Observations related to physical activities can involve specific body sites that may not be precoordinated in Observation.code. 

For example, time to balance on one foot (a predictor of longevity*) may depend on laterality (right foot might be considerably stronger than left foot). 

Strength observations might focus on a particular muscle group. 

Flexibility observations might focus on a particular joint (e.g., measuring how far a person's left index finger can flex or straighten). 

Therefore, bodySite should not be 0..0.

*https://www.health.com/news/10-second-balance-test-longevity