I feel when you push yourself too hard it will make you look less forward to your next workout. Best to end on a good/interesting note similar to how TV episodes do - making you want to come back for more.
The Google Distance API does not require an API key, but this is something that should be supported for business licenses and per-key quota limit tracking.
Here are the quota limits:
Users of the free API:
100 elements per query.
100 elements per 10 seconds.
2 500 elements per 24 hour period.
Maps for Business customers:
625 elements per query.
1 000 elements per 10 seconds.
100 000 elements per 24 hour period.
It actually might be a good idea to fetch the value fields as well, since that would make conversion to other metrics easier. Thanks for the suggestion.