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Downhills wreck your legs: how your training background protects your muscles

A new study of trail runners found that those who regularly run downhill repeats damage their muscles less and better preserve their squat strength. We break down what this means for your training.

AS
Anna Severova

Anyone who has run a mountain ultra knows the feeling: the climbs take your breath, and the descents take your legs. By the finish, your quads refuse to brake, every step down shoots with pain, and the next morning even walking down the stairs hurts.

The reason lies in biomechanics. On a descent, the thigh muscles work in eccentric mode: they lengthen under load, absorbing the body's momentum with every landing. This kind of braking creates far more micro-damage in the muscle fibers than ordinary running on flat ground. Hence the rise in blood markers of muscle damage, delayed-onset soreness (DOMS), and a drop in strength.

The question that has long intrigued trail runners: can you adapt to this? A new study by Spanish researchers offers the first answers — and they are encouraging.

What they studied

The study included 36 experienced trail runners (25 men and 11 women), average age 45 ± 8 years, with 15 ± 8 years of running experience and a weekly volume of 71 ± 22 km. All were preparing for a mountain ultra 106.1 km long, with +5584 m of ascent and −4369 m of descent.

The design was a standardized downhill test on a treadmill:

  • 5 km at a constant −15% gradient;
  • speed of 13.3 ± 1.6 km/h (at the level of the first ventilatory threshold, i.e. a light aerobic load);
  • blood draws before and 30 minutes after the protocol — for creatine kinase (CK), lactate dehydrogenase (LDH), and myoglobin;
  • isometric strength tests (plantar flexion of the foot and a half-squat);
  • running technique analysis: stride length and cadence, ground contact time, vertical oscillation.

By training background: 75.7% of participants did strength training, and 21.6% regularly included downhill repeats.

Results

Even an "easy" 5 km downhill produced noticeable muscle damage. The biggest rise was in myoglobin — by 247.8% (from 31 ± 16 to 94 ± 47 ng/mL, a large effect d = 1.85). Creatine kinase rose by 17.4% (229 → 261 U/L), LDH by 6.4% (405 → 428 U/L). Myoglobin proved the most sensitive marker of a short descent.

But the key finding is the difference between the groups. Those who regularly ran downhill repeats had lower creatine kinase (182 ± 73 vs 290 ± 192 U/L) and better preserved their squat strength: +4 ± 10% vs −9.1 ± 16.8% for the rest (p < 0.05, d = 0.87). In other words, specific adaptation to descents really did protect the muscles: one group even gained strength after the test, while the other lost almost a tenth.

Technique played a role too. A more "grounded" running pattern — less vertical oscillation and a shorter stride — was linked to better preserved strength (the relationship between strength loss and vertical oscillation r = −0.44, and stride length r = −0.37). Simply put: the less you "bounce" on a descent and the shorter your stride, the less your muscles suffer.

Another finding for practice: LDH levels after the standard downhill test correlated strongly with LDH after the race itself (r = 0.64; p < 0.01). The authors suggest that such a test could serve as an indicator of an athlete's readiness for the "downhill" stress of an ultra distance.

How to train downhills

The results point to a very concrete practice.

  • Include downhill intervals (downhill reps). This is exactly the specific work that set the "protected" group apart. Find a moderate descent, run down at a controlled pace, climb back up — and repeat.
  • Progress gradually. Eccentric work causes strong delayed soreness, especially in the first sessions (the "repeated bout effect"). Start with a small volume and a gentle gradient, and build up every 1–2 weeks.
  • Work on technique. Train a shorter stride, a slightly higher cadence, less vertical "bouncing," and a soft, "quiet" landing. This reduces impact load and strength loss.
  • Add strength work with an eccentric emphasis. Squats and lunges with a controlled lowering phase strengthen the quads for the mode in which they work on a descent.
  • Don't forget recovery. After a hard downhill session, the muscles need time: plan easy days and don't schedule two "killer" workouts back to back.

Limitations

The authors honestly call the work exploratory. The sample is small, and 7 participants combined both downhill repeats and strength training — so the contributions of these two factors can't be cleanly separated. The data show relationships, not strict cause and effect: you can't claim 100% that it was specifically the downhill repeats that "produced" the protection. The participants are experienced older runners from a single race, so the conclusions should be transferred to beginners with caution.

The bottom line

  • Downhills damage muscles even at an easy pace — due to eccentric work; the most sensitive marker of a short descent is myoglobin (+247.8%).
  • Regular downhill repeats protect you: lower creatine kinase and better preserved squat strength (+4% vs −9.1%).
  • Technique matters: a shorter stride and less vertical oscillation mean less strength loss.
  • Practical takeaway: build in downhill intervals and eccentric strength work, progress smoothly, and train a "grounded" run.
  • Remember the context: the study is exploratory and the sample is small — it's a guide, not dogma.

Source: Martinez-Navarro et al. Downhill Running-Induced Muscle Damage in Trail Runners: An Exploratory Study Regarding Training Background and Running Gait. Sports (Basel), 2026. DOI: 10.3390/sports14010012

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