The quarterback has set a new record for most touchdown passes in the first four games of the season.
The 37-year-old told the team's website: "I really think that the schedule, the way it's set up playing some of these what I call 'unfamiliar opponents' has helped.
"You're practising against some 'what ifs'. So preparation weeks are long, they've been kind of grinders if you will. So it keeps you on your toes and it keeps you from thinking about what happened the week before.
"It is early in the season. We do break the season into quarters, it's been a good start. But we're heading into the teeth of our schedule with some of these new teams. We battle injuries every single week and that presents challenges. So this is the second quarter and it's really a new start."
The Broncos face the Dallas Cowboys this weekend.