Heavy Slow Resistance for Tendons
Twenty years of running accumulates tendinopathy risk in the Achilles, patellar (front of knee), and gluteal (side of hip) tendons. This is what ends most master’s-athlete careers in the 50s and 60s — not the heart, not the joints, but the tendons giving up.
The fix is not stretching. Stretching a stiff or already-degraded tendon doesn’t reverse the pathology and can make it worse. The evidence-based intervention is Heavy Slow Resistance (HSR), developed by Kongsgaard and Magnusson at the University of Copenhagen.
The Kongsgaard / Magnusson protocol
The principle: a tendon needs to be loaded heavily and slowly. Slow contractions force the collagen fibres to remodel along the force axis, building stronger tissue.
Core parameters
- Tempo: 3-second eccentric (lowering), 1-second concentric (lifting). Some references go 3 sec eccentric + 3 sec concentric for full HSR; either is acceptable.
- Load: heavy. The last 2 reps of each set should be very hard. Roughly 6–8 reps to failure range.
- Sets: 3–4 working sets per exercise (after a light warm-up set)
- Frequency: 3× per week per tendon group
- Duration: the original protocol ran 12 weeks for clinical improvement; healthy maintenance is indefinite
This is not a “feel the burn” routine. It’s a deliberate, slow, heavy, controlled session. Each working set should take ~30–40 seconds because of the slow tempo.
Achilles tendon — heavy slow calf raises
- Setup: standing on a step with heels hanging off, holding a single heavy dumbbell at one side (or two dumbbells, one per hand)
- Tempo: 3 sec down → 1 sec pause at full stretch → 3 sec up → 1 sec pause at top
- Load progression:
- Starting: bodyweight only, 3×12 → too easy after a few sessions
- 6-week target: 16 kg held in one hand, 3×8
- 12-week milestone: 24 kg × 3×8
- 24-week milestone: 32 kg × 3×6
- Variation: to bias the gastrocnemius (upper calf), keep knees straight. To bias the soleus (lower calf, more involved in Achilles tendinopathy), bend knees ~90° and do seated calf raises with a dumbbell on the knee.
Do both straight-knee and bent-knee versions weekly.
Patellar tendon — slow eccentric leg extensions or split squats
If a leg extension machine is available:
- Tempo: 3 sec down, 1 sec pause, 3 sec up
- Load: heavy enough that 8 reps is hard. 3×8.
Without a machine, slow tempo split squats are the substitute:
- Bulgarian split squat with the front knee tracking forward (deliberate, controlled)
- 3-second descent, 1-second pause, fast drive up
- 12 kg × 3×6 per side as a starting target; build to 16–20 kg
Hamstring and gluteal tendon — Nordic hamstring curls
The single best exercise for hamstring tendon strength and posterior-chain protection. Nordics also reduce hamstring strain injury risk in distance runners by 50%+ in published trials.
- Setup: kneel on a pad, have a partner or sturdy anchor hold the ankles down. Or use a Nordic bench / loop-band anchor at home.
- Tempo: slowly lower the torso forward toward the floor, fighting gravity all the way down. 3–5 seconds to descend.
- Reps: 3×5–6 reps. Even partial-range reps count.
- Progression: start with hand-assistance to control the descent. Over months, less assistance.
- At the bottom: push the floor away with the hands and bounce back to start, then repeat.
These are brutal. The first session usually leaves the hamstrings sore for 4–5 days. Start with 2–3 reps at half range, build up over weeks.
Hip / gluteal tendon — heavy hip thrusts (slow)
The glute medius and proximal hamstring tendons benefit from heavy thrust work with slow tempo.
- Setup: shoulders on a bench, barbell or heavy dumbbell across the hips
- Tempo: 3 sec up, 2 sec pause at top (full hip extension, squeeze glutes), 3 sec down
- Load progression:
- Starting: bodyweight + 8–12 kg dumbbell, 3×10
- 6-week target: 20 kg × 3×10
- 12-week milestone: 30 kg × 3×8
- 24-week milestone: 40 kg × 3×6
Why this also fixes the “tight hamstrings” problem
A common runner complaint: “my hamstrings are too tight to deadlift to the floor.”
What feels like tightness is often active stiffness — protective tone the body holds because the tendon isn’t strong enough to safely lengthen. Heavy slow resistance does double duty:
- It lengthens the muscle-tendon unit because the slow eccentric reaches full range
- It strengthens the tendon so the body releases the protective tone
Static stretching alone neither addresses tendon weakness nor produces durable changes in flexibility. Six weeks of Nordic hamstring curls produces both more strength and more range of motion than six weeks of static stretching. This is well-documented.
Sample tendon week
Layered on top of running and lifting:
| Day | Tendon work |
|---|---|
| Mon | Heavy slow calf raises (3×8 straight-knee + 3×8 bent-knee), Nordic curls (3×5) |
| Wed | Slow tempo split squats (3×6/side), heavy hip thrust (3×8) |
| Fri | Heavy slow calf raises, Nordic curls |
Total time per session: ~20 minutes. Fits at the start or end of a normal gym session.
Pain rules
Some tendons are already symptomatic when this protocol starts. The rules:
- Pain up to 3/10 during the exercise is acceptable and even therapeutic
- Pain above 5/10, or pain that lingers more than 24 hours after, means the load is too high — reduce by 20%
- Sharp, sudden pain is different from heavy-loading discomfort — stop immediately
This protocol is not meant for acute injuries (recent tendon rupture, active tendinitis flare). Those require a clinician first. HSR is for prevention and management of chronic, low-grade tendinopathy and for protection going forward.