Krishna now introduces three dimensions of austerity — body, speech, and mind. This shloka covers the body. Physical austerity means: honoring the devas, scholars, teachers, and wise elders. Maintaining cleanliness of body and surroundings. Behaving with straightforward simplicity. Practicing brahmacharya (self-restraint). And causing no harm to any living being.
None of this requires retreating to a forest. Respecting elders, keeping oneself and one's home clean, being honest in conduct, exercising self-discipline, and being kind to all creatures — these are the five pillars of bodily austerity.
An elderly woman who does her daily puja, keeps her home spotless, treats everyone with warmth, and lives with quiet discipline — she practices sharira-tapas every day without naming it.