Sinfield ran the final of his seven marathons in seven days on Monday as the fund-raising hit an astonishing seven-figure sum.
On Saturday, the Leeds Rhinos legend completed his fifth marathon inside three hours and 43 minutes and was greeted at the finish by Burrow and his family.
The former Rhinos half-back was diagnosed with MND 12 months ago and Sinfield decided to run seven marathons in as many days in aid of his close friend and the MND Association.
An initial £77,777 target had been set but the support for the fundraising efforts have left Sinfield "blown away".
Sinfield had to take a minute to compose himself when greeted by Burrow at the weekend, after another emotional day for the Rhinos director of rugby.
"When I ran into Headingley and I saw him, I didn't stop straight away because I would have been a mess," said Sinfield on Saturday.
"I had a minute to gather myself but for him to be here was really, really special."
He continued: "I am completely blown away by the whole thing, I just want to thank everybody.
"When I was told en route we had reached half a million, I didn't really respond because I thought I was going to burst into tears again.
"I don't know if it is because I am tired or not sleeping well, or whatever it is, it is quite emotional out there at the minute.
"To hear we have hit half a million, is unbelievable. I am so grateful and thankful."
Sinfield was happy to complete another marathon in under four hours, considering he was running on an unknown route.
He has two more marathons to undertake and he is determined to fight through the fatigue.
"I am really happy with that again. It was a new course today, I didn't really know what to expect and there was a couple of big hills thrown in there," he said.
"The weather has been great and the support has been fantastic again.
"I am really pleased. I am in the unknown anyway but I was a little bit apprehensive to run a course I had never done before.
"I am delighted, to do five in a row is great and I know the route for tomorrow, so I will get the body back together and get ready to run.
"I am feeling it now but I knew that would be the case at some stage. I have just got to fight and get through it."
Sinfield was joined on parts of his run by Jamie Peacock and Rhinos captain Luke Gale.
He added: "JP [Peacock] today was brill and then Galey later on. One famous number seven to another, that was really nice.
"The team again has been fantastic and I am looking forward to getting tomorrow done."
To make a donation, visit: https://justgiving.com/crowdfunding/sinfield-7-in-7