The exercise intensity is increased in periods of about 4-5 minutes and blood samples are taken with a finger stick at the end of each period. Along with blood lactate concentration, heart rate, power output and VO2 are often measured. This process continues until the blood lactate concentration increases significantly. This tends to be a fairly obvious spike in the data. Because lactate threshold occurs sooner than VO2 max is reached, it is often measured as a percentage of VO2 max. Athletes and coaches measure the power output (usually in watts/kg) at their lactate threshold in order to design training programs.