High-intensity interval training (HIIT) has become popular in recent years for a number of reasons. It does not require as much time as regular exercises (some may take as little as 10 minutes).
Research shows that it improves fitness, lowers blood pressure, and helps people better manage blood sugar levels, which may aid in weight loss and disease prevention, such as type 2 diabetes. And recently, a review found that one form of HIIT exercise is called “low-volume HIIT.” It has benefits for heart health and metabolism, meaning that it can lead to similar – or greater – improvements in cardio-respiratory fitness, blood sugar and blood pressure control, and cardiac function compared to continuous aerobic exercise (such as running a five-mile run).
HIIT is characterized by alternating periods of low and high intensity exercise. For example, this might include cycling at an easy pace for a few minutes before increasing the effort to a high level or even to an extreme for a short period of time before returning to an easy pace.
Then this is repeated during the exercise session with the total time spent at a high intensity usually low. There are different classes of HIIT depending on the intensity of the exercise required.
In this study, researchers conducted an in-situ review of current evidence on low-volume HIIT, and its benefits for heart health. Thematic reviews provide an up-to-date overview of the latest information in a specific field or rapidly developing field of research.
They looked at a total of 11 studies. They defined low volume HIIT as an exercise that includes the total time spent in active periods (not including rest periods) of less than 15 minutes.
Overall, they found that low volume HIIT improves a person’s ability to burn fuel (such as carbohydrates and fats), which is directly related to controlling blood sugar – and may be important in preventing diseases, such as type 2 diabetes. For supervision in healthy people, obesity and type 2 diabetes, it is safe.
Low volume HIIT has also been shown to improve cardiac structure. This increases the volume of blood that the heart can pump to the rest of the body with each heartbeat.
These benefits were true for people without underlying health conditions, as well as for people with heart failure (where the heart is unable to properly pump blood around the body because it has become too weak or stiff).
Even moderate improvements in heart health have been shown to reduce cardiovascular events such as heart attacks and strokes by up to 30%.
These results show that even short exercise can improve health. Current WHO guidelines recommend adults get 150-300 minutes of moderate exercise or 75-150 minutes of vigorous exercise per week.
However, lack of time is often cited as the main barrier that prevents many people from exercising. And low volume HIIT has the potential to be more time efficient while offering similar or greater improvements in health outcomes as prolonged workouts.
The research is proposed by Matthew Haines, chair of the University’s Department of Sports, Exercise and Nutrition Sciences HuddersfieldLow-volume sports interventions can be used without feeling too hard or uncomfortable, which is important to motivate people to continue the exercise regimen. It may also be useful for people who are inactive or who have long-term health conditions.
How does HIIT work?
Regardless of the type of HIIT, health improvements are believed to result from the rate – not the amount – at which glycogen is used by the muscles and skeletal system (the carbohydrates that the body stores for energy). Muscle glycogen is an important reserve of fuel – so our body tries to replenish it as a priority.
HIIT exercises deplete muscle glycogen at a rate that the body increases the number and activity of the mitochondria (centers of cell strength) in our muscles to allow us to meet the energy demands of the exercise. This, in turn, leads to improvements in fitness, metabolic function, and health.
There are some limitations to HIIT’s search. Most of the studies were conducted in laboratory settings. This makes it difficult to know how effectively HIIT works as a real-world exercise strategy.
This review also has its own limitations. Typically, when analyzing the results of a wide range of research, experts use a systematic review or meta-analysis. This is the highest level of evidence within the research designs. They systematically assess the quality of studies and use methods that reduce bias. This allows us to draw reliable and accurate conclusions.
But the topical reviews do not – which means that this particular paper does not give the most objective view of the effectiveness of low volume HIIT.
Also, when considering the time involved to warm up and cool down, as well as the time taken to recover between high intensity periods, not all HIIT exercises can be considered more time-efficient than traditional exercises.
In this review, the average total time for each exercise was around 40 minutes – of which no more than 15 minutes are active.
But that doesn’t mean HIIT cannot be a substitute for prolonged workouts – especially given the growing body of evidence showing that it has a number of benefits similar to other types of exercise.
Current thinking also indicates that every part of the movement matters. So focusing on the quality (intensity) of the exercise, rather than its duration, and finding ways to incorporate a higher intensity movement into daily activities, may be beneficial in improving our health and fitness.