Pilates is safe for most people, and it helps knee arthritisEmerging evidence
No study gives a Pilates injury rate for the knee or any other part, and no country collects Pilates injury statistics. The nearest figure is instructors' own work aches: 35.5% of 166 Brazilian Pilates instructors reported knee pain (instructors, not clients). In a back pain trial, 1 of 44 people in the Pilates group had knee pain.
For knee arthritis, Pilates eased pain more than no exercise and about as much as other exercise across 11 small trials (476 people), at low to very low certainty. Side effects were rarely measured: only 2 of the 11 trials reported them, finding none of note, a pilot trial of 54 adults had no serious side effects, and a review of Pilates in adults over 50 with long-term joint and muscle conditions found no significant ones.
Sources 1, 2, 3, 4, 5, 6, 7, 8
What Pilates asks of the kneeEmerging evidence
On the mat, the knee hover, all-fours work (cat-cow, the bird dog) and the kneeling side kick put weight on the knees; rocking, the single-leg kick, rolling moves and hugging a knee in during the leg stretches bend it deeply; and the mermaid is often done side-sitting. On the reformer, footwork is a lying leg press against 2 to 4 springs, from a deep bend to straight; the knee stretches, kneeling abdominals and kneeling arm work kneel on the carriage; frogs and circles with the feet in straps bend and turn the knees; and standing work and the jump board load them upright.
The reformer maker lists ankle, knee and hip bending as precautions for footwork and an inability to kneel for kneeling abdominals, and the classical manual lists knee issues for the knee stretch series. A teaching encyclopedia's footwork cue is to avoid hyperextending the knees.
Sources 9, 10, 11
Kneeling and the kneecapEmerging evidence
In 10 adults kneeling in miners' postures, most of the pressure went through the tendon and the bony bump just below the kneecap rather than the kneecap itself, and knee pads lowered the peak but left high pressure over the bursa. Kneeling on one knee gave the highest knee forces of the kneeling postures. In cadaver knees, kneeling at about a right angle raised the pressure behind the kneecap compared with the same bend unloaded.
A Pilates class kneels for minutes, not hours. The kneeling linked with worsening kneecap cartilage, in 600 people at risk of arthritis, was 30 minutes or more on 6 or more days a week, and the link weakened once a high-riding kneecap was allowed for; kneeling at work for more than 30 minutes a day went with knee arthritis (odds ratio 1.29 across 14 studies) and about double the risk of meniscal damage. So in our reading, the kneeling in a class is a much smaller dose; these are studies of workers, not of Pilates.
Sources 12, 13, 14, 15, 16, 17
Deep bends, footwork and the kneecapEmerging evidence
In 20 healthy adults, kneecap stress in the gym leg press was higher than in a seated knee extension once the knee bent past about 48 degrees; in squats it was higher at 60 to 90 degrees of bend; and in another study, kneecap compression was greatest near full bend in squats and leg presses. A review of squat depth puts the peak stress behind the kneecap at about a right angle.
No study has measured knee load in reformer footwork. On an instrumented footbar, the force worked out from the springs differed from the force measured, so spring settings are only a rough guide to the load; and in 15 people doing footwork, two different muscle strategies appeared depending on the direction they pushed the bar. In our reading of the leg press and squat studies, a sore kneecap usually copes better with the knees bending less at the start of footwork and pushing in line with the feet.
Sources 18, 19, 20, 21, 22, 23
Deep twisting bends and the meniscusEmerging evidence
In 10 people in an MRI scanner, both menisci slid backwards in a deep knee bend and carried more of the contact. The risk factors for meniscal tears are age over 60, male sex, work kneeling and squatting, climbing many stairs, and contact and pivoting sports: a very different dose from a Pilates class. Frogs and circles in the straps, a deep single-leg kick or rocking can twist a deeply bent knee (our reading); an Australian Pilates body notes that frogs and bicycles may twist the knee and irritate a new knee replacement if not controlled well.
Sources 24, 25, 26, 27
Locked knees and very flexible kneesEmerging evidence
Knees that straighten more than 5 degrees past straight (genu recurvatum) can go with knee pain and poor control at the end of straightening, an expert commentary says. Snapping the knees straight at the end of each footwork push loads the back of the knee, and the teaching cue is not to (our reading). With hypermobility, the NHS says do not overextend your joints just because you can. In contact sport, hypermobile players had more knee injuries, and in 132 young dancers, those with both hypermobility and scoliosis mostly had kneecap pain, with weaker knee muscles and poorer balance (other groups, not Pilates).
Sources 28, 11, 29, 30, 31
Rare but serious: falls, an infected bursa and a clot
A fall from the reformer or the jump board can injure the knee: a news report describes a client who slid and fell off the reformer on her first jump, and an Australian Pilates body reported hearing of a broken leg in a reformer class. Kneecap bursitis is uncommon even in workers (0.6% of men and 0.2% of women in one regional workforce), but about a third of kneecap and elbow bursitis is infected, with a temperature over 37.8 degrees and broken skin among the signs. A swollen, red or painful calf can be a clot. These are rare: they show what the warning signs are for, not a risk.
Sources 32, 33, 34
Telling the causes apart, and when a scan mattersEmerging evidence
A general practitioner (GP) or physiotherapist asks which moves bring it on and where exactly it hurts, then examines the kneecap, the joint line and how the knee bends and straightens. Kneecap pain is pain around or behind the kneecap made worse by loaded bent-knee activity such as squatting, stairs and long sitting; the best single test is pain in a squat. The NHS sorts knee pain by pattern: a warm, red knee made worse by kneeling or bending suggests bursitis; a knee that gives way, won't straighten or popped at the time suggests a torn ligament, tendon or meniscus.
For an ache after class that is settling, no scan is needed (our reading). An X-ray matters after a fall or if you can't take weight. Meniscal tears are common on the magnetic resonance imaging (MRI) scans of knees that don't hurt: in 991 people aged 50 to 90, 61% of those with a tear had no pain, aching or stiffness in the past month, and a guideline panel calls them usually incidental. Catching or occasional locking wasn't helped by removing the torn piece more than by sham surgery; a truly locked knee that can't fully straighten is the exception that needs prompt assessment.
Sources 35, 36, 37, 38, 39, 40, 41
How it usually goesEmerging evidence
No study has followed Pilates clients with knee pain. The NHS says knee pain can often be treated at home and you should start to feel better in a few days, and to see a GP if it doesn't improve within a few weeks; bursitis should go away in a few weeks. Kneecap pain can linger: in a 5 to 8 year follow-up of two trials, more than half of those who answered reported an unfavourable recovery, but 48 of 50 who had an X-ray had no arthritis, and in 40 young women given education, graded training and a pain-monitoring system, 85% were doing sport without pain a year later.
Muscle soreness after a new class peaks at 1 to 3 days and goes within 5 to 7. Giving way is common in mid-life and later (11.8% of 2,351 adults over 3 months) and goes with knee pain and a weak thigh, so the thigh is the target. No one can promise a date.
Sources 35, 41, 42, 43, 44, 45
