Final answer:
Grade 1 in muscle strength grading refers to 'trace' muscle strength, which is a very weak or no detectable muscle contraction.
Step-by-step explanation:
In the context of grading muscle strength, grade 1 is categorized as 'trace' muscle strength. It indicates that there is a barely detectable muscle contraction when the muscle is tested, but no joint movement is observed. This is commonly seen in conditions where the muscle has minimal or very weak contraction ability.
For example, if a person has grade 1 muscle strength in their arm, it means that there is a very weak or no visible movement when they attempt to lift an object using that arm.