EQUATION FOR SAFETY:
First, it is not advisable for anyone to attempt interval training without first getting medical clearance preferable from a sports medicine physician who has a clear understanding as to the physical demands to be encountered. For any person having coronary heart disease the answer must be a big no. For a healthy person having a reasonably good level of aerobic fitness - (i.e., a minimum V02max of 50ml/kg/min) there should be no problem. However, as an added safety measure, it would be a good idea to take a treadmill stress test to be sure that there are no cardiac abnormalities.
For best results and safety, the intensity of the interval workouts should be set using a percent of one's age-related maximum heart rate. An easy method of determining maximum exercise heart rate for interval work is to subtract your age from 220 and then use 90-95 percent of that figure. For a 40 year old individual the interval exercise target heart rate would be 171 (220 - 40 = 180 x .95 = 171). Remember too, interval training is very stressful on the body and joints and should not be done more than two times a week. Yes, young athletes are more resilient than master age-group athletes. They recover quicker and more fully between workouts which allows them to do interval training with greater frequency.
INTERVALS
The 20:10 work-to-rest ratio in the Tabata study produced substantial improvement in both aerobic and anaerobic work capacity, while the 30-second:4-minute ratio failed to produce improvement in either category.
Generally, short hard intervals with long rest periods are recommended to improve anaerobic capacity; and many sets and repetitions of longer less intense intervals with short rest periods are suggested to overload the aerobic system.
The relatively long 2 minute rest periods in 1E2 allowed oxygen uptake to fall considerably and, therefore, when the next exercise bout started there was a delay before the oxygen uptake increased and began again to approach maximum. On the other hand, the short 10 second rest periods in 1E1 allowed only slight recovery, and therefore oxygen uptake increased in each succeeding bout, reaching maximum capacity in the final seconds of the last bout. The same was true for anaerobic energy release. The long rest periods in 1E2 stopped the buildup of lactate and allowed the resynthesis of phosphocreatine (see creatine article on this website) to occur. Again, the short rest periods in 1E1 caused the oxygen deficit to continue building from rep to rep, reaching maximum anaerobic capacity at the end of the exercise.
Dr. Tabata's 1E1 protocol may not be perfect, but he and his colleagues seem to have found a sweet spot where aerobic and anaerobic capacity peak simultaneously.
Here are more details on the study:
As a follow-up to the study discussed in article #10, Forget The Fat-Burn Zone, Dr.Tabata and his colleagues conducted a second study "to evaluate the magnitude of the stress on the aerobic and the anaerobic energy release systems" of the high intensity protocol used in the previous study and, additionally, of a second interval protocol. (Medicine and Science in Sports and Exercise (1997) 29, 390-395) The two protocols in the follow-up study differed in three ways: interval duration, intensity and rest between bouts.
As in the previous study, young male members of college varsity teams exercised on stationary bicycles. The two protocols were given the catchy names 1E1 and 1E2. Protocol 1E1 was the same as before: following a 10 minute warm-up, each subject did one set of 6-7 bouts of 20 seconds at approximately 170% of the subject's maximal oxygen uptake (VO2max), with 10 second rest periods, to exhaustion. The 1E2 group did 4-5 bouts of 30 seconds at 200% of VO2max, with 2 minute rest periods, to exhaustion. For each protocol, the criteria for exhaustion was that the subject was unable to maintain a pedaling speed of 85 rpm. Expired gas was collected continuously every 10 seconds to measure the oxygen uptake. As in the earlier study, accumulated oxygen deficit was used to measure anaerobic energy release.
The 1E1 protocol taxed both aerobic and anaerobic capacity significantly more than the 1E2 protocol. The peak oxygen uptake during the last 10 seconds of 1E1 was "not statistically different from the subjects' VO2max." But the peak oxygen uptake at the end of 1E2 "was much less than the VO2max." Likewise for anaerobic output: For 1E1, accumulated oxygen deficit was essentially 100% of the subjects anaerobic capacity, but for 1E2 it was only 67%. In short, the 20 second intervals, with 10 seconds rest, overloaded both aerobic capacity and anaerobic capacity to the max, while the longer and harder interval protocol, with two minute rest periods, did not. In both respects, the stress produced by 1E2 fell well short of maximum.
SCIENCE BEHIND INTERVALS:
Coaches and athletes need to understand however, that short-term intense interval training has very limited application to long-distance events such as marathon running and the Tour de France. Long distance endurance athletes need efficient "fat burning" bodies. Their muscles must be trained to utilize energy from free fatty acid oxidation while conserving the limited stores of glycogen which are necessary for nerve and brain function. (Nerves and the brain derive energy only from glycogen - not fat.)
Another important consideration in understanding aerobic and anaerobic metabolism is that muscles differ in their ability to utilize oxygen. Slow twitch muscles are noted for their endurance and have the ability to use large quantities of oxygen required for fat metabolism during aerobic exercise. Fast twitch muscles are the strength and power producing muscles. They are good for explosive bursts of anaerobic energy for sprinting, jumping, lifting and interval work. However, they fatigue fast and are not efficient fat burners. Glycogen is their main source of energy during intense work making them ideal for anaerobic exercise lasting up to three minutes. Exercise lasting longer than three minutes is aerobic.
The bottom line is that short-term intense interval work is not designed to train the body to become an efficient fat burner as is required for long-distance endurance activities. However, for sprint cycling or running (up to 400 meters) intense interval training definitely offers major physical benefits. In the overall scheme of training for athletes participating in stop and go power sports (e.g., football, basketball, ice hockey and gymnastics) short-intense interval work has a major role to play in maximizing performance.
long duration exercise is not as effective as short intense intervals in reducing body fat. It is relatively easy to explain why this is so.
During strenuous exercise, the rate of metabolism rises, going to about 15 times the basal metabolic rate (BMR) and even higher during intense interval work. For example, running 5 mi/hr the oxygen uptake required is 28 ml 02/min/kg of body weight with 3.7 cal/hr./lb burned, while a short burst of intense interval work may require 100 ml 02/min/kg with 13.8 cal/hr/lb burned. By maintaining the high level of training over a 5 or 6 week period one would expect a significant increase in the ratio of lean body mass to fat. Over a three month period you would be RIPPED like never before.
Intense interval work utilizes a greater percent of the body's muscles, both slow and fast twitch. Also, performing high intensity work places added energy demands on the respiratory system, cardiovascular system and nervous system. Thus more fat and glycogen are burned to support the expanding energy demands of the body during - and after - intense exercise. In other words, the cost of short intense interval exercise is very high in terms of energy demands in comparison to low intensity aerobic exercise. What's more, while at rest trained active muscles burn more fat night and day, contributing to further fat loss.
Intense interval work is an excellent way of losing weight while simultaneously getting ripped for peak contest shape.
