Lifting weights on Shabbos

Hi,

One may not lift weights on Shabbat, because this would violate the biblical requirement that one differentiate his behaviour on Shabbat from that of the week.

(Rivivot Ephraim 1:223:6)

[Note: One might contend that the requirement of differentiating one's behaviour is broad and vague, and could apply to a whole host of behaviours, including sitting in a chair, eating at a table, and sleeping in bed. However, the classic understanding of this requirement is to apply it to activities involving physical strain, which would prevent one from identifying Shabbat as a day of halting activity and of rest. See, for example, Ramban to Vayikra 23:24. - MT]

Have a great day,
Mordechai