the most important goal of rehabilitation for a lower limb amputee is the independent 
 performance of daily activities through restoration of functional walking ability .
miller et al . 
 reported that 52% of prosthesis users experienced falls and 49% of amputees have a fear of 
 falling .
it also said that the fear of falling limits the daily movement of amputees and 
 causes further deterioration of the balance ability required for walking1 .
therefore , physical therapy for lower limb 
 amputees should be focused on the prevention of falls during movement / walking for the 
 improvement of everyday activities . for this purpose , it is necessary to properly evaluate 
 the balance ability of amputees and to perform training to improve the balance ability based 
 on the results of that evaluation .
the objectives of the present study were to elucidate 
 what type of compensatory movement and postural strategy are used by lower limb amputees for 
 posture control during the period from prosthesis fitting to hospital discharge by analyzing 
 the muscle activity patterns of the lower limb muscles and to elucidate the changes over 
 time in the muscle activity pattern during the course of physical therapy .
elderly patients 
 also have a higher risk of falling than younger patients because of biomechanical , 
 physiological , and psychological differences .
however , no study has yet focused on comparing 
 time - dependant changes in muscle activity patterns between younger and elderly patients . 

therefore , the other purpose of this study was to reveal the differences in muscle activity 
 patterns during standing between younger and elderly patients .
a young male , 34  years old , and an elderly female , 84  years old , who had a lower limb 
 amputated were the subjects .
neither of the patients had a history of orthopedic or 
 neurological disease in the unaffected lower limb or the trunk . a patient who undergoes 
 below - knee amputation due to diabetes
has a normal deep sensation in the unaffected ankle 
 joint . in both of our cases ,
the fitting between the socket and the stump on wearing was 
 well adjusted with no pain in the stump .
the prosthesis used by the lower limb amputees was a total 
 surface bearing liner type and a sach foot ( table 
 1table 1 .
characteristics of the subjectssubjectssexage ( year)height ( cm)weight ( kg)amputation sitesocketankle jointcauseweek to start pt after amputationweek to wear prosthesis after amputationweek to discharge after wearing prosthesis for 
 the first timeyoungm3317572right bkatsbsachtumor174elderf8515045left bkatsbsachdiabetes1514 m : male , f : female , bka : below knee amputee , tsb : total surface bearing , sach : solid 
 ankle cushion heel ; j - foot m1170 , pt : physical therapy ) .
surface electromyography ( emg ) measurements were performed of the 
 gastrocnemius medial head ( ga ) of the unaffected lower limb .
the electrodes were placed on 
 the most prominent bulge of the ga muscle following seniam guidelines .
after sufficient 
 treatment with skinpure to reduce the inter - electrode resistance to no more than 10  k on 
 the skin , disposable electrodes ( blue sensor , nf-50-k / w , ambu ) were attached at an 
 inter - electrode distance of 2  cm .
the emg signals were amplified ( to 1.0  mv ) and band - pass 
 filtered between 201,000  hz using a synact mt-11 ( nec corp . , tokyo , japan ) .
the emg signals 
 were digitized using a waveform analysis system , power lab 16s ( ad instruments ltd , hasting , 
 uk ) , at a sampling frequency of 1,000  hz , and stored on a personal computer for off - line 
 analysis .
after data input , waveform processing was performed using waveform analysis 
 software , chart36.8 , ad instruments .
two different tasks of maintaining the static standing 
 position were performed on the floor .
the test subjects were asked to stand on the floor 
 with their feet shoulder - width apart and look at a point set at 1  m distance to the front at 
 the height of the eye for 10 seconds .
the first task , reference task , was to maintain 
 upright standing position on the prosthesis while holding parallel bars .
the second task , 
 experimental task , was forward weight shift while maintaining the standing position without 
 grasping the parallel bars .
the recorded data were smoothed using the root mean square ( rms ) 
 value of every 100  msec using waveform analysis software .
the reference contraction is 
 judged to be reliable by being reproducible , giving approximately equal results within 
 subjects over trial .
therefore , we used the emg of another task as a reference contraction 
 for emg normalization . the normalized level of % rmsemg was determined using the following 
 formula .
m : male , f : female , bka : below knee amputee , tsb : total surface bearing , sach : solid 
 ankle cushion heel ; j - foot m1170 , pt : physical therapy % rmsemg = experimental task rmsemg ( second task ) / reference task rmsemg ( first task )  
 100% maximum walking speed was measured in 10  m walking .
depending on the condition at the time of the measurements , subjects 
 were allowed to use a crutch , or a single cane on the unaffected side while walking .
the 
 surface muscle activity and the walking speed were measured once a week , a total of four 
 occasions , starting on the day of prosthesis fitting ( first week ) .
this study was conducted 
 after approval was obtained from the ethics committee of tohoku university graduate school 
 of medicine .
the study patients were sufficiently informed about the purpose and methods of 
 the study , and their consent to participation was obtained .
when the time - dependent changes in muscular activity of ga , which is the most active muscle 
 in the standing position , were investigated in the forward weight shift task , two unique 
 patterns were observed . for the younger subject ,
no muscle activity of ga was observed in 
 the standing position tasks in the first week , but the amount of muscular activity of ga 
 gradually increased over time . on the other hand , for the elderly subject , increased 
 activity of ga was observed in the forward weight shift task in the first week , when the 
 prosthesis was worn for the first time , followed by a gradual decrease in activity over time 
 ( table 2table 2 .
time shift of activity in ga ( % rmsemg ) and walking speed ( m / min)week%rmsemg ( % ) mws ( m / min)youngerelderlyyoungerelderlyfirst0.6618.4348.5815.12second4.7116.4873.8924.57third5.9812.6580.3224.33fourth8.855.4110043.17%rmsemg : % root mean square electromyography , mws : maximum walking speed ) .
the maximum walking speed gradually increased over the period from when the 
 prosthesis was worn for the first time to when the subjects were discharged from the 
 hospital ( table 2 ) .
the basic elements for the smoothest and most energy efficient walk are proper balance 
 ability and posture control function2 . in 
 lower limb amputation , the contralateral lower limb function influences subsequent ability 
 to perform daily living and transfer activities , and standing balance on the unaffected side 
 is an important determinant of whether walking with a prosthesis is possible or not3 .
reported that the muscle of 
 the unaffected lower limb of prosthesis wearers tended to adopt a balancing strategy to 
 compensate for the loss of the ankle joint and muscles due to amputation4 .
therefore , lower limb amputees need to 
 adapt to asymmetrical body weight and muscular strength when they exert effort to maintain 
 static standing while wearing a prosthesis . in the present study , we evaluated the changes 
 in surface emg activity of the gastrocnemius during standing , and the walking speed with a 
 prosthesis .
the muscular activity of ga is most conspicuous when the amputee is standing 
 with the prosthesis for the first time .
when the static standing position is maintained , the 
 ga is activated in preparation for the forward movement of the center of pressure5 , 6 .
we 
 found two unique muscle activity patterns were exhibited by the two below - knee amputees . 

when the prosthesis was first worn , the younger subject was so careful about maintaining the 
 standing posture that adequate forward movement of the center of gravity could not be 
 achieved . for the elderly subject
, however , marked activity of the ga was found , and ga 
 activity at the final assessment was lower than that of the initial measurement , especially 
 during the forward weight shift task .
these time - dependent changes in the muscular activity 
 of ga indicate how younger and elderly amputees adapt muscular force to maintain standing 
 posture , and it might also be as a cause of falls by elderly patients in the early stage of 
 standing or gait training .
the subjects learned the method for shifting the center of gravity forward in a 
 stable manner , resulting in the gradual reduction or increase of ga muscle activity .
there are many 
 factors known to contribute to the improvement of the walking speed of amputees .
as far as 
 the results of this study are concerned , it can be concluded that one important factor is 
 regaining the ability to be able to shift the center of gravity in the static standing 
 position through the efficient muscle activity of the unaffected lower limb . in conclusion , 
 the trend of muscle activities over time should contribute to the development of effective 
 rehabilitation programs .
due to the limited number of subjects included in this study , a statistical analysis of 
 sufficient power could not be performed .
furthermore , there were obvious differences in 
 biomechanical , physiological , and psychological attributes because of age differences . 

biomechanical or physiological perspective approaches are very important . in this study , 
 however , there was no history of disorders of the trunk , such as lordosis or kyphosis , so we 
 only focused on the differences in emg .
further studies with larger numbers of subjects 
 stratified by the causes and types of amputation are needed to clarify the specific factors 
 associated with the acquisition of the ability to walk by amputees , and the development of 
 efficient methods for physical therapy and programs .
   [ purpose ] dysfunction of lower extremity muscles is one risk factor of falls for amputee 
 patients . 
 however , the change in muscle activity pattern and balance ability of amputees 
 who have no experience in standing with prosthesis during the period from prosthesis 
 fitting to regaining the ability to walk has never been studied . 
 therefore , the objectives 
 of the present study were to elucidate changes over time in the muscle activity pattern 
 and walking speed from first prosthesis fitting to hospital discharge . 
 we also 
 investigated the differences of muscle activity during standing between younger and 
 elderly amputee patients . 
 [ methods ] electromyography measurements were performed on the 
 gastrocnemius of the intact leg during standing . 
 the test subjects were asked to shift 
 their center of gravity forward . 
 [ results ] two unique patterns of gastrocnemius activities 
 were observed over time . in a younger patient , 
 the amount of muscular activity of the 
 gastrocnemius gradually increased over time . in an elderly patient , however , the amount of 
 muscular activity of gastrocnemius gradually decreased over time . 
 [ conclusion ] the 
 time - dependent changes in gastrocnemius muscle activities are indicative postural control 
 ability . 
 therefore , understanding the time - dependent changes in muscle activities during 
 rehabilitation and the differences of postural control between younger and elderly 
 patients would contribute to the development of effective rehabilitation programs for each 
 patient . 