Effects of nociceptive and mechanosensitive afferents sensitization on central and peripheral hemodynamics following exercise-induced muscle damage

This study aims to test the separated and combined effects of mechanoreflex activation and nociception through exercise-induced muscle damage (EIMD) on central and peripheral haemodynamics before and during single passive leg movement (sPLM). Eight healthy young males undertook four experimental sessions, in which a sPLM was performed on the dominant limb while in each specific session the contralateral was: a) in a resting condition (CTRL), b) stretched (ST), c) resting after EIMD called delayed-onset-muscle-soreness (DOMS) condition, or d) stretched after EIMD (DOMS+ST). EIMD was used to induce DOMS in the following 24-48h. Femoral blood flow (FBF) was assessed using doppler ultrasound while central haemodynamics were assessed via finger photoplethysmography. Leg vascular conductance (LVC) was calculated as FBF/MAP. RR-interval were analyzed in the time (RMSSD) and frequency domain (LF/HF). Blood samples were collected before each condition and gene expression analysis showed increased fold changes for P2X4 and IL1β in DOMS and DOMS+ST compared with baseline. Resting FBF and LVC were decreased only in the DOMS+ST condition (-26ml/min and -50ml/mmHg/min respectively) with decreased RMSSD and increased LF/HF ratio. MAP, HR, CO, and SV were increased in ST and DOMS+ST compared with CTRL. Marked decreases of delta peaks and AUC for FBF (∆: -146ml/min and -265ml respectively) and LVC (∆: -8.66ml/mmHg/min and ±1.7ml/mmHg/min respectively) all p<.05. These results suggest that combination of mechanoreflex and nociception resulted in decreased vagal tone and concomitant rise in sympathetic drive that led to increases in resting central hemodynamic with reduce limb blood flow before and during sPLM.