Before I dive into it, movement is an incredibly important aspect of a healthy lifestyle, and I always tell clients to do what you like. It should be enjoyable. As always, nutrition and lifestyle go hand in hand. You can't exercise your way out of a bad diet, but you already knew that.
High Impact Workouts
High impact or high-intensity interval training refers to running, HITT classes, plyometrics boxing, etc. It is one of the most effective ways to burn more calories, which is why it has gained so much popularity. So it makes sense why people would think the more HITT you do, the better. The most well-established benefit of interval training is heart health.
What about fat loss and stress? How does HITT affect those areas?
Let's first quickly talk about the fuel used in HITT, running, and other high impact workouts. These workouts are anaerobic (without oxygen for fuel)… more on this later.
The Duration & Frequency of High Impact Training
You know the saying too much of a good thing, right? Studies show there is a fine line when it comes to things like HITT and running in regards to how long and how frequent they should be done.
Stress and Weight Gain
Too much HITT can lead to adrenal dysfunction (HPA axis dysfunction), which can lead to chronic cortisol. Say what? The body sees this as a stressor, and the adrenal glands, which manage stress, respond by sending out a host of hormones, including cortisol. Studies show chronic cortisol leads to rapid muscle breakdown, increased belly fat, sugar cravings, and can eventually lead to insulin resistance.
Increased cortisol is linked to an increase in fat gain. Period. It also messes with hunger hormones causing you to feel like a bottomless pit. Oh, and since cortisol spikes blood sugar, it also causes carb and sugar cravings.
Why isn't the scale moving?
Yes, muscle weighs more than fat, but if you find your stubborn areas aren't budging, you may want to re-think your current routine. Are you doing too much HITT? Are the classes over 30 minutes? Are you doing them back to back? How do you feel after? This is the most important: How do you feel after? Everyone is different.
I'm guilty of this too because we often allow our apple watch to dictate "how good" a workout actually is. If you feel exhausted and beat up after and feel like a bottomless pit all day long, maybe that's your body's way of saying it's time to slow down.
Cortisol 101
Basically, cortisol can cause a host of issues when chronic, including weight gain and muscle wasting. Click here if you want to read more on how cortisol is linked to weight gain.
So How Much Is Too Much?
According to some experts, intense workouts more than once a day and several days a week, especially back to back, can leave cortisol levels elevated. Studies show the sweet spot for HITT is 30 minutes or less. So less really is more. Why do an hour class when you can knock it out in 30 mins and have improved benefits? Read this study if you want to learn more, and this one.
Hey, ladies, there is something called the female athlete triad (the triad). It's an interconnection of menstrual dysfunction, low energy availability, and decreased bone mineral density. I have so many clients who have lost their period or have very irregular cycles, with over-training being the main cause. The body NEEDS reset and repair.
Verdict: Yes, HITT and running are 100% part of a healthy lifestyle, but overdoing it will result in physiological responses and it's not always a positive one.
Low Impact Workouts
Yoga, barre, walking, pilates…you hear those exercises and think great, those are for "rest days" but those won't get me the results I want.
Not so fast. At low intensities, a higher amount of fat is used as energy (though carbohydrates are always being used). Still, as exercise intensity increases from low to moderate/high intensity, the use of fat as fuel decreases, and carbohydrates are used as the primary fuel source. Why? There is more oxygen available. The more oxygen available the easier it is to use fat for fuel. Just so we're on the same page, your body can burns fat after exercises like HITT; however, it is when we over due long exercises. We're left inflamed and even bloated. Why? C-O-R-T-I-S-O-L. This is where balance comes in!
Here's a study where a group of researchers had participants exercise at 25%, 65%, and 85% of their V02 max, and tracked what fuel (fat and carbohydrates) sources their body utilized during this time. At moderate intensities (65%), there is an increased demand for muscle glycogen and muscle triglycerides (fat). At high intensities (85%), the body runs almost solely on an increased uptake of glucose from the blood and from muscle glycogen (stored carbs). If you are training at low intensity, you utilize mostly free fatty acids. So basically, as the intensity in exercise increases, your body needs more energy and increases the amount of carbohydrates used.
High intense = burning stored carbs for fuel
Low intense= burning stored fat for fuel
So is low intensity the best for fat loss? Yes and no. Lower impact certainly has less of an impact on cortisol which in turn increases fat loss. High intense can lead to weight-loss, too, BUT, if you find that is all you're doing and not seeing results, try doing less.
Side note: most you reading this are not elite athletes, so the notion of getting in carbs ASAP after a workout is really not needed. With athletes, they need to restore glycogen stores soon after as they most likely will have another training session and or game. Having a balanced with carbs like sweet potatoes with healthy proteins within two hours after a training session is a good idea, especially if you worked out in a fasted state. What about protein? Yes, if you worked out in a fasted state.
Several studies here, here and here all found lower impact workouts such as a brisk walk or a light jog is essential for visceral fat (midsection) reduction. Things like yoga and pilates can build strength and muscle. Muscle dictates metabolism and improves blood sugar regulation. I love some weight lifting, too!
Let’s talk about the benefits of a low-intensity steady state (LISS). It's essentially a low-intensity cardio workout, lasting anywhere from 30 to 60 minutes, and has been shown to increase fat loss. It is the exact opposite of HITT. Research has shown that LISS cardio may help burn fat more effectively than higher-intensity workouts. According to this study, many seem to find these workouts more enjoyable than a grueling HITT class. Taking a gentler approach to fitness is more likely to result in a sustained routine that will take you closer to your goals. LISS is a more sustainable workout with less chance of burnout. Examples of LISS: fast-paced walking, walking on an incline, biking with low resistance, pilates, barre, mega reformer, swimming, and other cardio activities that require low-intensity exercise.
Circadian Rhythm
It is the 24-hour cycle your body follows each day. It governs how awake and how tired we feel. The best way to support and enhance your circadian rhythm is to work out in the morning. This will improve your cortisol awakening response, which will improve energy levels throughout the day and can aid in sleep. The more awake you feel in the morning, the more tired you'll feel at night.
If you can't work out in the morning, skip the high impact at night. Go for low impact. We don't want cortisol high at night as it can impede sleep and have you feeling like a bottomless pit.
Men vs. Women
There are thousands of articles and studies out there highlighting the many benefits of high impact workouts. However, many of these studies include only men, or men and postmenopausal women. Women in their reproductive years have varying levels of cortisol during each phase of the cycle, so it's important not to overdo it.
Takeaways
A few things to consider:
Everyone will be different, so take what you can from this, and above all do what you enjoy! Mix it up!
Don't fear running or HITT or any other high impact exercises, just be sure to vary your workouts. Adjusted workouts!
Walking is an incredibly powerful type of movement for fat loss and cortisol balance. I talk more about here. I start and end every day with a walk.
If you're stressed out and combating stress with a grueling workout, and find yourself tossing and turning at night, you might want to slow down.
Still not convinced low impact can help you meet your goals? This study compared two groups, with one group partaking in low-intensity workouts and the other in high intensity. The low-intensity exercise group lost 37% more weight and burned almost twice as much fat than the high-intensity group.
Lastly, don’t underestimate the art of doing less. When it comes to increasing fat loss and improving energy levels, it’s all about our hormones. Belly fat is directly linked to cortisol and increased belly fat - aka visceral fat - increases your risk for serious diseases.
My Fav at Home Workouts: