Friday was the deadline for the seven-time Tour de France winner to respond to USADA's June 12 warning of pending charges.
The agency says Armstrong used performance-enhancing drugs and other improper methods to win cycling's premiere event from 1999-2005. Armstrong denies doping, noting that he never failed a drug test. He could be stripped of his titles if found guilty.
Armstrong's lawyers called the USADA claims "long on stale allegations disproved long ago and short on evidence." They believe USADA coerced false testimony from some of his former teammates.
The case now goes to a USADA review board.