Yoga and flexibility is one of my staple activities for every athlete I coach, in season I like them to do a more mellow relaxing version such as Yin or Restorative Yoga (favorite resources I suggest are books and videos by Sage Rountree and Kelly Starrett), but in the off season I encourage them to try the more challenging classes like Bikram, Power or Vinyasa Flow and have some fun with it! Endurance athletes typically have terribly tight hips and hamstrings to start with, and our balance can be a mess!
I like to see a flexibility practice focus on hips and the posterior chain first, then add some torso flexibility with movements we might not normally perform on a bicycle all year. This in a lot of ways is key to all off-season work – do things that are different than your primary sport that will benefit it when you return. Many endurance athletes have a hard time slowing down and struggle with breathing quietly at the end of a session or practice, but they should realize the benefits of the breathing and relaxation practice that not only affect us at rest, but learning to breath truly deeply and calmly even when going hard can have huge rewards.
Time In The Gym
It's very important to first consider what the goal should be with a strength program, is it building pure strength for track sprinters, building core stability for endurance athletes, perhaps rehab of existing injuries or imbalances? Often we find a combination of several approaches is best for that rider.
A well-designed program should be safe, not create injuries, reach achievable goals, and set the athlete up well for the abuse of the upcoming season.
Especially if an athlete is new to strength training, a sports focused personal trainer can work wonders, really speed up the learning curve, and teach proper form. Find a really good trainer and book an introductory session, see what you think , and go from there.