# Effects of Age and Sex on the Kinematics of the Sprinting Technique in the Maximum Velocity Phase
## 2 Materials and Methods
### Data Analysis  
Eighteen anatomical points of the body (tip of the toe, ankle, knee, hip, shoulder, elbow, wrist, and fingers on both sides of the body, the neck, and the head) and selected points in the filming view were manually digitized in each field. To calculate the Body Center of Mass (BCM) and the segmental inertia properties for the link segment model, the proportional to subject-specific height and weight characteristic formulas recommended by [PERSON] et al. [62] were used. Cut-off frequency for smoothing was set at 6 Hz [63]. Digitization, smoothing, and analyses were performed with the A.P.A.S. v.14.1.0.5 software (Ariel Dynamics Inc., Trabuco Canyon, CA, USA). The accuracy of the 2D reconstruction was determined by the root mean square error, after randomly re-digitizing 5% of the captured frames. An error of 1.1 cm and 0.7 cm was found for the X- and Y-axes, respectively.  
Regarding the examined parameters, RV was calculated by dividing the test distance by the time recorded by the photocells, while SF was defined as the steps taken per second. The touchdown was defined as the first field where the foot had clearly contacted the ground. The take-off was defined as the first field where the foot had clearly left the ground. Thus, the time of the contact and the flight phases were assessed for each step.  
Based on the XY coordinates of the digitized anatomical points, the experimental parameters were as follows:* SL: the horizontal distance between the touchdown points of the feet recorded for two consecutive supports;
* Touchdown distance (\(\mathrm{S_{TD}}\)): the horizontal distance between the toe of the support foot and the BCM projection at touchdown;
* Take-off distance (\(\mathrm{S_{TO}}\)): the horizontal distance between the toes of the support foot and the BCM projection at take-off;
* Horizontal BCM take-off velocity (\(\mathrm{V_{XTO}}\)): the horizontal velocity of BCM at take-off;
* Vertical BCM take-off velocity (\(\mathrm{V_{YTO}}\)): the vertical velocity of BCM at take-off;
* Angle of take-off (AngPr): the Arc-tangent of the vertical/horizontal BCM take-off velocity;
* Horizontal ankle touchdown velocity (\(\mathrm{V_{Xankle}}\)): the horizontal velocity of the ankle at touchdown;
* BCM height: the height of the BCM at touchdown (\(\mathrm{H_{TD}}\)), maximum lowering of the BCM (\(\mathrm{H_{AM}}\)), and take-off (\(\mathrm{H_{TO}}\));
* Knee joint angle: The angle formed between the thigh and the shank at touchdown (\(\mathrm{\theta knee_{TD}}\)), maximum knee amortization (\(\mathrm{\theta knee_{AM}}\)), and take-off (\(\mathrm{\theta knee_{TO}}\)). The minimum swing leg's knee angle at the support phase was also calculated (\(\mathrm{\theta knee_{MIN}}\));
* Ankle joint angle: the angle formed between the shank and the foot at touchdown (\(\mathrm{\theta ankle_{TD}}\)) and take-off (\(\mathrm{\theta knee_{TO}}\));
* Knee joint angular velocity (\(\mathrm{\omega_{KNEE}}\)): the angular velocity of the swing leg's knee joint at take-off;
* Ankle joint angular velocity (\(\mathrm{\omega_{ANLLE}}\)): the angular velocity of the support leg's ankle joint at touchdown;
* Thigh inclination (\(\mathrm{\varphi_{THIGH}}\)): the angle formed by the horizontal axis and the thigh of the swing leg at take-off;
* Leg inclination: the angle formed by the horizontal axis and the line passing from the support leg's ankle and hip at touchdown (\(\mathrm{\varphi leg_{TD}}\)) and take-off (\(\mathrm{\varphi leg_{TO}}\)).