Endurance training leads to better performance in aerobic activities by making it easier for the body to use oxygen and by increasing the skeletal muscle’s ability to break down substrates. Although it is not as well known, high-intensity interval training (HIIT) is just as good as, and might even be better than, the changes that are usually seen with traditional endurance training when it comes to improving physiology. This is because HIIT has been shown to be an effective way to improve endurance. Despite HIIT lasting for a shorter amount of time than traditional endurance training, it has been shown to have similar effects in healthy persons. Recenty, there has been a lot of research revolving around the topic of low-volume HIIT and its ability to improve aerobic energy metabolism. This research has brought to light how effective HIIT can be in regards to enhancing performance. A more comprehensive analysis can be found in other recent reviews by the present author and others, including work that has specifically focused on those at risk for, or afflicted by, cardiometabolic disorders. There have been two recent reviews that focus on the practical applications and prescription of HIIT training, with a particular focus on athletic performance.
RESEARCH REVIEW – WHAT IS HIIT?
HIIT is a type of exercise that is characterized by repeated sessions of brief, intermittent exercise, typically at intensities that elicit ≥85% of peak oxygen uptake (VO2peak), and interspersed by periods of rest or low-intensity exercise for recovery.
There is a lack of standardization in the literature when it comes to describing various interval training protocols, which has resulted in the use of many different acronyms. A new way of classifying HIIT protocols has been proposed, in which “HIIT” is used to describe those that are “near maximal” or 80-100% of maximum heart rate, and “sprint interval training” (SIT) is used for those that are “all-out” or “supramaximal”, at intensities greater than what is required to elicit VO2peak.
In this review, the term “HIIT” will be used exclusively for simplicity, but the interested reader is referred to Weston et al. (2014) for further consideration. There is no one definition of “low-volume” interval training, but it is generally considered to be a training protocol in which the total amount of intense exercise performed during a session is 10 minutes or less. The Wingate Test is a common protocol used to study physiological adaptations to low-volume HIIT. The test involves 30 seconds of maximal cycling on a specialized ergometer, typically using a braking force or resistance that is equivalent to 7.5% of body mass. The task is very demanding and people usually produce mean power output values that are 250-300% of what they could do during a test to determine (VO2peak). A typical training session lasts around 20-25 minutes, including a short warm-up and cool-down. subjects usually do 4-6 Wingate Tests with a few minutes of recovery in between.
Another common intervention employed in low-volume HIIT studies is repeated constant-load efforts performed at a high relative (but not all-out) work intensity; for example, ~10 60-s cycling efforts at 100% of the peak power output elicited during a ramp VO2peak test, or an intensity that elicits ~90% of maximal heart rate, interspersed with a similar amount of recovery between efforts.
PHYSIOLOGICAL ADAPTATIONS TO LOW-VOLUME HIIT
The physiological adaptations to HIIT are dependent on how often, how intense, and how much work is done. The amount of energy used by high-intensity exercise varies widely depending on the length and intensity of each burst of activity, the number of bursts, and the length and type of rest period between them. This means that during a 30-second all-out maximal cycling effort, approximately 20% of the energy needed comes from oxidative metabolism. If the exercise is repeated several times with short breaks in between, most of the ATP used during the final exercise bout will come from oxidative metabolism.
The reason why oxidative metabolism makes a bigger contribution during repeated high-intensity efforts than it does during a single effort is because both the rate of oxygen transport and utilization increases, and the ability to stimulate substrate phosphorylation through phosphocreatine hydrolysis and glycolysis decreases. High-intensity intermittent exercise is a type of exercise that uses both non-oxidative and oxidative metabolism to create energy. In other words, HIIT can cause a lot of different changes in the body, and the reader can find out more about those changes elsewhere. The following sections will summarize some of the main ways that HIIT affects metabolism and morphology, with a focus on recent studies that have looked at how HIIT causes rapid changes in skeletal muscle.
HIIT’s effect on a person’s “sprint” performance is related to increases in the activity of enzymes that help with energy provision (such as glycogen phosphorylase and phosphofructokinase), as well as the person’s increased muscle buffering capacity and changed ionic composition including an increase in sodium-potassium ATPase content and function. Muscle fiber composition can be shifted bidirectionally from type I to type IIa or from type IIa to type IIx, similar to the general trend observed after both endurance and strength training, although not all studies have found this to be the case. Although HIIT has not been shown to have a major effect on muscle size, a few studies have reported significant hypertrophy of both Type I and Type II fibers after many months of HIIT. An acute bout of Wingate-based HIIT does not activate signaling pathways within skeletal muscle that are linked to increasing muscle size.
Low vs. high intensity training – what’s the difference?
Human body can produce energy in 2 different ways.
When exercising at a low or moderate intensity, energy is generated by oxidizing fat in the mitochondria of the muscle. The process is slow and requires oxygen, so it is called aerobic.
Regular exercise at a low to moderate intensity level helps to improve the mitochondria density in muscles, as well as developing cardiovascular pathways. Regular aerobic exercise trains your body to be more efficient at generating energy from oxygen.
The mitochondria produces energy at a slower rate as the intensity of the exercise increases. The body starts to process stored glycogen into glucose to use as energy instead. This process doesn’t need oxygen and is called anaerobic.
The glycogen stores only have a small amount of carbohydrates, around 350 grams. This is only enough for a short amount of time, around 2 hours, of intense exercise. An athlete’s body begins to ‘shut down’ when he starts to run out of it.
It is often referred to as “hitting a wall” when athletes Tend to spend 2 hours racing and then hit a wall after 30 to 35 kilometers.
This type of training helps to improve the muscles’ ability to produce power and makes them more resistant to fatigue. While it might be difficult to run this fast pace for an entire marathon, if you can keep up a good speed for the first few miles it will help you in the long run In short races, it is beneficial to maintain a fast speed for a longer period of time. Even though it might be challenging to sustain this pace for an entire marathon, if you are able to keep up a good speed for the first few miles, it will be advantageous for you in the long run. . It also results in more speed in both long and short races.
How to measure training intensity
Training intensity as a concept may sound quite ambiguous. Who knows what exactly 70% of maximum is, right?
In other words, there are many ways to measure it.
Taking blood samples before, throughout, and after a training session is the best and most precise way to see how your body responds to intensity.
A more convenient way to measure training intensity is to use heart rate as a guide. The harder you train, the faster your heart beats, pumping blood to your muscles.
There are several exercise heart rate zones that categorize different intensity levels. These zones provide an easy framework to follow during a training session.
More experienced athletes would also benefit from measuring their exercise intensity using speed or power. It doesn’t take into account how your performance might drop if you’re tired or sick. So, it is critical to know your body, how it responds to stress, and when to back off.
The most important thing is that athletes actually measure training intensity, whichever way they prefer. Having a clear understanding of how hard you train will help you get the most out of each session.
Physiological impact of High Intensity Training (HIT) on the body
Intense exercise taxes athlete’s body reserves quite a lot. While you may only need to refuel after a low intensity training session, you may need several days to recover before you can train again at a high intensity.
HIT not only burns glycogen stores, but also creates small injuries in muscle tissue that take some time to heal.
At high intensity, blood sugar is turned into pyruvic acid, which is then converted into energy. Lactic acid is produced as a by-product.
What happens after makes all the difference. Lactic acid is quickly converted into lactate and hydrogen ions.
The accumulation of hydrogen ions causes muscle fatigue and is the root of all problems. The accumulation of these molecules leads to a decrease in performance and speed.
How to include high intensity training into a training plan
If you want to be efficient, you shouldn’t just focus on high or low intensity.
If you only train at a high intensity, your muscles won’t have enough time to recover and your endurance will suffer. Although low intensity workouts improve endurance, they will not do much to improve top speed.
Hard training sessions are only a small fraction of what athletes actually do.
The most eye-catching color is definitely used for advertising purposes.
The majority of an athlete’s time is spent at low intensity, with a focus on general endurance and strength, technique, flexibility, tactics, and other skills.
Other benefits of regular low intensity training include improved recovery and endurance, as well as a stronger mind-body connection. Doing the same movement multiple times helps improve and optimize the form and also builds supportive tissues. This leads to using less energy to do the same thing at a higher intensity.
Low intensity also helps to improve muscle efficiency and speed up the recovery process, making it possible for athletes to handle a greater training load and improve even further.
The 80-20 rule
In reality, athletes do a lot of training that is focused on either very short but very hard efforts (several seconds to several minutes) or long and easy efforts (half an hour and longer).
The art of balancing the overall training load. It can be difficult to find the right training intensity that will result in a significant improvement, but still avoid overtraining. In many cases it’s trial and error.
It can be difficult to create your own training plan without any previous experience because every coach usually keeps their own methods a secret.
This ratio may not be the same every time. It may be different from one session to the next, or even from one week to the next. As long as the ratio of easy to hard days is 80-20 over a prolonged period of time (several weeks to a month), the training plan will be balanced and the athlete will have enough energy to recover and go hard when needed.
The specific amount of time each training zone is used will depend on the training phase and the goal race distance.
Athletes may spend a lot of time in Zones 1 to 3 in the off-season or early season to build up the aerobic base. Zones 4 and 5 may only account for 5% or so. As race day gets closer, athletes may do more high-intensity training to get in the best possible shape for the race.
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