HIIT vs. Steady-State for Fat Loss: Can EPOC Really Explain the Benefits of Intense Interval Training (HIIT, SIE, HIE)?

HIIT vs. Steady-State for Fat Loss: Can EPOC Really Explain the Benefits of Intense Interval Training (HIIT, SIE, HIE)?

EPOC fat loss fatty acid oxidation HIIT hit LISS; MCT MIT SIE steady state wingate workouts

HIIT has been touted to work its fat burning magic by increasing post-exercise oxygen consumption aka EPOC, a marker of the amount of fat you burn after your workouts. Eventually, however, only the total oxygen consumption and energy expenditure count and this is where the putative mechanism behind the fat loss effects of HIIT lacks scientific backup.

Higher excess postexercise oxygen consumption (EPOC) after high-intensity interval exercise (HIIT / HIE) and sprint interval exercise (SIE) has long been touted to explain the greater fat loss scientists observed in several studies which compared the fat loss effects effects classic "cardio" aka steady-state exercise (SSE) to interval training (HIIT / HIE).

To elucidate whether that's a reasonable and, more importantly, sufficient  (meaning: "Is the increased energy expenditure high enough to explain the fat loss, even if the steady state exercise consumes more energy and fat on total?") explanation for the previously mentioned advantages, researchers from the Healthy Lifestyles Research Center at the Arizona State University conducted a study to compare the EPOC response to the three most common forms of aerobic training: high intensity interval exercise (HIE), sprint interval exercise (SIE), and steady state exercise (SSE).

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Ten recreationally active males (age 24 ± 4 y) participated in this randomized crossover study. On separate days, subjects completed a resting control trial and three exercise conditions on a cycle ergometer:

• HIE (four 4-min intervals at 95% HRpeak, separated by three min of active recovery); and 
• SIE (six 30-s Wingate sprints, separated by four min of active recovery); and 
• SSE (30 min at 80% of peak heart rate (HRpeak)). 

Oxygen consumption (VO2) was measured continuously during and for 3 h after exercise to estimate the actual amount of excess energy / fat that was consumed in the three treatment conditions.

Figure 1: Oxygen consumption and respiratory exchange ratio (higher numbers = higher carbohydrate to fat oxidation ratio) during the first three hours after exercise (Tucker. 2016).

Unsurprisingly, VO2 was initially higher than resting control for all three treatments. The increased oxygen consumption, which is a marker of fatty acid oxidation, however, didn't last long: After only 1 h, it returned to pre-exercise levels.

There's room for "cardio": Even though it is not popular, these days, it would be wrong to assume that classic steady state training is always the inferior choice. For someone who's killing it in the gym regularly, the additional HIIT training may in fact be too much of a sympathetic stimulus. The "boring" classic "cardio" training, on the other hand, is predominantly parasympathetic, which is why walking on an incline treadmill may eventually be a better complement to your 4-5 resistance training sessions per week than HIIT cycling or sprinting.

It is thus not really surprising that both, the complete 3-h EPOC and the total net EE after exercise were not extremely different and that that 3-h EPOC and total net EE after exercise were higher (p=0.01) for SIE (22.0 ± 9.3 L; 110 ± 47 kcal) compared to SSE (12.8 ± 8.5 L; 64 ± 43 kcal).

Figure 2: The total O2 consumption (and thus fat oxidation) and energy expenditure during the workout and the 3h thereafter shows that steady state exercise burns more fat and energy than any of the two HIIT regimen (Tucker. 2016).

What goes against the idea of increased fat oxidation after workouts due to HIIT (i.e. SIE or HIE), however, is the scientists observation that the "total (exercise + postexercise) net O2 consumed and net EE were greater (p=0.03) for SSE (69.5 ± 18.4 L; 348 ± 92 kcal) than for SIE (54.2 ± 12.0 L; 271 ± 60 kcal)" (Tucker. 2016), while those for for HIE were not significantly different from SSE or SIE, so that Tucker et al. rightly conclude that "EPOC after SIE and HIE is unlikely to account for the greater fat loss per unit EE associated with SIE and HIE training reported in the literature" (Tucker. 2016).

Bottom line: As Tucker et al. rightly point out, simple math shows that the increased energy expenditure and O2 consumption during the steady state trial more than compensates the significant, but small increase in energy expenditure and fat oxidation after the workout.

Figure 3: Minute-by-minute energy expenditure during a sedentary day and a day beginning with a single bout of sprint interval training (SIT). Data are mean values (Sevits. 2016).

It is important to know that this does not negate the results of previous studies that found beneficial effects of HIIT on fat loss. What the study does do, however, is to refute the hypothesis that these benefits were a result of an increase in EPOC and thus overall larger total energy expenditure. This, on the other hand, doesn't mean that any effects after the EPOC window of 3h investigated in the study could be responsible for said benefits. As Tucker et al. highlight, "another previously confirmed benefit of intense exercise is that it can increase the resting energy expenditure (REE) [... 17-24 h after exercise ...] in part due to an increase in sympathetic tone " (Tucker. 2016).

In conjunction with increases in the ease of locomotion (16, 17) and increase nonexercise activity thermogenesis (NEAT) (14), these effects could well explain the benefits of HIIT. Studies to confirm that are yet not just lacking, as Tucker et al. highlight, the whole-room calorimeter study of Sevits et al. (32) even suggests that SIE does not elevate REE at 24 h postexercise (see Figure 3). More studies to get to the bottom of the fat loss benefits of HIIT protocols appear warranted | Comment.

References:

• Sevits, Kyle J., et al. "Total daily energy expenditure is increased following a single bout of sprint interval training." Physiological reports 1.5 (2013): e00131.
• Tucker, Wesley J., Siddhartha S. Angadi, and Glenn A. Gaesser. "Excess postexercise oxygen consumption after high-intensity and sprint interval exercise, and continuous steady-state exercise." The Journal of Strength & Conditioning Research (2016).

Normal-Weight Women Lose >6kg Fat Mass in 6 Weeks With Three 15x60s HIIT Workouts/Week - Without Dieting

Normal-Weight Women Lose >6kg Fat Mass in 6 Weeks With Three 15x60s HIIT Workouts/Week - Without Dieting

high intensity HIIT interval training LISS lose fat low intensity steady state

I am still waiting for a study using only body weight exercises like squats, push ups, burpees and co as a HIIT regimen for weight or rather fat loss.

While HIIT is gaining ground especially in male muscle heads, women like the twenty-three previously untrained women (28.43 ± 12.53 years), who participated in a recent study from the Department of Sport at the School of Physical Education and Sport of the University of Sao Paulo in Brazil (Panissa. 2016), are gravitating rather towards training in the alleged (but non-existing) "fat burning" zone at an intensity of 70% of their individual HRmax.

I guess, Panissa et al. knew that, because in their latest study they compared the effects of 6 weeks of high-intensity intermittent training (HIIT) to those of moderate intensity continuous exercise (MICT-control group) on body composition (skinfold measures), hunger and food intake.

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As previously highlighted, the subjects were twenty-three previously untrained women (28.43 ± 12.53 years) who were randomly assigned to a HIIT (n = 11) or MICT group (n = 12).

• The HIIT group performed 15 1-min bouts at 90 % of maximum heart rate (HRmax) interspersed by 30-s active recovery (60 % HRmax). 
• The MICT group performed a continuous exercise at 70 % HRmax equalizing the training load method proposed by Edwards (1993) to a similar value achieved by the HIIT group. 

Training for both groups was performed on regular cycling ergometers three times per week for 6 weeks. More specifically, both groups performed the same warm up and cool down, composed by 3 min at 60 % of maximum heart rate, MICT sessions consisted of moderate intensity aerobic exercise, i.e., after warm up the subjects performed 29 min at 70 % of maximum heart rate. HIIT group performed 22 min of HIIE using a 2:1 effort–pause ratio, where the effort was 1 min at 90 % of maximum heart rate and recovery was a 30s exercise at the same load as warm up (60 % HRmax).Each training session was closely supervised, and load was adjusted according to individual HR prescription. During this period subjects were asked to avoid any supervised exercise and strenuous efforts during their daily routine.

Was the training load standardized? To equalize training load between groups, the scientists used a method proposed by Edwards (1993). He proposed a zone based method for the calculation of training load. According to Edwards model, the time spent in five pre-defined arbitrary zones is multiplied by arbitrary coefficients to quantify training load. You can read up on the method here.

The performance effects were assessed by the means of Astrand cycloergometer that were used to estimate maximal oxygen consumption (VO2max) 1 week before and after the training period.

"Feeding behavior was assessed by two methods: (1) a 3 days daily food recordatory, including 1 weekend day before the protocols at baseline and after the last session. A detailed explanation for filling the food diary was held at the end of the evaluation, to be returned completed during the first week of training. The analysis of food diaries was made from the application to FatSecret [Subar. 2010]; (2) Immediately after each training session, participants answered a Visual Analog Scale (VAS) of Hunger ranging from 1 to 10, where 1 corresponded to no sensation of hunger and the 10 maximum feeling of hunger" (Panissa. 2016).

The subjects body composition was calculated based on detailed measures of skinfold thickness (triceps, subscapular, chest, supra iliac, abdominal, thigh and leg and the circumference of waist, hip, arm, chest, thigh) and legs - a method that is, assuming it is done correctly, as accurate as an expensive DXA-scan (Eston. 2005; Steinberger. 2005).

Figure 1: Relative changes in BMI, fat free mass (FFM), fat mass (FM) and waist circumference over the 6 week study; absolute changes in kg/m², kg and cm are displayed as first number below the bars (Panissa. 2016).

As you can see in Figure 1, both interval and steady state training induced significant pre- to post-decreases for fat mass, fat percentage, waist circumference and sum of seven skinfolds.

This is no "HIIT is better than LISS / MICT study! Theoretically, the study at hand "proves" that HIIT is more effective than LISS, but let's be honest: if you volume-equate HIIT and light / medium intensity training you end up at durations for the LISS / MICT of which no one would be surprised that they don't trigger fat loss. Plus: Facebook Fans know: HIIT decreases MICT / LISS increases appetite when all things are considered (more). Furthermore, the women were untrained and didn't do extra resistance training which would add additional load on the sympathetic nervous system and may thus (if done 3+ times per week) better be combined with LISS or MICT which would provide a parasympathetic stimulus that could ideally complement your resistance training training.

With a 2:1 fat to muscle ratio, the HIIT regimen was yet significantly more successful in improving the subjects' body composition (which obviously depends on the relative, not the total amount of fat) and that despite the fact that the energy intake didn't change significantly in either of the groups.

Figure 2: Daily energy intake in kcal before and during / after the exercise intervention (Panissa. 2016).

Another parameter that showed a measurable, albeit not significant inter-group difference is the effect of the exercise intervention on the subjects' fitness, as it can be predicted based on the subjects VO2max, a value that increased by a whopping 31.12% in the HIIT group, and only 16.70% in the MICT group - a difference that can hardly surprise the average SuppVersity reader.

Isn't HIIT for everyone? Study suggests: Effective- and usefulness of high intensity interval training depend on age and fitness level | learn more

Bottom line: HIIT wins, but not with a statistically significant advantage. As the authors point out, "the main result of the present study was that although the HIIT was able to promote a higher decrease in body fat mass" (Panissa. 2016). Furthermore, the observed benefits of HIIT were not, as previous studies had suggested, due to changes in hunger and energy intake. This important observation leads the authors to conclude that "the hypothesis that changes in hunger (measured by analogical visual scale in all training sessions) and in energy intake (measured by food diaries preand post-training) would contribute to a higher efficiency of HIIT to decrease body fat was not confirmed by our results" (Panissa. 2014).

What the scientists forget to mention in said conclusion, however, is that the lack of statistical significant differences may be a consequence of the "short term" nature of their study, they emphasized in the title "Can short-term high-intensity intermittent training reduce adiposity?" (Panissa. 2016). I bet: In a longer term and/or better powered follow up study, the already visible changes will achieve statistical significance | Comment!

References:

• Edwards S. "High performance training and racing." In: Edwards S (ed) High performance training and racing. Feet Fleet Press (2013), Sacramento, pp 113–12.
• Eston, R. G., et al. "Prediction of DXA-determined whole body fat from skinfolds: importance of including skinfolds from the thigh and calf in young, healthy men and women." European journal of clinical nutrition 59.5 (2005): 695-702.
• Panissa, Valéria Leme Gonçalves, et al. "Can short-term high-intensity intermittent training reduce adiposity?." Sport Sciences for Health (2016): 1-6.
• Steinberger, J., et al. "Comparison of body fatness measurements by BMI and skinfolds vs dual energy X-ray absorptiometry and their relation to cardiovascular risk factors in adolescents." International journal of obesity 29.11 (2005): 1346-1352.
• Subar, Amy F., et al. "Assessment of the accuracy of portion size reports using computer-based food photographs aids in the development of an automated self-administered 24-hour recall." Journal of the American Dietetic Association 110.1 (2010): 55-64.