The overload training principle is the training principle he used.Explanation:
Here the jumping rope is the fitness training which is done again and again to strong his leg muscles.
There are many training principles like:Progression. Overload.Adaptation.Recovery.Reversibility.
This principle (overload) is done to use to get to the volume of work.
This means for improving their muscles communication during wrestling they have to do this practice again and again and they have learnt this technique like rope jumping in earlier life.
Transfer because you are using the skills you learned before and transferring them to now.
The right option is; transfer training principle
This scenario represents transfer training principle.
The transfer principle involves the effect of former experiences or learning on the performance of later skills or activities. The effects may be zero (without any influence), positive (better performance), or negative (worse performance). Right application of the transfer principle saves valuable training time, and it improves results.
Hope this helps :)