The number of people claiming the main long-term sickness benefit in many ex-coal mining areas has fallen by a fifth in seven years, figures obtained by BBC Wales have shown.
The areas in the south Wales valleys have historically had some of the highest levels of claimants in the UK.
The reduction across Wales was 15%.
The seven-year period marks Incapacity Benefit's phasing out, its replacement by the Employment Support Allowance (ESA) and a testing system.
But the UK government announced this week the testing system, Work Capability Assessments, is going to be overhauled.
Across the UK, there was a 4% reduction in the number of people claiming ESA in the period soon after it was introduced in November 2008 and the latest Office for National Statistics figures available in February 2016.
But in Wales, the corresponding figure was 15%, while in Rhondda Cynon Taff, Merthyr Tydfil and Blaenau Gwent there was a 20% drop.
The Department for Work and Pensions (DWP) said since the Work Capability Assessments were introduced in Wales, more than a fifth of all of those people who have gone through them have been judged to be fit for work.
Some 37% were put into the work related activity group which means they are capable of making some effort to find employment, while 43% were put into the support group, which means they are considered unable to work.
Current Work and Pensions Secretary Damian Green said he has begun the consultation into the Work Capability Assessment because he wants a personalised way to help more people find jobs.
Both the ESA and the assessments were originally introduced by Labour and then expanded by the UK coalition government in power between 2010 and 2015.
The former Labour Work and Pensions Secretary Lord Peter Hain, who introduced a system of incapacity benefit tests nearly a decade ago, welcomed the plans to overhaul the current assessments, describing them as "draconian".
"The main thing I introduced is that you were tested for what you could do, rather than what you could not do," he said.
"It is now being used in an oppressive way. People who previously were unable to work are now passing the test. My changes were never designed to do that."
The DWP says the system the government inherited in 2010 was not working, and good progress has been made to encourage those who can work, while ensuring a safety net for those who cannot.
Mr Green said: "We must be bold in our ambition to help disabled people and those with health conditions.
"This Green Paper marks the start of our action to confront the attitudes, prejudices and misunderstandings that, after many years, have become ingrained within the welfare state, within the minds of employers and across wider society."