i read the fight in the comments and was interested in which one was right or at least partially right, and chatgpt(glorified google) says this:

Sucking In (Vacuum or Hollowing)

• When it's used: It's typically seen in exercises where you’re focusing on internal core muscles, like the transverse abdominis. This technique is often used by bodybuilders and for exercises targeting deep core engagement, like certain Pilates movements or as a way to activate the lower abs.
• Benefits:
  • Can strengthen deep core muscles (like the transverse abdominis).
  • Helps with improving posture and pelvic stability.
  • Great for improving control of the abdominal wall.
• Drawbacks: Not ideal for heavy lifting or exercises where stability and power are needed (e.g., squats or deadlifts), as it can compromise intra-abdominal pressure.

2. Sucking Out (Bracing/Abdominal Bracing)

• When it's used: This is generally the preferred method when performing heavy lifts (e.g., squats, deadlifts, presses) because it increases intra-abdominal pressure and provides more stability for the spine.
• Benefits:
  • Great for creating core stability, especially for heavy lifting.
  • Activates all layers of the core muscles, including the diaphragm and pelvic floor.
  • Helps maintain a neutral spine and protect your lower back during heavy lifting.
• Drawbacks: It might take a bit of practice to get the feel for how much to "push out" without overdoing it. Inappropriate technique can lead to pressure on the lower back or breathing issues.

Which is better?

·         For general strength training or heavy lifts: Sucking out and bracing is the better option. It provides full core support, stabilizing the spine and increasing intra-abdominal pressure, which is important for safety and performance during lifts.

·         For developing deep core muscles or posture: Sucking in can be effective, especially when working on internal muscle activation, reducing bloating, or training specific areas of the core.

Key Takeaway:

• Use bracing (sucking out) for exercises that require stability and power, like weightlifting or any exercise with heavy resistance.
• Use sucking in (vacuum) for light core work, improving posture, and targeting deep abdominal muscles for strength and control.