IMPACT OF PHASE OF THE MENSTRUAL CYCLE ON THE LACTATE THRESHOLD

Leanne M. Redman^1,2, Robert J. Norman², G.C. Scroop¹, 1 Department of Physiology, University of Adelaide, Australia, 2 Reproductive Medicine Unit, Department of Obstetrics and Gynaecology, The University of Adelaide, SA 5000, Australia.

Whilst it has been postulated that the phase of the menstrual cycle affects exercise performance there have been no studies on the impact of the phase of the menstrual cycle on the lactate threshold (LT). The present study aimed to determine the lactate profile to maximal exercise during the follicular (FP) and luteal phase (LP) of the menstrual cycle. Fourteen sedentary, eumenorrheic females (21.8 ± 1.0 yrs; mean ± SE) performed incremental cycle ergometer exercise to exhaustion during the FP (day 6 ± 1) and LP (day 24 ± 1) of the cycle (30 ± 1 days). The protocol began with 2 min unloaded pedalling (50 rpm) and work load was incremented by 25 watts every 2 min thereafter until the subjects reached volitional exhaustion. Venous blood samples were collected at rest, in the last 30s of each workload and every min for 10 min post-exercise for plasma lactate concentration [La]. The LT was calculated by logarithmic data transformation¹. There was no difference between the FP and LP in the resting, end-exercise or peak post-exercise [La] or in the time to reach peak [La]. The LT when expressed relative to Vo₂ (L^.min^-1 or % Vo_2peak) was not affected by phase of the menstrual cycle. Furthermore, there was no difference in the HR response, plasma [La] or power output at the LT between the phases of the menstrual cycle. However when plasma [La] concentrations were plotted as an exponential function of relative exercise intensity, [La] concentrations were higher during the FP (P<0.04) at all levels of exercise intensity. Thus there is an increased lactate accumulation during incremental exercise in the FP of the menstrual cycle with no apparent impact on the lactate threshold.

(1) Beaver W, Wasserman K, Whipp BJ. Journal of Applied Physiology. 1985;59:1936-1940.