Training plan after a sick week: what your plan should actually do to itself

What detrains in a week and what does not

Inside 5 to 10 days off, the rider has lost cardiovascular adaptations and almost nothing else. Coyle and colleagues' classic detraining time-course study [Coyle et al. 1984] documented a 7% drop in VO2max across the first 21 days of inactivity in trained subjects, stabilizing around 16% below baseline by day 56. The peripheral adaptations — mitochondrial density, capillary density, fat oxidation capacity — barely move in a week.

The mechanism is almost entirely cardiovascular. Mujika and Padilla's foundational short-term detraining review [Mujika & Padilla 2000] documents that VO2max decline inside the 4-week window is driven primarily by a rapid reduction in blood volume and stroke volume, with maximal cardiac output dropping accordingly. Recently acquired gains drift fastest — a rider three weeks into a sweet-spot block has more to lose proportionally than a rider in week ten of a long base. The same cardiovascular adaptations rebuild quickly when load resumes, often within 2 to 3 weeks of structured riding. The plan does not need to mourn the missed block; it needs to hand the rider back a week that respects the temporarily lower ceiling.

The corollary is that fitness did not vanish. The chronic training load number — CTL in the Coggan and Allen framework [Allen et al. 2019] — drifts down by roughly 5 to 8 points across a 7-day off-week depending on starting CTL, but the underlying aerobic engine is largely intact. This is what the plan has to operate on: a real but modest decay, concentrated in the cardiovascular layer, with a 2 to 3 week rebuild horizon.

Skip versus compress: the most common amateur-coaching error

A static plan, faced with a missed week, compresses. The next week starts at 100% of the original target and the missed peak block is squeezed into fewer remaining weeks at the same or higher weekly intensity. This is the wrong answer in almost every case. The right move is to skip the missed work, accept the phase has shortened, and rebuild forward — not backward.

The compression failure is operationally a chronic-load ramp violation. Hulin and colleagues' acute:chronic workload framework [Hulin et al. 2016] places elevated injury risk above ratios near 1.5, with high-chronic-load athletes plus a two-week ratio of 1.54 reaching 28.6% injury risk in the cohort. A normal-volume week dropped onto a 7-day-decayed chronic load lands in that danger band by construction; a compressed week with extra intensity to make up missed work lands well outside it. Foster's training-monotony work [Foster 1998] reinforces the point: across his 25-athlete cohort, the strongest behavioral predictor of next-cycle illness was the combination of high load and low daily-load variance, exactly what stacking made-up sessions produces.

This is the implementation-level detail behind sign three from the sibling spoke on whether your plan is actually adapting: a sick week should make the plan restructure, not shrink. The ECSS and ACSM joint consensus on overtraining [Meeusen 2013] is explicit that resuming training without a graded reintroduction is a leading cause of non-functional overreaching — the failure mode amateurs most often produce by compressing out of guilt. The right behavior is asymmetric: skip the missed key session entirely, downgrade and shift if it was endurance volume, and treat the next week as the restart, not the catch-up.

What an adaptive plan should change: the four moves

A genuinely adaptive plan makes four specific moves when a 5 to 10 day illness gap closes. The chronic-load ramp resets to the new lower CTL. The first week back caps intensity time at 60 to 70% of pre-break load. The next deload moves up by one cycle. And the macro arc gets re-anchored to the new dates — not by compressing what got missed, but by accepting the phase is one week shorter.

The first two moves are the week-of mechanics. Allen and Coggan's CTL framework [Allen et al. 2019] provides the math: keep weekly TSS climbing inside the safe ramp band of roughly 4 to 7 TSS/day per week starting from the post-illness CTL number, not the pre-break one. The first week back is endurance-heavy by design — most of the missed cardiovascular adaptation rebuilds with low-intensity volume, not stacked threshold work. The graded-reintroduction principle the Meeusen consensus [Meeusen 2013] is built on is explicit on this point: resuming at pre-break load is the leading mechanism behind non-functional overreaching. Foster's monotony rule [Foster 1998] should govern the daily-load variance: the rebuilt week needs at least one genuine recovery day, ideally two, even if the original plan only had one.

Move three is structural. If the next deload was three weeks out, it now lands two weeks out — the post-illness week is in load terms already half a deload, and adding another high-load block before recovery violates the periodization invariant the build cycle was structured around. The build-block rhythm [Allen et al. 2019] is 2 to 4 weeks of progressive load, one week of recovery, repeat. A missed mid-block week shifts the rhythm one cycle, not zero. Move four is the macro-arc decision, which is the next section.

When the goal event has to move — and when it does not

The honest rule is mathematical: if more than six weeks separate the rider's first ride back from the event date, the goal almost certainly does not move. If fewer than three weeks separate them and the event is A-priority, the goal usually does. The middle band of three to six weeks is the judgment zone, and the answer depends on what phase the missed week was in.

Six-plus weeks out, a 5 to 10 day gap is absorbable. The post-illness CTL drop of 5 to 8 points is roughly one normal build block of recovery; the rider can rebuild, hit the planned peak, and taper into the date with the standard Bosquet protocol — 41 to 60% volume reduction over two weeks while preserving intensity [Bosquet et al. 2007]. The macro arc compresses by one week, the build runs one cycle shorter, the taper math holds. Inside three weeks, the math collapses. The taper window is the rider's cardiovascular-rebuild window, and the two cannot share the same days. An A-priority event inside that window either gets pushed back, downgraded to B priority with reduced expectations, or attended for participation rather than performance.

The middle band is where the missed phase matters. If the gap fell during a base block, the phase can usually still finish on time — the missed adaptations rebuild quickly. If the gap fell during a peak or specificity block, where the targeted stimulus is dose-response sharp, the plan should either extend the phase by a week or accept a smaller peak. AdaptCycling treats the goal-event date as a movable parameter inside the restructure flow — when the rider marks an illness, the engine reads the remaining weeks, the affected phase, and the priority level, then either holds the date or proposes a move with the math attached. This is what the parent pillar on adaptive cycling training plans means by life-adaptive: the plan absorbs the gap and reshapes the arc instead of asking the rider to be their own coach in the worst possible week. The single-day missed-workout case follows a different load-decay model — closer to a redistribution problem than a rebuild — and the sibling spoke on missed-key-workout-vs-missed-recovery covers it.

Quick answers

Sources cited in this guide

1. 01
   Coyle et al. 1984. Time course of loss of adaptations after stopping prolonged intense endurance training. Journal of Applied Physiology.
2. 02
   Mujika & Padilla 2000. Detraining: Loss of Training-Induced Physiological and Performance Adaptations. Part I: Short Term Insufficient Training Stimulus. Sports Medicine.
3. 03
   Allen et al. 2019. Training and Racing with a Power Meter (3rd ed.). VeloPress.
4. 04
   Hulin et al. 2016. The acute:chronic workload ratio predicts injury: high chronic workload may decrease injury risk in elite rugby league players. British Journal of Sports Medicine.
5. 05
   Foster 1998. Monitoring training in athletes with reference to overtraining syndrome. Medicine & Science in Sports & Exercise.
6. 06
   Meeusen 2013. Prevention, diagnosis and treatment of the overtraining syndrome: Joint consensus statement of the European College of Sport Science and the American College of Sports Medicine. European Journal of Sport Science.
7. 07
   Bosquet et al. 2007. Effects of tapering on performance: a meta-analysis. Medicine & Science in Sports & Exercise.

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