The use of "in" or "on" in context

Question

Tell me please which preposition is correct to use in the following sentence.

We are going to work the shoulders in/on the next workout.

I am leaning towards in, but not 100℅ sure if it is correct, if it is not, then why?

Answer 1

Using in sounds sounds more natural in this context; it implies that working the shoulders is a component of the next workout and is loosely synonymous with many alternative words which may be used in this phrase, for example:

We are going to work the shoulders in the next workout.

We are going to work the shoulders as part of the next workout.

We are going to work the shoulders during the next workout.

Whereas, the use of on in the same phrase focuses more on the time of the next workout and seems to evoke a similar meaning to:

We are going to work the shoulders next time.

We are going to work the shoulders on the next occasion.

Answer 2

First of all, your sentence is grammatically incorrect and needs a "the":

We are going to work the shoulders in/on the next workout.

In your example both are correct.

As an English speaker, though, I think in sounds nicer.