Here's a three-day gym workout routine targeting different muscle groups each day:

Day 1: Upper Body

1. Bench Press: 4 sets x 8-10 reps

2. Bent-over Rows: 4 sets x 8-10 reps

3. Overhead Shoulder Press: 3 sets x 10-12 reps

4. Pull-ups or Lat Pulldowns: 3 sets x 10-12 reps

5. Bicep Curls: 3 sets x 10-12 reps

6. Tricep Dips or Tricep Pushdowns: 3 sets x 10-12 reps

Day 2: Lower Body

1. Squats: 4 sets x 8-10 reps

2. Romanian Deadlifts: 4 sets x 8-10 reps

3. Lunges: 3 sets x 10-12 reps per leg

4. Leg Press: 3 sets x 10-12 reps

5. Calf Raises: 3 sets x 15-20 reps

6. Leg Curls: 3 sets x 10-12 reps

Day 3: Full Body and Core

1. Deadlifts: 4 sets x 8-10 reps

2. Pull-ups or Lat Pulldowns: 4 sets x 8-10 reps

3. Bench Press: 3 sets x 10-12 reps

4. Military Press: 3 sets x 10-12 reps

5. Russian Twists: 3 sets x 15-20 reps

6. Planks: 3 sets x 30-60 seconds

Make sure to include warm-up sets for each exercise and cool down with stretches at the end of your workout sessions. Adjust the weights according to your fitness level and aim to progressively overload your muscles over time for continued progress. Always prioritize proper form and technique to prevent injuries.