physical inactivity is being increasingly recognized as a major problem in global health . 
 the world health organization ( who ) estimates that 3.3 million people die around the world 
 each year due to physical inactivity , making it the fourth leading underlying cause of 
 mortality1 .
it is not surprising that 
 physical inactivity has a substantial cost burden in addition to a large health burden .
the 
 current guidelines on cardiovascular disease prevention recommend at least 30 minutes of 
 moderate intensity physical activity on five or more days per week or 20 minutes of vigorous 
 exercise on three days per week2 .
physical activities of moderate intensity , such as walking , jogging , and running can be 
 incorporated into everyday life .
walking has been established as a form of endurance 
 training for injury prevention and has sufficient training effects with little risk of 
 overstrain3 .
walking is a popular , 
 convenient , and relatively safe form of exercise and also holds great promise for weight 
 management4 . walking
has long been used by both fitness and rehabilitation professionals to improve 
 cardiovascular fitness and to rehabilitate musculoskeletal injuries .
humans generally learn 
 to walk and run in a forward direction with little difficulty .
this is inherently logical 
 since our field of view is in the forward direction .
because of its functionality , most 
 walking studies and clinical protocols have involved forward walking ( fw ) .
backward walking 
 ( bw ) reverses leg movement trajectories : the leg not only reverses its direction of 
 movement , it also travels in the opposite direction along virtually the same path as in 
 fw5 .
it has been reported that bw has 
 training effects that are different from those of fw6 .
furthermore , running or walking backward is used as a preferred 
 rehabilitation exercise for some conditions , in particular when the impact of heel strike 
 needs to be avoided7 . however , the 
 different effects of fw and bw in terms of their physiological aspects are still unknown . 

the purpose of this study was to compare forward and backward locomotion training and their 
 effects on physical performance , such as anaerobic capacity , and anthropometrical body 
 composition .
a convenience sample of 30 healthy male subjects with a mean age of 20.93  2.54  years , a 
 mean weight of 59.43  5.38  kg , and a mean height of 1.69  0.05  m were recruited on a 
 university campus for this study .
the present study was reviewed and approved by the 
 institutional ethical committee and written consent was obtained prior to the study from all 
 the participants .
inclusion criteria for study participation were : healthy young males , aged 
 between 1828 years , normal bmi and no active exercise / sports participation .
subjects with 
 any lower extremity injury in the past 6 months , cardiac or metabolic condition , or back , 
 hip , knee or ankle dysfunctions were excluded .
subjects were selected following the 
 inclusion and exclusion criteria , and were randomly and evenly divided into 2 groups : the 
 forward walking group ( fwg ) , and the backward walking group ( bwg ) ( n=15 in each group ) .
pre- and post - test anaerobic performance was calculated from the results of the 
 running - based anaerobic sprint test ( rast)8 , 9 .
a warm - up of light jogging for 5 minutes 
 was followed by 5 minutes rest .
then , each subject performed six sprints over 35 meters with 
 a 10-second rest between each sprint . the time taken for each sprint along with body weight 
 was used to calculate rast.power = body weight  distance    
 time ; average power ( ap ) = sum of all six values  6 pre- and post - test anthropometrical body composition measurements were used to calculate 
 body density ( db)10 , percentage body fat 
 ( % bf)11 , fat mass ( fm)12 , fat free body mass ( ffm)12 .
based on anatomical landmarks in the 
 anthropometric standardization reference manual , the skin folds of the triceps , subscapula , 
 and abdomen were used to calculate db .
the average values of the three skin folds sites , 
 i.e. triceps , subscapula , and abdomen were summed ( 3skf ) and entered into the equation to 
 determine db , which was subsequently used to calculate % bf , fm and ffm.db = 
 [ 1.0973-(0.000815  3skf ) ] + [ 0.00000084  ( 3skf ) 
 ] .percentage body fat ( % bf ) = [ 495  body density ( db ) ]  
 450.fat mass ( fm ) = body mass  % bf/100 ; fat free body mass 
 ( ffm ) = body mass  fm .
the subjects were given a familiarization session on the treadmill one week prior to the 
 start of the training of either fw / bw at a self - selected speed , without inclination 3 
 supervised 10 minute sessions . at the start of the intervention ,
the treadmill was 
 calibrated and adjusted to produce a constant speed of 4.0 mph and an uphill inclination of 
 10 degree13 .
the subjects were given 1 
 minute of accommodation followed by 6 minutes of training .
the purpose of the accommodation 
 phase was to gradually increase the speed and the inclination of the treadmill to 
 acclimatize the subjects to the walking pattern and to set the training parameters to the 
 desired training levels .
the fwg performed 6 minutes of forward treadmill walking at an 
 inclination of 10 and a constant speed of 4 mph , 3 sessions per week , for a period of 6 
 weeks with one day rest between sessions .
the bwg performed backward treadmill walking at 
 the same speed and inclination with the same training schedule .
outcome measures such as anaerobic performance and anthropometrical body composition ( i.e. 
 db , % bf , fm , and ffm ) were measured pre- and post - intervention .
the statistical software 
 package , spss version 17 , was used for data analysis .
the unpaired student s t - test was used to examine the significance of group differences for 
 all the dependent variables and the paired t - test was used to analyze within group 
 differences .
within group analysis of anaerobic performance showed significant differences within both 
 fwg and bwg ( p= 0.001 and p=0.000 respectively ; table 
 1table 1.comparison of anaerobic capacity and body composition between fwg and bwgvariablesfwgbwgpre - testpost - testpre - testpost - testap ( watts)317.932324.433317.143329.144db * ( g / cm)1.10.11.10.11.10.11.10.1%bf * ( % ) 15.22.715.22.714.92.614.92.6fm * ( kgs)9.12.59.12.59.12.49.02.4ffm * ( kgs)503.4503.450.8350.83*non - significant ) .
however , within group analysis of the pre- and post - test values of 
 anthropometrical body composition found no significant differences for db ( p = 0.164 p = 
 0.082 , bf% ( p = 0.164 p = 0.082 , fm ( p = 0.165 p = 0.083 , and ffm ( p = 0.165 p = 0.083 ) 
 after fw and bw training , respectively ( table 
 1 ) . when fwg and bwg were compared using the independent t - test for the effect of fw and bw on 
 the treadmill , a statistically significant difference ( p=0.033 ) in anaerobic performance 
 was found , and the mean improvement of bwg ( 12.06 6.95 watts ) was more than the mean 
 improvement of fwg ( 7.00 5.34 watts ) .
moreover , between group analysis of db , % bf , fm , and ffm found no significant differences 
 between fwg and bwg ( p=0.621p=0.632 p=0.710 and p=0.710 , respectively ) .
the present study revealed significant improvements in anaerobic power were elicited fw and 
 bw training and greater improvement was shown by bwg than by fwg .
in contrast , 6 weeks of fw 
 and bw intervention elicited no statistically significant changes in the body composition 
 values of db , % bf , fm , or ffm .
bw is a novel task in 
 which a larger number of motor units may be recruited , and this may result in increased 
 energy utilization .
increased motor unit recruitment would result in a greater amount of 
 skeletal muscle activation than in an equivalent familiar task .
reported that 
 a relatively new motor task increases motor unit recruitment , thus increasing the metabolic 
 cost of the activity14 .
a recent study 
 also demonstrated an improvement elicited by nordic bw training , due to more efficient motor 
 unit recruitment and as a result of practice15 .
others have also suggested that bw imposes a greater burden on the 
 medial sensorimotor cortices16 , and that 
 bw elicits greater activity in the medial motor cortices than forward walking17 .
consequently , greater motor unit 
 recruitment may increase oxygen demand to the point that the muscle contractile output 
 requires greater support through anaerobic pathways .
they observed that bw was 
 associated with increased cadence and decreased stride length compared to fw6 .
it has been reported that the muscle action 
 of the knee extensors is largely eccentric and concentric during fw , while it is isometric 
 and concentric during bw18 .
concentric 
 muscle contraction has been shown to have a higher energy cost than eccentric muscle work , 
 and a dramatically higher energy cost than that of eccentric resistance was reported in the 
 performance of concentric cycle ergometry19 .
it is postulated that during concentric contractions , when the 
 muscle fiber cross bridge has completed its power stroke and produced shortening , atp is 
 required for detachment and resetting of cross bridges .
conversely , during eccentric 
 contractions the cross bridge is forcibly detached and reattached without further atp 
 splitting19 . it has also been reported 
 that the work of the knee extensor increases during the stance phase of backward running 
 when compared with forward running20 . 

reported that total lower extremity muscle work was similar during forward 
 running and backward running at the same speed despite a significant change in muscle power 
 and work output21
. this could be the 
 reason behind the anaerobic power improvements observed in both fwg and bwg .
the body composition changes in the fw and bw groups were found to be not significant 
 ( p>0.05 ) .
similarly , hinkleman et al . suggested that moderate exercise training alone may 
 not be sufficient to affect body composition22 .
walker et al . also observed that normoglycemic women failed to 
 lose body fat after 12 weeks of exercise in a walking program23 .
it has also been demonstrated that the joint torque profiles of 
 the hip and knee in bw are quite similar to those of fw with a reverse sequence , but with 
 different time durations of flexion and extension24 .
these findings are also supportive of the lack of impact on body 
 composition observed in the fwg and the bwg in the present study .
however , it is also true 
 that the kinetic factors of ankle power and workload are lower during backward walking than 
 in forward walking . during backward walking plantar
flexion plays only a small role in 
 propulsion , and the propulsive force in backward walking may come from segments other than 
 the ankle .
possible sources of the propulsive force are strategies involving hip power and 
 the center of gravity25 . walking speed 
 and the mobility improvements
have also been observed after backward treadmill walking with 
 body weight support ( bws ) in the early phase of stroke , and it is postulated that bw is 
 superior to fw at increasing the exercise intensity of muscle activities because it requires 
 higher energy consumption , even in a short period of time26 .
positive correlations have been reported between the acceleration 
 values of c7 and s2 and the muscular strengths of the hamstrings , tibialis anterior , and 
 triceps surae , and these muscles contribute to acceleration of the trunk in the backward 
 stepping reaction27 . though bw has been proven to demand greater metabolic activity than its counterpart , 
 forward walking , the exercise intensity might not have been sufficient enough to elicit a 
 change in body composition in our present study .
the training duration is a possible reason 
 for the lack of significant changes observed in body composition in the present study .
the high levels of blood lactate measured in the study done by flynn et al .
suggest 
 backward walking relies on a higher percentage of anaerobic metabolism than forward 
 walking18 .
therefore , our study results 
 are supportive of previous findings , and we assume that higher metabolic demand is one 
 reason for the changes in anaerobic performance observed in the backward walking group in 
 the present study .
the present study was limited by the inclusion of participants with lower than normal bmi . 

we recommend conducting further studies to further explore the effects of forward and 
 backward walking training on body composition values of overweight and obese groups of 
 subjects .
we conclude that both backward and forward walking improve anaerobic performance , but not 
 anthropometrical body composition values . also , backward walking is more effective than 
 forward walking at improving anaerobic performance .
 [ purpose ] forward walking ( fw ) and backward walking ( bw ) on a treadmill is a common tool 
 for lower extremity rehabilitation in the clinical setting . the purpose of this study was 
 to evaluate the effects on anaerobic performance and anthropometrical adaptations during 
 fw and bw on a treadmill . 
 [ subjects and methods ] a convenience sample of thirty healthy 
 male subjects with a mean age of 20.93  2.54  years participated in this study . 
 subjects 
 were divided into 2 groups , a forward walking group ( fwg ) ( n=15 ) and a backward walking 
 group ( bwg ) ( n=15 ) , which performed fw and bw on a treadmill at 10 inclination , 
 respectively . 
 the training consisted of three sessions per week for 6 weeks . 
 study 
 outcomes such as anaerobic performance and anthropometrical body composition were measured 
 at pre- and post - intervention . [ results ] both fw and bw improved anaerobic performance 
 significantly , and the bw group showed better performance than fw . 
 however , changes in 
 anthropometrical body composition were found to be not significant after six weeks of 
 intervention in both the fw and bw groups . 
 [ conclusions ] bw training in rehabilitation can 
 be considered more effective than fw at improving anaerobic performance . 
 we also conclude 
 that six weeks of fw and bw training is insufficient for eliciting changes in the body 
 composition . 
INTRODUCTION
SUBJECTS AND METHODS
RESULTS
DISCUSSION