One of the most efficient and reliable observational technique allowing to probe the internal structure of a star is the determination of the apsidal motion in close eccentric binary systems. This secular precession of the binary orbit's major axis depends on the tidal interactions occurring between the two stars. The rate of this motion is directly related to the internal structure of the stars, in particular their inner density profile. The most common way to derive the apsidal motion of a binary from observations, together with the fundamental parameters of the stars, is the analysis of the times of minima of the eclipses. While this technique has been used for decades, it returned to popularity lately thanks to the incredible precision of observations acquired with space-borne facilities such as TESS and Kepler, among others. Aside, a less common – but not less accurate though – method to determine a binary's apsidal motion rate is through the fit of the stars’ radial velocity curves as a function of time. This technique relies on radial velocities collected over a (very) long timescale. While it points out the utility of gathering spectroscopic data of the same object over several decades, requiring dealing with the tricky task of combining and simultaneously analysing data from a variety of Earth-based instruments having their own characteristics each, it also gives old spectroscopic observations a second lease of life. But what do you think if we decide to simultaneously and consistently analyse both spectroscopic and photometric data, that is to say, all available data of the same binary, rather than ignoring part of them? This challenging objective comes with a real deserved reward: consistent physical and orbital parameters for the binaries, including the apsidal motion rate, are obtained with unprecedented accuracy. The confrontation of the observationally determined parameters to theoretical models of stellar structure and evolution then allows us to finely constrain the internal structure of the stars. This powerful technique has been known for years but has been seldom applied to massive stars. I will highlight its interest and reveal recent results concerning several massive binaries. While standard 1D stellar evolution models predict stars having a smaller internal stellar structure constant, that is to say, stars having a smaller density contrast, than expected from observations, I demonstrate that the addition