What is Interval Training?

Interval Training is a style of training that involves alternating extremely intense periods of exercise with lower intensity periods of exercise. It typically involves a ratio of work to rest, even if that “rest” period is standing, walking or slow jogging. 

This concept has gained in popularity in recent years with the rise in gyms that focus on a functional fitness type of programming and people who participate in aerobic activities work to increase their speed. 

The biggest benefit is efficiency. These types of programs tend to focus on packing a large amount of activity into a very focused amount of time. 

A recent review found that participants were more engaged in interval training and tended to find it more fun than traditional training that involved working at a continuous intensity. (1) 

We’ll discuss interval training including types, benefits, risks, some sample workouts, as well as final thoughts.

Types of Interval workouts

In the above mentioned 2021 review, the following types of workouts were defined:  (1)   

• Moderate intensity continuous training (MICT): This is typically a 30-60 minute exercise bout performed at 40-60% of your oxygen rate reserve. This is the typical workout that has been recommended for many years. 

It’s obviously not an interval workout but it used as a comparison to interval types of programs. 

This might involve an activity such as running at a relatively constant speed or resistance. Think of running on a treadmill or flat ground at a 9 minute per mile pace for 30 minutes. 

• High intensity interval training (HIIT): This mode of exercise typically involves submaximal efforts at 90% or greater of VO2 max or 75% of maximal power. 

Using running as an example, it would involve short intense bouts of sprinting at close    to maximal effort. This would involve running at a rate of perceived exertion of 6-9/10 (on a modified borg scale where 1/10 = rest and 10/10 = maximal exertion). 

There are multiple sub-categories of HIIT, including Tabata which is one of the most popular versions. 

HIIT workouts can be characterized into low volume (performing less than 15 minutes of high intensity time during a session) and high volume (performing greater than 15 minutes of high intensity activity).

Another 2021 review showed greater effects on cardiovascular fitness, glucose control (blood sugar), and improvements in blood pressure. This was for low volume HIIT and is compared to high volume HIIT and MICT. (2) 

• Sprint interval training (SIT): This mode involves highly intense but short bouts of supramaximal exercise at max effort (VO2 max or greater). It can be thought of as exercising hard as you can for a very short period

A sprint interval workout may include 4-7 rounds of 30 second sprints at maximal effort followed by 4 minutes of rest or light aerobic activity such as jogging or walking. The duration of these workouts tends to be very short. 

• Repeated sprint interval training (RST): Much like the SIT model, this involves short bouts (10 seconds or less) interspersed with a recovery of less than 60 seconds. This type of training is consistent with sports that involve repeated sprints during a longer session such as a soccer match.(3) 

An example of this is repeated shuttle runs (40 -50 foot out and sprints) with 45-60 seconds recovery between. Then repeat this multiple times. 

• High intensity functional training (HIFT): This is a high intensity workout regimen usually attributed to Crossfit(R). It involves a high intensity yet short duration exercise routine known as the workout of the day. This can involve: strength, gymnastic movements, and/or metabolic conditioning. 

Improvements in strength and endurance occur as a result of this type of training. However, it has also been shown to improve cardiovascular ability (improved max VO2). (4) 

Benefits 

There are numerous benefits to interval training. One of the most notable benefits is efficiency. Interval workouts are typically shorter than traditional moderate intensity training. 

One study found that HIIT workouts around 35 minutes of duration have been shown to have equal effects to MICT workouts of around 46 minutes duration. Sessions could be of shorter duration, but would still provide the same benefit as a longer workout of moderate intensity continuous training. (6) 

Another benefit of interval training is improved cardiorespiratory fitness compared to MICT training. This was seen in a variety of age ranges including adults, adolescents and children. (7)(8)  

Improved cardiorespiratory fitness was also seen across different healthy populations such as those with coranary artery disease, hypertension, obesity and heart failure. (9) 

Interval training also has similar benefits to traditional training in aiding with weight loss. This was demonstrated by an overall loss of weight as well as a reduction in fat mass. There were also reductions in blood pressure and cholesterol (LDL) seen. (10) 

Finally, high intensity functional training has similar aerobic and anaerobic benefits as HIIT. However, it has also demonstrated improvements in muscular strength and muscle power. (11) 

Risks

Risks were comparable to other forms of cardiovascular activity for HIIT and SIT. However, one review recommended avoiding sprint interval training for person’s with cardiac disease due to the rapid elevations in blood pressure that occur. (12) 

High intensity functional training had similar risks to other forms of resistance training, running and cycling. The most common areas of injury were the back, shoulders, and knees. These were more common in individuals who trained greater than 4 days per week and did not receive physiotherapy. (11)  

Sample Workouts

HIIT:  Start with a 10 minute slow jog. Then perform 4 rounds of 4 minute intervals of running at a rate of perceived exertion of 7-8/10 (rate how hard you are working on a 1-10 scale where 1= rest and 10 = maximum effort). After each speed interval do a 3 minute interval at a slow jog or walk  for 3 minutes to recover. After the last speed interval, walk or slow jog for 5 minutes to recover. If you want a longer workout, you can add more intervals as needed.

SIT: Start with a 10 minute slow jog. Then perform a 30 second sprint as fast as you can. After the sprint, slow down to a slow jog or walk for 3 minutes, then repeat. Perform 6 intervals followed by  a 5 minutes cool down walk or jog. You can increase the intervals to 60 seconds to increase the challenge.

RST: Start with a 10 minute slow jog. Perform a 10 second sprint as fast as you can followed by a 60 second slow jog or walk. Repeat 10 times followed by a 5 minute slow jog or walk cool down. 

HIFT: Start with a 10 minute walk or jog. Repeat as many rounds as possible in a 20 minute session of 50 jump ropes (you don’t have to have a rope), followed by a 100 foot walk carrying a moderate weight kettlebell or dumbbell (alternate the hand you carry it in every 50 feet), finish the round performing 10 burpees. Perform a slow walk to recover. 

Final Thoughts

Interval training is an efficient and eclectic way to improve your cardiovascular fitness. There are different types that involve varying degrees of duration of work compared to duration of rest. Thus, you’re likely to find one that suits your tastes. 

In addition, there are also modalities of interval training that include high intensity functional training that are different and have the added benefit of improving strength. 

Regardless of which you are interested in, the risk of injury is equal to moderate intensity/ traditional type programs. Yet they appear to have a greater effect on cardiorespiratory fitness. 

Try adding them to your exercise routine today and enjoy the benefits and variety. It can help to break up the stale effects of repeating the same distances at the same intensity each time.