> ## Documentation Index > Fetch the complete documentation index at: https://docs.uplift.ai/llms.txt > Use this file to discover all available pages before exploring further. # Tennis: Overhand Serve > Documentation of tennis overhand events, phases, and metrics. Evaluate serve mechanics to improve consistency and maximize energy transfer to the ball. ## Dimensions Required Inputs for processing: * **handedness:** the handedness of the player \['left', 'right'] * **serve stance position:** the stance type used for the serve \['pinpoint', 'platform'] ## Phases of the serve Stages adopted from [Kovacs & Ellenbecker, 2011](https://pmc.ncbi.nlm.nih.gov/articles/PMC3445225/). ( [Video](https://www.youtube.com/watch?v=EBLIZS_iNq8) ) | Phase | Stage | Start | End | Event or Phase | | ------------ | ------------ | ------------ | -------------------- | -------------- | | Preparation | Start | Initiation | Initiation | Event | | Preparation | Release | Initiation | Ball Release | Phase | | Preparation | Loading | Ball Release | Low Arm | Phase | | Preparation | Cocking | Low Arm | Max Shoulder Ext Rot | Phase | | Acceleration | Acceleration | Max Sho ER | Ball Contact | Phase | | Acceleration | Ball Contact | Ball Contact | Ball Contact | Event | | Follow Thru | Deceleration | Ball Contact | Termination | Phase | | Follow Thru | Finish | Termination | Termination | Event | ## Variables Output variables from tennis overhand serve analysis. ### Normative Ranges See [Tennis Overhand Serve Norms](/biomechanics/activities/tennis/tennis-overhand-serve-norms) for the full 5th–95th percentile reference tables by competition level (Youth, Professional, Broad). ### Generic Outputs Every capture includes session metadata, standard joint angle/velocity time series, and 3D keypoint positions common to all movements. See [Generic Outputs](/biomechanics/generic-outputs) for the full list. ### Events | Metric | Description | Column Name | | ----------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------- | -------------------------------------- | | [Initiation](/biomechanics/activities/tennis/events/initiation) | the start of the tennis serve | `initiation_event` | | [Ball Release](/biomechanics/activities/tennis/events/ball-release) | the estimated timing of ball toss release | `ball_release_event` | | [Low Arm](/biomechanics/activities/tennis/events/low-arm) | the low point of the dominant arm prior to ball contact | `low_arm_event` | | [Max Shoulder ER](/biomechanics/activities/tennis/events/max-shoulder-er) | the instant of maximum shoulder external rotation between ball release and apex | `max_shoulder_external_rotation_event` | | [Apex](/biomechanics/activities/tennis/events/apex) | maximum height of the dominant-side wrist joint center during the serve | `apex_event` | | [Termination](/biomechanics/activities/tennis/events/termination) | end of the tennis serve | `termination_event` | | [Peak Forearm Velocity](/biomechanics/activities/tennis/events/peak-forearm-velocity) | the instant of peak forearm forward angular velocity, used to determine forward kinematic sequence | \`\` | | [Peak Upper Arm Velocity](/biomechanics/activities/tennis/events/peak-upper-arm-velocity) | the instant of peak upper arm forward angular velocity, used to determine forward kinematic sequence | \`\` | | [Peak Torso Velocity](/biomechanics/activities/tennis/events/peak-torso-velocity) | the instant of peak torso forward angular velocity, used to determine forward kinematic sequence | \`\` | ### Forward Kinematic Sequence Metrics | Metric | Units | Description | Column Name | | -------------------------------------------------------------------------------------------------------------------------- | -------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ----------------------------------------- | | [Peak Torso Forward Angular Velocity](/biomechanics/activities/tennis/metrics/peak-torso-forward-angular-velocity) | degrees/second | Peak forward angular velocity of the torso segment in the serve direction | `peak_torso_forward_angular_velocity` | | [Peak Upper Arm Forward Angular Velocity](/biomechanics/activities/tennis/metrics/peak-upper-arm-forward-angular-velocity) | degrees/second | Peak forward angular velocity of the upper arm segment in the serve direction | `peak_upper_arm_forward_angular_velocity` | | [Peak Forearm Forward Angular Velocity](/biomechanics/activities/tennis/metrics/peak-forearm-forward-angular-velocity) | degrees/second | Peak forward angular velocity of the forearm segment in the serve direction | `peak_forearm_forward_angular_velocity` | | [Forward Kinematic Sequence](/biomechanics/activities/tennis/metrics/forward-kinematic-sequence) | N/A | Sequence of peak forward angular velocities. Optimal sequence is 'torso-upper\_arm-forearm' | `forward_kinematic_sequence` | | [Forward Trunk Arm Speedup](/biomechanics/activities/tennis/metrics/forward-trunk-arm-speedup) | N/A | Speedup factor of peak forward angular velocities from the torso to the upper arm. | `forward_trunk_arm_speedup` | | [Forward Upper Arm Forearm Speedup](/biomechanics/activities/tennis/metrics/forward-upper-arm-forearm-speedup) | N/A | Speedup factor of peak forward angular velocities from the upper arm to the forearm. | `forward_upper_arm_forearm_speedup` | | [Upper Arm Forward Angular Velocity](/biomechanics/activities/tennis/metrics/forward-angular-velocity-time-series) | deg/s | Time series values of the instantaneous forward angular velocity (serve direction) of the upper arm segment. Evaluate near apex (ball contact event) to visualize kinematic sequencing | `upper_arm_forward_angular_velocity` | | [Torso Forward Angular Velocity](/biomechanics/activities/tennis/metrics/forward-angular-velocity-time-series) | deg/s | Time series values of the instantaneous forward angular velocity (serve direction) of the torso segment. Evaluate near apex (ball contact event) to visualize kinematic sequencing | `torso_forward_angular_velocity` | | [Forearm Forward Angular Velocity](/biomechanics/activities/tennis/metrics/forward-angular-velocity-time-series) | deg/s | Time series values of the instantaneous forward angular velocity (serve direction) of the forearm segment. Evaluate near apex (ball contact event) to visualize kinematic sequencing | `forearm_forward_angular_velocity` | ### Twist Kinematic Sequence Metrics | Metric | Units | Description | Column Name | | ---------------------------------------------------------------------------------------------------------------------- | -------------- | ----------------------------------------------------------------------------------------- | ------------------------------------ | | [Peak Pelvis Twist Angular Velocity](/biomechanics/activities/tennis/metrics/peak-pelvis-twist-angular-velocity) | degrees/second | Peak twist angular velocity of the pelvis segment in the serve direction | `pelvis_peak_twist_angular_velocity` | | [Peak Torso Twist Angular Velocity](/biomechanics/activities/tennis/metrics/peak-torso-twist-angular-velocity) | degrees/second | Peak twist angular velocity of the torso segment in the serve direction | `trunk_peak_twist_angular_velocity` | | [Peak Upper Arm Twist Angular Velocity](/biomechanics/activities/tennis/metrics/peak-upper-arm-twist-angular-velocity) | degrees/second | Peak twist angular velocity of the upper arm segment in the serve direction | `arm_peak_twist_angular_velocity` | | [Twist Kinematic Sequence](/biomechanics/activities/tennis/metrics/twist-kinematic-sequence) | N/A | Sequence of peak twist angular velocities. Optimal sequence is 'torso-upper\_arm-forearm' | `twist_kinematic_sequence` | | [Twist Trunk Arm Speedup](/biomechanics/activities/tennis/metrics/twist-trunk-arm-speedup) | N/A | Speedup factor of peak twist angular velocities from the torso to the upper arm. | `twist_trunk_arm_speedup` | | [Twist Pelvis Torso Speedup](/biomechanics/activities/tennis/metrics/twist-pelvis-torso-speedup) | N/A | Speedup factor of peak twist angular velocities from the pelvis to the trunk. | `twist_pelvis_trunk_speedup` | ### Movement Flag Metrics Movement flags identify poor or suboptimal mechanics for timing and body positioning during the serve. | Metric | Description | Column Name | | ---------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------------------------------------------------------- | ---------------------------------------- | | [Release Phase Off-Arm to Body Position](/biomechanics/activities/tennis/flags/release-phase-off-arm-to-body-position) | Ball toss angle is outside the acceptable 90°–180° range at ball release. | `release_phase_off_arm_to_body_position` | | [Release Phase Elbow Not Straight](/biomechanics/activities/tennis/flags/release-phase-elbow-not-straight) | Non-dominant elbow flexion exceeds 30° at ball release. | `release_phase_elbow_not_straight` | | [Loading Phase Knee Asymmetry](/biomechanics/activities/tennis/flags/loading-phase-knee-asymmetry) | Front-to-back knee flexion difference exceeds 15° during loading. | `loading_phase_knee_asymmetry` | | [Loading Phase Pinpoint Break](/biomechanics/activities/tennis/flags/loading-phase-pinpoint-break) | Athlete breaks from a pinpoint stance during loading. | `loading_phase_pinpoint_break` | | [Loading Phase Lack of Trunk Coil](/biomechanics/activities/tennis/flags/loading-phase-lack-trunk-coil) | Trunk coil is below 110° during loading. | `loading_phase_lack_trunk_coil` | | [Loading Phase Lack of Pelvis Coil](/biomechanics/activities/tennis/flags/loading-phase-lack-pelvis-coil) | Pelvis coil is below 110° during loading. | `loading_phase_lack_pelvis_coil` | | [Loading Phase Lack of Shoulder Drop](/biomechanics/activities/tennis/flags/loading-phase-lack-shoulder-drop) | Trunk does not tilt toward the rear by at least 5° during loading. | `loading_phase_lack_shoulder_drop` | | [Loading Phase Lack of Pelvis Drop](/biomechanics/activities/tennis/flags/loading-phase-lack-pelvis-drop) | Pelvis does not tilt toward the rear during loading. | `loading_phase_lack_pelvis_drop` | | [Loading Phase Excessive Knee Valgus](/biomechanics/activities/tennis/flags/loading-phase-excessive-knee-valgus) | Front or back knee valgus classified as "high" during loading. | `loading_phase_excessive_knee_valgus` | | [Cocking Phase Lack of External Rotation](/biomechanics/activities/tennis/flags/cocking-phase-lack-external-rotation) | Max shoulder external rotation is below 180° during cocking. | `cocking_phase_lack_external_rotation` | | [Contact Phase Arm Out of Slot Position](/biomechanics/activities/tennis/flags/contact-phase-arm-out-of-slot-position) | Shoulder abduction is outside the 110°–140° range at ball contact. | `contact_phase_arm_out_of_slot_position` | | [Contact Phase Open Trunk Rotation](/biomechanics/activities/tennis/flags/contact-phase-open-trunk-rotation) | Trunk rotation has not passed -20° by ball contact. | `contact_phase_open_trunk_rotation` | | [Contact Phase Open Pelvis Rotation](/biomechanics/activities/tennis/flags/contact-phase-open-pelvis-rotation) | Pelvis rotation has not passed -30° by ball contact. | `contact_phase_open_pelvis_rotation` | | [Landing Phase Excessive Forward Lean](/biomechanics/activities/tennis/flags/landing-phase-excessive-forward-lean) | Trunk forward flexion exceeds 60° at finish. | `landing_phase_excessive_forward_lean` | | [Landing Phase Excessive Side Lean](/biomechanics/activities/tennis/flags/landing-phase-excessive-side-lean) | Absolute trunk side tilt exceeds 30° at finish. | `landing_phase_excessive_side_lean` | | [Landing Phase Excessive Forward Drift](/biomechanics/activities/tennis/flags/landing-phase-excessive-forward-drift) | Forward body displacement exceeds 0.50x height between contact and finish. | `landing_phase_excessive_forward_drift` | | [Landing Phase Excessive Side Drift](/biomechanics/activities/tennis/flags/landing-phase-excessive-side-drift) | Open-side body displacement exceeds 0.30x height (or -0.10x height) between contact and finish. | `landing_phase_excessive_side_drift` | ### Loading Phase Metrics | Metric | Units | Description | Column Name | | ---------------------------------------------------------------------------------------------------------------------- | -------- | ------------------------------------------------------------------------------------------------------------------ | --------------------------------------- | | [Loading Phase Max Knee Flexion Front Leg](/biomechanics/activities/tennis/metrics/loading-phase-knee-flexion) | degrees | Maximum amount of front leg knee flexion during the loading phase of the serve | `loading_phase_max_front_knee_flexion` | | [Loading Phase Max Knee Flexion Back Leg](/biomechanics/activities/tennis/metrics/loading-phase-knee-flexion) | degrees | Maximum amount of back leg knee flexion during the loading phase of the serve | `loading_phase_max_back_knee_flexion` | | [Loading Phase Trunk Tilt](/biomechanics/activities/tennis/metrics/loading-phase-trunk-tilt) | degrees | Maximum amount of trunk side-side tilt towards the rear during the loading phase of the serve | `loading_phase_trunk_tilt` | | [Loading Phase Pelvis Tilt](/biomechanics/activities/tennis/metrics/loading-phase-pelvis-tilt) | degrees | Maximum amount of pelvis side-side tilt towards the rear during the loading phase of the serve | `loading_phase_pelvis_tilt` | | [Loading Phase Shoulder Hip Separation](/biomechanics/activities/tennis/metrics/loading-phase-shoulder-hip-separation) | degrees | Maximum difference in rotation of the shoulders and hips during the loading phase of the serve | `loading_phase_shoulder_hip_separation` | | [Loading Phase Ball Release Angle](/biomechanics/activities/tennis/metrics/loading-phase-ball-release-angle) | degrees | Transverse plane arm angle at the instance of ball release | `loading_phase_ball_toss_angle` | | [Trunk Coil](/biomechanics/activities/tennis/metrics/trunk-coil) | deg | Maximum amount of trunk twist rotation away from the serve direction, like preloading the twist before the serve. | `trunk_coil` | | [Pelvis Coil](/biomechanics/activities/tennis/metrics/pelvis-coil) | deg | Maximum amount of pelvis twist rotation away from the serve direction, like preloading the twist before the serve. | `pelvis_coil` | | [Release Phase Elbow Angle](/biomechanics/activities/tennis/metrics/release-phase-elbow-angle) | degrees | Non-dominant (tossing) elbow flexion angle at ball release | `release_phase_elbow_angle` | | [Max Front Knee Valgus (Normalized)](/biomechanics/activities/tennis/metrics/max-front-knee-valgus) | × height | Maximum inward collapse of the front knee during the serve, normalized to athlete height | `max_front_knee_valgus_upward_per_ht` | | [Max Back Knee Valgus (Normalized)](/biomechanics/activities/tennis/metrics/max-back-knee-valgus) | × height | Maximum inward collapse of the back knee during the serve, normalized to athlete height | `max_back_knee_valgus_upward_per_ht` | ### Cocking and Acceleration Phase Metrics | Metric | Units | Description | Column Name | | ---------------------------------------------------------------------------------------------------------------------------------------------- | -------------- | ------------------------------------------------------------------------------------------- | ------------------------------------------------------ | | [Cocking Phase Max Shoulder External Rotation](/biomechanics/activities/tennis/metrics/cocking-phase-shoulder-external-rotation) | degrees | Maximum amount of shoulder external rotation during the cocking phase of the serve | `cocking_phase_max_shoulder_external_rotation` | | [Cocking Phase Shoulder Hyperangulation](/biomechanics/activities/tennis/metrics/cocking-phase-shoulder-hyperangulation) | degrees | Maximum amount of shoulder horizontal abduction during the cocking phase of the serve | `cocking_phase_shoulder_hyperangulation` | | [Cocking Phase Max X Factor](/biomechanics/activities/tennis/metrics/cocking-phase-max-x-factor) | degrees | Maximum hip-shoulder separation during the cocking phase of the serve | `cocking_phase_max_x_factor` | | [Cocking Phase Shoulder Horizontal Abduction](/biomechanics/activities/tennis/metrics/cocking-phase-shoulder-horizontal-abduction) | degrees | Maximum horizontal abduction of the dominant shoulder during the cocking phase of the serve | `cocking_phase_shoulder_horizontal_abduction` | | [Acceleration Phase Max Knee Extension Velocity Front Leg](/biomechanics/activities/tennis/metrics/acceleration-phase-knee-extension-velocity) | degrees/second | Maximum knee extension velocity of the front leg during the acceleration phase of the serve | `acceleration_phase_max_front_knee_extension_velocity` | | [Acceleration Phase Max Knee Extension Velocity Back Leg](/biomechanics/activities/tennis/metrics/acceleration-phase-knee-extension-velocity) | degrees/second | Maximum knee extension velocity of the back leg during the acceleration phase of the serve | `acceleration_phase_max_back_knee_extension_velocity` | | [Acceleration Phase Max Elbow Extension Velocity](/biomechanics/activities/tennis/metrics/acceleration-phase-elbow-extension-velocity) | degrees/second | Maximum extension velocity of the dominant elbow during the acceleration phase of the serve | `max_elbow_extension_velocity` | ### Contact Phase Metrics | Metric | Units | Description | Column Name | | ---------------------------------------------------------------------------------------------------------------------------- | ----------- | ------------------------------------------------------------------------------ | ------------------------------------- | | [Contact Phase Elbow Flexion](/biomechanics/activities/tennis/metrics/contact-phase-elbow-flexion) | degrees | Amount of elbow flexion at apex | `contact_phase_elbow_flexion` | | [Contact Phase Shoulder Abduction](/biomechanics/activities/tennis/metrics/contact-phase-shoulder-abduction) | degrees | Amount of shoulder abduction at apex | `contact_phase_shoulder_abduction` | | [Contact Phase X Factor](/biomechanics/activities/tennis/metrics/contact-phase-x-factor) | degrees | Angle between the shoulders to hips in the transverse plane (twisting) at apex | `contact_phase_x_factor` | | [Time to Contact](/biomechanics/activities/tennis/metrics/time-to-contact) | seconds | Duration from initiation to ball contact | `time_to_contact` | | [Contact Phase Trunk Tilt](/biomechanics/activities/tennis/metrics/contact-phase-trunk-tilt) | degrees | Degrees of side-side trunk tilt at apex | `contact_phase_trunk_tilt` | | [Contact Phase Trunk Flexion](/biomechanics/activities/tennis/metrics/contact-phase-trunk-flexion) | degrees | Forward/backward trunk flexion at apex | `contact_phase_trunk_flexion` | | [Contact Phase Trunk Rotation](/biomechanics/activities/tennis/metrics/contact-phase-trunk-rotation) | degrees | Trunk rotation relative to its starting orientation at apex | `contact_phase_trunk_rotation` | | [Contact Phase Pelvis Rotation](/biomechanics/activities/tennis/metrics/contact-phase-pelvis-rotation) | degrees | Pelvis rotation relative to its starting orientation at apex | `contact_phase_pelvis_rotation` | | [Contact Phase Wrist Height (Normalized)](/biomechanics/activities/tennis/metrics/contact-phase-wrist-height-normalized) | × height | Wrist height at apex, normalized to athlete height | `contact_phase_wrist_height_per_ht` | | [Contact Phase Wrist Velocity (Normalized)](/biomechanics/activities/tennis/metrics/contact-phase-wrist-velocity-normalized) | unconfirmed | Wrist speed at apex, reported alongside the height-normalized dataset | `contact_phase_wrist_velocity_per_ht` | | [Trunk Stretch](/biomechanics/activities/tennis/metrics/trunk-stretch) | deg | Twist range of motion of the trunk. | `trunk_stretch` | | [Pelvis Stretch](/biomechanics/activities/tennis/metrics/pelvis-stretch) | deg | Twist range of motion of the pelvis. | `pelvis_stretch` | ### Landing Phase Metrics | Metric | Units | Description | Column Name | | ----------------------------------------------------------------------------------------------------- | -------- | ------------------------------------------------------------------------------------ | ---------------------------- | | [Finish Phase Trunk Flexion](/biomechanics/activities/tennis/metrics/finish-phase-trunk-flexion) | degrees | Forward/backward trunk flexion at the finish of the serve | `finish_phase_trunk_flexion` | | [Finish Phase Trunk Tilt](/biomechanics/activities/tennis/metrics/finish-phase-trunk-tilt) | degrees | Lateral trunk tilt at the finish of the serve | `finish_phase_trunk_tilt` | | [Forward Displacement (Normalized)](/biomechanics/activities/tennis/metrics/displacement-forward) | × height | Forward body displacement between contact and finish, normalized to athlete height | `displacement_forward` | | [Open-Side Displacement (Normalized)](/biomechanics/activities/tennis/metrics/displacement-open-side) | × height | Open-side body displacement between contact and finish, normalized to athlete height | `displacement_open_side` | | [Vertical Displacement (Normalized)](/biomechanics/activities/tennis/metrics/displacement-vertical) | × height | Vertical body displacement between contact and finish, normalized to athlete height | `displacement_vertical` | ## Notes * Kinematic data typically captured at 240Hz for Tennis Overhand Serve