age - related changes in skeletal muscle result in loss of muscle mass and weakness . this 
 leads to a decrease in daily physical activity in older adults , and can result in poor 
 health and a need for professional care . muscle loss and weakness cause serious health 
 problems , such as decreased strength and aerobic capacity1 . the world health organization ( who ) ranked lack of physical 
 activity as the fourth leading cause of mortality worldwide2 . according to who recommendations , older adults should aim to 
 maintain or increase their daily amount of moderately or vigorously intense physical 
 activity3 . many older people , 
 particularly those 65  years of age or older , who are interested in enhancing their health do 
 perform some kind of exercise training4 ; 
 however , the chosen exercise often has a low intensity level ( e.g. , walking ) . this is not 
 strenuous enough to effectively improve either muscle strength and mass or aerobic 
 capacity5,6,7,8 . hatamoto et al.9 showed that turning 
 during sports increased the energy cost of running and that the magnitude of the increase 
 depended on both the turn frequency and running velocity . in this study , we examined a new 
 exercise pattern called slow walking with turns ( swt ) , which incorporates turns to increase 
 the work load of walking . we have already shown that swt increases the exercise intensity 
 relative to normal walking at the same velocity and hypothesized that the reason for this 
 increase was extra muscle contraction resulting from the turns . the walking velocity and 
 turn frequency is easily adjusted to provide an exercise intensity of 3 to 10 metabolic 
 equivalents ( mets ) over a 3-m distance , and it is thus easy to prescribe an exercise program 
 tailored to individual needs10 . in the 
 current study , the swt ( tempo , turn frequency , and method of turning ) was adjusted to reduce 
 individual differences and make it easy to perform even for older people . the purpose of 
 this study was to confirm the exercise intensity of swt and examine the muscle activity 
 during turns . eight recreationally active volunteers participated in order to confirm the exercise 
 intensity of swt . the participants mean age was 24.9 ( standard deviation ( sd ) , 5.0 ) years , 
 mean stature was 1.66 ( 0.10 ) m , and mean mass was 58.0 ( 6.8 )  kg . none of the participants 
 had any injury that might have influenced their athletic performance . all participants 
 performed swt over five fixed distances and treadmill walking ( tw ) at five different 
 velocities in random order . oxygen consumption ( vo2 ) , rating of perceived 
 exertion ( rpe ) , and heart rate ( hr ) were measured during each exercise . during swt , the participants walked back and forth over several fixed distances and 
 performed 20 turns per minute . the distances were 1.5 , 2.0 , 2.5 , 3.0 , and 3.5 m ; the average 
 velocities for walking back and forth were 2.7 , 3.6 , 4.5 , 5.4 , and 6.3  km / h ; and the cadence 
 was 180 steps per minute . the participants took six steps for each distance during walking 
 and three steps per turn . the tw velocities were set at 2.7 , 3.6 , 4.5 , 5.4 , and 6.3  km / h , 
 which were the same velocities as during the walking portion of the swt . all sessions consisted of 4 minutes 
 of exercise at each velocity with 1 minute of rest between different velocities ( fig . 1fig . swt involved 
 shuttle walking for a short distance , including 20 turns per minute . the distance in 
 each stage was 1.5 , 2.0 , 2.5 , 3.0 and 3.5  m. ) . when participants 
 could not maintain the cadence , the trials were stopped and restarted . swt involved 
 shuttle walking for a short distance , including 20 turns per minute . the distance in 
 each stage was 1.5 , 2.0 , 2.5 , 3.0 and 3.5  m. all participants completed a familiarization session prior to the actual trial session . the 
 experiments were conducted in an indoor facility with hard flooring , and the participants 
 were instructed to wear the same indoor sports shoes for all trials . turning consisted of 
 three steps , a deceleration step , a change of direction step , and an acceleration step out 
 of the turn . the turning technique was adapted from the cross - step turn , and participants 
 turned towards the striding foot during the deceleration step . the participants practiced 
 the cross - step turn technique until they could repeat it consistently . all participants were 
 instructed to avoid food , caffeine , tobacco products , and alcohol for 3 hours prior to the 
 exercise sessions . during the exercise , the participants wore a face mask to collect exhaled gas , which was 
 measured at 12-second intervals using an mass spectrometer ( arco 2000 ; arco system , chiba , 
 japan ) . the mean vo2 of the last minute of each stage was used in the data 
 analysis . the hr ( polar ce0537 hr monitor ; polar electro , kempele , finland ) was measured 
 just before the end of each 4-minute stage , and subjective exercise intensity was assessed 
 using the borg rpe scale11 . measured 
 vo2 was converted into mets ( 1 met=3.5  ml / kg / min ) . second , the participants for measurement of muscle activity were six healthy men with a 
 mean age of 25.0 ( 4.4 ) years , mean stature of 1.74 ( 0.05 ) m , and mean mass of 68.3 ( 5.0 )  kg . the swt protocol was the same as 
 above - mentioned , except the walking distances were 1.5 , 2.0 , and 2.5  m. the tw velocities 
 were 2.7 , 3.6 , and 4.5  km / h ; these were chosen to be the same as the walking velocities 
 during swt . the activity of 11 muscles during swt , tw , and isometric maximum voluntary 
 contractions ( mvc ) was measured using electromyography ( emg ) ( lp - ws1221 ; logical product 
 corp . , fukuoka , japan ) to compare muscle activity during the stance phase of tw and the 
 turning phase of swt . the 11 muscles selected for emg were the rectus abdominis ( ra ) , erector spinae ( es ) , 
 gluteus maximus ( gmax ) , gluteus medius ( gmed ) , hip adductor ( ha ) , vastus lateralis ( vl ) , 
 rectus femoris ( rf ) , vastus medialis ( vm ) , biceps femoris ( bf ) , tibialis anterior ( ta ) and 
 soleus ( sol ) . all measurements were taken on the right side using wireless emg sensors 
 attached over the muscle belly . a foot sensor was attached to the right heel . before 
 application of the sensors , the skin area was shaved , cleaned with alcohol , and abraded with 
 coarse tape to reduce skin impedance and ensure good adhesion of the sensors . the researcher manually fixed 
 the posture of the participant , applying resistance against the direction of mvc . the 
 participant then exerted an isometric mvc against the resistance while emg was performed on 
 the muscle being tested . the mvc for each muscle was measured as follows : ra : the participant lay in a supine position with his knees positioned at 90 flexion and 
 ankles restrained by an assistant . he then raised his shoulders and exerted enough force to 
 further elevate their upper body while the researcher applied resistance against the 
 direction of force . es : the participant lay face down with his hands on the back of his head and raised his 
 upper body ( trunk extension ) . gmax : the participant lay face down with his knee flexed to 90 and extended his hip joint . gmed : the participant lay on his side with the test leg uppermost and abducted his mildly 
 extended hip joint . ha : the participant lay on his side with the test leg down and resting on the bed . the researcher then applied 
 resistance while the participant attempted to elevate ( adduct ) the test leg . vl , rf , and vm : the participant sat on a chair with back support . his trunk was secured 
 with a belt and his feet did not touch the floor . his hip and knee joints were fixed at 90 
 angles by fastening a belt around his lower legs . he then extended his knees against the 
 resistance of the belt to allow for measurement of the mvc . bf : the participant lay face down on the floor with his lower legs held in an upright 
 position perpendicular to the floor , knees flexed at 90 and hips flexed at 0. he then 
 tried to further flex his knees against resistance applied by the researcher . ta and sol : the participant sat horizontally on a tilt table with his knees fixed to the 
 table and his ankles in a neutral position ( 0 dorsi / plantar flexion ) and his feet fastened 
 to a foot cradle with a belt . he then made maximal attempts to dorsiflex and plantar flex 
 his ankle against the resistance of the belt . two trials were conducted for each muscle , 
 with a rest of 2 minutes or more between trials . after the trials , the emg data were downloaded onto personal computer ( vaio ; sony , tokyo , 
 japan ) . the emg data were full - wave rectified , and the integrated emgs data were averaged 
 during mvc over 1 second including the point at which the torque was maximal . the muscle activities 
 during the stance phase of tw and the turn phase of swt were calculated by integrating the 
 emg value in the reaction time of the foot sensor . each emg level was averaged for five 
 times of turns in swt and five steps in tw . the emg data in swt were adopted from five turns 
 at the beginning of the exercise . in tw , the measurement was started after walking had 
 become stable , and the data were adopted from first five steps . the averaged integrated emg 
 data during the actions were quantified and normalized as the values relative to those 
 during mvc ( i.e. , % mvc ) . all statistical analyses were conducted using spss software ( v21 ; 
 ibm corporation , armonk , ny , usa ) . differences between swt and tw were assessed using 
 t - tests in experiment 1 and one - way analysis of variance in experiment 2 . this study was approved by the ethical committee of fukuoka university , fukuoka , japan 
 ( number 10 - 02 - 02 ) , and informed consent was obtained from all participants . this study 
 followed the guidelines of the world medical association declaration of helsinki : ethical 
 principles for medical research involving human subjects , as well as the ethical guidelines 
 for epidemiological research outlined by the ministry of education , culture , sports , science 
 and technology and the ministry of health , labour and welfare , japan . oxygen consumption during the last minute of each stage remained in a steady state with no 
 difference between the 3rd and 4th minute from the start of the exercise . the results of 
 mets , hr and rpe were shown in table 
 1table 1.mets , rpe and hr for swt and twtwswt2.7  km / h3.6  km / h4.5  km / h5.4  km / h6.3  km / h1.5 m2.0 m2.5 m3.0 m3.5 mmets2.6  0.23.0  0.23.5  0.24.2  0.35.2  0.24.0  0.4***4.4  0.5***4.8  0.4***5.3  0.6**6.3  0.6**rpe7.8  1.08.1  1.09.3  0.910.4  0.711.6  0.78.5  1.69.0  1.59.4  1.510.5  1.311.6  1.1hr84  1689  1493  12102  8112  1089  1598  17 * 102  18 * 107  22119  19mean  sd . distances of 1.5 , 2.0 , 2.5 , 3.0 and 3.5  m during swt correspond to average walking 
 velocities of 2.7 , 3.6 , 4.5 , 5.4 , and 6.3  km / h , respectively . * p<0.05 , * * p<0.01 and * * * p<0.001 , comparison between swt and tw at a 
 velocity corresponding to walking of swt .. the mets of swt were significantly higher than those of tw at a velocity 
 corresponding to walking of swt ( p<0.01 ) . the difference in mets between swt and tw 
 appeared to be larger at slower speeds , but not significantly . the hr and rpe values were 
 measured just before the end of each stage . there was no significant difference in hr and 
 rpe except for the hr at distances of 3.6 and 4.5  km / h ( p<0.05 ) , despite the 
 significantly higher exercise intensity in the swt . mean  sd . distances of 1.5 , 2.0 , 2.5 , 3.0 and 3.5  m during swt correspond to average walking 
 velocities of 2.7 , 3.6 , 4.5 , 5.4 , and 6.3  km / h , respectively . * p<0.05 , * * p<0.01 and * * * p<0.001 , comparison between swt and tw at a 
 velocity corresponding to walking of swt . muscle activity was significantly greater in the es , vl and vm during the turn phase of swt 
 relative to the stance phase of tw at all stages ( table 
 2table 2.% mvc at the turn phase in swt and the stance phase in tw of each muscletwswt2.7  km / h3.6  km / h4.5  km / h1.5 m2.0 m2.5 mra6.86.87.28.79.09.5es5.56.27.514.5**17.7**15.5*gmax5.57.210.18.5 * 9.39.3gmed10.710.611.311.512.712.6ha10.910.811.313.013.213.9*vl7.29.410.913.5**13.5**13.7**rf9.39.410.610.411.011.5vm4.75.05.710.3**9.9**10.9**bf11.312.312.415.9 * 16.618.0ta10.011.813.714.213.313.6sol13.315.517.517.620.321.9*p<0.05 , * * p<0.01 , comparison of muscle activity levels for swt and tw at a 
 velocity corresponding to walking of swt . ) . the activity of the es , vl , and vm during the turn phase of swt was about 
 twice the activity level during the stance phase of tw . further , the activity of gmax and bf 
 at 1.5  m and ha at 2.5  m during the turn phase of swt was significantly greater than during 
 the stance phase of tw . increases in walking velocity in tw did not increase the activity 
 levels of any of the assessed muscles . * p<0.05 , * * p<0.01 , comparison of muscle activity levels for swt and tw at a 
 velocity corresponding to walking of swt . the primary findings of this study were that swt training increased vo2 and the 
 activity of the quadriceps and es muscles relative to tw at the same velocity . the addition of 
 turns caused more muscle contraction due to the acceleration and deceleration associated 
 with the change of direction . we previously reported that vo2 was increased by 
 turns10 , and our current results 
 confirm the results of our previous study . a turn involves deceleration , a change of 
 direction , and acceleration , and this can be difficult for older adults who often suffer 
 from balance disorders . therefore , in this study we divided the turn phase into three 
 separate steps ( acceleration , change of direction , and deceleration ) to make swt a simpler 
 and easier exercise . this prolonged the turn time and reduced the walking distance per hour ; 
 however , the oxygen consumption during swt was still significantly higher than during tw at 
 the same velocity . because of this , performing swt at the fastest natural walking pace 
 resulted in an exercise intensity of up to 6 mets . the physical activity of older people is significantly lower than the recommended 
 amount12 , which results in decreased 
 aerobic capacity , muscle mass and muscle strength , further reducing the amount of physical 
 activity1 . because muscle weakness and 
 loss are associated with physical disability13,14,15 , 
 older adults must perform adequate physical activity to maintain or improve aerobic capacity 
 and muscle mass and strength . the popularity of walking is due 
 to its safety and simplicity , the fact that it does not generally cause hemodynamic stress 
 and the lack of requirement for special equipment . however , it is known that walking 
 training ( excluding race walking ) has little effect on aerobic capacity or muscle strength 
 and volume5,6,7,8 . the regular walking speed of older adults is reportedly slow16 , 17 , and thus walking is not a sufficiently intense exercise to result in 
 aerobic or strength improvements . however , the exercise intensity required to maintain and improve physical fitness in 
 older adults is 3.0 to 6.0 mets18 . adding 
 turns while walking , as in swt , increases the exercise intensity from light to moderate . furthermore , because swt did not result in significant increases in hr or rpe relative to tw 
 in the present study , many older people should be able to perform swt easily and safely . we focused on muscle activity during the turn phase of swt and compared it with the muscle 
 activity during the stance phase of tw . the activity levels of the es , vl , and vm were 
 significantly greater while turning during swt than during tw . this indicates that it is 
 possible to increase the stimulation provided by regular walking by adding turns . performing 
 swt instead of tw or simple straight walking may increase the strength of the knee and trunk 
 extensors and muscle mass in the thigh and back . only a few studies have examined the effect of aerobic training on muscle strength and mass 
 in older adults . several cross - sectional studies have reported no significant differences 
 between the leg strength and power of chronically aerobically trained and sedentary older 
 people19 , 20 . longitudinal studies have shown no effect of regular walking 
 training on leg strength and muscle mass5,6,7,8 . the few studies that have shown positive 
 effects of exercise on the mass and strength of the thigh muscles used brisk walking , 
 jogging at 85% hr reserve21 , or interval 
 training at 70% to 85% vo2 peak6 , 22 as exercises . cycling at 70% 
 vo2 max or 80% hr reserve has been shown to increase quadriceps muscle strength 
 and power and thigh muscle volume23 , 24 . aerobic exercise can increase muscle 
 strength and mass depending on the intensity , frequency , and duration of the exercise . importantly , to facilitate the development of a training habit , it is better that exercisers 
 do not feel fatigue . muscle strength significantly decreases when training is stopped ; if 
 training is resumed , its muscle strengthening effects are then less than they were 
 previously24 . however , no studies have examined the 
 effects of moderate endurance training ( except for the bench step exercise25 ) on muscle strength . the muscle activity of the vm during the turn phase of swt was twice that seen during 
 regular walking . gazendam and hof26 
 reported the emg profile during walking and jogging at 4.5 to 8.1  km / h ; the emg amplitude of 
 the vm during the turn phase of swt at 2.5 to 4.5  km / h in the current study was equal to 
 what they reported during jogging at 8.1  km / h and brisk walking at 5.2  km / h . thus , muscle 
 activity that occurs while turning during swt is equal to or greater than that seen during 
 brisk walking or jogging . because brisk walking and jogging have been confirmed to increase 
 the muscle mass and strength of the thigh , our results suggest that swt may also increase 
 muscle mass and strength . additionally , in a study comparing running and soccer in young and 
 middle - aged subjects , the vl cross - sectional area and knee extensor strength were increased 
 only by soccer27 , 28 . training consisting of varying intensities and motions , such as 
 swt , has the potential to result in muscle hypertrophy and strength gains . at present , the 
 research on muscle hypertrophy and strength gains caused by aerobic exercise has been 
 limited to the lower limbs ; further studies clarifying the effects of aerobic exercise on 
 the muscles of other regions of the body , including the trunk , are needed . the purpose of this study was to investigate whether swt is useful for older people ; 
 however , we chose , young people as subjects . the characteristics of walking in older people 
 are a decreased : stride caused by a reduced range of motion of the hip and ankle , a lower 
 walking speed cause by the decreased stride , and extension of the two - leg supporting moment . however , walking adjusted to 180 strides per minute is unlikely to be affected by the 
 characteristics , showing an operation pattern similar to that of young people29 . in future work we will examine the 
 effects of swt on the physical function of the older adults in terms of increased aerobic 
 capacity , prevention of muscle ageing , and improvement in balance . our findings suggest that swt may help to preserve the muscle strength and mass of the 
 trunk and lower limbs that is needed to maintain an independent lifestyle . even slow walking 
 can be performed easily by older people , and the exercise intensity can be adjusted as 
 required for each individual . furthermore , swt requires the participant to have greater 
 control of their center of gravity during lateral , sagittal , and up and down movements than 
 during regular walking . complex exercise training consisting of strength , balance , and 
 walking training for older adults has been expected to effectively prevent falls30 . swt is done over short distances ( maximum 
 of 3.5 m ) , which allows its performance in a small indoor space and eliminates the need for 
 supervision or equipment .