Hey @Oscard1987,
Thanks for the post. Without looking at the specific activity that is causing this, it's difficult to know what is going on. 

Several different factors can contribute to changes in your Fitness and Freshness score. Here are the main ones:
1. The intensity of your activities has changed.
2. The frequency of your activities has changed.
3. Your heart rate zones were recently updated. (Updating your heart rate zones will only affect future activities)
4. If your activities are using power, your FTP may have recently been updated. You can update your FTP here: https://www.strava.com/settings/performance

If you still have questions or need any clarification, please submit a support ticket and include links to any activities where you started seeing this change. This will help our team to further investigate.