What nobody has countedEmerging evidence
No study counts hip pain in treadmill users. US emergency departments saw about 70,302 injuries from home exercise machines in 2007 to 2011, 66% of them from treadmills, mostly sprains, strains and falls, and in an Australian series of 2,873 gym injuries, trips and falls from cardio machines were a common cause. Neither counted hip pain without an injury.
In runners in general, the hip and groin made up 7.0% of injuries in surveys and 11.3% of new injuries in studies that followed runners forward, with gluteal strains or tendon pain 4.5% of new injuries; a gait study puts the hip region at about 2% to 11% of running injuries. New runners had 17.8 injuries per 1,000 hours of running against 7.7 in recreational runners. So the map on this page is built from lab studies, condition studies and trials, and NHS, NHS inform and NICE pages, and it says so.
Sources 1, 2, 3, 4, 5
The belt moves your hip much as the ground doesStrong evidence
Across 22 studies of 409 healthy young adults, treadmill and overground walking were largely comparable, with small differences, including the hip's bend in women and the hip's extending effort. In 19 adults, the belt asked a little more of the hip extensors but leg movement barely changed. In running, 5 of 17 hip measures differed slightly in 10 runners at matched speeds, and a review of running studies concluded that treadmill and outdoor running are largely comparable.
So the belt itself is an unlikely cause of hip pain. What changes on a treadmill is how easy it is to add slope, speed and time, and to hold the rails (our reading).
Sources 6, 7, 8, 9
The slope: much more work for the glutes and hamstringsStrong evidence
In 10 young adults on a treadmill, walking up 9 degrees (about 16%) raised the main buttock muscle's activity to 345% of level walking and the outer hamstring's to 635%, and the rise was bigger at faster speeds. Walking uphill, the extra support came mainly from the hip's extending effort, and most leg muscles worked longer and harder. In uphill running, almost all the extra work came from the hip, and a review sums up uphill running as more power at every joint, particularly the hip. At a 20% slope, buttock muscle activity rose in steep walking but not in jogging at 1%, and impact at the foot and lower back was lower in the steep walk.
In a model of 18 young men walking on slopes, hip joint force rose as the slope steepened. The same model found the deep hip flexor (iliopsoas) did less work uphill, not more, while the glutes and hamstrings did more. These are small lab studies in healthy adults; none measured hip pain.
Sources 10, 11, 12, 13, 14, 15, 16, 17, 18
The stride: the front of the hipEmerging evidence
In a model built from the walking of 5 healthy men, steps with about 2 degrees more hip extension (the leg further behind you) raised the force at the front of the hip joint by about 20% of body weight, and the authors suggest this could contribute to pain at the front of the hip. An earlier model found weaker glutes raised that force too. That front-of-hip pain on the treadmill is driven more by stride than by slope is our reading of these models and the slope studies above; it hasn't been tested against pain.
In running, 45 healthy runners on a treadmill who took 10% more steps a minute at the same speed lowered the hip's loading and its drift inwards, and in 30 runners the same change cut the gluteal muscles' peak forces but asked a little more of the hip flexors and hamstrings as the leg swung through.
Sources 4, 19, 20, 21
How the causes are told apartEmerging evidence
A consensus says pain from the hip flexors at the front of the groin is more likely if resisting hip bending or stretching the front of the hip hurts. A deep pinch with deep bending in a younger active adult can be hip impingement, which another consensus says needs symptoms, examination signs and imaging together. From mid-life, a stiff groin ache with morning stiffness of 30 minutes or less is often arthritis, which the National Institute for Health and Care Excellence (NICE) diagnoses without imaging from 45.
Outer hip pain from the gluteal tendons is worse lying on that side and with the legs crossed, and NHS inform lists increased walking distance or pace among its triggers. Hip joint pain was felt in the buttock in 71% of 51 people, the groin in 55% and the thigh in 57%, and never in the lower back. A stress fracture of the hip (femoral neck) is rare, 3% of sport-related stress fractures, mostly in marathon and long-distance runners, and causes groin pain that builds with exercise.
Sources 22, 23, 24, 25, 26, 27, 28
Groin lumps and children's hipsStrong evidence
A hernia lump may get bigger when you cough, sneeze or cry and smaller when you lie down. Femoral hernias mainly happen in women over 50 and can become strangulated, which is serious; an inguinal hernia is repaired when it causes symptoms or to prevent complications, the NHS says.
Hip pain in a child should always be checked, the NHS says. It is usually irritable hip, which isn't usually serious, but less often it is an infected joint, a fracture or Perthes' disease, and a slipped upper femoral epiphysis (SUFE) in older children can be felt in the thigh or knee.
Sources 29, 30, 31, 32, 33, 34, 35
When a scan helps, and how it usually goesEmerging evidence
Not at first for most people. Hip shapes and tears are common in hips that don't hurt: a cam shape was found in 37% of 2,114 hips without symptoms (54.8% in athletes), and a labral tear in 54% of people without hip pain against 62% with it. A suspected stress fracture of the hip needs an X-ray and then a magnetic resonance imaging (MRI) scan, because a delay makes the break more likely to shift.
The NHS says see a GP if hip pain hasn't improved after 2 weeks at home. Outer hip pain is often slow: in the LEAP trial, 51 of 66 people rated themselves a success at 8 weeks with education and exercise, against 20 of 68 with wait and see. For hip joint pain in active adults, exercise-based care should run for at least 3 months. In new runners, injuries took a median of 71 days to recover. No one can promise a date.
Sources 24, 36, 37, 28, 38, 39, 40, 41
