Why runners should embrace ‘hard days hard, easy days easy’

By Henry Howard

As a masters athlete and running coach, I subscribe to the training philosophy of “hard days hard, easy days easy.”

This approach is backed by exercise science and used by elite athletes across endurance sports. As the description suggests, athletes push on targeted workouts and ease back on other days, keeping the intensity low to allow for recovery.

Let's explore why the concept of “hard days hard, easy days easy” is so effective and how you can implement it in your training.

The benefits

The "hard days hard, easy days easy" principle creates a polarized training model, avoiding medium-intensity “junk miles” that don't provide optimal training stimulus or recovery. Other benefits include:

• Improved recovery: By making easy days truly easy, your body has time to repair and adapt from hard efforts. This reduces injury risk and prevents burnout.

• Higher quality workouts: When you're well rested from easy days, you can push harder during intense sessions, leading to greater fitness gains.

• A fresher mindset: Alternating between hard and easy efforts keeps training engaging and prevents mental fatigue.

• Better prep for race day: Hard workouts simulate race demands, while easy runs build your aerobic base.

What the science says

The exercise science behind the "hard days hard, easy days easy" principle supports the anecdotal evidence I’ve experienced and also seen in my athletes. A summary of some key research:

Physiological adaptations: Research has shown that high-intensity training stimulates different physiological adaptations compared to low-intensity training. A study by Seiler and Kjerland (2006) in the Scandinavian Journal of Medicine & Science in Sports found that elite endurance athletes typically spend about 80% of their training time at low intensity and 20% at high intensity.

Stress and recovery: The hard-easy approach aligns with Hans Selye's General Adaptation Syndrome theory. Hard workouts provide the stress needed for adaptation, while easy days allow for recovery and supercompensation. A 2014 study in the Journal of Applied Physiology by Stöggl and Sperlich demonstrated that polarized training (hard-easy approach) led to greater improvements in endurance performance compared to high volume or threshold training.

Glycogen replenishment: Easy days allow for better glycogen replenishment. Muscle glycogen is used during long bouts of aerobic exercise. And to a large degree, aerobic performance is directly related to glycogen stores. A classic study by Costill et al. (1971) in the Journal of Applied Physiology showed that glycogen stores take 24 to 48 hours to fully replenish after hard efforts, supporting the need for easy days between intense workouts.

How to implement “hard days hard, easy days easy”

Of course, there is more to know than the basic premise, science and approach. Here are some more specific workouts that fall under the two categories:

Hard days:

• Interval workouts

• Tempo runs

• Hill repeats

• Long runs (at moderate effort)

Easy days:

• Recovery runs at a truly easy pace — think conversational pace.

• Cross-training activities like swimming or cycling

• Rest days

Remember, “easy” should feel genuinely easy, regardless of your physical activity on that day. For example, doing three hours of physically tasking yardwork really isn’t “easy.”

In conclusion

Elite athletes like top Kenyan marathon runners, ultra running GOAT Kilian Jornet, Olympic bronze medalist Molly Seidel and others follow the hard-easy approach. It's worth noting that while elite athletes use this concept, their training plans are highly individualized and adapted over time. The hard-easy principle is a framework that's adjusted based on each athlete's needs, goals and responses to training.

Still the approach works for athletes of all levels.

By embracing the “hard days hard, easy days easy” philosophy, you'll likely see improvements in your running performance while reducing your risk of injury.