Get Ripped with High Intensity Interval Training


TEAM MD

There is a prominent tissue in the body that is nearly universally hated; vehement, irrational anger is evoked. Entire industries have arisen to deprive, deplete, even hack away and suck out the vile offender— fat. Nearly everyone is so mad at fat that they want to burn it. Fat can take a punch, but can it take a HIIT (high intensity interval training)?


The low-cost and low-tech approaches have ranged from simple “calories in, calories out” programs to Forrest Gump-like marathons wrapped in rubber. It takes a level of crazy to follow some of these examples, à la Bradley Cooper’s character in “Silver Linings Playbook.” The saner approach is to consider what it takes to get rid of fat, focusing on active interventions as well as dietary restrictions. Walking, jogging, sprinting, weight training, etc. all increase the rate of energy expenditure (calorie burning). To reduce fat, one needs to find the activity that best “burns” calories during and following exercise; what type of exercise burns the greatest percentage (and total number) of fat calories as opposed to sugar (glycogen, circulating glucose, ketones); what option does not break down lean mass or cause harm; and what type of activity people will enjoy enough to commit to regularly. People need to work smarter, not just harder.

The maximal number of calories that can be burned at any one point in time might seem like the goal, but the body is not designed to maintain that rate for more than a few seconds. There is a metabolic term, “lactacte threshold,” that defines the maximal intensity a person can reach before he/she begins to accumulate lactic acid from the “sugar burning” component of energy production, rather than sending the breakdown parts of sugar into the mitochondria.1 It is sensed as “pain” to prevent cellular damage (Richard Edwards’ “catastrophe theory”), resulting in an increased likelihood that the exercise will not be enjoyed or adhered to by participants.2 The mitochondria are specialized “organelles,” or compartments, within the cell that use small fragments of sugar, amino acids and fatty acids to generate ATP. ATP is the “energy molecule” that drives cell functions, such as muscle contraction/relaxation. ATP is like a spark that you see shooting off a wire— it takes a coordinated and sustained progression of sparks to form an electrical current. Similarly, ATP needs to be abundantly available to maintain muscular activity. As lactic acid, ammonia (as a breakdown products of amino acids) and other metabolite concentrations build in the muscle cell and blood, contraction force and frequency is rapidly reduced. Eventually, the muscle and the mind “fatigues” despite available sugar, fatty acids and ATP (upon recovery).3,4

Less Bang for Your Buck?
Aerobic metabolism within the mitochondria is so much more efficient than anaerobic metabolism in the cytoplasm (cell “innards”) that the hardest-working muscle— the heart— is nearly entirely dependent upon aerobic metabolism. The constant energy demand causes the muscle of the heart to be considered as a different tissue than skeletal muscle. Exercise below the lactate threshold can be continued for hours, as evidenced by endurance athletes. However, the rate of calories burned is less, and the movements that are allowed are necessarily efficient, giving less “bang for the buck.” Whereas some people enjoy long runs or bike rides, many people do not have the luxury of open time or any enthusiasm for the activities.

Further, though runners wish to believe they represent the pinnacle of health, recent research is suggesting otherwise. Reminiscent of the death of Jim Fixx (author of The Complete Book of Running) at age 52 of a heart attack after his daily run, a review was published in the journal Mayo Clinic Proceedings.5 Despite the fact that regular exercise is strongly associated with a longer and healthier life span, there are significant and harmful changes that occur in those who practice more extreme endurance training (e.g., marathons, triathlons, cycling). The strain associated with these sports can be so severe as to result in long-term damage to the structure and function of the heart; as well as calcification of the coronary arteries (the blood vessels that bring oxygen to the heart) and large vessel stiffening. This sets up the endurance athlete for a heart attack, such as the one that took the life of Jim Fixx, or dangerous rhythm disturbances in the heartbeat. This agrees with a prior study published in 1999 that followed experienced runners for 12 years. The authors concluded by noting that the changes seen may be deleterious (harmful) in rare cases.6

Still, people want to believe that simple “cardio” will lead to weight loss. Every January, there is a temporary flood of new members flocking to gyms. Invariably, they get on the treadmill, as it is a non-threatening piece of equipment, hoping it will improve their health and aid in weight loss. Six weeks later, the wall-mounted television screens project reality shows to empty rows as unfulfilled goals are postponed to the next year’s resolution (again). One common factor among those who “drop out” of training studies is a low level of physical fitness or exercise experience.7,8

Another consideration is the effect of the exercise on lean mass. How many endurance runners have you seen with significant muscle? Very, very few. This is a function-specific effect, as the body sheds all excess weight, whether it be fat, muscle or bone. Hours long endurance events rob the muscle of amino acids, and their breakdown products are used for energy (about 1-6% total energy requirement), resulting in less muscle mass over time.9 This is particularly relevant in the setting of caloric restriction (dieting) as the effect can be avoided or minimized if adequate carbohydrates and protein are consumed— particularly during the post-exercise window.

Lastly, though the rate of calorie burning is increased during low-intensity “aerobic” exercise, the effect does not last.10 There is also a “time spent exercising” factor involved, so brief (e.g., five minute) periods of high-intensity work do not have lasting value either (i.e., increase calorie or fat burning the remainder of the day).

However, it is not a “damned if you do, damned if you don’t” situation. The best exercise mode for fat burning and increasing total energy expenditure (all-day calorie burning), without sacrificing muscle mass, is a combination of high- and low-intensity exercise called interval training. To make it sound sexier, the advocates call it “high-intensity interval training” or HIIT, but logically if something is interval training, there are at least two components that differ in some aspect.

Train Smarter and Harder
HIIT offers all of the advantages needed to train smarter, as well as harder. However, it must be performed properly. HIIT still requires a considerable amount of time— it is not just a few sprints on the treadmill. HIIT is not standardized, but proper programs require (after a warm-up) four to six all-out, max-effort sprints of 30-60 seconds. This is “interval-ed” with four minutes of low-intensity (not resting) effort. An easy example is the typical quarter-mile (or 400-meter) track. After warming up with a one-lap walk, jog, side shuffle or whatever, a series of four to six intervals alternating between a 200-meter sprint (approximately 30 seconds for recreational runners, 45 seconds for beginners) and then walking 400 meters at a brisk pace (approximately four minutes at just under four miles per hour pace); repeat. This can be altered for variety sake by changing the terrain (e.g., hills), setting (e.g., swimming pool, neighborhood, park) or using training tools (e.g., resistance bands, drag chutes). Treadmills are an option during inclement weather, but the great outdoors are best. Following this protocol results in 20-30 minutes of “cardio” with constant activity and bursts of high-intensity movement. It is important to get not only an intense workout, but also one of sufficient duration.10 Additionally, as one becomes more aerobically “fit,” recovery after exercise is improved.11 Creatine supplementation may also be beneficial.

As opposed to plodding along on a treadmill long enough to overwhelm your deodorant for a few weeks until you give up, this is something many people enjoy. A recent study looked at the preference of elementary school boys, who were following a stationary bike program to combat obesity.12 When sprint intervals were added (four seconds every minute), more calories were burned (though most of the extra calories during exercise were carbohydrate based) and the activity was more enjoyable. This promotes adherence (sticking with it), which is one of the biggest hurdles.

Sprinting, as the high-intensity portion of a HIIT program, may depend more on carbohydrates than fat during the actual sprint. However, when examined over time, the effect is greater fat loss, due in part to post-exercise calorie burning. A study in the Journal of Obesity reported that men who performed three 20-minute sessions of HIIT cycling (eight seconds of sprinting with 12 seconds recovery) weekly for 12 weeks lost a significant amount of fat (4.4 pounds) and visceral fat, while adding a small amount of muscle (1.2 pounds).13 These effects were greater than the same amount of energy spent cycling at a moderate pace for 40 minutes three times a week, and required less time.

Other studies have confirmed a net benefit on body composition in young adults following a HIIT-type program, agreeing with the above-mentioned study.13-15 This is associated with reductions in insulin resistance, improved glucose tolerance, increased adiponectin (beneficial fat cell hormone), cardiovascular and metabolic benefits, increased fat oxidation and increased growth hormone response to exercise.15-18

Timing is one factor many people inquire about. Despite challenges by many gurus, there is a fair amount of scientific support for performing weight loss-oriented exercise in the fasting state (e.g., before breakfast).19,20 It is important to be well hydrated, and to be cautious as coordination or reaction time may be impaired when hungry.

For many people, engaging in regular walks or moderate-intensity recreation (e.g., rollerblading) is rewarding. It requires an admirable amount of discipline and dedication; activities can be done solo or as part of a social group. Undoubtedly, moderate-intensity “cardio” has been the mainstay of weight-loss programs for many people. Success is not guaranteed, any more so than for any other program. However, in terms of maximizing the possibility for success, following an interval-style training program— incorporating brief periods of maximal effort with longer recovery periods at a moderate intensity— is associated with a number of changes that promote weight loss, and fat-loss success. Many people report the interval training to be more enjoyable, and it increases both the total energy expended during exercise (calories burned), as well as keeping the metabolic rate elevated throughout the day. Hormonal changes not seen with moderate, steady-paced exercise occur with HIIT training and the changes promote fat loss and metabolic health (e.g., better insulin sensitivity). The net result has been shown in studies, including improved cardiovascular function and body composition. Additionally, the loss of lean mass that is common with endurance training is avoided with HIIT training; many subjects demonstrated an increase in lean mass during periods of fat loss.

New Year’s is coming so its resolution time. If the treadmills failed you, and you just can’t face another year of wishing you were slimmer or lean, consider HIIT training.