Chris Farhood
cced0ea6b8
The skill had mtb-xco-demands.md but road/TT demands were only diffused through the general docs — an asymmetry given the balanced MTB+road scope. Add two dedicated, self-contained demand profiles (kept separate because mass-start racing and TT differ as much as XCO differs from marathon MTB): - references/road-racing-demands.md: stochastic power profile (Vogt 2007, Ebert 2005/2006, Sanders/van Erp 2021), drafting economics (Blocken 2018), fatigued finishing sprint (Menaspà 2013/2015, Etxebarria 2019), durability as a success determinant (van Erp/Sanders/Lamberts 2021); power governs, HR unreliable (intermittent) — mirrors the MTB doc. - references/tt-demands.md: aero drag dominance + CdA as the top lever (Crouch 2017, Martin 1998, García-López 2008), critical power as predictor (Smith 1999), even-vs-variable pacing (Swain 1997, Atkinson 2007), long-TT durability (Maunder 2021); HR more usable than MTB but still secondary. All new quantitative claims carry verified PMIDs/DOIs (verified via PubMed/ CrossRef); citations.md gains Road-racing and Time-trial sections. Honesty flags: Blocken 2018 and Martin 1998 have no PMID (DOI only); the '~90% aero' soundbite (Kyle & Burke 1984) is unverifiable and marked approximate; criterium-specific literature flagged as a gap; no unverified HR-reliability citation added (TT HR defers to data-confounds.md). Router (SKILL.md) and README layout updated with both docs. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01TqrhBhC3GEcKyaw8RTk8G6
89 lines
5.5 KiB
Markdown
89 lines
5.5 KiB
Markdown
# Time-trial (TT) demands
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**Load this doc when:** planning for an individual time trial, prologue, or any sustained
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solo effort against the clock (road TT, triathlon bike leg, "the race of truth").
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**Data/knowledge split:** MCP gives you power, critical-power/FTP, and the ride streams. This doc
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explains the *demand profile* — what actually limits a TT and how to pace and prepare for it.
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**Contrast with the other demand docs:** a TT is the near-opposite of `mtb-xco-demands.md` and
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`road-racing-demands.md`. Those are intermittent, stochastic, and tactical; a TT is **steady,
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solo, and self-paced** — a quasi-time-invariant effort where physiology, aerodynamics, and pacing
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discipline decide the result, not positioning or surges.
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---
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## What limits a TT: sustainable power vs aerodynamic drag
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TT performance is a tug-of-war between the **power you can sustain** and the **power the air steals
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back**. Both matter, and the second is bigger than most riders assume.
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- **Aerodynamic drag is the dominant resistance at TT speeds.** At racing speeds the rider's body
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is roughly **~80% of total system drag**, and overcoming air resistance consumes the large
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majority of power output (Crouch et al. 2017, *Sports Eng* 20(2):81–110;
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DOI 10.1007/s12283-017-0234-1). The classic validated power model that decomposes road cycling
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power into aerodynamic, rolling, gravitational, bearing, and inertial terms — and shows aero
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dominates on the flat — is Martin et al. 1998 (*J Appl Biomech* 14(3):276–291;
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DOI 10.1123/jab.14.3.276; **no PMID — cite by DOI**).
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- *(The often-quoted "~90% of power goes to aero at 40 km/h" figure traces to Kyle & Burke 1984,
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a trade-magazine article not indexed in PubMed — treat the exact percentage as approximate;
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the verifiable anchors are Crouch 2017 and Martin 1998. See `citations.md`.)*
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- **Reducing aerodynamic drag area (CdA) is the single largest performance lever.** Wind-tunnel-
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guided position changes reduced professional cyclists' drag by **~14%**, with corresponding TT
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time savings (García-López et al. 2008, *J Sports Sci* 26(3):277–286; PMID 17943597;
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DOI 10.1080/02640410701501697). Position first, then equipment. A watt saved on the body is often
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cheaper than a watt gained in the legs.
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## The physiological determinant: critical power / threshold
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A TT is run at or near the highest power sustainable for its duration, so the key predictor is
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**critical power / functional threshold**, not peak or anaerobic power.
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- Critical power correlated with 17-km and 40-km TT performance at **r = −0.77 to −0.91** — more
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strongly than ventilatory threshold or VO2max (Smith, Dangelmaier & Hill 1999, *Int J Sports Med*
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20(6):374–378; PMID 10496116; DOI 10.1055/s-2007-971147). *(Negative r: higher power = faster
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time.)*
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- **Training implication:** the engine that matters is threshold/critical power and the fraction of
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VO2max you can hold for the event duration. Build it with threshold and VO2max work
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(`vo2max-intervals.md`) on a high aerobic base (`periodization.md`).
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## Pacing: even power on the flat, variable on terrain/wind
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- On a **flat, windless** course, **even / constant power is near-optimal** — resist the urge to
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surge (Atkinson, Peacock & Passfield 2007, *J Sports Sci* 25(9):1001–1009; PMID 17497402;
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DOI 10.1080/02640410600944709).
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- On **hilly or windy** courses, **vary power with the terrain**: push *above* target into climbs
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and headwinds, ease *below* on descents and tailwinds. Because time is lost disproportionately
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where you're slow, spending extra effort where it buys the most speed nets a faster overall time
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than constant power (Swain 1997, *Med Sci Sports Exerc* 29(8):1104–1108; PMID 9268969;
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DOI 10.1097/00005768-199708000-00017; refined by Atkinson et al. 2007 above).
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- **Prescribe pacing from power**, not feel — the whole point of a TT is holding a target the
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cardiovascular system can't self-regulate under adrenaline.
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## Durability matters for long TTs
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For 40 km and up (and for TTs late in a stage race), **fatigue resistance** decides whether your
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threshold holds to the line. Durability is the resistance to deterioration of threshold/economy/
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power over prolonged exercise (Maunder et al. 2021, *Sports Med* 51(8):1619–1628; PMID 33886100;
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DOI 10.1007/s40279-021-01459-0). Train it via `durability.md`; for a long TT, your *fatigued*
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threshold is the one that counts.
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## HR in a TT: more usable than MTB, still secondary
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Unlike the intermittent efforts in `mtb-xco-demands.md`, a TT is steady-state, so HR tracks effort
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more faithfully and **aerobic decoupling is a valid durability signal** on a TT-pace effort. But:
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- HR still **lags the first minutes** (don't chase it off the start ramp) and **drifts upward**
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from cardiac drift, heat, and dehydration over a long TT.
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- **Pace by power; use HR as a secondary check**, and screen the usual confounds
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(`data-confounds.md`) before trusting a decoupling or drift number.
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## Practical checklist (pull data from MCP, reason here)
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- [ ] **CdA** addressed — position dialed before equipment (García-López 2008)
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- [ ] **Target power** set from current critical power / FTP for the event duration (Smith 1999)
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- [ ] **Pacing plan** matched to course: even on flat, terrain-variable on hills/wind (Swain 1997;
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Atkinson 2007) — expressed in power, not HR
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- [ ] **Durability** trained if the TT is long or late in a stage race (`durability.md`)
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- [ ] **Warm-up** appropriate to duration (short TT = fuller prime; long TT = lighter)
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