You can practise core strength without sit-ups. That does not make sit-ups inherently harmful or another exercise automatically safer. Choose a movement you understand and can manage comfortably, rather than treating one exercise as compulsory.

Your core includes muscles around your trunk and pelvis. A breathing pause alone is not the same as a strengthening exercise, and a perfectly still posture is not the goal of every daily movement.

One option to learn: a bridge

A bridge is one of the core exercises described by Mayo Clinic. It involves lying on your back, so it is only an option if getting down, lying in that position and getting up are appropriate for you. Use individual advice if an injury, pregnancy, recent surgery or another condition affects participation.

1. Lie on your back with your knees bent and feet supported on a stable surface. Keep your back in a comfortable neutral position rather than forcing it flat or arching it.
2. Gently engage your abdominal muscles and lift your hips towards a line with your knees and shoulders. Do not push higher by arching your back.
3. Keep breathing during the movement. Lower back down with control and rest before deciding whether another attempt feels manageable.

Read the linked demonstration before trying an unfamiliar exercise. You do not need to match a photograph, hold for a fixed time or complete repetitions through discomfort.

If floor exercise does not fit

Do not replace the bridge with an improvised one-leg balance or a harder plank simply to keep the session going. Ask an appropriately trained instructor or physiotherapist for an option that fits your access and movement needs.

Describe the practical difficulty: "I cannot get to the floor comfortably" is more useful than assuming you need to work harder. A chair or wall may help with some exercises, but neither makes every movement suitable.

Keep the session manageable

Choose one familiar exercise and give yourself time to understand it. You can stop before five or ten minutes; a timer does not establish the right amount for you. Progress can mean clearer control or a more suitable choice, not a longer hold every session.

Stop for pain, dizziness or unusual symptoms. New or persistent back pain needs appropriate assessment rather than a promise that core exercises will fix it. If your purpose is rehabilitation, follow an individual plan instead of using this article as one.

Core work can be part of a broader activity plan. It does not guarantee freedom from injury or replace every other type of movement.

Sources

• Core exercises: why you should strengthen your core muscles (opens in a new tab), Mayo Clinic: core muscles and a bridge example, not approval of an individual exercise plan.
• Older adult activity: an overview (opens in a new tab), CDC: different types of activity matched to abilities, relevant to older readers.