How long an adaptation lingers
A training residual is how long a developed quality persists after dedicated training for it stops. Different adaptations fade at different rates, which is central to block periodization's logic of training qualities in sequence. Aerobic endurance and maximal strength tend to have the longest residuals, often described as roughly thirty days plus or minus, while speed and anaerobic qualities decay faster, on the order of days.
These figures, popularized by sport scientist Vladimir Issurin, are approximate population averages rather than precise guarantees for any individual.
Why the differences matter
Knowing that a quality lingers lets a program develop it in one block and let it coast while attention shifts elsewhere, returning before it fades meaningfully. Short-residual qualities like sprint speed must be touched more frequently or trained close to competition because they slip away quickly.
Reading the numbers cautiously
Residual durations vary with training history, age, and how much the quality was developed in the first place, so the published ranges are planning guides, not exact timers. This is general educational information about training theory, not medical advice.