"It just came to a point where I would come back from an injury and have a couple of weeks where everything was fine, then things would go downhill again," the 31-year-old, who will quit Tests after the ongoing Ashes, told The News of the World.
"I've done something like two years rehabilitation out of the last four and for my body, for my family's sake I have decided to call time on the Tests and concentrate on the shorter form of cricket," he said.
Flintoff said fast bowling had put extreme stress on his body, something he found very hard to deal with.
"You're whacking your foot down with something like 10 times your bodyweight going through it, you put your body in positions that are unnatural and, frankly, nobody's body is designed to do that hour after hour," he said.
"I weigh 16st 7lb and I've bowled with injuries most of my career -- most fast bowlers do. At Lord's I was in discomfort for most of the game although it never got to the point where I was thinking 'This will be my last Test'," he added.
Flintoff said much before he took to international cricket he was broken down by injuries in his teenage days.
"Everything my body has been through over the years was bound to take a toll. Even playing in my teenage years, I experienced injury from time to time, so you could say I am used to it," he said.
"Most people think my injuries have only come to light over the last five years but there was a spell as a teenager when I struggled for five or six years because my back was so bad," he added.
"The fact is, fast bowling can produce injuries and injury and pain have gone hand-in-hand with me throughout my cricketing life."
Flintoff refused to blame his Test retirement on the increasing amount of cricket.
"I'm not going to sit here and say we play too much cricket.
"That's an argument that has gone on for a long time. But gone are the days when fast bowlers play on to their late 30s. People have asked me about my long-term well-being with all the cortisone injections I've had," he said.
The all-rounder said he is hopeful of playing the entire Ashes series.
"I'm only focusing on what happens next week at Edgbaston. I'm hopeful I can get through the next three Tests. There are no guarantees I can play through 15 days of cricket in such a short space of time but I will do everything physically possible," he said.
Photograph: Reuters