Learn Hardcore German: Die Trainerin erklärt, die Verletzungsgefahr beim Bergsteigen sei gering, wenn alle Regeln beachtet werden. - The female trainer explains the risk of injury in mountaineering is low when all the rules are followed.

The form sei is the subjunctive I (Konjunktiv I) of sein and is typically used for reported (indirect) speech in written and formal German.

Think of the direct version first:

Direct speech:
Die Trainerin erklärt: „Die Verletzungsgefahr beim Bergsteigen ist gering, wenn alle Regeln beachtet werden.“

When this is turned into indirect speech, German often changes the verb into Konjunktiv I:

Indirect speech:
Die Trainerin erklärt, die Verletzungsgefahr beim Bergsteigen sei gering, wenn alle Regeln beachtet werden.

Using sei signals: “This is what she says; I (the narrator) am not necessarily confirming it as a fact, just reporting it.”
If you used ist, it would sound more like the narrator fully endorses the statement as objective fact, and it would be less clearly marked as reported speech — though in everyday spoken German, ist is actually quite common.

What grammatical form exactly is sei, and how is this mood used in German?

Sei is Konjunktiv I, 3rd person singular, present tense of sein.

Full Konjunktiv I of sein:

ich sei
du seiest
er/sie/es sei
wir seien
ihr seiet
sie seien

How Konjunktiv I is generally used:

Reported / indirect speech
- Er sagt, er habe keine Zeit.
  “He says he has no time.”
- Die Trainerin erklärt, die Verletzungsgefahr sei gering.
  “The trainer explains (that) the risk of injury is low.”
Less commonly in modern usage, it can appear in:
- Set phrases: Es sei denn (“unless”), Wie dem auch sei (“be that as it may”).
- Very formal or literary style, e.g. wishes or instructions, but that’s rarer now.

For most verbs, Konjunktiv I is formed from the stem of the infinitive + special endings:

machen → er mache
kommen → sie komme
haben → er habe

In modern spoken German, people often avoid Konjunktiv I and use dass + indicative instead. In written German (news, reports, academic texts), Konjunktiv I is still very common for neutral reporting.

Why is there a comma after erklärt but no dass?

This is a case of indirect speech without a conjunction (called an uneingeleiteter dass-Satz in German).

Logically, the sentence corresponds to:

Die Trainerin erklärt, dass die Verletzungsgefahr beim Bergsteigen gering sei, wenn alle Regeln beachtet werden.

In more formal German, especially with reporting verbs like erklären, sagen, berichten, the dass can be omitted, and then the clause keeps main-clause word order (verb in 2nd position):

with dass (subordinate clause, verb at the end):
…, dass die Verletzungsgefahr beim Bergsteigen gering sei, …
without dass (no conjunction, verb in 2nd position):
…, die Verletzungsgefahr beim Bergsteigen sei gering, …

So:

The comma indicates that a new clause starts (the content of what she explains).
The missing dass is stylistic. Leaving it out gives the sentence a somewhat formal, written, or journalistic flavor.

Could I rephrase this sentence without Konjunktiv or without this formal reported-speech style?

Yes. Several natural alternatives are possible, depending on what you want to emphasize.

Most common neutral style (with dass
- indicative):
Die Trainerin erklärt, dass die Verletzungsgefahr beim Bergsteigen gering ist, wenn alle Regeln beachtet werden.
– This is very normal in modern spoken and written German.
Colloquial spoken style (just saying the fact):
Die Verletzungsgefahr beim Bergsteigen ist gering, wenn alle Regeln beachtet werden, erklärt die Trainerin.
– Here you present the fact first and add erklärt die Trainerin like a tag.
Without any reporting at all (just the statement):
Die Verletzungsgefahr beim Bergsteigen ist gering, wenn alle Regeln beachtet werden.
– Now we don’t know who says this; it’s presented as the narrator’s own claim.
With man instead of passive in the condition:
Die Trainerin erklärt, dass die Verletzungsgefahr beim Bergsteigen gering ist, wenn man alle Regeln beachtet.

All of these are grammatically fine; they differ in formality and in how strongly you mark this as her statement versus a general fact.

What does beim Bergsteigen literally mean, and why is the verb turned into a noun?

Beim Bergsteigen literally means “while (doing) mountain climbing” or “during mountain climbing”.

Grammar:

beim = contraction of bei dem
- bei = preposition “at, by, during, while (doing sth)”
- dem = dative singular article (here for a neuter noun)
Bergsteigen is a nominalized infinitive:
- The verb bergsteigen (to climb mountains) is turned into a noun.
- As a noun, it is capitalized: das Bergsteigen.
- It behaves like a neuter singular noun.

So beim Bergsteigen = bei dem Bergsteigen = “during the activity of mountain climbing”.

This is a very common pattern in German, roughly equivalent to English -ing forms used as nouns:

beim Schwimmen – while swimming
beim Lesen – while reading
beim Kochen – while cooking

Compare:

beim Bergsteigen – while mountain climbing
im Gebirge – in the mountains (location, not necessarily climbing)

So the verb becomes a noun to let you treat it like a thing/activity you can put a preposition in front of.

Why is beachtet werden used instead of something like man beachtet die Regeln?

Beachtet werden is the present passive (Vorgangspassiv) of beachten.

Active: Man beachtet alle Regeln.
“One/people/you observe all the rules.”
Passive: Alle Regeln werden beachtet.
“All the rules are observed.”

In the sentence:

… wenn alle Regeln beachtet werden.
= “if all the rules are observed.”

Reasons for using the passive here:

Focus on the rules, not on the people.
The important part is that the rules are followed; who exactly follows them is not important.
Typical style with rules, regulations, and safety statements.
German often uses passive for such general statements:
- Wenn die Anweisungen befolgt werden, …
- Wenn die Sicherheitsvorschriften eingehalten werden, …

You could say:

… wenn man alle Regeln beachtet.

That is also correct and common, especially in spoken German. It just shifts the focus slightly more to the (unspecified) people (“you/one”) who follow the rules.

Why does the verb go at the end in wenn alle Regeln beachtet werden?

Because wenn introduces a subordinate clause, and in standard German subordinate clauses have the finite verb at the end (verb-final order).

Structure:

wenn = subordinating conjunction (“if/when”)
alle Regeln = subject
beachtet werden = verb complex, with finite auxiliary werden last

So:

…, wenn alle Regeln beachtet werden.

More examples:

Wenn es regnet, bleiben wir zu Hause.
Wenn du Zeit hast, ruf mich an.
Wenn das Problem gelöst ist, können wir gehen.

In contrast, main clauses or clauses without a subordinating conjunction typically have verb in 2nd position:

Alle Regeln werden beachtet. (main clause)
Die Verletzungsgefahr sei gering … (reported clause without dass → verb in 2nd position)

So in your sentence:

Die Trainerin erklärt, → main clause (verb 2nd: erklärt)
(dass) die Verletzungsgefahr … gering sei, → indirect speech clause, verb 2nd (sei) because no dass
wenn alle Regeln beachtet werden. → subordinate condition clause with wenn, verb at the end (werden)

Can I move beim Bergsteigen to another position in the sentence, and does that change the meaning?

Yes, you can move beim Bergsteigen quite freely; the basic meaning stays the same, only the emphasis changes slightly.

Some natural variants:

Original-style indirect speech:
- Die Trainerin erklärt, die Verletzungsgefahr beim Bergsteigen sei gering, wenn alle Regeln beachtet werden.
Emphasizing the activity first:
- Die Trainerin erklärt, beim Bergsteigen sei die Verletzungsgefahr gering, wenn alle Regeln beachtet werden.
- This puts more focus on beim Bergsteigen (“when it comes to mountain climbing, the risk is low if …”).
Neutral main-clause version:
- Beim Bergsteigen ist die Verletzungsgefahr gering, wenn alle Regeln beachtet werden, erklärt die Trainerin.
End position:
- Die Verletzungsgefahr ist gering, wenn alle Regeln beachtet werden, beim Bergsteigen.
  – This is possible but stylistically awkward; German usually doesn’t like such “trailing” prepositional phrases in formal writing.

So: you may front beim Bergsteigen or put it after the subject; both are fine. Just avoid overly clumsy end-heavy versions in careful writing.

What is the nuance of erklärt compared to sagt, meint, or behauptet here?

These verbs differ subtly in meaning and tone:

erklären = “to explain”
- Suggests that the speaker is providing reasons, context, or expertise.
- Die Trainerin erklärt, … implies she’s speaking as a professional, giving a reasoned statement.
sagen = “to say”
- Very neutral; no implication about expertise or truth.
- Die Trainerin sagt, die Verletzungsgefahr sei gering.
  Just reports what she says, nothing more.
meinen = “to think, to be of the opinion”
- Emphasizes it is her opinion, possibly subjective.
- Die Trainerin meint, die Verletzungsgefahr sei gering.
behaupten = “to claim, to assert”
- Often implies doubt or controversy: maybe others don’t agree, or it isn’t clearly proven.
- Die Trainerin behauptet, die Verletzungsgefahr sei gering.
  Sounds like the narrator is skeptical.

So erklärt fits well here because:

We’re dealing with a trainer speaking as an expert.
The sentence sounds like part of a report, brochure, or article where expert explanations are being quoted.

Why is it Die Trainerin and not Der Trainer here, and how regular is this feminine ending -in?

Die Trainerin is the feminine form of der Trainer.

In German, many profession and role nouns form the feminine with -in:

der Lehrer → die Lehrerin (teacher, f.)
der Arzt → die Ärztin (doctor, f.)
der Student → die Studentin (student, f.)
der Trainer → die Trainerin

Key points:

Gender of the person:
- Die Trainerin = clearly a female trainer.
- Der Trainer = a male trainer (or historically the generic masculine).
Plural feminine: add -nen:
- die Trainerinnen (female trainers)
- die Lehrerinnen, die Studentinnen.
Regular pattern:
- Very common and productive: -er → -erin, -ent → -entin, -e → -in, etc.
- There are some stem changes (Arzt → Ärztin, Koch → Köchin), but the -in ending is standard for feminine forms of human roles.

In modern, gender-inclusive language, writers may:

Use die Trainerin when they specifically mean a woman.
Use der Trainer oder die Trainerin / Trainer*innen / Trainerinnen und Trainer when they mean all genders.

In this sentence, Die Trainerin simply tells you the trainer is female.

How is the compound noun Verletzungsgefahr formed, and is it countable?

Verletzungsgefahr is a compound noun:

die Verletzung – injury
die Gefahr – danger

→ die Verletzungsgefahr = literally “danger of injury” → risk of injury.

About its grammar:

Gender:
In German compounds, the last part decides the gender.
- Last part: Gefahr (feminine)
- So: die Verletzungsgefahr (feminine)
Usage and countability:
- Usually treated as a kind of mass/abstract noun in this meaning:
  - Die Verletzungsgefahr ist gering/hoch/erhöht.
- You don’t usually say „eine Verletzungsgefahr“ in everyday language unless you qualify it, e.g.:
  - Es besteht eine hohe Verletzungsgefahr.
    (“There is a high risk of injury.”)
- Plural Verletzungsgefahren is possible but rare; you’d use it if you were talking about different types of injury risks in a technical/specialist context.

Typical collocations:

hohe Verletzungsgefahr – high risk of injury
geringe Verletzungsgefahr – low risk of injury
erhöhte Verletzungsgefahr – increased risk of injury
Verletzungsgefahr besteht – there is a risk of injury

So in the sentence, die Verletzungsgefahr … sei gering = “the risk of injury is low.”