specificity is one of the foundational components of training success . in sport performance training ,
one of the initial steps in the design of an exercise regimen is the identification of movements specific to the needs of the individual , which may include joint angles , and muscle actions and recruitment ( 1 , 4 ) .
movement analysis is an integral step in the selection of exercises that mimic sport - specific actions and transfer to competition .
furthermore , the intensity and movement velocity ( explosiveness ) utilized in the performance of an exercise can be a vitally important component of specificity ( 1 , 4 ) . sprinting , and the acceleration phase in particular , is characterized by the explosive extension of the hip , knee , and ankle joints ( 3 ) , with a greater overall contribution of the hip joint particularly as speed increases ( 2 ) .
the kettlebell swing ( kbs ) is similarly characterized by activation of the posterior chain muscles , particularly in relation to the hip , in the horizontal plane that occurs during the sprint motion ( 3 , 8 , 11 , 16 ) thereby indicating movement specificity .
additionally , the rapid concentric phase and ballistic nature of the kbs ( 8 , 10 ) may align well with sprint performance , which also requires rapid force production .
comparisons between the kbs and a traditional one - repetition maximum back squat resulted in a greater impulse demand in the kbs , pointing towards the potential for a large rate of force development despite differences in load , and demonstrating the importance of the velocity of this exercise ( 8) .
thus , it is likely that this velocity specificity would also align well with sprinting . despite the popularity and potential applicability of kettlebell training in multiple domains ( 7 , 10 , 13 )
, the sport performance community has not responded with an appropriate depth of rigorous scientific studies into how kettlebell training may transfer into sprinting . in 2012 ,
lake and lauder reported six weeks of two - handed kbs exercise progressing to 60% of maximal loads , improved maximal and explosive strength ( 7 ) .
conversely , results from a comparison study suggested that kbs at 60% of maximal loads are not sufficient to develop lower body maximal and explosive strength , and concluded that the kbs may be best used as adjuvant training during a strength and conditioning program ( 8) . additionally , otto et al . reported that six weeks of traditional weightlifting induced significantly greater improvements in strength compared with kbs training , however , both were effective in increasing muscular strength and power in recreationally - active men ( 13 ) .
regardless of training modality , it is understood that volume plays an important role in the degree of muscular strength and power improvement .
it is plausible that different training volumes used in the aforementioned studies may have resulted in ambiguous conclusions about the efficacy of kbs on power performance .
moreover , though hypothesized , it has yet to be determined whether kbs training can have positive effects on sprint performance ( 7 ) .
therefore , the present study examined the effect of an eight - week kbs program versus a program of equal intensity , volume , and movement specificity using the stiff - leg deadlift ( sdl ) on sprint performance .
the sdl was chosen as it utilizes very similar muscle recruitment as the kbs , while allowing a slower movement velocity ( 1 , 4 ) . in this fashion , it is possible to utilize similar movement specificity and volume , while addressing the additional velocity specificity of the kbs .
therefore , it was hypothesized that the eight - week kbs program would improve sprint performance to a greater degree than an eight - week sdl program .
twenty ( n=20 ) healthy college - age female students ( 1825 yrs ) were recruited for the current investigation .
approval by the slippery rock university institutional review board was acquired and all participants completed informed consent .
participants were instructed to maintain their current aerobic exercise and dietary programs throughout the duration of the study .
no participants had extensive experience with kettlebell exercise or completed sprint or resistance training in the previous 6 months as a means to limit extraneous variables from prior training history .
study investigators , however , were trained in the safe and effective implementation of resistance exercise , and completed specific sessions on coaching the kbs and sdl .
participants were excluded from the present study if they were not cleared by their physician for vigorous exercise , were currently utilizing a resistance training program , were outside of the age range ( 1825 ) , or were unable attend the scheduled sessions .
participants were assigned into one of two groups ( kbs or sdl ) based on their initial sprint performance , to ensure that there were participants of similar ability in each cohort . following the group assignment
all participants participated in one instructional session on their assigned exercise prior to data collection .
technique mastery was not necessary during the single instructional session as the participants were observed ( i.e. appropriate cueing ) throughout the duration of the training intervention for both safety and effectiveness .
each group underwent an 8-week ( twice - weekly ) exercise intervention consisting of sixteen training sessions . quite simply
, this schedule was chosen as it fulfilled training frequency guidelines for beginners ( i.e. 23 sessions per week ) , and fit within the time constraints of a university academic semester .
each training session began with a 5 min light ( <3 mets ) aerobic warm - up on a treadmill followed by two 15 meter striders with a 30 second rest .
all training sessions were performed using a tabata interval timer ( 20 seconds of exercise ; 10 seconds of rest ; 8 rounds ) based on previous work demonstrating a large anaerobic component to this training approach ( 5 , 15 ) .
the participants were required to elect two non - consecutive days each week to exercise under the supervision of a project coordinator .
a  hardstyle kettlebell swing emphasizing maximal hip recruitment and minimal knee flexion was utilized in this study ( 7 ) .
training started with a consistent prescribed weight ( ~9.1 kg ) with the potential for a ~2.3 kg ( next kettlebell weight increment ) increase following week three , and another ~2.3 kg increase at week six , if the participant maintained proper form throughout each session .
form was monitored by trained instructors throughout the sessions , and included emphasis on maintaining an explosive concentric phase during maximal hip recruitment .
training started with a consistent barbell weight ( ~27.3 kg ) , with the potential for a ~4.5 kg increase following week 3 , and another ~4.5 kg increase at week 6 , if the participant maintained proper form throughout each session .
form checks for the sdl group included the maintenance of a two - second up / two - second down exercise tempo and maximal hip recruitment .
each participant completed both a 30-meter sprint test and countermovement vertical jump test on a consistent , indoor track .
identical post - testing was completed between 48 and 72 hours of the final exercise session .
if a participant performed the vertical jump test before the sprint test in pre - testing , they were asked to perform the sprint test first for post - testing .
each participant performed the same warm - up during the pre- and post - training testing .
this warm - up consisted of a 400-meter jog followed by a 40-meter interval of the following drills : high knees , butt kicks , walking knee - to - chest stretch , walking quad stretch , toe touches , hamstring swings , carioca , and striders .
participants were given the option to add additional warm - up striders before performing their maximal sprint ability .
thirty meter sprint performances were timed using a tc - photogate ( brower timing systems , draper , ut ) .
participants used a standing position and began the maximal sprint individually without a formal start .
the tc - photogate recorded when the participants crossed the start and the finish line .
each participant performed two sprint trials with a two - minute rest in between attempts , with the fastest sprint recorded .
a vertical jump measurement device ( vertec , jump usa , sunnyvale , ca ) was used to measure maximal vertical jump height .
participants reached to maximum vertical height on the vertec with their dominant arm while their feet were flat on the ground .
each participant performed two countermovement jumps with arm swing and displacement of the highest vane was determined . to calculate maximum vertical jump height ,
all analyses were performed using a standard statistical software program ( ibm spss statistics for windows , version 21 , 2012 ) .
pre- and post - testing differences among groups were assessed using an independent t - test .
a repeated measures anova was utilized to assess potential differences in pre- and post - testing differences across groups .
an a - priori -significance level of 0.05 was accepted as a reflection of differences in the mean .
twenty ( n=20 ) healthy college - age female students ( 1825 yrs ) were recruited for the current investigation .
approval by the slippery rock university institutional review board was acquired and all participants completed informed consent .
participants were instructed to maintain their current aerobic exercise and dietary programs throughout the duration of the study .
no participants had extensive experience with kettlebell exercise or completed sprint or resistance training in the previous 6 months as a means to limit extraneous variables from prior training history .
study investigators , however , were trained in the safe and effective implementation of resistance exercise , and completed specific sessions on coaching the kbs and sdl .
participants were excluded from the present study if they were not cleared by their physician for vigorous exercise , were currently utilizing a resistance training program , were outside of the age range ( 1825 ) , or were unable attend the scheduled sessions .
participants were assigned into one of two groups ( kbs or sdl ) based on their initial sprint performance , to ensure that there were participants of similar ability in each cohort . following the group assignment ,
all participants participated in one instructional session on their assigned exercise prior to data collection .
technique mastery was not necessary during the single instructional session as the participants were observed ( i.e. appropriate cueing ) throughout the duration of the training intervention for both safety and effectiveness .
each group underwent an 8-week ( twice - weekly ) exercise intervention consisting of sixteen training sessions . quite simply
, this schedule was chosen as it fulfilled training frequency guidelines for beginners ( i.e. 23 sessions per week ) , and fit within the time constraints of a university academic semester .
each training session began with a 5 min light ( <3 mets ) aerobic warm - up on a treadmill followed by two 15 meter striders with a 30 second rest .
all training sessions were performed using a tabata interval timer ( 20 seconds of exercise ; 10 seconds of rest ; 8 rounds ) based on previous work demonstrating a large anaerobic component to this training approach ( 5 , 15 ) .
the participants were required to elect two non - consecutive days each week to exercise under the supervision of a project coordinator .
a  hardstyle kettlebell swing emphasizing maximal hip recruitment and minimal knee flexion was utilized in this study ( 7 ) .
training started with a consistent prescribed weight ( ~9.1 kg ) with the potential for a ~2.3 kg ( next kettlebell weight increment ) increase following week three , and another ~2.3 kg increase at week six , if the participant maintained proper form throughout each session .
form was monitored by trained instructors throughout the sessions , and included emphasis on maintaining an explosive concentric phase during maximal hip recruitment .
training started with a consistent barbell weight ( ~27.3 kg ) , with the potential for a ~4.5 kg increase following week 3 , and another ~4.5 kg increase at week 6 , if the participant maintained proper form throughout each session .
form checks for the sdl group included the maintenance of a two - second up / two - second down exercise tempo and maximal hip recruitment .
each participant completed both a 30-meter sprint test and countermovement vertical jump test on a consistent , indoor track .
identical post - testing was completed between 48 and 72 hours of the final exercise session .
if a participant performed the vertical jump test before the sprint test in pre - testing , they were asked to perform the sprint test first for post - testing .
each participant performed the same warm - up during the pre- and post - training testing .
this warm - up consisted of a 400-meter jog followed by a 40-meter interval of the following drills : high knees , butt kicks , walking knee - to - chest stretch , walking quad stretch , toe touches , hamstring swings , carioca , and striders .
participants were given the option to add additional warm - up striders before performing their maximal sprint ability .
thirty meter sprint performances were timed using a tc - photogate ( brower timing systems , draper , ut ) .
participants used a standing position and began the maximal sprint individually without a formal start .
the tc - photogate recorded when the participants crossed the start and the finish line .
each participant performed two sprint trials with a two - minute rest in between attempts , with the fastest sprint recorded .
a vertical jump measurement device ( vertec , jump usa , sunnyvale , ca ) was used to measure maximal vertical jump height .
participants reached to maximum vertical height on the vertec with their dominant arm while their feet were flat on the ground .
each participant performed two countermovement jumps with arm swing and displacement of the highest vane was determined . to calculate maximum vertical jump height ,
all analyses were performed using a standard statistical software program ( ibm spss statistics for windows , version 21 , 2012 ) .
pre- and post - testing differences among groups were assessed using an independent t - test .
a repeated measures anova was utilized to assess potential differences in pre- and post - testing differences across groups .
an a - priori -significance level of 0.05 was accepted as a reflection of differences in the mean .
one individual was removed due to an unrelated ankle injury ; and following the eighth week of training , another individual withdrew due to an appendectomy .
pre- and post - testing data were recorded for eight kbs participants , and ten sdl participants .
kbs had 95% adherence to the training intervention , with a total training volume of 15,850 swings .
the average number of repetitions performed was 124 , with an average training session volume - load of ~1378.2 kg .
however , only 6,746 sdls were completed ( due to the intentionally slower repetition velocity ) , with the average number of repetitions per training session at 43 . despite lower repetitions ,
there were no significant differences noted in the pre - training 30 m sprint times between the kbs and sdl cohorts ( table 1 , p>0.05 ) .
likewise , there were no significant differences in the post - training 30 m sprint times between the kbs and sdl groups ( table 1 , p>0.05 ) . in kbs or sdl pre- to post - testing sprint times were not significantly different ( table 1 , p>0.05 ) .
there were no significant differences noted in the pre - training vertical jump performances between the kbs and sdl groups ( table 1 , p>0.05 ) .
likewise , there were no significant differences in the post - training vertical jump performance between the kbs and sdl groups ( table 1 , p>0.05 ) .
however , across groups , pre- to post - testing vertical jump performances improved by approximately 4% ( table 1 , p<0.05 ) , with no effect of training group .
to the knowledge of the authors , this is the first study to determine the effect of an 8-week kbs program versus a program of similar volume - load , and movement specificity using sdl on sprint and counter movement vertical jump performance .
the primary finding in the current investigation was kbs training ( 8 week ; 16 sessions ) did not significantly increase sprinting performance when compared to sdl .
additionally , vertical jump performance was improved with training . due to the design of the study , no differences existed in pre - intervention sprint times or vertical jump heights between groups . the current investigation measured recreationally - active females who did not partake in resistance training activities .
it is known that training status and modality can influence determinants of power ( e.g. sprinting ) .
our recreationally - active cohort was not unusual in that they demonstrated similar average 30 meter sprint times for females when compared to those studied by mangine and colleagues ( 5.20.2 v. 5.50.5 seconds ) ( 9 ) .
interestingly , no differences in the post - intervention sprint performances between kbs and sdl were observed . while both cohorts increased training loads and volumes over the course of the eight - week intervention , likely indicating adaptation , kbs training provided no additional transfer to the actions of sprinting , though a modest increase in countermovement vertical jump performance was observed . to our knowledge
, few investigators have attempted to quantify the efficacy of kettlebell exercise with equivocal findings .
kbs has been reported to improve strength and power ( 7 , 10 ) , while another study has reported no additional benefit over traditional training ( 13 ) .
it is likely that improvements with kbs may be due to the cyclical , eccentric loading phase of the exercise combined with the rapid reversal of force necessary to transition to the concentric phase .
furthermore , the mechanical demand of the kbs is dictated by both a vertical and horizontal mechanical output ( 8) , with a ballistic component provided by the long lever arm and variable center of mass of the participant / kettlebell system .
therefore , considering the movement- and velocity - specificity between kbs and sprinting , additional explanations for a lack of observed transfer in our findings must be considered .
the multifaceted nature of sprint performance must be considered first and foremost in the discussion of the current findings . based on the duration of the training intervention , neural adaptations
would likely account for a majority of the participants ability to adapt to the training regimen and increase training volume ( 1 , 12 ) .
neural adaptations , while important , may not account for the spectrum of underlying changes necessary for improved sprint performance .
it is likely that structural adaptations including muscle hypertrophy ( 3 ) , increases in stride frequency and length , and enhanced sprint technique ( 12 ) are critical components of sprint performance , but were not addressed in this intervention .
the results of this study suggest that kbs training alone may not provide a sufficient stimulus to improve sprint performance in recreationally - active females even with a focus on movement and velocity specificity .
it is likely that the present study may not have supplied a great enough training volume - load and intensity for improved sprint performance . in comparison to a study that demonstrated increases in explosive strength ( vertical jump ) in athletes using kbs ( 7 ) , our training volume was likely inadequate . assuming similar kbs movement and velocity specificity , when extrapolating an average training session from our study ( < 70 kg subject ; ~9.1 kg kettlebell ; 15 swings/20 seconds ; eight work intervals ) to training parameters of similar work in athletes ( < 70 kg subject ; 12 kg kettlebell ; ~22 swings/30 seconds ; twelve work intervals ) , our trainees received only one - third of the average training session volume ( 7 ) .
additionally , it is likely that the work to rest ratio ( 2:1 ) of the tabata protocol resulted in muscular fatigue which limited participants from generating maximum power outputs throughout the exercise sessions .
thus , the drop in power output and relative intensity could limit the transferability of the intervention to sprint performance , which utilizes maximum power output .
it is likely that an altered work to rest ratio ( e.g. 1:4 or 1:5 ) would preserve movement quality and explosiveness to a greater degree than the tabata protocol . while athletes may respond differently to training , and pose greater challenges than their recreationally - active counterparts
( 12 ) , it is probable that the volumes and intensities used in this investigation were underestimated .
a conservative starting load was chosen for the kbs group , as the best current guidelines for power programming highlight the need for rapid force development ( 5 ) .
consistent load assignment was deemed for this experiment in order to ensure similar training volume across participant groups , though it is likely that some means of individual strength or power testing in order to more accurately assign participant loads may have improved measured outcomes
. currently , however , specific load , intensity and volume recommendations for the various potential applications of the kbs are not readily available . with
the effectiveness of kbs training on vertical jump performance documented ( 7 , 13 ) , vertical jump was used as a comparable benchmark to gauge participant responsiveness to training . as countermovement vertical jump height changed significantly in both training cohorts ( approximately 4% improvement ) it is more likely that a lack of emphasis on sprint mechanics and technique may have had a larger impact on the lack of transfer to sprint performance than a simple lack of training volume . though correct form and adherence to the  hardstyle kettlebell swing and stiff - legged were coached across all 16 training sessions ,
nonconsecutive training days per week was chosen purely out of a need for freedom in scheduling between the participants and investigators , a more rigorous schedule format may have altered the findings of the study .
it is plausible that both sprint and jump performances are sensitive to diurnal variation ( 14 ) . in the current study
, scheduling conflicts resulted in a difference between pre- and post - testing time of day ( 12:002:00 pm and 7:009:00 am , respectively ) .
furthermore , changes in the time of testing may have also impacted variables related to food consumption , hydration , body temperature , motivation , and sleep patterns . in conclusion
, an eight - week kbs program was not shown to improve measures of sprint performance when compared to an sdl program .
training volumes are an important consideration for effectiveness in interventions designed to improve sprint outcomes , however , an equal consideration must be placed on mechanics and technique . due to movement- and velocity - specificity , the kbs should not be excluded from resistance training programs designed to accompany sprint training , especially given the limited volume of literature currently available .
recently , it has been reported that a two - handed kbs is appropriate for the training of ballistic or explosive outcomes ( 6 ) .
it is plausible that an appropriate kbs prescription as part of a comprehensive training program ( e.g. teaching sprint technique ) can improve sprint performance .
however , data from the current investigation do not confirm or support the efficacious use of kbs in sprinting .
therefore , future research is still needed to determine the value of kbs in sprint - training programs and provide volume and intensity recommendations .
 the kettlebell swing ( kbs ) , emphasizing cyclical , explosive hip extension in the horizontal plane , aligns with movement- and velocity - specificity of sprinting . 
 the present study examined the effect of an eight - week kbs intervention on sprinting in recreationally - active females , in comparison to an eight - week intervention using the stiff - legged deadlift ( sdl ) . following a pre - testing session measuring 30 meter sprint and countermovement vertical jump performance , 
 participants were divided evenly by sprint time into kbs ( n=8 ) and sdl ( n=10 ) cohorts . following familiarization with the exercises , 
 kbs met twice weekly to perform swings using the tabata interval ( 20s work , 10s rest , 8 rounds ) , stressing a rapid , explosive tempo . 
 in contrast , the sdl group performed their tabata stiff - legged deadlifts at a conventional resistance training tempo ( 2 seconds concentric , 2 seconds eccentric ) . 
 following eight weeks and greater than 95% training adherence , the sdl group only had a slightly greater average training volume ( ~3% ) than kbs . 
 no significant differences in pre - test values , or changes were noted in sprint performance from pre- to post - intervention in either group . 
 an improvement in vertical jump performance was noted across groups . 
 potential explanations for the lack of sprint improvement compared to previous studies include differences between recreationally - active and athletic females , and low exercise volume ( ~46% of a comparable study with improvements in vertical jump ) . 
 future studies should seek to determine the appropriate volume and intensity for kbs components of sprint programming . 
INTRODUCTION
METHODS
Participants
Protocol
Statistical Analysis
RESULTS
DISCUSSION