“To be really great in little things, to be truly noble and heroic in the insipid details of everyday life, is a virtue so rare as to be worthy of canonization.” – Harriet Beecher Stowe 

The ARXFit Alpha providing this particular session’s HIIRT train caboose.  Huh…

Curious as to what the differences are between HIT, HIIT and HIIRT?  Well, what follows are what I consider to be the high points.  Tomes could be written on the similarities between these methodologies, but I think the following gives a pretty good overview.

First, a couple of definitions:

HITHigh Intensity Training: The area covered by the overarching umbrella of classic High Intensity Training (HIT) is wide indeed, including such broad-stroke methodologies as classic, single-set-to-failure HIT, and various super-slow routines.  Included too, are all manner of TUL (time under load), repetition tempo, and rest period manipulations. Methodologies here are largely those popularized by Arthur Jones (of Nautilus fame) and bodybuilding’s Mike Mentzer.

Note: for info on “training to failure” see this post.

HIIT High Intensity Interval Training: Most studies on classic High Intensity Interval Training (HIIT) focus on only sprint (running) and/or cycle sprint sessions, because that’s what’s available and most easily studied in a lab setting.  A good article summarizing HIIT, and its positive effects, here.

HIIRTHigh Intensity Interval Resistance Training: At it’s most basic, HIIRT is a powerful burst of output (typically 20 – 80 seconds), followed by a scaled rest period.  Wash, rinse, repeat.  Think HIIT Tabata sprints — but with heavy resistance exercises.  Brief, brutal and basic are key words here.  I’ve fused elements of CrossFit, and the work of folks such as Scott Abel, Istavan Javorek,  and Joel Jamieson (in addition to whole slew of others) — along with my own, 35+ years-in-the-trenches experience — to create my own methodology.  Hints of HIT?  You know it.  Shades of HIIT?  Yeah, that too.  I come from a background of slinging iron as a way of bettering performance on the track and on the gridiron.  I came of age in an atmosphere that knew no S&C dogma — if it worked, it worked, and that’s all that ultimately mattered.  And that’s the credo I operate by today.

HIT, HIIT, or HIIRT — what’s the difference?

Generally speaking, the distinction lay in the overall intent of each individual “set” (or output burst).  HIT attempts to attain total muscular failure (within an allotted time window) in the targeted musculature, whereas HIIT and HIIRT attempt to attain as many repetitions (or highest cumulative work or power output) as possible within a set, or established time period.  With HIT, each exercise is generally performed once through, to failure.  In HIIT or HIIRT, an exercise may be performed 2, 3 or even many more times within a workout.  I say “generally” here because there is much overlapping and gray area within these methodologies.  HIIT is definitely a conditioning-biased protocol — i.e., Metabolic Conditioning, or MetCon, for short — whereas we can consider HIIRT a hybrid of both HIT and HIIT.  And a HIIRT session may be, depending upon how it is set up, strength, hypertrophy, or MetCon (strength endurance) biased. Confused? Don’t be; this will all make sense soon enough.

Can you give an example?

Sure.   Here’s an example of what I consider to be a classic HIIRT workout: six distinct exercises, 3 upper body dominant exercises alternated with 3 lower body dominant, all set in a circuit format.  Each exercise is performed all-out, full-bore (as many reps or the most force and/or power developed as possible) for 1 full minute.  Then, rest for 1 full minute before beginning the next exercise in succession.  Wash, rinse and repeat.  Each exercise will be performed twice during the 2-round duration of the workout.  If you’re doing the math, we’ve got 24 minutes worth of work and rest here.  Even allowing for some degree of spillover, we can still get this workout done in 30 minutes.  Brief, brutal, basic…and extremely effective.  Consider this scenario:

(A1) Tbar swings
(A2) Powermax 360 push-pull/cross-punch (30 secs each exercise, shift on the fly)
(A3) ARXFit leg press
(A4) ARXFit flat press
(A5) Reverse lunge iso hold with dumbbell curls (30 secs each leg, shift on the fly)
(A6) Blast strap rows

The actual exercises are not so important at this juncture; what is important is the overall workout setup.  I could crank the intensity up a notch here by reducing the rest period between each exercise to say 45 or even 30 seconds, by bumping-up the work period, or by increasing the exercise resistance.  By virtue of me using resistance exercises here I’ve just morphed a classic HIIT setup (which could have used sprints, hops, jumps, bodyweight exercises, etc.) into a resistance-based interval circuit, or HIIRT, with, in this example, a decidedly MetCon (metabolic conditioning) bias.

So achieving total muscular failure is not a goal of a HIIRT session?

Not necessarily.  Remember when I said that there are no hard lines of distinction between these various protocols?  Consider the following, more strength/hypertrophy-biased (as opposed to the previous example’s MetCon-biased), upper body emphasis HIIRT workout:

(A1) OmniFit pec flye x 5 hyper reps
(A2) Leverage machine flat press (negative emphasis, to failure), 50X0
(A3) Bent over row 20X0, 7 reps short pause, 7 more reps

(B1) Hip press with bands, (negative emphasis, to failure), 50X0
(B2) Russian leg curls 30X0,  7 reps short pause, 7 more reps

Notice the very HIT-like feel of the flat press and hip press execution.

*note: the (for example) 30X0 annotation denotes the exercise repetition tempo in the eccentric, pause, concentric, pause format.  30X0 would, therefore, be performed with a 3 second negative, followed by no pause leading into a fast-as-possible concentric, with an immediate return to the subsequent negative.  Note, too, that there is a profound difference between “exploding” into the concentric portion of a movement, and “jerking” into the motion.  There is a time and place for ballistic, “jerking” movements for sure — just not with this protocol.

Two rounds of each can certainly be accomplished in 30 minutes if the rest period between exercises is held sufficiently brief (i.e., less than 1 minute). Extending the rest period will require eliminating the pre-exhaust exercise (in this case, the OmniFit flye), which is fine, considering that if a client is not yet up to the fast-paced nature of the workout to begin with, they probably aren’t in need of a pre-exhaust anyway.

So what are the advantages of HIIRT vs other forms of training?

Well, what we’ve done at Efficient Exercise is essentially turn what would be considered a huge disadvantage (a 30-minute session time constraint) into a decided advantage for the client.  Not only do Efficient Exercise clients need only invest an hour or so per week in the studio to achieve an optimum level of health, but that investment pays huge dividends when it comes to effective fat loss and muscle gain.

How does HIIRT maximize fat loss?

Well, there are many ways and associated reasons, but here are the main points to consider:

  • Intense, intermittent physical activity, and the resultant advantageous hormonal modulation and increased metabolic rate, expedites release of fat stores and increases the released fatty acids into the mitochondria to be used as fuel.
  • Decreased fat accumulation by decreasing excess inflammation, improving insulin sensitivity, and optimizing cortisol secretion.
  • Target fat loss while maintaining (in our case, accumulating) muscle tissue; this is done by maximizing anti-catabolic hormones and growth factors (GH, Testosterone, IGF-1).

The bottom line? In order to maximize fat loss, we must elevate growth hormone secretion, minimize insulin spikes, improve muscle insulin sensitivity, and keep cortisol under control.  This is best achieved by keeping training sessions brief, brutal, basic and intermittent.

The other side of the coin is, of course, muscle gain.  To induce muscle growth we must stimulate protein synthesis in muscle tissue.  Protein synthesis is initiated by an exercise/movement that most effectively:

  • Recruits all available muscle fibers with exercises that create sufficient muscle tension through an optimal range of motion.  Compound movements (as opposed to isolation exercises) most effectively fit this bill.
  • Fatigues as many recruited muscle fibers as possible with sufficient volume.
  • Ensures adequate availability of amino acids and energy to amplify protein synthesis.

And the take-home message is this: Recruit and fatigue as many muscle fibers as possible, as fast as possible, and ensure adequate post-workout recovery and nutrition following the workouts.  Remember, exercise ought to be considered a high-amplitude signal that subsequently affects the body’s on-going, anabolic hormonal milieu.  Too much is too much; too little is too little.  Profound, I know — and yet it is so very true.

So how do we get these two processes to work hand-in-hand, creating an anabolic environment for muscle growth, while at the same time forcing the body to use fat stores to help meet energy demands?

Note: diet plays a HUGE role here as well.  The focus of this section, though, is exercise protocol selection.

1. Stimulate muscle growth with compound exercises, performed for 6-20 repetitions to failure (if strength/hypertrophy is sought), or for max work or power output (if MetCon biased).

The repetition range, together with the execution tempo, will determine the nature of muscle fiber recruitment. We want to recruit, tax and fully exhaust as many fibers as possible, including slow twitch, intermediate, and fast-twitch fibers. As with all strength exercises, slow twitch fibers are recruited first, then as the muscles fatigue, intermediate and finally fast twitch fibers are recruited if and only if the set is continued until fatigue sets in.

Muscle growth is best achieved when the exercises are performed with controlled eccentric movements and continuous tension. Make an effort to minimize momentum unless the nature of the exercise dictates otherwise.

2. Improve insulin sensitivity by performing a sufficient volume of work.

Multiple (2 or 3) sets performed within the 6-20 repetition range is best for depleting muscle glycogen (and stimulating protein synthesis). During HIIRT training, muscle glycogen is broken down at a rapid rate, which results in improved muscle insulin sensitivity and increased LPL (lipoprotein lipase) activity on muscle tissue, causing nutrients to be preferentially partitioned towards muscle tissue.  Insulin sensitivity increases on muscle cells when glycogen stores are low. When this occurs, nutrients are partitioned into the muscle tissue and fat stores are broken down.

3. Increases in testosterone.

4. Maximize GH production with short rest interval HIIRT circuits.

GH is most effectively released performing strength circuits where both upper and lower body muscles are fully taxed, and keeping rest intervals short.

HIIRT leads to a significant drop in blood pH (via the rapid breakdown of glycogen and subsequent release of hydrogen ions), which in turn triggers increased production in GH.

An interesting aside: contrary to popular belief, it’s not lactic acid that causes muscle burn; this is actually the result of lowered blood pH creating an acidic environment, thereby resulting in that old, familiar, muscle burn and fatigue. The brain senses the situation and increases output of GH.

We know that testosterone is important for recovery, shedding fat and building muscle — but what’s so great about growth hormone?

Plenty.  GH has been shown to stimulate fat breakdown (lipolysis), increase the utilization of fat, and decrease the use of carbohydrate as fuel.  GH has beneficial effects on muscle mass, bone density, body fat, and it can help reverse some of the age-related changes in lean body mass (sarcopenea).

GH has also been shown to act as a suppressive on myostatin.  And myostatin, you may remember, inhibits muscle growth and is a negative regulator of muscle tissue. Higher GH release means lower myostatin expression; lower myostatin can result in increased anabolic activity and an increase in androgen receptor expression.

Research shows that circuit strength training (and high intensity sprint training) are both effective methods for naturally elevating GH secretion in healthy adults.  It is my opinion that these effects can be greatly enhanced by adding a resistance exercise element — HIIRT — to the mix.

*Also*: please check out my post ARXFit, and the Perfect Rep.  Because all of this methodology is less-than-effective unless the basic building blocks are solidified.  And yes, ARXFit for sure enables a perfect repetition, but the lessons learned here can for sure be applied to conventional exercise methods.

Heal thyself, hone thyself, change the world –

Take the 15 minute FREE assessment to discover YOUR unique nutritional needs


  1. Good article full of prelimary thoughts. Here’s some additional thoughts for consideration.

    More recent thinking focuses on incorporating skeletal muscle into the endocrine system, or at least shifting emphasis to hormonal events stimulated within muscles with activity, putting less emphasis on indigenous testosterone, etc as but minor players in facilitating protein turnover. The gating element is mTOR with muscle, accounting for usually more than the 850 separate mRNA events just within a target muscle.

    Insulin sensitivity, also, is localized in production with systemic outcomes due to GLUT4.

    With HGH, you need to consider the anabolic element – IGF-1.

    Recent studies indicate 3x sets at 80 1RM and 3x sets at 30% 1 RM, 8-10 reps for the former, upwards of 30 for the later, result in equal hypertrophy. Intensity is key, as is reasonable volume HIT dogma increasingly fails the test of science.

    Scott Abel’s training regimes are far more demanding, requiring 60-90 minutes, and with his specialized Cycle Diet. Scott’s MET – metabolic enhancement training – is five to six days weekly, incredibly demanding since he goes for EPOC.

    I’d add Ronnie Coleman’s approach, classic barbell based training, in rep pyramids of 20-15-12-10 reps, 3-4 sets of 3 movements.

    Training with intensity versus training to failure are rather different. Steve Hollman’s recent contributions for drug-free training are incredible for amping metabolism while favoring both contractile and sarcoplasmic hypertrophy. Training to failure routines tend to favor only contractile hypertrophy, hence do half the job. Like Coleman, Hollman favors TUT and non-lockout movements.

    All of which is to say there’s not one fixed system, instead a wide range of options consistent with evolutionary science dismissing ‘survival of the fittest’ in favor of diversity within niches of expressive opportunities. Or as Scott puts it: keep the workout varied (his innervation training principle based on deep neuroscience).

    Looking to training for fat reduction is fraught with mistakes, ones clarified in UT dept of Kinesiology chair Dr John Ivy’s Hardwired for Fitness. That’s the other half of classical Physical Culture: a diet of nutrient dense whole foods, including supplements. Mindfulness of caloric intake fine tuned with total activity – not just training, but all activity – are the keys to success.

  2. Very nice summary. Just by a process of trial and error, I’ve landed upon doing one each of these kinds of workouts during the course of a week:

    Monday – HIT: I do a “big 5″ Body By Science sort of routine with free weights (slow controlled reps to failure), throwing in some extra exercise for calves, low back, glutes/hips.

    Wednesday – HIIT: I do a 20 minute session of sprints on an exercise bike (30 seconds hard as possible, 90 seconds easy)

    Friday – HIIRT: I do a joint friendly Cross-Fit style WOD, taking 25 minutes to complete 3 circuits of 5 resistance exercises with light weights, not to failure: kettle bell swings, push ups, reverse rows, front squats, dumb bell curl to overhead press.

    It works pretty well for me: I’m avoiding injuries from over-training, and feel pretty good, both after the workout, and on subsequent days. I can do it at home without a lot of equipment, and it doesn’t take that much time.

    I also eat toward the low carb end of the spectrum, mostly whole foods, not much junk. And yet…. I still can’t seem to get rid of that last bit of fat around my middle, or that last stubborn 10 lbs (I’m 5’6”, 165 lbs, ~23% body fat).

    Any suggestions?

    • I like the workout setup you’ve got going on. Smart programming, using the tools you have available to you. That’s what it’s all about! In regards to fat loss in the umbilical (spare tire) area, remember that fat deposit is a hormonally-driven phenomena, and the overriding hormone in this case is cortisol. That said, anything to reduce *chronic* cortisol elevation *or* out-of-whack cortisol cycling is a must. Reducing daily chronic stress, getting adequate and quality sleep, ditching the caffeine if your adrenals are suffering are all musts in order to get control of cortisol levels and, therefore, to reduce fat in this area.

  3. Interesting article Keith! I’ve been looking for a way to better maximize hypertrophy and I think I will start using the HIIRT approach.

    Do you mind critiquing a routine I just thought up of?
    I would do 2 circuits of an upper body and lower body routine. Each exercise would be 1 minute.

    Upper body:
    Machine chest press: 40X2
    Pulldown: 40X2
    Shoulder press for first round and machine row for the second: 40X2

    Lower body:
    Machine leg press: 40X2
    machine leg curl: 40×2

    I’m not sure what to do for the last one, I was thinking of doing either a dumbbell lunge or a calf raise.

    Any suggestions on where I can improve on the routine? I’m trying to make due with the equipment available to me.

    • Kinda depends on what equipment you do have at your disposal, Jack. For instance, I like to “surf” the force/velocity curve when selecting exercises — in other words, mixing in “heavier/slower” movements with “lighter/faster” ones. But again, the ability to do this depends on what tools you have to work with, and your comfort level with each force/velocity modality.

      BTW, I would always opt for the more metabolically challenging movement in this schema — choosing the DB lunge over the calf raise. If you think you need them, perform calf raises after the fact. Or before you jump into the circuit, if you think your calves are really lacking.

      • Thanks for the suggestions Keith. I won’t be doing any lighter faster movements because they usually bother my finicky shoulders and knees.

        Wonder if you can shed some light a few other things.

        1) What would you suggest to do as a warm up?

        2) Should I do 2 rounds of the upper body circuit than switch over to 2 rounds of the lower body circuit or alternate between the two circuits. Does it matter?

        3) How would you suggest to go about weight increases, should I increase the weight each workout or use some other method.

        4) I was thinking of changing the lower body circuit to just deadlifts and db lunges, do you think this would be preferable to the previous circuit I had in mind?

        Thank you!

        • 1) a light circuit of DB clean and thrusts coupled with chins is a good warm up. Or a circuit of light DLs, push ups and chins. Something to target the whole body.
          2) Either way works fine. If I wanted to concentrate on hypertrophy, though, I’d group the upper body/lower body exercises together. For a more overall metabolic response, I’d perform 2 full circuits. This is really splitting hairs, though.
          3) A combination of autoregulation and density training. I’ll post on density training soon, but essentially we’re looking to maximize work output per unit of time (or power). Essentially, the exercise’s range of motion will ultimately — together with the number of performed reps — determine total “distance”. The two variables then become load and reps. Now the idea is to maximize output via manipulation of these two variables. Of course, increased reps with a higher load is always a win. It gets tricky, though, when that increased load results in fewer overall reps. Do the math going in, load as required to hit a new output PR in a movement, and let ‘er rip. Realize that overall metabolic fatigue will play a part as well. Shifting exercise placement withing the circuit adds another variable.
          4) good choice.

          • Thanks for all the help Keith, I really appreciate it.

            There’s just 1 more thing itching on my mind.

            What do you think about substituting the time limit with having a rep goal. eg) Instead of doing as many reps as I can on the bench press within 1 minute, I set a goal of hitting 10 reps. I feel like it would be easy set up for auto-regulation this way, just wanted your opinion.

            Again, thanks for all the help.

          • Yep, absolutely. In fact, it’s good to play these two parameters — autoreg via a set number of reps, and autoreg via cumulative power output/time unit — against one another. For one thing, it keeps the body “guessing” and, probably more important, keeps one mentally fresh in the gym. Work one mode until progress stalls, then shift back to the other. It’s a simple, yet effective, plan.


Please enter your comment!
Please enter your name here

This site uses Akismet to reduce spam. Learn how your comment data is processed.