What are some strategies for effectively pacing yourself during fartlek sessions on Zwift, especially when joining a virtual group ride where youre surrounded by more experienced riders who seem to be able to maintain a blistering pace for the entire ride, and how do you avoid getting caught up in the excitement of the group and blowing up mid-ride, while still pushing yourself to get the most out of the workout? Is it better to focus on your own power output and ignore the groups pace, or try to stay with the group and adjust your effort on the fly, and what are some tips for communicating with the group and getting feedback on your pacing during the ride? How do you balance the desire to stay with the group and get a good workout with the need to avoid overexerting yourself and risking burnout or injury, especially during longer or more intense rides? Are there any specific features or tools within Zwift that you can use to help pace yourself and stay on track during group fartlek sessions, and how do you incorporate these tools into your overall training plan?