MariposasTempo Run
A tempo run is a sustained effort at a pace that sits right at the upper edge of your aerobic capacity, commonly described as "comfortably hard," where you can still speak a few clipped words but definitely not hold a full conversation. Physiologically, this pace corresponds to your lactate threshold, the point where lactic acid accumulates in the blood faster than your body can clear it. Training at this specific intensity pushes that threshold higher over time, so your body learns to sustain faster paces before fatigue compounds. The nuance most people miss is that too easy defeats the purpose, but too hard turns it into an interval session, and both mistakes produce far less adaptation than hitting the actual threshold zone. A true tempo run is typically held for 20 to 40 continuous minutes, not broken into short hard bursts. That sustained, steady pressure on the aerobic system is exactly what drives the performance gains runners and cyclists chase with this type of session.
Example
A runner whose easy pace is 10 minutes per mile and race pace is 8 minutes per mile might find their tempo pace lands around 8:45 to 9:00 per mile. They hold that effort for 25 minutes in the middle of a 40-minute run, feeling the burn accumulate but staying controlled the whole way through. The next morning they feel genuinely tired in the legs, which is the signal that the session hit the right stimulus.