Super popular Bulgarian Bag is the best strength training for middle muscles. This design is so called straight design which can also be used as a bicep weight for its even load.
Fits for middle muscles better than kettlebell because the weights center of gravity is detached on to the body. Filling is made of heavy but soft sand which doesn’t hurt when you throw the bag on your neck. On either on of the bag there are cordu handles.
Weights: 5 kg – 20 kg