This is a great read about endurance activity and increased heart metabolism.
One of the key points is that the research was done with heart rates at 65-75% of capacity. Since maintenance pace keeps you in the 65-80% MHR range this study is highly applicable to running. The fact that these stimuli seem to return the heart to a metabolic state of youth could be paramount in heart disease prevention and overall cardiac throughput.
In theory our threshold/10K/VO2 work could stimulate an even greater cardiac metabolism since we operate closer to 85-95% of MHR.
If you’re in anywhere between 30-90 years old, this is a great read.