Alternating chest flies target your chest muscles, but really challenge your core. Since your center of gravity is shifting, you have to stay tight through your center to ensure you arms are the only thing moving. You can put one foot forward to make it easier, but feet together is an awesome challenge!
Related workouts
2 Minute Plank Series
Simple Upper Body
Intermediate Upper Body
Upper Body BONUS
Reformer Standing Upper Body!
1 Minute Legs
Chest Press, Rows & Russian Twists Triplet
Hold it. Pulse it.
Day 11 Upper Body with Alise!