Fatigue Data Book: Light Structural Alloys Rapidshare Human Physiology - Grip Strength?

Human Physiology - Grip Strength? - fatigue data book: light structural alloys rapidshare

Normally, the relative cost of grip strength is 40% of the maximum increase over time to keep (see the data record and) fatigue. Explain why increasing the relative effort with the times.

Why not increase with time, compared with grip strength?