OnTracx measures mechanical load and identifies individual breakpoints, turning invisible load into actionable insights. This allows runners and experts to align training with both physiological and mechanical readiness for safer, smarter progression.
Runners are driven by progress like longer distances, faster splits, stronger results. But that same drive often leads to a familiar cycle: injury, rehab, recovery… and relapse.
The challenge isn’t motivation — it’s that physiological adaptations happen much faster than mechanical adaptations (Kjaer et al., 2009; Harrington et al., 2019). Cardiovascular and metabolic adaptations occur within weeks, while tendon and bone adaptation occurs over months. Your cardiovascular system or muscles might feel ready for a new pace or volume, but your tendons, bones, and joints often lag behind. That’s why, especially after injury or during a renewed start, mechanical load should guide the progression first, and later on the real art is balancing both mechanical and physiological load.
We all know the classic advice: build up gradually, don’t do too much too soon, listen to your body. But in practice, that guidance rarely answers the real questions runners face. What is too much for me? Can I handle another session? Why did I feel great during the run but sore or uncomfortable two days later?
To truly grasp how training choices impact load and injury risk, runners need tangible feedback, and experts need the ability to interpret it. Only then can physiological readiness and mechanical tolerance be aligned safely and progression finally becomes something you can trust rather than guess.
Mechanical load is far more than “mileage” or “time on your feet.” It’s influenced by many factors: speed and cadence, duty factor, foot strike pattern, terrain and slope, fatigue, footwear and more (Bonnaerens et al., 2019; Kyrolainen et al., 2001; Heiderscheit et al., 2011; Daoud et al., 2012; Giandolini et al., 2016; Christina et al., 2001; Bonacci et al., 2013).
Because of these variables, generic rules like the “10% increase in distance per week” often don’t work injury preventive (Buist et al., 2010). They don’t account for how forces per step change with different running conditions. Studies show that mechanical load for the same runner can vary by 20–30% depending on these factors (Nielsen et al., 2014). Between runners, the variability is even larger.
Physiological load is more tangible: you feel out of breath or you feel relaxed. Mechanical load is slower to manifest: discomfort or pain usually appears after the session, often 24–72 hours later (Bertelsen et al., 2017). One run may trigger symptoms, but the cause usually lies weeks earlier in unnoticed load spikes. A runner may feel fit physiologically while their tissues are quietly accumulating mechanical stress beyond their limits.
Physiological parameters such as lactate threshold, heart-rate zones and VO₂max are widely known and routinely used to guide training. Mechanical load and its individual variability, however, is less understood: rarely talked about, poorly understood, and almost never considered in coaching or rehabilitation practice.