Effects of additional repeated sprint training on heart rate variability in soccer players during the competitive season

Heart rate variability (HRV) has become a usefulmethod to screen, monitor and track physical preparednessfor optimal performance. Although it has been widely used insports practice, little is known about its variation followinga repeated sprint ability (RSA) training. Therefore, the mainpurpose of the study was to examine the effects of the RSAon HRV in soccer players.Twenty professional soccer players participated in a6-week additional repeated sprint training program duringthe competitive season, which included 1-2 X 6-8 sprintsin 25-meter length intervals with a resting period of 25seconds two times per week. The HRV for each week wascalculated using the natural logarithm of the square rootof the mean squared difference of successive R-R intervals(LnRMSSD).Over a 6-week period, no significant ‘time’ (F5,120 =0.348, P = 0.883), ‘group’ (F1,120 = 0.105, P = 0.747) and‘time*group’ interaction (F5,120 = 0 .433, P = 0 .825) f orLnRMSSD were observed. Based on the group, EXPexhibited more stable LnRMSSD up to week 5, after whichLnRMSSD decreased towards the end of the intervention.An increase-decrease pattern of LnRMSSD from week 1till week 4 for CON was shown, with a plateau reachedbetween week 4 and week 6.RSA training had no significant effect on LnRMSSDin soccer players during the competitive season. Despitea decrease in LnRMSSD in the last week for EXP, thefollow-up period of 6 weeks in a competitive period mightnot be adequately long to obtain more impactful effects onLnRMSSD.