While a dynamic simulation will be more automatic, it doesn't give you the same degree of control as an influence object, an animated lattice, or a blend shape. This is actually one area where SDKs really comes in handy. You have explicit control over how a muscle should deform. With a dynamic simulation, you sort of get what the system gives you. Steve Stahlberg over at cgtalk.com has an interesting tutorial on how to use blend shapes to simulate muscle deformations. Seems to work really well.