A user exercise-tolerance measuring pulse oximeter system, for determining the exercise tolerance or capacity of a user undergoing exercise, the system comprising: an elastic wireless fingerband comprising an optical sensor to provide an oxygen saturation signal, a chargeable power supply, and a wireless transmitter/receiver; a motion detector to provide a user motion signal; and a signal processor coupled to said wireless fingerband to process data from said optical sensor, and coupled to said motion detector; wherein said signal processor is configured to: process a combination of said oxygen saturation signal and said user motion signal to determine exercise tolerance data, wherein said exercise tolerance data is dependent upon said oxygen saturation signal and a level of exertion of said user determined from said user motion signal; and to time or count a period or quantity of user motion or movements, during said exercise, identified by said motion detector, to determine said level of exertion; to measure a degree of oxygen desaturation of blood of said user due to said exercise; and to output an exercise tolerance parameter; wherein said exercise tolerance data comprises said exercise tolerance parameter; and wherein said exercise tolerance parameter is a function of both said degree of desaturation and said level of exertion; wherein said processor is further configured to use said oxygen saturation signal to measure a level of oxygen saturation during said exercise and to determine a derivative of said level of oxygen saturation with respect to time to determine an oxygen desaturation rate; and wherein said exercise tolerance data includes data representing one or more values of said derivative during said exercise such that said exercise tolerance parameter is dependent on said oxygen desaturation rate. an elastic wireless fingerband comprising an optical sensor to provide an oxygen saturation signal, a chargeable power supply, and a wireless transmitter/receiver; a motion detector to provide a user motion signal; and a signal processor coupled to said wireless fingerband to process data from said optical sensor, and coupled to said motion detector; wherein said signal processor is configured to: process a combination of said oxygen saturation signal and said user motion signal to determine exercise tolerance data, wherein said exercise tolerance data is dependent upon said oxygen saturation signal and a level of exertion of said user determined from said user motion signal; and to time or count a period or quantity of user motion or movements, during said exercise, identified by said motion detector, to determine said level of exertion; to measure a degree of oxygen desaturation of blood of said user due to said exercise; and to output an exercise tolerance parameter; wherein said exercise tolerance data comprises said exercise tolerance parameter; and wherein said exercise tolerance parameter is a function of both said degree of desaturation and said level of exertion; wherein said processor is further configured to use said oxygen saturation signal to measure a level of oxygen saturation during said exercise and to determine a derivative of said level of oxygen saturation with respect to time to determine an oxygen desaturation rate; and wherein said exercise tolerance data includes data representing one or more values of said derivative during said exercise such that said exercise tolerance parameter is dependent on said oxygen desaturation rate. process a combination of said oxygen saturation signal and said user motion signal to determine exercise tolerance data, wherein said exercise tolerance data is dependent upon said oxygen saturation signal and a level of exertion of said user determined from said user motion signal; and to time or count a period or quantity of user motion or movements, during said exercise, identified by said motion detector, to determine said level of exertion; to measure a degree of oxygen desaturation of blood of said user due to said exercise; and to output an exercise tolerance parameter; wherein said exercise tolerance data comprises said exercise tolerance parameter; and wherein said exercise tolerance parameter is a function of both said degree of desaturation and said level of exertion; wherein said processor is further configured to use said oxygen saturation signal to measure a level of oxygen saturation during said exercise and to determine a derivative of said level of oxygen saturation with respect to time to determine an oxygen desaturation rate; and wherein said exercise tolerance data includes data representing one or more values of said derivative during said exercise such that said exercise tolerance parameter is dependent on said oxygen desaturation rate.