"Spring of ribs" describes a dog with nice, full spring of the bone part of the ribs. Good "spring", however does not mean a "barrel chest". A "barrel chest" does not taper near the bottom, allowing the dog's elbow to be placed (correctly) close to the body.
Here a weight pulling dog shows how more power is generated from an arm straight under the dog then one pushed out to the side; a more effective fulcrum. Dogs "out at the elbow" because of faulty shoulders or chest wall would be stronger if they did not have those faults.