I don't have an article but 60 minutes is a guideline. Optimal is probably closer to 45 minutes but may be up to 90 if properly hydrated and nutrients are consumed during the workout. (warmups are not counted in this) The big benefit of the shorter workout is the ability to work more intensly. A short intense workout will almost always provide more benifits than a long easy workout. This applies to both cardio and strength training.
Hormonal changes take place as the workout progresses. T levels drop and cortisol increases at about the 45 min mark. At this point the value of the workout deminishes and eventiually can negate the benifit of the workout.
Here's a fairly definitive discussion:
The general recomendation is 45-75 minutes and if you need to workout more, split into 2 workout.