We're experiencing a heat wave in Melbourne! How does training in hot weather affect your heart? On a hot day, blood flow is rerouted so more of it goes to your skin surface to help your body let off your internal heat (and you break a sweat). The redirection of blood flow to the skin makes less oxygen available to your muscles and hence your heart beats faster and pumps harder to compensate for the loss of oxygen going to your muscles. This results in a higher heart rate for your usual...