I don't think causation is impossible to prove, I just think its risky. We don't need to prove that exercise causes harm to a scientific/medical standard. The civil standard of proof is the balance of probabilities - we just need to prove its more likely than not that exercise causes harm. I think we can prove that. I think you just need a strong lawyer and the ability to pay them.
There's a mountain of evidence on our side. We can look at Appelman et al who found that exercise causes muscle damage in LC. We can argue PACE showed harm, but the authors misinterpreted the data. We can use the survey evidence. We can use testimony from ME/CFS patients who got worse. We can get the leading ME/CFS experts to testify. We can point to the IOM report as the consensus of expert opinion.
What's the argument on their side? The Cochrane review looked at a number of RCTs involving GET and none of them reported any cases of permanent deterioration. This argument can be undercut by the fact the only one of these RCTs that formally reported safety data was the PACE trials. I think one or two others anecdotally mentioned there was no deterioriation but it wasn't formally measured. The other evidence they have is expert evidence. But is there any expert who believes ME/CFS is biological who doesn't believe exercise causes harm? The only one I can think of is Andrew Lloyd. He runs a GET clinic so one could undercut his credibility by pointing out his conflict of interest. I would dearly love for a highly paid KC to put Lloyd on the stand so he can shred his credibility to bits.
The standard of care is a more difficult barrier, but I think it can still be overcome, particularly in Australia where the legal test is slightly different.
Most of us can't afford a good lawyer (heck, given the cost most working lawyers can't afford a good lawyer), but one scenario where I can see this getting up is through insurance. If you successfully claim on your insurance, the doctrine of subrogation means the insurer can sue on your behalf against your doctor.
just to check is there a risk of you getting landed with the legal fees for the other side in the worst case scenario, even if your own legal is on no-win no-fee (for you)?
Yes, this is a risk. The no win no fee agreement only covers costs incurred by your lawyers (billable hours, consulting doctors etc). It does not cover costs in the event you lose.