are you burnt out?

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Your jog to "burn off steam" totally deflates you.
If you're really frazzled when you start to exercise, your body reacts differently than if you aren't in such a state, explains Sarah L. Berga, MD, professor of obstetrics and gynecology at Wake Forest University School of Medicine in Winston-Salem, North Carolina. Berga and her colleagues have observed that moderately intense exercise can cause cortisol levels to spike even higher in women who are already so stressed that they've been missing their periods. At the same time, the "hyperstressed" women's glucose levels dropped, which meant there was less available energy to fuel their exertion. Berga suggests taking a break from hard workouts and signing up for a package of Pilates classes instead.