Bike Fitting Phase Five: Adaptation Of Dartfish Motion Capture Software and Quintic Biomechanics Software

Motion capture in 3D

ATA Cycle’s FitLab was one of the first to incorporate the use of Dartfish’s motion capture software in its fitting process – all the while taking advantage of each and every update and iteration of the platform over the years.

The important feature of Dartfish, is that it enables FitLab to analyze critical data such as a rider’s pedal mechanics and overall posture on the bike in real-time analysis, while quantifying each and every change in position and ruling out any biomechanical anomalies. This “platform” allows FitLab to “fine tune” the rider’s position, with goal of maximizing power, while at the same time enhancing comfort and safety.

Dartfish’s latest software, TeamPro Data, now supports data integration with video, which allows FitLab to import a rider’s “power map” from his or her power meter, and subsequently analyze it on-screen in conjunction with Dartfish’s software in real-time. This latest feature brings a whole new level of data collection and power analysis to the Dartfish platform.

Quintic

Quintic is but another important “tool” in ATA Cycle’s vast arsenal of bike fit capabilities.

A cyclist’s maximum power output is a major determinant of performance. Overall power output can be recorded accurately and reliably using an on-bicycle device such as a power meter. And, while overall power output is a very useful performance metric, it is limited as a biomechanical measurement which does not reveal any indication of “positional movement” adopted by the rider.
Quintic allows for a more detailed analysis of power through inverse dynamic analysis, which allows for the calculation of joint-specific power outputs. Therefore, by determining hip, knee and ankle power transfer, FitLab can understand in much greater detail how the rider produces his or her maximum overall power output.

In turn, this provides FitLab with valuable information as how to analyze and correct a rider’s position, via inverse dynamic analysis.

The process involves three segments of analysis: force output (kinetics), kinematics and body segment parameter data

Data for the inverse dynamics analysis are collected during a short “all-out” test of maximum power output. For this step, the rider is instructed to apply as much force as possible throughout his or her pedal stroke via a cycling ergometer. For the kinematics step, a high definition camera is used to capture the segment. Before the data collection occurs, a calibration square is placed next to the ergometer, while a short video clip is imported into the Quintic Biomechanics calibration procedure, wherein reflective markers are placed on the pedal spindle, 5th metatarsal joint on the foot, ankle joint center, knee joint center and hip joint center of the rider. From there, a video is captured during the “power output” stage and Quintic’s software is used post-event to obtain the kinematics data from the video.

Following the data collection stage, the video is imported into Quintic’s Biomechanics v17 onscreen menu to set the frame rate and calibrate the file. A five-point cycling model template is then created and saved linking the pedal spindle, 5th metatarsal, ankle joint, knee joint and hip joint. Using the imported video, the five joint markers are tracked and digitized automatically for 3 complete pedal revolutions. Once imported, the built-in filtering options are set to optimally smooth the raw data. Position, velocity and acceleration data of the hip, knee and ankle are viewed and analyzed in the angular analysis menu. Finally, the kinematics data is exported directly to Microsoft Excel, where the inverse dynamics analysis is completed with the kinetics and body segment parameter data.

In the final analysis, these results demonstrate the relative contribution of each of the lower limb joints to overall maximal power output. This information can be used to make cross-sectional comparison between different riders, or different bike setups, and also as a longitudinal measure to monitor the effect of different training intervals. This information is highly relevant to riders and coaches.

The automatic digitization procedure available in Quintic Biomechanics allows for the easy collection of kinematics data from video clips. Other options of collecting kinematics data (e.g. manual digitization or 3-D motion analysis) are either too time consuming or too costly to be considered for most bike fit settings. Another benefit of collecting kinematics data from the video capture, is it allows for the movement to be analyzed both quantitatively (collecting kinematics data) and qualitatively (analyzing movement directly from the video).

In summary, Quintic Biomechanics can be used to accurately and reliably generate kinematics data to use in an inverse dynamics analysis. This procedure allows the calculation of joint-specific power outputs in cycling, which is a highly relevant measure for the understanding of cycling performance.

Next step:

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