But which activities are a great addition to your training? And how intense should your cross-training activities be?
Cross-Train Tip No.2: Go Hard...But Not Too Hard
"Choose workouts that are closest to running in terms of muscles used and aerobic systems taxed. Good options include elliptical trainers, cross-country ski machines, stationary bikes, and water running.
When cross-training, keep your heart rate at or above 70 percent of your maximum heart rate (220 minus your age) most of the time. In other words, you should be working hard and sweating a lot.
"Check your morning heart rate regularly. An elevated morning heart rate is a sign of overtraining, which can occur if you add too much cross-training too soon."