The 23-year-old Brit was among the medal contenders but she made a poor start and never recovered – eventually finishing in a time of 39.247 seconds.
But Reade believes the small amount of time between the semi-finals and the final contributed to what she felt was a more than below-par performance.
“At the moment, I'm pretty emotionless,” said Reade, who failed to finish in Beijing in 2008.
“I do not have any emotion in me yet, but I am sure it will sink in. The Games is the biggest platform you can race at and you've just got to give it your best.
“The race schedule has been pretty hard – with the back-to-back laps.
“It's been hard to recover, but I just tried to stay focused and do my absolute best, but today it just wasn't good enough.”
Reade applauded race winner Mariana Pajon of Colombia, despite her disappointment, and she also paid tribute to the passionate home crowd who packed into the BMX Track, next to the velodrome.
She said: “She's obviously a fantastic athlete.
“I felt like I was fast enough and I had done all the work that I needed to. Unfortunately, I just didn't have the start I wanted or needed to win the race. That was it.
“I can't thank all these people enough for supporting me and I don't really know what to say. I just didn't get the start I needed to win the race and that was it."