What is 'stacking' in NMES and why is it undesirable?

• A. Stacking refers to longer rest periods between bursts.
• B. Stacking increases muscle recruitment efficiency.
• C. Stacking decreases fatigue.
• D. Stacking is repeated stimulation bursts with little to no off time; increases fatigue, skin irritation, and reduces tolerance.

Answer: (D)

Stacking in NMES means delivering stimulation bursts with little to no off time, so the effects of each burst accumulate without a true recovery period. This quickly pushes the muscle and skin toward fatigue and irritation. Metabolic byproducts build up, force production drops, and tolerance to the stimulation decreases, making contractions weaker and the sensation more uncomfortable. Prolonged charge delivery can also heat the skin and increase impedance, leading to more irritation. Using appropriate rest between bursts and ramping the stimulus helps motor units recover, maintains contraction quality, and improves comfort and safety.