Probing active forces via a fluctuation-dissipation relation: Application to living cells P. Bohec, F. Gallet, C. Maes, S. Safaverdi, P. Visco and F. van Wijland EPL, 102 5 (2013) 50005 Published online: 21 June 2013 DOI: 10.1209/0295-5075/102/50005