The Weight of the Evidence: Why Heavy Slow Resistance Wins for Tendons

If you’ve ever dealt with a cranky Achilles or a "jumper’s knee," you know tendons can be the divas of the musculoskeletal world. They don’t like sudden changes, and they certainly don’t like being ignored. For decades, the "Alfredson Protocol" (eccentric-only loading) was the gold standard. But there’s a heavy hitter that has shifted the clinical landscape: Heavy Slow Resistance (HSR) training.

What is HSR?

HSR involves lifting significant loads—usually starting around 70-85% of your one-rep max—with a very deliberate tempo. We’re talking a 3-second concentric (up) phase and a 3-second eccentric (down) phase. It’s not about "feeling the burn" through speed; it’s about controlled, high-magnitude tension.

The Science: Kongsgaard and Beyond

The shift toward HSR gained momentum largely thanks to the seminal work of Kongsgaard et al. (2009). Their research compared HSR to traditional eccentric training for patellar tendinopathy. The findings were a game-changer:

• Clinical Outcomes: Both groups saw similar improvements in pain and function at 12 weeks.

• Biological Change: Only the HSR group showed a significant increase in collagen turnover and a reduction in tendon vascularity (signs of actual structural remodelling).

• Patient Satisfaction: At the 6-month follow-up, the HSR group was significantly more satisfied with their results than the eccentric group.

Why Your Tendons Love the Load

Tendons respond to a process called mechanotransduction. When you apply a heavy, slow load, the tenocytes (tendon cells) "sense" the strain and trigger a cascade of collagen synthesis.

Feature	Eccentric Training	Heavy Slow Resistance (HSR)
Focus	Lowering phase only	Both lifting and lowering
Load	Body weight or light	High (70-85% 1RM)
Frequency	Often daily	3 times per week
Adherence	Can be tedious	Generally higher satisfaction

The Verdict

HSR isn't just about the tendon; it strengthens the entire muscle-tendon unit and the kinetic chain. By slowing things down, you remove the "dynamic" peak loads that often irritate a sensitised tendon while providing the high-intensity stimulus needed for repair.

If you're tired of doing 180 heel drops a day with no results, it might be time to add some iron to the mix. Just remember the golden rule: Go heavy, but go slow.