“Using a novel technique of high-density surface EMG decomposition and motor unit tracking, we compared changes in the properties of vastus medialis and vastus lateralis motor unit after endurance and high-intensity interval training.”

“16 men were assigned to the endurance or the high-intensity interval training group….”

“……performed six training sessions for 14 days.”

“Each session consisted of 8 – 12 × 60-seconds intervals at 100% peak power output separated by 75 seconds of recovery (high-intensity interval training) or 90–120 minutes continuous cycling at ~65% V˙O2peak (endurance).”

“The high-intensity interval training group showed enhanced maximal knee extension torque by ~7% (P = 0.02) and was accompanied by an increase in discharge rate for high-threshold motor unit (≥50% knee extension MVC).”

“By contrast, the endurance group…..showed no change in motor unit discharge rates.”

“High-intensity interval training and endurance induce different adjustments in motor unit discharge rate despite similar improvements in cardiopulmonary fitness. Moreover, the changes induced by high-intensity interval training are specific for high-threshold motor units. For the first time, we show that high-intensity interval training and endurance induce specific neuromuscular adaptations, possibly related to differences in exercise load intensity and training volume.”

E. Martinez-Valdes, et al
Differential Motor Unit Changes after Endurance or High-Intensity Interval Training
Medicine & Science in Sports & Exercise — Volume 49 #6 — June 2017 — page 1126