variable resistance
training

Variable Resistance Training (VRT) or Dynamic Variable Resistance Exercise is a form of strength training that applies dynamic forces to target muscles. Variable resistance mimics the natural strength curve of the body during movement. VRT forces the muscles to work harder when they are at their strongest to meet the demands of the exercise.

Gradually increasing external resistance can cause instability during training, which optimizes muscle strength growth stimuli and increases neuromuscular control demands. This leads to greater motor unit recruitment and rate coding, likely improving coordination between agonistic and antagonistic muscles. Variable resistance training (VRT) heightens load variability and instability, enhancing neural adaptations, motor unit recruitment, and muscle coordination. These improvements boost muscle strength performance, including 1RM and RFD, while also enhancing fatigue resistance in some trainees.

A sticking point in resistance training is a speed loss during movement, typically occurring between 35% and 45% of the range of motion. This region is the least efficient, especially when loads reach 80%-90% of 1RM, as muscles struggle to meet demands. Recent research shows that VRT can increase RFD and muscle strength more effectively than traditional training by enhancing neural impulses and muscle activation, leading to greater force generation during the final part of the concentric phase.

In traditional resistance training, muscle force varies with joint mechanics. To address this, variable resistance equipment adjusts resistance in real-time based on joint angles, maximizing muscle output and improving power training by compensating for mechanical disadvantages and acceleration changes.