Method of estimation of a useful power provided by an individual during a physical activity consisting in executing an alternating pedalling movement on a pedal device, the method comprises an estimation (E1 - E3) of a mean useful effort ( F u [ CP j]) exerted by the individual during a current pedalling cycle (CP j), by implementing a method involving: - a step of measurement of a bearing force (Fp n) on a pedal of the pedal set by a force measurement sensor (Cf) outfitting the pedal, different from the useful effort, exerted by the individual during a pedalling cycle (CP j), - a step of determination of a maximum ( max(Fp n)) of the bearing force measured during the pedalling cycle (CPj), and - a step of estimation of a mean useful effort exerted by the individual during said pedalling cycle (CP j) from the maximum of the bearing force ( max(Fp n)) determined and with the aid of a predetermined correlation function (f aff, D) between a maximum bearing force during a pedalling cycle and a mean useful effort in said cycle, characterized in that said correlation function (f aff, D) being stored in a memory of a device, said predetermined function (f aff, D) is an affine linear regression function defined by the function y=αx+β where y designates mean useful effort provided by the cyclist during said pedalling cycle, where x designates the maximum of bearing force during the pedalling cycle, and where α and β are parameters which are predefined during a calibration phase, the method of estimation of a useful power comprising: - a step of measuring an acceleration of the pedal set during a succession of pedalling cycles by an acceleration sensor, - a step of determination of a pedalling rhythm valid for the current pedalling cycle (CP j) from the measurements of acceleration, and - a step of calculating the mean useful power ( P u [ CP j]) developed during the current pedalling cycle (CPj) from the mean useful effort estimated for said current pedalling cycle (CPj) and the estimated pedalling rhythm valid for said current pedalling cycle (CPj), the method of estimation of a useful power being implemented by a control unit, integrating an estimator of useful effort and a calculator of useful power, the control unit being adapted to communicate by wireless link with the force sensor and with the acceleration sensor outfitting one pedal of the pedal set. - a step of measurement of a bearing force (Fp n) on a pedal of the pedal set by a force measurement sensor (Cf) outfitting the pedal, different from the useful effort, exerted by the individual during a pedalling cycle (CP j), - a step of determination of a maximum ( max(Fp n)) of the bearing force measured during the pedalling cycle (CPj), and - a step of estimation of a mean useful effort exerted by the individual during said pedalling cycle (CP j) from the maximum of the bearing force ( max(Fp n)) determined and with the aid of a predetermined correlation function (f aff, D) between a maximum bearing force during a pedalling cycle and a mean useful effort in said cycle, characterized in that said correlation function (f aff, D) being stored in a memory of a device, said predetermined function (f aff, D) is an affine linear regression function defined by the function y=αx+β where y designates mean useful effort provided by the cyclist during said pedalling cycle, where x designates the maximum of bearing force during the pedalling cycle, and where α and β are parameters which are predefined during a calibration phase, - a step of measuring an acceleration of the pedal set during a succession of pedalling cycles by an acceleration sensor, - a step of determination of a pedalling rhythm valid for the current pedalling cycle (CP j) from the measurements of acceleration, and - a step of calculating the mean useful power ( P u [ CP j]) developed during the current pedalling cycle (CPj) from the mean useful effort estimated for said current pedalling cycle (CPj) and the estimated pedalling rhythm valid for said current pedalling cycle (CPj),