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Can Injections Destroy Muscle & Muscle Gains?

Since 1994 I have been weightlifting and making successful muscle gains. But this trend has been cut short since 2013 when I was prescribed vitamin B12 injections. The doc instructed that I inject the needle an inch deep directly into my thighs every day for a month or so.

But after this time I noticed my leg muscles wouldn’t grow. Years ago before this squats produced my strong muscular legs. Now its been degraded. Is there a connection between injections making deep contact in my muscle and muscle degradation?