When we engage in high-intensity exercise, our muscles become mini biochemical laboratories, synthesizing compounds like lactate and myokines that circulate throughout the body and travel to our organs, where they exert a variety of signaling effects, including the synthesis of brain-derived neurotrophic factor (BDNF) in the brain. Some of these molecules have anti-cancer properties.

Vigorous exercise is also the most potent way to increase your VO₂ max, also known as cardiorespiratory fitness, which is one of the strongest predictors of longevity. Essentially, the higher your fitness, the longer you’ll live.

High-intensity exercise has certainly received its share of the spotlight, in large part thanks to researchers like Dr. Martin Gibala who has helped to establish the wide-ranging benefits of HIIT on metabolic health, cardiovascular health, and fitness.

Yet the longevity space has recently focused on low-to-moderate intensity aerobic exercise, or so-called zone 2 training, for promoting health and longevity. In contrast to high-intensity exercise, zone 2 training prioritizes fat burning and is performed for a longer duration at a lower heart rate.

Then there are “exercise snacks” and vigorous intermittent lifestyle physical activity or VILPA—which aren’t really exercise in the classic sense. Rather, they’re brief, higher-intensity bouts of physical activity performed several times throughout the day. Even though less research has been devoted to investigating the benefits of exercise snacks and VILPA, they’re consistently associated with better fitness and metabolic health.

All of this begs the question: With so many types of exercise to choose from, what should we be doing to live longer?

The importance of exercise intensity

Before getting into what defines intense exercise, also known as vigorous exercise, it might be helpful to define what is not vigorous exercise.

Moderate-intensity aerobic exercise, sometimes referred to as zone 2 training or aerobic base training, is performed at an intensity below vigorous intensity. It can be sustained for hours and is performed at 60–70% of one’s maximal heart rate or an intensity where one could hold a conversation. Think of zone 2 training as low- to moderate-intensity steady-state exercise that, while effortful, won’t leave you on the floor gasping for air.

Vigorous exercise represents a level of exertion above zone 2 and beyond the lactate threshold. It corresponds to a heart rate at or above 85% of maximal heart rate. However, there are many intensities or training zones included under the umbrella of vigorous exercise.

During vigorous exercise, lactate accumulates at a faster rate than during lower-intensity training. This type of training can only be sustained for a few minutes.

For this reason, vigorous exercise usually takes the form of interval training including HIIT (85+% of maximal heart rate or maximal speed/power output) and sprint interval training or SIT, which involves “all out” efforts or an intensity corresponding to 100% or more of one’s maximal power output or speed associated with VO₂ max. During interval training, hard intervals are separated by brief periods of recovery or low-intensity activity.

One of the allures of HIIT and SIT are their time-efficiency—both can induce potent benefits for metabolic and cardiovascular health in half the time (or less) compared to moderate-intensity training.

The benefits of vigorous exercise on metabolic health

The metabolic benefits of HIIT include:

• Improved triglycerides and glucose regulation
• Increased insulin sensitivity
• Decreased fat mass and improved body composition
• Enhanced mitochondrial function

Furthermore, HIIT outperforms moderate-intensity continuous exercise, leading to greater improvements in:

• Cardiorespiratory fitness (e.g., VO₂ max)
• Systolic and diastolic blood pressure
• High-density lipoproteins
• Triglycerides
• Fasting blood glucose
• Oxidative stress and inflammation
• Appetite-regulating hormones and beta-cell function
• Markers of mitochondrial biogenesis
• Cardiac function

What explains the unique benefits of HIIT?

During high-intensity exercise, our mitochondria and muscles undergo a significant energetic stress—our body can’t keep up with energy production via fat metabolism alone, so our body switches to using glucose and glycogen (glycolysis) for ATP production. In the process of breaking down glucose, lactate is produced. Rather than a toxic byproduct, lactate can be used as a source of energy for the body and the brain.

The lactate shuttle

But that’s not all, lactate is also a potent signaling molecule that allows for cross-talk between our muscles and other organs throughout the body. Among its other signaling effects, lactate increases GLUT4 transporters in skeletal muscle, allowing for a greater amount of glucose uptake. This effect lasts for up to 48 hours, with the first 24 hours representing the most robust period of enhanced glucose control.

High-intensity training also benefits body composition—it reduces fat mass and body fat percentage and increases fat-free mass (i.e., lean body mass). Running and cycling HIIT protocols appear to be the most effective, especially when the following parameters are adhered to:

• Duration: More than 8 weeks of training
• Frequency: At least 3 sessions per week
• Interval structure: Less than 60 seconds per interval with 90 seconds or less of active recovery

HIIT corrects mitochondrial dysfunction in type 2 diabetes

People with type 2 diabetes demonstrate markers of mitochondrial dysfunction, characterized by 40% lower mitochondrial respiration and enlarged, fragmented mitochondria, indicative of mitochondrial damage. These structural and functional changes are correlated with insulin resistance.

High-intensity exercise increases a cellular repair process known as mitophagy—it sends a signal to clear out and recycle damaged or dysfunctional mitochondria. In this way, long-term exercise training leads to more and healthier mitochondria. Mitophagy is a similar process to autophagy, which is enhanced during intermittent fasting or periods of low energy availability. But exercise appears to be a much more robust signal for mitophagy than fasting. In fact, exercise enhances mitophagy whether or not it’s performed in the fasted state.

Mitophagy

HIIT also enhances mitochondrial biogenesis in skeletal muscle in addition to increasing the effectiveness of existing mitochondria. This is the result of the potent effects of lactate, which send a signal to the body to increase mitochondria as an adaptation to produce more energy.

Other metabolic benefits of HIIT occur through increasing a muscle protein called PGC-1α. Higher levels of PGC-1α can improve a muscle's oxygen use, antioxidant defense, and glucose management, and may also protect against muscle loss with aging and reduce inflammation.

Vigorous exercise and longevity

In contrast to the well-researched cardiovascular and metabolic benefits of vigorous exercise, there’s a lot less known about the benefits of intense exercise on mortality risk.

Does frequent HIIT promote the most robust improvements in longevity? Or is low-intensity and long-duration zone 2 training the better option? If we only engage in short, frequent bouts of VILPA or exercise snacks, can we still reduce our risk of disease?

This is hard to answer since it would require performing a head-to-head comparison in large groups of people for several decades. As informative as that would be, it’s not a very feasible research study.

What we have to rely on are reports that establish an association between the types of activities people perform and their risk of dying.

One study published in 2024 suggested that physical activity intensity, rather than volume, appeared to be the main driver of reduced mortality risk among a large group of adults. In fact, when it came to the risk of dying from cardiovascular disease, only physical activity intensity stood out as an important factor—physical activity volume wasn’t associated with a lowering of cardiovascular disease mortality. This sparks an interesting discussion about the relative importance of each exercise intensity for health and longevity.

Intensity outshines volume for mortality

In the study, which analyzed physical activity data from more than 7,500 adults in the United States, the volume and the intensity of physical activity were associated with all-cause mortality risk—engaging in more volume or more intense exercise reduced one’s risk of all-cause mortality. However, the effect of intensity was stronger.

The risk of all-cause mortality was 37.1% lower for participants with levels of high-intensity activity at the midpoint of the population compared to those in the lower 25%. The risk decreased by 19.8% when comparing participants at the midpoint of high-intensity activity to those in the upper 25%.

For physical activity volume, all-cause mortality risk was reduced by 14.4% and 13.7% when comparing the lower 25% to the midpoint and the midpoint to the upper 25% of participants, respectively.

The results for cardiovascular disease mortality revealed something very interesting.

Just like for all-cause mortality, more high-intensity activity was associated with a lower risk of cardiovascular disease mortality—a 41% reduction and a 29.8% reduction when comparing the lower 25% of participants to the midpoint and the midpoint to the upper 25%, respectively.

On the other hand, there was no association between physical activity volume and cardiovascular disease mortality—doing more did not seem to provide a benefit.

Relationship between exercise volume and intensity and all-cause mortality | Schwendinger et al., 2024

Longer activity bouts are beneficial

The importance of intensity for mortality reduction has been established. But how does the pattern of activity factor in?

At any level of intensity, there were greater benefits for all-cause and cardiovascular disease mortality when activity was accumulated in bouts of 5 minutes or more compared to shorter bouts.

Let’s take a minute to put this into perspective. Let’s say that you engage in 30 minutes of high-intensity activity per day. You’re much better off (from a mortality perspective) doing three 10-minute activity bouts than ten 3-minute bouts.

Yet again, the pattern or fragmentation of physical activity didn’t appear to be as important for volume: Activity bout length was not significantly associated with all-cause or cardiovascular disease mortality. There was no difference in the benefits of doing more low- and moderate-intensity exercise in bouts of 5 minutes or less or more than 5 minutes.

HIIT it to live long

There’s an easy way to explain these results if we think about the myriad benefits of vigorous exercise—it’s overall better for improving blood lipids, glucose regulation, cardiac function, and inflammation and oxidative stress compared to less-intense exercise. So even though exercise volume is important, exercise intensity is what really leads to physiological improvements that can enhance health and longevity.

This is especially apparent when it comes to the heart and might explain why, at least in this study, exercise intensity, but not volume, was associated with a lower cardiovascular disease risk.

If you’re not exercising hard enough to stress your heart, muscles, and brain, it doesn’t matter how much you do after a certain point.

According to this study, all of your vigorous exercise should be completed in bouts of 5 minutes or more. But that doesn’t mean there are no benefits to engaging in shorter bouts.

That’s because of the strong evidence in favor of VILPA (remember that VILPA refers to ~1–2 minute bouts of vigorous activity done as part of daily life) for reducing mortality risk. Just 3 VILPA bouts per day reduces all-cause mortality by up to 40%. This inconsistency might just reflect the different ways in which physical activity bouts were characterized in the VILPA studies compared to this large cohort study. Nonetheless, there is a good reason to make sure you’re engaging in at least a few longer-duration bouts of vigorous exercise each day and multiple times per week—just to be safe. Exercise snacks and VILPA probably shouldn’t make up the foundation of your aerobic exercise training despite their massive health benefits.

Conclusion

All discussions on exercise eventually boil down to one conclusion: You need to do a variety of low-, moderate-, and high-intensity training every week.

This study does not say we should only be doing intense exercise because it’s better for reducing all-cause and cardiovascular disease mortality. That’s not the message we should take away.

Rather, the results reinforce how important, or rather, how necessary vigorous exercise is for longevity.

Just doing zone 2 training isn’t going to cut it if your goal is optimizing healthspan and lifespan. This is especially true for the people who might dedicate very little time each week to cardiovascular training—more intense is better overall in an absolute sense.

Vigorous activity—which stresses the body and stimulates the brain—is one of the strongest longevity-promoting tools that we have at our disposal. It’s not “easy” to do in the physical sense, but it’s perfectly simple. Go hard, rest, repeat, and your health will thank you.

A few HIIT protocols to get you started

• Tabata training: Tabata training involves performing 8 intervals total alternating between 20 seconds at 170%+ of a power output or speed corresponding to VO₂ max and 10 seconds of rest. Not including the warmup and cooldown, this workout takes 4 minutes to complete.
• Wingate intervals: Wingate training, named for the exercise test for which this workout was named, involves performing 4–6 intervals total. The hard portion is 30 seconds at an “all out” intensity followed by 4 minutes of rest or active recovery. Not including a warmup and cooldown, this workout takes 18–27 minutes to complete.
• One-minute intervals: This protocol involves performing 10 intervals total alternating between 60 seconds at 90%+ of heart rate reserve and 60 seconds of rest or active recovery. Not including a warmup and cooldown, this workout takes 20 minutes to complete.
• Norwegian 4x4 training: Named because it’s performed by the Norwegian ski teams, this workout involves performing a total of 4 intervals alternating between 4 minutes at 85–95% of maximal heart rate and 3 minutes at 60–70% of maximal heart rate. Not including a warmup and cooldown, this workout takes 25 minutes to complete.

HIIT protocols for improving metabolic health