HIIT v. LISS exercise: Effects on metabolism and weight management

If your goal is to add more cardiovascular exercise (cardio) to your fitness routine, you’ve probably heard about HIIT and LISS as different methods of cardio. 

HIIT has you work through short bursts of high-intensity exercise followed by periods of rest, and LISS cardio consists of longer periods of less-demanding work. 

While both types of exercise can help improve your health and overall fitness, they differ in how they impact heart rate, hormones, glucose, and more. Whichever form of cardio you decide to incorporate into your fitness routine depends on your personal preferences and health goals. 

Below, we break down the biggest differences between HIIT and LISS and how they can fit into your lifestyle.

What are HIIT and LISS? 

HIIT 

High-intensity interval training (HIIT) is a style of cardiovascular exercise where you alternate short periods of intense anaerobic exercise with less intense recovery periods.¹ Typically, HIIT sessions are short and range from 10 to 30 minutes in total. 

The key to HIIT is really pushing yourself and giving it your all during the “on” periods.  

“The main mistake I see with HIIT training is that people are not truly doing HIIT if they are not pushing at least 80% of their maximum heart rate,” says personal trainer and coach Sana Shirvani, CFSC-certified functional strength coach and EXOS-certified performance coach.  

“This is considered a heart rate zone where you should struggle to hold a sentence as you should be exerting a lot of effort.” 

These intense efforts are interspersed with periods of rest or lower-intensity exercise for recovery or complete rest. The ratio between high- and low-intensity can vary depending on your goals, but common work to rest ratios include 1:1, 1:2, or even 1:3, depending on your fitness level and the workout's intensity. For example, you might try 10 intervals of a 60 second sprint followed by 60 seconds of rest. 

You can apply HIIT to running, cycling, stair climbing, and other cardio exercises. You can also combine HIIT style training with weightlifting, which has additional benefits. 

LISS   

Low-intensity steady state (LISS) cardio generally involves longer durations of activity (think: 25 to 60 minutes) performed at a consistent low-to-moderate intensity. This is usually between 60 and 70% of your maximum heart rate, also known as your zone 2 heart rate. You should be able to hold a conversation at this pace.   

Examples of LISS include brisk walking, light jogging, biking, hiking, and swimming. 

Both HIIT and LISS training improve your cardiometabolic health and can aid in fat loss.^2,3 In addition to each of these methods of exercise burning calories overall, you are training your body to burn fat more efficiently as a fuel source.    

Benefits of HIIT vs LISS 

Let’s see how these two forms of exercise compare when it comes to their health benefits. 

Effects on blood glucose 

Both HIIT and LISS improve glucose regulation, although you may notice differences in your glucose levels in the short term surrounding each of these sessions.  

HIIT 

HIIT workouts may cause glucose levels to spike in the short term because your body requires more fuel during intense exercise and uses glucose as the fastest source of energy. These spikes initiated from muscles contracting are not a cause for concern as the muscles need the fuel, and this pathway allows glucose uptake without a rush of insulin.⁴ 

“The body responds by releasing glucose stored in the liver and muscles as glycogen, so this process will increase the amount of glucose in the bloodstream,” Shirvani explains. This is why you may see a spike during intense exercise if you wear a continuous glucose monitor (CGM), such as Lingo, to track your glucose.  

HIIT can also release stress hormones like adrenaline and cortisol, which can increase glucose levels by signalling the liver to release more glucose.  

This increase in blood glucose may last for an hour or so after exercise, but it varies from person to person. Glucose will eventually return to the normal range with the help of both insulin and the muscle contraction pathway working to lower blood glucose levels and restore glycogen in muscles.   

Even though HIIT can cause a temporary rise in blood glucose, these types of glucose spikes with exercise are beneficial in the long run. It’s an example of hormesis, which is a short-term stress that enables long-term adaptation. Think: in the same way that exercise spikes your heart rate and blood pressure temporarily but provides heart health benefits in the long run.  

Overall, HIIT can improve insulin sensitivity and glucose regulation, reducing the risk for type 2 diabetes and metabolic syndrome—a group of health conditions that raise your risk of cardiovascular disease and diabetes when combined.⁵ Many people prefer this method of exercise due to its time efficiency and positive effect on body composition, which is discussed more below. 

Remember that the “on” intervals in HIIT should be at least 80% of your maximum heart rate, or zone 4. It’s a hard effort that will leave you out of breath, difficult to talk, and that you’re pushing yourself, but not at your absolute limit.  

LISS 

With LISS cardio, your heart rate is mostly in zone 2 (typically 60–70% of your maximum heart rate), which Shirvani calls her personal favourite. 

“LISS cardio is less likely to cause significant spikes in stress hormones, which means glucose levels are less likely to spike,” Shirvani says. 

If you're tracking your glucose levels with a CGM, you may notice your glucose levels during LISS are steadier, or that engaging in LISS may even blunt a spike from a recent meal. That said, just because you don’t see a glucose spike during LISS activity doesn’t mean it’s necessarily “better” for you than HIIT. As mentioned above, the temporary rise in glucose during HIIT can lead to long-term benefits.  

With LISS cardio in a zone 2 heart rate, it should feel like you’re breathing a bit heavier but not gasping for air. You can still hold a conversation, but it’s more difficult.  

Weight management and fat loss 

Fat loss ultimately comes down to a calorie deficit, which is when your body burns more calories than you consume. 

HIIT burns more calories than LISS in a shorter period of time. However, research shows that both HIIT and LISS are similarly effective in promoting weight loss.⁶ And when it comes to working out, it’s best to choose the exercise that best fits your lifestyle and health and fitness goals. 

For example, some people might benefit from starting with LISS initially before adding in some HIIT. And others might prefer HIIT workouts to save time, but add in longer LISS sessions when their schedule allows like an incline walk on the treadmill or moderate bike ride.  

Recovery time and injury prevention  

Shirvani incorporates LISS with her clients because they can partake more days per week with minimal fatigue. Since HIIT is a more intense activity, it may require more rest between sessions to recover and repair. 

What you enjoy along with your schedule may determine what exercise you add to your routine. Many prefer LISS more days per week, while others with less time to devote to exercise may prefer HIIT sessions on fewer days of the week. 

Whichever you choose, make sure you allow adequate recovery time, as too much too soon can lead to overtraining and increase the risk of injuries. 

Shirvani says overtraining may impact your strength workouts or lead to a plateau.  

While the advantages of exercising significantly outweigh the potential for injury, HIIT has been associated with knee and ankle sprains and strains.⁷  

HIIT is fast-paced, and high intensity functional training sessions can include jumping and plyometric work—exercises that involve rapid stretching and contracting of muscles—which puts more stress on the bones and joints. It’s important to include neuromuscular training (exercises to improve body control) and pre-strengthening programs when engaging in HIIT exercise. 

LISS training, while generally less demanding on the bones and joints than HIIT, can still lead to overuse injuries due to its repetitive nature.⁸ Certain activities like outdoor cycling, hiking, and incline walks on a treadmill come with their own environmental risks like crashing or falling. 

Ultimately, it’s best to choose a type of cardio that works best for your fitness level, goals, and lifestyle, and be mindful to also incorporate rest to avoid overtraining. 

A final note from Lingo 

While both HIIT and LISS have their own perks, it doesn’t mean you have to choose one form of cardio over the other.  

“I believe that incorporating a mix of exercise types, including both LISS and HIIT, can offer comprehensive health benefits," Shirvani says. 

Adding both HIIT and LISS to your workout routine could also make your training plan more interesting, which may help with motivation and long-term commitment. After all, the best form of exercise is the one you’re most likely to stick with—and consistency is key to lasting results. 

Using Lingo can help you see how your workouts are impacting your individual glucose responses and help you make the right decision for your health and fitness goals.  

^ALB-03311