Warm-up, pre-main, main set and cool-down — what each phase does, what the science says, and what to cut when time is short.
Most athletes judge a workout by its main set. The intervals are what show up in the file, what gets shared with training partners, and what feels like the work. But the minutes before and after the main set decide how much you get out of it — and when life squeezes your training window, they're also the first place people cut, usually in the wrong order.
Every well-built session has four parts: warm-up, pre-main, main set and cool-down. Each has a specific job. Understanding those jobs tells you what to protect and what to trim when you have 40 minutes instead of 75.
Intensities below use the CEC zone system: bike as a percentage of FTP, run anchored to threshold (LT2) pace, around 5K pace, and swim anchored to Critical Swim Speed (CSS).
Quick reference
The four phases at a glance
- Warm-up — Raise: temperature, blood flow and breathing come up.
- Pre-main — Prime: rehearse the intensity and movement of the main set.
- Main set — Perform: deliver the training stimulus the session was written for.
- Cool-down — Return: bring the system back toward baseline.
1. Warm-up: raise
The warm-up's job is to raise muscle and core temperature, increase blood flow to working muscles, and bring your heart and lungs up to speed before you ask them for real work. Active warm-ups — easy swimming, riding or jogging — create bigger cardiovascular and metabolic changes than passive options like a hot shower, and they're the practical choice for nearly everyone.
Its effects fall into two groups:
• Temperature-related: faster nerve signaling, faster metabolic reactions, easier release of oxygen from hemoglobin and myoglobin, and less stiffness in muscles and joints.
• Non-temperature-related: more blood flow to working muscles, a higher baseline oxygen uptake, a short-term boost in muscle performance, and the mental side of feeling ready.
That short-term boost is often called post-activation potentiation (PAP), but the research has moved on. Classic PAP is a lab-measured twitch effect that fades within about 30 seconds. The performance boost athletes actually feel minutes later is now called post-activation performance enhancement (PAPE), and it appears to be driven partly by muscle temperature and activation (Blazevich & Babault, 2019).
One claim to be careful with is injury prevention. A 2024 review of 300 stretching trials found only five that measured injuries at all, and they did not support stretching as injury protection (Afonso et al., 2024). The same research group argued in 2026 that we still lack the study designs to say confidently whether warm-ups reduce injury risk (Afonso et al., 2026). Warm up because it makes the session better — not because a few leg swings make you bulletproof.
Short on time?
Compress it, don't skip it. Keep 5–10 minutes of progressive easy work in the session's own sport. Foam rolling and static stretching go first.
2. Pre-main: prime
The pre-main is the most skipped part of a session and the most underrated. While not all sessions have a Pre-main set, those that do its job is to rehearse the specific intensity, movement pattern and skill the main set will demand, so your first interval is a quality interval.
It works on two fronts:
• Metabolic priming: a short bout of moderately hard work speeds up how quickly your aerobic system responds when the main set starts. Researchers first described this "priming effect" in 1996, and the most consistent benefits come from heavy, below-threshold efforts rather than all-out ones (Goulding et al., 2023).
• Neuromuscular and skill priming: drills, strides, build 25s and 50s in the pool, and high-cadence spin-ups on the bike sharpen coordination and contribute to the PAPE effect.
More is not better here. Go too hard, or start the main set too soon after a hard primer, and you spend W′ — your limited reserve of work above critical power — before the main set begins. The same review found that severe priming efforts followed by short recoveries can reduce performance (Goulding et al., 2023). Keep primers at or just below threshold, and give yourself a few easy minutes before rep one.
Short on time?
Cut the drill volume, but keep 2–3 short efforts at main-set intensity. That's the minimum effective dose, and it protects the quality of everything that follows.
3. Main set: perform
The main set is where the training stimulus lives — threshold, VO2max, tempo or aerobic endurance. It's the reason the session exists, and it's where your zone targets and weekly intensity distribution actually happen.
This is also where the first two phases pay off. When the warm-up and pre-main are done well, you hit target power, pace or CSS from the first rep. When they're skipped, the first rep or two quietly become an expensive extra warm-up.
Short on time?
Protect it. Cut reps, not intensity, and keep the recoveries between reps full. Four quality intervals beat five rushed ones.
4. Cool-down: return
The cool-down's job is to bring heart rate and breathing back toward baseline gradually and give you a mental transition out of the session.
The evidence is more modest than most athletes assume. The most comprehensive review on the topic found active cool-downs do little for same-day or next-day performance and don't appear to prevent injuries (Van Hooren & Peake, 2018). They clear lactate from the blood faster — though not necessarily from the muscle — and may help the heart and lungs recover sooner. The idea that you need a cool-down to "flush lactate" from your legs is a myth.
The same review noted that a long active cool-down may slow glycogen refilling. If you're short on time after a hard session, a recovery snack and fluids will do more for tomorrow than an extra 15 minutes of easy spinning.
Short on time?
Cut it first. After hard sessions, keep 3–5 minutes of easy, low-impact movement so you don't finish lightheaded. After an easy aerobic session, it's fine to skip it entirely.
The trim order
When a session has to shrink, cut in this order:
1. Cut first: extended cool-down and static stretching.
2. Cut second: pre-main drill volume — keep the intensity openers.
3. Compress, don't cut: the warm-up, down to a 5–10 minute minimum.
4. Protect: the main set's intensity and recoveries, trimming reps if needed.
Sample sessions: swim, bike and run
Here's what that looks like in practice. Each session shows the full version next to a time-crunched version that follows the trim order.
Swim: CSS session
About 2,600 yd full · about 1,600 yd time-crunched
Coach's note: In the pool, the pre-main does double duty: it primes the aerobic system and locks in stroke mechanics before fatigue sets in. That makes drills harder to drop than on the bike or run. If you're short on time, keep one 50 of drill and cut the rest.
Bike: VO2max session
About 75 min full · about 45 min time-crunched
Coach's note: This is the clearest example of priming. The 3-minute Z4 effort is hard enough to prime the aerobic system without draining W′, and the 5 easy minutes afterward let you start rep one ready rather than already tired. Keep the primer below threshold.
Run: threshold session
About 65 min full · about 40 min time-crunched
Coach's note: Running carries the most impact of the three sports, so cool-downs should stay low-impact — and walking counts. Strides are worth protecting even when you cut drills; they're the run's version of the bike spin-ups.
The bottom line
The trim order is the same in every discipline. The cool-down shrinks first. The pre-main loses volume but keeps its intensity. The warm-up gets compressed, never dropped. And the main set keeps its intensity and recoveries, even if it loses a rep.
A shorter session built this way still delivers the stimulus you planned. A shorter session built by skipping the warm-up and hoping for the best usually doesn't. Every detail intentional, every step backed by science.
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1. Afonso J, Andrade R, Rocha-Rodrigues S, et al. What we do not know about stretching in healthy athletes: a scoping review with evidence gap map from 300 trials. Sports Medicine. 2024;54(6):1517–1551. https://doi.org/10.1007/s40279-024-02002-7
2. Afonso J, Warneke K, Lohmann LH, Pizzari T, Boullosa D. Does the warmup really reduce injury risk? Why we need new approaches to confidently answer this question. Journal of Science and Medicine in Sport. 2026;29(3):259–261. https://doi.org/10.1016/j.jsams.2025.09.013
3. Blazevich AJ, Babault N. Post-activation potentiation versus post-activation performance enhancement in humans: historical perspective, underlying mechanisms, and current issues. Frontiers in Physiology. 2019;10:1359. https://doi.org/10.3389/fphys.2019.01359
4. Goulding RP, Burnley M, Wüst RCI. How priming exercise affects oxygen uptake kinetics: from underpinning mechanisms to endurance performance. Sports Medicine. 2023;53(5):959–976. https://doi.org/10.1007/s40279-023-01832-1
5. Van Hooren B, Peake JM. Do we need a cool-down after exercise? A narrative review of the psychophysiological effects and the effects on performance, injuries and the long-term adaptive response. Sports Medicine. 2018;48(7):1575–1595. https://doi.org/10.1007/s40279-018-0916-2
