The time course of different neuromuscular adaptations to short‑term downhill running training and their specific relationships with strength gains

Purpose: Due to its eccentric nature, downhill running (DR) training has been suggested to promote strength gains through neuromuscular adaptations. However, it is unknown whether short-term chronic DR can elicit such adaptations. Methods: Twelve untrained, young, healthy adults (five women, seven men) took part in four weeks’ DR, comprising 10 sessions, with running speed equivalent to 60-65% maximal oxygen uptake (V̇O2max, assessed at weeks 0 and 4). Isometric and isokinetic knee-extensor maximal voluntary torque (MVT), vastus lateralis (VL) muscle morphology/architecture (anatomical cross-sectional area, ACSA; physiological CSA, PCSA; volume; fascicle length, Lf; pennation angle, PA) and neuromuscular activation (VL EMG) were assessed at weeks 0, 2 and 4. Results: MVT increased by 9.7-15.2% after four weeks (p<0.01). VL EMG during isometric MVT increased by 35.6±46.1% after four weeks (p<0.05) and correlated with changes in isometric MVT after two weeks (r=0.86, p=0.001). VL ACSA (+2.9±2.7% and +7.1±3.5%) and volume (+2.5±2.5% and +6.6±3.2%) increased after two and four weeks, respectively (p<0.05). PCSA (+3.8±3.3%), PA (+5.8±3.8%) and Lf (+2.7±2.2%) increased after four weeks (p