High Intensity Interval Training

What is HIIT?

High intensity interval training (HIIT) is a training technique which consists of altering intervals of short periods of very intense anaerobic exercise. Followed by periods of low intensity exercise or active recovery. The maximum heart rate (MHR) can be used as a guide to estimate an individual’s workout intensity, with 80% MHR considered high intensity. Most intervals last between 10 seconds and 1 minute, with the total workout lasting for about 4-20 minutes. An example of a HIIT workout is 30 seconds of sprinting and 30 seconds of rest repeated for 10 minutes or 20 seconds on the cross-trainer and 10 seconds of rest repeated for 4 minutes.(1)

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Why HIIT?

HIIT can involve almost any exercise activity if it can be done with intervals, e.g. sprints, kettlebells swings, squats jump. It is not as time consuming as other exercise regiments, as a typical HIIT workout is between 4-20 minutes.(2)

 HIIT provides a big variety in the workout as it’s a simple protocol not a specific exercise. The exercises are adaptable and versatile, with the ability to involve equipment such as free weights, or not.

Studies have showed that participants are more likely to stick with HIIT than other forms of cardio.(2) This could be related to versatility of the exercise which avoids boredom. HIIT also results in a more improved VO2 max in comparison to other forms of cardio. VO2 is the amount of oxygen that can be used during intense maximum exercise. The better the VO2 max the longer and harder an exercise can be done more intensely, which results in better health.(3,4)

A 20 minutes HIIT session give the same afterburn effect as a 60 min steady cardio session. This was measured by EPoC (excess post-exercise oxygen consumption) which is the burning of extra calories after a workout.(5)

 

Benefits of HIIT for Type II Diabetes Mellitus (T2DM) Patients

HIIT & Insulin Resistance:

In individuals with T2DM the insulin produced by the pancreas cells cannot attach to their protein receptors on the cell. This means that the glucose cannot enter the cell to be used as energy. The build-up of glucose can lead to hyperglycaemia. As a response, the pancreas cells secrete more insulin. Eventually the overworked pancreas cells lose their ability to make insulin.(6)

Meta-analysis of 50 studies investigated the effects of HIIT on markers of glucose regulation and insulin resistance. The criteria for this meta-analysis included studies that focused on adult participants who suffered from T2DM or were at risk compared with healthy controls and with the HIIT interventions lasting for the duration of more than 2-weeks. As a result, it was found that both T2DM patients and at risk patients both experienced reduction in fasting glucose (-0.92 mmol L(-1), -1.22 to -0.62, P < 0.001) alongside an improvement in metabolic health. (7)

Additionally Shaban,N. et al (2014)(8) investigated T2DM individuals (n=9, age=40.2±9.7 y;BMI=33.9±5.3) and the effects of a 2-weeks HIIT regiment, using the homeostatic model of insulin resistance (HOMA-IR). The HIIT session consisted of 4×30 seconds at 100% of estimated maximum workload, followed by 4 minutes of active rest. The results showed that 6/9 individuals had a reduction in HOMA-IR after the training period.(8)

 

 

 

 

 

 

 

Figure 1. Blood glucose concentration pre and post 2-week HIIT intervention. The bar-chart shows a decrease in blood glucose post HIIT session in 6/9 individuals.(8)

 

HIIT and Glucose Tolerance

T2DM individuals suffer from the loss of glycaemic control, meaning that over time the blood glucose levels progressively increase. The high glucose levels can put the individual at risk of irreversible complications  that are mainly due to microvascular and macrovascular damage.(9)

A study investigated the effect of low volume HIIT on glycaemic control, pancreatic function and total fat mass in elderly individuals. The study consisted of (n=10, 56 yrs±2) T2DM patients and healthy controls (n=13, 52 yrs±2) over the period of 8 weeks. The HIIT sessions were composed of 10×60 seconds on a cycle ergometer 3 times a week. Resting blood pressure was measured, a 2 hours glucose tolerance test (OGTT) was taken followed by incremental maximal oxygen uptake (VO2max) a cycle ergometer test and a whole-body dual X-ray absorptiometry (DXA) were performed before and after the 8-week training. The results showed that the average fasting venous glucose concentration (p=0.01), glycosylated haemoglobin (0.04) and end point 2-hour OGTT (0.04) which determines the glycaemic control were significantly reduced in the T2DM group. In both groups there was also a loss in the abdominal fat mass.(10)

Figure 2. The bar-charts represent the glycaemic control in T2DM patients (T2D) and healthy controls (CON) pre and post 8-week of low volume HIIT intervention. The data for T2D group shows a statistically significant reduction for fasting venous glucose concentration (A), HbA1c (glycosylated haemoglobin), (B) and phosphorylated glucose concentration 2 hours after OGTT (C). The CON group show no statistically significant difference in A, B and C.(10)

 

HIIT and Cardiovascular Health

One of the irreversible complications due to macrovascular damage is cardiovascular disease (CVD), which is related to high blood glucose.(9)

Research shows that HIIT has been proven to reduce the cardiovascular risk in obese individuals with T2DM. The study consisted of 40 sedentary obese males with T2DM. The individuals were randomised in two groups, group A (n=20) which took part in a 12-week HIIT program and group B (n=20) the control group which maintained their normal activity. HIIT sessions were composed of 3 minutes warming up followed by 4 high intensity periods (4 minutes each) interspersed with 4 moderate intensity recovery intervals (2 minutes each), and finishing with 3 minutes cooling down. The findings showed a positive correlation between the overall heart rate variability with VO2 peak changes.(11)

Hughes, I, L. and Higgins, T. (2019)(12) investigated the effect of a 6-week HIIT program on a variety of different T2DM risk markers. The study consisted of 18 participants aged 20-24, which were split into a control (n=9) and a test (n=9) group. Physiological tests were taken at week 0 and at week 6. HIIT sessions were done on a cycling spinner at maximum effort 3 x 1 minutes with intervals of resting periods lasting 2 minutes. The results for the test group showed that a significant decrease in systolic blood pressure by 4.4% (p=0.004) and diastolic blood pressure by 7.2% (p=0.049) as well as a decrease in body fat index by 0.94% (p=0.033).(12)

Figure 3. Bar-charts showing diastolic and systolic blood pressure in test and control groups, pre and post HIIT intervention. The data for post HIIT diastolic blood pressure shows large increase in 47A and 48A and a large decrease pre HIIT intervention in 44A, 50a, 43B and 54b. The data for systolic blood pressure, post HIIT shows a large decrease in 44A and 54B and a large increase in X.(12)

 

Conclusion

HIIT has been proven very beneficial with tackling issues associated with T2DM, therefor. Therefore, should be considered alongside treatment prescribed to T2DM patients, especially those at risk. HIIT has been proven to improve symptomatic issues associated with T2DM as well as being a relatively easy exercise regime to upkeep. The sessions can be customised to anyone’s needs and preferences. It can also be implemented with other types of exercises like Endurance or Resistance.

 

Reference list

  1. McCall, P., 2009. What is High Intensity Interval Training (HIIT) and what are the benefits? [online] Available at: <https://www.acefitness.org/education-and-resources/lifestyle/blog/104/what-is-high-intensity-interval-training-hiit-and-what-are-the-benefit> [ Accessed 5 December 2019]
  2. Gillen, J.B. and Gibala, M.J. 2014. Is high-intensity interval training a time-efficient exercise strategy to improve health and fitness? [e-journal] 39(3) pp. 409-12. Avalable Through: National Centre for Biotechnology Information website <https://www.ncbi.nlm.nih.gov> [ Accessed 5 December 2019]
  3. Karstoft, K., et al., 2013. The effects of free-living interval-walking training on glycemic control, body composition, and physical fitness in type 2 diabetic patients: a randomized, controlled trial, [e-journal] 36(2) pp. 228–36. Available through: National Centre for Biotechnology Information website <https://www.ncbi.nlm.nih.gov>[ Accessed 5 December 2019]
  4. Bækkerud, F.H., et al., 2016. Comparison of Three Popular Exercise Modalities on V˙O2max in Overweight and Obese, [e-journal] 48(3) pp. 491–8. Available through: National Centre for Biotechnology Information website < https://www.ncbi.nlm.nih.gov> [Accessed 5 December 2019]
  5. Skelly. L., et al., 2014. High-intensity interval exercise induces 24-h energy expenditure similar to traditional endurance exercise despite reduced time commitment. Applied physiology, nutrition, and metabolism [e-journal] 6 pp. 39. Available thorugh: Research Gate website <https://www.reseachgate.net> [Accessed 5 December 2019]
  6. Germann, W.J. and Stanfield. C.L. 2005 Principles of human physiology. 2nd ed. San Francisco: Pearson; pp. 254–256.
  7. Jelleyman C, Yates T, O’Donovan G, Gray LJ, King JA, Khunti K, et al. The effects of high-intensity interval training on glucose regulation and insulin resistance: a meta-analysis. Obes Rev. 2015 Nov;16(11):942–61.
  8. Shaban. N. et al., 2014. The effects of a 2 week modified high intensity interval training program on the homeostatic model of insulin resistance (HOMA-IR) in adults with type 2 diabetes. [e-journal] 54(2) pp. 203–9. Available through: National Centre for Biotechnology Information website < https://www.ncbi.nlm.nih.gov> [Accessed 5 December 2019]
  9. Donnelly, R., 2000 Vascular complications of diabetes. [e-journal]. 15;320(7241) pp. 1062–6. Available through ABC of arterial and venous disease <https://www.bmj.com> [Accessed 5 December 2019]
  10. Madsen. S. M. et al., 2015. High Intensity Interval Training Improves Glycaemic Control and Pancreatic β Cell Function of Type 2 Diabetes Patients. [e-journal] 1;10(8) Available through: Directory of Open Access Journal website < https://doaj.org> [Accessed 5 December 2019]
  11. Abdelbasset, W.K.M., et al., 2019. Effect of high intensity interval training on heart rate variability and aerobic capacity in obese adults with type 2 Diabetes Mellitus. Available through: DSpace Repository <http://repository.psau.edu> Accessed 5 December 2019]
  12. Hughes. I, and Higgins. T. 2019. Six Weeks High Intensity Interval Training (HIIT) Improves a Variety of Different Diabetes Mellitus Type 2 Risk Markers. [e-journal] Available through: International Journal of Physical Medicine & Rehabilitation website <https://pdfs.semanticscholar.org>[Accessed 5 December 2019]
  13. Image 13: https://9hutsyoga.com/2019/09/23/lets-hiit-it/

 

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