Muscle soreness but not neuromuscular fatigue responses following downhill running differ according to the number of exercise bouts

Repeated sessions of eccentric-biased exercise promote strength gains through neuromuscular adaptation. However, it remains unclear whether increasing the number of these sessions can mitigate the extent of neuromuscular fatigue and exercise-induced muscle damage (EIMD) in response to a standardised eccentric-biased bout. Twelve healthy untrained adults (five females and seven males; 25.1 ± 4.9 years; and $$: 49.4 ± 6.2 mL kg⁻¹ min⁻¹) completed two blocks of five downhill running (DR) sessions on a motorised treadmill at a speed equivalent to 60%–65% $$ for 15–30 min. Knee extensor maximal voluntary isometric torque (MVT), electrically evoked measures of neuromuscular fatigue (peripheral and central components), and lower-limb perceived muscle soreness (PMS) and perceived load (RPE × session duration) were assessed before and immediately after a 15 min standardised DR bout at baseline and after 5 and 10 DR sessions. MVT decreased following a standardised DR bout (p < 0.01) similarly at all three time points (−14%, −11% and −9%; p > 0.05). The same observations were found for all peripheral and central neuromuscular fatigue indicators after 0, 5 and 10 DR sessions. Quadriceps (but not plantar flexor or gluteus) PMS was lower after 10 DR sessions (8.7 ± 8.5 mm) compared to baseline (29.6 ± 22.2 mm and p = 0.01), but no difference was observed after 5 DR sessions (15.4 ± 11.9 mm and p = 0.08). Ten repeated sessions of eccentric-biased exercise led to a reduction in quadriceps femoris PMS following a standardised DR bout but neither 5 nor 10 sessions altered the central or peripheral fatigue responses to the same standardised DR bout. These findings suggest distinct physiological adaptations to repeated eccentric-biased exercise regarding EIMD and neuromuscular fatigue.