What a treadmill asks of the foot, and what no study has countedMixed evidence
Walking on a belt is close to walking outside: across 22 studies the measures were largely comparable, and foot forces were, if anything, slightly lower on the belt. No study has compared the pressure under the foot walking on a treadmill against walking outside. For running there are two: in 27 recreational runners, peak pressure under the foot was 26% to 32% lower on a treadmill than overground, mostly under the heel, the inner forefoot and the big toe, and in 16 runners it was lower than on concrete or grass. A cushioned treadmill deck lowered force under the front and middle of the foot in 20 men.
Against that, the Achilles tendon took about 12.5% more force on the belt in 18 runners, and in 71 adults wearing sensors on a 5 km run, shock and the speed at which the foot rolled in were higher on an indoor treadmill than outside. A review also warns that more regular strides on the belt load the same tissue again and again. No study counts foot pain from treadmills or walking pads; US emergency data count accidents, with the foot in about 1 in 5 of the leg and foot injuries.
Sources 1, 2, 3, 4, 5, 6, 7, 8, 9
Incline, decline and speed move the loadEmerging evidence
Walking uphill on a treadmill raised the load under the big toe and the first metatarsal (the inner ball of the foot) and lowered it under the heel in 20 adults, and in 40 adults, uphill walking raised the push-off peak and downhill the heel-strike peak. Jogging up a 15% slope cut heel pressure by 27% in 20 young women, and in heel-strikers running at about 12 km/h, heel pressure fell about 24% uphill and rose about 32% downhill, while pressure under the forefoot didn't change uphill.
Steeper slopes raised the estimated strain on the sole's band (the plantar fascia) in 23 men walking on a platform, a finding read only from the study's summary, and uphill running raised modelled Achilles load. Speed matters too: jogging faster raised heel pressure by 33%, speed was the main driver of foot force across 78 treadmill settings in 10 runners, and faster running raised stress in the second metatarsal, as did a weighted vest. Our reading, from these studies in healthy people: for a sore heel, a slower pace and a gentle slope rather than a decline; for a sore ball of the foot or big toe, a flatter, slower belt; and steep, long sessions last for both. No study has tested a slope against heel or forefoot pain.
Sources 10, 11, 12, 13, 14, 15, 16, 17
Shoes, laces and fitEmerging evidence
Most people's shoes don't fit: between 63% and 72% of people in the studies wore shoes that didn't fit the width or length of their feet, and poor fit went with foot pain, corns and toe problems. A podiatry leaflet says shoes should have the right length, width and depth for your foot, with about a thumb's width of room at the toes, and laces or a strap to hold the foot.
In 20 runners, lacing up to the top eyelet gave the lowest pressure under the heel, and loose, low lacing let the foot slide in the shoe; under the tongue, pressure peaked over the top of the midfoot, and less pressure on the tendons there went with comfort. In 20 adults walking, loosened laces raised the load under the big toe and the other toes by about 15% and let the foot slip. The idea that feet swell with exercise has little support: in 9 volleyball players, foot volume didn't change after 2 hours of training, though the authors still advise room in front of the longest toe because the foot slides forward. Our reading: snug laces to the top eyelet hold the heel, while a lace pressing on a sore spot on top of the foot can be loosened or skipped there.
Sources 18, 19, 20, 21, 22, 23
Who gets it, and how the causes are told apartStrong evidence
Plantar heel pain is common: about 1 in 10 adults aged 50 and over had it in the past month in a UK survey of 5,109 people, and it affects about 4.5% to 10% of runners. The NHS says it's more likely to be plantar fasciitis if the pain is much worse on your first steps after sleeping or resting, and lists being 40 to 60, starting exercise on hard surfaces, a tight calf, doing a lot more standing, walking or running than usual, poorly cushioned shoes and being overweight. A higher body mass index went with more heel pain in people who aren't athletes, and long spells of standing showed some link.
Pain under the ball of the foot is often from exercise such as running, shoes that are too tight or arthritis. Morton's neuroma is a shooting, stabbing or burning pain between the 3rd and 4th toes, like a pebble under the foot, sometimes with tingling or numbness, often linked to tight or high-heeled shoes and a lot of running; it is commonest in women in their late 40s and 50s and is usually worse in closed shoes. Pain on top of the foot can come from shoes that are too tight. Foot stress fractures are most often in the second and third metatarsals, from overuse or an increase in training without enough rest. Ordinary pins and needles from pressure lasts a few minutes, while burning, tingling or numbness in both feet can be nerve damage, most often from diabetes. So foot pain on the treadmill is most likely after a jump in time, pace or slope, a new walking pad or step target, from mid-life with heel pain, and in shoes that don't fit (our reading).
Sources 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36
When a scan or test helpsStrong evidence
Rarely at first. In 174 people with plantar fasciitis followed for up to 15 years, how thick the fascia was and whether there was a heel spur at the start made no difference to recovery. On magnetic resonance imaging (MRI), 30% of 70 people without foot symptoms had a Morton's neuroma, and ultrasound found a thickened nerve in 54% of 48 people without forefoot symptoms, so the examination, not the scan, makes the diagnosis. A suspected stress fracture is when imaging matters: it is often hard to see on an X-ray at first, and an MRI or bone scan can show it sooner.
Sources 37, 38, 39, 33
How it usually goesEmerging evidence
NHS inform says many new foot problems begin to settle within 6 weeks, and the NHS says see a GP if heel pain hasn't improved after 2 weeks of treating it at home. Heel pain can be slow: in new runners, plantar fasciitis took a median of 159 days to clear, and in 174 people diagnosed at a hospital clinic, a group with longer-lasting pain than most, half still had symptoms 5 years after they started. A stress fracture usually takes 6 to 8 weeks to heal.
No one can promise a date, which is why the plan keeps foot and calf strength work going after your sessions come back.
Sources 40, 41, 42, 37, 43
