noun which may take the genitive case particle 'no'
best of one's life; lifetime best
Used as a no-adjective to describe a personal record or achievement that is the best in one's life so far. Often seen in sports, career, or personal milestones.
He broke his lifetime best record.
This is the best work of my life.
自己最高 is more common for personal bests in sports or measurable achievements, while 生涯最高 emphasizes the entire lifespan and can sound more dramatic or final.
Compound of 生涯 (lifetime) and 最高 (best, highest). The exact origin is uncertain, but it follows a common pattern of combining nouns to form a no-adjective.