After watching the video, here are a couple of things to try when you are out riding:

 

First, use the Pilates powerhouse checklist: shoulders down, belly in, squeeze your butt... concentrate on actively engaging your powerhouse before you take off and on keeping your powerhouse engaged while sprinting. 

 

Now contrast this. Don't use your powerhouse and see how it feels to try to generate power quickly. Be aware of how much extra effort it takes to sprint without your powerhouse.

 

Then once again use your powerhouse to accelerate. Be aware of your increased ability to accelerate faster and maintain the speed with less effort.

 

Let the sprints begin!