Hip mobility is the phrase the whole lower body gets filed under, which is a shame, because the hip is one of three quite different problems and the other two are usually the ones stopping you. This cluster keeps them apart: the hip, which is limited by bone as often as by tissue; the hamstrings, which are the most measured and least understood line in the body; and the ankle, which quietly decides how deep you can squat and gets almost none of the attention.
The single most useful idea in this cluster is that not every limit is a stretching problem, and that the ones which are not will not move however long you hold them. Knowing which kind you have is worth more than any particular movement.
Bone sets a ceiling you cannot stretch
Hips vary. The socket faces a different way in different people; the neck of the femur meets the shaft at a different angle; the shape of the bone at the head-neck junction differs enough to be classified. When bone meets bone, the joint stops, and no amount of holding a position changes where.
Frank and colleagues reviewed the imaging studies of people without symptoms in Arthroscopy in 2015 and found cam-type morphology in roughly a third of asymptomatic volunteers, and in over half of asymptomatic athletes. Two things follow from that, and they point in opposite directions from the usual conclusion. First, a hip shape that limits range is extremely common in people who feel entirely fine. Second, finding that shape on a scan does not explain anyone's symptoms by itself.
Grade: reasonably solid for the prevalence, unsettled for what it means. The imaging findings are well replicated. What they cause, and in whom, is not.
The practical consequence is undramatic. If your hip stops with a hard, blocked, bony end feel in the front of the joint, and it stops at the same place on the same day every time you test it, that is a ceiling. Working under it is fine. Grinding at it is not, and pinching in the front of the hip is a signal to ease out rather than to breathe into. If it hurts, that is a matter for a clinician who can examine the joint, not a matter for a longer hold.
Hip mobility is six directions
The hip flexes, extends, abducts, adducts, and rotates internally and externally. Almost every routine sold as hip work trains flexion, external rotation, and hip flexor extension — the pigeon, the lunge, the figure-four — and leaves the other three alone.
Internal rotation is the one most commonly missing and the one most likely to matter, because it is the direction a hip needs in order to stand on one leg, to change direction, and to sit into a squat without the pelvis rolling under. Hip internal rotation covers what it is and how to test it; the 90-90 position is the clearest way to work both rotations at once.
Hip flexors are the desk-shaped problem and are covered from that side in desk and posture; the movement side lives in hip flexor stretches and the couch stretch. Tight hips: causes is the article that grades the explanations, because "tight" is doing a great deal of unexamined work in most writing about this joint.
Hamstrings: the most measured line
Hamstring range is the most studied stretch in the literature, largely because it is easy to measure, which is a reason to trust the findings about hamstrings more than the findings about anything else — and a reason to be careful about generalising them to joints nobody has studied.
Two old papers still set the practical dose, and both hold up.
Bandy and Irion, in Physical Therapy in 1994, compared 15, 30 and 60 seconds of static hamstring stretching over six weeks. Thirty seconds beat fifteen. Sixty seconds did not beat thirty. Three years later, Bandy, Irion and Briggler asked the frequency question in the same journal and found that one 30-second hold a day produced the same gains as three.
Grade: solid, and narrow. Young healthy adults, one muscle group, a six-week window. The finding that a short hold is enough is the useful part; the finding that more is not better is the part people ignore.
Konrad and Tilp, in Clinical Biomechanics in 2014, looked at what changed after a six-week stretching programme that increased range: muscle and tendon structure had not changed measurably. That is the same conclusion the wider literature reaches, set out in mobility, measured — the range moves before the tissue does, because what moves first is your tolerance.
The test everyone uses is the forward fold, and it deserves a caveat. Mayorga-Vega and colleagues meta-analysed the sit-and-reach family in the Journal of Sports Science & Medicine in 2014 and found moderate validity for hamstring extensibility and low validity for lumbar extensibility. A fold is the whole posterior chain and the spine at once. That is exactly why the toe touch test reports what it measures and what it does not, and why in Limber the toe touch feeds the hamstring reading in full but only half of the lower-back reading, with the deep squat supplying the rest. The app names what it is inferring instead of pretending one fold measured five things.
How to tell if your hamstrings are tight works through separating the hamstring from the rest of the fold; hamstring stretches is the practice.
Ankles decide the squat
Ankle dorsiflexion — how far the shin can travel forward over the foot — is the least glamorous reading in the lower body and one of the most consequential. It is the constraint that decides whether you can keep your heels down at the bottom of a squat, and it is measurable in centimetres against a wall by anyone, with no equipment.
Macrum and colleagues, in the Journal of Sport Rehabilitation in 2012, artificially restricted dorsiflexion in healthy people and watched the squat change: less knee travel, more forward trunk lean, altered muscle activation. That is a controlled demonstration that the ankle changes the movement above it.
Grade: solid mechanically, weaker clinically. That restricted ankles change squat mechanics is well shown. That restoring dorsiflexion prevents injuries is not, and anyone telling you otherwise is ahead of the evidence.
The knee-to-wall measure is the standard self-test, and it is one of the few home tests with published reliability behind it — Bennell and colleagues reported good intra-rater and inter-rater agreement for the weight-bearing lunge measure in the Australian Journal of Physiotherapy in 1998. It is measured in centimetres, which makes it one of the two readings in Limber's battery precise enough to score on a continuous scale rather than in bands.
You can take it here for nothing: the knee-to-wall test reads both sides in centimetres and scores them on the app's own anchors. One centimetre is worth 5 to 10 points on that scale, which makes it the only reading in the battery fine enough to show a small change — and fine enough to punish careless foot placement. The knee-to-wall test explains the protocol, ankle dorsiflexion explained covers what the number means, and ankle mobility drills plus calf tightness cover the work.
Glutes, and words used loosely
The glutes get stretched a great deal and are rarely the limit. A figure-four or a pigeon loads the posterior hip capsule, the external rotators and the glute together, and which of them you are feeling is not something you can tell from the inside.
The piriformis deserves a specific warning, because it is named with far more confidence than the evidence supports. "Piriformis syndrome" as a diagnosis has no agreed definition or test; Hopayian and colleagues reviewed the reported clinical features in the European Spine Journal in 2010 and found them inconsistent across studies. Deep buttock pain that travels down the leg has several possible sources, some of which are the spine and none of which you can distinguish from a web page.
Grade: thin. Stretching the area is low risk and may feel good. Naming a structure and treating the name is where this goes wrong.
If you have pain that radiates below the knee, numbness, pins and needles, or weakness in the leg or foot, that combination is a reason to be examined by a clinician rather than to hold a stretch longer. Piriformis stretches and glute stretches both carry that framing; the spinal side is covered in lower back.
Left and right are two different legs
The single most informative thing in this whole cluster costs nothing: measure both sides and record them separately.
Almost everyone is asymmetric, most asymmetry is unremarkable, and a large gap is still worth knowing about because it is the one finding a group average cannot give you. Limber flags a left–right difference of 12 points or more as an imbalance, because a gap that size is larger than the noise in the measurement, and the engine gives the low side an extra move each session until the gap closes to under 6. That threshold is the app's own, not a clinical standard, and it exists so that a difference has to clear the measurement error before anything is claimed about it.
Where to start
Four of the five instruments read the lower body, and all four are free here with no signup: the knee-to-wall test for the ankle in centimetres, the hip flexor test for the front of the hip, the deep squat test for the whole leg at once, and the toe touch test for the posterior chain. Each takes a minute or two and scores on the same 0–100 anchors the app uses; the Range Score composes whatever you have taken. The hip mobility test groups the hip half of that into one sitting — a 30-second squat hold, the hip flexor reading, and a seated rotation check compared side against side rather than scored, because nothing validated exists to score it against. Write down the date. Then read deep squat mobility if a squat is what you are after, or hip mobility exercises if the hip is. Take the reading again in three weeks, in the same conditions, and let the two numbers tell you whether the plan is working — because six weeks of a stretch that is not moving your number is six weeks you could spend on the constraint that actually applies.
Questions
Why are my hips so tight?
"Tight" covers at least four different situations: short tissue, a nervous system unwilling to allow more range, a joint whose bone shape has run out of room, and a position you lack the strength to hold. They feel similar from the inside and need different work. A hard blocked stop in the front of the hip that appears at the same place every day suggests bone; a stretchy stop that moves once you are warm suggests tolerance.
Can you change your hip anatomy with stretching?
No. Bone shape is not a tissue property and does not respond to stretching. What can change is everything on the way to the bony limit — tissue tolerance, muscle length, and your strength in the position. Many people have more room available than they currently use, which is why the ceiling is worth finding but not worth assuming.
How long should I hold a hamstring stretch?
About 30 seconds, on the best available evidence, and doing it more often across the week matters more than doing it longer in one go. Bandy and Irion found 30 seconds matched 60 and beat 15 over six weeks, and their follow-up found one hold a day was as effective as three. Those trials were on young healthy adults and on hamstrings specifically, so read them as a sensible default rather than a law.
What is a good knee-to-wall score?
In Limber's battery, 0–2 cm reads 15 and 12 cm or more reads 95, with the marks between at 4, 6, 8 and 10 cm. Those anchors are the app's own scale, built so that the distance between two of your own readings means something — not a population percentile and not a clinical cut-off. Most people land somewhere in the middle, and both ankles are worth measuring because they frequently disagree.
Should I stretch my piriformis?
You can stretch the area safely, but be careful with the name. There is no agreed test for piriformis syndrome and the reported clinical features are inconsistent across the literature, so a deep buttock ache that travels is not something you can attribute to one muscle from the outside. If leg symptoms include numbness, weakness or pain below the knee, see a clinician who can examine you rather than adding another stretch.
Do I need to stretch my ankles if I do not squat?
Dorsiflexion is used in walking downhill, on stairs and in almost every step of a run, so it is not squat-specific. That said, its clearest documented consequence is what it does to squat mechanics. If deep squatting is not something you do or want, an ankle at the low end of the range is a reading worth having and not automatically a problem worth fixing.