the countermovement jump ( cmj ) is an explosive movement that is essential in many sports , 
 including basketball and volleyball1 . cmj 
 height , which is determined by measuring the jump height starting from an erect position 
 followed by a downward movement before starting to push off , is an important criterion in 
 athletic evaluation . athletes spend much time and effort in various training activities to 
 improve their athletic performance2 . many 
 researchers have reported the performance characteristics of the cmj and have discussed 
 multiple issues related to achieving better cmj height3,4,5 . ugrinowitsch et al.6 reported that better 
 cmj height was the result of an increased vertical shift in the body s center of mass . to 
 improve cmj performance , ankle flexibility4 , muscle strength3 , 7 , 8 , 
 initial jumping posture ( squat depth)5 , 
 and take - off velocity during vertical jump1 are required . robertson and fleming9 investigated the contributions of the extensors in the lower limb 
 and found that the greatest contributor to jump performance was the hip ( 40% ) followed by 
 the ankle ( 35.8% ) and the knee ( 24.2% ) . furthermore , another study suggested that ankle 
 joint flexibility contributes significantly to increasing cmj height4 . during a vertical jump , the contribution of the ankle joint 
 depends on the torque produced by the plantar flexors as well as the ankle dorsiflexion 
 range of motion ( df rom)10 . toe flexor muscles ( tfm ) , which support the longitudinal arch of the foot against the 
 reaction of the floor on the forefoot , also affect athletic performance11 . previous studies reported that tfm strengthening may have 
 a positive effect on athletic performance7 , 12 . in addition , tfm strength may affect the 
 use of the metatarsophalangeal joint ( mpj ) before take - off during the cmj10 . to date , no studies on the effects of tfm 
 strength on cmj height have been conducted . therefore , this study investigated the correlations between peak tfm strength , df rom , and 
 cmj height . the results of this study may help identify the factors for improving cmj height 
 in training athletes . eighteen healthy volunteers ( age : 23.3  2.5  years , body weight : 71.9  11.2  kg , height : 
 174.6  3.8  cm , df rom : 19.6  3.9 , cmj height : 46.3  10.3  cm ) participated in this study . all participants were free of injuries , especially in the ankle joints , feet , and mpj . the 
 exclusion criteria were ( 1 ) any cardiovascular , respiratory , abdominal , neurological , 
 musculoskeletal , or other chronic disease and ( 2 ) any symptoms that could affect the 
 musculoskeletal system . the study procedure was approved by the yonsei university wonju 
 campus human studies committee ( approval number : 1041849 - 201508-bm-018 - 03 ) ; all participants 
 provided written informed consent before enrollment . peak tfm strength , df rom , and cmj height were used as the variables in this 
 cross - sectional study . each participant s body weight and height were determined at the 
 beginning of the test protocol . prior to gathering data , participants performed a warm - up 
 that consisted of 5 minutes of walking up and down the stairs . three cmjs were performed by each 
 participant , and the mean value ( mean cmj height ) was used for analysis . peak tfm strength was measured using a digital dynamometer ( msc-200 , ametec inc , largo , fl , 
 usa ) . for a stable measurement setting , the digital dynamometer was attached to a wooden 
 frame consisting of a platform , a vertical board , and a footboard13 , 14 . each 
 participant was instructed to sit comfortably with his or her back supported by a chair 
 backrest and to place the foot to be tested on the footboard . the hip , knee , and ankle 
 joints were positioned at 90 during the test . the toe to be measured was inserted into a 
 leather cuff that was placed on the plantar side of the proximal phalanx , and the 
 participant was instructed to pull the cuff downward as hard as possible for 5 seconds . each 
 of the 5 toes ( phalanges ) was measured 3 times in the same way . for familiarization with the 
 testing procedure , participants were allowed to practice before measurement . for analysis , 
 the highest value of 3 tfm strength measurements in each toe was used . a 3-minute rest 
 period was provided between the strength measurements of each toe to minimize muscle 
 fatigue . a blinded tester with experience working with a digital dynamometer read and 
 recorded the strength value for each tfm on the digital display to eliminate experimental 
 bias ( table 1table 1.mean (  sd ) of peak toe flexor muscle strengths by participants ( n=18)first toesecond toethird toefourth toefifth toepeak tfm strength13.1  3.93.1  1.02.8  0.83.1  1.0 4.2  1.3values are presented as the mean  sd . tfm : toe flexor muscle the maximal df rom of the dominant leg was measured with a universal goniometer in 1 
 increments with the participant lying prone with 90 knee flexion . one lever of the 
 goniometer was positioned on the proximal fibular head , while the pivot was placed on the 
 lateral malleolus . the measuring arm was positioned on the fifth metatarsal bone , and its 
 position was used to determine the passive df rom15 . participants were instructed to perform 3 maximal cmjs with the use of both arms , trying to 
 cover the longest possible vertical distance . the highest successful cmj height among the 3 attempts of each participant was chosen 
 for jump height analysis7 . two - dimensional 
 ( 2d ) kinematics measurement was obtained during the procedure with regular sampling at 
 25  hz . a camera ( canon 500d , tokyo , japan ) was mounted on a tripod , which was placed 5  m 
 away from the participants , to record movements in the sagittal plane . a marker was placed on the sacrum at the 
 approximate center of mass ( com ) , and the camera lens was focused on each participant s 
 sacral marker in the standing position16 . video 
 sequences were digitized and examined using virtualdub software ( avery lee , version 1.5.10 , 
 cambridge , ma , usa ; http://www.virtualdub.org/ ) . the images were then analyzed using the 
 imagej computer program ( national institutes of health , bethesda , maryland usa ; 
 http://rsb.info.nih.gov/nih-image ) for height comparison . the data were analyzed using pasw version 18.0 ( chicago , il , usa ) for windows . pearson 
 correlation coefficients ( r ) were used to determine the strength and directionality of the 
 relationships among the variables ( peak tfm strength , df rom , and cmj height ) . mukaka17 suggested threshold values of 0.00.3 , 
 0.30.5 , 0.50.7 , 0.70.9 , and 0.91.0 for negligible , low , moderate , high , and very high 
 correlation coefficients , respectively . in addition , the coefficient of determination 
 ( r ) was used to account for the variation among the variables . in all 
 analyses , table 2table 2.correlation coefficients between peak tfm strength , df rom , and cmj 
 heightfirst tfmsecond tfmthird tfmfourth tfmfifth tfmdf romcmj heightfirst tfm strength1.0second tfm strength0.161.0third tfm strength0.0820.7011.0fourth tfm strength0.2280.5030.7901.0fifth tfm strength0.2080.6250.6230.5851.0df rom0.7100.2190.1860.0070.0291.0cmj height0.7650.0210.2330.1020.0630.6421.0*p<0.05 ; * * p<0.001 . cmj : countermovement jump , df rom : ankle dorsiflexion range of motion , tfm : toe 
 flexor muscle shows the pearson s correlation coefficients between peak tfm strength , df 
 rom , and cmj height in the participants . cmj height showed a moderate correlation with df 
 rom ( r=0.642 , r=41.3% , p<0.001 ) and a high correlation with peak first tfm 
 strength ( r=0.765 , r=58.5% , p<0.001 ) . the relationships between cmj height 
 and peak tfm strength of the other toes were negligible ( r=0.021 to 0.233 , p>0.05 ) . * p<0.05 ; * * p<0.001 . cmj : countermovement jump , df rom : ankle dorsiflexion range of motion , tfm : toe 
 flexor muscle the results of this study indicate that cmj height is correlated with peak first tfm 
 strength and df rom in healthy subjects . several previous studies investigated multiple issues related to cmj and reported a 
 proximal - to - distal sequence of muscle activation hip extensors , followed by knee extensors 
 and finally ankle plantar flexors3 , 18and a proximal - to - distal transfer of 
 energy during jumping10 , 19 . papaiakovou4 reported that the ankle should be a key joint in transmitting the 
 energy generated by the proximal part ( hip extensor , knee extensor , and ankle plantar 
 flexor ) to the ground during cmj execution . however , the mpj is smaller than the other 
 joints in the leg , but the mpj force amounts to about 86% body weight during push - off in the 
 gait cycle20 . the tfm around the mpj may 
 have a profound effect on forefoot loading and force transmission21 , and improvements of tfm strength training may have a 
 significant effect on athletic performance enhancement7 , 12 . the results of this study indicate a high correlation between peak first tfm strength and 
 cmj height ( r=0.765 , r=58.5% , p<0.001 ) . cohen22 reported that the coefficient of determination could be used to 
 more fully interpret the r value . thus , 58.5% of the total variation in peak first tfm 
 strength can be explained by variation in cmj height . nihal et al.23 reported that dancers had greater hallux muscle strength 
 than non - dancers ( 7  4n vs. 6  4n , respectively ; p<0.049 ) . in addition , the first tfm 
 strength was twice the second tfm strength ( 9  4n vs. 4  1n , respectively ; p<0.001 ) . 
 furthermore , tanaka et al.24 demonstrated 
 that the tfm are important contributors to sustaining dynamic balance ; in particular , the 
 tfm of the hallux was greater than the sum of the others combined . tfm strength may 
 influence mpj stiffness before take - off during cmj performance . stefanyshyn and nigg10 reported that increasing mpj stiffness 
 would decrease the energy lost at the mpj , which would correspond to a positive effect on 
 jump height . this finding may indicate a lack in the peak first tfm strength leading to a 
 large amount of energy loss and , therefore , would not adequately transmit energy via the 
 lower limb extensors before take - off during a cmj . thus , the results of this study suggest 
 that the peak first tfm strength is an important factor not only in stabilization of the 
 forefoot but also in the transmission of energy generated from the lower limb extensors to 
 the ground , as well as in improving athletic performance ; it is a major contributor in 
 performing a higher cmj . df rom during a full squat before take - off was reported to affect cmj height25 . in this study , cmj height showed a 
 moderate positive correlation with df rom ( r=0.642 , r=41.3% , p<0.001 ) , 
 consistent with the results of a previous study4 . individuals with a greater df rom were reported to have the ability 
 to place their heels in contact with the ground during a full squat , which causes the ankle 
 plantar flexor muscles to achieve sufficient force - generating capacity for a deeper squat 
 position before take - off4 . it has been 
 shown that an active muscle , when lengthened , may sustain high forces and stretch the tendon 
 sufficiently so that it can store elastic energy for the late concentric phase when the 
 muscle activity starts to decay26 . however , studies have shown that people lacking df rom raised their heels off the ground , 
 had greater horizontal shift rather than vertical shift of com , and achieved a low jump 
 height25 , 26 . thus , df rom is thought to be a second contributor to achieving 
 sufficient force - generating capacity and proper vertical shift of com during cmj 
 performance . first , the participants performed the experiment 
 barefoot , but they wear shoes for actual athletic activities . second , other related muscles 
 that may contribute to the cmj , including the ankle plantar flexors , knee extensors , and hip 
 extensors , were not investigated . however , this 
 study is the first to examine the relationship between peak tfm strength and cmj height . 
 further study is needed to investigate the correlation between peak tfm strength and ankle 
 plantar flexors . second , further research will need to examine whether improvement in peak 
 tfm strength and df rom can have a clinically useful impact on cmj performance . this study was performed to investigate the correlations between df rom , peak tfm strength , 
 and cmj height . the results of this study indicate that the peak first tfm strength and df 
 rom are the main contributors to cmj performance . measuring the strength of peak first tfm , 
 ankle plantar flexors , knee extensors , and hip extensors in the lower limb and df rom may be 
 useful in clinical practice for improving jump performance in athletes such as volleyball 
 and basketball players .
[ purpose ] this study assessed the relationships between peak toe flexor muscle strength , 
 ankle dorsiflexion range of motion , and countermovement jump height . [ subjects and 
 methods ] eighteen healthy volunteers participated in the study . 
 each participant completed 
 tests for peak toe flexor muscle strength , ankle dorsiflexion range of motion , and 
 countermovement jump height . 
 [ results ] the results showed ( 1 ) a moderate correlation 
 between ankle dorsiflexion range of motion and countermovement jump height and ( 2 ) a high 
 correlation between peak first toe flexor muscle strength and countermovement jump height . 
 peak first toe flexor muscle strength and ankle dorsiflexion range of motion are the main 
 contributors to countermovement jump performance . 
 [ conclusion ] these findings indicate 
 that the measurement of peak first toe flexor muscle strength and ankle dorsiflexion range 
 of motion may be useful in clinical practice for improving jump performance in athletes 
 training for sports such as volleyball and basketball .