"Regular lunges" refers to a specific exercise where you step forward or backward, bending your knees to work out your leg muscles and improve strength and stability. Full definition
The only reason for this is because it is a cue for regular lunges and squats to help you keep a straight back. (neatstrength.com)
If mobility issues make these ones tough, do regular lunge hops with your torso upright instead of getting so low through the upper body. (pumpsandiron.com)
Elevated Front Foot - Placing the front foot on a step or small platform may be another modification to try if regular lunges make your knees ache. (verywellfit.com)