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

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 ($$\dot{V}$$ V ˙ O2max, 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 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 Lf (+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. $$\dot{V}$$ V ˙ O2max (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.

Uphill versus downhill high-intensity training effectiveness in preserving vascular function and exercise performance in runners who reduce their regular endurance training

“…Moreover, there were no changes in Isometric Mid-Thigh Pull Test scores pre- vs post-HIT in both UP and DOWN. Our data contrast with previous findings suggesting improvements in lower-limb muscle strength after a short downhill running training at low intensity [ 10 ]. Indeed, Bontemps et al [ 10 ] reported that eccentric muscle strength augmented already after 2 weeks of downhill running training at an equivalent running speed to about 60% V̇O 2max , while knee extension torque in both isometric and isokinetic modalities augmented after 4 weeks of training.…”

“…Our data contrast with previous findings suggesting improvements in lower-limb muscle strength after a short downhill running training at low intensity [ 10 ]. Indeed, Bontemps et al [ 10 ] reported that eccentric muscle strength augmented already after 2 weeks of downhill running training at an equivalent running speed to about 60% V̇O 2max , while knee extension torque in both isometric and isokinetic modalities augmented after 4 weeks of training. The discrepancy between the results of Bontemps et al [ 10 ] and ours might be explained by the different initial training status of the subjects (untrained adults vs trained adult runners, respectively).…”

“…The greater cardiorespiratory improvements in UP are consistent with the greater exercise intensity while running uphill at the same running speed than in DOWN and with the major impact on the central and peripheral components affecting V̇O 2max [ 4 , 36 ]. On the other hand, downhill HIT has been suggested to provide minor effects on the V̇O 2max [ 10 ], but to improve the lower-limb muscle strength [ 10 ], which is an important factor related to running economy [ 11 , 12 ]. Indeed, V̇O 2max changes alone do not explain the 2000 m time performance changes (Fig.…”

“…Indeed, Bontemps et al [ 10 ] reported that eccentric muscle strength augmented already after 2 weeks of downhill running training at an equivalent running speed to about 60% V̇O 2max , while knee extension torque in both isometric and isokinetic modalities augmented after 4 weeks of training. The discrepancy between the results of Bontemps et al [ 10 ] and ours might be explained by the different initial training status of the subjects (untrained adults vs trained adult runners, respectively). However, regardless of the ground slope, our HIT plan was also effective to maintain neuromuscular indexes related to lower-limb muscle strength compared to CON despite the threefold training volume reduction.…”

“…Specifically, the recovery was performed by walking on the treadmill at a walking speed of 4 km/h. Our training lasted 6 weeks as this HIT duration led to significant improvements in endurance parameters in previous studies [ 10 , 20 ]. Runners provided their average perceived exertion through the Borg Category Ratio 0–100 (CR100) scale and average heart rate after each session.…”