The cycle-to-run transition: running is metabolically "compromised" after prior locomotion
The transition-fatigue effect
Key Findings
Running right after cycling raises the energy cost of running by 1.6–11.6% vs control running; the size of the increase reflects triathlete ability level (better athletes less compromised).
Transition running → hyperventilation, increased HR, decreased pulmonary compliance and exercise-induced hypoxaemia; proposed drivers = intensity, ventilatory-muscle fatigue, dehydration, muscle-fibre damage, shift toward fat oxidation, glycogen depletion after the 40 km cycle.
Most biomechanical parameters unchanged; the most significant kinematic change is a more forward-leaning trunk. Sensorimotor perturbation from the posture change may also alter running pattern and economy.
How the preceding cycle was ridden (steady vs stochastic power, drafting vs non-drafting) is likely to influence how fast the athlete adjusts to running; how much 10 km speed actually drops in competition still needs investigation.
Practical Application
In triathletes, running immediately after cycling costs 1.6–11.6% more energy than fresh running, and the better the athlete the smaller the penalty — the penalty depends on ability, not a fixed tax (whether it can be trained down is inference; the review does not test training).
Inference, not tested: program "compromised-running" transitions — run a segment immediately after a sled push/pull, lunges, or wall-balls — the HYROX analogue of triathlon brick sessions. The paper studies cycle→run, not station→run.
Expect and pace for a real per-km penalty off heavy stations; don't set run splits from fresh-run pace.
Limitations
Narrative review; cycling→running not station→running (analogy); HYROX-station compromise magnitude unquantified; data from competitive triathletes.
How this entry was checked and changed
Why this level
regraded 2026-09-27 from C: narrative review without systematic method (rubric C+); the HYROX transfer is adjacency, stated on the Applicability line, not in the level
Content correction 2026-09-27
Lead line "run 400 m–1 km immediately after a sled push..." was house programming with distances not in the paper -> lead is now the review's finding (1.6–11.6% energy-cost increase, scaling with ability); the HYROX brick prescription is labelled inference without distances.
Level C -> C+ per rubric (narrative review); Tier "mixed" -> Tier 2-4 (junior to elite triathletes).
Resync 2026-09-28: Called running off a prior load a 'trainable' skill; the review only shows the penalty scales with ability -> trainability labelled inference.