Many of you will surely have found yourselves in the situation of having to conduct a rallentando or allargando.
Most probably at first, you will have tried to hold back the orchestra by suddenly conducting the beats more slowly in a big and flashy way, and separated from each other; even in some cases by resorting to subdivisions, by a way of solfège. Usually, contact is lost with the orchestra, the musicians begin to get out and the results are quite embarrassing, but nothing is stranger than retrying the passage a few times and still being unable to obtain something.
The flaw in the way of realising a rallentando that I mentioned above, consists of showing only the individual beats and not the rallentando itself, its evolution
This in fact, is transmitted by what happens in the space in time between one beat and the next, and not from individual beats separated one from another. So we infer that in the realisation of a rallentando (as well as in a stringendo) it is extremely important to show the continuity, the evolution of it, in time.
https://www.youtube.com/watch?v=C4pkJNo8Iqc
In other contexts, it can also be of particular help to support ourselves with a clear gesture of the shoulders.
https://www.youtube.com/watch?v=HFGDtvC0wTk
