Variable Resistance Training - The Path to New Muscle Growth

The use of variable resistance while weight training normally includes the use of elastic bands or chains. Attachment of elastic bands, or chains, to the barbell alters the resistance of the movement through the entire range of motion, while standard free weights provide a constant resistance throughout the entire lift. The primary advantage of variable resistance comes from the unique capacity of this training method to alter the resistance on the bar throughout the entire range of motion, effectively lowering the resistance during the lifter’s weakest range of the lift (sticking point) while increasing resistance within the stronger segments of the lift, where the lifter is naturally stronger. For instance, typically, the initial phase and lockout phase are stages of the bench press with a greater inclination for muscular force production than the middle portion of the lift, which is typically where the sticking point occurs. The impact of variable resistance techniques that successfully match resistance on the bar to maximal strength output of the lifter throughout the entire movement produces a greater overall load on the lifter, resulting in greater muscular activity and function, which ultimately promotes greater strength gains.^1,2 Furthermore, reducing the impact of the sticking point tends to increase the velocity of the bar throughout the entire range of motion, which activates the more powerful fast-twitch muscle fibers, further enhancing strength development.

Variable Resistance From Elastic Bands Activates More Muscle

 Elastic bands provide greater resistance through the entire movement as the band is stretched throughout the movement, causing increased tension within the band that generates greater resistance. This form of variable resistance from elastic bands provides benefits in certain weightlifting movements such as the bench press. Since greater muscular force occurs in the initial phase of the bench press, greater momentum is generated throughout the rest of the movement when using free weights, because free weights provide a constant resistance. Once the weight has built up momentum in the initial phase, less muscle activity is required to continue moving the weight throughout the rest of the movement, thus diminishing the training effect. However, the increase in resistance generated from elastic bands negates the production of momentum, disallowing the momentum-driven propulsion of the bar through the rest of the movement, creating a demand for greater muscle activity that ultimately stimulates greater size and strength. This effect was clearly demonstrated in a study by Jalal et al.³, which showed a 15 percent increase in muscle activity during elastic resistance training when compared to free-weight training. Moreover, the comparison between elastic training and free-weight training in this study also showed a considerably higher level of muscle activation in the later phases of the movement, supporting the concept that the increased resistance from elastic bands as they are stretched required the continual development of muscular force throughout the entire concentric portion of the movement.

Elastic Bands Generate Greater Muscle Tension, Boosting Muscle Growth

Elastic resistance naturally produces a greater amount of tension on the muscle compared to free weights, because, as previously stated, it has the capacity to minimize momentum— increasing muscle activity throughout the entire movement, which effectively increases the amount of time the muscle is under tension. In addition, elastic bands also produce resistance independent of gravity, which fails to produce tension on the muscle during specific phases of certain lifts. For example, free-weight biceps curls produce very little muscle tension at the top of the concentric phase, due to the prominent horizontal movement of the weight that no longer creates gravitational resistance. On the other hand, the precisely positioned use of elastic bands that causes the elastic material to be stretched throughout the movement places resistance on the biceps throughout the entire range of motion. The continuous tension from elastic resistance training should stimulate greater muscle growth, as it has been well documented⁴ that greater time under tension potently increases mechanical tension on the muscle cell, producing more muscle cell damage and/or increased metabolic stress, which powerfully enhances muscular size. Clearly demonstrating the ability of elastic bands to build muscle, a study by Colado et al.⁵ found that elastic resistance is as effective as, if not better than, free weights or resistance machines at increasing both lean body mass and strength.

Chains Cause Strength Gains

The positive impact on strength from variable resistance coming from chain-loaded training occurs when appropriately positioned chains on the barbell, that settle to the ground one link at a time during the descent portion of the movement, effectively decrease the resistance on the bar as more and more links in the chain rest on the ground. In addition, going in the upward direction lifts the chain off the ground one link at a time, incrementally increasing the resistance of the bar throughout the ascent phase of the lift. Once again, when the variation in resistance adequately matches the increase or decrease in muscular force that naturally occurs during the movement, the chains effectively provide a potent stimulus that uniquely drives strength gains.

Trigger Fast-Twitch Muscle Fibers

The key impact on strength from the use of chains is a relatively greater velocity of the bar throughout the entire movement, which is crucial for maximizing strength— as greater velocity on the bar throughout the movement preferentially stimulates the growth of the more powerful fast-twitch muscle fibers, promoting a superior propensity for strength and power.

Because training with chains inherently increases the velocity of the bar, the use of chains plausibly activates fast-twitch muscle fiber contraction over slow-twitch muscle fibers. This is based on a well-established rule called the size principle, which asserts that more force production required by the muscle preferentially activates the larger, fast-twitch muscle fiber. The requirement for greater force production when bench pressing at high velocity is based on the simple relationship between velocity and acceleration, where an increase in velocity also increases acceleration, and according to the well-known equation (Force = Mass x Acceleration), the increased acceleration of the bar increases the force required to lift the bar. As a result, fast twitch-fibers are preferentially activated, improving strength, as fast-twitch muscle fibers produce much more force relative to slow-twitch muscle fibers.

For most of Michael Rudolph’s career he has been engrossed in the exercise world as either an athlete (he played college football at Hofstra University), personal trainer or as a research scientist (he earned a B.Sc. in Exercise Science at Hofstra University and a Ph.D. in Biochemistry and Molecular Biology from Stony Brook University). After earning his Ph.D., Michael investigated the molecular biology of exercise as a fellow at Harvard Medical School and Columbia University for over eight years. That research contributed seminally to understanding the function of the incredibly important cellular energy sensor AMPK— leading to numerous publications in peer-reviewed journals including the journal Nature. Michael is currently a scientist working at the New York Structural Biology Center doing contract work for the Department of Defense on a project involving national security.

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