About The Kinetic Whip

• Pick a card to try a different way of swinging. The faint grey figure is the real stroke; the solid one is the card you picked.
• Drag the bar to any moment; 0.05× plays at one twentieth of real speed. Drag the picture to turn it, or use the three view buttons at its lower left.
• Switch between right-handed and left-handed at the top right. Mirroring changes no physics, so the numbers stay the same.
• The pro view (on a phone, the “Charts” and “What if…” tabs) holds how fast each part of the body turns, where the ball lands, and sliders for the hips, legs and trunk.
• Colours: pelvis red, torso green, arm blue, racket or club dark; brighter means turning faster. The legend at the lower right of the picture lists them.

• The real strokes come out right: the simulated racket-head and club-head speeds are within 3% of what the capture markers measure directly, and the golf ball’s speed, spin and carry are within 10% of TrackMan’s tour averages.
• Changing one thing has the effect the research literature describes. On the tennis body cards the racket is only 5–30% slower, but the face changes with it and the ball mostly no longer lands in: speed is not the only thing that matters.
• The real stroke is neither the fastest nor the safest possible one; it sits between them. A forehand tuned only for head speed is 9% faster, but with its timing 10 ms off in the worst way no ball lands in.
• A golf ball starts mostly where the face points (about 85%) and curves by how far the face and the path differ, as the D-plane describes.

• The data are optical motion capture: reflective markers on the player and the racket or club, each recorded as a 3D position. No video.
• A skeleton scaled to each player is fitted to the markers frame by frame, including how the grip sits in the hand.
• The stroke is then worked out again with multibody dynamics: a joint pushed past its normal range is eased back, and an upper arm meeting the chest is pushed off it. The cards change the timing or size of the effort in this step.
• The strike uses a collision model and the ball flies with drag and spin lift, all from measured coefficients.
• Everything runs in your browser; no AI model, and the same settings always give the same result. The timing optimisation and tolerance analysis were done offline.

• Each sport rests on one stroke by one player; another player would give other numbers.
• The body’s mass distribution and muscle strength are averages from the literature; the golfer’s height and weight were not published and are estimated.
• There were no force plates, so ground forces are inferred; the model has no shoulder blades and one fewer turn in the ankle.
• To stay on the capture markers, the tennis racket wrist and the golf lead wrist go past their usual range at a few moments.
• The golf loft is assumed and the shaft is treated as rigid, so launch is too low; the face being square at address is also assumed, so whether the reference drive flies straight or fades is uncertain. The cards are compared with the real swing.
• The incoming tennis ball is a typical one, not the ball this player received; no ball is drawn for the volley.

• This is an illustration for understanding how speed is built, not coaching and not a prescription for you.
• It is not medical or injury advice either. Joint angles and effort are model estimates; for any pain or discomfort see a professional.
• The models are simplified and the measurements come from a few players and pieces of equipment; real strokes differ. It is provided as it is, without any warranty, and we accept no liability for decisions made from it.

• 3DTennisDS
• Skublewska-Paszkowska M., Powroznik P., Lukasik E., Smolka J., Tennis patterns recognition based on a novel tennis dataset – 3DTennisDS, Advances in Science and Technology Research Journal 18(6):159–176 (2024)
• UpstreamDrift (D-sorganization), tour-average driver swing, C3D_TA_Driver.c3d
• OpenSim models: bone shapes
• Rajagopal A., Dembia C.L., DeMers M.S., Delp D.D., Hicks J.L., Delp S.L., Full-body musculoskeletal model for muscle-driven simulation of human gait, IEEE Trans. Biomed. Eng. (2016)

Numbers are taken from these studies and cited; figures and text are not reproduced.

• de Leva P., Adjustments to Zatsiorsky-Seluyanov’s segment inertia parameters, J. Biomech. 29:1223 (1996)
• Anderson D.E., Madigan M.L., Nussbaum M.A., Maximum voluntary joint torque as a function of joint angle and angular velocity, J. Biomech. 40:3105 (2007)
• Delp S.L. et al., OpenSim: open-source software to create and analyze dynamic simulations of movement, IEEE Trans. Biomed. Eng. 54:1940 (2007): passive joint limits
• Norkin C.C., White D.J., Measurement of Joint Motion; AAOS normal ranges of joint motion
• Kwon S. et al., Influence of tennis racquet kinematics on ball topspin angular velocity and accuracy, J. Sports Sci. Med. 16:505 (2017)
• Landlinger J. et al., Key factors and timing patterns in the tennis forehand of different skill levels, J. Sports Sci. Med. 9:643 (2010)
• Reid M., Elliott B., Crespo M., Mechanics and learning practices associated with the tennis forehand: a review, J. Sports Sci. Med. 12:225 (2013)
• Genevois C. et al., Performance factors related to the different tennis backhand groundstrokes: a review, J. Sports Sci. Med. 14:194 (2015)
• Cross R., Effects of friction between the ball and strings in tennis, Sports Eng. 3:85 (2000); Cross R., Lindsey C., Measurements of drag and lift on tennis balls in flight, Sports Eng. 17:89 (2014)
• Choppin S., Goodwill S., Haake S., Impact characteristics of the ball and racket during play at the Wimbledon qualifying tournament, Sports Eng. 13:163 (2011)
• Carson H.J., Richards J., Mazuquin B., Examining the influence of grip type on wrist and club head kinematics during the golf swing: benefits of a local co-ordinate system, Eur. J. Sport Sci. 19(3):327 (2019)
• Sweeney M., Mills P., Mankad A., Elliott B., Alderson J., Wrist kinematics during the golf drive from a bilaterally anatomical perspective, ISBS conference proceedings (2012)
• Chu Y., Sell T.C., Lephart S.M., The relationship between biomechanical variables and driving performance during the golf swing, J. Sports Sci. 28:1251 (2010)
• Nesbit S.M., Serrano M., Work and power analysis of the golf swing, J. Sports Sci. Med. 4:520 (2005)
• TrackMan PGA Tour averages (2014); D-plane after Jorgensen T.P., The Physics of Golf (1999)
• King M.A., Yeadon M.R., Optimisation of tumbling and diving take-offs with constraints and timing perturbations, ECCOMAS (2008); Felton P.J., Yeadon M.R., King M.A., Optimising the front foot contact phase of the cricket fast bowling action, J. Sports Sci. (2020)
• Hansen N., The CMA Evolution Strategy: a tutorial, arXiv:1604.00772 (2016)

• The tennis strokes are from 3DTennisDS. As its terms of use ask: The used tennis motion capture dataset was obtained from https://tennisdb.cs.pollub.pl at the Lublin University of Technology. The article describing it is listed above.
• The golf swing is UpstreamDrift’s tour-average driver swing (MIT License).
• The bone shapes are from the Rajagopal et al. 2016 full-body model for OpenSim (distributed on SimTK under the MIT License), citing Rajagopal et al. 2016 and Delp et al. 2007 as it asks.
• Built with three.js (© 2010-2026 three.js authors, MIT License) and Vite; the full licence texts are in the third-party notices.

Not connected with 3DTennisDS, OpenSim, TrackMan or the authors and institutions of the cited work; citing them implies no endorsement.

The motion capture is public. Turning it into motion that can be simulated is LifeVen LLC’s own work:

• The methods for handling the capture: calibrating how the racket or club sits in the hand from the whole swing when the hand has no markers; borrowing joint-centre offsets from another dataset when only outer markers exist; editing the pelvis while both feet stay planted; joint limits that stiffen the further they are pressed; contact between the upper arm and the chest.
• The processed motion, the skeleton scaled to each player, and the timing and size of the effort on every card.
• The results of the timing optimisation and the tolerance analysis.

These data and parameters are available under CC BY-NC 4.0: use them in research and teaching with the credit “The Kinetic Whip by LifeVen” and a link to this page. For commercial use, please write to hello@lifeven.com first. The recordings the motion comes from keep their own terms, listed above.

• © 2026 LifeVen LLC. All rights reserved in the page, its code, pictures and text; the third-party data and software listed above keep their own licences.
• You are welcome to use it and share it. When you share screenshots or recordings, please credit “The Kinetic Whip by LifeVen” and link to this page.
• Please do not copy the page, its code or its screenshots and publish them as your own.