Does heart rate matter in interval and aerobic training?

You can easily find mathematical patterns to count “fat burning zones” in aerobic training done on the machines in a club on the Internet. Even I used one of those myself, e.g. the HR max = 220-age. However, there are many problems connected with using patterns and the attitude towards “fat burning” - problems, which derive from effort physiology and rooted “beliefs”.

Basic problem is setting the maximal heart rate for an individual

Are there any patterns, which count proper heart rate during workout?

The most frequent pattern used to count the maximal heart rate is this: HR max = 220 - age (for a 30-year-old the maximal heart rate during training should be 190 beats per minute). Other way is the method of maximal reserve.

HR max = percentage of the planned effort x (HR max – HR rest) + HR rest

Where HR max = maximal heart rate for a particular person. For a 30-year-old the maximal heart rate (HR max) should reach 190 beats per minute (from the first pattern). HR rest = rest heart rate (without doing any effort), i.e. 70 beats per minute. Then, we should count heart rate reserve (HR max – HR rest): 190 – 70 = 120. The plan is to do workout in the range of 70-90 % of HR. It means we should multiply 0.7 * 120 = 84 and 0.9 * 120 = 108. Then you should add rest heart rate (70). That's how you get two ranges: 70 (HR rest) + 84 (the range of 70%) = 154 and 70 + 108 (the range of 90%) = 178 beats per minute. As you can notice, when using the first pattern for the value of 70% of HR max (190), you would get the result of 133 beats per minute. The results differ significantly within the lower limit of the advised heart rate (133 beats per minute from the first pattern and 154 from the second).

But, the patterns cannot be sufficient interpretation, because the heart rate you achieve during physical effort is individual. After Jack Daniels: “I checked a 30-year-old runner from the top myself, whose HR max was 140 beats per minute […], I also met many famous 50-year-old runners whose maximal heart rate was over 190”. As you can see, counting the percentage of HR for those people, which would base on common patterns would make their training impossible!

To sum up: don't follow heart rate only. Until you do very expensive tests, you are not able to tell what level of heart rate during work is optimal for you. Treat the patterns just as a reference point. If you plan to increase your speed, reduce fat, improve sports results – remember, that only training at the lactate threshold occurs to be efficient within longer perspective. Elliptical machines in fitness clubs and very intensive workout, which allows reading newspaper will make you stay fat. How do you want to lose fat when doing an exercise and watching TV or chatting with friends at the same time? Without sweating and intensity you will not gain results.

“There is nothing like the fat burning zone”

It is said that: “fat is burnt only in the zone of 60-70% of the maximal heart rate with moderate aerobic work – running slowly, walking on the machines, cycling, marching, etc.”

Fact: the most efficient fat burning training is that, when during increased pace (e.g. sprint, ascent, clean and jerk and pulling the load, jumps) your heart rate ranges between 85-95% of the maximal heart rate. The rest zone (aerobic) is only coplementary for hard work in intervals. Aerobic exercises (low-intensity workout, in the zone of 50-70% of the maximal heart rate) may be efficient as a completion of interval training.

It was stated that, in order to reduce fat, not only the work in aerobic zone may be efficient. The thresholds of aerobic and anaerobic changes are connected with gaining energy from various energy systems. During high intensity, in other words, anaerobic changes – the sources of energy are phosphocreatine and glucose (e.g. sprint/intervals, resistance training, punching). In the aerobic changes, the source of energy is glucose (after few minutes the work is supplied in majority from the aerobic system) and fat (especially physical effort taking many hours). Attention: For each individual the lactate threshold starts with different pace of running! According to J. Gorski, in his publication “physiological basics of physical effort”: “young, healthy people can achieve lactate threshold running even 9-12 km/h, whereas moderate-distance runners of 14-17 km/h and marathon runners and long-distance runners can reach it with the pace of 16-20 km/h!”. The higher the lactate threshold – the better efficiency. It means the ability of running fast sustained for many kilometres. High-intensity interval training (VO2 max) is working alternately in the aerobic and anaerobic zone.

Do you need facts and research about the effectiveness of intervals?

The interval group lost 2.5 kg of fat within 15 weeks – doing only three workouts a week. Each workout lasted 20 minutes (8 seconds of speed, 12 seconds of rest on an elliptical machine); another group of ladies did 3 low-intensity sessions a week (aerobic), lasting 40 minutes – they did not lose fat. Paradoxically, ladies who did intervals sacrificed half of the time of the aerobic group and, opposite to the other group, achieved results! What's more, the ladies from the interval group increased muscle mass by 0.6 kg, and the aerobic group did not build any muscles! [Trapp, 2008]

Boudou et al. checked how the interval training would influence men suffering from diabetes (type 2); after 8 weeks of doing exercises, abdominal obesity decreased by 44%!

It turned out in the study, that it would be necessary to do 7 one-hour workouts of aerobic training (e.g. the expenditure of 520-550 kcal per hour of using the elliptical machine), what can be replaced with two interval sessions. In one of the tests the men exercised only one hour a week and they achieved significant results (seven times shorter time of training).

Australian scientists checked the thesis on 46 obese men. All of them were over 20 years old (24.7 +/- 4.8 and 25.1 +/- 3.9), average BMI ranged between 28-29. There were no significant changes in diet. Half of the men trained 3 x a week for 20 minutes (on elliptical machines). They did 5-minute warm-up, then 8-second sprint with the rest of 12 seconds (40 turns per minute). The men were exercising within 80-90% of HR max (120-130 turns per minute) and they finished their workouts with 5-minute cool down. Their heart rate during the test was on average 160 +/- 9 beats per minute. After 12 weeks of workouts they lost 2 kg of fat (the loss by 17% of visceral fat; few cm less in waistline), they increased their maximal aerobic threshold (VO2 max) by 15% and their lean body mass increased slightly (i.e. muscle growth). The balance of weight loss was 1.5 kg. The biggest growth of muscles was within the upper body, smaller in legs and the smallest in arms (0.4 kg for legs and 0.7 kg for trunk).

In the study from 2008, which compared classic aerobic workout with interval workout – one group was running with steady pace (with the speed of 12.6 – 13.4 km/h), averagely for 52.3 (+/- 2.4) minutes, 4 x a week, doing 11.3 km during one running session and 45.2 (+/-5.1) km per week. The other group, during the experiment, did only warm-up, low-intensity interval training (8-12 sprints lasting 30 seconds with the breaks of 3 minutes) and cool down after the intervals. The total time of the additional run was only 9.9 +/- 0.3 km per week. During the intervals the volunteers speeded up to 22.4 (+/- 0.4) km/h.

Despite the weekly distance lower by 65% in the interval group, the volunteers sustained the endurance letting them achieve the same time of running for 10 km. Conclusion? You can save 65% of your time and achieve the same results. Additionally, those who were running intervals expended less energy with the submaximal speed (increase by 5-8%).

In another study, the cyclists improved their time per 40 km by 2-4% - doing only 2 interval sessions a week (12 sprints lasting 30 seconds).

Conclusions?

Interval training is efficient in burning fat, despite being far from low-intensity work (60-70% of HR). It is effective, because it bases on the influence on metabolism (excretion of growth hormone, testosterone, adrenaline, noradrenaline, lowering the level of insulin, improving the insulin tolerance). Aerobic training (especially long-lasting and frequent) may have negative influence on hormones (among others, it may contribute to losing fast fibres, decrease the level of testosterone, muslce mass and power).

Additionally, interval training may speed up metabolism to 24% within 24 h after finishing work. Aerobic workout has insignificant influence on metabolism.

Does it mean that I should forget about aerobics? No, you just have to introduce interval training in your plan, too. Classic aerobic exercises compose wonderfully with interval training, e.g. jogging can be treated like a warm-up before intervals or it can be a tool for after-workout fat burning after intervals. However, if you plan the whole sessions, it's impossible to rely on mathematical patterns, which set heart rate – there's nothing better than knowing the tempo of work of your own body.

Sources: 1. “Four weeks of speed endurance training reduces energy expenditure during exercise and maintains muscle oxidative capacity despite a reduction in training volume”. F. Marcello Iaia, Ylva Hellsten, Jens Jung Nielsen, Maria Fernström, Kent Sahlin, Jens Bangsbo1. http://jap.physiology.org/content/106/1/73.long 2. “Effect of high-intensity interval training on cardiovascular function, VO(2)max, and muscular force.” J Strength Cond Res. 2012 Jan;26(1):138-45. http://www.ncbi.nlm.nih.gov/pubmed/22201691 3. „High-intensity aerobic interval training increases fat and carbohydrate metabolic capacities in human skeletal muscle.” Appl Physiol Nutr Metab. 2008 Dec;33(6):1112-23. 4. “The Effect of High-Intensity Intermittent Exercise on Body Composition of Overweight Young Males” J Obes. 2012; 2012: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3375095/#B8 5. http://www.ergo-log.com/interval-training-helps-the-obese-lose-weight.html 6. http://potreningu.pl/artykuly/1017/mity-dotyczace-hiit-oraz-innych-form-treningu-interwalowego 7. “The effects of high-intensity intermittent exercise training on fat loss and fasting insulin levels of young women. “ Trapp EG, Chisholm DJ, Freund J, Boutcher SH. International Journal of Obesity. 2008;32(4):684–691. http://www.ncbi.nlm.nih.gov/pubmed/18197184