Complex sentence: German Volume Training is very intense and should not be done consistently for more than 12 weeks because training the body in such a way for longer than this may cause muscle to lose strength and inhibit performance.
Split into simpler sentences: German Volume Training is very intense and shouldn't be done consistently for more than 12 weeks. This is because training the body in such a way for more than 12 weeks may cause muscle to lose strength and inhibit performance.