High Intensity Interval Training

What is this? If you are into fitness, you might have heard of this recently.


HIIT Cycling


Aerobic exercise is very important in reducing body fat. In due time, your body will come into a state where it will cope to your regular exercise routine and that’s commonly known as a gym jargon of fitness plateau. This is one of the problems when you stick to one program that you will gradually be stuck in achieving your goal. Although other forms of exercises may help you in other forms of body composition like heavy weight training, preparing for a marathon and endurance training.

Recently, High Intensity Interval Training (HIIT) proves a scientific study that it maybe be more effective not just in losing your body fat (BF), take note, not total body weight (TBW) especially in reducing subcutaneous and abdominal body fat than any other exercises after performing the skin fold test. Also, HIIT can help you lower your insulin resistance levels because of different muscle adaptations due to enhanced skeletal muscle fat oxidation and glucose tolerance. This is a perfect workout for Type II diabetes individuals.


Treadmill Running

Regular Steady State Exercises (SSE) such as walking, jogging and other aerobic exercises require a moderate intensity effort. Yes, these workouts are proven and been a long time form of exercise that can decrease weight loss. For people who have stagnant lifestyle, SSE can help them increase their aerobic efficiency, improve their fitness level and help them lose weight.

HIIT involves repeated brief sprint exercises with an all-out intensity and it is immediately followed by a low intensity exercise or rest. The sets from the sprint to the recovery period may vary from 6 seconds up to 4 minutes. Most of HIIT sprints are performed using a stationary cycle ergometer until you reach an intensity level of 90% of your maximum oxygen uptake or commonly called VO2 Max. Computing for your maximum heart rate (MaxHR) can help you determine your VO2 Max.

Response and Adapation to HIIT

Studies have been performed in adolescents, young men and women and older people. They performed HIIT in a period of 2 to 6 weeks at 3 times a week. Acute responses to HIIT resulted to change in heart rate level, blood glucose, lactate levels, autonomic, hormones and metabolic reactivity.

Heart Rate – during the study, recorded peak HRs of 170 beats per minute (BPM) immediately after doing a 30-second maximum cycle sprint. HR averages at 150 BPM within 5 minutes seconds of doing the cycle sprint and increases to 170 BPM within 15 minutes, with 8 to 12 seconds of recovery period. The heart rate decreased between 5 to 8 BPM during the 12 second period of rest.

Hormones – catecholamines, cortisol, and growth hormones.

Catecholamine is released by adrenal gland – a part of the fight-or-flight response. This has effect on heart rate, blood pressure, blood glucose level and reaction to the sympathetic nervous system, in which it increases these effects in your body.

Epinephrine and Norepinephrine levels were elevated after 20 minutes of HIIT when done with 8 sec/12 sec cycle sprints. When compared to SSE, only a small difference in these hormones were secreted.

Cortisol – also produced by the adrenal gland. This is released to the body’s response to stress. It increases the blood sugar, suppresses the immune system and helps metabolize fat, protein and carbohydrates metabolism. When you lack sleep, exercise burnout, trauma and anorexia can increase cortisol level.

Growth Hormones – this stimulates basically growth and cell reproduction. Secreted by the pituitary gland, it is known to have an anabolic effect that is why this is abused by athletes and body builders. This increases muscle mass, protein synthesis and stimulates your immune system.

Lactate Acid – depsite that increase of lactate levels were observed during HIIT, free fatty acid transport also increased. This is very important as a source of energy and adenosine triphosphate (ATP).

Blood sugar – people with Type 1 diabetes who suffer hypoglecemia or low concentration of sugar in the blood can benefit to this effect. The stabilization of glycemia, the content of sugar in the blood, associated with elevated levels of the hormones mentioned above, remained at near baseline level.

Increased aerobic and aerobic fitness, skeletal muscle adaptation and decreased fasting insulin and insulin resistance are the body’s chronic responses to HIIT. Two weeks of doing HIIT on a cycle sprint with a 4-minute recovery and doing it 4 to 6 times increased the VO2 Max by 7% to 13%. This has greater effect that you can achieve of up to 41% and 46% in Type 2 diabetic and older people.

Aerobic and Anaerobic Capacity

HIIT and SSE Fat Loss

HIIT and SSE Fat Loss
Chart provided by NCBI

(a) is Subcutaneous Fat and (b) is Abdominal Fat Loss. This is the result after 15 weeks of doing HIIT or High Intensity Interval Training compared in doing the Steady State Exercise or SSE.

Significant abdominal fat loss is recorded especially to untrained individuals. Possible causes would be of increase exercise and postexercise fat oxidation and decreased postexercise appetite. Yes, HIIT can help you reduce your appetite due to corticotropin releasing factor (CRF), a hormone that has effect on stress and anxiety.


HIIT is not recommended for those individuals who are just starting their exercise regime and would want to lose fat. Strong aerobic and anaerobic level must be attained first before attempting this program. If you have been doing exercises for a while, it is a great opportunity to ask for your personal trainers if they have HIIT programs. This has greater benefits than doing your normal walking, jogging, swimming, cycling.

Les Mills is releasing a new exercise program called GRIT Strength. It offers weightlifting, running and plyometrics for a full body workout in a short 30-minute workout which passes the criteria for a HIIT exercise.

Doing HIIT can have a significant increase in aerobic and anaerobic fitness and gives signification skeletal muscle adaptations that are oxidative and glycolytic in nature. This can also help you achieve a greater result in losing your abdominal fat.