e pa sad, hocu kakit necu kakit, ili je HIIT ili nije HIIT.
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High Intensity Interval Training For Maximizing Health Outcome
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Essentials of High Intensity Interval Training (HIIT)
Interval exercise training (ET) with HIIT may be a particularly effective way for increasing VO2peak and improve CV health compared to moderate intensity continuous training (MICT). The terminology used to describe HIIT unfortunately varies across research groups. Here we use the definition suggested recently using HIIT when the intervals’ are of aerobic character and the target intensity is between 85-95% of peak heart rate (HRpeak),38 with a distinction to more sprint interval training (SIT), using low-volume supramaximal (i.e. all-out performance) ET.39 The principle of HIIT is based upon high intensity aerobic ET bouts (but still at an intensity below VO2peak) that are separated by periods of lower intensities that allow for recovery, making an individual able to reengage in high-intensity ET (Figure 1). Typically, HIIT is performed in activities involving dynamical work with large muscle mass (such as brisk uphill walking, running or cycling), at intensities close to peak heart rate (HRpeak: 85-95%) or VO2peak (80-90%) for 4 minutes. The recovery periods consist of walking or “jogging” at considerably lower intensities (60-70% of HRpeak of the intensity during the high-intensity interval) for approximately 2-3 minutes.38 It is important to note that the ET intensity is relative to the individual’s VO2peak and HRpeak and that every participant needs to be tailored individually such that two subjects exercising next to each other may look very different, one running very fast and the other walking, although they both are exercising at the same relative intensity. The differences stem from different CRF levels, but they would be experiencing the same relative exercise stress. This is illustrated in Figure 2 where two individuals with different CRF levels and HRpeak (Olympic athlete and CHD patient) have performed 4x4 minutes HIIT with the aim of reaching 90-95% of HRpeak. They possess widely different absolute heart rates (beats/min) and energy consumptions; however, they exercise at identical relative intensity (percentage of HRpeak). This also raises the point that HRpeak (preferably as close as possible to the individual’s true maximal heart rate HRmax) ideally should be measured for each individual before engaging with HIIT, in order to control the relative ET intensity properly. The training HR could then be monitored during the course of the HIIT program in order to adjust the absolute workload so that the relative exercise intensity remains constant as exercise capacity improves. However, if exercise testing prior to interval training is not possible, a rule of thumb is that the relative strain during the work-bouts should be perceived as 16-18 on the Borg scale,40 i.e. heavy breathing without getting too stiff in the legs. In addition, one should aim to maintain the chosen workload during all the repeated intervals during a HIIT session. If unable to maintain exercise intensity throughout the exercise session, a too high starting workload has been chosen. If a fifth or sixth interval is easily manageable after having completed the prescribed 4x4 minute intervals, a too low exercise intensity has been chosen. In addition, if the 3 minutes active recovery period feels very short, exercise intensity is likely too high and may interfere with the ability to complete a 4x4 minute HIIT session. If the three-minute active brake feels too long, a too low exercise intensity has been chosen. A typical HIIT session consists of 4x4 minutes interval, but HIIT can well be performed as 4x5 minutes, 3x5 minutes, 5x3 minutes, or something similar. Importantly, as illustrated in Figure 1 & 2, the increase in HR during HIIT occurs gradually during the first 1-3 minutes of the intervals. Typically, it takes longer time to reach 90% of HRpeak during the first interval. Reaching 90% of HRpeak at the end of the first 4-minute interval is normal, and an acceptable performance. In the continuation of the interval session, the aim is to reach higher in the target heart rate zone, 1-3 minutes into the intervals (as illustrated by the gradual increase in heart rate from intervals 1 – 4 in figures 1 and 2). It is crucial to avoid “sprinting” exercise to reach target intensity exercise zone as soon as possible and allow for good dynamic working conditions. The ET mode used during HIIT may thus be important. Uphill walking or running facilitate good dynamical work for most individuals, and the pace is actually rather slow. It is noteworthy that peak exercise during stationary biking normally produces 10-15% lower VO2peak compared to treadmill walking or running.41 If a CPET is performed before training, it is therefore crucial to test HRpeak/VO2peak in the specific exercise mode used during ET. However, testing of VO2peak is not of vital importance before performing interval training. It is more desirable to test HRpeak, but also that is not a prerequisite. One may instead reach the targeted intensity zone of 85-95% HRpeak guided by that one should be breathing heavily without being able to hold a conversation going, but still be able to continue for the whole 4-minute period, and 16-18 on the Borg scale of perceived exertion.
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Safety of HIIT
Even if ET is considered relatively safe,85 also for CVD patients,86 HIIT transiently elevates the risk of a CVD event in both young subjects with inherited CVD and adults with occult or diagnosed CHD.87 However, no evidence suggests that the risks of exercise outweigh the benefits. Indeed, the converse appears to be true.87 In a prospective study of over 12 000 U.S. male physicians who were healthy at baseline, it was found that habitual vigorous ET diminished the risk of sudden death during vigorous exertion.88 Although the safety profile of HIIT has not been fully established yet, there is data demonstrating that in stable and selected patients, such ET can be performed with relatively low risk. Our research group examined the risk of CVD events during organized HIIT and MICT among 4846 CHD patients in four Norwegian CR centers.89 Of a total of 175 820 ET hours, where all patients performed both types of training in separate sessions, we found one fatal CVD arrest during MICT (129 456 hours of exercise) and two non-fatal cardiac arrests during HIIT (46 364 hours of exercise). There were no myocardial infarctions associated with exercise in the data material. As the number of HIIT hours was 36% of the number of MICT hours, the rates of events to the number of patient exercise hours were 1 per 129 456 from MICT and 1 per 23 182 from HIIT. The absolute event rates were thus very low after exposure to both types of ET. Even if the low event rates after exposure to both types of ET modes may give a glimpse regarding the risk, we believe that larger RCTs are needed to further evaluate the risk of HIIT among CHD patients. Still, due to the more extensive use of HIIT in CR worldwide, we believe that this study gives an indication about the risk of such ET for secondary CR. A recently published systematic review also evaluated the safety of HIIT.90 The investigators included 11 HIIT studies with 156 patients with cardiometabolic disease and found the incidence of adverse responses during or within 24 hours post exercise to be around 8%, ‘mild in nature’ and only ‘somewhat higher compared to the previously reported risk during MICT’. They concluded based on this that: “caution must be taken when prescribing HIIT to patients with cardiometabolic disease”. A review assessed the efficacy and safety of HIIT for HF patients.91 Despite documented benefits of HIIT in patients with CVD, including CHD and HF, the authors stated that currently there is still insufficient evidence to supplant a MICT approach with HIIT.
https://ntnuopen.ntnu.no/ntnu-xmlui/bitstream/handle/11250/2486658/Karlsen.pdf
