Mechanical stress refers to the force or pressure that is applied to an object, causing it to deform or change shape. It could be due to pulling, pushing, or stretching an object beyond its capacity or limit. Full definition
Working out without weights makes implementing progressive overload (increasing mechanical stress on muscles) a bit more of a creative task. (neatstrength.com)
You need to put your body under enough mechanical stress in order to elicit the right response and give it a reason to become bigger and stronger. (fitnessandpower.com)