The 140 bpm is no longer an ACOG (the American College of Obstetrics and Gynecology) recommendation. There is no science to support this recommendation. When the 1985 ACOGs guidelines were written, target heart rates were used in nonpregnant women. ACOG felt pressure to come up with a target heart rate, but there was no evidence to base it on so it was guesstimated. The changes in the cardiovascular system alone result in the heart rate a poor indicator of intensity. For example, the heart rate increases until it reaches 10-15 beats above the prepregnant heart rate during the 2nd tri and my increase 15-20 bpm above the prepregnant heart rate during the last tri.
This is from Sheila Watkins the forum moderator:
I am the moderator of this forum, along with Cathe. I just wanted to give you the latest research regarding heartrate monitoring during pregnancy. In 1994 ACOG (the American College of Obstetrics and Gynecology) came out with the first revised guidelines for prenatal exercise in nine years. Gone was the 140 bpm uppper heart rate limit for prenatal exercise. This change was inevitable due to the fact that the latest research had shown that heart rate was NOT a valid indicator of exercise intensity during pregnancy, due to the vast changes in the cardiovascular and respiratory system. It was, and still recommended that one use "Rating of Perceived Exertion" (RPE) or the "Talk Test" to monitor intensity rather than heart rate. The "140 bpm one number fits all" is 'old news'." I would suggest that you use the above measures of intensity rather than heartrate monitoring, which can fluctuate wildly during pregnancy. Using perceived exertion, one should work at a "fairly light to hard" level depending on fitness level and stage of pregnancy. One should also be able to speak 2-5 word sentences while exercising. That is the actual definition of the "talk test."
There is insufficient data to support that elevated temp with exercise is harmful to the developing baby based on what I've read. Hopefully, Sheila will pop in here.
I'll link a "Guidelines of the American College of Obstetricians and Gynecologists for exercise during pregnancy and the postpartum period" (2003) in my signature. You have to work your way through all the research lingo. There is a section titled "Thermoregulatory Control" that discusses temperature, and there is also the section "EXERCISE PRESCRIPTION" that may be helpful.
HTH!
