There are many cheap swimming belts that work with rubber or expander ropes, but the swimming sensation is permanently distorted by the principle of inertia.
Inertia principle what does that mean?
The principle of inertia states that a uniformly moving body retains its straight-line, uniform motion.
Temperature differences have an enormous impact on rubber and expander ropes, which do not bother the pool trainer (steel no big impact) and the pool athlete (fiberglass reinforced plastic no impact). No matter how often and how strong you swim, the pool coach and the pool therapist always respond equally to their swimming style.