT their performance greatly suffered. A carb-depleted diet typically isn’t conducive to successful high-intensity interval training.
The goal of high-intensity exercise is to push hard during the active intervals and then partially recover so you can ramp up the intensity again. Yes, you’re using mostly carbohydrates (glycogen) as fuel, but your body burns more fat during the recovery period due to the after-burn you get with high-intensity exercise. Despite the fact that you’re not primarily oxidizing fat DURING high-intensity exercise, a HIIT workout boosts fat burning AFTERWARDS. That’s why high-intensity exercise is effective for fat loss.
Maximizing Nutrition for HIIT Training
To get the most out of a HIIT workout, you need to have sufficient glycogen stores beforehand. That’s why restricting calories excessively or eating a very low carbohydrate diet isn’t optimal if you do HIIT training. According to ACE Fitness, along with eating a healthy diet that contains sufficient fiber-rich carbohydrates, you should consume a high-carbohydrate meal with protein 3 to 4 hours prior to a high-intensity workout. Follow up with a carbohydrate snack an hour before beginning a HIIT workout.
As you know, HIIT training places significant stress on your body. That’s why recovery nutrition is critical as well. Not only do you need to replenish your muscle’s glycogen stores, but you need to give your muscles the building blocks they need for repair. According to research published on ACE Fitness, the ideal post-workout snack is one with a 3 to 1 ratio of carbohydrates to protein. Plus, you want to enjoy that snack within 30 minutes to an hour after your workout when your muscles are most in need of nutritional reinforcement. Of course, your body also needs rest, so don’t do a high-intensity interval workout every day. Twice a week is enough to get the benefits if you push yourself hard during each session. With HIIT training, it’s not how LONG you work but how hard.
The Bottom Line
High-intensity interval training is a fun and effective way to improve your fitness level, body composition, and health, but make sure you’re consuming enough carbohydrates and calories beforehand. Anytime you do very intense exercise, you need adequate glycogen stores or your performance may suffer. Fuel up right and maximize your performance.
Science News. “High-intensity interval training has great gains — and pain”
Medical Daily. “High-Intensity Interval Training More Effective, Efficient Than Traditional Exercise For Weight Loss Or Managing Diabetes”
SupperVersity – Nutrition and Exercise Science for Everyone. “Carbohydrates Timing Boosts Training Effect”
The American Journal of Cardiology (Impact Factor: 3.28). 02/2006; 97(1):141-7.
ACE. “Pre and Post-Workout Nutrition for High-Intensity Interval Training”
Exercise Physiology: Theory and Application to Fitness and Performance. by Scott Powers, Edward Howley. (2011)
Fat Facts. Len Kravitz, Ph.D.
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