[CALCULATOR]
Are you building, or about to get hurt?
[WHAT THIS DOES]
Divide this week’s endurance minutes by the average of the previous four weeks. Between 0.8 and 1.3 is a productive build. Past about 1.5 the injury-risk curve turns sharply upward, and for a hybrid athlete a spike week also competes directly with lifting recovery.
What the ratio is measuring
Acute load is what you did recently. Chronic load is what your body is adapted to. The ratio between them is a crude but genuinely useful proxy for whether a given week is a stimulus your tissues are prepared for or a shock they are not.
The window that shows up repeatedly in the literature is roughly 0.8 to 1.3. Below it you are detraining or tapering. Inside it you are building. Above about 1.5 the injury-risk curve turns sharply upward, and it turns for connective tissue in particular — tendons and bone adapt on a slower timescale than muscle and cardiovascular fitness do, which is precisely why the athlete feels fine right up until they do not.
Why minutes, and not something cleverer
There are better load metrics. Training Stress Score, session RPE times duration, and cumulative TRIMP all capture intensity in a way that raw minutes cannot.
Base uses minutes anyway, on purpose. It needs no power meter, no heart-rate strap and no lab test, and the thing it is being used to catch is a large sudden jump, which is coarse enough that a coarse measure finds it. A metric that requires equipment you might not own, on every session, is a metric with holes in it — and a load history with holes is worse than a crude one that is complete.
The hybrid-specific problem
Every published version of this ratio was developed for single-sport athletes. For a hybrid athlete there is a second effect that no endurance-only model captures:
A spike week in endurance does not only raise your injury risk. It draws down the same recovery budget your lifting is spending.
The interference between concurrent strength and endurance training is much smaller than folklore claims — three recent meta-analyses found no significant compromise to strength or hypertrophy overall. But the moderators are specific, and volume is one of them: moderate endurance frequency at two to four sessions a week is safe, while high endurance volume combined with frequent lifting raises the risk.
So the ratio is doing double duty here. It is asking "will this week hurt you" and "will this week cost you the squat session on Thursday" at the same time, and a reading above 1.5 is a yes to both.
What a build actually looks like
| Week | Minutes | Ratio | Note |
|---|---|---|---|
| 1 | 200 | — | Baseline |
| 2 | 220 | 1.10 | Building |
| 3 | 245 | 1.17 | Building |
| 4 | 150 | 0.68 | Deliberate down week |
| 5 | 260 | 1.24 | Building from a recovered base |
Note week four. The down week is what makes week five's larger absolute number a lower relative shock — and it is the week most people skip, because nothing feels wrong yet.
What to do next
Add up your endurance minutes for the last five weeks. If this week is more than 1.3 times the four-week average, the useful question is not whether you can handle it. It is what you are going to move.
Questions
What is a safe weekly increase in running volume?
Keep this week under about 1.3 times the average of the previous four weeks. That is a more useful rule than the familiar "10% per week", because it is relative to what you are actually adapted to and it survives a down week — 10% compounding from a rest week under-loads you badly.
What is the acute-to-chronic workload ratio?
This week’s training load divided by the average of recent weeks, used to catch a load spike before it becomes an injury. Roughly 0.8 to 1.3 is a productive build; past about 1.5 injury risk climbs sharply, because connective tissue adapts more slowly than muscle and cardiovascular fitness do.
Does adding running affect my lifting recovery?
A steady moderate volume, largely no — the concurrent-training meta-analyses find no significant compromise to strength or hypertrophy at two to four endurance sessions a week separated from lifting. A sudden spike, yes. High endurance volume combined with frequent lifting is one of the specific conditions under which interference does show up.
Is a low ratio bad?
No. Below 0.8 is reported as neutral rather than as a warning, because a taper week and a rest week both live there and both are deliberate. It only matters if it persists for several weeks without intent, which is detraining rather than recovery.