Heart rate alteration during a constant load exercise in the different menstrual phases

In fitness centres, the most common way to modulate exercise’s intensity is heart rate (HR) control and therefore training at constant heart rate (CHR) is widely used but this method assume that exercise’s response to exercise should be always the same; Instead there are conflicting results about menstrual cycle’s effects on physiological response to exercise (Jense de Jonge 2003). Many researches have investigated the influences of estrogenic hormone levels in sport performance (Sarwar 2006; Phililps 1996), muscle strength and heart rate during maximal and submaximal exercise (Oosthuyse 2005; Kishali 2006). No study has attempt to verify if CHR correspond to a constant load of endurance exercise throughout the 28 days of menstrual cycle and therefore if this method could be suitable to right size training stimulus also in the different phases of menstrual cycle. 20 women (25±8,66 years old an 56,1±8,82 kg) was tested at cycloergometer in each phases of menstrual cycle (follicular (FOL) days 1-13, ovulation (OV) days 14-15, luteal (LUT) days 15-21, menstruation (MES) days 21-28); subjects didn’t take oral contraceptive during the experiment period. Cycle phases were preliminary confirmed by temperature and LH urine concentration measurement (Lebrun 2003). HR, blood lactated and RPE value was collected and analysed during every training session (FOL, LUT, OV, MES). The results showed a significantly lower HR during the MES phase compared to the other phases whilst there were no significant changes in other variables: blood lactate and RPE values, confirming the steadfastness of the internal load. These results suggest that ovarian hormones variation during menstrual cycle could influence heart response to constant load endurance exercise. In conclusion our data suggests that CHR could underestimate exertion during the menstrual phase therefore female subjects would be forced to increase the external load to maintain the same (supposed) relative training intensity. References • Janse de Jonge XA. Sports Med. 2003;33(11):833-51 • Sarwar R et al. J Physiol. 1996 May 15;493 ( Pt 1):267-72 • Philips SK et al. J Physiol. 1996 Oct 15;496 ( Pt 2):551-7 • Oosthuyse T et al. Eur J Appl Physiol. 2005 Jun;94(3):268-76 • Kishali NF et al. Int J Neurosci. 2006 Dec;116(12):1549-63 • Lebrun CM et al. Br J Sports Med. 2003 Aug;37(4):315-20