Nature | Exercise: Powering up.

In the spring of 2006, Janice Hayes-Cha was recovering from a gruelling series of treatments for breast cancer. She had both breasts and both ovaries removed, to shut off her body’s supply of oestrogen, which can fuel the growth of breast cancers. The busy mother of four was at the time executive director of the MassGeneral Institute for Neurodegenerative Disease in Boston, Massachusetts. The surgical procedures, plus four months of chemotherapy and two months of radiotherapy, left her physically and emotionally exhausted. Continue.