Treadmill training is a perfectly valid alternative for developing a runner's physical fitness, provided one does not focus blindly on the speed data displayed by the machine and remains vigilant regarding the risk of injury linked to the repetitiveness of the movement.

noli's read

The community largely agrees on the physiological effectiveness of treadmill running, which is confirmed by research: cardiovascular and metabolic adaptations are similar to those of outdoor running (observational studies on interval training, e.g., Journal of Strength and Conditioning Research). However, it is true that the treadmill offers a more uniform and mechanically constant surface, which reduces the load on stabilizer muscles and may increase the risk of repetitive stress injuries if the volume is too high without varying angles or terrain. The idea that the treadmill is "less effective" is often exaggerated; however, the lack of air resistance and the absence of micro-adjustments to the terrain (proprioception) make the energy expenditure slightly lower, which a 1% incline often compensates for in a laboratory setting. It is accurate that treadmill calibration varies enormously, making precise pace tracking less reliable than outdoors via GPS. Finally, the community is converging toward a pragmatic view: the treadmill is a serious training tool, but surface diversity remains a key factor for long-term joint health.

the sources

1. 1Schoenfeld BJ, Grgic J, Ogborn D, Krieger JW 2017
2. 2Refalo MC, Helms ER, Trexler ET, Hamilton DL, Fyfe JJ 2022
3. 3r/AdvancedRunning