Lifting a free weight (a barbell or a dumbbell) possesses an inherent limitation: As you lift the weight, your muscles are stronger at specific positions and weaker at specific positions throughout the range of motion. Your strength changes, but the free weight always weighs the same amount. A free weight provides “constant resistance.”

In 1971, Arthur Jones attempted to overcome this limitation by inventing Nautilus exercise machines. Nautilus machines contained cams (odd-shaped pulleys) that varied the amount of resistance your muscles were exposed to as you lifted a weight. The intent was to have the amount of resistance the machine was providing to match the strength of your muscle at any given position in the range of motion. A Nautilus machine represented a breakthrough in “variable resistance.”

Authors of a brand-new research study published in the International Journal of Environmental Research and Public Health conducted a systematic review and meta-analysis (a statistical tool that pools together all of the research on a particular topic to synthesize what we really know about that topic) and sought to understand, what works better for increasing strength, Constant Resistance or Variable Resistance strength training?

The results? The authors concluded, “Our findings suggest that Variable Resistance Training is better than Constant Resistance Training in improving maximum muscle strength.” The authors also stated that both trained subjects (people experienced with strength training) and untrained subjects (people new to strength training) had greater strength improvements with Variable Resistance.

This study surprised even me. It’s no secret that Discover Strength has a leaning toward sophisticated strength training machines. However, our official stance has always been, “It’s not the tool, it’s how the tool is used that is of the utmost importance” conceding that free-weights are just as effective as fancy machines. This new study provides powerful evidence that if improving strength is your goal, Variable Resistance is likely superior to Constant Resistance.