The strength of the electron-phonon coupling parameter and its evolution throughout a solid's phase diagram often determines phenomena such as superconductivity, charge- and spin-density waves. Its experimental determination relies on the ability to distinguish thermally activated phonons from those emitted by conduction band electrons, which can be achieved in an elegant way by ultrafast techniques. Separating the electronic from the out-of-equilibrium lattice subsystems, we probed their reequilibration by monitoring the transient lattice temperature through femtosecond x-ray diffraction in La2−xSrxCuO4 single crystals with x = 0.1 and 0.21. The temperature dependence of the electron-phonon coupling is obtained experimentally and shows similar trends to what is expected from the ab initio calculated shape of the electronic density of states near the Fermi energy. This study evidences the important role of band effects in the electron-lattice interaction in solids, in particular, in superconductors.