No worries. The amount of resistance of a single surgical tubing (especially for someone with Nadal's arms) is more than zero, but not much more...
That's not true.
It depends on the elasticity/resistance of the tubing (they come in different colors), also it increases as a function of the displacement
F=kx
where
F - the (resistance) force
k - factor of elasticity (a property of the material)
x - the displacemet, distance travelled
Thus it's gradually increasing resistance.
I am doing SHADOWING (imitation) of all major shots (FH, BH, serve), also swimming (butterfly) shadowing:
2 series of 15 reps to the limit (I can't extend it any more), for each of the shots/motions
in large amplitudes of motion.
The weights are different in this respect: they apply the resistance to the joint instantly, while the tubing does it gradually.
The latter is much better/healthier for the warmup and even in active training. Proof: I haven't seen tennis pros coming to the court with dumbells, but many have tubing.
I simply do NOT believe the dumbells promote the joint flexibility to the same extent the tubing does.