Exercising after ovulation - at the midpoint of the menstrual cycle - is easier, and burns more fat, than exercising in the first week of the menstrual cycle, according to the results of a new Australian study.

Researcher Leanne Redman, a PhD student at the University of Adelaide’s Exercise Physiology Laboratory, reports the findings.

She examined the effect of exercise on a group of young, healthy women with normal menstrual cycles. In the first week after menstrual bleeding began the women were given two exercises to do, and repeated them in the week after they ovulated. These times were chosen because the levels of the hormones oestrogen and progesterone increase toward the end of the menstrual cycle.

Focus on oestrogen
Redman explained to Reuters Health that her reason for focusing on hormone levels was that in menopause the level of oestrogen drops, and women frequently find that they can't keep weight off.

"In Australia," she said, "cardiovascular disease is one of the biggest killers in women, so if we can somehow quantify the level of oestrogen needed to burn off fat, one day down the track we can have a 'wonder pill' not for weight loss, but for weight maintenance."

The role of different types of metabolism
Although the women got to the same level of peak fitness when exercising during the two phases, the way they got there was different, said Redman, explaining "that means they're using different types of metabolism to perform the exercise."

She added that the women burned more fat for the same amount of exercise in the second half of the menstrual cycle, and that these women perceived the exercise and their recovery from it quite differently from those exercising in the first half of the cycle.

Energy levels during the menstrual cycle
"Women will often come in and say they feel tired and sluggish and headachy at the beginning of the month," she said. "On those days when they're not performing as well, even though they're achieving the same level, they're finding the exercise a lot harder."

Redman said that when levels of waste products like blood lactate, which causes a burning sensation in muscles, were tested, the levels were much higher after exercise in the early part of the menstrual cycle.

"At the beginning of the month, both oestrogen and progesterone are low, and that's when performance wasn't as good. In the second half of the cycle, when both hormones are high, that's when we're getting an increase in fat metabolism," Redman concluded.

Work harder when you have the energy
She advised women that "if we find that we're quite tired at the beginning of the month just going to work and looking after children and doing the things we do every day, that's normal. There are things happening in the muscle, driven by oestrogen, unfortunately making us tired. When we do have more energy, let's utilise it. Push yourself a bit harder in the second half of your cycle, because you'll definitely reap more reward."

The study is soon to enter its last phase, where the impact of synthetic hormones such as those contained in the oral contraceptive pill will be studied. - (HealthScout)

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