selecting an optimal stride length in distance running affects metabolic cost demonstrated by increases found in oxygen uptake when non - ideal stride lengths are used ( 5 ) .
well - trained runners naturally select stride rates and lengths that minimize oxygen uptake at distance running speeds ( 1 , 5 , 12 , 13 , 16 ) .
a recent study found a lack of optimization of stride frequency among novice and trained runners ( 6 ) .
this was unexpected due to the multiple previous studies showing the ability to self - optimize stride frequency for economy .
running can be represented as a spring - mass system . while variations exist in the stiffness of this spring between people and across different speeds , for any given situation , a spring constant can be determined ( 2 , 8 , 14 ) .
the natural oscillation of a spring may be what determines preferred stride rate for a given person , running surface , and speed .
the stiffness of the leg spring is primarily determined by the reactions of muscles , tendons , and bones to the ground reaction force ( 7 ) .
assuming the leg spring adjusts to its natural frequency , inexperienced runners should also have the ability to self - economize stride length .
along with previous studies showing self - economizing of stride length in a non - fatigued state ( 1 , 5 , 12 , 13 , 16 ) , hunter and smith showed stride length is self - optimized at the end of a one - hour high intensity run ( 12 ) .
many of their subjects had changes in preferred stride length ( psl ) from the early to late stages of the run .
these changes in psl matched changes in the most economical stride length ( esl ) .
so , whether rested or fatigued , these runners were capable of self - optimizing stride length for economy even when a change is required during the course of the run .
since experienced runners self - regulate stride length to optimize economy , changing stride lengths will likely result in a greater metabolic cost .
if self - economization of stride length is based upon musculoskeletal factors , inexperienced runners should also be able to select their own preferred stride length without modification .
on the other hand , self - economization may be something that is learned through running experience .
this study aims to determine whether stride self - economization is different between experienced and inexperienced runners ( figure 1 ) .
we expect that if preferred stride length is determined by musculoskeletal parameters , inexperienced runners will also self - economize stride length .
preferred and economical stride length was measured in 33 subjects ( 19 experienced and 14 inexperienced ) .
an experienced runner averaged at least 20 miles per week for the past two years .
ten of the experienced runners were intercollegiate distance runners with the same coach , the rest were taken from elsewhere in the university population .
inexperienced runners were defined as never having run more than five miles in one week throughout their lives .
an informed consent document was signed by each subject before he / she was allowed to begin .
, preferred stride length was calculated by timing 30 strides multiplied by treadmill speed , then dividing by 30 . this stride length along with plus and minus 8 and 16% of this length
were used during the preliminary run to practice running at these non - preferred lengths .
these percentages of modified stride lengths were used as a results of pilot testing and matching a previous study that used similar methodologies ( 12 ) .
the pace averaged 3.66 m / s for the experienced group and 3.04 m / s for the inexperienced group .
the data collection run was completed at the pace determined during the preliminary run . a metabolic cart ( parvo medics , salt lake city , ut ) reported average oxygen uptake for every 15 seconds during the entire run .
preferred stride length was measured during the fourth minute of the data collection run with the help of a customized computer program ( microsoft visual basic , microsoft corp , seattle , wa ) .
the investigator would click the mouse button every time the right foot came in contact with the treadmill for twenty strides .
the computer would then divide 20 strides by the amount of time needed to complete 20 strides to get the stride rate . dividing treadmill speed by stride rate provided stride length . following the data collection run ,
after the fourth minute of the data collection run , subjects ran the five different stride lengths for two minutes each in random order .
following the first five minutes of running , economical stride length was measured by having subjects run with five different stride lengths ( preferred and plus and minus 8 and 16% of preferred ) .
the minimum value of a best - fit second - degree polynomial with oxygen uptake ( taken from the final minute of each stride length ) as a function of stride length was used to determine esl ( figure 1 ) .
an independent t - test was used to compare differences between experienced and inexperienced runners in how much more oxygen was required to maintain preferred stride length over economical stride length .
the resulting means , standard deviations , and samples sizes were used to determine statistical power .
preferred and economical stride length was measured in 33 subjects ( 19 experienced and 14 inexperienced ) .
an experienced runner averaged at least 20 miles per week for the past two years .
ten of the experienced runners were intercollegiate distance runners with the same coach , the rest were taken from elsewhere in the university population .
inexperienced runners were defined as never having run more than five miles in one week throughout their lives .
an informed consent document was signed by each subject before he / she was allowed to begin .
they self - selected this preferred pace . during this preliminary run , preferred stride length was calculated by timing 30 strides multiplied by treadmill speed , then dividing by 30 . this stride length along with plus and minus 8 and 16% of this length
were used during the preliminary run to practice running at these non - preferred lengths .
these percentages of modified stride lengths were used as a results of pilot testing and matching a previous study that used similar methodologies ( 12 ) .
the pace averaged 3.66 m / s for the experienced group and 3.04 m / s for the inexperienced group .
the data collection run was completed at the pace determined during the preliminary run . a metabolic cart ( parvo medics , salt lake city , ut ) reported average oxygen uptake for every 15 seconds during the entire run .
preferred stride length was measured during the fourth minute of the data collection run with the help of a customized computer program ( microsoft visual basic , microsoft corp , seattle , wa ) .
the investigator would click the mouse button every time the right foot came in contact with the treadmill for twenty strides .
the computer would then divide 20 strides by the amount of time needed to complete 20 strides to get the stride rate . dividing treadmill speed by stride rate provided stride length . following the data collection run ,
after the fourth minute of the data collection run , subjects ran the five different stride lengths for two minutes each in random order .
following the first five minutes of running , economical stride length was measured by having subjects run with five different stride lengths ( preferred and plus and minus 8 and 16% of preferred ) .
the minimum value of a best - fit second - degree polynomial with oxygen uptake ( taken from the final minute of each stride length ) as a function of stride length was used to determine esl ( figure 1 ) .
an independent t - test was used to compare differences between experienced and inexperienced runners in how much more oxygen was required to maintain preferred stride length over economical stride length .
the resulting means , standard deviations , and samples sizes were used to determine statistical power .
no difference was found between experienced and inexperienced groups for the extra oxygen required for non - optimization of stride length ( table 1 , t=1.49 , p=0.23 ) .
the average percent increase in oxygen uptake required for non - optimization are reported in table 1
. statistical power of 0.80 existed for the ability to detect a difference of 2.73% .
the average oxygen uptakes while running at preferred stride length for inexperienced and experienced runners were 33.6 ml / kg / min and 39.4 ml / kg / min respectively ( figure 2 ) .
although all subjects were considered optimized for economy in terms of stride length , the steepness and shape of each curve varied from subject to subject .
the most commonly observed curves showed equally increased oxygen uptake for shorter or longer strides .
other curves had small increases in oxygen uptake with shorter strides , but large increases with longer strides ( figure 3 ) .
inexperienced runners are equally capable of optimizing stride length for minimal oxygen uptake as experienced runners .
the small non - significant average difference and the sufficient power to detect a difference of 2.73% provided confidence that if any difference exists between experienced and inexperienced runners , it is quite small .
different running paces might alter how impactful a slight deviation between psl and esl will be .
our study included metronome use during the psl testing whereas de ruiter s did not .
we chose to use the metronome during psl in case there is an effect on metabolic cost due to focusing on the cadence .
taking both studies into consideration , there is still a need to determine the specific conditions where inexperienced runners differ from experienced .
one thing that is not conflicted between the studies is that psl may change with experience of running .
many factors may lead to this including changes in : stride length , vertical oscillation , leg stiffness , body segment parameters , preferred joint angles , and preferred body positions ( 15 ) .
while no relationship between leg stiffness and running economy was investigated , this study supports the idea of the body acting as a mass - spring system ( 7 , 8 , 11 ) .
stride frequency is closely connected to leg stiffness ( 8) . springs have a resonant frequency at which they will oscillate .
this resonant frequency is determined by the stiffness and the applied mass with the equation : where fn is the resonant frequency , k is the stiffness of the spring , and m is the mass .
the stiffness depends upon the properties and reactions of the tissues that act as a spring , while the average applied force depends upon the flight time and ground contact time .
heise and martin ( 11 ) showed that the less economical runners possess a more compliant running style during ground contact .
although the stiffness may be different for a trained versus untrained group , assuming the untrained is less economical , the current stride a runner uses appears to be the most economical for their conditioning . over time it is reasonable to assume the stiffness and
the mass may change through training , but at any given time the stiffness should lead to a preferred stride rate and length that is also the most economical .
some were capable of using stride lengths substantially different than preferred without large increases in oxygen uptake .
in a few cases , shorter strides than preferred were less detrimental than longer strides within a given subject ( figure 3 ) . for most subjects ,
however , the further away from preferred a subject would go , oxygen uptake increased dramatically .
shorter strides result in smaller peak forces and range of motion at the hip and knee ( 10 ) .
if decreased forces and range of motion are desired for someone , they may be able to accomplish that with minimal increase in effort .
however , there is still a greater perceived exertion when choosing shorter strides ( 10 ) .
when using a shorter stride , more repetitions will be required if a run of equal length is completed .
however , the extra repetitions may not be detrimental since patellofemoral load is considerably less when using a shorter stride ( 17 ) .
however , whenever running technique is modified , stresses on the body are altered and care should be taken if one has a desire to make this kind of modification . as an inexperienced runner becomes experienced
, changes may occur in endurance capacities , running economy , body weight , body composition , muscle strength , and muscle power ( 3 , 4 , 9 ) .
however , at any point of the spectrum from inexperienced to experienced , the chosen stride length is probably ideal for economy .
inexperienced and experienced runners may not need to manipulate stride length to economize their running technique .
when maximizing running speed over short distances is the main concern , runners may choose to sacrifice some economy to increase top speed .
more consideration and experimentation should be completed to determine how to optimize technique for maximizing running speed .
 experienced runners appear to naturally select a stride length which is optimal for minimizing oxygen uptake . however , whether this ability is naturally built into the human body or whether it is learned through experience has not been previously tested . 
 this study investigated whether inexperienced runners are as capable as experienced runners of self - optimizing stride length to minimize oxygen uptake . 
 thirty - three subjects ( nineteen experienced and fourteen inexperienced ) ran for twenty - minutes while preferred and economical stride lengths were measured . 
 a t - test checked for differences between the experienced and inexperienced groups in the percent increase of oxygen uptake due to not running at the most economical stride length . 
 no difference was found between groups with the increase in oxygen uptake due to not being optimized ( p=0.47 ) . 
 the average percent increase in oxygen uptake above the most economical for inexperienced and experienced runners was 1.8% and 1.2% respectively . 
 we concluded that inexperienced and experienced runners are equally capable of matching preferred stride length to economical stride length , thus athletes and coaches do not need to alter runner s stride length when economy is the main concern . 