Neural inhibition during maximal eccentric and concentric quadriceps contraction: effects of resistance training

Despite full voluntary effort, neuromuscular activation of the quadriceps f emoris muscle appears inhibited during slow concentric and eccentric contra ctions. Our aim was to compare neuromuscular activation during maximal volu ntary concentric and eccentric quadriceps contractions, hypothesizing that inhibition of neuromuscular activation diminishes with resistance training. In 15 men, pretraining electromyographic activity of the quadriceps muscle s [vastus medialis (VM), vastus lateralis (VL), and rectus femoris (RF)] wa s 17-36% lower during slow and fast (30 and 240 degrees /s) eccentric and s low concentric contractions compared with fast concentric contractions. Aft er 14 wk of heavy resistance training, neuromuscular inhibition was reduced for VL and VM and was completely removed for RF. Concurrently, electromyog raphic activity increased 21-52, 22-29, and 16-32% for VL, VM, and RF, resp ectively. In addition, median power frequency decreased for VL and RF. Ecce ntric quadriceps strength increased 15-17%, whereas slow and fast concentri c strength increased 15 and 8%, respectively. Pre- and posttraining median power frequency did not differ between eccentric and concentric contraction s. In conclusion, quadriceps motoneuron activation was lower during maximal voluntary eccentric and slow concentric contractions compared with during fast concentric contraction in untrained subjects, and, after heavy resista nce training, this inhibition in neuromuscular activation was reduced.