Timing of muscle activation of the lower limbs can be modulated to maintain a constant pedaling cadence.

This study investigated changes in muscle activity when subjects are asked to maintain a constant cadence during an unloaded condition. Eleven subjects pedaled for five loaded conditions (220 W, 190 W, 160 W, 130 W, 100 W) and one unloaded condition at 80 rpm. Electromyographic (EMG) activity of six lower limb muscles, pedal forces and oxygen consumption were calculated for every condition. Muscle activity was defined by timing (EMG onset and offset) and level (integrated values of EMGrms calculated between EMG onset and EMG offset) of activation, while horizontal and vertical impulses were computed to characterize pedal forces. Muscle activity, pedal forces and oxygen consumption variables measured during the unloaded condition were compared with those extrapolated to 0 W from the loaded conditions, assuming a linear relationship. The muscle activity was changed during unloaded condition: EMG onset and/or offset of rectus femoris, biceps femoris, vastus medialis, and gluteus maximus muscles were delayed (p<0.05); iEMGrms values of rectus femoris, biceps femoris, gastrocnemius medialis and tibialis anterior muscles were higher than those extrapolated to 0 W (p<0.05). Vertical impulse over the extension phase was lower (p<0.05) while backward horizontal impulse was higher (p<0.05) during unloaded condition than those extrapolated to 0 W. Oxygen consumptions were higher during unloaded condition than extrapolated to 0 W (750+/-147 vs. 529+/-297 mLO(2) x min(-1); p<0.05). Timing of activation of rectus femoris and biceps femoris was dramatically modified to optimize pedal forces and maintain a constant cadence, while systematic changes in the activation level of the bi-articular muscles induced a relative increase in metabolic expenditure when pedaling during an unloaded condition.

A cycle ergometer mounted on a standard force platform for three-dimensional pedal forces measurement during cycling.

This report describes a new method allowing to measure the three-dimensional forces applied on right and left pedals during cycling. This method is based on a cycle ergometer mounted on a force platform. By recording the forces applied on the force platform and applying the fundamental mechanical equations, it was possible to calculate the instantaneous three-dimensional forces applied on pedals. It was validated by static and dynamic tests. The accuracy of the present system was -7.61 N, -3.37 N and -2.81 N, respectively, for the vertical, the horizontal and the lateral direction when applying a mono-directional force and -4.52 N when applying combined forces. In pedaling condition, the orientation and magnitude of the pedal forces were comparable to the literature. Moreover, this method did not modify the mechanical properties of the pedals and offered the possibility for pedal force measurement with materials often accessible in laboratories. Measurements obtained showed that this method has an interesting potential for biomechanical analyses in cycling.

Relationship between the increase of effectiveness indexes and the increase of muscular efficiency with cycling power.

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 degrees)), the downstroke phase (IE(180 degrees Desc)) and the upstroke phase (IE(180 degrees Asc)). IE(360 degrees) and IE(180 degrees 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 degrees 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 degrees Asc) could also explain small variations of GE and NE for a recreational group.

Supra-maximal cycling efficiency assessed in humans by using a new protocol.

This study proposed a non-invasive method to determine the gross (GE, no baseline correction), net (NE, resting metabolism as the baseline correction) and work (WE, unloaded cycling as the baseline correction) efficiencies during cycling at an intensity higher than the maximal aerobic power (MAP). Twelve male subjects performed two exercises consisting of 4 min at 50% MAP followed either by 8 min at 63% MAP or by 8 sequences of 60 s divided into 10 s at 130% MAP and 50 s at 50% MAP (i.e., 63% MAP on average). Oxygen uptake was continuously measured to calculate GE, NE and WE at 50%, 63% and 130% MAP, and the data presented as the means and standard deviations. The GE values were 18.2%, 19.1%, 22.7%, the NE values were 22.4%, 22.8%, 24.3% and the WE values were 34.2%, 31.4% and 27.2% at 50%, 63% and 130% MAP, respectively. The GE and NE increased (P < 0.001) whereas the WE decreased (P < 0.001) with each increment in power output. The GE was lower than the NE (P < 0.001) at 50% and 63% MAP and than the WE (P < 0.001) at all intensities. The NE was lower (P < 0.001) than the WE at 50% and 63% MAP. These results showed that (1) efficiency index values obtained during supra-maximal exercise were consistent with previous proposals and (2) the efficiency-power output relationships were not limited to sub-maximal intensity levels but were confirmed at higher power output.