HIIT For Health
High-Intensity Interval Training (HIIT) is a form of interval training that alternates short periods of intense anaerobic exercise with less-intense recovery periods. HIIT sessions may vary from 4–30 minutes. Examples include: Running stairs or hills, sprints and bodyweight circuit training.
Due to the physiological effects of this style of exercise, there are a number of metabolic adaptations that occur which can have profound effects on one’s fitness and health.
Physiological Effects of HIIT Include:
1) Elevated heart rate
2) Increased catecholamines (Epinephrine and norepinephrine)
3) Initial blood glucose elevation from glycogen breakdown for fuel followed by glucose uptake by exercising muscles
4) ATP and phosphocreatine decline to meet rapid fuel needs of contracting muscles
5) Breakdown of triglycerides (Lipolysis)
6) Increased growth hormone production
7) Enhanced venous blood return to the heart and an increase in stroke volume (amount of blood ejected by the heart during a contraction)
8) Increased lactic acid
9) Autonomic nervous system adaptations (elevated sympathetic and decreased parasympathetic activity)
Effects of HIIT on Health and Fitness
- Improvements in Cardiovascular Fitness (VO2max)
- Improvements in Insulin Resistance
- Cholesterol reduction
- Blood pressure reduction
- Fat loss and Weight management
Effect of HIIT on Cardiovascular Fitness
HIIT can improve cardiorespiratory fitness (VO2max) 4% to 46% in training periods lasting from 2 to 15 weeks.
HIIT training is proposed to increase stroke volume due to an increase in the heart muscles’ contractile capability during near maximal exertion.
HIIT has also been shown to increase mitochondrial (the cell’s powerhouse for energy production) size and number.
Some studies have shown that vigorous exercise intensity is more beneficial at positively altering risk factors to coronary heart disease than steady state aerobic exercise.
From a health perspective, a low VO2max is predictive of cardiovascular fatalities and all-causes of mortality.
Effect of HIIT on Insulin Resistance and Type 2 Diabetes
Insulin sensitivity is the ability of cells to regulate and metabolize glucose. It is commonly increased during and after exercise.
Studies indicate that insulin sensitivity can be improved up to 58% over 2 weeks to 16 weeks of HIIT.
The mechanism appears to be related to the ability of skeletal muscle to stimulate the glucose shuttle transporters known as GLUT4, to take up glucose into the working muscles from the blood.
- Obesity and Type 2 diabetes are linked
- 80 per cent of people with type 2 diabetes are either overweight or obese
- Diet and physical activity interventions are the cornerstones for management of both type 2 diabetes and obesity
HIIT should be used preventatively as well as a management strategy for Obesity and Type 2 diabetes.
Effect of HIIT on Cholesterol Levels
Cholesterol is transported in the blood by lipoproteins, which exchanges triglycerides within the liver, intestines, and peripheral tissues.
There are four main classes of lipoproteins:
1) Chylomicron, which transports triglycerides and cholesterol from the small intestines
2) Very low density lipoprotein (VLDL), made in the liver for the transport of triglycerides
3) Low-density lipoprotein (LDL), the primary transporters of cholesterol
4) High-density lipoprotein (HDL), the “good” cholesterol, that transports cholesterol from the artery walls to the liver, where it is converted to bile and used for digestion or disposed of
HIIT has been shown to improve HDL cholesterol after about 8 weeks of training. HIIT also results in decreased body fat along with concomitant improvements in total cholesterol, LDL cholesterol and blood triglycerides levels.
Effect of HIIT on Blood Pressure
HIIT has been shown to improve cardiorespiratory fitness, endothelial function, insulin sensitivity, sympathetic activity and arterial stiffness in hypertensive and normotensive subjects.
There is compelling evidence suggesting larger beneficial effects of HIIT for several factors involved in the pathophysiology of hypertension when compared to steady sate cardio at moderate intensity.
Effect of HIIT on Impacting Fat Loss and Weight Management
HIIT training results in a surge in epinephrine and norepinheprine which may serve a catalyst role for improving fat loss.
Both of these fight or flight hormones have been shown to drive lipolysis (fat break down) and are largely responsible for fat release from fat stores to be used for fuel in exercise.
HIIT may also have the potential to specifically lower visceral fat stores, which have been implicated as metabolic risk factors.
At least 12 weeks of HIIT is needed in order to result in notable changes in body weight and/or percent body fat.
Summary of The Effects of HIIT
- Significant improvements in VO2max, which is directly related to enhanced cardioprotection
- Improvements in insulin sensitivity.
- Favorable effects on visceral fat and subcutaneous fat loss
- Systolic and diastolic blood pressure reduction
- Improvements in HDL cholesterol
- Impacts Fat Loss and Weight Management
As the name implies, HIIT is “intense” and should be done once one has built an aerobic base through stage training.