Twenty affirmations for a strong body — about what your body can do, not how it looks doing it.

Strength is one of the few things about a body that is unambiguously improvable and almost never the thing people are anxious about. That is a strange arrangement: the measurable, trainable part gets ignored while the appearance, which changes far less, gets all the attention.
These twenty affirmations move the attention back. They are about capability — what your body carries, climbs, recovers from — and they suit anyone training, rehabbing, or simply trying to stop treating their body as a problem.
The useful shift is from "fixing" to "maintaining". A project has an end date and a verdict; a relationship has ordinary weeks, off days, and continued attendance. Bodies respond much better to the second.
Say one of these before training rather than after. Before, it is an intention that changes how you show up; after, it is a report card, and report cards are how people end up quitting.

1. “My body is wise and my intuition is strong.”

2. “My body is fit and strong.”

3. “My body is getting stronger every day.”

4. “I am glowing with pride over my strong, capable, powerful body.”

5. “I support my body by moving it and growing strong.”

6. “I am strong and calm and beautiful.”

7. “I am healthy. I am strong. I am well.”

8. “I see myself as strong, attractive, and healthy.”

9. “My body is strong.”

10. “I am strong, confident, and motivated to work out.”

11. “I appreciate my strong body and am grateful for what it allows me to do.”

12. “I am a strong and resilient individual.”

13. “I am thankful for my strong, powerful body and for everything it does for me.”

14. “I am strong, both mentally and physically.”

15. “My body is strong and capable of amazing things.”

16. “I am patient with my body as it gets stronger.”

17. “My body is strong, it is getting me through this.”

18. “I take excellent care of all areas of my health, including keeping my body strong and healthy.”

19. “I feel powerful, strong, and downright amazing today.”

20. “I feel strong and powerful after each workout session.”
They are arguably more useful then. Strength here means capability relative to your own life — stairs, shopping, a long day on your feet — not a number in a gym.
Choose the lines about patience, wisdom and recovery over the ones about workouts. "I am patient with my body as it gets stronger" holds up in rehab in a way that performance language does not.
Before movement, ideally. Two or three repetitions on the way to a session does more for consistency than any amount of post-workout reflection.
For most people's motivation, yes. Strength gives frequent, unambiguous feedback, whereas weight moves slowly and noisily — which makes it a poor thing to hang a habit on.