ORIGINAL INVESTIGATIONS

lOURNAL OF APPLIED BIOMECHANtCS, 1993, 9, 15-26© 1993 by Human Kinetics Publishers, Inc.

Changes in Sprint Stride KinematicsWith Age in Master's Athletes

Nancy HamiltonA study was undertaken to determine the kinematic nature of the decline insprint velocity that has been found to occur with aging. Subjects included162 Master's sprinters ranging in age from 30 to 94 years. Data were collectedat a national championship meet and a World Veterans Championshipsthrough use of videotape and the Peak Performance Motion MeasurementSystem. From the digitized videotape data, measures of sprint stride velocity,stride length, stride period, support time, swing time, flight time, and hip,knee, and trunk range of motion were calculated. Velocity, stride length,flight time, swing time, and range of motion in the hip and knee all decreasedsignificantly (p<,05) with age, whereas stride period and support time in-creased. Further, the proportional relationship between the components ofthe stride was significantly ip<.05) altered. From this it was inferred that asthese sprinters aged there was a decreased ability to exert muscle force aswell as a decrea.sed ability to move quickly through a full range of lowerextremity motion.

Agitig does not have to mean years of physical decline, illness, and confine-ment. Thousands of senior citizens worldwide have instead chosen to becomeor to remain highly competitive athletes. Among these athletes, as among allcompetitors, the quest to improve, to better one's performance, remains a constant.Yet it also remains a fact that as athletes get older, velocities and distancesdecrease (Heinonen, 1989; Moore, 1975). In other words, regardless of trainingor practice, performance declines with age. Moore (1975), for example, reportedthat in the 200-m dash the age group record velocity for 60-year-old male runnersreached only 74% of the overall world record velocity. Roberts, Cheung, Hafez,and Bullard (1986) found a similar decrease among middle-distance runners,with velocity differences between 20- to 22-year-old runners and 60- to 65-year-old runners ranging from to 1.6 to 4.4 m/s.

Stride length divided by stride period produces the kinematic measuresprint velocity. Any alteration in stride velocity must be a direct result of achange in stride length, stride period, or both. Based on examination of the stridekinematics of older sprinters, a decline in sprint velocity has long been apparent.

The author is with the University of Northem Iowa, 203 West Gymnasium, CedarFalls. IA 50614-0241.

15

16 Hamilton

The question has remained as to the nature of this decline in velocity. The possibleexplanations include a decrease in stride length, an increase in stride period, orsome combinatioti of both. Once the magnitude of changes in stride length andstride period becomes evident il becomes necessary to examine the relationshipbetween the two in order to understand the mechanism through which stridevelocity decline occurs.

The preponderance of research on gait and aging has focused primarily onage-based alterations in the walking gait. The majority of these studies havefound that with increasing age and inactivity of subjects, the range of motionused in the lower extremity during the walking gait decreases, whereas the relativetiming of the gait remains constant (Cunningham. Rechnitzer, Pearce. & Donner,1982; Himan, Cunningham. Rechnitzer, & Patterson, 1988; Imms & Edholm,1981; Lundgren-Lindquist, Aniansson, & Rundgren, 1983; Marino, Finch, &Young. 1984; Murray. Gardiner, Mollinger, & Sepic, 1980). The changes inwalking gait have been linked variously to height, VO^max, and muscle strengthas covariates of age.

In the 1986 study of five Master's distance rurmers and three youngerrunners, Roberts et al. reported a decrease in stride length from a maximum of4.6 m to 3.08 m (a 1.52-m decrease) in older runners, a decline of as much as33%. In comparison, stride length for gold medal-winning sprinters in the 1984Olympics peaked at approximately 4.96 m (reported stride length x 2) (Mann &Herman. 1985).

In order to examine stride velocity changes that occur with aging, one mustalso examine the relative, or proportional, nature of the components of the sprintstride. Shapiro, Zemicke, Gregor, and Diestel (1981) found that the proportionalrelationships between stride components remained constant when subjects volun-tarily altered stride velocity. This held true for voluntary alterations in both thewalking and tbe running gaits.

TTie purpose of this study was to investigate the nature of the kinematicchanges observed in the sprint stride across ages in adult runners. This includesvariations in sprint velocity, stride length, and stride period. In addition, theproportional relationships of the support time, swing time, and flight time compo-nents of the sprint stride were examined to determine if the stride pattern varieswith age. Joint range of motion in the hip and knee and trunk excursion wereexamined as they related to the alterations that occur in the sprint stride.

Methods

Data collection for this field-based study took place during competition at aMaster's track and field national meet and two simultaneously used venues at aWorld Veterans Championships. Each final, semifinal, and preliminary heat ofboth the 100-m dash and the 2(K)-m dash from each meet provided videotapedata. The data collection procedure utilized a video camera located 40 m beforethe fmish line at each venue. Cameras were placed 4 m from the inside curb ofthe track. The field of view varied from 2.7 m of track surface in Lane 1 (notused) to 7.8 m of track in Lane 8, with each lane line marked at 1-m intervalsin order to provide scale references.

sprint Stride Kinematics 1 7

Subjects

Approximately 800 runners were videotaped; the top runners in each age groupwere digitized, providing a final subject pool of 162 runners. This subject poolincluded the fastest one to three clearly visible runners in each final heat andthe fastest one to three clearly visible runners in each semifinal and preliminaryheat, exclusive of any runners already selected for analysis in any other heat.This process produced a subject pool that included the fastest runners in eachage group. The variance in age group sample size reflected the overall differencesin participation. The age group and gender breakdowns of the subject pool appearin Table I.

Procedures

Data collection instrumentation included two Panasonic AG 120 high-speedshutter camcorders with the shutter speeds set at 2(KX) Hz, used simultaneouslyat separate venues. The Peak Performance Motion Measurement System videointerface allowed computer frame splitting to yield an actual frame rate of60 Hz. Scale reference marks on the track made it possible to calculate scaleconversion factor for each lane on each track.

Competition conditions and a reluctance to interfere with the athletes pre-cluded joint marking and made il necessary for the researcher to locate jointcenters approximately while digitizing to the computer. The landmark pointsused for digitizing included the toe of each shoe, the heel of each shoe, the lateralmalleolus of the near leg and the medial malleolus of the far leg, both kneecenters, the near hip joint center (far hip joint center was inferred), the nearshoulder center (far shoulder was inferred), both elbows, both wrists, the tips ofthe third fingers, the crown of the head, and the stemal notch.

Filtering of raw digitized data made use of a forward and backward passButterworth filter with a cutoff frequency of 6 Hz, cbosen to achieve the bestcompromise between noise and signal over the wide variance in running harmon-ics that occurs with a large variance in velocity. Further processing of the filtered

Table 1

Age and Gender of Study Subject Groups

Age

30-3940-4950-5960-6970-7980-B990+Total

Male

816161913102

83

Female

921172192

—79

Both

1737334022122

162

Hamilton

data by tbe Peak Performance software yielded tbe time and position data requiredto calculate the derived variables of stride length, stride period, support time,swing time, and fiight time.

Calculating the horizontal displacement of one foot immediately prior totoe-off to tbe next point of contact of that same foot produced the measure ofstride length. Calculations of stride period involved multiplying tbe number offrames elapsed between same-side foot contacts (one stride) by the frame time.This method of calculation produced a margin of error of .0167 s, that being theelapsed time of eacb frame. Within a single stride tbe stride pattern involves aperiod of support (support time) and a pieriod of nonsupport. Support time wasidentified as the elapsed time from first foot contact to toe-off in tbe same foot.Nonsupport time breaks down into swing time and flight time. Fligbt time occurredfrom toe-off until opposite foot contact. Flight time includes a portion of theswing time from tbe stride cycle of eacb leg, being that part of the stride wbenboth feet are clear of the ground. Once the opposite foot has touched the track,flight time ends while swing time continues until first contact of the measuredfoot, beginning the next stride.

Dividing stride length by stride period yielded the average borizontal veloc-ity over the total stride. No attempt was made at tbis point to quantify anyinstantaneous accelerations that might occur as a result of foot strike or pusb-off.

In addition, range of motion (ROM) data for the knee, hip, and trunk weregathered (Figure 1). Tbe minimum and maximum measures of relative knee angleand relative bip angle were utilized to produce the total range of motion for thosetwo joints. Tbe total arc of excursion of the trunk provided a measure of trunkROM.Data AnalysisA multivariate analysis procedure (MANOVA) produced the F statistic used todetermine the presence or absence of a significant difference among age groups

Figure 1 — Angle measures: (a) knee angle, (b) hip angle, (c) trunk angle.

sprint Stride Kinematics 19

in measures of stride length, stride period, stride velocity, and joint ROM. TheMANOVA was used to test these several dependent variables against the singleindependent variable, age. Variance.s were pooled in this MANOVA to accountfor the differing N sizes between age groups. Wilks's lambda, Hotelling's trace,and Pillai's trace provided tests of the null hypothesis, acceptable at the p<.0\level of rejection. The Tukey's post hoc analysis used subsequent to theMANOVA provided a measure of the significance of differences between eachpossible pair of age groups. Beyond this, multiple regression tests producedstatistics intended to clarify the nature of the relationships between stride velocityand both stride length and stride period, and between stride period and thepartitioned measures of swing time, support time, and fiight time. The multipleregression technique was also used to examine the relationship between jointROM and velocity. A probability of p<.05 was required for significance.

ResultsSignificant differences existed among age groups in measures of stride length,F(6, 151) = 13.24, p<.0\. The change in stride period with age is significant,F{6, 151) = 3.34, /7<.O1, only if the 90-year-old age group is included in theMANOVA. Stride velocity, a function of stride length and stride period, alsovaries significantly with age, F{6, 151) = 13.02, p<.0\. Data analysis furtherindicated a relationship between the partitioned elements of the stride and strideperiod. Means and standard deviations for all performance measures are displayedin Table 2.

VelocityVelocity decreased significantly, F(6, 151)= 13.02,/7<.O1, from 8.93 m/s in 30-to 40-year-old runners to 4.91 m/s in runners over 90. Tukey's post hoc test

Table 2Stride Parameter Means by Age Group

Parameter

Velocity (m/s)

Stride length (m)

Stride period (s)

Support time (s)

Swing time (s)

Air time (s)

MSDMSDMSDMSDMSDMSD

30-39

8.931.224.350.50

481.04.126.02.358.03.120.02

40-49

8.570.994.060.35

-472.04.125.02.347.03.112.02

50-59

8.511.043.980.37

.467

.04

.128

.02

.340

.03

.106

.015

Age group60-69

7.851.123.790.42

.485

.04

.140

.02

.345

.025

.102

.01

70-79

7.031.333.460.58

.500

.03

.158

.03

.341

.03

.089

.02

80-89

6.271.173.100.37

.504

.06

.180

.06

.342

.02

.075

.03

90+

4.91—

2-84—.578—204—374—.085—

20 Hamilton

indicates tbat tbis decline in sprint velocity is cumulative, first reaching statisticalsignificance {p<.05) at age 60. Although there were no significant differences insprint velocity with age from ages 30 through 50. velocity at age 60 (M = 7.85m/s, SD = 1.12) is significantly less (p<.05) than at age 30 (M = 8.93 m/s, SD =1.22). Sprint velocity among runners over 70 years of age significantly slows asecond time (p<.05). Tbe first sharp drop in sprint velocity occurs slightly later infemales than in males. Tbe 70- and 80-year-old female runners were significantlyslower than those in any other age group, whereas no significant differenceswere found among the younger runners in tbe Tukey's post hoc test (Figure 2).Tbese findings contradict tbose reported by Moore (1975), who found that femalesprint speed declined more rapidly than that of males, starting at age 45.

Stride Length

Stride lengtb showed a significant relationship to velocity, F{6, 151) = 29, p<.01.The slope of the regression is positive, indicating that velocity decreased withdecreased stride length. Because velocity derives, in part, from stride length,such a relationship would be expected.

Tbe top 30-year-old runners achieved a mean stride lengtb of 4.35 m, whicbthen declined to 2.84 m among 90-year-olds. Tbis decline, although not linear,showed some consistency. Runners tended to lose between .20 and .30 m ofstride length per decade of life. The greatest drop in stride length occurred atage 60 (M = 3.79 m, SD ~ .42), with a second significant (p<.05) drop at age80 (M = 3.10 m, SD = .37). Females again sbow this decrease 2 decades latertban males (Figure 3).

Stride Period

A significant relationship also existed between stride period and velocity, F(6,15!) = 99.3, p<.0\). Tbe negative slope of this regression indicates that an

•acouvtntn0)

10-

9 -

8 -

7 -

6 -

5 -

420

V e l o c i t y

MaleFemale

40 60 10060Age

Figure 2 — Stride velocity changes with age for both males and females.

sprint Stride Kinematics 21

Stride Length

n

0)

S-1

4 -

3-

MaleFemale

20 40 60Age

BO 100

Figure 3 — Changes in stride length with age Tor both males and females.

increase in stride period correlates with a decrease in stride velocity. No significantrelationship existed between stride length and stride period, F(6, 151) = 1.56,/J = .21). The 30-year-old runners produced a mean stride period of 0.48 s, whichthen increased to 0.58 s in runners over 80. A Tukey's post hoc produced notwo age groups significantly different at the p<.05 level when the total subjectpopulation was considered. Stride period, then, remains steady until the 90-year-old age group (Figure 4).

Stride ComponentsBecause stride period remains neariy constant until late in the athletic career andstride length decreases steadily over the same period, there must be some changesin the overall pattern of the stride. In fact, there is a significant increase in supporttime with increasing age among all runners, f(6, 146) = 12.17, p<.0\. The firstsignificant (p<,05) change occurs at age 70 (Figure 3). As in previously mentionedmeasures, male runners experience declines in performance earlier than dofemales.

A positive relationship existed between support time and stride period, F(\,162)= 170.96,/j<.01. As stride period increa.sed with age, support time increased.The relative change in support time indicates that the stride pattern changessignificantly. F(6, 162) = 15.25,/7<.O1, from approximately 26% support to 36%support with age (Figure 4). Among females this change in stride pattern is evenmore dramatic, with support time increasing to 45% of the stride by age 80.

Swin^ titne, although producing no significant change across age groups,did show a positive relation to stride period, F(l, 162) = 136.83, p<.0]. Only a.05-s difference existed between minimum and maximum swing times. Relatively,however, the percentage of the stride used for free-leg swing-through decreasedfrom 74% to 65%. Female runners presented less actual difference in swing time(total difference = .027 s), but the relative decrea.se of swing time in the stridecycle grew, with swing decreasing to only 55%- of the stride (Figure 5).

22 Hamilton

Stride Components

0)E

0,5

0.4

0.3

0^

0.1 -

0.0

Period

Support TimeSwing Time

20 40 60Age

80 100

Figure 4 — Variation in stride period, air time, support time, and swing time withage.

80-1

60 Hc0)" 40 H

a20H

AirSupportSwing

20 40 60Age

60 100

Figure 5 — Components of the stride as a percentage of the stride pattern. Percent-ages in each age group lotal more than 100% due to the overlap between air timeand swing time.

Flight time, that period in the stride cycle when both feet are off the ground,decreased significantly with age. F(6, 151) = 11.51, p<.Ol, but did not producea significant relationship to stride period, F(l, 162) = .021, ;7<.0I. From age 30to 90 the time spent in the flight dropped from .12 s to .085 s, with a slightlylarger drop among 80-year-olds {to .075 s). The 60-year-o!ds differed significantly(p<.05) from the 30-year-olds, and 70- and 80-year-old runners differed signifi-cantly (p<.05) from all younger groups. Over the span from 30 to 90 years ofage, flight time decrea.sed significantly, f(6. 162) = \5A2, p<.0\, from 25% ofthe stride cycle to 15% of the cycle.

Sprini Stride Kinematics 23

Joint ROMThere is a significant relationship between aging and ROM in the knee joint,F(l, 162) = 53.14, p = .001. With aging, ROM in the knee decreased from 122°of motion to only 95°. Thi.s decrease in knee joint mobility, however, did nothave a significant relationship to velocity (p = .0933). Conversely. ROM in thehip joint did not vary significantly with age (p = .097) but was significantlyrelated to velocity, F(l, 162) = 50.46, p = .001. Trunk ROM varied significantlywith age, F(l, 162) = 2.9, p = .027. but not with velocity (p = .29) (Table 3).

»Discussion

Velocity in any running pattern is determined by stride length and stride frequency.Any variation in either of these two measures affects the velocity of the run. Inthis study there was a significant shortening of the stride iength with increasingage. There was no similar change in stride period, which is a measure of stridefrequency. It can be stated, therefore, that the primary alteration in stride velocitythat takes place with aging is a decrease in the length of the stride rather thanin the amount of time used for each stride. To state this in a different way, thetiming of the run. or its rhythm, stays relatively constant across ages: The feetstrike the ground with the same frequency. The loss in velocity occurs becauseless ground is covered in each stride.

Table 3

Relative Joint Angle Maximums and Minimums and Joint Rangeof Motion (ROM) for Knee and Hip Plus Trunk Excursion ROM (in degrees)

KneeMaximum angle

Minimum angle

ROM

HipMaximum angle

Minimum angle

ROM

TrunkROM

MSDMSDMSD

MSDMSDMSD

MSD

30

379.6

1606.3

12213.8

1196.4

1968.0

7711.2

205.5

40

409.1

1615.5

12110.9

1177.9

2007.0

839.9

174.3

50

4412.2

1646.4

11914.1

1178.5

1949.2

7812.4

174.8

Age60

477.2

1644.9

1178.8

1176.9

1957.2

788.8

184.1

70

6214.9

1625.2

10016.2

1248.3

1938.3

6812.8

157.0

80

6414.7

1604.4

9615.8

1279.4

1917.6

6413.3

163.5

90

57—

163—

106—

129—

197—68—

18—

24 - Hamilton

Stride length in the sprint run is determined by the forces generated duringthe support phase of the running stride. The impulse developed during the propul-sion portion of the support phase will determine both the time and trajectory of\hc flight phase of the stride. A longer flight phase correlates with a greater stridelength, as the body becomes a projectile, with time in the air directly related tohorizontal displacement. If the impulse generated through ground reaction forceduring propulsion is limited, the flight phase will be shortened. less time will bespent in the air. and less distance will be covered. A significant increase insupport time coupled with the significant decrease in stride length leads to thespeculation that of the two components of impulse, it is force, rather than time,that is reduced.

Decreased force production and therefore decreased impulse in propulsionmay be linked to several factors. The significant decrea.se in maximum hip andknee extension during propulsion suggests a decrease in the angular distanceover which muscle force is applied, thereby decreasing the resulting propulsiveimpulse. If this is coupled with the decrease in muscle strength that has beenshown to occur with aging (Buskirk & Segal, 1989; Murray et al.. 1980; Stamford,1988). there may be significant decline in the magnitude of the force applied,thus adding further to the decline in the propulsive impulse generated.

Although the period of the flight phase decreased significantly, there wasa significant increase in the period of the supptirt phase. There are two majorareas of concern to be addressed in this pha.se besides the propulsive action justdiscussed. During initial contact in the support phase considerable impact forcesare transmitted to the foot and hence throughout the kinetic link system. In theaging musculoskeletal system it is likely that these impact forces may produceexcessive stress on bone and joint structures that may be losing both bone mineraland elastic properties (Stamford. 1988). An increase in the time through whichthese impact forces are absorbed may minimize the magnitude of these forces.The mechanism through which this increase in time occurs was not closelyexamined in this study. A second mechanism that may increase the period ofthe suppjort phase of the stride is the decrease in the muscle's ability to generatehigh-velocity muscle contraction. The evidence for such a decline is not convinc-ing, as evidenced by Stamford's (1988) review of aging muscle. There is aquestion, however, conceming the speed with which older muscle tissue canchange from the lengthening, eccentric state that is produced in the hip and kneeextensors during the flexion of impact and the concentric contraction requiredof these same muscles during the forceful extension of propulsion. If there is.in fact, a loss in fast-twitch muscle fiber, as Buskirk and Segal have described,the velocity of this change in contraction type might be significantly slowed.The slower contraction capability coupled with a decrease in strength will decreasethe impulse.

In addition to the decrease in flight time and the increa.sed period of thesupport phase there is some alteration in the swing phase among older runners.The decrease in the relative proportion of the stride used for swinging the non-support leg through is most likely a direct result of the decreased range of motion.With a loss of up to 20° of motion in the hip joint, the arc covered by the swingleg will be greatly shortened, also adding to the decline in stride length. Alongwith this decrease in hip mobility there is a decrease in range of motion at theknee. Although varying significantly only with age, not with velocity, the de-

sprint Stride Kinematics 25

creased flexion in the swing leg likely contributes to the truncation of the swingphase by substantially increasing the moment of inertia of Ihe leg.

Conclusions

From the data it is evident that with increasing age there are significant alterationsin the stride velocity, stride length, stride period, support time, swing time, flighttime stride pattem, and hip and knee ROM of sprinters. Each of these alterationsbegins at specific ages. The decrease in velocity that has been noted in otherstudies and verified here can be attributed primarily to a decrease in stride length.This decrease is the result of the following variations in the other measures ofstride kinematics: decreased flight time, decreased swing time, increased supporttime, and decreased range of motion in the hip and knee joints.

All of these changes produce an overall decrease in sprint velocity with aminimal change in stride timing. Although no evidence in this study substantiatesa rea.son for these changes, it is suggested that further research be conductedinto the nature of muscle tissue and neurological change as it occurs in olderelite athletes.

References

Buskirk. E.R., & Segal, S.S. (1989). The aging motor system: Skeletal muscle weakness.The Academy Papers, 11, 19-36.

Cunningham, D.A., Rechnitzer, P.A., Pearce, M.A.. & Donner, A.P. (1982). Determinantsof self-selected walking pace across ages 19 to 66. Journal of Gerontology, 37,560-564.

Himan, J.E.. Cunningham. D.A., Rechnitzer, P.A., & Patterson, D.H. (1988). Age-relatedchanges in speed of walking. Medicine and Science in Sports and Exerci.'ie, 20,161-166.

Heinonen, J. (Ed.) (1980). Results of the VIII world championships. Eugene, OR: Organiz-ers of VIII World Veterans Championships.

Imms. F.J., & Edholm, O.G. (1981). Studies of gait and mobility in the elderly./l^e andAging, 10, 147-156.

Lundgren-Lindquist. B., Aniansson, A., & Rundgren, A. (1983). Eunctional studies in 79-year-olds. Scandinavian Journal of Rehabilitation Medicine. 15. 125-131.

Mann,R.,& Herman, J. (1985). Kinematic analysis of Olympic sprint performance: Men's200 meters. International Journal of Sport Biomechanics, 1(2). 151-162.

Marino. G. W., Einch, C , & Young, W. (1984). Variations in walking movements of olderadults. In Proceedings of the third biannual conference of the Canadian Societyof Biomechanics: Human locomotion III (pp. 61-62). Winnipeg, MB: ConferenceOrganizing Committee.

Moore, D.H. (1975). A study of age group track and field records to relate age and runningspeed. Nature, 253, 264-265.

Murray. M.P., Gardiner, G.M., Mollinger. L.A., & Sepic, S.B. (1980). Strength of isometricand isokinetic contractions: Knee muscles of men aged 20 to 80. Physical Therapy,60,412-419.

Roberts, E.M., Cheung, T.K.. Hafez, A.A.M., & Bullard, S.K. (1986). Biomechanicalcharacteristics of the swing limh in masters runners. In Proceedings of the North

26 Hamilton

American Congress on Biomechanics: Locomotion IV (pp. 181 -182). Montreal, PQ:Congress Organizing Committee.

Shapiro. D.C.. Zemicke. R.F.. Gregor, R.J., & Diesiel. J.D. (1981). Evidence for general-ized motor programs using gait analysis. Journal of Motor Behavior, !3( I), 33-47.

Stamford. B.A. (1988). Exercise and the elderly. E.xerci.ie and Sports Sciences Review,16.341-379.