Relationship between work and electromyographic activity during repeated leg muscle contractions in orienteers.

Contraction work (CW) was recorded for each of 200 repetitive isokinetic plantar flexions (1.05 rad.s-1) and knee extensions (1.57 rad.s-1) in 14 elite male orienteers. Simultaneous recordings of integrated electromyograms (iEMG) were obtained from the 3 parts of triceps surae and from 3 superficial portions of quadriceps femoris. CW in both muscle groups decreased significantly during the first 30 contractions (the fatigue phase), followed by a steady state level. The relative steady state level was higher for the plantar flexors (70 +/- 17%) than for the knee extensors (56 +/- 12%). For quadriceps a significant increase in iEMG occurred during the first 10 contractions followed by a decrease, whereas the iEMG of the plantar flexors showed a gradual decrease to the steady state level, which was similar for the two muscle groups (71-72%). The chosen expression of output/input balance (CW/iEMG) was constant throughout the plantarflexion test but decreased during the initial 20 knee extensions down to 82%. Thus, the fatigue phase of the knee extensions appeared to be divided into two; the first part had decreases in both CW and CW/iEMG and the second part with a decrease in CW alone. In contrast the plantar flexors only showed the characteristics of the second part.