Atmospheric neutrinos are produced during cascades initiated by the interaction of primary cosmic rays with air nuclei .
In this paper , a measurement of the atmospheric \nu _ { \mu } + \bar { \nu } _ { \mu } energy spectrum in the energy range 0.1 - 200 TeV is presented , using data collected by the ANTARES underwater neutrino telescope from 2008 to 2011 .
Overall , the measured flux is \sim 25 % higher than predicted by the conventional neutrino flux , and compatible with the measurements reported in ice .
The flux is compatible with a single power-law dependence with spectral index \gamma _ { meas } = 3.58 \pm 0.12 .
With the present statistics the contribution of prompt neutrinos can not be established .