http://hybridfitnesssystems.com “How to Tone Your Stomach” With This Core Superset Finisher In this video, Hunter Grindle of Hybrid Fitness Systems teaches you “How to Tone Your Stomach” With This Core Superset Finisher. This superset consists of two different exercises: 1. Upper Ab Crunch 2. Back Extension Perform 3 sets of 10-15 reps of each exercise…