Certainly, I can help you create an optimal training plan for gaining muscle mass with a time constraint of 60 minutes per session and a commitment to three training days per week. It's important to note that nutrition and rest are also crucial components of a successful muscle-building program. Make sure you are consuming enough calories and protein to support muscle growth and getting adequate sleep for recovery. Here's a 3-day workout plan for you: Day 1: Upper Body 1. Warm-up (5 minutes): Start with light cardio, such as jogging in place or jumping jacks, to increase your heart rate and warm up your muscles. 2. Bench Press: 3 sets of 8-10 repetitions with a 1-minute rest between sets. 3. Pull-Ups or Lat Pulldowns: 3 sets of 8-10 repetitions with a 1-minute rest between sets. 4. Dumbbell Rows: 3 sets of 10-12 repetitions per arm with a 1-minute rest between sets. 5. Overhead Shoulder Press: 3 sets of 8-10 repetitions with a 1-minute rest between sets. 6. Bicep Curls: 3 sets of 10-12 repetitions with a 1-minute rest between sets. 7. Tricep Dips: 3 sets of 10-12 repetitions with a 1-minute rest between sets. 8. Cool Down (5 minutes): Finish with light stretching for the upper body. Day 2: Lower Body 1. Warm-up (5 minutes): Similar to Day 1, start with light cardio to warm up. 2. Squats: 3 sets of 8-10 repetitions with a 1-minute rest between sets. 3. Deadlifts: 3 sets of 8-10 repetitions with a 1-minute rest between sets. 4. Leg Press: 3 sets of 10-12 repetitions with a 1-minute rest between sets. 5. Lunges: 3 sets of 10-12 repetitions per leg with a 1-minute rest between sets. 6. Calf Raises: 3 sets of 12-15 repetitions with a 1-minute rest between sets. 7. Cool Down (5 minutes): Finish with light stretching for the lower body. Day 3: Full Body and Core 1. Warm-up (5 minutes): Start with light cardio and some dynamic stretching. 2. Deadlifts or Romanian Deadlifts: 3 sets of 8-10 repetitions with a 1-minute rest between sets. 3. Push-Ups: 3 sets of 10-12 repetitions with a 1-minute rest between sets. 4. Planks: 3 sets of 30-60 seconds with a 1-minute rest between sets. 5. Russian Twists: 3 sets of 15-20 twists per side with a 1-minute rest between sets. 6. Leg Raises: 3 sets of 10-12 repetitions with a 1-minute rest between sets. 7. Cool Down (5 minutes): Finish with light stretching for the entire body. This 3-day workout plan will help you target all major muscle groups while allowing for proper rest between sessions. Remember to focus on progressive overload by gradually increasing the weight or resistance as you become stronger. Additionally, ensure you're consuming enough calories and protein to support muscle growth, and get adequate sleep and recovery on non-training days. Adjust the weights and repetitions as needed to match your current fitness level and goals. It's also advisable to consult with a fitness professional or a doctor before starting any new exercise program, especially if you have any underlying medical conditions.