For those juggling a hectic schedule and trying to navigate a healthy work-life balance, maximizing the benefits of a workout is top of mind. Whether you love a long endurance session or dread it, squeezing in a 10-mile run or a 1-hour gym session might seem near impossible to fit into an already overflowing calendar. 

Enter interval training – a versatile way to train that enhances endurance capacity and boosts metabolism. Interval training provides equivalent or potentially greater benefits gained in much less time than a standard endurance or moderate-intensity exercise session.

What is interval training?

Interval training features brief intervals of high intensity, “all-out” exercising, such as sprinting, followed by shorter intervals of rest.

The three most common types of interval training are high-intensity interval training (HIIT), sprint interval training (SIT), and repeated-sprint training (RST).1

HIIT is generally characterized by several repetitions of a high-intensity exercise at greater than 75 percent of maximal power, followed by periods of rest or active recovery. Completing four repetitions of 4-minute high-intensity exercise, followed by 1-minute rest intervals between repetitions is an example of HIIT. 

SIT is a more intense version of HIIT, with effort exceeding maximal power. The RST model features a high number of sprints that last less than 10 seconds each, interspersed with relatively shorter recoveries compared to SIT.1 

HIIT is generally the most utilized of the three types of interval training because HIIT enables longer periods of rest compared to the other two types. Greater recovery time spent within the workout tends to increase the overall enjoyment of the workout, and therefore it enhances future compliance with training sessions.

What are the benefits of interval training?

Interval training benefits include:1

  • Time-efficient workouts
  • Increased endurance capacity and VO2 max
  • Increased resting metabolic rate (meaning you burn more calories at rest)
  • Improved body composition 
  • Improved insulin sensitivity
  • Improved cognitive function and mood

Why is HIIT so effective?

The health of our mitochondria – the powerhouses of our cells and the site of cellular energy production – is a key factor related to healthy aging and overall wellness. However, mitochondrial number and function tend to decline with age. 

Notable benefits of interval training include the up-regulation of key mitochondrial proteins related to endurance response, as well as the up-regulation of proteins involved in the metabolism of NAD+ − one of the most important cellular co-factors for improving mitochondrial number and function.2

A study of eight untrained men (ages 23-38), engaging in three days of HIIT weekly for five weeks, found significant improvements in both exercise performance and mitochondrial number in the muscle tissue.2 Each workout consisted of four intervals of cycling, with each interval lasting 4-5 minutes and performed at greater than 90 percent of maximum target heart rate, followed by two minutes of active recovery.2 The participants had muscle biopsies collected and analyzed from their vastus lateralis − the largest of the quadriceps muscles, located on the outside of the thigh – both at baseline and at the end of the five weeks. The biopsies revealed that HIIT training had remodeled skeletal muscle in favor of mitochondrial biogenesis – the growth and division of pre-existing mitochondria.2 In other words, HIIT exercises benefited mitochondrial growth, particularly in skeletal muscle where there is a high demand for energy production to sustain endurance pursuits.

By the end of the study, participants also experienced a 14-percent improvement in maximal oxygen consumption (VO2 max) and a 17-percent improvement in incremental peak power output with HIIT compared to their baseline assessments.2

So, what can you expect from a HIIT workout before and after?

Although you probably won’t see a significant difference in exercise performance or efficiency after a single workout, HIIT workout results can be seen in as soon as five days, including improved metabolism, enhanced energy, and beneficial changes to body composition. The benefits of interval training are enhanced the longer one engages in such workouts, with training programs that lasted 12 months correlating with even greater improvements in exercise efficiency, as well as a reduced risk for cardiovascular disease, metabolic syndrome, and arthritis.1

HIIT versus running: Which is more beneficial?

Running is generally considered a form of moderate-intensity, continuous training (MICT). Although interval training methods such as HIIT can include running, interval training generally features shorter, more intense bursts compared to a sustained run or jog.

Several studies have investigated the benefits of interval training compared to moderate exercise and found that an equivalent health benefit could be gained in far less time. A clinical trial on 24 overweight or obese middle-aged men found that just 10 repetitions of one minute of running at 80-90 percent of maximum heart rate followed by one minute of recovery for a total of a 10-minute workout and 10 minutes of rest, had the same benefits to weight and cardiovascular fitness as 50 minutes of continuous jogging at 65-70 percent of maximum heart rate.3

What are the disadvantages of HIIT?

Strenuous activity paired with low resting periods can ultimately decrease the enjoyment one experiences during a workout, so one of the disadvantages of HIIT training is that it can potentially lead to burnout if adequate resting intervals are not included. 

That said, the intensity and volume of HIIT exercises can be scaled to the individual, and “more” does not translate to “better.” HIIT is generally separated into two categories: low-volume (less than 15 minutes of high intensity per session) or high-volume (greater than 15 minutes of high-intensity training per session).4

The findings from recent studies support the fact that low-volume HIIT can induce similar or potentially greater benefits to glucose control, cardiorespiratory fitness, blood pressure, and cardiac function compared to high-volume HIIT or MICT.4

You might be wondering, are HIIT workouts good for everyone, and should I do HIIT every day? 

High-intensity workouts are just that − intense. Therefore, if you have a medical condition, you should consult with your health-care practitioner prior to integrating any new training exercise, and even after you are cleared for participation, it is recommended to start slowly.

The researched benefits of HIIT were found when training takes place 3-4 days a week, and while increased quantity could potentially be beneficial, adequate rest days are essential to achieve optimal benefits. Most trainers advise taking at least 1-2 days per week to completely rest and recover from high-intensity workouts.

Although you can still stay active during the days you are not engaging in interval training, you can opt for a low-intensity exercise, such as walking or yoga. 

Supporting NAD+ and mitochondrial health to optimize healthy aging

As mentioned above, HIIT increases mitochondrial growth in muscle tissue, at least in part due to stimulation of NAD+ production, which is known to support mitochondria number and function.1,2 

For cohesive healthy aging and mitochondrial support, you might also consider integrating Thorne’s NiaCel 400® or ResveraCel®, both of which deliver 415 mg of nicotinamide riboside (NR) per serving – NR is a unique form of vitamin B3 that has been clinically studied to enhance NAD+ production.* NiaCel 400 benefits lean body composition, athletic performance, and cellular energy production;* it is also NSF Certified for Sport®. 

ResveraCel pairs NR with resveratrol and quercetin phytosome, which provide synergistic benefits to metabolic health and cellular communication by activating the sirtuin proteins ­– an important class of protein enzymes that up-regulate positive functions associated with healthy aging.* 

You can explore the Thorne formulas that feature NR here or take a look at the full offering of Thorne’s sports performance supplements.

HIIT − the efficient exercise solution to your over-scheduled calendar

Whether you have tried HIIT in the past or are new to this type of workout, consistency is the key to achieving the full benefits of interval training. If you are just testing the waters of HIIT, don’t be afraid to start out slowly to ensure you can build a tolerance for it and avoid the feelings of burnout that can occur by going too hard, too fast, too soon. 

Although HIIT should push your limits, the adage, “no pain, no gain” need not apply here. 

Because HIIT improves endurance, energy levels, and cardiovascular health, and induces positive changes to body composition, all with far less time commitment than a standard endurance session, it could be the solution you are looking for to optimize the delicate time-management dance required to maintain that healthy work-life balance.

References

  1. Atakan MM, Li Y, Koşar ŞN, et al. Evidence-based effects of high-intensity interval training on exercise capacity and health: A review with historical perspective. Int J Environ Res Public Health 2021;18(13):7201. doi:10.3390/ijerph18137201
  2. Hostrup M, Lemminger AK, Stocks B, et al. High-intensity interval training remodels the proteome and acetylome of human skeletal muscle. Elife 2022;11:e69802. doi:10.7554/eLife.69802
  3. Poon ET, Little JP, Sit CH, et al. The effect of low-volume high-intensity interval training on cardiometabolic health and psychological responses in overweight/obese middle-aged men. J Sports Sci 2020;38(17):1997-2004. doi:10.1080/02640414.2020.1766178
  4. Sabag A, Little JP, Johnson NA. Low-volume high-intensity interval training for cardiometabolic health. J Physiol 2022;600(5):1013-1026. doi:10.1113/JP281210