Load management

Tissue adapts to the loads it is progressively exposed to; harm follows spikes in load relative to preparedness, not load itself. Cartilage shows the same inverted-U as other tissues — moderate doses build, extremes (including rest) degrade — and biomarkers of cartilage breakdown do not rise with structured exercise. Pain during sensible loading does not equal damage. The question is how to dose it, and the best-tested answer is a monitoring system rather than a fixed program.

The pain-monitoring trial

In a randomized trial of 38 people with Achilles tendinopathy, one group was allowed to keep training with pain up to 5/10 — provided it settled by the next morning and wasn't worsening week to week — while the other rested for six weeks first. The continue-training group recovered just as fully (VISA-A 57→85 vs 57→91, no significant differences), with no harm. This is the origin of the "acceptable pain, 24-hour rule" used throughout this section.

The rules, as used on this site

1. Traffic-light pain scale. 0–2/10 is safe, 3–5/10 is acceptable, above 5/10 is too much.
2. The 24-hour rule. Pain and swelling should return to baseline by the next morning. If they haven't, the dose was too high — reduce, don't stop.
3. Progress one variable at a time — load, volume, or frequency — and avoid spikes relative to your recent weeks of training.
4. Total rest is itself a harmful dose. Complete unloading thins cartilage measurably within weeks to months.

The supporting dose data agree with the structure: supervised, regular (three or more sessions weekly), focused programs outperform sporadic mixed ones in knee OA trials, and in an OA cohort each additional 1,000 daily steps predicted a 16–18% lower risk of functional decline.

What this extrapolation cannot claim

The pain-monitoring RCT is a tendon study. No trial validates the 5/10-and-settles thresholds for cartilage lesions or OA — applying them there is principled extrapolation, which is exactly why this entry is promising rather than strong. The acute:chronic workload ratio popularized in sports science has been criticized on statistical grounds; treat "avoid spikes" as a heuristic, not a metric to compute. And effusion and irritability after cartilage repair may not follow tendon-style pain rules — post-operative protocols override these generic rules entirely (see the post-op rehab entry).

Safety and red flags

Monitored loading produced no worse outcomes than rest in the RCT, exercise shows no cartilage-damage signal on imaging across 9 RCTs, and degradation biomarkers mostly fall or stay flat across 12 RCTs. But some signals override the model rather than feed into it: increasing swelling, night pain, or mechanical locking warrant clinical evaluation, not another week of titration. That escalation advice is standard clinical practice, not trial-derived.

Open questions

An RCT of pain-monitoring rules in knee OA or post-cartilage-repair populations is the obvious gap — along with whether morning-after effusion, rather than pain, is the better dial for cartilage patients.