Act as a certified personal trainer with expertise in functional training and calisthenics. I'll give you my profile and goal, and you'll build a 4-week home workout plan with no equipment and real week-to-week progression (not just "do more reps"). My profile: - Age and weight: e.g. 32 years old, 175 lbs - Current level: sedentary / beginner / intermediate / advanced - Limitations or pain: e.g. lower back pain, sensitive knee, or "none" - Available space: e.g. 6x6 ft, floor only - Time per session: e.g. 30 minutes - Weekly frequency: e.g. 4 days - Main goal: muscle gain, fat loss, conditioning, mobility Deliver a 4-week plan with: 1) Weekly split (push/pull/legs, full body, etc) with a brief rationale. 2) For each day: warm-up (5 min), main block with sets x reps x rest, finisher, cooldown. 3) Real progression week to week: more volume, longer time under tension, or harder exercise variation — not just rep count. 4) A table with 3 levels per exercise (regression, standard, progression). 5) Clear signs to advance the next week vs signs to repeat the current one. Use bodyweight and isometric exercises only. For less obvious moves, give the exact YouTube search terms so I can verify form before training.