Apex Run surfaces a variety of advanced running performance metrics to evaluate your cardiovascular output and pacing consistency. Here is a breakdown of what the numbers mean and how to use them.
1. VO2 Max#
- Definition: The maximum volume of oxygen your body can use per minute per kilogram of body weight (mL/kg/min). It is the gold standard measure of aerobic fitness.
- How it is read: Apex Run reads this directly from Apple Health, where it is estimated by Apple Watch from your workout data.
- Trend: A rising VO2 Max over months of consistent training is a reliable sign of improving cardiovascular fitness.
2. Running Power#
- Definition: An estimate of the mechanical power output of your running, expressed in watts (W).
- Value: Power is more consistent than pace on varied terrain, helping you regulate effort on hills or windy days.
3. GAP (Grade Adjusted Pace)#
- Definition: Your running pace adjusted to remove the effect of gradients. Running uphill at 6:00/km takes roughly the same effort as running 5:00/km on flat ground.
- Value: GAP normalizes this gradient impact so you can compare efforts accurately across hilly and flat courses. Apex Run shows a GAP chart in the run detail view.
4. Efficiency Factor (EF)#
- Definition: A measure of how efficiently your cardiopulmonary system converts effort into forward motion.
- Formula:
EF = GAP (m/s) ÷ Average Heart Rate (bpm) - How to read: To remove the effect of hills, EF uses Grade Adjusted Pace rather than raw pace. The result represents how many meters you travel per heartbeat. As fitness improves, you will run faster at the same heart rate—reflected as a gradual rise in EF over time.
- Typical range: 1.00 – 2.50 (higher = better aerobic efficiency)
- Long-term trend: A rising EF confirms your aerobic base training is working.
- Alerts: A significant drop in EF at your usual effort may suggest fatigue, dehydration, or heat stress.
Note
Because EF depends on your individual max HR and running form, it is most useful as a personal trend. Do not compare your EF score directly to other runners.
5. Pace Stability Index (PSI)#
- Definition: Apex Run’s custom metric measuring how consistently you hold your pace across a run. A stable rhythm generally means better energy distribution and lower risk of hitting the wall in long-distance races.
- Formula:
PSI = (1 − GAP Standard Deviation ÷ GAP Average) × 100%
| PSI Range | Interpretation |
|---|---|
| > 90% | Very steady rhythm, excellent energy distribution |
| 85 – 90% | Good rhythm, handles terrain changes well |
| < 85% | Large pace swings — try focusing on cadence to find a steadier rhythm |
Tip
In interval or fartlek workouts, drastic pace switching is the goal, so a low global PSI is expected and normal. Focus on segment performance instead.
See also:
- Training Zones — Heart rate zones and pace zones in detail.
- 80/20 Training Structure — How to balance your training load across intensity levels.
- Running Form Metrics — Cadence, stride length, ground contact time, and other technique measures.
- Training Load & ACWR — Evaluating fatigue and fitness progression.