Tendons do get stronger
Across 27 studies of healthy adults, training raised tendon stiffness by a moderate to large amount and tendon size a little. A stiffer tendon passes your muscles' pull on to the bone faster.
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Training guide
How to strengthen tendons and ligaments: how they adapt, heavy slow lifts and holds, how long it takes, collagen and diet claims, and when tendon pain needs a different plan
Tendons join muscle to bone and pass on your muscles' pull. They do get stronger with training: across 27 studies, heavy strength work made them stiffer, which means better at passing that pull on, and a little thicker. Strengthening them takes slow, heavy lifts, with holds if you like and springy work last, 2 or 3 times a week for 12 weeks or more.
What matters is load: weights above about 70% of your maximum worked, light ones didn't, and holds, lifts and slow lowering worked about equally. It takes months, and one review estimates that muscles get stronger a month or two before tendons change. Ligaments are a different story: no trial has tested training them in people.
This guide covers how tendons and ligaments adapt, the exercises and doses for healthy tendons, how long it takes, what's known about ligaments, collagen, gelatin and vitamin C, older adults, and when tendon pain, a pop or a medicine needs its own plan first. Our tendon strengthening workout puts the holds and heavy slow work into one session.
The short version
Heavy is what counts
Loads above about 70% of your maximum stiffened tendons; lighter loads didn't. Holds, lifts and slow lowering worked about equally, and in a 14-week trial only the leg trained at high tendon strain adapted.
It takes months
The biggest effects came from programmes of 12 weeks or more, and one review estimates that muscle strength rises a month or two before tendons change. Build jumps and sprints up gradually.
At any age
Older adults' kneecap tendons got about 58 to 65% stiffer after 12 to 14 weeks of heavy training, but not with light loads.
Painful tendons, and ligaments
For a painful tendon, loading is the treatment, and each tendon has its own guide and pain rule. For ligaments we know very little: no trial has trained healthy people and measured their ligaments, so our reading is that strength, balance and landing control protect them indirectly.
Collagen, and when to stop
Collagen supplements gave small, mixed results in partly industry-funded trials, always alongside training. A pop or snap with sudden weakness, or a tendon that starts to hurt while you take a fluoroquinolone antibiotic, needs help first: see the warning signs below.
Tendons and ligaments: what they are and how they change
Tendons and ligaments
Tendons join muscle to bone and pass the muscle's pull on: the Achilles, the kneecap (patellar) tendon and the tendons at the elbow, for example. Ligaments join bone to bone and steady a joint, such as the ACL (anterior cruciate ligament) in the knee and the outer ankle ligaments. Both are mostly collagen, as our collagen guide explains.
What stronger means for a tendon
Mostly stiffer. Across 27 studies, training changed tendon stiffness and the stiffness of the tendon material far more than its size. A stiffer tendon passes force on faster and stretches less under the same load (our reading of that review).
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How tendons renew
In 14 young men, collagen building in the kneecap tendon rose after an hour of hard exercise, peaked at about 24 hours and was still raised at 72. Eating didn't raise it in tendon in another study. Carbon dating of 28 adult Achilles tendons showed the core is laid down while you grow and barely renewed afterwards, though the outer tendon may renew.
Tendons lag muscles
One review estimates that muscle strength rises a month or two before tendon stiffness changes, from its authors' own studies. In 18 elite volleyball players followed from about 16 to 18, muscle strength rose 13% while the kneecap tendon grew 27% and stiffened 25%: the tendon caught up later.
Ligaments
Ligament growth in people has been seen only in snapshot studies of athletes: in 52 figure skaters and divers who began training before puberty, the ACL on the landing leg was 4.9% larger, and a small study found larger ACLs in weightlifters. A 2026 review says human studies report ligament growth in athletes who begin high-load training during adolescence.
How people differ
Older tendons still adapt to heavy loads, and a review finds no loss of tendon tissue with age in people who stay similarly active. Teenagers' tendons can lag their fast-growing muscle strength, so their jump and sprint loads need building gradually (our reading). Some medicines, such as fluoroquinolone antibiotics, go with tendon injuries.
What the evidence says
Most tendon studies are small, in healthy young adults, and measure stiffness and size, not injuries.
Training stiffens tendonsStrong evidence
Across 27 studies of 264 healthy adults aged 18 to 50, training raised tendon stiffness by a moderate to large amount (an effect size of 0.70) and the stiffness of the tendon material about as much (0.69), but size only a little (0.24). A review describes tendon growth with training as fairly modest.
Heavy loadsStrong evidence
Loads above about 70% of the maximum gave a large effect on stiffness (0.90); lower loads gave none (0.04).
Source 1
Holds, lifts and loweringEmerging evidence
Isometric holds, lifting and lowering, and lowering alone didn't differ (effect sizes of 0.95, 0.82 and 1.04). In 21 adults training one leg at high and one at low Achilles strain for 14 weeks, only the high-strain tendon adapted. In 8 people, 12 weeks of isometric knee extensions at 70% of maximum raised the stiffness of the thigh muscle's tendon structures from 67.5 to 106.2 N/mm.
Twelve weeks or moreEmerging evidence
Programmes of 12 weeks or more had slightly bigger effects than 8 to 12 weeks (0.91 against 0.81), not a significant difference, and the authors advise a high load over more than 12 weeks.
Source 1
Muscles first, tendons laterEmerging evidence
One review estimates that muscle strength rises 1 to 2 months before tendon stiffness changes, drawing on its authors' own studies, which we didn't open. In adolescent volleyball players followed for 2 years, the kneecap tendon grew 27% while muscle strength rose 13%, as the tendon caught up.
Older adults' tendons still adaptEmerging evidence
In 9 adults aged about 74, 14 weeks of heavy training made the kneecap tendon 65% stiffer; in 17 older adults, 12 weeks at about 80% of their maximum made it about 58% stiffer, while about 40% did nothing. A review finds no loss of tendon tissue with age in people who stay similarly active.
How quickly collagen turns overEmerging evidence
Collagen building in tendon rose for about 3 days after a hard session in 14 young men, eating didn't raise it, and the core of the adult Achilles tendon is barely renewed. These are small lab studies; together they fit with tendons changing slowly, over months of steady loading (our reading).
The guidelinesStrong evidence
The World Health Organization (WHO) and the NHS ask adults for strength work for all the major muscle groups on 2 or more days a week.
How to strengthen your tendons: how much and how often
How often
Two or 3 sessions a week, on your strength days. For a painful Achilles, our Achilles guide reports a guideline's suggestion of at least three a week.
How heavy
Start with a weight you can lift about 15 times, and over the weeks build to one you can lift only about 6 to 10 times, roughly above 70% of your maximum: the range that stiffened tendons in trials. Our jumper's knee guide builds the leg press from 4 sets of 15 to 4 sets of 6 in the same way.
Slow
About 3 seconds up and 3 seconds down, as the heavy slow calf raises in our Achilles guide use.
Holds, if you like
In a trial in people with kneecap tendon pain, the first stage was 5 holds of 45 seconds at about 70% of their maximum, every day. Holds are an option, not a must, and they raise blood pressure: breathe normally and never hold your breath.
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Rest
One to 2 minutes between holds; 90 seconds to 2 minutes between heavy leg sets and 60 to 90 seconds between calf raise sets, as our plans' notes and move pages suggest.
Springs last
Add ankle bounces, pogo hops and landings only once the heavy slow lifts are comfortable, and build them up gradually, as the return stages of our Achilles and jumper's knee guides do.
How long
At least 12 weeks; after that, keep a session or two a week going (our suggestion).
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A tendon strength session, step by step
Our editorial session, the shape of our tendon strengthening workout. The order of holds, heavy slow lifts and springy work follows a trial in people with kneecap tendon pain (Breda 2021), and the doses come from our Achilles and jumper's knee guides and move pages. No trial has tested this session in people without tendon pain.
- Warm up: march on the spot for 60 seconds, then 5 slow ankle circles each way and 15 easy calf raises.
- Holds: Spanish squats, a strap round a post behind your knees, leaning back and sitting down to a comfortable depth: 4 holds of 30 to 45 seconds at a hard-but-OK effort, 1 to 2 minutes apart. Then 4 calf raise holds of 30 to 45 seconds.
- Heavy and slow: the leg press, or split squats holding dumbbells or a loaded backpack at home, 3 sets, about 3 seconds up and 3 seconds down.
- Calves: standing calf raises holding a dumbbell, then seated one-leg raises with a weight on your knee, 3 sets each at the same slow pace.
- Choose a weight you can lift 12 to 15 times at first, and over about 8 weeks build to one you can lift only 6 to 10 times.
- From week 6, if your sport needs it and the heavy work feels comfortable: ankle bounces, then pogo hops, 2 sets of 20.
- Cool down with calf stretches, 30 seconds each leg. Repeat 2 or 3 times a week for at least 12 weeks.
Loading the 3D figure…
The movement on the figure: Spanish squat (band squat hold)
Holds (isometrics): a gentle start
Isometric calf raise holds: the move page's dose is "5 holds of 30 to 45 seconds, once or twice a day. An editorial starting point: the 2024 Achilles guideline lists isometric loading among the effective types of tendon loading, but this dose is not from a trial." Spanish squats: the move page's dose is "4 to 5 holds of 30 to 45 seconds at a hard-but-OK effort, with 1 to 2 minutes' rest, once a day in the isometric stage. Modelled on the Breda 2021 trial's machine holds (5 holds of 45 seconds at about 70% effort); the Spanish squat itself has not been tested in a trial." Wall sits, 5 holds of 30 to 45 seconds, and leg extension holds with the knee bent about 60 degrees, 5 holds of 30 to 45 seconds with about 2 minutes' rest (our jumper's knee guide); reverse wrist curls held still for the elbow, 5 holds of 30 to 45 seconds (our tennis elbow guide). Breathe normally and never hold your breath.
Heavy slow lifts: the main loading
Slow and heavy, about 3 seconds up and 3 seconds down: slow calf raises, 3 sets of 15; standing calf raises holding a dumbbell, 3 to 4 sets of 6 to 10, heavy; seated one-leg calf raises, 3 to 4 sets of 8 to 12 each leg; the leg press calf press, 3 to 4 sets of 8 to 10, heavy (our Achilles guide's stages). The leg press, 4 sets of 15 building over weeks to 4 sets of 6, and split squats, 3 sets of 8 to 10 each leg (our jumper's knee guide). For the elbow, slow wrist-extensor lowering, as our tennis elbow guide's stages use it.
3D demoSlow calf raiseBeginner · A wall
3D demoStanding dumbbell calf raiseIntermediate · A dumbbell
3D demoSeated one-leg calf raise with a dumbbellBeginner · A dumbbell + A bench or box
3D demoCalf press on the leg pressIntermediate · Strength machine
3D demoLeg pressBeginner · Strength machine
3D demoSplit squatIntermediate · No equipment
3D demoWrist-extensor eccentricsBeginner · A dumbbellSpring: storing and releasing energy, last
Ankle bounces and pogo hops, 3 sets of 20, and skipping, 3 sets of 20 m (our Achilles guide's return stage); box drop landings, 3 sets of 5, and single-leg hop and stick, 3 sets of 5 each leg, for jumpers (our jumper's knee guide). Only once the heavy slow work is comfortable.
Can you strengthen ligaments?
No human training trialMixed evidence
We found no trial that trained healthy people and measured their ligaments. Athletes who trained hard from before puberty had a 4.9% larger ACL on the landing leg, and a small study found much larger ACLs in weightlifters. These are snapshot studies, so they can't show that training caused the difference.
Animal studiesEmerging evidence
In animals, training made ligaments heavier and stronger, and immobilising a joint weakened them.
Exercise and knee loosenessEmerging evidence
Squats didn't loosen the knee in power lifters, while basketball and a 10 km run loosened it briefly, by 18 to 20%.
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What protects ligaments in practice
Our reading, which no human trial has tested: since training hasn't been shown to make ligaments themselves stronger in people, what protects them is the strength, balance and landing control around the joint. Balance training did cut ankle sprains by about a third in trials, as our ankles guide reports, and our knees guide and ACL injury guide cover landing control.
Balance and control: protecting ligaments
One-leg balance, about 20 to 40 seconds, twice, made harder every week or two (our ankles guide). The reach matrix: the move page's dose is "3 rounds of 5 reaches in each direction, each leg (our editorial starting point). In trials in athletes, neuromuscular (balance and control) training lengthened reaches on the test and roughly halved ankle injuries." The balance board: the move page's dose is "Several holds of 20 to 30 seconds on most days (our editorial starting point). In one trial a wobble board programme ran daily for 6 weeks, then weekly for 6 months."
How long does it take to strengthen tendons?
Healthy tendonsEmerging evidence
Plan on 12 weeks or more: the biggest stiffness changes came from programmes that long, and one review estimates that muscles get stronger a month or two before tendons change.
Painful tendonsEmerging evidence
In the wait-and-see groups of 6 trials (518 people), elbow, kneecap and Achilles tendon pain hadn't fully settled by 12 to 16 weeks. Our Achilles guide asks for at least 12 weeks of progressive calf strengthening, and says full recovery can take many months.
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Why tendons are slower than muscles
The core of the adult Achilles tendon is barely renewed, while collagen building rises for only a few days after each hard session. Change comes from steady loading over months, not from a few hard weeks (our reading).
When a tendon already hurts
Loading is the treatmentEmerging evidence
In 58 people with Achilles tendinopathy, 12 weeks of heavy slow calf raises worked as well as heel drops at 12 and 52 weeks, and people did more of their sessions (92% against 78%). In 39 men with kneecap tendon pain, heavy slow resistance helped in the short and long term, while a steroid injection helped short term and did poorly later.
A staged programmeEmerging evidence
In 76 people with kneecap tendon pain, a programme of daily holds, then heavy slow lifts, then jumping, then sport beat eccentric squats at 24 weeks (28 against 18 points on a 100-point score). Adherence was under half in both groups, and the trial was partly funded by the NBA and GE Healthcare.
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Holds are an option, not a better oneEmerging evidence
Holds eased kneecap tendon pain straight away in 6 volleyball players, but in 21 people pain fell by only 0.9 out of 10, and holds and ordinary lifting did equally well in 29 athletes in season. Reviews of 10 and 13 trials found holds no better than lifting.
Lowering alone isn't specialEmerging evidence
Across 32 studies, there was little evidence for isolating the lowering (eccentric) part of the lift.
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Steroid injectionsEmerging evidence
Across 41 trials, steroid injections eased tendon pain in the short term, but the effect reversed in the medium and long term.
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The Achilles rule: up to 5 out of 10
This site's suggested rule: pain during exercise up to 5 out of 10, back to its usual level by the next morning, and not creeping up week on week. If it is worse the next morning, lighten the load for a few sessions rather than stopping.
The kneecap tendon rule: 3 out of 10
The largest patellar tendon trial kept exercise pain at 3 out of 10 or less, a lower ceiling than for joint pain. Keep the rest of your activity within the same limit, and expect the tendon to settle back to its usual level by the next morning.
The elbow rule: 3 to 4 out of 10
Some discomfort during forearm exercises is fine. Keep it mild: no more than about 3 to 4 out of 10. It should settle within an hour or so, and your elbow should be no worse the next morning. If it is worse, go lighter next time (a lighter weight, a bendier bar, fewer reps or a shorter hold), not nothing. When a set no longer causes any discomfort, it's time to progress.
The shoulder rule: about 5 out of 10
Keep shoulder pain to about 5 out of 10 or less during the exercise, back to its usual level by your next session, as our shoulder guides advise. A sharp pinch means lower, lighter or stop.
Where to go
Our Achilles tendinopathy, jumper's knee, quadriceps tendinopathy, tennis elbow, golfer's elbow, triceps tendinopathy and distal biceps tendinopathy guides have the staged plans.
Collagen, gelatin, vitamin C and diet
Gelatin and vitamin C before exerciseEmerging evidence
In 8 men, 15 g of gelatin with vitamin C an hour before 6 minutes of skipping doubled a blood marker of collagen building; in 10 men, a similar test wasn't significant. Neither study measured tendons.
Collagen with trainingMixed evidence
In 40 men training for 14 weeks, a branded collagen peptide gave a bigger Achilles tendon (11.0% against 4.7%) but no more stiffness or strength, in a trial funded by its maker. In 39 young men, 15 g a day for 15 weeks did nothing for tendon size or stiffness, and a week of it didn't raise connective tissue building in 25 men. A small maker-funded trial in Achilles pain found faster improvement with collagen alongside calf strengthening. A 2026 review of 8 small trials, almost all in men, called the evidence strong while listing small samples and short, varied protocols.
No trial of collagen on its ownMixed evidence
We found no trial of collagen without training, and a review by authors funded by a collagen maker found no data showing that collagen peptides raise connective tissue building.
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Food first
Loading comes first, and the NHS says most people get the vitamins and minerals they need from a varied and balanced diet, as our collagen guide reports. Our collagen pages cover supplements, safety and the detail.
Tendons and ligaments by body part
Each guide has the plan for its body part; the pain guides have the plans for painful or injured tendons and ligaments.
- Achilles tendon: how to strengthen your calves
- A painful Achilles: Achilles tendinopathy
- Knee tendons and ligaments: how to strengthen your knees
- Pain below the kneecap: jumper's knee
- Elbow tendons: how to strengthen your arms
- Wrist and forearm: how to strengthen your wrists
- Pain on the outside of the elbow: tennis elbow
- Ankle ligaments: how to strengthen your ankles
- A sprained ankle
- Shoulder tendons: how to strengthen your rotator cuff
- Fingers and grip: grip strength
Workouts to follow
The tendon strengthening workout is holds, heavy slow calf and leg work, then springs. The calf, bounce and knee sessions load the Achilles and kneecap tendons; the wrist and grip sessions the forearm tendons; the balance and warm-up sessions train the control that protects ankle and knee ligaments.
Tendon strengthening workout: holds, heavy slow calf and leg work, then springs
A 35-minute editorial session for healthy tendons: calf and Spanish squat holds, heavy slow leg and calf lifts, then springs once the heavy work is easy.
35 minIntermediate13 movesA wall, A band
Calf workout: straight-knee and bent-knee raises with a step
A 25-minute calf workout with a step and a dumbbell: single-leg raises for the big calf muscle, then seated raises for the soleus, with gym swaps for each move.
25 minIntermediate7 movesA wall, A step
Springy starter: calf strength and gentle bounces
A beginner's springy session: calf strength first, then heel drops, calf springs and gentle bounces, building towards skipping and pogo hops.
20 minBeginner11 movesA wall, A step
Knee strengthening workout: from first steps to full range
A 25-minute session for knees that don't currently hurt: thigh and hamstring strength, single-leg control, then an optional full-range block with knees over toes.
25 minBeginner14 movesA bench or box, A wall
Strength and landing workout for jumpers: landings, complex pairs, tendons and trunk
A 50-minute session for jumpers and vaulters: landings and hops, squats and Romanian deadlifts paired with jumps, then tendon holds and trunk work.
50 minIntermediate15 movesCardio machine, A step
Wrist and forearm routine
Wrist mobility and forearm strength for desk work, climbing, push-ups and handstands.
10 minBeginner7 movesA wall, A dumbbell
Grip strength workout: squeezes, curls, carries and hangs
A 20-minute grip session: warm up the wrists and fingers, train the hand and forearm muscles, then carry and hang to load your grip the way everyday life does.
20 minBeginner10 movesOther / check instructions, A band
Foot and ankle strengthening routine: toes, arches, calves and balance
A 15-minute barefoot routine for stronger toes, arches, calves and ankles, finishing with balance. You need only a towel, a wall and a resistance band.
15 minBeginner11 movesA wall, Other / check instructions
Balance training workout: from standing still to moving
A 20-minute balance workout for steady adults: harder stances, head turns and eyes closed, single-leg reaches and hinges, step-ups and stuck landings.
20 minIntermediate13 movesA wall, A dumbbell
FIFA 11+ warm-up
FIFA's 11+ injury prevention warm-up as its manual sets it out: running drills, strength, balance and jumping at three levels, then faster running.
20 minBeginner20 movesCardio machine, A wall
Knee control warm-up
A 20-minute warm-up that trains your knees to track over your toes: side-hip strength, squats and lunges with alignment practice, balance and quiet landings.
20 minBeginner10 movesA wall, A bandPlans
Each builds heavier lifting over weeks, the load tendons respond to.
2 days a week
Strength training plan for runners
A 12-week strength plan for runners: two sessions a week of heavy lifts, single-leg work, calf raises and hops, fitted around your runs.
2 training days45 minBeginner3 days a weekWorkout plan for seniors (65 and over)
A 12-week exercise plan for over-65s: strength and balance three times a week, short balance sessions and daily walks, based on falls-prevention trials.
3 training days40 minBeginner3 days a weekBeginner strength program: a 5x5-style barbell plan
A 12-week beginner barbell program: squat every session, alternate bench and row with press and deadlift, and add weight each time until it stalls.
3 training days50 minBeginnerWho should change their tendon training
Older adults
Tendons still stiffened with heavy loads in trials of older adults, including people in their 70s. Build up from a weight you can lift about 15 times, and add balance work; our exercise for older adults guide has the plan.
Teenagers in jumping and sprinting sports
Tendons can lag fast-growing muscle strength in young athletes, so build jump and sprint loads up gradually (our reading of a review).
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Medicines
In 15 observational studies, fluoroquinolone antibiotics went with 2.52 times the odds of an Achilles rupture and 3.95 times the odds of Achilles tendinitis. Steroid injections and anabolic steroids can weaken tendons too, as our triceps tendinopathy guide lists.
You're taking a fluoroquinolone antibiotic and a tendon starts to hurt or swell: stop taking it, contact your doctor straight away, and rest the painful area until you've been seen.
After a tendon rupture or ligament surgery
Follow your surgical or rehab team's stages; our Achilles rupture, patellar tendon rupture, ACL surgery and ankle ligament surgery guides cover them.
Holds and blood pressure
Wall sits raise blood pressure while you hold them, so breathe normally and never hold your breath. Ask your GP first if your blood pressure is 160/100 or higher and untreated, or if you have heart disease, and skip them with Marfan syndrome, vascular Ehlers-Danlos syndrome or aortic disease.
Our suggestion: treat Spanish squats and long calf raise holds the same way, as they're similar hard holds.
A new tendon injury
The NHS tendonitis page, which is past its review date, advises trying to avoid moving the tendon for 2 to 3 days, then keeping it moving once pain allows, and avoiding heavy lifting, strong gripping or twisting that makes the symptoms worse. For long-standing tendon pain, loading is the treatment, and our Achilles guide says the guideline advises against complete rest.
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Warning signs: when to get help
A snap at the back of the heel
Same day: a sudden snap or pop at the back of the heel or calf, or a feeling of being kicked there, then walking flat-footed and being unable to push off, stand on tiptoe or climb stairs. It could be an Achilles tendon rupture or a broken heel bone. Go to A&E or a minor injuries unit, or contact NHS 111.
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A pop at the front of the knee
A pop or tearing feeling at the front of the knee after a fall, a jump, a landing or a heavy squat, then you can't straighten the knee or lift the straight leg, there's a dent above or below the kneecap, or the kneecap sits higher or lower than on the other side. Go to A&E or an urgent treatment centre, or get help from NHS 111, as our knee pain when squatting guide explains. In the US, go to urgent care or the emergency department.
Same day: a pop just above the kneecap, then you can't straighten your knee or lift the straight leg, or there's a dent above the kneecap. This can be a quadriceps tendon tear, which almost always needs surgery and does better if it's repaired soon. Our torn kneecap tendons guide covers that injury.
A pop at the elbow
A sudden pop at the front of the elbow during a heavy pull, with bruising, a gap at the front of the elbow or a bulge in the upper arm, can be a torn biceps tendon. Go to an urgent treatment centre or A&E (in the US, urgent care or the emergency department), and don't wait for it to settle: repair is best done within the first 2 to 3 weeks.
Urgent treatment centre or A&E: a pop or snap at the back of the elbow during a push, a press or a dip, or after a fall onto an outstretched hand, then sudden pain and swelling, bruising at the back of the elbow or forearm, a gap above the point of the elbow, or weakness straightening the arm, especially overhead. Don't wait to see if it settles: a full tear in an active person is usually repaired, and expert guidance favours repairing it early.
A pop at the chest or shoulder
A pop or tearing at the front of the armpit or chest during a lift, followed by bruising into the chest or upper arm, a change in the shape of the chest or armpit, or weakness pushing, can be a torn chest tendon. Don't wait for it to settle: get help the same day from NHS 111 or an urgent treatment centre, as our pec strain guide explains.
Same day (GP or NHS 111): sudden weakness lifting the arm after an injury or fall. A rotator cuff tear caused by an injury needs urgent referral to a shoulder specialist. After a dislocation in anyone over 40, the rotator cuff should be checked: about 40% have a tear.
Any tendon you think you've torn
If your arm hurts when you exercise but the pain goes away when you rest, if you think you've torn a tendon, or for severe wrist pain, a snap, grinding or popping, or lost feeling in your hand. In the US, your doctor or urgent care.
Source 41
A tendon that hurts on an antibiotic
You're taking a fluoroquinolone antibiotic and a tendon starts to hurt or swell: stop taking it, contact your doctor straight away, and rest the painful area until you've been seen.
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A sprained ankle
Call 999 or go to A&E: after an injury, you heard a crack, the foot or ankle has changed shape or points at an odd angle, a bone is sticking out, there is a bad cut over it, you're in severe pain, or the toes look blue or white, feel numb or are cold to touch. These can mean a broken bone. Don't drive yourself.
Same day (NHS 111 or an urgent treatment centre): after an injury, you can't put weight on it or walk more than a few steps, the pain is very bad or getting worse, there is a lot of swelling or bruising or it is getting worse, it feels very stiff, or it's not feeling any better after treating it yourself. Get the same help if you also have a very high temperature, or feel hot, cold or shivery: this could be an infection. If you think it's broken, don't treat it yourself.
A knee injury
Go to A&E (accident and emergency) if you've injured your knee and it has changed shape, it becomes very swollen very quickly, you felt a pop or snap, you can see bone sticking out, or it's bleeding heavily. Don't drive yourself: ask someone to take you, or call 999 if the pain means you can't move your leg to get there.
Get advice from NHS 111 now: the knee locks, gives way or clicks painfully. Painless clicking is normal.
See a GP or physiotherapist
An ankle that keeps giving way months after a sprain.
Pain that is getting worse week on week despite cutting back, or is stopping your normal activities.
A clot in the leg
Same day (urgent GP appointment or NHS 111): throbbing pain in one leg (rarely both), usually the calf or thigh; swelling in one leg (rarely both); red, blue or darkened skin around the painful area, which may be harder to see on brown or black skin; or swollen veins. It could be a blood clot (deep vein thrombosis, DVT), which is more likely while you're moving about much less than usual or after a hospital stay.
Also call 999 for pain and swelling in one leg with breathlessness or chest pain: it can be a blood clot that has reached the lungs.
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After unusually hard training
Call NHS 111 (in the US, your doctor or urgent care) for severe muscle pain and weakness with dark (cola-coloured) or reduced urine after unusually hard training. This can be rhabdomyolysis, which can harm the kidneys and needs prompt care.
Stop and get medical help
If you get chest pain or pressure, feel faint or dizzy, are unusually breathless, or your heart races or beats irregularly during exercise, as our plans advise.
Call 999 (911 in the US)
For chest pain that comes on suddenly and doesn't go away, feels tight or like squeezing, spreads to your arms, neck, jaw, stomach or back, or comes with sweating, feeling sick, light-headedness or breathlessness; severe difficulty breathing; someone who faints while exercising; palpitations that don't go away, or come with chest pain, shortness of breath or feeling faint; or a headache that starts suddenly and is extremely painful, especially while lifting or straining, or comes with numbness or weakness, difficulty speaking or loss of vision. The NHS says a bleed on the brain may be more likely when lifting something heavy. Don't drive yourself to A&E.
Ask for an urgent GP appointment or call NHS 111
Ask for an urgent GP appointment or get help from NHS 111 for a headache that's triggered or made worse by coughing, sneezing, bending down or exercising. In the US, contact your doctor or urgent care.
During any session
Stop straight away if you feel any pain or become unwell, the NHS says, and contact 111 if your symptoms worry you or don't go away.
A dull ache in your muscles for a day or two after something new is normal. Joint pain that's sharp, gets worse during a set or lingers into the next day means switching to the easier option, and seeing a GP or physiotherapist if it carries on (our plans' rule). Our muscle soreness guide has more.
Check first
Speak to your GP first if you haven't exercised for some time or have medical conditions or concerns, as the NHS advises. Get advice before heavy lifting or hard straining work if your blood pressure is uncontrolled, or you have heart disease or chest pain when you're active, a pacemaker or defibrillator, diabetic eye disease, glaucoma, a hernia, recent eye or tummy surgery, or you're pregnant, as our breathing guide lists. After a recent shoulder dislocation or shoulder surgery, follow our shoulder dislocation guide or your surgical team first.
Speak to a GP first if you haven't exercised for some time, or if you have a medical condition or concerns. Get advice first, too, if you have a health problem, an injury or symptoms, have recently had a heart attack or an operation, or are pregnant or have recently given birth.
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Hernia
See a GP if you think you have a hernia, a bulge or lump that may get bigger when you strain and smaller when you lie down. Get help from NHS 111 if you have a hernia and pain in or around it, a bloated tummy, you feel or are sick, you're vomiting blood or your vomit looks like coffee grounds, you're constipated, you have a high temperature or feel hot, cold or shivery, or you've suddenly become confused. Call 999 or go to A&E for a femoral hernia (a small lump at the top of your thigh, in your groin) with very bad tummy pain, sickness, being unable to fart or poo, a high temperature or sudden confusion.
Myths
"Tendons can't get stronger"Strong evidence
They can. Across 27 studies, heavy training stiffened tendons by a moderate to large amount; 12 weeks of isometric training raised the stiffness of the thigh muscle's tendon structures from 67.5 to 106.2 N/mm; and older adults' kneecap tendons stiffened by about 58 to 65%. What's true is that they change slowly, mostly in stiffness rather than size.
"Collagen supplements rebuild tendons on their own"Mixed evidence
No trial has tested collagen without training. With training, one maker-funded trial found a bigger Achilles tendon but no extra stiffness or strength, a 15 g trial found nothing, and a review found no data that collagen peptides raise connective tissue building. The gelatin and vitamin C study measured a blood marker in 8 men.
"Isometric holds are the best exercise for tendons"Emerging evidence
They work as well as lifting and lowering when the load is heavy, but no better, and reviews found no advantage for tendon pain.
"Light weights and high reps are kinder and better for tendons"Strong evidence
Loads of about 40% of the maximum or less didn't change tendons in pooled trials or in older adults. Start light if you're new or sore, then build up.
"Rest a sore tendon until it stops hurting"Emerging evidence
For long-standing tendon pain, loading is the treatment and complete rest isn't advised, and untreated tendon pain hadn't settled by 12 to 16 weeks in trials. A new tendon injury may need a couple of days' rest first, as the NHS advises.
"You can strengthen ligaments like muscles"Mixed evidence
We found no human training trial; the best evidence is snapshot studies of athletes who trained from a young age. Strength, balance and landing control protect ligaments indirectly (our reading).
"Sitting at a desk weakens your tendons"
We found no study showing it. Regular strength work is what we know stiffens tendons.
Read next
- Tendon strengthening workout
- How to strengthen your calves
- How to strengthen your knees
- How to strengthen your ankles
- How to strengthen your arms
- How to strengthen your wrists
- How to strengthen your rotator cuff
- How to do a wall sit
- How to do calf raises
- How to build explosive power
- Progressive overload
- Collagen and fascia
- Collagen in food
- The knee joint
- The ankle and foot
- The elbow joint
- Achilles tendinopathy
- Jumper's knee
- Quadriceps tendinopathy
- Tennis elbow
- Golfer's elbow
- Triceps tendinopathy
- Distal biceps tendinopathy
- Achilles rupture
- Patellar tendon rupture
- Ankle sprain
- Exercise for older adults
- Calf workout
- Knee strengthening workout
- All training guides
Questions people ask
Can you strengthen tendons?
Yes. Heavy strength training made tendons stiffer by a moderate to large amount across 27 studies, and a little thicker, in older adults too. They change more slowly than muscles.
What exercises strengthen tendons?
Slow, heavy lifts for the muscles concerned, such as calf raises for the Achilles and the leg press or split squats for the kneecap tendon, plus holds if you like, and springy work last for running and jumping. Loads above about 70% of your maximum worked; lighter ones didn't.
How long does it take to strengthen tendons?
Months. The biggest changes came from programmes of 12 weeks or more, and one review estimates that muscle strength rises a month or two before tendon stiffness does. Painful tendons usually need 12 weeks of loading or longer.
Do isometric exercises strengthen tendons?
Yes, as well as lifting and lowering do when the load is heavy. For tendon pain they can be a gentle start, but they weren't better than ordinary lifting in reviews.
Can you strengthen ligaments?
Possibly, but no trial has tested it in people: athletes who trained hard from childhood had slightly bigger ACLs on the loaded side. Strong muscles, balance and good landing control are how ligaments are protected in practice, which is our reading of the evidence.
Does collagen strengthen tendons?
The evidence is small and mixed: one maker-funded trial found bigger Achilles tendons with collagen plus training, another found no difference, and none found extra strength. Our collagen guide covers the details.
Should I take gelatin and vitamin C before training?
In 8 men it doubled a blood marker of collagen building, but no trial has shown stronger tendons or fewer injuries from it. The NHS says most people get the vitamins they need from a varied and balanced diet.
How do I strengthen my Achilles tendon?
Heavy slow calf raises, standing and seated, building to single-leg raises with a weight, 2 or 3 times a week, then hops if you run or jump. Our calves guide and Achilles tendinopathy guide have the plans.
How do I strengthen the tendons in my knee?
The leg press, split squats and leg extensions, done slowly and built up to heavy over weeks, with holds as an option. With pain below the kneecap, our jumper's knee guide keeps tendon pain at 3 out of 10 or less.
How do I strengthen the tendons in my elbow?
Slow wrist and forearm work, curls and triceps work, built up gradually. With pain on the outside of the elbow, our tennis elbow guide's holds, lifting and lowering come first, keeping pain to 3 to 4 out of 10.
Can certain medicines weaken tendons?
Fluoroquinolone antibiotics went with higher odds of Achilles rupture in observational studies. You're taking a fluoroquinolone antibiotic and a tendon starts to hurt or swell: stop taking it, contact your doctor straight away, and rest the painful area until you've been seen. Steroid injections and anabolic steroids are linked with tendon problems too.
Do tendons get weaker with age?
Not necessarily. Older adults' tendons still stiffened with heavy training, by about 58 to 65%, and a review found no loss of tendon tissue with age in people who stay similarly active.
Sources
- Bohm 2015 · How healthy tendons adapt to loading: 27 studies (systematic review and meta-analysis, Sports Med Open)
- Arampatzis 2007 · Achilles tendon adaptation depends on the size of the strain, in 21 adults (training study, J Exp Biol)
- Mersmann 2017 · Muscle and tendon developing out of step in young athletes (narrative review, Front Physiol)
- Reeves 2003 · Fourteen weeks of strength training and the kneecap tendon in 9 adults aged about 74 (training study, J Physiol)
- Grosset 2014 · Heavy against light training and tendon stiffness in 17 older adults (training study, Age)
- Beyer 2015 · Heavy slow calf training against heel drops for Achilles tendinopathy in 58 people (randomised trial, Am J Sports Med)
- Kongsgaard 2009 · Steroid injection, eccentric decline squats or heavy slow resistance for patellar tendinopathy in 39 men (randomised trial, Scand J Med Sci Sports)
- Beaulieu 2021 · A larger ACL on the loaded side in 52 elite athletes who trained from before puberty (MRI study, Am J Sports Med)
- Jerger 2022 · Collagen peptides with 14 weeks of training and the Achilles tendon (randomised trial of 40 men, industry-funded, Scand J Med Sci Sports)
- Balshaw 2023 · Collagen peptides during 15 weeks of leg training: tendon size and stiffness (randomised trial of 39 men, Med Sci Sports Exerc)
- Miller 2005 · Collagen building in tendon and muscle after exercise in 14 men (tracer study, J Physiol)
- Babraj 2005 · Collagen building in human tendon, ligament, muscle and skin (tracer study, Am J Physiol Endocrinol Metab)
- Heinemeier 2013 · Carbon dating shows the adult Achilles tendon core is barely renewed (study of 28 tendons, FASEB J)
- Mersmann 2017 · Muscle and tendon adaptation over 2 years in 18 adolescent volleyball players (cohort study, Scand J Med Sci Sports)
- Grzelak 2012 · Larger cruciate ligaments in elite weightlifters (MRI study, Int Orthop)
- Staniucha 2026 · How the ACL adapts: structure, mechanics and healing (review, Sports Med)
- Magnusson 2019 · Loading, unloading, ageing and injury and the human tendon (review, J Physiol)
- Alves 2019 · Fluoroquinolone antibiotics and tendon injury: 15 studies (systematic review and meta-analysis, Eur J Clin Pharmacol)
- Kubo 2001 · Twelve weeks of isometric knee extension training and the stiffness of the thigh muscle's tendon structures in 8 people (training study, J Appl Physiol)
- Bull 2020 · World Health Organization 2020 guidelines on physical activity and sedentary behaviour (guideline, BJSM)
- NHS · Physical activity guidelines for adults aged 19 to 64
- Breda 2021 · Progressive tendon loading against eccentric squats in 76 people with patellar tendinopathy (randomised trial, Br J Sports Med)
- Tipton 1975 · Physical activity and ligaments and tendons (animal studies, Med Sci Sports)
- Woo 1982 · Immobilisation, exercise and tendon and ligament remodelling (animal study, Biorheology)
- Tipton 1986 · Physical activity and ligaments, tendons and joints: experimental studies (review of animal studies, Acta Med Scand Suppl)
- Steiner 1986 · Exercise and front-to-back knee laxity: squats, basketball and running (study, Am J Sports Med)
- Garzón 2024 · How long tendinopathy lasts if left untreated: the wait-and-see groups of 6 trials (systematic review and meta-analysis, Musculoskelet Sci Pract)
- Rio 2015 · Isometric holds and kneecap tendon pain in 6 volleyball players (randomised crossover study, Br J Sports Med)
- Holden 2020 · Held against moving exercise and patellar tendon pain in 21 people (randomised crossover trial, J Sci Med Sport)
- van Ark 2016 · Isometric and isotonic programmes for patellar tendinopathy in season in 29 athletes (randomised trial, J Sci Med Sport)
- Clifford 2020 · Isometric exercise for tendon pain: 10 trials (systematic review and meta-analysis, BMJ Open Sport Exerc Med)
- Soliman 2026 · Isometric exercises for tendon pain: 13 trials (systematic review, Clin Ther)
- Malliaras 2013 · Achilles and patellar tendinopathy loading programmes: 32 studies (systematic review, Sports Med)
- Coombes 2010 · Steroid and other injections for tendinopathy: 41 trials (systematic review, Lancet)
- Shaw 2017 · Vitamin C-enriched gelatin before skipping and collagen building (crossover trial of 8 men, Am J Clin Nutr)
- Lis 2019 · Gelatin, hydrolysed collagen or gummies before skipping (crossover trial of 10 men, Int J Sport Nutr Exerc Metab)
- Kirmse 2024 · Collagen peptides during a week of hard training and connective tissue building (randomised trial of 25 men, Med Sci Sports Exerc)
- Praet 2019 · Collagen peptides with calf strengthening for Achilles tendinopathy (industry-funded pilot crossover trial of 20 people, Nutrients)
- Buchalski 2026 · Collagen supplements and tendons: 8 trials (systematic review, J Funct Morphol Kinesiol)
- Holwerda 2022 · Collagen protein and connective tissue remodelling (narrative review, Nutr Rev)
- NHS · Tendonitis (past its review date: reviewed June 2023, review due June 2026)
- NHS · Heel pain
- NHS · DVT (deep vein thrombosis)
- NHS · Hernia
- NHS · Femoral hernia
Exercise education, not a personal prescription, and clinical review of these guides is pending. Check with a GP before starting hard training if you have a heart condition, chest pain, dizziness or breathlessness when active, and stop for sharp or increasing pain. Health disclaimer.