Triathlon

Move · High-Intensity · Movement, Typed Supps

The legs coming off the bike have spent an hour pushing without ever absorbing an impact, and running asks them to do the opposite immediately.

Stage by stage

Across the week (Concurrent training load): Three disciplines stacked in one week make total load, rather than any single session, the main driver of adaptation and risk.
In transition (Concentric to eccentric switch): Legs move from impact-free pushing to rapid eccentric loading within seconds, alongside a redistribution of blood flow.
First ten minutes (Running economy impaired): Economy is measurably worse early in a run off the bike, which is exactly the deficit brick sessions reduce.
Months later (Cumulative overuse risk): Achilles, patellar and iliotibial band problems cluster where running volume rises on top of already high cycling load.

Muscles trained

Primary: quads, hamstrings, shoulders, heart, lungs
Secondary: calves, glutes, lower back

Intensity

11 METs (Running, 7 mph (8.5 min/mile)).

Time to effect

Weeks: Swim-to-bike and bike-to-run transitions get noticeably smoother within a few weeks of practicing them together, and that first rubbery mile off the bike starts to feel less jarring.
Months: A genuine aerobic base across all three disciplines, along with the race-pace endurance to hold effort through a full event, typically builds over several months of overlapping training.

Related supplements

Common myth

“Triathlon training is just three separate sports stacked together.” In reality: General aerobic fitness transfers well across swimming, cycling and running, but each discipline has its own technical skill and specific muscular demands, and treating them as interchangeable is a common way triathletes underprepare for one leg of the race.