After a one-month break from training, it is not cardio or speed that decreases most rapidly, but muscular endurance—that is, the ability to maintain prolonged effort without excessive fatigue.

noli's read

The observation by Running Addict aligns well with sports physiology principles regarding detraining. Research, particularly reviews on exercise physiology (e.g., Mujika & Padilla), shows that while maximal oxygen uptake (VO2max) does decrease, it is better maintained over a short period than local peripheral adaptations. Muscular endurance depends heavily on mitochondrial density and the ability of muscle fibers to utilize oxygen, adaptations that fade more quickly than pure cardiac capacity when specific muscle loading ceases. What the creator describes as difficulty 'holding on for a long time' is a common experience reported by runners, validated by observational studies on the loss of exercise tolerance. It is important to note, however, that every individual reacts differently based on their training history. The analysis is therefore highly consistent with what sports science observes in the field.

the sources

No named source held this one up — that absence is part of the verdict.