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The day is over and you have enough time to squeeze in a workout, but not enough time to waste.
So you push. You increase the speed, turn up the resistance, and finish breathing hard. At least you made those minutes count.
That is understandable. When time is limited, an easier workout can feel like a missed opportunity.
But a useful training question is not just, “How hard can I make this?” It is, “What is this session supposed to accomplish?” Enter polarized training.
A recent study offers a reason to reconsider the assumption that every cardio session should be hard. It compared polarized training, high-intensity interval training, and threshold training in individuals with obesity. All three approaches improved aerobic fitness, and the polarized group had the largest reported gains. That is promising—but it is not proof of the perfect training plan for every busy guy. 1
What The Researchers Actually Tested
The study included 40 untrained college students ages 19–23. They were randomly assigned to four groups of 10: polarized training, high-intensity interval training, threshold training, or a non-exercising control group. The exercise groups completed three supervised sessions per week for 10 weeks. 1
Polarized training combined a large share of low-intensity exercise with a smaller share of high-intensity exercise. In this study, approximately 75% of prescribed weekly exercise time was below the first ventilatory threshold, and 25% was above the second. Those thresholds were determined through exercise testing and used to separate easier, middle-intensity, and harder work. 1
The HIIT group performed high-intensity work intervals separated by very-low-intensity active recovery. This was not uninterrupted hard exercise. The threshold group divided its prescribed exercise time approximately equally between low-intensity work and work between the two thresholds. 1
The important feature of the polarized approach was the combination: plenty of easier work, some harder work, and little time in the middle. It was not an “easy exercise only” program. 1
All Three Approaches Improved Fitness
The study measured VO₂max, the maximum rate of oxygen use during exercise, expressed relative to body weight. The polarized group’s average increased from 28.3 to 32.7 milliliters per kilogram per minute. The HIIT group’s average increased from 27.8 to 30.7, and the threshold group’s average increased from 28.2 to 30.9. 1
Those were group-average increases of 4.4, 2.9, and 2.7 milliliters per kilogram per minute, respectively. 1
The researchers also reported improvements in body weight, estimated fat mass, resting heart rate, fasting glucose, and several cholesterol-related measures in the exercise groups, with larger reported changes in the polarized group. Blood pressure and HDL cholesterol did not change significantly. The control group showed no significant changes in the measured outcomes. 1
My first takeaway is not that HIIT failed or that threshold training was pointless. All three exercise approaches improved fitness. The polarized group performed better on several measures in this particular study, but the other programs still produced useful changes. 1
Easier Work Does Not Need To Be Earned
Here is the coaching lesson I would take into a busy guy’s week: stop treating an easier session as something you are allowed to do only after you have proved how hard you can work.
Decide what a session is for before you start it. If the purpose is easier aerobic work, do not automatically increase the pace because you feel guilty about having time to exercise. If the purpose is a harder session, make that a deliberate decision rather than the default for every workout.
That is my practical interpretation, not an outcome the researchers tested. The study did not measure whether this approach made participants better parents, less stressed, or less tired after work. It also did not establish better recovery. 1
For people living lives outside a research study, the distinction matters. I want your training plan to have a clear purpose and fit the life you actually have—not require you to prove your commitment through exhaustion every day.
This Is Not Proof That Zone 2 Is Bad
One detail can make the discussion confusing: zone labels.
This paper used a three-zone system based on laboratory-measured ventilatory thresholds. Its Zone 1 was below the first threshold, Zone 2 was between the thresholds, and Zone 3 was above the second. You should not assume those labels map directly onto a five-zone system on your watch. 1
So “little time in Zone 2” in this paper does not automatically mean “avoid the aerobic work your watch calls Zone 2.” The boundaries and definitions matter more than the number.
It also does not mean middle-intensity training is inherently useless. The threshold group improved fitness in this trial. 1 As I discussed in Why Black Hole Cardio Is Not A Bad Thing, the useful question is whether that work serves your goal and fits alongside the rest of your training.
What This Means For You
The following are coaching recommendations—not a recreation of the study’s protocol.
1. Start With The Routine You Can Repeat. If you are returning to exercise, choose manageable activity before worrying about an exact intensity split. A walk during lunch or a short bike session after work can be a starting point. Build gradually rather than jumping straight into the study’s high-intensity proportion.
2. Give Easier Sessions A Clear Purpose. Plan which sessions are intended to be easier and resist turning all of them into tests. The talk test can help you notice intensity: at moderate effort, you can talk but not sing; at vigorous effort, you can say only a few words before pausing for breath.
3. Add Hard Work Deliberately. If you already exercise consistently, consider whether a harder session has a useful role in your plan. The amount should reflect your training history, goals, and response—not a percentage copied from a small trial.
4. Keep The Bigger Health Picture In View. You do not need an optimized endurance-training distribution before making progress toward the general activity guidelines. Adults should aim for at least 150 minutes of moderate-intensity aerobic activity, 75 minutes of vigorous activity, or an equivalent combination each week, plus muscle-strengthening activity on at least two days. Activity can be divided into smaller chunks. 4 5
For your next week, start with one decision: identify a session that is meant to be easier, and let it stay that way. Then review whether your overall plan supports your goals and fits around work and family.
You do not need to prove that you care about your health by making every workout hard. You need a plan with a purpose.
Want help building a plan around your work, family, and fitness goals? Schedule a discovery call with RJB Health Coaching. We can talk about a practical next step for your life—not someone else’s ideal schedule.