There are both acute and chronic physiological responses to exercise. Acute responses occur during and after exercise and include increased heart rate, respiration rate, stroke volume, cardiac output, VO2, tidal volume, systolic blood pressure, and blood flow to working muscles. Chronic responses take at least 6 weeks to develop and include increased oxygen carrying capacity of blood, number of blood vessels and capillaries, lung function, heart size, stroke volume and decreased resting heart rate. These long-term adaptations improve the body's ability to perform exercise.