1. "Wow, it seems that your life is really healthy! What sports do you usually like to do? "
2. "This gym looks great! Have you practiced here for a long time? "
3. "I saw that you were still working out when you replied to my message. You are really focused! I appreciate your perseverance. "
4. "Your self-discipline is really admirable! How do you usually keep such a healthy life? "
5. "It seems that your exercise effect is very good! I should also do more exercise. "
6. "You like fitness, so do you like the feeling of tight muscles?"
The above are just some reference replies, and you can make appropriate adjustments according to your relationship and the context of the conversation. If the relationship between you is not close enough, it is recommended not to be too intimate or too deep, so as not to make the other person feel uncomfortable.