To exercise different muscles, position the bass drum a bit further away. The leg is not forming the 90-degree angle in the knee, but a larger one.
The muscles involved:
- To develop calf muscles, play heel-down single-stroke double bass; 5 minutes at 80 bpm, 16th notes. Speed up over time. Develop control and muscles.
- To develop hip muscles, use anchor-weights of 1-2kg.
- Flat-foot Technique, for hip flexor muscles (link). Start doing 16th notes at 80bpm and work upwards at 5bpm increments.