Interest in tests of short-term maximal exercise capacity has increased during recent years. The purpose of this investigation was therefore to study how heart rates and ratings of perceived exertion increase during a work test when the subjects only have to exercise at each work load for 0.5 min and to study predictability of maximal performances. A differential test is obtained by using a series of submaximal ratings to estimate the exercise intensity that can be maintained for only 30 s. The validity of the estimated intensity was checked by having the subject exercise at that load. The test time obtained was then used to correct the estimated exercise intensity according to the general function describing the relation between exercise intensity and exercise time for maximal performances. In the validation the test performances were compared to results from (a) common submaximal ergometer test, and (b) a special test measuring dynamic muscular strength.