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Most of us, at some point in our careers, will have had a client that’s experienced persistent, niggling tendon pain. The patellar tendon that flares on the stairs, the Achilles that is stiff for the first ten minutes of every run, the shoulder that complains on the overhead press. The old advice was rest, then eccentrics, then more rest. But evidence is starting to show that a “heavy-slow” approach may lead to faster recovery.
For the best part of two decades the default prescription for a grumpy tendon was eccentric-only loading. Drop slowly under control, lift back up with the other leg or with assistance, repeat for sets that often ran into three figures, twice a day, for twelve weeks. It worked for a lot of people. It also asked a great deal of the client and left a sizeable minority no better off. Heavy-slow resistance on the other hand, usually shortened to HSR, has emerged as the loading approach that matches or beats eccentric-only protocols on pain and function, while being far easier to do. For any PT working with general or active clients, it may be something that will be helpful for those troubled clients.
Now, this is not some fringe idea. It traces back to a controlled trial by Kongsgaard et al. (2009) out of Copenhagen, which compared corticosteroid injection, eccentric decline-squat training and HSR for painful patellar tendons. All three reduced pain in the short term, but only the two loading groups held their gains, and HSR produced the highest treatment satisfaction at six months. The injection group, notably, had relapsed by then. That study set the direction of rehab from then on.
It helps to be clear about what is going wrong inside the tendon, because it explains why loading is the treatment rather than rest. The most widely used framework is the continuum model from Cook and Purdam (2009), two Australian physiotherapy researchers whose paper is one of the most cited in the field. They describe tendon pathology not as a single state but as a sliding scale with three overlapping stages.
The first stage is reactive tendinopathy. The tendon has been overloaded, often by a sudden spike in training, and responds by thickening to spread the load. This is a short-term, largely reversible reaction. The second stage is tendon disrepair, where the early response has failed to settle and the internal structure starts to break down. The third is degenerative tendinopathy, where areas of the tendon have lost their normal organised collagen and will not fully recover, although the surrounding healthy tissue can still be strengthened.
The point that is so important for programming is that the tendon can move back down this scale. Adding the right amount of load, at the right speed, encourages the tendon cells to lay down better-organised collagen and stiffen the tissue so it tolerates force again. Too much load too soon pushes it the wrong way. Complete rest does nothing useful at all, because an unloaded tendon gets weaker. The job is to find the dose that drives remodelling without the tendon flaring up, and that is exactly what heavy-slow resistance is built to do.
The clue is in the name. Two things are being manipulated, the load and the tempo, and both have a job to do.
The heavy part provides the mechanical stimulus. Tendon is living tissue, and like muscle it adapts to the demands placed on it. High loads, in the region of a six to fifteen repetition maximum, signal the tendon cells to increase collagen production and reorganise the existing fibres into a stiffer, more aligned structure. This is tendon remodelling in plain terms, the tissue rebuilding itself to handle force. Light loading does not provide enough of a signal to drive that change.
The slow part does two things. A deliberate tempo, roughly three seconds to lift and three seconds to lower, keeps the muscle and tendon under tension for longer in each repetition. That extended time under tension is thought to be a large part of what makes the stimulus effective. The slow speed also keeps the movement controlled and comfortable, which is the practical difference that clients feel. Fast, jerky loading is what tends to provoke a painful tendon. Slow loading lets a client work at a genuinely heavy weight while keeping the discomfort within a manageable range.
There is also a pain-relieving side to heavy loading that clients notice quickly. Working a tendon through a controlled heavy contraction tends to reduce its sensitivity, so many people find the tendon feels better immediately after a session rather than worse. This analgesic effect is one of the reasons clients build confidence in the approach. They expected loading to hurt the tendon and instead it calms it down, which makes the next session easier to commit to.
HSR uses the full range of the movement, both the lifting (concentric) and lowering (eccentric) phases. Older eccentric-only protocols deliberately took the lifting phase out, which is part of why they were so time-consuming and awkward. HSR is just a normal, heavy, slow-tempo resistance exercise, which is one reason adherence tends to be better. It looks and feels like training, not like rehab homework.
The evidence on HSR is now reasonably mature. The cleanest comparison comes from Beyer et al. (2015), a Copenhagen randomised controlled trial of 58 people with chronic mid-portion Achilles tendinopathy. Half did the classic eccentric protocol, half did HSR, both for twelve weeks. At the end of the programme and again at the one-year follow-up, both groups had improved and there was no real difference in pain or function between them. What did differ was satisfaction. At twelve weeks, more of the HSR group reported being satisfied with their treatment, which fits with the lower time burden of the protocol.
That equivalence shows up repeatedly across reviews. An earlier systematic review by Malliaras et al. (2013), which pulled together the Achilles and patellar loading literature, concluded that clinicians should consider eccentric-concentric loading, which includes HSR, alongside or instead of eccentric-only loading. The review flagged that up to around 45 per cent of people do not respond to isolated eccentric training, which is the gap HSR helps to fill.
For patellar tendons specifically, a network meta-analysis by Challoumas et al. (2021), from the tendon research group at Glasgow Caledonian University, compared 33 different interventions across 37 trials. Progressive tendon-loading approaches, including HSR, came out ahead of eccentric-only training for longer-term function, and well ahead of passive treatments and injections. A 2024 network meta-analysis in the journal Heliyon reached a similar conclusion for patellar tendinopathy, placing eccentric-only training at the bottom of the loading options for restoring knee function.
On the Achilles side, a 2023 systematic review and meta-analysis by Maetz et al. (2023) looked specifically at whether one loading protocol beats another for mid-portion Achilles tendinopathy. The honest finding was that no single loading protocol was clearly superior, but that all of them comfortably beat passive treatment. In other words, the loading itself is what counts. HSR earns its place because it delivers that loading in the most tolerable, adherable programme.
A painful tendon is not simply inflamed in the way a sprained ankle is. The pain is more about a tendon that has lost the capacity to handle the load being placed on it. The fix, then, is not to calm inflammation and wait, it is to rebuild capacity.
Progressive loading is the tool that does this. As the tendon is exposed to heavy, slow contractions over weeks, the cells respond by producing and organising new collagen, and the tendon becomes stiffer and stronger. Stiffness here is a good thing, it means the tendon transmits force efficiently and is less likely to be overstrained at a given load. This is why the programme has to progress. A weight that was challenging in week two will be too easy by week six, and a tendon only keeps adapting if the demand keeps climbing.
This also explains why patience is part of the programme. Muscle responds to training within days. Tendons are slower, with adaptation measured over weeks and months rather than sessions. Clients who expect a quick fix need to understand from the start that this is a twelve-week project at minimum, and that early sessions may not feel like they are achieving much. Setting that expectation up front is one of the most useful things a PT can do.
The single biggest worry PTs and clients have about loading a sore tendon is that working through pain will make it worse. The reassuring part is that the research-backed approach is not no pain at all, it is acceptable pain that settles.
The widely used rule of thumb is that pain during and after loading is acceptable up to around 5 out of 10 on a simple pain scale, provided two conditions are met. First, the pain must settle back to its baseline within 24 hours. Second, the tendon must not be progressively more painful or stiff from one session to the next over a week. If the morning stiffness is creeping up day on day, the load is too high and needs backing off. If the pain spikes to an 8 during a session, the load is too high for that day.
It is worth writing this down with the client using a simple traffic-light system. Green is acceptable ache during loading that settles overnight, keep going. Amber is pain that lingers into the next day or morning stiffness that is creeping up across the week, hold the load steady or drop it back a notch. Red is sharp pain during the movement, a sudden flare or pain that is clearly worse week on week, stop and reassess. A client who self-services that system stops needing to ask you whether every twinge is a problem, which is good for them and good for your time.
This monitoring model gives the client a clear, simple framework they can self-manage. A bit of familiar tendon ache during a heavy slow squat that has gone by the next morning is fine and expected. Sharp, escalating or lingering pain is the signal to ease off. Framing it this way removes the fear that often drives clients to avoid loading altogether, which is the very thing that keeps the tendon weak.
The practical protocol that comes out of the Copenhagen trials and the reviews is reassuringly simple. Here is a workable structure for a general or active client with a stable, non-acute tendinopathy.
Choose a loaded version of the movement that targets the affected tendon. For the patellar tendon this is usually a slow squat, often on a slight decline to bias the tendon, leg press or leg extension. For the Achilles it is a heavy calf raise, frequently with the knee both straight and bent across different exercises. For the rotator cuff it is loaded shoulder work such as external rotation and overhead pressing variations within tolerance.
Work in the range of roughly 3 to 4 sets per exercise, at a load corresponding to about a 15 repetition maximum to begin with, progressing over the block towards a heavier 6 repetition maximum as the tendon tolerates it. Use a slow, controlled tempo, in the region of 3 seconds to lift and 3 seconds to lower, through the available pain-free or acceptable-pain range. Train the tendon around 3 times a week, leaving at least a day between sessions so the tissue can respond.
Progress the load gradually over a 12-week block, adding weight as the client’s pain-monitoring stays green and the previous load starts to feel easy. The early weeks are about establishing tolerance, the middle weeks about building load, and the later weeks about getting the tendon strong enough for the demands of the client’s sport or daily life. Many clients keep a maintenance dose of one or two heavy sessions a week well beyond the twelve weeks, because a detrained tendon will slowly lose the capacity it gained.
| Variable | Practical Prescription |
|---|---|
| Sets | 3 to 4 working sets per exercise |
| Load | Start around 15RM, progress towards 6RM as tolerated |
| Tempo | Slow and controlled, roughly 3 seconds up and 3 seconds down |
| Frequency | About 3 times a week, a day or more between sessions |
| Acceptable pain | Up to about 5 out of 10, settling to baseline within 24 hours |
| Duration | A 12-week progressive block, then a maintenance dose |
The HSR principles hold across tendons, but a few region-specific points are worth keeping in mind. For the patellar tendon, the classic exercise is a slow squat on a 25-degree decline board, which increases the load through the tendon at the knee. A leg press or leg extension works well too and is often more comfortable for an anxious client to start with. Jumpers and runners tend to respond well, but the load has to be respected because the patellar tendon takes on the very high forces experienced in sports.
For the Achilles, the picture splits between mid-portion tendinopathy, where the sore spot is a few centimetres above the heel, and insertional tendinopathy right at the heel bone. Mid-portion responds well to standard heavy calf raises through full range. Insertional tendons are usually happier if the range is limited so the heel does not drop below the step, because the extra stretch at the bottom can compress and irritate the insertion. This is a small but useful distinction to make when a client is not settling.
For the rotator cuff, the tendons sit inside a more complex joint, so loaded shoulder work needs to stay within a range and intensity the client tolerates, and technique counts for a lot. Heavy slow external rotation, loaded carries and graded pressing all have a place. This is also the region where referral to a physiotherapist is most often worthwhile early, because shoulder pain has more possible drivers than a knee or ankle tendon.
The first and most common mistake is going too light. A tendon needs a genuine load to remodel, and a client doing three sets of fifteen with a token weight is not giving the tissue a reason to adapt. The discomfort of working at a real 15RM, building towards a 6RM, is the point. If it feels like a warm-up, it is too light.
The second is rushing the tempo. The moment the lift speeds up, the time under tension drops and the movement gets more provocative. Coaching a genuine three-second lift and three-second lower, ideally with a count or a metronome at first, is one of the highest-value cues you can give.
The third is stopping too soon. A client who feels better at week five may want to drop the programme, but the tendon has not finished adapting and the gains are easily lost. Hold them to the full twelve weeks and a sensible maintenance dose after that. The fourth is chasing pain to zero before loading at all. Waiting for a tendon to be completely pain-free before starting usually means waiting forever, because the tendon stays weak. Acceptable, settling pain during loading is part of the process, not a reason to stop.
Heavy-slow resistance is a strong fit for the stable, longstanding tendinopathies that PTs see most often. It is not a substitute for medical assessment when the picture is unclear. Refer a client on to a GP or physiotherapist if the pain came on suddenly with a pop or tearing sensation, if there is significant swelling, bruising or loss of function that suggests a partial or full tendon rupture, or if the tendon is hot, red and painful at rest in a way that points to something other than overload.
Equally, refer on if a sensible loading programme has been followed properly for a good length of time, usually around three months, with no improvement at all. Some tendons need imaging, a steer from a physiotherapist on technique and dosing, or investigation of other contributing factors. Knowing the boundary of your scope and working alongside a physio when needed is part of doing this well, not a sign that the approach has failed.
Many of us find our clients arrive with a tendon they have been nursing for months and a belief that they simply have to live with it or stop the activity they love. The most valuable thing a PT can offer is a calm, structured plan that says the opposite. The tendon is not fragile, it is undertrained, and a sensible heavy-slow programme over twelve weeks gives it the chance to rebuild.
The main point here is that loading is the treatment, the tempo keeps it tolerable, the pain monitoring keeps it safe and the progression keeps it working. Get those four things right and you have a programme that is grounded in good evidence, easy for clients to stick with and well within the scope of a confident, qualified personal trainer to deliver.
Kongsgaard, M., Kovanen, V., Aagaard, P., Doessing, S., Hansen, P., Laursen, A.H., Kaldau, N.C., Kjaer, M. and Magnusson, S.P. (2009). Corticosteroid injections, eccentric decline squat training and heavy slow resistance training in patellar tendinopathy. Scandinavian Journal of Medicine and Science in Sports, 19(6), pp.790-802. Click here to review the full research article.
Beyer, R., Kongsgaard, M., Hougs Kjaer, B., Ohlenschlaeger, T., Kjaer, M. and Magnusson, S.P. (2015). Heavy Slow Resistance Versus Eccentric Training as Treatment for Achilles Tendinopathy: A Randomized Controlled Trial. The American Journal of Sports Medicine, 43(7), pp.1704-1711. Click here to review the full research article.
Cook, J.L. and Purdam, C.R. (2009). Is tendon pathology a continuum? A pathology model to explain the clinical presentation of load-induced tendinopathy. British Journal of Sports Medicine, 43(6), pp.409-416. Click here to review the full research article.
Malliaras, P., Barton, C.J., Reeves, N.D. and Langberg, H. (2013). Achilles and patellar tendinopathy loading programmes: a systematic review comparing clinical outcomes and identifying potential mechanisms for effectiveness. Sports Medicine, 43(4), pp.267-286. Click here to review the full research article.
Challoumas, D., Pedret, C., Biddle, M., Ng, N.Y.B., Kirwan, P., Cooper, B., Nicholas, P., Wilson, S., Clifford, C. and Millar, N.L. (2021). Management of patellar tendinopathy: a systematic review and network meta-analysis of randomised studies. BMJ Open Sport and Exercise Medicine, 7(4), e001110. Click here to review the full research article.
Maetz, R., Dube, M.O., Tougas, A., Prudhomme, F., Dubois, B. and Roy, J.S. (2023). Systematic Review and Meta-analyses of Randomized Controlled Trials Comparing Exercise Loading Protocols With Passive Treatment Modalities or Other Loading Protocols for the Management of Midportion Achilles Tendinopathy. Orthopaedic Journal of Sports Medicine, 11(5). Click here to review the full research article.
If this article has changed how you think about loading painful tendons, the natural next step is to deepen the strength and conditioning side of your practice. Heavy-slow resistance is really applied strength and conditioning, and the more confident you are with loading, progression and programming, the more clients you can take on the journey from sore tendon to resilient performance.
The Strength & Conditioning Exercise Specialist & Master Diplomas™ build exactly that capability, taking you well beyond general gym instruction into structured, progressive loading for performance and rehabilitation contexts.
Strength & Conditioning Exercise Specialist & Master Diplomas™ – Distance Study, In-Person & Live-Virtual
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