Gymnast 2929 Interaction Interactions of the Gymnast and Spring Floor William Sands Professor East Tennessee State University Gymnast 30 Interaction Fig. 1 The exciting gymnastics you see weight – per foot (8). The floor on television is formally known exercise apparatus also results as artistic gymnastics. Artistic in a large proportion of gymnas- gymnastics involves competition tics injuries (3). for men and women on several One of the most devastating in- apparatuses, six for men and juries in floor exercise tumbling four for women. Men and women is a ruptured Achilles tendon. share vaulting and floor exercise Tendon ruptures occur most fre- apparatuses. Vaulting involves quently during tumbling take- a single skill performed over a offs and somewhat less so dur- ‘tongue-shaped’ raised surface ing landings. Figure 2 shows the called a table. Floor exercise is acute angle of ankle dorsiflexion contested on a large 12m square matted and carpeted area that is raised by fiberglass-laminate panels on springs (Figure 1). Gymnasts use the springs to fly higher and farther while reduc- ing the harshness of take-offs and landings. Impact forces in gymnastics tumbling can exceed the published limits for bone, lig- ament, and tendon in the asso- ciated lower leg structures (1, 2), and exceed 14 times body Fig. 2 Gymnast 31 Interaction captured from high-speed video ral frequency of the elastic stiff- at 1000 fps. This ankle position ness of the tumbling surface, occurs in less than 60ms of to- then the mismatch will result in tal take-off duration that is less wasted energy and poor trans- than about 150ms. Concentrat- fer of muscle and connective ing ground reaction forces of a tissue tensions to the support- dozen or more times body weight ing surface. Of course, the gym- in less than a tenth of a second nast also suffers from the asyn- requires skill, strength, power, chrony with altered force and and coordination. Moreover, torque distributions throughout this circumstance also requires the lower extremity. Although a predictable elastic response breaking the tumbling surface of the floor exercise apparatus. panels is not unknown; the usu- Unfortunately, the musculo- al ‘losers’ in the battle to main- skeletal actions of the gymnast tain the coupling of coordinated do not always synchronize with stiffness between gymnast and the elastic deflection and recoil spring floor are the gymnast’s properties of the spring floor legs. In short, the disparity may (10). result in a ruptured Achilles ten- Jumping activities, like a gym- don. nastics take-off, exhibit an initial Videos of gymnastics take-offs knee flexion action as the lower were analyzed with the ProAna- extremity contacts the floor ab- lyst(R) motion analysis software sorbing the impact. The flex- for biomechanics and sports ion continues smoothly until the analysis. The software provides downward portion of the jump is easy determination of positions, complete. The knee position an- velocities, accelerations and an- gle may hesitate for a very brief gles of the stressed body parts. period prior to extension actions Figure 3 shows a common pat- that raise the gymnast into the tern of motion from 500 frame following take-off. Although the per second video (Quantum Fig. 3 actions described above are normal and common, however, observations show that many gymnasts flex and extend their knees twice during the tumbling take-off impact (Figure 3). I be- lieve that the cause of this odd phenomenon is the asynchro- nous motion interactions of the spring floor and the gymnast. If the gymnast’s take-off jumping actions do not match the natu- Gymnast 32 Interaction Technologies), and screen imag- floor vibrations during the gym- es of the knee of a highly trained nast’s take-off actions along gymnast performing at the with electromyographic varia- Olympic Training Center in Colo- tions reflective of twisting versus rado Springs, CO, using ProAna- non-twisting somersaults (Fig- lyst(R) motion analysis software ure 4). Extraneous vibrations from Xcitex Inc. (Woburn, MA). or asynchronous responses of Following the examination of a jumping surface, particular- kinematic records of gymnasts’ ly when unexpected and un- knee angles, many of the gym- learned, may spell disaster for a nasts showed a knee motion di- weakened Achilles tendon. rection reversal. Instead of the Unfortunately, the analysis of knee of the gymnast continuing the potential contributions of in the horizontal direction of the the spring floor to Achilles ten- tumbling pass, the knee flexes don and other lower extremity forward relative to the gymnast injuries is staggeringly complex. (who is traveling backward). The The spring floor is not only influ- knee reversal motion is indicative enced by the immediate take- of a ‘collapse’ of the knees, likely off actions of the gymnast, but due to impact forces and poorly the entire floor is subject to vi- applied muscle torques. How- brations induced by a series of ever, the genesis of this collapse impacts from the run-up and may lie in the stiffness charac- other preceding tumbling skills. teristics of the spring floor. Our Most frequently, the rearward reasoning lies with the fact that tumbling take-off follows a run even Olympic champions can of several steps, a skill called a show this odd jumping behavior round-off, and a back hand- making strength and skill not the spring. Gymnasts come in all only, or perhaps even the domi- different sizes, shapes, and nant factors. abilities. Moreover, the role of How does the spring floor con- strength and power in tumbling tribute to the incidence of two cannot be overestimated and knee flexions? Work by Paine may be the most accessible at the University of Utah on an countermeasure in the short- earlier version of the spring floor term. It is my hope that con- showed that the spring floor’s tinued work will enlighten the natural frequency response gymnastics community on the was about twice that of the potential contributions of the gymnast’s take-off actions (6, floor exercise apparatus to low- 7). Moreover, work by McNeal er extremity injury. and colleagues (4, 5), again at Gymnastics has recognized that the University of Utah, found a the elastic properties of the number of extraneous spring Gymnast 33 Interaction apparatuses may influence the gymnast’s neuromuscular range of performance proper- performance and safety (1, 2, system cannot adapt to the ties. That youngsters are the 9, 11). The gymnastics vault stiffness characteristics of most common participants in board that is used for jumping the spring floor as presented, gymnastics should raise our following a run to the vault the gymnast’s performance concern and encourage con- table, and modification of the suffers and the route to injury tinued research to understand vault board by adding and is enhanced – particularly spring floor and gymnast in- removing coil springs has been with the space-age skills teraction properties. a coaching tactic for some that modern gymnasts time. Unlike the adjustable perform. In competition, floor fulcrum in springboard exercise apparatuses may References for this article can diving, gymnastics has no be placed on undersurfaces be found at corresponding technology such as a flexible platform http://bit.ly/P0GG3L to modify the stiffness of the (Olympic Games), floating spring floor. Gymnasts must wood floor (basketball gyms), adjust their neuromuscular carpet (hotel ballrooms), and system during a brief concrete (conference/meeting opportunity at the warm-up on facilities). the floor exercise apparatus. Gymnasts must essentially Given the potential serious relearn their take-off actions nature of injuries to gymnasts, in a matter of minutes, who are often upside-down often prior to performing during a fall, gymnastics ap- complex and potentially paratus behaviors should be dangerous airborne skills. If maintained within a small Fig. 4.