The maximum heart rate during exercise, calculated roughly as 220 minus one's age, decreases with advancing years. Thus, during exercise, older adults become short of breath (dyspnea) and tire more quickly than do younger individuals. A related problem, probably also caused in part by insufficient sympathetic nervous system activity, is postural, or orthostatic, hypotension, which is a fall in systemic blood pressure upon rising from a supine to a standing position (usually too quickly). It can cause lightheadedness when a person stands up and can thus increase the risk of falling.