Stop Guessing What Your Workouts Are Worth: Week Two Summary

How do you know if a workout helped? It shifts your Projected Time by at least 2 seconds. That is the one clear test. Not your step count. Not how many miles you logged. Not how tired your legs felt. A run did its job when it adds a real change to one of your five drivers. The engine behind PIRX reads every run you sync. It scores all five drivers after each session. It updates your Projected Time only when the shift across them adds up to at least 2 seconds. That keeps the number clean and honest. Every update you see is earned.

Week 2 covered all five drivers from different angles. This post pulls the week together. It shows what each driver needs, and what it really takes to move your number.

Driver	How to train it	What moves your number
Aerobic Base	Easy miles at a pace you can talk through; build volume slowly over months	Steady volume that lifts your fuel efficiency until the gain crosses 2 seconds
Threshold Density	Hard-steady efforts at the pace you can hold for 20 to 40 minutes	Weekly minutes near your lactate pace that push your driver score past 2 seconds
Speed Exposure	Short fast intervals with full rest between each rep	Fast sessions that raise your top aerobic ceiling by at least 2 seconds
Load Consistency	Smooth week-to-week builds with no big spikes and no sudden drops	Steady training weeks without injury breaks that push the total past 2 seconds
Running Economy	Long easy runs; relaxed form; drills that cut wasted motion	A pace-at-same-heart-rate improvement that adds up to 2 or more seconds gained

How do you know if a workout helped?

A workout helped when it moves your Projected Time. That move happens only after the change in your drivers adds up to at least 2 seconds. Think of it like filling a bucket. Each session adds a little. When the bucket tips, your number moves. The engine is always running. You do not see every small addition. But nothing is lost. Every run that builds your drivers is tracked and held.

This idea matters because most runners use vague signals to judge their training. A hard run feels like progress. An easy run feels like a day off. But feeling is not a score. A 30-minute easy jog may do more for your Aerobic Base than a tired, sloppy hard effort. A short speed session may sharpen your top end more than another long, slow run. The five drivers remove the guessing.

A week of easy runs and one tempo session adds to both Aerobic Base and Threshold Density. When the combined change crosses 2 seconds, your Projected Time drops. You see the result of the week, not just one run.

What did the 10K post teach about two key drivers?

Aerobic Base and Speed Exposure come at the 10K from opposite ends. One builds the floor. The other sharpens the top. About 97 percent of the fuel in a 10K effort comes from the aerobic system (Gastin, 2001). Both drivers are aerobic. But they are built in very different ways. And most runners have a clear gap in one of them.

Aerobic Base grows from easy running. Slow, relaxed miles over weeks raise your lactate threshold. That threshold is the fastest pace you can hold before your body starts to slow you down. It is the strongest predictor of distance race results in trained athletes (Denadai & Greco, 2022).

Speed Exposure does the opposite job. Short, fast intervals push your top aerobic power higher. High-intensity sessions raise this power more than any other training type (Helgerud et al., 2007). Together the two frame your 10K ceiling. Grow the weaker one, and your number moves. Let the gap sit, and it costs seconds on every race day.

How does late-race marathon strength come from two drivers?

The marathon wall post traced the hard fade at mile 20 back to one cause. Glycogen runs dry. Your muscles store about 500 grams of it when fully loaded (Murray & Rosenbloom, 2018). At race pace, that fuel can run out near mile 20. When it does, your legs get heavy. Your pace drops fast. The wall is a fuel problem, not a mental one. And training can fix it.

28%

of men hit the wall late in a marathon, against 17% of women (Smyth, 2021)

About 28 percent of men and 17 percent of women hit the wall in a large study of recreational marathoners (Smyth, 2021). Two drivers push back against the wall. A strong Aerobic Base teaches the body to rely more on fat and less on glycogen. That stretches the tank. Steady Load Consistency builds the muscle endurance to hold form through the last 10 kilometers. Both take months to build. But both protect you at the points in a race where most runners fade.

Your Load Consistency score is how PIRX tracks this durability quality over time. Steady weeks build it. Spikes in mileage do not.

What is the link between fueling, pacing, and Threshold Density?

Metabolic fitness and pacing showed that your ability to hold a strong race pace rests on the same driver that shapes your hard training sessions. That driver is Threshold Density. Your lactate threshold is the fastest pace you can hold before lactic acid builds faster than your body can clear it. This is the speed ceiling for a 10K, half, and marathon. Lactate threshold is the main predictor of endurance results in well-trained runners (Faude et al., 2009).

Threshold Density tracks how many minutes per week you spend near this pace. More time there, and the driver score climbs. When that climb crosses 2 seconds on your Projected Time, the update shows. A runner with a high Threshold Density score can hold their goal pace with less effort. That leaves fuel and form for the final miles, where most races are won or lost.

How do the five drivers stack into one Projected Time?

The five drivers hub post tied all five together. Each driver gets a score from 0 to 100. Each one adds or subtracts seconds from your race total. A weak driver does not erase your other gains. But it costs you real seconds. And a low score is also your biggest chance to move your number fast.

Think of it like five accounts that all pay into one race time. Aerobic Base is the largest for most runners. Threshold Density pays the most race-day return per hard-pace minute. Speed Exposure and Load Consistency sharpen and protect the others. Running Economy is the rate at which you spend energy per kilometer.

Here is a real example. Say Aerobic Base adds 18 seconds. Threshold Density adds 12. Speed Exposure adds 6. Load Consistency adds 4. Running Economy costs 5. The net is 35 seconds faster than your baseline. Each driver earns its own share. No single trait hides the others.

Why does high mileage alone fail the half marathon?

Peak mileage and the half marathon pushed back on a common belief. More miles do not always mean a better race. You can hit a big training week and still leave your speed or economy behind. Volume builds Aerobic Base. But it does not sharpen Speed Exposure on its own. And it does not fix poor Running Economy without the right kinds of runs mixed in.

Research shows that more weekly miles and a longer long run both track with stronger finish times (Fokkema et al., 2020). But balance matters just as much. A runner who only piles on miles has one strong driver and four softer ones. The half marathon needs all five. When training is too flat in intensity, the number stops moving. Add one sharp speed session and some relaxed form work, and the other four drivers start to gain.

How do you find your running leak before race day?

Finding your running leak starts with one question. Which driver score is lowest? That score is your leak. Not a failure. A target. Physiologists who study elite runners are clear: no single fitness trait wins a long race on its own. Top aerobic power matters. So does your threshold pace. So does your running economy. All three must be strong at once (Joyner & Coyle, 2008). The five drivers are built on that same idea.

A big Speed Exposure score with a thin Aerobic Base leads to a fast start and a hard fade. A strong Threshold Density with poor Load Consistency leads to missed training weeks from injury. Each weak link costs its own seconds. And the weakest one is always the most urgent fix. PIRX shows all five scores side by side. The lowest one tells you where to aim next. Train the gap, and the whole picture improves.

How is PIRX different from a generic watch or calculator?

A one-size-fits-all calculator gives you a race time from your last result. It runs a single fixed formula. Every runner gets the same math. Your training history does not factor in. Your weak driver does not factor in. The formula has no way to learn you. So it cannot tell you what to change, or how many seconds the change would earn.

PIRX is a proprietary machine-learning prediction engine. It reads your actual runs, not just your race time. It does not apply a formula designed for an average runner. It learns from your sessions over time. Your easy miles score your Aerobic Base. Your hard-steady work scores your Threshold Density. Your interval sessions score your Speed Exposure. Your week-to-week pattern scores your Load Consistency. Your pace at the same heart rate over time scores your Running Economy.

Each score stands on its own and adds to your total. Your Projected Time comes with a Supported Range that shows the spread of likely finish times. After every run you sync, the engine recalculates. When any combination of driver changes crosses 2 seconds, your number moves. That is a real change. Your body earned it. Not an estimate. Not a guess. A result from an engine that knows your runs, not just your last race.

98%

validated prediction accuracy (PIRX users)

Connect your watch and score your five drivers

Stop guessing what your training is worth. A generic watch score treats every runner the same. PIRX does not. Connect your Garmin, COROS, or Strava in under 30 seconds. Score your five drivers. See where each one stands. Find the gap that costs you the most seconds. Get a Projected Time built on your own data, not a formula made for someone else. It is free. You need no new device. Your runs have already done the work. Find out exactly how much they are worth.

Sources

• Gastin, P.B. (2001). Energy System Interaction and Relative Contribution During Maximal Exercise. Sports Medicine, 31(10), 725-741. (The aerobic system supplies roughly 96 to 98 percent of energy in a 10K-duration effort.)
• Denadai, B.S. & Greco, C.C. (2022). Could middle- and long-distance running performance of well-trained athletes be best predicted by the same aerobic parameters? Current Research in Physiology. (Lactate threshold is the primary predictor of 10K performance in trained runners.)
• Murray, B. & Rosenbloom, C. (2018). Fundamentals of glycogen metabolism for coaches and athletes. Nutrition Reviews. (Muscle glycogen stores average about 500 g when fully loaded; trained runners spare more glycogen by burning fat at race pace.)
• Rapoport, B.I. (2010). Metabolic factors limiting performance in marathon runners. PLoS Computational Biology. (Models when glycogen runs dry during a marathon, pointing to the wall near miles 18 to 20.)
• Smyth, B. (2021). How recreational marathon runners hit the wall: a large-scale data analysis of late-race pacing collapse in the marathon. PLOS ONE. (Around 28 percent of men and 17 percent of women hit the wall, with a pace drop of at least 25 percent over the closing kilometers.)
• Faude, O., Kindermann, W. & Meyer, T. (2009). Lactate threshold concepts: how valid are they? Sports Medicine. (Lactate threshold is the strongest correlate of endurance race performance.)
• Helgerud, J. et al. (2007). Aerobic high-intensity intervals improve VO2max more than moderate training. Med Sci Sports Exerc. (Short, hard intervals raise top aerobic power more than moderate steady training.)
• Fokkema, T. et al. (2020). Training for a (half-)marathon: training volume and longest endurance run related to performance. Scandinavian Journal of Medicine and Science in Sports. (More weekly miles and a longer long run both track with stronger race-day finish times.)
• Joyner, M.J. & Coyle, E.F. (2008). Endurance exercise performance: the physiology of champions. J Physiol. (Endurance performance rests on oxygen power, lactate threshold, and running economy working together, not any single trait.)
• Maunder, E. et al. (2021). The importance of 'durability' in the physiological profiling of endurance athletes. Sports Medicine. (Two athletes with the same fresh-state fitness can differ greatly in late-race performance due to durability differences.)