Depending from muscle length identical muscular strain causes different muscular activation levels

Purpose: Is it possible to prove a relationship between changing neuromuscular activation and muscle length at identical strain levels? Materials and methods: In a test and training unit (IKA-RUS) isometric contractions at 50 % MVC level were performed in sagittal, frontal and horizontal plane. In every plane four angular positions were chosen and both opposite force directions were measured respectively. In a group of 15 healthy men SEMG was taken from 13 arm and shoulder muscles. Results: Equal force strain levels require different central nervous drive intensities. They depend on the actual muscle length. All investigated muscles reached their highest SEMG amplitude in joint positions in which they showed the strongest shortening. Although these positions showed the lowest force levels these non fatigued muscles reached their highest SEMG amplitudes. This could be proven as statistically significant in ten out of all 13 investigated muscles. Conclusion: At identical strain levels the most shortened muscle positions require the highest central nervous drive intensities. This reveals new perspectives concerning rehabilitation strategies of functionally caused pareses after traumata or operations.