The time course of different neuromuscular adaptations to short-term downhill running training and their specific relationships with strength gains
Bastien Bontemps, Mathieu Gruet, Julien Louis, Daniel J. Owens, Stella Miríc, Robert M. Erskine, Fabrice Vercruyssen
Abstract
Abstract 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 (5 women, 7 men) took part in 4 weeks’ DR, comprising 10 sessions, with running speed equivalent to 60–65% maximal oxygen uptake ( $$\dot{V}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:math> O 2max , 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, L f ; 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 4 weeks ( p < 0.01). VL EMG during isometric MVT increased by 35.6 ± 46.1% after 4 weeks ( p < 0.05) and correlated with changes in isometric MVT after 2 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 2 and 4 weeks, respectively ( p < 0.05). PCSA (+3.8 ± 3.3%), PA (+5.8 ± 3.8%) and L f (+2.7 ± 2.2%) increased after 4 weeks ( p < 0.01). Changes in VL volume ( r = 0.67, p = 0.03) and PCSA ( r = 0.71, p = 0.01) correlated with changes in concentric MVT from 2 to 4 weeks. $$\dot{V}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mover> <mml:mi>V</mml:mi> <mml:mo>˙</mml:mo> </mml:mover> </mml:math> O 2max (49.4 ± 6.2 vs. 49.7 ± 6.3 mL·kg −1 ·min −1 ) did not change after 4 weeks ( p = 0.73). Conclusion Just 4 weeks’ moderate-intensity DR promoted neuromuscular adaptations in young, healthy adults, typically observed after high-intensity eccentric resistance training. Neural adaptations appeared to contribute to most of the strength gains at 2 and 4 weeks, while muscle hypertrophy seemed to contribute to MVT changes from 2 to 4 weeks only.