Table of Contents
2 Table of literature
2.1 Low-volume high-intensity interval training reduces hyperglycaemia and increases muscle mitochondrial capacity in patients with type 2 Diabetes (15)
2.2 High Intensity Interval Training Improves Glycaemic Control and Pancreatic β Cell Function of type 2 Diabetes (16)
2.3 High intensity intermittent exercise improves cardiac structure and function and reduces liver fat in patients with type 2 Diabetes: a randomised controlled trial (17)
2.4 The effects of a 2 week modified high intensity interval training program on the homeostatic model of insulin resistance in adults with type 2 Diabetes (18)
2.5 Acute high-intensity interval exercise reduces the postprandial glucose response and prevalence of hyperglycaemia in patients with type 2 Diabetes (19)
2.6 Table of comparison
3 Review summary and practical applications for exercise science practice
Low volume High Intensity Interval Training (HIIT) is a new popular modality of endurance training which primarily improves cardiorespiratory and metabolic functions(1 ). Gibala and McGee(2 ) have defined HIIT as repeated sessions of relatively brief intermittent exercise, often performed with an ‘all-out’ effort or at an intensity close to that which elicits VO2peak (i.e., =/>90 % of VO2peak). Because traditional endurance training cannot be established by aerobic adaptations alone, HIIT works above the anaerobic threshold to reach a new adaptation. The main difference to other endurance modalities is an increasing intensity with a shorter bout (<45sec to 2-4min) interspersed with a decreasing recovery period during a HIIT session(3 ). That means that the ratio between a higher stress and a shorter rest is different than usual training methods(4,5 ). Some studies designed their intensity and recovery intervals based on a ratio of 1:1 (stress:rest)(6,7 ). Within the work intervals the participants aim to achieve maximum heartrate, VO2 peak or RPE(2 ). This high intensity is defined by a rate that reaches at least 90% of the maximal heart rate(8 ). Because of a high intensity the workout is much shorter than the common training methods it usually lasts 15-30 minutes.
High intensity interval training induces numerous morphological and metabolic adaptations in skeletal muscle(9 ). On one hand it includes mitochondrial biogenesis and therefore an enhanced capacity to oxidize fuels such as glucose and fats(10 ). This implies that a combination of anaerobic and aerobic energy systems rely on muscle glycogen and/or blood glucose as an important substrate for energy production(10 ). On the other hand high intensity intermittent modalities improves aerobic respiratory control sensitivity resulting from increased mitochondrial density(9 ). Also V O2max and time to exhaustion is improved by HIIT(4 ). High intensity and reduced volume of the workout utilizes type 2 muscle fibres. This muscle fiber has an anaerobic glycolytic metabolism and produces lactate by using glycogen(11 ). This results in the production of the growth hormones testosterone and somatropin(11 ).
This research question plays an important role for people who are affected by type 2 diabetes or obesity which increases morbidity and mortality. Stroke, hypertension and heart disease are some of the most common disorders associated with these conditions(1 ). As mentioned above type 2 muscle fibers are primarily activated during high intensity interval training. These muscles only work with glycogen and glucose. Thus, hyperglycemic blood glucose decreases. This happens because skeletal muscles are the major tissue where insulin stimulates insulin receptors which activate glucose uptake by GLUT 4 receptors at the cell membranes to remove glucose from the blood(12 ). The glucose taken up can be converted into glycogen(13 ). Also plasma insulin rises to transport glucose into cells(14 ). The insulin resistance at insulin receptors (HOMA-IR) at muscle cells is important for patients with type 2 diabetes. Another factor called HbA1C is glycosylated hemoglobin and also plays an important role for patients with diabetes mellitus. It is a longterm (4-12weeks) control value to diagnose blood glucose(15 ) with a value of 7% equivalent to 156mg/dl(16 ).
The high blood glucose levels which decrease the sensitivity of insulin at cells can be increased by activating type 2 muscle fibers during HIIT as such, high intensity interval training is highly recommended for people who are affected by type 2 diabetes and obesity.
2 Table of literature
Four databases (PubMed, MedLine, Sports Discus and Google Scholar) were wholly searched. The first variable terms ‘High intensity interval training’, ‘High intensity training’, ‘HIT glycemic control’, ‘exercise and glycogen’, ‘HIIT glycogen’, ‘HIT Diabetes’ and ‘HIIT metabolism’ gave a total of 9816 responses. Search years were limited from 2000 to the present generating 7113 results. These were then refined using the second terms ‘Scientific basis for high intensity interval training’, ‘HIT glycemic control’, ‘HIIT glycemic control’, ‘HIT glycaemic control’, ‘HIIT Diabetes’ and ‘HIT glycogen Diabetes’. These second variables returned a total response of 46. This review assesses these 46 original and review articles and their reference lists.
Low-volume high-intensity interval training reduces hyperglycaemia and increases muscle mitochondrial capacity in patients with type 2 Diabetes (17)
Eight participants (age: 62.5±7.6; HbA1C: 6.9±0.7%) all with type 2 diabetes (at least three months) volunteered. They underwent a 24h continuous glucose monitoring before and after training. Three 90% maximal heart rate, interspersedsessions/week for two weeks consisted of 10×60s cycling efforts at with 60s recovery, were completed. Blood glucose concentration over 24h was significantly (p<0.05) reduced after training (Baseline: 7.6±1.0mmol/l, post: 6.6±0.7mmol/l). HIIT has a significant effect on the improvement of blood glucose in patients with T2D. (78 words)
High Intensity Interval Training Improves Glycaemic Control and Pancreatic β Cell Function of type 2 Diabetes (18)
23 participants were split into a HIIT group (female:7, male:3; age: 56±2; HbA1C: 8.2%) with type 2 diabetes (diagnosed for at least 1 year) and a healthy control group (female:8, male:5; age: 52±2; HbA1C:
90%5.8%). Both completed three HIIT sessions/week for 8weeks consisting of 10×60s cycling efforts at maximal heart rate, interspersed with 60s recovery. T2D group had significances (p<0.05) in all parameters between baseline and post training (Blood glucose concentration pre: 8.0mmol/l, post: 7.2mmol/l; HOMA-IR pre: 3.0, post: 2.4; HbA1C pre: 8.2%, post: 7.8%). The control group had no significances. The results demonstrate a healthy beneficial outcome in T2D by exercising HIIT. (104 words)
High intensity intermittent exercise improves cardiac structure and function and reduces liver fat in patients with type 2 Diabetes: a randomised controlled trial (19)
23 participants all with type 2 diabetes (diagnosed for at least 6 month) were randomized into HIIT (n=12; age: 61±9; HbA1C: 7±1%) and control-groups (n=11; age: 59±9; HbA1C: 7±0.5%). The HIIT-group completed 3sessions/week for 12weeks, efforts at RPE 16-17points. Consisting of 2min interval in week one, progressed 10s each week, such that week 12 had a 3.50min interval, interspersed 3min recovery. The control group absolved their standard activity. Glycaemic control was measured at baseline and after 12weeks. A significance (p<0.05) in HbA1C (HIT post: 6.8±0.9%; control post: 7.4±0.7%) between groups were given. HIIT is recommended for T2D by showing a beneficial decrease in HbA1C. (104 words)
The effects of a 2 week modified high intensity interval training program on the homeostatic model of insulin resistance in adults with type 2 Diabetes (20) Nine Participants (male:3; female:6; age: 40.2±9.7; BMI: 33.9±5.3; HbA1C: 7.3±1.2%) all with type 2 diabetes (diagnosed for at least 1 year) volunteered for 2weeks of HIIT with 3sessions/week. Each session consisted of 4x30sec HIIT with 100%eWLmax (~80% max Heart rate) on a cycle and 25%eWLmax for 4min recovery. Blood was collected prior to (5min) and after (immediately) each interval. A significance (p<0.05) in blood glucose was measured acutely pre-post each session (mean reduction:0.95mmol/l) but not in HOMA-IR. Yet a significant decreasing trend from baseline was measured in HOMA-IR but not in HbA1C. HIIT shows a beneficial decrease in HOMA-IR and blood glucose in T2D. (104 words)
Acute high-intensity interval exercise reduces the postprandial glucose response and prevalence of hyperglycaemia in patients with type 2 Diabetes (21)
Seven participants (age: 62±3; HbA1C: 6.9±0.7%) all with type 2 diabetes (diagnosed for at least 3 months) 90% maximal heartvolunteered. They underwent one HIT session consisted of 10×60s cycling efforts at rate, interspersed with 60s recovery; followed by a non-exercise control day. Time spent in hyperglycaemia was significantly (p<0.05) reduced in the 24-h period (HIT: 4.5±4.4 vs. control: 15.2±12.3%, p=0.04). But blood glucose concentration did not significantly change (HIIT: 7.2±1.2mmol/l; control: 7.8±1.1mmol/l). One single HIIT session already highlights the improvement of glycaemic control in T2D patients. (87 words)