How Keelo Recommends Your Next Workout

Hoon Kim
Published in
4 min readJun 3, 2016


We look at the following to recommend your next best workout:

  • The compound muscle groups you’ve worked on
  • The movements you’ve performed and when
  • The workouts you’ve done
  • The time length of your workouts
  • And more

Great question! We thought we’d write this post to explain what we do today and why.

The Goal with Workout Programming (The Why)

We started Keelo because we believe that access to great fitness shouldn’t be expensive or exclusive, but available to all.

To fulfill this goal, we want to help develop your whole body — the musculoskeletal system, central nervous system, cardiovascular system, and metabolic system.

To us, it’s not optimal to have big biceps, chest, but small legs. Or, to have long-distance cardio, but no muscle strength or stamina to lift and move heavy objects.

Rather, we want you to have it all!

With this as our motivation, when we recommend your next workout, it’s our best attempt to develop the best physical you over time.

For every workout recommendation, we look at a number of factors, including these four, to determine your next best workout:

  • Compound muscle groups you’ve worked on
  • Specific movements you’ve done, e.g. burpees
  • Recency of workouts
  • Time length of workouts

Compound muscle groups you’ve worked on

We’re firm believers in functional fitness. That is, we practice fitness so that we can be more athletic and fit for the real world. Lifting heavy furniture, hiking for long distances, being physically capable and independent as we age, and so on.

Functional fitness, in turn, involves compound muscle groups. We identify muscle groups for:

  • Pushing
  • Pulling
  • Pressing overhead
  • Squatting (hips, leg, posterior chain)
  • Core stabilizing (abs, back)
  • Driving the engine (cardio system).

Assuming you follow our recommendations at least three times a week, we ensure that you work out each muscle group at least once.

Specific movements you’ve done

Although burpees are fantastic full-body movements, we get that doing burpees every time would not be fun.

Conversely, doing just the movements we enjoy wouldn’t be optimal either, because there would be no muscle confusion.

With this in mind, when we suggest your next workout, we look at what movements you’ve done recently, and then determine which workouts will give you the best variety in the movements you haven’t done.

Recency of workouts

Similar to movements, if we did the same workouts repeatedly, that’d get boring fast, along with no variation.

To avoid duplicating workouts, we look at your workout history to determine what workouts you haven’t done.

That said, we do suggest the same workouts over time. This way, you can compare your scores to see how much you’ve improved. If you do the same workout but faster, guess what? You’re now fitter!

Time length of workouts

In an earlier post, we discussed the three different energy pathways of the human body.

As a quick refresher, we rely on these pathways to fuel our activities (1):

  • The Phosphagen System
  • The Glycolytic System, and
  • The Aerobic System

The phosphagen and glycolytic systems don’t use oxygen (anaerobic) to produce energy. We rely on them to give us fast, explosive energy for activities that take under three minutes.

For longer activities, we rely on the aerobic (or oxidative) system, which uses oxygen (2). We can use the aerobic energy pathway for a long time, but it’s limited to 50% of max power intensity.

During a high intensity workout, when these energy systems are graphed together, it looks like this (3):

When we exercise for 1–2 minutes at high intensity, we rely primarily on the glycolytic system, and very briefly on the phosphagen system.

Then, as we inevitably slow to a less intense pace (e.g. 50% of max effort) while breathing hard, we rely on the oxidative system for energy. During this same time, however, we’re recruiting more glycogen to kickstart the more powerful glycolytic system again.

It turns out that developing the glycolytic system also develops the oxidative system. People who do mostly short, high intensity workouts find themselves (surprisingly) being able to work for longer periods of time.

So, how do energy curves relate to different time lengths of workouts?

We want you to be good at utilizing all energy systems, because in real life, you’ll need both explosive energy (e.g. sprinting, lifting) and endurance to keep going (e.g. hiking, racing, swimming).

If you only do workouts less than 10 minutes long, you’ll only occasionally use the oxidative system and miss out on training your body for longer workouts.

If you only do long aerobic workouts, you’ll miss out on training and improving your anaerobic systems.

Thus, every week, assuming you do at least three workouts a week, we mix in both short and long workouts (i.e. 16 minutes or longer) into your program.

Summary and Future Improvements

When we recommend what workout to do next, we look at the workouts you’ve already done, and examine them across four factors to determine your next best workout.

For future improvements, we’ll incorporate more user-specific data and other important factors (such as modality) to more intelligently recommend your next workout.



Hoon Kim
Editor for

Founder of @KeeloFit. New dad. Two dogs named Charlie and Ernie. Stanford alum.