Abstract
To analyze on-water rowing performance, a valid determination of the power loss due to the generation of propulsion is required. This power los can be calculated as the dot product of the net water force vector () and the time derivative of the position vector of the point at the blade where is applied (). In this article we presented a method that allows for accurate determination of both parameters using a closed system of three rotational equations of motion for three different locations at the oar. Additionally, the output of the method has been validated. An oar was instrumented with three pairs of strain gauges measuring local strain. Force was applied at different locations of the blade, while the oar was fixed at the oarlock and the end of the handle. Using a force transducer and kinematic registration, the force vector at the blade and the deflection of the oar were measured. These data were considered to be accurate and used to calibrate the measured strain for bending moments, the deflection of the oar and the angle of the blade relative to its unloaded position. Additionally, those data were used to validate the output values of the presented method plus the associated instantaneous power output. Good correspondence was found between the estimated perpendicular blade force and its reference (ICC = .999), while the parallel blade force could not be obtained (ICC = .000). The position of the PoA relative to the blade could be accurately obtained when the perpendicular force was ≥ 5.3 N (ICC = .927). Instantaneous power output values associated with the perpendicular force could be obtained with reasonable accuracy (ICC = .747). These results suggest that the power loss due to the perpendicular water force component can be accurately obtained, while an additional method is required to obtain the power losses due to the parallel force.
Highlights
For an accurate determination of the average power lost to the generation of propulsion per stroke cycle (Pblade; see Table 1 for a list of all abbreviations), valid information about the net water force vector at the blade of the oar (~Fw;o) and its associated point of application (PoA)
The estimated displacement of the beginning of the blade in y-direction and its reference are depicted. These examples imply that output of the strain gauges can be calibrated for bending moments, the deflection of the oar, and the orientation of the blade relative to the earth-bound frame of reference
The aim of this study was to describe and evaluate a method that allows for an accurate determination of the power loss due to the generation of propulsion in rowing
Summary
For an accurate determination of the average power lost to the generation of propulsion per stroke cycle (Pblade; see Table 1 for a list of all abbreviations), valid information about the net water force vector at the blade of the oar (~Fw;o) and its associated point of application (PoA). Þ dt ð1Þ where T is the time duration of a stroke cycle and~r_PoA=w is the time derivative of the position vector (i.e. the velocity vector) of the point of the blade where ~Fw;o is applied relative to an earth-bound frame of reference (~rPoA=w). Determination of ~Fw;o,~rPoA=w and its time derivative is not trivial due to the (1) deflection of the oar and (2) a constantly changing force distribution at the blade resulting in an unknown and time-variant point of application of the water force.
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