HIIT, SIT, and RST: Are You Really Doing High-Intensity Training?

In the fitness world, high-intensity interval training (HIIT) is a buzzword, sparking the interest of recreational athletes looking to maximize their workout efficiency. It promises improvements in metabolic, cardiovascular, and psychological health, but many people who believe they are performing HIIT might not be getting the full benefits. Fitness classes that advertise “HIIT” workouts are enticing, and people find themselves looking for "HIIT classes near me". However, often they are not structured following the principles of true high-intensity training. So, what exactly is HIIT, and how can you ensure you're performing it correctly? 

HIIT definition?

True HIIT involves submaximal effort performed at more than 90% of your VO2 max or over 75% of your maximal power. In layman’s terms, it should feel "hard to very hard" on a perceived exertion scale of 1 to 10, where 10 is your absolute maximum effort. These bursts of effort are typically sustained for only a few seconds and up to one minute, with rest periods varying in time from seconds to several minutes between bouts. A complete HIIT session may last up to 15 minutes (including rest breaks) and is shorter than a typical workout.

Due to the high intensity of the workout, the body's demand for oxygen exceeds its ability to produce oxygen. The body is forced to produce energy quickly through a process known as anaerobic respiration and lactic acid is produced as a byproduct.

Many fitness classes claiming to be HIIT offer circuits or stations where participants perform an exercise for 45 seconds to two minutes, followed by a short rest. While these sessions can leave you feeling exhausted and cause muscles to burn, they don’t actually push you to the 75+% intensity that true HIIT requires. In fact, if you’re able to sustain an exercise for a couple of minutes, you’re likely doing moderate-intensity continuous training (MICT), which, while beneficial, doesn’t offer the same rapid, high-intensity benefits that HIIT does.

Different Forms of Interval Training

HIIT is just one of several forms of interval training, each with similar benefits but slightly different methods. Here’s a breakdown of the most common types as defined by Atakan et al.:

1. HIIT: This involves performing exercises at over 90% of your VO2 max or over 75% of your maximal power. The exercise is completed for up to a minute, with rest periods of a few minutes between bouts. It’s designed to push you to your limit, ensuring you can’t sustain the activity for longer than the prescribed time.

2. Sprint Interval Training (SIT): A more intense version of HIIT, SIT is performed at maximal effort, reaching 100% of your VO2 max. These intervals last less than 30 seconds, with rest periods of around four minutes. Since the intensity is higher, the work period is shorter, but the benefits are consistent with the benefits of traditional HIIT training.

3. Repeated Sprint Training (RST): RST involves repeated maximal sprints for less than 10 seconds, with rest breaks of under a minute. Unlike HIIT and SIT, the rest periods are shorter, making it a high-intensity method with a focus on repeated bursts of all-out effort.

The key similarity between all three methods is high-intensity that leaves you completely depleted and requires a relatively longer rest break. If you’re working for longer periods or pacing yourself, you’re likely performing MICT.

The Benefits of HIIT, SIT, and RST

Why go to the trouble of doing such intense exercise? According to a study by Atakan et al., true high-intensity training provides numerous health benefits that MICT doesn’t match. These include:

• Improved VO2 max: VO2 max is a measure of your cardiovascular fitness, or the maximum amount of oxygen your body can use during intense exercise. Improving VO2 max boosts endurance and overall health.

• Enhanced resting metabolic rate: This means you burn more calories even at rest.

• Better body composition: High-intensity training can improve your muscle-to-fat ratio.

• Improved insulin sensitivity: HIIT can help your body use insulin more efficiently, lowering your risk of diabetes.

• Cognitive function improvements: Research shows that high-intensity exercise can help enhance focus, memory, and brain function.

• Reduced risk of chronic diseases and all-cause mortality: HIIT has been shown to lower the risk of cardiovascular disease, cancer, metabolic syndrome, osteoarthritis, and rheumatoid arthritis.

Incorporating just a few minutes of high-intensity exercise into your routine can make a huge difference. Studies indicate that even a single session of SIT or RST can elicit the desired changes, with research suggesting that performing two to eight bouts of high-intensity exercise at least once a week is sufficient. That’s just one to four minutes of actual work per week to see notable health benefits!

How to Incorporate HIIT Into Your Routine

The best part about HIIT, SIT, or RST is that they don’t require a significant time commitment. Even busy individuals can fit this form of exercise into their weekly routine. Here’s how you can start:

1. Pick an activity you enjoy: You don’t need fancy equipment or a gym membership to perform HIIT. You can sprint on a treadmill, bike, or track, or do functional exercises like air squats, jump lunges, burpees, or box jumps. The key is giving an all-out effort during the intervals.

2. Plan your sessions: Aim to add HIIT sessions to days when you’re not doing other cardio or circuit-style exercises. It’s often best tolerated at the end of a resistance training session, or you can even fit it into your lunch break if you work from home.

3. Track your intensity: To ensure you’re hitting the correct intensity, use a perceived exertion scale or track your heart rate. For HIIT, you should feel like you’re pushing yourself to your limit, where talking becomes difficult, and you’re out of breath.

Don’t Forget About Moderate Intensity

While true HIIT training has immense benefits, that doesn’t mean you should entirely skip moderate-intensity continuous training (MICT). MICT, which includes exercises like jogging, biking, or steady-state cardio, helps your muscles extract oxygen from the blood and improves metabolic efficiency. Both HIIT and MICT have a place in a well-rounded fitness routine, and combining them will provide the best overall health results.

The Bottom Line

HIIT, SIT, and RST offer an efficient way to improve your cardiovascular, metabolic, and psychological health without spending hours in the gym. However, it’s important to remember that true high-intensity training is not the same as the long-duration circuits often advertised as HIIT. By incorporating just a few minutes of true high-intensity exercise into your weekly routine, you can significantly improve your fitness levels and reduce your risk of chronic disease. Give it a try—your body (and mind) will thank you!

Remember this post is for informational purposes only and does not constitute a patient-provider relationship. Always reach out to your health care team with questions or concerns about your health.

References: 

Atakan MM, Li Y, Koşar ŞN, Turnagöl HH, Yan X. Evidence-Based Effects of High-Intensity Interval Training on Exercise Capacity and Health: A Review with Historical Perspective. International Journal of Environmental Research and Public Health. 2021; 18(13):7201. https://doi.org/10.3390/ijerph1813720