The lactate threshold, or the highest exercise intensity where the body is able to clear the waste product ‘lactic acid’?? as fast as it is being produced, is a physiological variable shown to be consistently related to endurance performance, i.e. those with a higher lactate threshold will be able to maintain a higher exercise intensity for longer and consequently perform better in endurance events. Almost all of the studies investigating the lactate threshold and endurance performance to date, have been conducted on male athletes, with very minimal attention being paid to females. Female ovarian hormones; oestrogen and progesterone may influence certain physiological variables and as such, endurance performance. Changes in these hormone levels (mainly oestrogen) throughout the menstrual cycle can affect which fuel source (carbohydrates or fats) is used at rest and during exercise. For example, it has been shown that during the luteal phase of the menstrual cycle (10-14 days after the beginning of menstruation) it has been shown that more fats than carbohydrates are used for fuel this is beneficial since sparing carbohydrate can potentially delay the onset of fatigue. This is complicated by the use of Oral contraceptive pills (OCs). OC provide a synthetic dose of oestrogen and progesterone to mimic the normal cycle with the added benefit of being able to control the menstrual cycle and premenstrual symptoms, as well as to potentially improve bone health. However OC appear to significantly reduce peak oxygen uptake (VO2peak) in trained women. Little is known in regards to the effect of OC use on endurance performance at this stage, however it appears necessary to control menstrual cycle and OC use in females when conducting research in order to establish meaningful results. For this reason, we conducted a study at the University of Queensland which aimed to examine the relationship between the lactate threshold and cycling performance whilst controlling for hormone concentrations through use of an OC. Thirteen trained female cyclists and triathletes who had been taking an OC for 3 months or more completed a lactate threshold test and a 40 km cycling time trial in our laboratory. Winner of the women’s Olympic triathlon Brigitte McMahon of Switzerland, right, in action during the cycle leg of the event Saturday, September 16, 2000 in Sydney. (AP Photo/Rick Rycroft)[/caption]The results showed that when related to power output (or Watts), the lactate threshold was a good predictor of 40 km time, i.e. those with a higher power output at lactate threshold completed the 40 km faster than those with a lower threshold power output. Interestingly, when related to heart rate, the lactate threshold was not a good predictor of 40 km time, i.e. those with a higher heart rate at lactate threshold did not necessarily complete 40 km faster than those with a lower threshold heart rate. More research is needed to establish the reason for the difference in power output and heart rate for female athletes taking an OC, however it appears that power output rather than heart rate may be the more suitable variable when determining training zones and exercise intensities for trained female endurance athletes. If you are a triathlete please share your training experience in the comments! I will do my best to respond to your questions here. Samantha Fisher Samantha Fisher is a 2013 PhD Student at the School of Human Movement Studies at The University of Queensland. Samantha also works as a Strength and Conditioning Coach at UQ Sport Academy.