Variable Resistance Methods for Training
◆ ☕️☕️ 8 min readVariable, often called accommodating, resistance involves using special equipment (resistance bands or chains) to increase the resistance of the load throughout the range of motion of an exercise.
This can be explained through the concept of strength curves. Every exercise has a strength curve, which is a graph of force output against the joint angle. As such, the strength curve shows how much force you produce at different joint angles as you move through the range of motion of an exercise. The relevance of the strength curve is that it describes the way in which the difficulty of a movement changes over its range of motion.
For exercises with an ascending strength curve more force can be produced at greater joint angles. The mechanical advantage we possess to lift the weight changes at every position along the movement. Mechanical advantage is greater at joint extension and decreases when moving away from extension (hence the ascending curve). In a squat, mechanical advantage is greatest at the top of the movement and the least at the bottom, at the end of the eccentric phase.
Faster movement speeds can be reached when mechanical advantage is greater. Referring to the concentric force-velocity relationship, the relationship between force and velocity is inverse. This also means that a position of mechanical advantage allows us to move fast, but our ability to produce force is diminished, as there is less time to produce force.
Without the use of variable resistance methods to modify the nature of the lift, we are always limited by the most disadvantaged position in the range of motion of an exercise. In case of the squat, we are most disadvantaged at the bottom, but if we are able to overcome that position, we are training the upper part of the lift at intensities below our capabilities. This is also why you can half squat more than you can full squat. We are only really challenging the most difficult point in the lift. Variable resistance methods provide us with solutions to the limitations that the ascending strength curve presents.
Applying variable resistance helps us vary the load experienced throughout the movement. This means we are able to add more load to the positions of greater mechanical advantage, while applying less load at less advantaged positions. This can result in a greater training effect, as high-threshold motor units are kept active for longer throughout the movement. This, in turn, leads to the production of higher peak forces compared to lifting the same load or at the same velocity without variable resistance.
The three forms of variable resistance commonly used are chains, band-assisted, and band-resisted methods. These methods are not interchangeable. Rather, they should be used in different contexts.
In reference to the concentric force-velocity curve, if we have velocity on the horizontal x-axis and force on the vertical y-axis, using resistance bands will help shift the curve to the right, as they provide a velocity stimulus. The bands provide no added mass, thus their impact on force production is rather limited. On the other hand, using chains does actually add mass to the exercise, which can help advance the curve upwards, reflecting improvements in force production capabilities. In terms of the profile of the curve, shifting it up and to the right means improvements in both force and velocity capabilities. This is the way we want to advance things, as improvements in both force and velocity will mean improvements in power, as power is the product of those two qualities.
The Chain Method #
In the chain method, the chains are simply attached to the bar and allowed to hang off it towards the ground.
If we refer back to the concentric force-velocity curve, chains can be used to target the force end of the curve. This is where absolute strength capabilities lie along with strength-speed, which is a step towards the velocity side of the curve, whereas force still remains the dominant half in power output (remember, power = force x velocity).
As stated, chains simply add mass to the lift, which directly affects force production, as force is the product of mass and acceleration (F = ma). Referring back to the squat example, chains allow us to deload the bar in mechanically weaker positions (the bottom of the squat as more of the chain will be resting on the floor) and load in stronger positions (the top of the squat as most if not all of the chain is lifted off the floor).
The chains method can result in increased concentric force output and increased power. This could be explained by the added load leading to greater eccentric velocities and forces as you descend into the squat. As the eccentric velocities are higher, the potentiation of the initial concentric phase via the stretch shortening cycle is possibly greater. As the chains are deloaded at the bottom of the squat, the transition into the concentric phase of the squat is easier, leading to potentially more effective utilization of the stored elastic energy due to the stretch shortening cycle function.
Additionally, as during the concentric phase of the exercise (i.e. the ascend of the squat), the load gets incrementally heavier due to more and more of the chain coming off the floor, a longer acceleration phase is allowed for. This means that the utilization of chains on a basic compound lift like the squat makes the exercise more ballistic in nature.
The Band-Assisted Method #
In case of the band-assisted method, the bands are attached to something directly above the bar, such as the power rack or hooks in the ceiling.
The band-assisted method is great for improving the velocity end of the force-velocity curve and speed-strength capabilities, where the power output is velocity-dominant.
Bands don’t add mass to the lift like chains. Rather, they augment the velocity of the movement, thus impacting power output directly. Also, the elastic nature of the band makes the loading and deloading as the band lengthens and shortens exponential in nature. This means that the more the band is stretched out, the more resistance it will provide as it is further lengthened the same unit of distance. In case of the chains, the loading and deloading is linear – the resistance added or removed per unit of distance does not change.
Band assistance deloads the exercise at the bottom of the movement where isometric contraction occurs as the direction of movement is reversed. As the bottom is the mechanically weakest position, assistance from the bands helps us out of the “hole”, allowing for greater velocities to be reached faster. The increased velocity of movement can help with neuromuscular activation.
Band assistance also increases force and power outputs due to the increase in movement velocity. Force and power are both impacted by velocity. If the force output is maintained and velocity is increased, power output will increase. If the mass is maintained and acceleration is increased (through velocity, as acceleration is change in velocity over time), force production will increase.
The increase in movement velocity is relevant in a sporting context, as sports require for quick force and power production. You won’t be given a lot of time to produce force in a competitive scenario, unless you’re a powerlifter. At the end of the day, speed kills.
The band assistance method is a double-edged sword. A limitation is that the assistance from the band resistance deloads the eccentric phase of the exercise, meaning there is less eccentric force available to be transferred into the concentric when the direction of movement is reversed at the bottom of the lift. This can be used as a positive when the athlete has a rate of force development issue. Because the eccentric phase is deloaded, the athlete can rely less on the stretch-shortening cycle to supercharge the subsequent concentric phase. As such, the muscles will be forced to produce the high velocity without much help from the stretch-shortening cycle.
The Band-Resisted Method #
In case of the band-resisted method, the resistance bands are attached to something below the bar in the direction of gravity, like the ground or the bottom of the power rack.
This method is effective for the enhancement of strength-speed and speed-strength, or the middle portion of the force-velocity curve.
The band resistance speeds up the eccentric phase of the exercise, supercharging the stretch-shortening cycle as higher eccentric forces are created. The stimulus trains the athlete to better handle the eccentric forces. If this is not done well or stiffness is not created fast enough at the end of the eccentric to decelerate into the isometric phase, the eccentric phase will last longer than is effective for concentric potentiation. If the eccentric phase lasts for too long, the elastic energy loaded up will dissipate instead of being redirected into the concentric phase and less of a potentiation of the concentric is experienced. As such, a slow eccentric will destroy the stretch-shortening cycle’s ability to supercharge the concentric phase. The band resisted method overloads the eccentric phase, training the body to better handle the forces so that more can be effectively transferred into the subsequent concentric movement.
Additionally, it adds resistance in the concentric phase without adding mass. This, like chains, allows for a longer acceleration period, as the mechanically more advantageous positions experience a higher load than the weaker positions. As a consequence, higher concentric forces are also created.
These are the three main variable resistance methods. For someone who showcases more limitations on the force side of things, emphasizing chain work could be a more relevant choice. For an athlete who struggles on the velocity side, resistance band methods could be used to improve those capabilities.
Variable resistance is just another tool that can be very useful, but is by no means essential. In case you decide to use those methods, make sure you actually know what you are doing and why you are doing it. Put in the time to learn the physics and the mechanisms behind those methods. There’s nothing worse than throwing some bulky chains on a bar just because you saw some elite athlete train like that so it must work. Be smarter than that.