If you are interested in more about the "short bursts of activity" thing, The Daily Hiit is a whole community based around free workouts in a bit of an open source type format, like Crossfit but was more accessible and definitely without the astronomical box fees.
Another thing to look into are programs like Insanity, P90X, etc..
And there's always the tried and true personal trainer.
I've noticed the biggest difference in my body when I ditched trying to get into LD running and started lifting and training in a style more towards the Olympic lifts. And bonus, my training sessions got a lot shorter, with a lot more impact. That being said, you do also need to balance any heavy lifting with a lot of stretching and muscle care. I also do hot yoga (which is amazing just by itself) and acupuncture/massage therapy to help my muscles stay healthy and build correctly.
Fitness is so important for athletes. We are starting to realize this with our horses and moving towards having them out in fields and getting them in the horsewalker and out for hacks, along with riding. But the riders also need to get on the fitness train. I like Adelinde Cornelissen's approach "Train Hard or Die"!!
They say money doesn't buy happiness -- well happiness doesn't buy horses!