Jump Height - Figure Skaters

8/12/2019 Jump Height - Figure Skaters

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The American Journal of Sports

http://ajs.sagepub.com/content/18/4/400Theonline version of this article can be found at:

DOI: 10.1177/036354659001800412

1990 18: 400Am J Sports MedAnatol Podolsky, Kenton R. Kaufman, Thomas D. Cahalan, Sergei Y. Aleshinsky and Edmund Y.S. Chao

The relationship of strength and jump height in figure skaters

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The relationship of strength and jump heightin figure skaters

ANATOL PODOLSKY,* MD, KENTON R. KAUFMAN,* PhD,THOMAS D. CAHALAN,* PT, SERGEI Y. ALESHINSKY, PhD,AND

EDMUND Y. S. CHAO,* PhD

From the*

Biomechanics Laboratory, Department of Orthopedics, Mayo Clinic/MayoFoundation, Rochester, Minnesota, and the t United States Figure SkatingAssociation Sports

Medicine and Science Program, Colorado Springs, Colorado

ABSTRACT

Eighteen junior elite figure skaters were filmed whileperforming axel and double axel jumps. These sameskaters were assessed for strength of the shoulders,knees, and hips at multiple angular velocities using aCybex II system. The height of the jumps was signifi-cantly correlated with the strength data. Knee exten-sion at 240 deg/sec and shoulder abduction at 300

deg/sec were shown to be the most important strengthparameters in determining the height of the jump. Thisinformation may be useful for designing strength train-

ing programsfor

figureskaters.

Figure skating is a popular winter Olympic sport, attractingmore and more new competitors every year. The growingroster of the United States Figure SkatingAssociation is anindication of this popularity. United States figure skaters do

quite well in international competitions. In the last OlympicGames, however, the Gold Medal in the womens event wastaken by the East Germans. The Soviets traditionally dom-inate the pairs and dance competitions. The success ofeastern bloc countries in figure skating as well as in other

sports is partly attributed to their well-developed sportsscience research

programsand continued

developmentof

new and better training methods.

Figure skating is an art as well as a sport. It is judged ontechnical merit and artistic impression. One of the corner-stones of a figure skating performance is the height of askaters jump.A well-performed jump of significant heightmay raise the technical merit mark as well as the artistic

impression score. In contrast to speed skating or high jump-ing, there are no objective measurements in figure skating.Nevertheless, physical qualities that affect speed and jump-ing contribute a great deal to the success of a skater. The

height of the jump is probably determined by the physicalabilities of a skater, provided that the skater has the tech-nical skills necessary to successfully complete the jump.

Although McMaster et al. have presented a method ofendurance training for skaters, the scientific literature doesnot contain any description of the specific qualities neededfor higher jumps in figure skating.

This study was thus conducted to 1) test the hypothesis

that the height ofjumps in figure skating is related to musclestrength about the knee, hip, and shoulder, and 2) determinethe specific type of strength most important in regard tomuscle groups and speed of exercise.

MATERIALSAND METHODS

Subjects

Eighteen skaters, selected for participation in the EliteJunior Sports Science Development Camps by the UnitedStates Figure SkatingAssociation, were the subjects of thestudy. Each athlete was selected based on skating abilityand the potential for becoming a world class competitor.There were 8 females (age, 14.7 1.6 years; height, 1.58 0.05 meters; and weight, 53.4 4.6 kg) and 10 males (age,17.5 1.6 years; height, 1.69 0.09 meters; and weight, 64.7 10.1 kg).

Strength testing

The dynamic strength of shoulder abduction and adduction,hip flexion and extension, and knee flexion and extensionwas assessed using a Cybex II isokinetic dynamometer sys-

tAddress correspondence and repnnt requests to. Edmund Y. S Chao,PhD, Biomechanics Laboratory, Department of Orthopedics, Mayo Clinic/MayoFoundation, Rochester, MN 55905

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tem (Cybex, Division of Lumex, Inc., Ronkonkoma, NY).Data was recorded with the Cybex Dual Channel Recorderas well as the Cybex Data Reduction Computer (CDRC).The torque channel was electronically damped at a settingof 2.

Shoulders were tested in the upright, seated position withthe aid of the Cybex Upper Body Exercising and Testing

(UBXT) device. The shoulder was isolated from the elbow,wrist, and hand by keeping the elbow flexed to 90 using athermoplastic splint. In order to achieve maximum abduc-tion with the arm in this position, motion in the plane ofthe scapula was tested. Test speeds used were 60, 180, and300 deg/sec.Hip and knee testing employed the positions described in

the Cybex users manual. The hip was tested at speeds of240 and 300 deg/sec and the knee at speeds of 60, 120, 180,240, and 300 deg/sec.Data collected by the CDRC included peak torque, angle

at which the peak torque occurred, angle-specific torque,and torque as a percentage of body weight.All torque meas-urements were recorded with gravity correction.Angle spe-cific torques were assessed at 30 and 120 of abduction forthe shoulder, 30 and 90 of flexion for the hip, and 30 and60 of flexion for the knee.

Kinematic analysis

Two high speed, 16 mm, pin-registered, electronically phase-locked, Redlake LoCam cameras were positioned at 90 fromeach other. The frame rate for each camera was set nomi-

nally at 50 frames per second and was calibrated internallyin each camera by timing diodes flashing at 100 Hz.A three-factor shutter allowed for exposure time of 1/150 seconds.Eastman Ectachrome

HighSpeed 7250 film was used.

Before filming the skaters, a 7 x 12 m field of view of thecameras was calibrated by filming a set of calibration frameswith markers positioned at known distances from each other.After an adequate warm-up period, the skaters were askedto perform axels and double axels within this field of view.Eachjump was analyzed through the use of a computerized

digitizing system consisting of a Vanguard projector, Cal-comp digitizing table, and a Data General Eclipse MV/1000minicomputer. The points digitized included hands, wrists,elbows, shoulders, ankles, knees, hips, tips of the toes, navel,xiphoid process, ears, and the top of the head.A custom-designed system ofcomputer programs was usedto provide a mathematical description of the three-dimen-

sional motion of the body segments. The model generatedby the system consisted of 15 links corresponding to thebody segments of hands, forearms, upper arms, feet, legs,thighs, head, chest, and pelvis. The computer program wasused to calculate the maximum height of the center of mass

during the jumps. The center of mass of each body segmentwas estimated using anthropometric data based on a largeanthropometric study and a regression formula for deter-

mining the centers of mass. For the purposes of this study,the vertical distance between the top of the skaters body

mass center trajectory in flight and the body mass centerposition at the instant of take-off was used for analysis.

Statistical methods

The height of the jump was normalized for the weight of the

athlete by converting the jump height to potential energy,i.e., mass x gravity x height of the body mass center. Thus,all statistical analyses compared the peak strength of theathlete, in terms of energy, to the potential energy that was

generated during the jump. Two statistical approaches wereused to determine the relationships between the height ofthe jump (dependent variable) and the strength of the ath-lete (independent variable).

Linear least-squares regression was used to assess the

strength of the best-fitting relationship between the inde-pendent and dependent variables. The strength of the rela-tionship was determined from 1) the correlation coefficient,r, which represented an index of association between

strength and jump height, 2) the F-statistic value, which

tested the null hypothesis that there is no significant rela-tionship between the variables, and 3) the P-level, which

gave the probability of getting a greater F-statistic than thatobserved if the null hypothesis is true. The P-level can alsobe referred to as the significance probability.

Stepwise regression was used to select the speed at whichthere was the highest correlation of strength for each jointwith the height of the jump. It was also used to determinethe most important parameters influencing the height of thejump.All strength parameters were considered for entry intothe model. The stepwise technique proceeded by addingvariables one by one into the model.At each point, the F-statistic was assessed for a variable to be added-that vari-

able needed to be

significantat the 0.05 level for

entry. Byusing the stepwise method, after a variable was added, wecould look at all of the variables already in the model anddelete any not producing a significant F-statistic.

RESULTS

Comparison of joint speed

Stepwise regression was used to select the joint speed mosthighly correlated with the jump height. The highest corre-lations (P < 0.01) were obtained for knee extension at 240

deg/sec, hip extension at 240 deg/sec, shoulder abduction at300 deg/sec, and shoulder adduction at 300 deg/sec. Thesespeeds were the same for both the single and double axel.The speeds for maximum correlation of hip flexion strengthwith jump height varied. The highest correlation (P < 0.01)between the hip flexion strength and the height of the singleaxel was obtained at 240 deg/sec, whereas the 300 deg/sectest speed was more highly correlated for the double axel.The strength measured at these speeds was used for subse-quent analyses.



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Relationships between jump height and strength

Linear regression analysis was used to determine the

strength of the relationship between each strength parame-ter and the jump height. The results for a single axel areshown in Figure 1. There was a positive correlation betweenall strength parameters and the jump height. Further, all of

the correlations were significant (P < 0.01). The results fora double axel are shown in Figure 2. Once again, there wasa positive correlation between all strength parameters andthe double axel height. Likewise, all correlations were sig-nificant (P < 0.01).

Overall, the same trends were observed for both the singleand double axel. The most significant relationship observedwas for knee extension, whereas the least significant rela-

tionships were for shoulder adduction and hip extension.The strength of the relationships for shoulder abduction and

hip flexion were interchanged. It can be also seen that the

strength of the relationship between the jump height andthe strength parameters was stronger for the double axel

than for the single axel, with the exception of knee exten-sion. The linear relationships (expressed in correlation coef-

ficient, r, and the F-statistic) between each of the strength

parameters and the single axel and double axel heights aresummarized in Tables 1 and 2, respectively.

Important strength parameters

Stepwise regressionwas used to rank the order of importanceof the strength parameters for jump height. The correlation

coefficient squared, r2, measures the power of the linearrelationship between the athletes joint strength and the

jump height. The results for a single axel show that the most

important strength parameter (primary parameter) was kneeextension (Table 3), accounting for 79.2% (square of the

partial correlation coefficient) of the variability in the singleaxel jump height. The second most important parameter(secondary parameter) was shoulder abduction, accountingfor an additional 5.5% (square of the partial correlation

coefficient) ofthe variability injump height. Together, theseparameters accounted for 85% (square of the model corre-lation coefficient) of the variability in the single axel height.None of the other strength parameters contributed signifi-cantly to the single axel jump height.The results for a double axel, once again, show that the

most important strength parameter (primary parameter)was knee extension (Table 4). This parameter accounted for

SHOULDER &dquo;IDUCTION ro&dquo;out:INm- -

Figure 1. Correlation between single axel height (reported as potential energy) and strength: knee extension, hip flexion, hipextension, shoulder abduction, and shoulder adduction.



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Figure 2. Correlation between double axel height (reported as potential energy) and strength: knee extension, hip flexion, hipextension, shoulder abduction, and shoulder adduction.

TABLE 1

Linear regression: Single axel height versus strength

77.4% (square of the partial correlation coefficient) of the

variability in the double axel. The second most importantparameter (secondary parameter) was shoulder abduction,accounting for an additional 7.8% (square of the partialcorrelation coefficient) of the variability in jump height.These two parameters accounted for 86.5% (square of themodel correlation coefficient) of the variability in the doubleaxel height. None of the other strength parameters contrib-uted significantly to the double axel height.

TABLE 2

Linear regression: Double axel height versus strength

TABLE 3

Stepwise regression analysis to determine the most significantstrength parameters correlating with single axel jump height



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TABLE 4

Stepwise regression analysis to determine the most significantstrength parameters correlating with double axel jump height

DISCUSSION

An axel is one of the main figure skatingjumps. Performanceof a double axel is a required element of the Gold test.Askater who has passed the Gold test may compete on thesenior level at the U. S. National Championships.The heightof the jump determines the length of time in flight. Highjumps allow multiple revolutions and contribute to higherperformance scores.

Knowledge of the axel jumping technique is necessary toelucidate the relevance of testing joint strength. The per-formance sequence is shown in Figure 3. The take-off isdone from the forward outside edge of the left skate. Beforetake-off, the free (right) leg and both arms are swung upand forward to help accelerate the body mass center. The

support (left) knee and hip are thus extending and the free

(right) hip is flexing forcefully as both arms abduct at theshoulder joints to achieve greater vertical velocity and

height.At the moment of take-off, both arms and the free

(right) lower extremity decelerate to combine their momen-tum with that of the rest of the body, which means that thearms now adduct at the shoulders and the free (right) hipextends. During flight, a skater completes 1.5 revolutionsfor a single axel and 2.5 revolutions for a double axel. This

is accomplished by &dquo;pulling in&dquo; the arms and the free lower

extremity, i.e., bringing them closer to the center of thevertical axis of rotation. This action decreases the skaters

moment of inertia, in turn increasing the angular velocity,since the angular momentum is conserved during free flight.The skater lands by &dquo;checking out&dquo; or opening the arms andfree lower extremity, thus slowing down (decelerating) the

angular velocity, and then stepping down onto the backoutside edge of the right skate and holding this position for

approximately 1 second.The Cybex tested strength speed, which had the highest

correlation with the jump heights. The Cybex results are

important since they reflect the most specific speeds for themovements of interest. Interestingly, the joint angular ve-locities of a recent Olympic Gold medalist, calculated fromthe same filming technique used in this study, were approx-imately the same as those reported as being important inthis study. For our skater, the hip extension speed was 193

deg/sec and the knee extension speed was 263 deg/sec.2The results of this study show that the height of the single

and double axel is significantly correlated with the musclestrength of the shoulder in abduction and adduction, theknee in extension, and the hip in extension and flexion. The

hypothesis of this study, i.e., that strength is related to the

height of figure skating jumps, was thus proven.Ankle strength was not included as a parameter because

of the stiff nature of the figure skating boot. Plantar flexionis restricted during take-off, limiting the plantarflexors toan isometric or support function.

Probably, the most significant finding of this study is the

relatively high contribution of shoulder abduction strengthat 300 deg/sec to the height of the jumps. During thetraditionalon ice training method, in which jump repetitions

Figure 3. The axel technique: 1) just before take-off, 2) the moment of take-off, 3) midflight, and 4) the landing.



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are performed to develop strength, the muscles of the lowerextremities contract specifically with the load of the skaters

body mass. In contrast, shoulder abduction is performedwith no extra load (except for the weight of the upperextremities). The shoulder abductors are at more of a dis-

advantage in terms of progressive resistance. Indeed, singleskaters may have greatly developed lower extremity strength

and relatively poorly developed upper extremity strength.~7

Therefore, shoulder abductors are a relatively untouchedresource for specific strength development and constitutethe greatest potential for increasing the height of figureskating jumps. Strength training of the shoulders may make

quadruple jumps a reality for national and international

competitors in the near future.Skaters generally do no weight training off the ice. There-

fore, a singles figure skater, as mentioned above, usuallydevelops his or her strength by repeating the jump on theice during regular skating free-style sessions (45 minutes, 2or 3 times a day, 10 to 20 repetitions of each jump persession). Such a method is angle, speed, and muscle group

specific, but, physiologically,the neuromuscular

signalof

each jump is too short and not necessarily of maximal

magnitude.4In order to develop strength faster and to a

greater degree, one must use the principle of progressiveresistance, that is, the need to &dquo;continually increase the

stress placed on the muscle as it becomes capable of produc-ing greater force.3 To achieve this on the ice by addingweights to a skater would increase the danger of injuries and

might interfere with technical skill. Specifically designedweight training off the ice is safer and may actually help askater to acquire better skills. Weight training may also

shorten the time necessary to develop adequate strength forhigher jumps. Development of this strength takes several

years by the traditional methods of jump repetition on theice. Weight training will allow faster progress in learningmultiple revolution jumps and may also reduce the rate ofoveruse injuries frequently sustained by figure skaters.8,9

9

ACKNOWLEDGMENTS

The authors thank Drs. Sarah Smith and Steven Fleck and

Mr. Frank Ramirez for their invaluable contributions to this

study.This study was funded in part by a grant from the United

States Figure SkatingAssociation.

REFERENCES

1 Aleshinsky SY Modeling of the 3-dimensionalhuman movements Doctoraldissertation, Moscow State University, USSR, 1977

2 Aleshinsky SY, Smith SL, Jansen LB, et al Companson of biomechanicalparameters demonstrated by Bnan Boitano in triple and double axel jumps.ProcAm Soc Biomech 201, 1988

3 Fleck SJ, Kraemer WJ Designing ResistanceTraining Programs.

Cham-

paign, IL, Human Kinetics Books, 19874 Green HJ. Glycogen depletion patterns in continuous and intermittent ice

skating. Med Sci Sports 10 183-187, 19785 Isolated-Joint Testing and Exercise A Handbook for Using Cybex II and

the UBXT. Ronkonkoma, NY, Cybex, 19806 McMaster WC, Liddle S, Walsh J Conditioning program for competitive

figure skatingAm J Sports Med 7. 43-47, 19797. Niinima V Figure skating What do we know about it? Physician Sportsmed

10(1). 51-56, 19828 SmithAD Figure skating, in Schneider RC, Kennedy JC, Plant ML (eds)

Sports Injuries. Mechanisms, Prevention, and Treatment Baltimore, Wil-liams & Wilkins, 1985, pp 516-531

9 SmithAD, Micheli LJ Injuries in competitive figure skaters PhysicianSportsmed 10(1) 36-47, 1982


Jump Height - Figure Skaters

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