Cross-training activities to incorporate into existing work-out schedule.

Since joining Bulletproof Cycling Club, I eliminated my running activities to focus on cycling, and to avoid over-training risks. I may be too cautious, but i would like to know how to safely and effectively incorporate running activities into my cycling schedule. When I run and cycle, the two activities seem to complement each other - running worked on a certain set of muscles, and cycling seemed to work a different set, and tended to stretch muscles that running tightened.