Back in January of 2006 I wrote a post on Ellington Darden’s forum about an idea I had for a single progression system I call “isochronal progression”. This is something I have experimented with periodically in the years since, mostly during the development of my bodyweight high intensity training program Project Kratos, and it is covered in the book. I have recently started phase three of Project Kratos, which involves incorporating feedback from participants and refinements I have made, and am experimenting with this again.
“Isochronal” means equal in duration, or occurring at equal intervals of time. Exercises are performed for a predetermined TUL, rather than for a range of repetitions or time, using a timer (I recommend the Seconds Pro app if you have a smart phone or tablet). If momentary muscular failure is achieved before reaching the target TUL, after a ten second rest the exercise is continued in a rest-pause fashion for the remaining time, using a five second rest pause. As an alternative the exercise can be continued for the remainder of the TUL using a static hold or timed static contraction (TSC) in the mid-range position or position of maximum lever. It is a pass/fail system. Resistance is increased when it becomes possible to perform the exercise for the target TUL before achieving momentary muscular failure.
Isochronal progression alone does not provide as accurate a measure of progress from workout to workout as a repetition count or TUL (it can, however, be combined with these if desired) but it has several advantages which some may find helpful.
One advantage is making it easier for people who self-train to focus on form since they don’t have to count repetitions or monitor a stopwatch. Also, because the duration of the exercise will be the same regardless of the repetition count it removes the temptation to move too quickly or compromise form in other ways for the sake of completing more repetitions, and the temptation to move too slowly or “sandbag” in easier parts of the range of motion to increase the TUL. It allows you to forget about measurement and focus entirely on performance.
Another advantage of isochronal progression is the ability to design workouts with a specific duration or work to rest ratio to emphasize cardiovascular and metabolic conditioning. I find this works well with 3×3 workouts as an alternative to the repetition count, and makes it possible to train multiples of three people simultaneously without anyone either having to wait for the others to finish their exercises to continue or being tempted to stop when someone else does, by having each person in each group of three start with a different exercise.
The ability to design workouts with a specific duration can also make it easier for extremely busy people to fit them in their schedule, and for people teaching group training to stay on schedule.
One disadvantage is of isochronal progression and single-progression systems in general is it lacks the resolution or granularity of measuring progress with the repetition count or TUL. It is purely pass or fail. Workout progress can still be evaluated, just not as easily. In this case, you may be better off making adjustments to your program when necessary based on goal-specific measurements, like changes in weight and body composition or performance in other physical tasks, rather than on exercise performance.
Another disadvantage is some people may take longer to recover when performing a significant number of rest-pause repetitions or lengthy static holds after achieving momentary muscular failure. In this case, they should modify the exercise duration to reduce these. This could be managed in a group setting by counting off the exercise duration in seconds at regular intervals, i.e., “60 seconds, 70 seconds, 80 seconds…” However, to maintain a consistent starting time for exercises the individuals using shorter times would have a longer rest.
Despite the advantages, I still prefer to use the repetition count for dynamic exercises and time under load for static holds and timed static contractions, because I like to have more meaningful data on exercise performance and progress, I’m able to maintain good focus on form even when counting repetitions, and I work out alone and do not need to stay in sync with others. I would only recommend isochronal progression if you self-train and find it extremely difficult to focus on form while also counting repetitions or using a stopwatch, if you are trying to maintain a specific work to rest ratio, or for some group training situations.
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This method of training is very good for metabolic conditioning. It allows the trainee to achieve the desired and optimal amount of TUL for their working muscles, making sure that the entire workout was done over a set period of time.
Taking your 3 X 3 workout of Squats, Chin-ups and dips, I added in a ‘forfeit’. They had a target for 20,15,10 reps for squats in 3 sets (descending as fatigue set in). For every rep short of their target, they would do a 10 second wall squat. So for example, if in the 1st set they only managed 17 reps, they’ll have to do a 30 second wall squat. For chins and dips, it was a 10 second negative. This achieved 2 things:
1) They got the TUL, increasing the metabolic and cardiovascular demand.
2) They were motivated to complete more reps (albeit, under strict form! It doesn’t count otherwise!). When they knew that the forfeits would be longer the less reps they did (and wall squats and negatives are REALLY hard after concentric failure), they pushed a few more reps then they would have. Before, they would skip maybe 1 or 2 reps as it’ll mean an immediate rest and relieve from pain. In this method, no rest is forthcoming, only more work (and the less reps you did, the more work).
Hey Jason,
I love your idea of a forfeit when using isochronal progression. One of the hardest things about getting people to train to true momentary muscular failure is that most people’s psychological limitations are far below their physiological limitations, and this is a great way to do it. I’ve had a few of my clients using isochronal progression with Project Kratos perform a static hold instead of rest-pause repetitions for the time remaining after failure but for physiological rather than psychological reasons. Your idea is too good to leave here in the comments where a lot of people might miss it, so I’ll be quoting it in a new post.