Getting used to running is a multi-layered process that requires physical, cardiovascular, and psychological adaptation, making it difficult to answer “how long it takes” with a single number. The initial discomfort that makes running feel like a struggle is a normal biological response as your body begins to reorganize itself for this new activity. Understanding that this initial feeling of being winded and sore is temporary can provide the motivation needed to move through the first few weeks of training.
The Immediate Physical Changes
The first phase of adaptation is highly physical, focusing on the acute discomfort experienced as your musculoskeletal system adjusts to the impact forces of running. This initial hurdle typically lasts for the first two to four weeks of consistent training. New runners frequently experience delayed onset muscle soreness (DOMS), which makes legs feel heavy and stiff after a run. The high-impact nature of running stresses muscles, tendons, and bone tissue in ways that walking does not.
A common issue during this period is the inflammation of the muscles and tendons around the shin bone, known as shin splints, which results from overloading the lower leg too quickly. Your body also has to adjust its breathing mechanics, leading to the sensation of being winded even at a very slow pace. Consistently training during this phase allows the connective tissues and muscles to strengthen, leading to a noticeable reduction in soreness and stiffness.
Establishing Aerobic Endurance
Once the initial physical soreness subsides, the focus shifts to a deeper, systemic physiological change that makes running feel less taxing. This phase of establishing true aerobic endurance generally occurs between four weeks and three months of regular training. The most significant change is the improvement in maximal oxygen uptake, or VO2max, which represents the maximum rate at which your body can use oxygen during exercise. Training leads to noticeable VO2max increases, improving your capacity for sustained effort.
Running efficiency also improves as your body increases the density of mitochondria within muscle cells. These cellular powerhouses become more numerous and efficient at generating energy aerobically, allowing your body to use fat more effectively as fuel. This improved efficiency shifts your running from a high-effort struggle to a comfortable, conversational pace. As your cardiovascular system adapts, your heart pumps more oxygenated blood, and your lungs become more practiced at oxygen extraction.
Forming the Running Habit
Beyond the physical timelines, a different kind of adaptation takes place: the mental and behavioral shift of forming a stable running habit. This psychological phase is completed when running stops feeling like a chore and becomes an automatic part of your weekly schedule. Research suggests that it takes an average of 66 days of consistent practice for a new behavior to achieve a plateau of automaticity.
The psychological hurdle involves pushing past initial resistance and building behavioral consistency. Running facilitates this shift through the release of neurochemicals like dopamine, linked to motivation, and endorphins, which can lead to the “runner’s high.” As the brain associates physical effort with these positive chemical rewards, the desire to run shifts from conscious willpower to an internal, self-reinforcing routine.
Variables That Affect Adaptation Speed
The speed at which an individual moves through these physical and psychological phases is not uniform and is influenced by several variables. The greatest factor determining adaptation speed is training consistency, meaning the frequency and duration of your runs. A sporadic training schedule will slow down physiological gains in VO2max and mitochondrial density.
Pre-existing fitness level also plays a role; someone who already has a strong walking base or cross-trains will adapt faster than a sedentary person. Age and body weight affect the timeline, as greater body weight increases the impact forces the musculoskeletal system must absorb. Utilizing a strategic training method, such as a run/walk approach, can accelerate the process by allowing the cardiovascular system to improve without overloading connective tissues.