How do you make your decisions in life? You use your conscious mind to weigh up the evidence, then perhaps your gut instinct too. So why do you need to muscle test?
Why do you suddently give up your God-given faculties of reason?
If I gave you something and asked you to muscle test, then told you it was poison, would you take it? Of course you wouldn't. Your conscious mind would over-ride your muscle testing.
Of course I do believe that the body has great inherent wisdom, but we should learn to access that through our minds (conscious and subconscious) rather than relying on muscle testing.