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Sub-Max Intervals Everyone Can Use

Intervals give more bang for the buck, right? So why do we seldom see anybody in fitness centers doing them? Simple: Intervals are fast, time efficient, effective—and hard. They can be daunting. For beginners and those not accustomed to exercise, intervals can be downright scary.

In 1997, we reported that 6 to 8 very hard 20 second intervals with 10 second rest periods may be one of the best possible training protocols. A total of two minutes of all-out effort has been shown to produce the same or better results than two hours of traditional endurance training. The problem is that the training can be brutally hard. The subjects in the original research (highly trained speed skaters) collapsed on the floor, gasping for breath, after doing the protocol. The original researcher was frankly surprised that some health and fitness trainers were interested in doing his protocol. A conditioning expert for Reebok opined that most people would not want to do interval training “because it is so uncomfortable, but for those willing to endure it would work.”

Researchers Hood, Little, Tarnopolsky, Myslik, and Gibala at McMaster University in Canada have an answer. They’ve come up with--and tested--a protocol that’s suitable for sedentary individuals. And it works. What’s more, the regimen is also appropriate for experienced trainers, perhaps as part of a larger and varied program.

Recognizing that all-out intervals may not be realistic for many people, the McMaster team devised and tested a more measured and practical interval protocol. Here’s the new protocol and the results.

The Study

“Much of [the work on interval training] has focused on young active individuals and it is unclear if the results are applicable to older, less active populations,” the McMaster wrote in introducing their report. “In addition, many studies have employed ‘all out,’ variable-load exercise interventions that may not be practical for all individuals. We therefore examined the effect of a more practical low-volume, sub-maximal, constant-load HIT [High-intensity Interval Training] protocol on skeletal muscle oxidative capacity and insulin sensitivity in middle-aged adults…”

Seven sedentary, healthy volunteers (4 men and 3 women), average age 45, were selected to perform six training sessions spread over two weeks (Monday, Wednesday, and Friday). Subjects had not done any regular exercise for at least a year. Each session involved 10 one-minute bouts of cycling at about 60% of measured maximum capacity with one minute recovery between intervals. Resistance was the same for each interval, but heart rate increased from the first interval to the last. Pedal resistance was easy between intervals. Training sessions lasted 20 minutes, plus 3-min warm-up and 5-min cool-down. Blood and muscle samples were taken before training began and 72 hours after the final training session.  

All subjects completed all prescribed exercise bouts. That’s a good sign, because these intervals were not exactly a walk in the park. They weren’t all out, but they weren’t altogether easy either. The effort became difficult at the end—about 95% of heart rate reserve after the last interval. The main difference is that the exercise only becomes hard at the end. In spite of the best efforts of the researchers, there is no free lunch.

Overload was a necessary part of the plan, but the results were well worth it.


The major novel finding, according to the researchers, was that six sessions of constant load intervals over two weeks improved insulin sensitivity by about 35% and increased muscle mitochondria content by about 35%. Muscle glucose transport capacity increased by about 260%. These markers were selected because they are typically found to be depressed in sedentary individuals.

All of those benefits, from two weeks of training, totally two hours (plus warm up and cool down), and only a few minutes of it taxing. Wow! That’s an amazing demonstration of the power of practical interval training.

“These data support the notion that low-volume, constant-load HIT is a time-efficient strategy to promote mitochondrial biogenesis [a marker of fitness and youthfulness] and induce metabolic adaptations that may reduce the risk for insulin resistance and type 2 diabetes…,” the report concluded.

Unlike previous interval studies, the researchers emphasized, the two weeks of training was “a lower-intensity, constant-load protocol as opposed to all out efforts.” It has been suggested that duration is more important than intensity for improving insulin sensitivity, but this study suggests “an important role for exercise intensity.”

Insulin sensitivity and muscle mitochondrial capacity may be related, according the researchers. “The mechanisms by which exercise training improves insulin sensitivity are not fully understood, but changes in mitochondrial capacity may be one factor,” they wrote. “People with insulin resistance and type 2 diabetes have been shown to have reduced gene expression and impaired mitochondrial capacity.”

Notably, increase in muscle mitochondria content and improvement in insulin sensitivity went hand in hand, both increased 35% in this study.

My Experience and a Few Suggestions

I’ve now tried sub-max intervals (one minute work and one minute recovery) on the Airdyne, the Concept 2 Rower, and the Lifecycle—and I like them a lot. Sixty percent intensity makes it challenging on the 10th rep, but not so challenging that you dread doing it again. That’s the point. It feels good. You want to do it again. As I said earlier, all-out intervals can be very hard—and aversive. In a short time you burn out. You just don’t want to do them any more. Sub-max intervals are different; they make you want to keep doing them.

If you decide to try sub-maximal intervals, you’ll wonder how to determine 60% of peak capacity. To do that accurately you’d have to go to an exercise physiology lab at a nearby university or medical facility. That would be time consuming and expensive. I suggest you experiment a little and then guess. (That’s what I did.) Give it a trial run on a treadmill, exercise bike, or rower; anything with a good performance monitor. Be conservative to start, guess low. If you run out of steam—or come close—on the 10th interval you’re on the mark. Add speed or load gradually as your fitness improves; take your time. Don’t be in a hurry to move up. If you get ahead of yourself, back off and try again. Make it challenging, but not so hard that you flame out and quit.

You don’t have to do all ten reps at the beginning. You can start with 5 one-minute intervals, and then add reps as you feel able. 

I suggest doing intervals once or twice a week, in combination with a weight or resistance workout on separate days.

For experienced trainers, I suggest adding this protocol to a varied repertoire of interval programs, some with short, hard intervals and others with longer more moderate intervals. The only limit is your imagination. When you tire or top out on one protocol, move on to another.

For more on how I do it, checkout Train Hard, and Go Home—Intervals My Way http://www.cbass.com/GoHardGoHome.htm

You’ll find balanced routines, weights and aerobics, in my book Lean For Life http://www.cbass.com/PROD03.HTM 

If you have questions about your health or exercise capacity, consult you doctor or health care provider.

(The full text of the study was published online ahead of print on March 25, 2011 in the journal Medicine & Science in Sports and Exercise.)

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