Data models for a tracking app

Hey guys and gals,

I’m flirting with the idea of building a self tracking app and have a question for you.
I read the Notes to Developers and I do get the wish for fully customizable datafields.
That (for me at least) comes with a few distinct technical challenges in implementation, so I’d like to start out with the plain old predefined data models.

I’d like your help in coming up with some.
Following is an idea of what models could look like, and I’d love some input from you to see what you would like.

If you can, please include info on the relationships of the data:
One workout has many exercises, one exercise has many sets, etc.

Here are some models I have come up with so far:

A Workout has:
start_time
end_time
location
duration
notes (TextField)
heavyness
starting_heartfrequency
ending_heartfrequency
starting_bloodpressure
ending_bloodpressure
many exercises
many workout_types (cardio, strength, etc.)

One Exercise has:
many sets
target_setcount
setcount
name
trained muscles

One Set has:
number_of_repetitions
target_repetitions
weight
cadence_in (breathing: five seconds or 2 seconds)
cadence_out (breathing, see above)
form_rating
heavyness_rating

One of the challenges I’m facing is exemplified by Set and Weight: What if I’m measuring running or rowing? Should I make weight_sets, rowing_sets etc. or is there an elegant way of combining these in fewer models?

If anyone is interested in working with me here please reply, you can also PM me or reach me through email or Twitter.