Martial arts expert's pounds 11k in benefits.
Adrian Blayney, 48, a black belt in Choi Kwang Do, was observed running courses at Michael Sobell leisure centre in Aberdare despite claiming he was so chronically ill even walking was painful.
Neath Magistrates' Court heard he was claiming mobility allowance at the highest level when the Department for Work & Pensions (DWP) got a tip-off that he was running the martial arts business.
A fraud investigator discovered that Blayney, of Cimla, Neath, was running two two-hour martial arts classes a week at the centre.
Blayney was observed walking around the centre helping to run the classes during two surveillance operations at the end of 2006.
David Williams, a DWP investigator, yesterday told the court on one occasion he saw Blayney running a course for children and "always on his feet".
On another, largely run for adults, he sawhim "lifting his armand turning his body".
Both periods of observation were for 15 minutes. Mr Williams said that it was decided not to film any of the courses for evidence because of the number of children attending.
But Blayney was later interviewed and accused of failing to notify the authorities of a positive change in his condition. The court heard he acknowledged at the time his condition had improved.
But in a day-long trial he denied that his condition had changed for the better and he had legitimately continued to claim benefits.
Giving evidence, Blayney told the court that he injured his back while working at a food processing plant in Swansea in 2002. A year later his condition worsened after he suffered a heart attack.
He told the court he was constantly taking painkillers. He insisted his role in the martial arts business was one of guidance and he took only a small physical role.
But magistrates found him guilty of the single charge. They said it had been proved that his condition had improved but he had continued to claim benefit having failed to inform the authorities of a change in his condition.
This resulted in Blayney falsely claiming money between April 2003 and December 2006.
He was sentenced to a 15-month community order, told to pay pounds 250 costs and will have to pay back the full amount falsely claimed.