Michael C. MacAvoy and David P. Green
The purpose of this study was to critically evaluate the current standard for manually assessing strength both clinically and in the scientific literature: the 0-to-5 scale that evolved from the post–World War II report of the British Medical Research Council. Although widely used by surgeons and researchers, no physical analysis of its validity is available. With the elbow used as an example, a static physics experiment is devised to quantify the enormous difference between maximum strength (grade 5/5) and the strength needed to statically flex against gravity (grade 3/5). The authors conclude that of the 6 possible grades from 0 to 5, the single grade 4/5 represents more than 96% of potential elbow flexion strength. For elbow flexion, grade 4/5 includes both the very weak and the very strong. Grade 3/5 strength may be much weaker than is generally assumed.
The Journal of Hand Surgery, Volume 32, Issue 2,