Matt Perryman Matt Perryman

Interval Training, HIIT, and Tempo Training for Fat Loss

As I mentioned in the last post on the role of anaerobic metabolism in fat-loss training, you’re definitely better off doing some kind of activity that’s more intense than light jogging on the treadmill for miles at a stretch. That is, if you’re specifically trying to improve body composition. If you’re training for a race or something like that, it’s a different matter.

This is due to the adaptations that anaerobic exercise can create, which seem to be beneficial not just from the standpoint of weight loss, but with regards to actually reducing fat mass while retaining muscle tissue. In other words, “hard” exercise seems to favor changes in body composition as opposed to “merely” dropping weight. Although there are some potential reasons to question the claims generally made regarding interval training, the gist of it is that you do need some kind of intensive exercise to truly change your appearance.

However, I also mentioned that there was a downside: high-intensity anaerobic training represents a powerful stress on your body, and it can’t necessarily fit in with an aggressive strength-training program or a typical fat-loss diet. “HIIT” (short for High-Intensity Interval Training) has become the buzzword; want to lose fat in a hurry? Do HIIT!

The thing is, by adding in “HIIT” without any context, people may well be setting themselves up for problems. I figured I might as well expand a little bit more on what I mean, and lay out some useful guidelines.

What Are Intervals?

Much like strength training, cardio exercise has both an intensity and a volume component. Strength training measures these as weight on the bar (intensity) and either total poundage or total reps done (volume). Cardio training measures it with power output and duration.

When we speak of “high intensity” in this context, we’re talking about power output. You might have seen an indicator on the exercise bike or the rower that indicates wattage. This is power. In physics, we can express this in a few different ways, but the applicable description here is rate of doing work.

If it takes X force to move your body over distance Y, or to move a bike pedal through one cycle, or to row one stroke, then that represents the work done: X times Y. Obviously the greater the force you create, the greater the work done. Now, power is the rate of doing work – so Wattage is the force created per unit of time, or the work done each second.

That’s a bit of an awkward definition for non-physics people, I realize. To make this as easy as possible to grasp, we can say that power output will increase by either 1) increasing the force created (running/cycling/rowing “harder”) or 2) moving faster, which may involve a lower force output, but still represents a large power value as the rate will be high.

The thing about high power output is that it’s very taxing on the energy-producing systems of the muscle, as I’ve explained previously. Maximum power output will heavily involve the alactic-anaerobic pathway, and thus you can’t keep it up for very long – 15-30 seconds is the usual number given. What we want for fat-loss purposes is a value of maybe 30-120 seconds of continuous work in order to activate the glycolytic pathway, which would suggests a not-quite-maximal power output.

This is not unlike the suggestion made in weight training for muscle mass; you don’t want your best effort, or a 1RM, to create growth. You want to back off that to a weight that is heavy, but allows more total reps to be done. Instead of maximal power output, you’d want to look at maybe 70-80% of your best effort, which is still challenging, but allows you to do 30-90 seconds of work before you get exhausted.

The question is, how do you rack up a large volume of work if you can only last for 30-90 seconds? That’s the problem intervals are made to solve.

High-Intensity Interval Training (HIIT)

Interval training, by definition, is the alternation of work intervals and rest intervals.

The problem is, based on a scant few research studies, the trend has been to blow yourself out with maximal exertion: run as fast as you can, blow yourself out, and spend the next 5 minutes trying to get your heart rate under 170bpm. Thing is, that’s good in some instances for improving speed or speed-endurance, but for fat loss, not so much.

My point has always been that you need to maximize anaerobic output, not power output – yet people still confuse the two. They are not the same thing.

Now, I think a lot of this boils down to terminology issues; the original Tremblay study that got everyone excited about “HIIT” actually used short intervals (15-30 seconds) and long intervals (45-60 seconds) as part of its protocol. If maximal power is the determinant of HIIT, then this only halfway qualifies.

This would suggest that, for fat-loss purposes, we’d want to steer away from the “high-intensity” elements.

Tempo Training

Tempo training, as I’ve mentioned previously, is an idea I got from Charlie Francis, and subsequently have used with some success in training figure competitors. It’s based on the notion of “moderate intensity” interval training, used to preserve fitness and general endurance without adding further stress to a sprinter’s weekly training.

Charlie’s tempo training would involve something like 100m + 100m + 200m + 100m + 100m, where the + is a brief jog of 100m. That would be one set or round. The suggestion is to use 70-75% of best speed, so that would probably work out to a 15-20 second run for an elite-level sprinter (give or take). You might end up doing 4-6 rounds in one workout.

Since I’m assuming most people concerned with this aren’t sprinters or cyclists or competitive rowers, we don’t necessarily have to follow the prescription to go down to the track and rack up 2-4km worth of distance. What I’ve done for the physique people is adapt it to time, and then lay out it out as rounds or sets – and yes, it’s identical to a set in a strength workout.

It’s easy enough to set up a tempo-style program on a cycle or a rower. The treadmill has never been ideal for any kind of interval training, and this is no different. Some of the newer models that allow fast adjustments might work, but otherwise there’s generally a 5-10 second lag-time as the treadmill changes speed.

Pick a 30-60 second work interval which is moderately uncomfortable. It does not have to be maximal exertion so that you feel like dying towards the end. In fact, that’s counterproductive as you’ll be doing several of these work intervals with only a minimal rest. You’ll do a work interval, rest, do another work interval, etc, until you complete the set. So it might end up as a 4-5 minute block where you alternate between work and jog intervals. After that, rest for a minute or two by switching to a very easy “walking” pace. That’s one set.

The net effect is that over a workout, you end up with more total work done (more calories burned) because the average output was higher, and the total duration of work was longer. This is following with the theme I mentioned before about how fat-loss interval training is going to look more like steady-state exercise than pure intervals.

Contrast this to HIIT sprint-type training. You might rack up what, 5-10 work intervals? Of maybe 15-30 seconds? At most, that’s 300 seconds or around 5 minutes of actual exertion; most of your time is spent resting. A moderately comfortable tempo session might be 4-5 sets of 5 minutes each – a total of 25 minutes of more or less constant work, not counting rest times between sets.

If you’re looking at it from a standpoint of calorie-burning, then there’s little comparison to be made. This is combined with the fact that, done correctly, tempo training is not going to represent the profound stress of a HIIT workout. Which means you can do it more frequently.