(2/2) Does Cultivation Never End?!?

Without any suspense, they easily broke through to the Tendon Refining Realm. This was done by consolidating all the improvements made to their muscles at once, finalizing the cultivation of it. 

Picture it like this, it was like a clown at a festival wrapping up balloons together. Level 1-10 of the cultivation realm is like taking a new balloon and weaving it around the other. 

Breaking through is like when the clown pulls two ends, and the things suddenly tighten and become its final shape, a nice little horsie. 

You could also use string to picture it, like tying a knot. 

They were technically still in the 10th level of the Muscle Tempering Realm. Cultivation was not automatic, but a manual process. Until they actually put Qi into their tendons using the method they had, they had not begun 'Tendon Refining'.