When thinking about consistency, it’s easy to focus on the psychological benefits. Numerous studies on habit formation show that completing small tasks just a few times a week for a month can support long-lasting behavior change. That’s cool, and I personally need to apply it to core work and flossing. But what I am most interested in as a coach is how the body adapts to consistent stimuli. How can short, daily workouts make such a big difference for fitness?
The science of adaptation is murky. While the certainty-seeking part of my brain wants to say Outcome B follows Intervention A via a direct path, the actual flow chart of underlying cellular-level processes is full of squiggles and turns. The most important variation from a linear adaptation model happens as a stimulus is first introduced. Many studies and case studies (particularly on less experienced athletes) follow a pattern:
Intervention A? A small dose of exercise, like 15 minutes a day, sometimes with intensity.
Outcome B? Four to six weeks later, a significantly stronger and faster athlete.
That exponential growth is so common that I imagine it has little to do with the specific study protocol, and more to do with the underlying physiology of initial athletic progress. I have four favorite explanations. Let’s go from least to most interesting.
One: Musculoskeletal adaptations
This is the vanilla ice cream of initial adaptations—delicious and a good base, but not knocking anyone’s doors off. If your musculoskeletal system isn’t adapted to a stimulus, 15 minutes of activity might leave you feeling exhausted. But muscle fiber recruitment and strengthening kicks off with any stimulus, no matter how small. 15 minutes a day (or even less) begins the soft tissue strengthening process, laying an indispensable base for longer or faster efforts. Bone modeling works similarly, as osteoblasts and osteoclasts adapt to minor stresses related to force absorption and transmission. That’s why runners usually start out with very short run:walk approaches, and the same principles apply to any sport. Stronger muscles and denser bones then interact via ligaments and tendons to create positive feedback cycles where one strengthens the other. That’s how a 15 minute run that might have led to exhaustion and injury risk in week 1 can become a 5 mile run with less effort in week 10.
Two: Aerobic and metabolic adaptations
During exercise, the aerobic system supplies oxygen and fuel to working muscles, and the circulatory system begins expanding capillaries via angiogenesis, allowing more oxygen to reach muscles. With consistent endurance stress, both these systems become more efficient. As the body uses energy, metabolic rate increases at rest and gets more efficient during activity. Cardiac output increases, leading to each beat of the heart doing more work, while blood volume expands by up to 20%. And there is some evidence that these adaptations are most rapid in the time just after exercise starts – so simply getting your heart rate elevated for 15 minutes a day can have outsized benefits.
Three: Neuromuscular and biomechanical adaptations
Now we’re getting to the really fun stuff. Endurance athletes are not lungs with legs—there is an immensely complex web of neuromuscular interactions involved in every movement we do. Just like someone might get better at dancing with practice, any endurance sport is a learned biomechanical movement pattern. Efficiency can skyrocket rapidly, but it’s essential to have consistent reinforcement. Add in a bit of intensity, and the neuromuscular system could undergo fundamental alterations in just a few weeks.
Four: Epigenetics and environmental stimuli
Here is my favorite element. Our genetics are not just a set of instructions that we can’t influence. External stimuli change how our genetic code expresses itself via epigenetics, and there is even some evidence that epigenetic changes can be heritable. With endurance sports, relatively small stimuli may start turning some of those epigenetic switches toward endurance. While it’s debated, that could be one explanation for how bodies can undergo such fundamental and positive changes over time even if exercise routines are a few minutes a day.
All of that physiological goodness combines with countless other non-linear adaptations, like those related to hormone production and endocrine system health. But even if none of that is relevant, there is a reason that most kids have recess at school. Short amounts of exercise can have major benefits, and it can be fun.
Give yourself 15 minutes, and your body can give you an unstoppable boss athlete in return.
Join the 1% Better Challenge and commit to 15 minutes of exercise, 5 days a week for 4 weeks.
David Roche partners with runners of all abilities through his coaching service, Some Work, All Play. With Megan Roche, M.D., he hosts the Some Work, All Play podcast on running (and other things).