As one stretches the resistance band with movement, stress upon the tethered locations and along the band increases. The stresses cause muscles to build strength and increase mass. The stresses build strength and mass to the bones.
The stretch in an elastic band occurs in all three dimensions but when resistance training, we are only interested in what would be called “normal stretch” which occurs longitudinally.
The force produced by an elastic band or tube is determined by this formula:
Force = cross sectional area x percent elongation
The cross sectional area is essentially the total amount of elastic material (width x height) while the percent elongation is the percentage of change in length from the resting length. For example, a three foot length of band with no tension stretched to a final length of 6 feet has elongated 100 percent (50-51).
RTM Training and FW training use gravity against the weights (isotonic resistance) to generate stressful forces. Resistance bands do not rely on gravity to generate force; rather, resistance force depends only on how strong the band is and how much the band is stretched.
Resistance bands provide a resistance force that increases as the band is stretched. RBT adds “progressive” resistance that is variable during the exercise. Resistance band force mimics the “strength curve’ of most muscles.
Key Takeaway: Resistance band force curve is almost the same a the stretch curve of muscles