why

A command that explains the research behind a training choice, such as interval workouts, tapering, recovery, or nutrition.

In plain words
What is it for?
Use it to investigate training concepts, workout choices, performance problems, recovery, injury prevention, and race preparation.
Why use it?
It turns expert training information into an explanation of why a decision may help and how it relates to the athlete’s situation.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/rlacombe/switchback-running/why
Any agent
npx skills add rlacombe/switchback-running --skill why
Clone the repo
git clone --depth 1 https://github.com/rlacombe/switchback-running

Made for: Claude Code, Codex.

Per session 14 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 584 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00014 $0.00584
Opus 5 $0.00007 $0.00292
Sonnet 5 $0.00003 $0.00117
Haiku 4.5 $0.00001 $0.00058

Measured 2d ago against content hash c9e7b4db45a2, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

why scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/why/SKILL.md · 57 lines

How it starts

The opening of the file, as written. The whole thing — 57 lines — stays where its author put it; the contents beside it link to each section on GitHub.

/why — Training Science Explained

The athlete asks about any training concept, workout choice, or decision. Read the relevant knowledge base files, present expert positions, and connect the science to the athlete's situation.

Examples:

  • /why VO2max intervals
  • /why am I running so slow on easy days
  • /why weighted hiking for muscular endurance
  • /why reverse periodization
  • /why should I taper two weeks out

Step 1: Identify the topic

Map the athlete's question to the relevant knowledge base file(s) in knowledge/:

  • aerobic-base.md, volume-progression.md, workout-types.md, muscular-endurance.md
  • strength-training.md, periodization.md, long-runs.md, taper.md
  • race-execution.md, recovery-overtraining.md, heat-altitude.md, mental-performance.md
  • nutrition.md, downhill-training.md, injury-prevention.md, age-gender.md

Read the relevant file(s). If the question spans multiple topics, read all of them.

Step 2: Gather athlete context (if relevant)

If the question relates to the athlete's current training, use MCP tools to personalize the explanation:

  • Zones are cached in athlete/profile.md — use those to reference actual numbers
  • Fitness endpoint — their current CTL/ATL/TSB
  • Activities or events endpoint — recent training context

Skip this step if the question is purely conceptual (e.g., "what is ADS?").

Step 3: Explain

Structure the response as:

  1. The concept — What it is and why it matters, in plain language
  2. What the experts say — Present each expert's position with their reasoning:
    • Scott Johnston's view and logic
    • Jason Koop's view and logic
    • Steve Magness's view and logic
  3. Where they agree — Common ground
  4. Where they disagree — The tension, presented fairly with both sides
  5. What this means for you — Connect to the athlete's actual data, goals, and current training phase. If approaches conflict, explain which might fit their situation and why — then let them choose.

Guidelines

  • Lead with the science, not opinions
  • Use the athlete's actual zones and data when available — "your AeT is at 145bpm" is better than "your aerobic threshold"
  • When experts disagree, present both sides honestly. Don't pick a winner unless the athlete's data clearly favors one approach
  • Keep it conversational, not like a textbook
  • Include key quotes from the experts — they carry weight
  • If the athlete's question reveals a misconception, address it directly but respectfully

Read the full file on GitHub · 57 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 57 lines · 14 tokens per session scan A c9e7b4db45a2

Subscribe to this mod's changes

why is a skill published in the GitHub repository rlacombe/switchback-running (11 stars, last pushed 7d ago), licensed MIT. It adds 14 tokens to every session and 584 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

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