Understanding Force Curves For Greater Gains
Yesterday I posted about doing a 550 lbs Good Morning (I could've gone a lot heavier) using this machine.
This machine is a version of a Rogers Power Squat Pro (below). They're kind of a rare piece of equipment but if you ever come across one it probably means you go to a good gym and yes, you HAVE to give it a try.
https://rogersathletic.com/products/power-squat-pro/
Someone then pointed out that there were to places to load the machine, a top rack and a bottom rack, and asked why I chose to top rack to load my plates. This is where force curves or "tension profiles" (I've heard them used interchangeably) come into play.
Understanding Force Curves
So why do I load up the top rack and not the bottom? The answer to this is important to making BETTER GAINS so try to follow along.
It's really just basic physics.
The direction the weight moves through space matters. This movement affects the force curve -- where tension is felt the most/least throughout the movement. Think of it like this: The more up and down the weights move when using free weights, the more you are moving directly against gravity. In other words, you are moving the FULL load of the free weight.
In the case of the Rogers Power Squat Pro, the weights move in an arching motion. Neither to top nor the bottom rack move directly up and down but they move more up and down depending on the range of motion.
At the bottom of the range of motion, the top rack is moving at nearly 90Ëš (vertically). Meanwhile the bottom rack is moving diagonally. This means that when the top rack is loaded, there is MORE tension at the bottom stretch position.
In addition to this information on force curves, we also know that the stretch position is likely where the best growth happens. Since we want the force curve to have the highest tension in the stretch position, this is why I chose the top rack.
Other Types of Force Curves
We've already discussed how the direction a weight moves through space in relation to the source of tension determines where the most and least tension will be through the full range of motion.
When it's free weights moving through space, it's fairly easy to figure out what it's force curve might be and how to utilize for better gains because that source of tension is just the earth (gravity). With levers and pulley systems, it's less obvious where the source of greatest tension lies.
Take a look at this Gymleco Bicep Curl.
At the start of the bicep curl, when the arm is fully extended, the bicep is in a lengthened position. In this position, the belt is oriented such that the force exerted by the weight is most directly opposed to the action of the bicep muscle. This means the muscle must overcome the greatest resistance to start the curl, as the pull of gravity on the weight translates into maximal tension on the belt due to the alignment of the pulley system.
As the curl is executed and the weight is lifted, the angle of force application changes due to the movement through the pulley system. The initial high tension is because the pulley system's alignment maximizes resistance at that specific angle. As the arm curls the weight upwards, the alignment with this point of maximal tension changes, altering the force dynamics.
This alteration in alignment with the point of maximal tension effectively decreases the perceived load on the biceps. As the arm moves away from the 30-degree mark below horizontal, the resistance felt by the muscles diminishes. This is not because the actual weight changes, but because the pulley system's design reduces the effective resistance by changing the force angle, making the lift easier as the arm approaches the peak of the curl.