The time course of different neuromuscular adaptations to short-term downhill running training and their specific relationships with strength gains
Twelve untrained young adults (5 women, 7 men) did 4 weeks of downhill running — 10 sessions at a speed equivalent to 60-65% VO2max. Knee-extensor maximal voluntary torque rose by 9.7-15.2%. Vastus lateralis EMG rose by 35.6 ± 46.1%, and its change correlated with the isometric strength change after 2 weeks (r = 0.86).
Muscle size (ACSA, volume) increased already after 2 weeks and more after 4; PCSA, pennation angle and fascicle length increased after 4 weeks. VO2max did not change. The authors conclude that neural adaptations explained most of the strength gain at 2 and 4 weeks, and hypertrophy contributed only from week 2 to week 4.
Participants
n=12 (abstract: "Twelve untrained, young, healthy adults"): 5 women, 7 men. VO2max 49.4 ± 6.2 mL·kg-1·min-1 at week 0.
Protocol
Downhill running (DR): 4 weeks, 10 sessions, at a running speed equivalent to 60-65% VO2max. The gradient and session duration are not given in the abstract.
Measured at weeks 0, 2 and 4: knee-extensor maximal voluntary torque (MVT), both isometric and isokinetic; morphology and architecture of the vastus lateralis (VL), namely anatomical and physiological cross-sectional area, volume, fascicle length and pennation angle; and VL EMG.
VO2max at weeks 0 and 4.
No control group.
Key Results
| Measure | After 2 weeks | After 4 weeks |
|---|---|---|
| Knee-extensor MVT | — | +9.7-15.2% (p < 0.01) |
| VL EMG during isometric MVT | — | +35.6 ± 46.1% (p < 0.05) |
| VL ACSA | +2.9 ± 2.7% | +7.1 ± 3.5% (p < 0.05) |
| VL volume | +2.5 ± 2.5% | +6.6 ± 3.2% (p < 0.05) |
| VL PCSA | — | +3.8 ± 3.3% (p < 0.01) |
| Pennation angle | — | +5.8 ± 3.8% (p < 0.01) |
| Fascicle length | — | +2.7 ± 2.2% (p < 0.01) |
| VO2max (mL·kg-1·min-1) | — | 49.4 ± 6.2 → 49.7 ± 6.3 (p = 0.73, unchanged) |
Neural link: the change in VL EMG correlated with the change in isometric MVT after 2 weeks (r = 0.86, p = 0.001).
Muscle link: the change in concentric MVT from week 2 to week 4 correlated with VL volume change (r = 0.67, p = 0.03) and with PCSA change (r = 0.71, p = 0.01).
Practical Application
In twelve untrained young adults, 4 weeks of downhill running (10 sessions at a speed equal to 60-65% VO2max) raised knee-extensor strength by 9.7-15.2%, first through neural adaptation (EMG change vs strength change at 2 weeks r = 0.86) and then with muscle growth (VL volume +6.6% by week 4), while VO2max did not change (uncontrolled pre-post). Moderate downhill running is a real strength stimulus for the quadriceps, and about ten sessions over a month is enough to see it in someone new to it.
The authors compare these adaptations to those typically seen after high-intensity eccentric resistance training; inference, not tested here: for a trail runner, a block of downhill sessions may do part of the job of eccentric gym work for the quadriceps, but this study did not compare the two.
The timeline matters for planning: strength gains in the first 2 weeks were mostly neural; the muscle itself was growing by week 2 and more by week 4.
Not from this paper; the base's own practice: introduce downhill running gradually (short, moderate descents first) because unaccustomed descending causes muscle damage (REF-660, REF-317), and finish a descent block well before a mountain race; this study measured strength, not protection from race-day damage.
VO2max did not change: downhill running at this intensity is a muscular stimulus, not an aerobic one.
Limitations
Twelve untrained young adults; trained runners, who already descend, may adapt less.
No control group, so learning and test familiarisation cannot be separated from training.
The downhill gradient and session length are not in the abstract, so the dose cannot be fully reproduced from this entry.
EMG change varied widely (± 46.1% on a mean of 35.6%).
Muscle damage, soreness and running performance were not reported in the abstract.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level
uncontrolled pre-post, n=12