"Social currency" is a relatively new specialist term, so it might be easier for you to look it up - it won't appear in many dictionaries yet, but there will be plenty of sites explaining what it is.
Briefly, it's an expansion of the term social capital, which has been around longer. Social capital is, broadly speaking, the relatively static value of relationships, image and so on in a social situation. There's a lot of interpretations, so it's hard to give a single definition. If an organisation has a lot of social capital, it means that it is well thought of in its community - it is recognised as a good thing.
Just like currency is, in a sense, a "flowing" form of capital, social currency is social activity that positively reflects on someone or something. When a product or company is talked about positively, whether it's in person, in the media, or on social media, that is social currency.
If we take this person's word with this understanding, they are essentially saying that having big muscles will make people talk to one another about him in a good way.
However, it's possible that he has another understanding of the term - it's new, so there's a range of understandings. It's also possible that he's misusing it.