verkrampft
tense
Describes behavior or an atmosphere that is tense, unnatural, and not loose or relaxed.
Er versuchte zu lächeln, aber es wirkte sehr verkrampft und gezwungen.
He tried to smile, but it seemed very tense and forced.

tense / cramped
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tense
Describes behavior or an atmosphere that is tense, unnatural, and not loose or relaxed.
Er versuchte zu lächeln, aber es wirkte sehr verkrampft und gezwungen.
He tried to smile, but it seemed very tense and forced.

The word is derived from the noun 'der Krampf' (cramp). The prefix 'ver-' often describes a process or entering a state. 'Verkrampft' (tense/cramped) therefore literally means being in a state of cramp, which applies both to muscles and to tense behavior.
Seine Hand war nach dem Schreiben ganz verkrampft.
His hand was completely cramped after writing.
You can recognize the meaning from the context. If people are talking about body parts or muscles, it refers to physical tension. If it is about people, behavior, an atmosphere, or a smile, it refers to the figurative meaning of being tense or not relaxed.
Meine Schulter ist nach der Gartenarbeit total verkrampft.
My shoulder is completely cramped after the gardening.
In the figurative meaning, 'verkrampft' (tense) is often combined with behavior and situations. Typical phrases are 'ein verkrampftes Lächeln' (a tense smile), 'eine verkrampfte Atmosphäre' (a tense atmosphere), or saying that someone 'verkrampft wirkt' (seems tense).
Er wirkte beim Vorstellungsgespräch sehr verkrampft.
He seemed very tense during the job interview.
In the literal, medical meaning, 'verkrampft' (cramped) always refers to muscles or body parts. Common phrases are 'verkrampfte Muskeln' (cramped muscles), 'eine verkrampfte Hand' (a cramped hand), or 'sich verkrampft anfühlen' (to feel cramped).
Nach dem Sport fühlten sich seine Beine verkrampft an.
After exercising, his legs felt cramped.
loose / relaxed
'locker' and 'verkrampft' are opposites when it comes to behavior or atmosphere. 'Locker' means relaxed, natural, and informal. 'Verkrampft' means tense and unnatural, as if someone does not feel free. 'Locker' is used for pleasant conversations, calm behavior, or a relaxed mood. 'Verkrampft' fits when a situation feels stiff or someone is too nervous.

Wegen der vielen Fragen wirkte Tom im Bewerbungsgespräch verkrampft.
Because of all the questions, Tom seemed tense in the job interview.
Das Gespräch mit der neuen Nachbarin war überraschend locker.
The conversation with the new neighbor was surprisingly relaxed.