The study of force and endurance necessitates the use of special instruments designed by physiologists and psychologists at the turn of the 20th century. It was the Italian physiologist Angelo Mosso (1846-1910) who invented the ergograph in the early 1880s, a device intended to measure muscular fatigue in humans. The success of Mosso’s ergograph obscured the importance of the dynamograph, the most famous type of which remains the one developed by the French psychologist Charles Henry (1859-1926) in 1904 and widely used in France in psychology and physiology laboratories before World War II. This paper presents the history of the technical evolution of ergographs and dynamographs that were used in most psychology and physiology laboratories at the turn of the century. These instruments have greatly contributed to the development of the nascent psychology by allowing the objective study of psychological factors during physical tests of strength and endurance.