Nobody needs a coach to gain fitness. Anyone can tell you to add mileage, do harder intervals or lift heavier. It always works – assuming you have spare time or work capacity. 

It’s also the only way to improve across all event durations. Most runners care about their mile time as well as their marathon; most rowers need to maintain a strong 30min test as well as a sprint. 

For them, more is more, and good training is textbook. Athletes who train like this have a predictable fatigue profile. You can estimate and improve their race results from a few lab data points or even just rules of thumb:

“Do 90min of UT2 every day, and add 10sec to your 2K pace for the erg test!”  …  “Do  long rides to maximise FTP/kg, then race at 78% of that!” … “Build mileage until 3 weeks out and look up your pace from the VDot tables!”   

But if your performance goal is very specific:

… such as one standardised event or a distance you focus on

… or is limited by muscular endurance as well as fitness

… or there’s only one day in the calendar that matters

then “doing more” could be holding you back.

–  You don’t need a 6:40 2K to pull 1:43 splits for 5K

–  You don’t need a “330-watt FTP” to comfortably push 275w for an IRONMAN

–  You don’t even need to be a quick runner to consistently go sub-3 off the bike.