Clause:Adiposity and low aerobic fitness in children are associated with a clustering of cardiovascular risk factors.
Analysis:Adiposity and low aerobic fitness in children: Token
are associated with: Process: relational: intensive
a clustering of cardiovascular risk factors: Value
Reasoning:Viewed from 'round about', this clause is the receptive agnate of the clause:
People associate adiposity and low aerobic fitness in children with a clustering of cardiovascular risk factors
where people functions as Assigner/Agent.
If ASSIGNMENT is only an option for relational clauses of the intensive kind (Halliday & Matthiessen 2004: 237), then the process is intensive, not circumstantial.
Viewed 'from above', association is a type of extension in figures of being-&-having (Halliday & Matthiessen 1999: 145-6), so this is an instance of extension (meaning) being realised as elaboration (wording). (The meaning of extension is here lexicalised rather than grammaticalised.)