I am a bit confused. Is lifting weights for exercise work? While it is not necessary to live, does it not qualify as what Rabbi Kook would call t’shuva of the body or what the Torah would require in terms of carefully guarding our lives? This then begs the question of why must we exercise on Shabbat? According to most physiologists or trainers it makes sense to workout on a set schedule with Intermittent days of exercise and rest. This could result in being directed to exercise on the Shabbat. Please advise. THANK YOU!
If one is weight lifting for health – this is a good and positive act and may qualify the Teshuvah you mentioned from rav Kook. Yet not all good things are permitted on Shabbat; a Brit Milah for a nine day old baby is good and a mitzvah but doesn’t override Shabbat. Exercising is therefore good, but not for Shabbat; as it is a mundane week-day activity.