By Daimy Ruiters
Regular physical activity has great health benefits. An active lifestyle is important to maintain since it is associated with a longer healthspan by delaying the onset of many (chronic) diseases . ‘High-Intensity Interval Training’ (HIIT) is a form of physical activity that, as the name already suggests, involves high-intensity bursts of cardio exercise followed by short periods of recovery. This allows you to maximize your results in building both strength and endurance at the same time.
To illustrate, a typical HIIT workout takes about 30 minutes and can be done on a (stationary) bike. A training involves 30-60 seconds of a difficult pace aiming for a heart rate of 80-90% of your maximum heart rate followed by a rest period for the same amount of time, repeating this cycle for several times. The active and rest split may differ depending on the level of physical activity. Another form of HIIT involves resistance training exercises with a similar active and rest split. Popular exercises are battle ropes (see cover picture), burpees, jumping jacks, push ups and (jumping) squats.
It is easy to see why HIIT has become very popular recently: it is energizing, less time-consuming, applicable to all levels of physical activity, there are endless variations of exercises available and the results are impressive . Next to the positive effects on your physical health, increasing numbers of scientific studies suggest that HIIT also benefits mental health . So, if you are looking for a workout that will make you feel good inside out, HIIT may be the answer. But how exactly does HIIT benefit your brain? And what sets HIIT apart from other forms of exercise?
Brain changes associated with HIIT
Brain metabolism and perfusion boost sleep, memory and emotion
Several positive effects are associated with HIIT; the initial noticeable effects are improved sleep, memory, and emotion. This can be explained by two mechanisms. Firstly, glucose metabolism is increased after a HIIT workout when compared to medium-intensity continuous training (e.g. jogging or cycling at one pace for 30-60 min). It is found to be increased specifically in brain regions that are involved in important processes such as executive function, memory, sleep, language, and emotion [4, 5]. Secondly, blood flow in the brain is improved in similar cortical regions after HIIT, this reflects increased oxygen use and is the result of active functioning brain areas . These improvements translate into more efficient brain metabolism and perfusion, and such adaptations contribute to the benefits attributed to HIIT.
Increased release of neurotrophins improves cognition
Exercise induces the release of neurotrophins: proteins released by cells in the brain that promote neuronal survival, development and function. One of the most well-known neurotrophins released through exercise is the Brain-Derived Neurotrophic Factor (BDNF), which is closely related to different cognitive processes such as attention, working memory and self-control . Since BDNF is a reliable marker of brain function, this neurotrophin has been studied intensively to examine the effect of HIIT on cognitive processes. Interestingly, recent studies comparing different forms of physical activity found that HIIT is superior in the release of BDNF [7, 8]. These studies compared HIIT to continuous forms of training, like jogging for example. In the HIIT-group, higher BDNF levels were found along with learning and reaction time in various cognitive processes [7, 9, 10].
Endorphins give that euphoric feeling
Physical activity improves mental health by boosting your mood and reducing stress. These positive effects decrease symptoms related to depression and anxiety, and are mediated by the release of a family of neurotransmitters called endorphins. Endorphins are your body’s natural opioid, and therefore relieve pain. Moreover, endorphins can cause mood upliftment. A famous example is the ‘runner’s high’, which describes a feeling of euphoria after long-distance running.
Only some forms of physical activity can cause the release of endorphins. HIIT is associated with the release of endorphins comparable to long-distance running. An imaging study compared HIIT with rest state and found increased endorphin release in brain regions involved in pain, reward and emotion (see figure 1), which explains the fact that HIIT improves mood and gives this energized/rewarded feeling after a workout .
HIIT as a treatment for disease
The positive effects of HIIT on the healthy brain can be extended to the diseased brain. Therefore, many HIIT interventions have been trialled on patients with different neurological disorders, and have shown to improve both mental and physical symptoms. For example, by reducing stress, anxiety and depression, as well as improving cardiorespiratory fitness, vascular function and blood glucose levels [3, 12].
HIIT also benefits patients with Parkinson’s Disease to a great extent. Parkinson’s Disease is a neurodegenerative disorder that is characterized by the deterioration of dopaminergic neurons which results in motor symptoms (shaking, stiffness, difficulty walking, imbalance), but also non-motor symptoms (cognitive impairments, dementia, depression, anxiety). A recent study showed that 12 weeks of HIIT already improved a number of disease symptoms . Previous studies have established that physical activity improves motor symptoms in Parkinson’s Disease. However, this study showed that this exercise regimen improved various non-motor symptoms including cognitive function. Interestingly, the patients that took part in HIIT also showed less symptoms progression and improved the quality of life. It was suggested that these improvements are mediated by the increased BDNF levels measured in these patients, which are important for the normal function and proliferation of dopaminergic neurons – those mostly affected in Parkinson’s Disease .
Applicable to many
Why HIIT has gained scientific attention recently is because it is applicable to different subjects and study designs. Firstly, HIIT can be applied to every level of physical activity. The intensity of HIIT can be tailored to every individual and it has endless variation of exercises. Therefore, both healthy subjects and patients can participate in HIIT. Secondly, HIIT exercise protocols are easy to implement and monitor in scientific studies. As explained earlier, during the active state of a HIIT workout the heart rate should be about 80-90% of the maximum heart rate. To monitor this, a subject’s heart rate is measured which is an easy, reliable and fast method that can be applied in many study designs.
Because of this increased scientific attention, much research is done. Studies suggest HIIT benefits the brain through better brain perfusion and metabolism which increases BDNF levels and the release of endorphins, which together result in improved sleep, cognitive function and decreased depression- and anxiety-like symptoms. Remarkably, these effects extend to the Parkinson’s affected brain as well. And since this workout is applicable to almost everybody, many can benefit from a HIIT regimen that will make you feel good inside out!
About the writer
Daimy is a second year neuroscience masters student. Neuroscience has fascinated her since she was little. Right now, she is very interested in Neurodegenerative diseases; her last internship was on Huntington’s Disease and now she is researching biomarkers for Alzheimer’s Disease. Her research interests include clinical neuroscience, focusing on conceptualising, diagnosing disorders and developing novel treatments.
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