If you've researched plantar fasciitis online, you've probably come across references to "high-load strength training" or the "Rathleff protocol." It's a genuinely useful, evidence-informed approach, but it's often described with more certainty than the underlying study actually supports. Here's what the trial found, what the programme involves, and where the evidence has real limits.
What the Trial Actually Tested
The 2015 Rathleff trial randomised 48 patients with plantar fasciopathy into two groups: one performing a progressive high-load strength training programme, the other performing plantar fascia-specific stretching. Both groups also used shoe inserts.
At three months, the strength training group reported better function on a patient-rated outcome measure than the stretching group. However, by 6 and 12 months, there was no longer a meaningful difference between the two groups, both had improved by similar amounts.
The honest summary: progressive loading produced better self-reported function at three months in this trial, but the difference was no longer present at six or 12 months. That doesn't mean loading is "the answer" while other approaches don't work.
What the Programme Involves
The loading protocol used in the trial is a specific, structured exercise:
- Unilateral (single-leg) heel raises
- Performed with a rolled towel positioned under the toes, to engage the windlass mechanism of the foot and increase load through the plantar fascia
- Done every second day rather than daily, allowing recovery between sessions
- Progressed gradually over several weeks, from higher repetitions at lower load towards fewer repetitions at higher load
The towel under the toes is an important part of the original protocol. The exercise was designed to increase loading through the plantar fascia specifically, rather than simply serving as a generic calf-strengthening exercise, which is why people encounter the towel-under-the-toes version described online.
It is a more structured and progressively loaded approach than a simple stretching routine, with the load increased gradually over time.
What We Don't Know From This Trial
It's worth being clear about the limits of the evidence:
- The trial involved 48 participants, a relatively small sample for drawing firm conclusions
- The comparison was against stretching, not against doing nothing, so we can't say how much of the improvement in either group was simply the natural course of the condition
- The specific biological mechanism sometimes cited, that high tensile load stimulates collagen synthesis and tissue remodelling in the fascia, is a plausible extrapolation from tendon and fascia research generally, not something this particular trial demonstrated directly
None of this means the approach isn't worth using. It means it's one evidence-supported option among several approaches used in plantar heel pain rehabilitation.
Where This Fits Into a Wider Plan
In clinical practice, progressive loading can be combined with calf and plantar fascia-specific stretching where appropriate, sensible activity modification, and footwear or orthotic support when these are relevant to the individual's presentation. For the full picture on evidence-based management, read Plantar Fasciitis: Understanding Heel Pain.
How IP Physio Can Help
Where appropriate, we use objective strength testing to establish your baseline capacity, then build a progressive loading programme suited to where you're starting from, adjusting as your symptoms and function respond, rather than applying a fixed protocol regardless of how you're progressing.
References
- Rathleff MS, Mølgaard CM, Fredberg U, et al. High-load strength training improves outcome in patients with plantar fasciitis: a randomized controlled trial with 12-month follow-up. Scand J Med Sci Sports. 2015;25(3):e292–300. doi:10.1111/sms.12313.
- Koc TA Jr, Bise CG, Neville C, Carreira D, Martin RL, McDonough CM. Heel Pain – Plantar Fasciitis: Revision 2023. J Orthop Sports Phys Ther. 2023;53(12):CPG1–CPG39. doi:10.2519/jospt.2023.0303.
- Guimarães JDS, et al. Effects of therapeutic interventions on pain due to plantar fasciitis: a systematic review and meta-analysis. Clin Rehabil. 2023;37(6):727–746. doi:10.1177/02692155221143865.