Title: Fluctuation theorem for time-averaged work

Abstract: There is evidence that taking the time average of the work performed by a thermally isolated system ``transforms'' the adiabatic process into an isothermal one. Also, such a measurement accesses the inherent quantities of the system, which were not available to obtain with the usual work. I add here one more fact to this case by showing that the difference of the time-averaged Helmholtz's free energies is equal to the quasistatic work of the system. I also show a fluctuation theorem relating the time-averaged work and the quasistatic work. Numerical evidence for such an equality is also presented for the classical harmonic oscillator with a driven linear equilibrium position parameter. In the end, it is proposed that a more useful way to measure the spent of energy of a thermally isolated system is made by the time-averaged work instead of the usual work.