He added: "It will take me a couple of days to get right."
The former Leeds Rhino player defied a serious muscle injury picked up in November to complete his 'Running Home for Christmas' challenge.
Sinfield admitted he suffered a "tear in the back of my calf".
The 44-year-old said: "It put the whole thing in jeopardy, but now I have a lot of back pain and hip stuff.
"But there is a difference between being injured and being in pain. It was really demanding and really tough.
"Some days we were on our feet for nine hours. But we got through it. It was great to finish back home."
The Oldham-born star met members of the MND community as he did his marathons.
He said: "There was a lot of emotion from the stories you hear from the time you spend with people.
"It did mean that it was more emotional and some ways energised us from some of the stories you hear.
"It drives you forward and Rob was never far from my thoughts."