What is HIIT
High intensity interval training (HIIT) is a protocol of short work intervals<60s–8min of vigorous (70%–90% MHR or RPE Borg scale 14–16) to high intensity (≥90%MHR or ≥RPE Borg scale 17) interspersed with active (40%–70%MHR or RPE Borg scale 8–13) or passive (cessation of movement) recovery periods of 1–5min
HIIT utilizes repeated short to long bouts of relatively high-intensity exercise alternated with recovery periods of either low-intensity exercise or rest
Scientific Facts:
Interval training and moderate-intensity continuous training. both reduce body fat percentage (%). Interval training provided 28.5% greater reductions in total absolute fat mass (kg) than moderate-intensity continuous training.
HIIT encompasses exercise prescriptions that are tailored to individual needs and can be used in most any exercise setting. This ability to adapt makes HIIT a valuable tool in the exercise programming of patients with a chronic disease
A study using healthy individuals, reported that the high-intensity components of HIIT resulted in greater training improvements in maximal aerobic capacity compared to the improvements elicited by moderate-intensity continuous training
HIIT may have added benefits by producing peripheral muscle changes. This results in fewer negative training symptoms (less reported ratings of dyspnea and leg discomfort).
Patients with cardiovascular disease demonstrate improved functional capacity and quality of life without increasing medical risk with HIIT exercise
HIIT should always be considered in conjunction with, or as a supplement to, moderate-intensity continuous training in the medical management plan for patients with a chronic disease, and those individuals who are not able to tolerate high-intensity Exercise intensity.
HIIT presents little risk for stable patients when the prescribed exercise protocols are followed
HIIT is an effective method to improve Cardiorespiratory Fitness in adolescents, irrespective of body composition
HIIT does not out-perform moderate-intensity continuous training in positively affecting total cholesterol (TC), triglycerides (TRG), low-density lipoprotein cholesterol (LDL-C) and the TC/ high-density lipoprotein cholesterol (HDL-C) ratio. However, moderate-intensity continuous training seems to be inferior to HIIT for inducing positive changes to HDL-C --> age, gender and presence of Metabolic Syndrome (MetS) or MetS factors/risk) and intervention (weight-bearing) characteristics do appear to influence effect size
An abnormally elevated or lowered blood lipid profile, known as dyslipidaemia, is a significant risk factor of cardiovascular disease (CVD) ischaemic stroke ; non-alcoholic fatty liver disease (NAFLD) and chronic pancreatitis.Dyslipidaemia frequently coexists with other Metabolic Syndrome (MetS) factors such as obesity and type 2 diabetes (T2D)Studies have shown aerobic exercise reduces elevated total cholesterol (TC), triglycerides (TRG) and low-density lipoprotein cholesterol (LDL-C) and increases high-density lipoprotein cholesterol (HDL-C) in subclinical and clinical populations
Moderate-intensity and vigorous intensity aerobic physical activity positively impacts MetS factors, thus lowering CVD risk
The multiplicity of HIIT protocols is an obstacle to endorsing a specific HIIT regime most effective for positively impacting blood lipids while accounting for time and enjoyment needs, although HIIT could be chosen in preference to moderate-intensity continuous training for improving HDL-C.
HIIT has been shown to increase peak oxygen consumption (VO2MAX or VO2PEAK) compared with moderate-intensity continuous training in cardiovascular disease (CVD) populations,
Studies have shown a minimum volume of weekly aerobic exercise for a minimum duration and a weekly aerobic exercise energy expenditure (EEE) threshold of 1200–2200 kcal is necessary to induce positive changes to lipids
References:
Wood, G., Murrell, A., van der Touw, T., & Smart, N. (2019). HIIT is not superior to MICT in altering blood lipids: a systematic review and meta-analysis. BMJ open sport & exercise medicine, 5(1), e000647. https://doi.org/10.1136/bmjsem-2019-000647
Martin-Smith, R., Cox, A., Buchan, D. S., Baker, J. S., Grace, F., & Sculthorpe, N. (2020). High Intensity Interval Training (HIIT) Improves Cardiorespiratory Fitness (CRF) in Healthy, Overweight and Obese Adolescents: A Systematic Review and Meta-Analysis of Controlled Studies. International journal of environmental research and public health, 17(8), 2955. https://doi.org/10.3390/ijerph17082955
Ross, L. M., Porter, R. R., & Durstine, J. L. (2016). High-intensity interval training (HIIT) for patients with chronic diseases. Journal of sport and health science, 5(2), 139–144. https://doi.org/10.1016/j.jshs.2016.04.005
Viana RB, Naves JPA, Coswig VS, de Lira CAB, Steele J, Fisher JP, Gentil P. Is interval training the magic bullet for fat loss? A systematic review and meta-analysis comparing moderate-intensity continuous training with high-intensity interval training (HIIT). Br J Sports Med. 2019 May;53(10):655-664. doi: 10.1136/bjsports-2018-099928. Epub 2019 Feb 14. PMID: 30765340.