My go to training platform is and has been Training Peaks
In total transparency, I do not sell Training Peaks, I am not paid by Training Peaks, although there is a way as a coach to generate income from Training Peaks. I do not get any special deals available only to me nor do I get any products or discounts.
Also, there are lots of other platforms that track athletic performance data. There are spread sheets as well for those who want to “DIY”. Look around and pick what works best for you.
If you want my opinion and my suggestions related to using Training Peaks as your platform of choice to track data, go to the MENU at the top right and look under the Rat Racer Coaching header or click the link below