How to Fix Tension Variability when Standing vs. Sitting with an Elastic Strap

Elastic straps are a great way of applying external tension for foreskin restoration. However, anyone who uses one will notice right away that the amount of tension decreases significantly when sitting versus standing. Tension will also change to some extent every time you take a step while walking. It is important for the skin to be under sufficient tension to stimulate growth, and this can be a problem if you spend a lot of time sitting or have to switch between sitting and standing often. There is actually one easy trick for mitigating this tension difference, but first you need to understand how force is calculated in an elastic band.

Hooke’s law states that force is equal to displacement times the spring constant, or F = xk. Displacement in this case is the distance that the elastic band is stretched. The spring constant is the elasticity of the material, which in this case is dependent on the type of material, and the thickness of the material. Since we are trying to achieve a constant force, the two variables we can work with are the thickness of the material, and the distance it is stretched.

To demonstrate this, I tested two different elastic bands of different thicknesses while standing and sitting:

First, I measured the force and distance stretched using a 1-inch-wide suspender strap that restorers commonly use. With the strap fixed below my knee and attached to a device, I had to stretch it only 3 cm while standing to get 8 ounces of tension. When sitting down with my hips and knees both at 90-degree angles, the band shortened by 6 cm. Since this distance is more than what it took to go from zero tension to 8 ounces, the band goes completely slack, and the tension goes to zero. 

Next, I measured the force and distance stretched using one of the elastic bands that I make, which has a relatively thin elastic cord. When standing, I had to stretch the band 12 cm to get 8 ounces of tension. When sitting down in the same position as before, the cord again shortened by 6 cm, but this time the tension ony decreased to 4.5 ounces.

So, why is the difference so much less with a thinner elastic band? The reason is that the relative change of distance is much less, and therefore the change in tension will be less as well.

Could we just keep making the elastic thinner until the relative change is so small that it is insignificant? Theoretically you could, but there are some limitations in our situation. In Hooke’s law, there is a limit to how far a spring or string can be stretched until it deforms or breaks. A band that is too thin will break at the tension needed in foreskin restoration. We are also dealing with a limited amount of space between the device and where the band is anchored on the leg, which is only about two feet at the most. The only way to perfect the elasticity in this situation would be to play with different elastic materials or springs. Just using regular rubber elastic though, the elastic bands that I offer have pretty close to the ideal thickness within the tension and distance parameters we are dealing with in foreskin restoration.

With my bands, the tension variations while walking are very minimal. With the same scenario above of it taking 12 cm of distance to get 8 ounces of tension, each step while walking only reduces the distance stretched by 1-2 cm, so you are only losing about 1 ounce of tension at the most. With a 1 inch suspender strap, reducing the distance stretched from 3 cm by 1-2 cm is a much larger relative reduction, and it reduces the tension by about half for every step.

Even though my elastic bands have less of a difference when sitting versus standing, it is still significant and should be mitigated through other means. Some people will anchor the band to the outside of the leg so that it wraps over the thigh, but this can actually cause the tension to increase while sitting, and it also angles the force less evenly. If you have a desk job or other similar situation, it is best to use a standing desk if you can, or a higher chair or stool where you can keep your leg straighter. You can also change the tension by shortening the band every time you sit down. My bands make this easier, but it is still cumbersome and not practical in a public setting. Although there is always going to be some variation in tension and you can never get it to be constant in every position, these strategies will make tension more consistent, and hopefully make progress more consistent as well.