Apex Run monitors your weekly work accumulation to help you build endurance safely. By analyzing the relationship between short-term training fatigue (Acute Load) and long-term fitness baselines (Chronic Load), the app helps you balance recovery and progression.
1. What is Acute Load in Running?#
- Acute Load (Last 7 Days): A rolling calculation of the physical stress and fatigue accumulated over your last 7 days of training. It represents your short-term fatigue state.
- Chronic Load (Last 28 Days): The rolling average of your training volume over the last 28 days (4 weeks). It reflects your habitual fitness baseline and capacity to absorb work.
- Load Trend: The direction your overall load is moving. Gradual increases of 10% or less per week are generally safe, while sharp spikes dramatically raise injury risk.
2. ACWR (Acute:Chronic Workload Ratio)#
- Definition: The core model Apex Run uses to evaluate whether your training volume is increasing at a healthy rate.
- Acute Load (last 7 days) — Represents current training fatigue.
- Chronic Load (last 28 days) — Represents your long-term fitness baseline.
- Calculation:
ACWR = Acute Load ÷ Chronic Load
The ratio flags whether you are training in the optimal “sweet spot” or pushing into zones that increase injury risk:
| ACWR Range | Zone | Meaning |
|---|---|---|
| 0.8 – 1.3 | 🟢 Productive | Sweet Spot. Acute load is slightly above chronic—stimulating aerobic adaptation while minimizing injury risk. Maintain current rhythm. |
| 1.3 – 1.5 | 🟠 High Exertion | Functional Overreaching. A significant breakthrough attempt. Monitor closely; follow with a dedicated recovery week. |
| > 1.5 | 🔴 Overreaching | Danger Zone. Weekly load increased too fast (>150% of your long-term average). Rest or reduce training volume immediately. |
| < 0.8 | 🔵 Recovery | Detraining / Recovery. Recent load is well below your habitual level. Good after a major race, but long-term maintenance causes detraining. |
To maintain your ACWR within the productive sweet spot, balance your weekly volume using an 80/20 Polarized Training Structure.
The current version of Apex Run calculates training load based on distance. Short high-intensity runs (like track intervals) may be slightly underestimated. Heart-rate-based load (TRIMP) is planned for a future app version.
Frequently Asked Questions#
What is acute load in running?#
Acute Load is the total volume and physical stress accumulated in your running over the most recent 7-day period. It represents your short-term fatigue. Comparing acute load to your 28-day Chronic Load yields the Acute:Chronic Workload Ratio (ACWR), which accurately predicts injury risk.
What is Acute:Chronic Workload Ratio (ACWR)?#
ACWR divides your short-term 7-day fatigue load by your 28-day chronic fitness baseline. It evaluates whether your training load is increasing at a safe pace.
What is the optimal ACWR range for runners?#
The safe “sweet spot” ACWR range is 0.8 to 1.3. Ratios above 1.5 significantly increase injury risk.
What should I do if my ACWR enters the danger zone (> 1.5)?#
Reduce your weekly running volume and intensity immediately for 5-7 days to allow your body to absorb cumulative fatigue.
Related Tools & Guides#
- Heart Rate Zones — 5-zone HR model, LTHR, and calculation methods.
- 80/20 Training Structure — How to balance your training load across intensity levels.
- Performance Metrics — VO2 Max, Running Power, GAP, EF, and PSI.
- Running Form Metrics — Cadence, stride length, ground contact time, and other technique measures.
References & Further Reading#
- Gabbett, Tim J. (2016). “The training—injury prevention paradox: should athletes be training smarter and harder?” British Journal of Sports Medicine, 50(5), 273-280. PubMed ID: 26758673
The seminal paper establishing the Acute:Chronic Workload Ratio (ACWR) and the 0.8–1.3 sweet spot.