Personal trainer James Blatch publicly boasted about his ability to improve the appearance of his clients but he didn't advertise one of his alleged methods - supplying them with steroids.

The body builder and personal trainer is in custody after police charged him with allegedly supplying steroids at Anytime Fitness, Kings Cross where he based his company, The Muscle Makers.

Charged with supplying steroids: Kings Cross personal trainer James Blatch.

The 26-year-old from Sutherland was caught by a lengthy undercover police operation which found him allegedly selling illegal steroids at the gym.

He appeared at Parramatta Bail Court on Saturday facing multiple changes of possessing and supplying illegal drugs.