Muscle contraction is triggered by electrical activation of the muscle fibres. This excitation is dependent on ion gradients across the muscle cell membrane. In this study stimulation of intact perfused rat muscles caused breakdown of the sodium ion gradient as measured by ion-sensitive microelectrodes. This might render the muscle less excitable and cause reduced force. Lactate could play no or little role in muscle fatigue if muscles become inexcitable due to breakdown of ion gradients across the membrane.
https://physoc.onlinelibrary.wiley.com/doi/epdf/10.1113/JP285870
