You use any or all of the following: EMG, Biodex, Lactate Measurement, Heart Rate, GPS, Accelerometers, HRV. You feel like a mad scientist, buried in numbers and reams of graph paper. Now what do you do with all this information. What is real and useful and what is noise? How do you turn the numbers into action? Just because you measure something does it mean it actually has value in terms of significantly impacting how you train your athletes? Taken in isolation all the previously mentioned measurement tools are just random number generators. It is up to you the coach, hopefully with some help from others on the performance team, (if you have that kind of support) to interpret the data and make it meaningful. I have learned after using many sophisticated monitoring systems over the years that simpler is better, and less is more. Decide what measurements are meaningful and consistently use those, don’t look for more. The measurement tools you use must be part of a system and provide useful information to help execute the training plan. There is no substitute for the eyes and ears of the coach with a good plan. Technology cannot take the place of a coach. At the end of the day if you use session RPE and have the athletes keep a very detailed training log it will serve you well.