Cross-training can be a valuable tool for ultrarunners, but it should always serve a clear purpose.

In this episode of The Trail Running Briefing, I explore why specificity still matters, especially for mountain ultrarunners. A long ultra is not simply one discipline: it involves running uphill, running flats, running downhill and, very importantly, power-hiking steep climbs.

We look at why uphill walking can be one of the most race-specific forms of “cross-training”, how cycling can build additional aerobic volume with less impact, and where swimming can be useful during recovery, injury management or high-load periods.

I also explain why strength training should not really be considered cross-training at all, but rather an essential part of ultramarathon preparation.

The key question is not: “What is the best cross-training?”

It is:

“What adaptation am I trying to create, and what is the most specific way to achieve it without adding unnecessary fatigue?”

Train the engine but train the movement too.

Key references:

1. Endurance Coach GmbH et al. (2026). Cross-training between running and cycling: effects on VO₂max and running performance — a systematic review and meta-analysis. Frontiers in Sports and Active Living.

2. Finiel, L., Carron, S., Margot, C., et al. (2026). Energetic cost of locomotion closely aligns with the preferred uphill walk-run transition at constant vertical speed in runners. European Journal of Applied Physiology.

3. Martinez-Navarro, I., Vicente-Mampel, J., López-Grueso, R., et al. (2026). Uphill Walking Economy and Maximal Oxygen Consumption in Trail Runners: Relationship with Ultra-Trail Performance. International Journal of Sports Medicine.

4. Brill, J.W. & Kram, R. (2021). Does the preferred walk-run transition speed on steep inclines minimize energetic cost, heart rate or neither? Journal of Experimental Biology, 224, jeb233056.

5. Vernillo, G., et al. (2020). Steep (30°) uphill walking vs. running: COM movements, stride kinematics, and leg muscle excitations. European Journal of Applied Physiology.

6. Tanaka, H. (1994). Effects of cross-training: transfer of training effects on VO₂max between cycling, running and swimming. Sports Medicine.

7. Reilly, T., Morris, T. & Whyte, G. (2009). The specificity of training prescription and physiological assessment: a review. Journal of Sports Sciences.

8. Eihara, Y., et al. (2024). Effect of Strength Training Programs in Middle- and Long-Distance Runners' Economy at Different Running Speeds: A Systematic Review with Meta-analysis. Sports Medicine.

9. Recent umbrella review (2025). The Effect of Strength Training on Endurance Performance Determinants in Middle- and Long-Distance Endurance Athletes.