I found the following instruction from the web, Is this what LZ is talking about? It is a pretty challenging workout.

Starting With The Basics - The Elbow Bridge Plank

• Your Position
  
  
  
  
  1. Start by lying face down on the ground or use an exercise mat. Place your elbows and forearms underneath your chest.
     
  2. Prop yourself up to form a bridge using your toes and forearms
     
  3. Maintain a flat back and do not allow your hips to sag towards the ground.
  
  
  
  
• Target Muscles
  
  
  
  
  1. The Core - Abdominals, Hips, Back
  
  

  
  

• Step By Step Instructions
  
  
  
  
  1. Hold this position *focusing on tightening your abs* until you can no longer maintain a flat bridge. For beginners, start with 10 seconds
     
  2. Return to start position.