The phrase "stability challenge" refers to a situation or problem that tests how steady or secure something is. It means facing difficulties that can affect the normal functioning or balance of a person, system, or situation. Full definition
They provide constant tension like most machines, but they offer an increased stability challenge when compared to machines. (all-about-arm-exercises.com)
In this progression there is even more stability challenge in the form of a load, albeit with a fairly short lever. (rugbystrengthcoach.com)
The goal is the same as before but now there is a greater stability challenge due to the absence of the box. (rugbystrengthcoach.com)