In healthy young adult males, the preferred walk-run transition speed is consistently slower than the energetically optimal transition speed, and changes in muscle activity in the tibialis anterior and soleus are associated with the transition, indicating that factors beyond whole-body energy expenditure influence gait transition.

When walking faster, the muscles in the lower leg work harder and start using faster-tiring muscle fibers. To avoid getting too tired too soon, the body switches to running, which lets those muscles work less hard and use slower, more fatigue-resistant fibers instead. This switch happens before running becomes the most energy-efficient option because avoiding muscle fatigue is more urgent than saving total body energy.