Abstract  We determined the index of effectiveness (IE), as defined by the ratio of the tangential (effective force) to the total force applied on the pedals, using a new method proposed by Mornieux et al. (J Biomech, 2005), while simultaneously measuring the muscular efficiency during sub-maximal cycling tests of different intensities. This allowed us to verify whether part of the changes in muscular efficiency could be explained by a better orientation of the force applied on the pedals. Ten subjects were asked to perform an incremental test to exhaustion, starting at 100 W and with 30 W increments every 5 min, at 80 rpm. Gross (GE) and net (NE) efficiencies were calculated from the oxygen uptake and W _Ext measurements. From the three-dimensional force’s measurements, it was possible to measure the total force (F _Tot), including the effective (F _Tang) and ineffective force (F _Rad+Lat). IE has been determined as the ratio between F _Tang and F _Tot, applied on the pedals for three different time intervals, i.e., during the full revolution (IE_360°), the downstroke phase (IE_180°Desc) and the upstroke phase (IE_180°Asc). IE_360° and IE_180°Asc were significantly correlated with GE (r=0.79 and 0.66, respectively) and NE (r=0.66 and 0.99, respectively). In contrast, IE_180°Desc was not correlated to GE or to NE. From a mechanical point of view, during the upstroke, the subject was able to reduce the non-propulsive forces applied by an active muscle contraction, contrary to the downstroke phase. As a consequence, the term ‘passive phase’, which is currently used to characterize the upstroke phase, seems to be obsolete. The IE_180°Asc could also explain small variations of GE and NE for a recreational group.