While QB Peyton Manning has been medically-cleared to resume his footballl career, there are still questions about his ability to return to his previous level of performance.  The issue is with the nerve regeneration to his triceps.  Manning's neck has stabilized, but without a full recovery of those nerves, his arm strength and accuracy would be impacted.  "It's not a safety issue; it's a performance issue," a source told ESPN's Chris Mortensen.  Manning has intensified his workouts and had a throwing session with WRs Anthony Gonzalez and Blair White on Tuesday.  He's certainly making progress, but Peyton isn't out of the woods just yet.