Personally, I'm not very surprised by this (testosterone causing larger increases than exercise). There are plenty of examples in nature of relatively "lazy" animals with large amounts of muscle (e.g. gorillas, lions, etc).
Of course, we're comparing animals with large genetic differences to each other, but my point is that exercise does not seem to be the primary cause of muscle, in general. It just happens to be the main parameter we're in control of.
Of course, we're comparing animals with large genetic differences to each other, but my point is that exercise does not seem to be the primary cause of muscle, in general. It just happens to be the main parameter we're in control of.