EMG and atrophy and weakness

  I've had recurrent muscle twitches, cramps, mild atrophy and weakness for 3 months but my latest EMG was completely normal.  The symptoms are very persistent and I can even feel atrophy in my calves which was never picked up by the EMG.  I also experience weakness in my fingers and wrists and left arm which the EMG didn't either pick up.  How accurate are EMG's in picking up on atrophy and weakness?  I wanted to add that I have recently been working out a lot (to compensate for the atrophy in my calves and right arm bicep and tricep muscle) and was wondering if the newly acquired muscle mass could be skewing the results.
  Thanks,
  Michelle
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Dear Michelle:
An EMG is an extremely sensitive test for detecting and diagnosing atrophy and weakness from nerve problems (including pinched nerves, pinched nerve roots, peripheral neuropathy, or disorders of motor neurons such as ALS). A negative EMG rules out these possibilities with fair certainty. An EMG is acceptably sensitive for diagnosing muscle diseases as a cause of atrophy/weakness, but may miss such disorders in some cases. A routine EMG is not a very sensitive test for diagnosing disorders of the neuromuscular junction (such as myasthenia gravis). The EMG is a poor test for diagnosing atrophy with/without mild weakness from disuse, or for figuring out the cause of congenitally small muscle for any reason. Exercising does not affect the results of the test.
I hope this answers your question.