You wake up, take your first steps of the day, and feel a sharp pain in the bottom of your heel, like you stepped on a stone. You walk it off and the pain fades, almost disappears, until it comes back at the end of a workout or after sitting for a while. This pattern is especially frustrating if you run, walk, or train on a treadmill regularly, because the pain is rarely bad enough to stop you cold, but it is persistent enough to threaten the streak you have been building. The technical name is plantar fasciitis, and it is one of the most common injuries among people whose feet take the brunt of the impact.
What is actually happening in the plantar fascia
The plantar fascia is a thick band of connective tissue that runs from the heel bone to the toes, supporting your foot's arch and absorbing part of the impact with every step. When you run, walk briskly, or jump repeatedly, this structure takes on far more mechanical load than it does during an ordinary day. If your training volume climbs faster than the tissue can adapt, microtears start to form right where the fascia attaches to the heel bone.
The name fasciitis implies acute inflammation, but most chronic cases are better described as a degenerative process from repeated overload, not unlike what happens in overloaded tendons: disorganized fibers, thickened tissue, and reduced capacity to tolerate load, rather than classic inflammation with redness and heat. That distinction matters in practice, because it directly changes how you should treat it, as you will see below.
Source: PubMed
Why this shows up precisely in people who train consistently
Plantar fasciitis tends to show up not in people who barely train, but in people who ramp up volume or intensity too fast: a sudden jump in running distance, a change in training surface, or picking an old volume back up after time off. A prospective study on runners found that those running more than 40 km a week had six times higher odds of developing plantar fasciitis than those running between 6 and 20 km a week, which points to total training volume as one of the most consistent risk factors.
Beyond volume, other factors raise the risk: a very low or very high foot arch, tight calf muscles, recent weight gain, long hours on your feet at work, and switching footwear without a gradual transition. No single factor guarantees the injury on its own; they stack up, which is why two people running the same weekly distance can end up with completely different outcomes.