Questions & Answers about No tengo fuerza hoy.
Because Spanish often drops subject pronouns when they are not needed.
The verb tengo already tells you the subject is I, so yo is usually unnecessary:
- No tengo fuerza hoy = I don’t have strength today
You can say Yo no tengo fuerza hoy, but that usually adds emphasis, contrast, or clarification:
- Él sí puede, pero yo no tengo fuerza hoy.
He can, but I don’t have the strength today.
So the version without yo is the most natural neutral sentence.