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Metabolic energy demand and optimal walking speed in post-polio subjects with lower limb afflictions
Applied Ergonomics 1982, 13.4, 259-262
Metabolic energy demand and optimal walking speed in post-polio subjects with lower limb afflictions A.K. Ghosh, S. Ganguli, and K.S. Bose Bioengineering Unit, Department of Orthopaedics, University College of Medicine, Calcutta University, India. The metabolic demand, using the relal;ionship between speed and energy cost, and the optimal speed of walking, estimated by means of speed and energy cost per unit distance travelled, were studied in 16 post-polio subjects with lower limb affliction and 20 normal subjects with sedentary habits. It was observed that the post-polio subjects consumed higher energy than the normal persons at each walking speed between 0.28 and 1.26 m/s. The optimal speed of walking in post-polio subjects was lower than that of the normal persons and was associated with a higher energy demand per unit distance travelled. It was deduced that the post-polio subjects, not having used any assistive devices for a long time, have acquired severe degrees of disability which not only hindered their normal gait but also demanded extra energy from them.
Keywords: Metabolism, limbs, disability
Introduction Walking is the commonest of all day-to-day living activities. It involves contraction and relaxation of the various muscles of the body, involving the use of energy which may be measured indirectly by collecting and analysing the expired air. The progression of a person, during walking, depends on two major factors, the stepping frequencies or cadence and the step length. Speed of walking is a function of cadence and step length. An understanding of the speed of walking as well as the metabolic energy demand during walking of lower extremity handicapped people, as well as a comparison between them and normal people, will aid the clinician in identifying or evaluating the pathological condition and in making the necessary prescription. The performance of normal people during walking has been evaluated by several workers (Cavagna et al, 1965; Durnin and Passemore, 1967; Astrand and Rodahl, 1970; Davies and Burnea, 1972; Margaria, 1976) using energy cost studies. Similar studies have also been made by scientists on some groups of lower extremity handicapped persons, such as below-knee amputees (Ganguli eta/, 1973; 1975), on above-knee amputees using prostheses (Ganguli et al, 1974a) and also on leg amputees using axillary crutches (Ganguli et al, 1974b; Ghosh et al, 1980). Studies have also been compared there with normal persons not only to evaluate the performance of the lower extremity handicapped but also to assess the efficacy of prosthetic appliances and the effectiveness of the handicapped-appliance system.
In India, amputees and poliomyelitis victims constitute the largest among the orthopaedically handicapped (Bhatt, 1963; Taylor and Taylor, 1970). The present study is restricted only to post-polio subjects who have a history of suffering from poliomyelitis in their childhood. When the disease is detected they are usually treated by means of physiotherapy and sometimes also operated upon, and are prescribed the use of an assistive device. The device, which is liable to frequent damage, has to be changed as they grow up. Sufferers cannot cope themselves with either the frequency of repairing the device or purchasing a new one, obviously due to the costs in a poor country like India. Hence, they used to accommodate themselves in their daily living and working conditions with the acquired degree of disability for the rest of their life. The purpose of the present investigation was to study the performance of post-polio subjects without assistive devices during walking, and also the optimal speed of walking, by means of measuring the metabolic energy demand on them. This study was intended to aid the clinician, so that he could identify or evaluate the condition for not using any assistive devices, and make the necessary optimum prescription for these disabled people.
Materials and method The investigation consisted of 20 normal individuals with sedentary habits and 16 post-polio subjects with lower limb afflictions. Mean and standard deviation of the subjects' height, weight and age are presented in Table 1.
0003-6870/82/04 0259-04 $03.00(~) 1982Butterworth& Co (Publishers)Ltd
AppliedErgonomics December1982
259
Table 1: Personal data of normal and post-polio subjects
(Mean + SD) Numbers in parentheses denote the range
Subject
n
Height (m)
Weight (kg)
Age (years)
Normal
20
1.65-+ 0-07 46.7-+ 7-6 28.5-+ 5.8 (1-54- 1.77) (31.5 - 65.3) (23.0- 42-0)
Postpolio
16
1.57 + 0.07 (1.43-1.76)
40.5 + 8.8 23.1 +- 4.0 (29-0-68-5)(16.0-31.0)
In an ergonomics laboratory, walking is usually simulated on a treadmill. But in Indian conditions, it involves an extra expenditure to provide such sophisticated instrument in a clinic or in hospital. Besides, it can also affect the walking pattern of normal as well as disabled persons (Garton, 1978; 1979). Previous researchers have also concluded that walking on a road or on a treadmill was identical (Ralston, 1960; Margaria, 1976). Hence, in the present investigation, floor walking on the level was preferred. Analyses of normal and disabled gait during level walking have been made by several researchers (Edwards et al, 1961 ; Murray et al, 1966; Waters et al, 1976) using the method of free and fast chosen pace walking, The subjects were asked to walk along an 11 m long walkway to-and-fro, for 5 min, at first at their free comfortable natural speed and after a sufficient recovery period, they walked faster for the same period. In the case of the post-polio subjects, a slow walk was also registered for about the same period, besides free and fast walking. Hence, the normal subjects were administered free and fast chosen pace walking and the post-polio subjects, slow, free and fast chosen pace walking. This was because the range between free and fast walking speed was not so wide in the post-polio subjects. However, during a pre-test condition, each subject's walking pace was determined by estimating the time taken to cover the 11 m distance. Walking pace of each subject was controlled by a metronome, Laboratory dry bulb (°C) and wet bulb (°C) temperatures in the case of the normal person's experiments were 33-0 -+ 2.5 and 27"2 +- 3"3, and for the post-polio subjects' tests were 32-0 -+ 2"5 and 26-1 -+ 2-8. Speed was measured as the distance covered in 5 min duration which was converted into m/s. The expired gas was collected in a meteorological balloon for the last 2 min period of the 5 min walking event, assuming the last 2 min period as steady state. The gas was analysed in a Lloyd's gas analysis apparatus, and energy expenditure was calculated according to Consolazio et al (1963). The meteorological balloon, instead of a canvas Douglas bag, for collection of expired gas was found suitable for the walking test because it could be hung easily and comfortably on the subject's back (Ghosh et al, 1980). The precautions taken included the careful sealing of the attachment of the 3-way valve to avoid leakage problems and the rapid transfer of the sample from the balloon to the sampling bottle, and the rapid measurement of its volume, to prevent diffusion of the gases and avoid experimental error,
Results
In Fig. 2, the energy expenditure per unit distance travelled (J/kg/m) was plotted against walking speeds (m/s), to determine the optimal speed in case of the post-polio subjects and to compare them with the normal persons. However, in this case, the relationship between energy expenditure per unit distance travelled and walking speed was found to b e , E ' = 7.27V " : - 15-85V+ 12-367 (r =0.928) and El' = 12"V12 - 23-0V1 + 18-6 (r = 0.933) for the normal and post-polio subjects respectively. E ' and El' represent the energy expenditure in J/kg/m and V and V1, the walking speeds in m/s.
Discussion Many scientists have opined that within a short range of walking speed, energy expenditure increased linearly for both 08 oz
Applied Ergonomics
December 1982
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,,,,e
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polio
o
~=~i•
~ o2
o o
Post-
//SO
•
~ o.4 e= ~ o.3
I 028
I 056
I I 084 1.12 Speed (m/s)
I 140
I 168
Energy expenditure in relation to walking speed in normal and post-polio subjects
14 12
Q
~ Ic v ~ 8 ~= ~ ~
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•
. ~ l e •
,~
O
~ 4
e •
e/
~
Post-polio
o
° ~oN°rm°l
0u
o
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In Fig. 1, the energy expenditure, expressed in kJ/min/kg were plotted against different walking speeds, expressed in
260
m/s. The relationships between the energy expenditure and walking speed were found to be E = 0-1 V 2 + 0-106V + 6-046 (r =0-901) andEl = 0"181112 + 0"27111 + 0.09 (r = 0"987), for the normal and post-polio subjects respectively. E and E~ represent the energy expenditures in kJ/min/kg and V and V1, the walking speeds in m/s.
I 028
I 0.,56
I I 0.84 1.12 Speed (m/s)
I 1.40
I L68
Energy expenditure per unit distance travelled in relation to walking speed in normal and post-polio subjects
normal (Durnin and Passemore, 1967) and lower extremity handicapped persons (Ganguli et al, 1974c). But within a very wide range of walking speed, energy expenditure does not hold this linearity (Cotes and Meade, 1960; Durnin and Passemore, 1967; Margaria, 1968), instead it is curvilinear in nature. In the present investigation, within a range of 0-28 - 1"26 m/s walking speed, energy expenditure in the case of post-polio subjects increased curvilinearly. However, in the case of normal subjects also, the relationship was curvilinear within a range of 0.56 to 1.68 m/s walking speed. The post-polio subjects expended higher energy than normal people at the obtained range of walking speeds and their degree of demand was higher than for the normal people walking at high speed. At lower speed, the degree of demand was not so high. Previous scientists have demonstrated that some of the lower extremity disabled, such as below-knee and above-knee amputees using prostheses, may consume higher energy than the normal individuals at different walking speeds (Inman and Ralston, 1962; Ganguli et al, 1974c) obviously due to their disabilities, poor prostheses alignment or due to poor training. In a study on crutch-users, Ghosh et al (1980) observed that the crutch-users consumed significantly higher energy than the normal people at walking speeds of 0-56 and 0.84 m/s. But at walking speeds of 1.12 and 1.40 m/s, the energy expenditure of crutch users was not so high above that of normal people to be statistically significant. They concluded that during walking at lower speeds, the crutchusers faced difficulties in maintaining the balance of their body and also maintaining a rhythm. However, they did not face this problem while walking at higher speeds. In the present investigation, the post-polio subjects consumed much higher energy than the normal individuals at the obtained range of walking speeds (Fig. 1). This might have been brought about by the fact that in this study the post-polio subjects had not been using any caliper for a long time. They were rather accustomed to ambulate themselves keeping one hand on the upper part of the affected knee. Probably this way they counter-balanced weak extensors of the knee (quadriceps) and erector muscle of the spine and also partly supported their own torso. Clinical examinations revealed that the disabilities in the post-polio subjects were due to weak muscle power in the hip, thigh and/or calf region, lumber lordosis, abnormal plantar or dorsi-flexion of the ankle joint. In some cases, pelvic tilting during walking was also observed. All these factors were responsible for diminishing the active locomotor muscle mass in the post-polio subjects. Naturally, the metabolic energy output per unit body weight was much higher for these types of disabled persons. Also the above factors may have been responsible for deviating the body's centre of gravity from its normal path, thus demanding higher energy than the normal individuals. The normal subjects consumed minimum energy per unit distance travelled while walking at 1"12 m/s. Below and above this range, energy expenditure was higher. Hence, the optimal speed of walking of normal subjects was found to be 1-12 m/s. This may support the findings of Bard and Ralston (1959), Inman and Ralston (1962), Margaria (1968), and Ghosh et al (1980) on normal individuals. On the other hand, the post-polio subjects consumed minimum energy per unit distance travelled when walking at 0.98 m/s. Hence, obviously, the optimal speed of walking in post-polio subjects.was lower than that of normal individuals. Inman
and Ralston (1962) observed that optimal speed of walking in the case of above-knee amputees using constant friction prostheses was lower than that of the normal individuals. Ganguli et al (1974c) opined that the comfortable speed for walking in case of below knee amputees using patellartendon-bearing prostheses was supposed to be 0.84 m/s, which is obviously lower than that of the normal individuals. Although the optimal speed of walking in post-polio subjects was lower than that of the normal individuals, the metabolic energy demand per unit distance travelled was about 90-0% higher. This high energy demand may be due to the acquired degree of disabilities which may have become severe as a result of not using any assistive aids.
Conclusions The above investigation may conclude the following: (i)
Metabolic energy demand during walking in post-polio subjects was much higher than for normal people. The degree of demand was not so high with low walking speed as in higher walking speed. Lack of use of any assistive devices by post-polio subjects might have incurred severe disabilities which increased the difficulty of normal gait of the post-polio subjects and demanded extra energy for them.
(ii)
The optimal speed of walking in post-polio subjects not using any assistive devices was obviously lower than that of the normal people, but the energy demand per unit distance travelled for post-polio subjects was about 90% higher than the demand on the normal people.
(iii)
Rehabilitation of the post-polio subjects is needed. A suitable ergonomic and economic assistive device is needed for optimum rehabilitation of the postpolio subjects with lower limb affliction so that the energy demands on this group of the physically disabled are not higher than those of normal people.
(iv)
The frequency and cause of damage of the assistive device should be studied, to prevent these disabilities being aggravated.
(v)
For immediate and short term use, auxiliary crutches or elbow crutches should be prescribed to this group of disabled persons. Observations by Ghosh et al (1980) revealed that the optimum speed of walking in normal as well as in auxiliary crutch-users was the same, though the latter group consumed insignificantly higher energy than those of the normal people while walking at the same speed.
Acknowledgements "i'he work reported here is part of the Research Project funded by the Science and Engineering Research Council, Department of Science and Technology, Government of India, New Delhi, India. The authors wish to acknowledge the help and assistance received from their colleagues at the Bioengineering Unit, Department of Orthopaedics, University College of Medicine, Calcutta, and from Mr S. Sethuraman, Superintendent, Vocational Rehabilitation Centre for the Physically Handicapped, Calcutta, India.
Applied Ergonomics December 1982
261
References Astrand, P.O., and Rodahl, K. 1970 Textbook of work physiology, McGraw-HillKogakusha Ltd.
Bard, G., and Ralston, H.J. 1959 Archives of Physical Medicine and Rehabilitation, 40, 415-420. Measurement of energy expenditure during ambulation with special reference to evaluation of assistive devices.
Bhatt, U. 1963 The physically handicapped in India, Popular Book Depot, Bombay, India. Cavagna, G.A., Saibene, F.P., and Margaria, R. 1965 Journal ofAppliedPhysiology, 18.1, 1-9. External work in walking.
Consolazio, C.F., Johnson, R.E., and Pecora, L.J. 1963 Physiological measurements of metabolic functions in man, New York, McGraw-Hill, 1st Edition.
Cotes, J.E., and Meade, F. 1960 Ergonomics, 8, 97-119. The energy expenditure and' mechanical energy demand in walking.
Davies, C.T.M., and Burnea, C. 1972 Ergonomics, 15.2, 121-131. Physiological responses to walking uphill and downhill on a motor driven treadmill. Durnin, J.V.G.A., and Passemore, R. 1967 Energy, work and leisure, Heinemann, London. Edwards, B.A., Lucas, D.B., and Ralston, l-l.J. 1961 Biomechanics Laboratory, Technical Report No 44, University of California, San Francisco, Berkeley, Effect of immobilisation of the hip on energy expenditure during level walking. Ganguli, S., Bose, K.S., Datta, S.R., Chatterjee, B.B., and Roy, B.N. 1973 Ergonomics, 16,797-810, Performance evaluation of an amputee-prostheses system in below-knee amputees.
Ganguli, S., Bose, K.S. Datta, S.R., Chatterjee, B.B., and Roy, B.N. 1974a Ergonomics, 17.2, 199-210, Ergonomic evaluation of above-knee amputee-prostheses combination.
Ganguli, S., Datta, S.R., Bose, K.S., Chatterjeee, B.B., and Roy, B.N. 1974b Ergonomics, 17.3,365-374. Biomechanical approach to the functional assessment of the use of crutches for ambulation.
262
AppliedErgonomics December 1982
Ganguli, S., Datta, S.R., Chatterjee, B.B., and Roy, B.N. 1974c Journal of Applied Physiology, 36.4,440-443. Metabolic cost of walking at different speeds with patellar tendon-bearing prostheses.
Ganguli, S., Bose, K.S., and Datta, S.R. 1975 Acta OrthopaedicaScandinavica, 46, 123-134, Performance of BK amputees using PTB prostheses.
Garton, W.T. 1978 Annual Report of Biomechanical Research and Development Unit, Roehampton, London, 187-198, Investigation of treadmill walking.
Garton, W.T. 1979 Annual Report of Biomechanical Research and Development Unit, Roehampton, London, 47-60, Measurement of metabolic energy expenditure in the disabled.
Ghosh, A.K., Tibarewala, D.N., Dasgupta, S.R., Goswami, A., and Ganguli, S. 1980 Ergonomics, 23.6,571-577. Metabolic cost of walking at different speeds with auxilliary crutches.
Inman, V.T., and Ralston, H.J. 1962 Final Project Report, Veterans Administration Research and Development Division, Prosthetics and Sensory Aids Service, USA, Energy expenditure in certain types of disability. Margaria, R. 1968 International Zeitschrift angewansandlePhysiologie einschliechisse Arbeitsphysiologie, 25, 339-351, Positive and negative work performances and their efficiencies in human locomotion. Margaria, R. 1976 Biomechanics and energetics of muscular exercise, Clarendon Press, London.
Murray, M.P., Kory, R.C., Clarkson, B.H., and Sepic, S.B. 1966 American Journal of Physical Medicine, 45, 8-24. Comparison of free and fast walking pattern of normal men.
Ralston, H.J. 1960 Journal of Applied Physiology, 15, 1156, Comparison of energy expenditure during treadmill walking. Taylor, W.W., and Taylor, I.W. 1970 Services for the handicapped in India. International Society for Rehabilitation of the Disabled, New York.
Waters, R.L., Parry, J., Antenelli, D., and Hisllop, H. 1976 Journal of Bone and Joint Surgery, 58A.1, 42-46. Energy cost of walking in amputees : the influence of level amputation.
Metabolic energy demand and optimal walking speed in post-polio subjects with lower limb afflictions A.K. Ghosh, S. Ganguli, and K.S. Bose Bioengineering Unit, Department of Orthopaedics, University College of Medicine, Calcutta University, India. The metabolic demand, using the relal;ionship between speed and energy cost, and the optimal speed of walking, estimated by means of speed and energy cost per unit distance travelled, were studied in 16 post-polio subjects with lower limb affliction and 20 normal subjects with sedentary habits. It was observed that the post-polio subjects consumed higher energy than the normal persons at each walking speed between 0.28 and 1.26 m/s. The optimal speed of walking in post-polio subjects was lower than that of the normal persons and was associated with a higher energy demand per unit distance travelled. It was deduced that the post-polio subjects, not having used any assistive devices for a long time, have acquired severe degrees of disability which not only hindered their normal gait but also demanded extra energy from them.
Keywords: Metabolism, limbs, disability
Introduction Walking is the commonest of all day-to-day living activities. It involves contraction and relaxation of the various muscles of the body, involving the use of energy which may be measured indirectly by collecting and analysing the expired air. The progression of a person, during walking, depends on two major factors, the stepping frequencies or cadence and the step length. Speed of walking is a function of cadence and step length. An understanding of the speed of walking as well as the metabolic energy demand during walking of lower extremity handicapped people, as well as a comparison between them and normal people, will aid the clinician in identifying or evaluating the pathological condition and in making the necessary prescription. The performance of normal people during walking has been evaluated by several workers (Cavagna et al, 1965; Durnin and Passemore, 1967; Astrand and Rodahl, 1970; Davies and Burnea, 1972; Margaria, 1976) using energy cost studies. Similar studies have also been made by scientists on some groups of lower extremity handicapped persons, such as below-knee amputees (Ganguli eta/, 1973; 1975), on above-knee amputees using prostheses (Ganguli et al, 1974a) and also on leg amputees using axillary crutches (Ganguli et al, 1974b; Ghosh et al, 1980). Studies have also been compared there with normal persons not only to evaluate the performance of the lower extremity handicapped but also to assess the efficacy of prosthetic appliances and the effectiveness of the handicapped-appliance system.
In India, amputees and poliomyelitis victims constitute the largest among the orthopaedically handicapped (Bhatt, 1963; Taylor and Taylor, 1970). The present study is restricted only to post-polio subjects who have a history of suffering from poliomyelitis in their childhood. When the disease is detected they are usually treated by means of physiotherapy and sometimes also operated upon, and are prescribed the use of an assistive device. The device, which is liable to frequent damage, has to be changed as they grow up. Sufferers cannot cope themselves with either the frequency of repairing the device or purchasing a new one, obviously due to the costs in a poor country like India. Hence, they used to accommodate themselves in their daily living and working conditions with the acquired degree of disability for the rest of their life. The purpose of the present investigation was to study the performance of post-polio subjects without assistive devices during walking, and also the optimal speed of walking, by means of measuring the metabolic energy demand on them. This study was intended to aid the clinician, so that he could identify or evaluate the condition for not using any assistive devices, and make the necessary optimum prescription for these disabled people.
Materials and method The investigation consisted of 20 normal individuals with sedentary habits and 16 post-polio subjects with lower limb afflictions. Mean and standard deviation of the subjects' height, weight and age are presented in Table 1.
0003-6870/82/04 0259-04 $03.00(~) 1982Butterworth& Co (Publishers)Ltd
AppliedErgonomics December1982
259
Table 1: Personal data of normal and post-polio subjects
(Mean + SD) Numbers in parentheses denote the range
Subject
n
Height (m)
Weight (kg)
Age (years)
Normal
20
1.65-+ 0-07 46.7-+ 7-6 28.5-+ 5.8 (1-54- 1.77) (31.5 - 65.3) (23.0- 42-0)
Postpolio
16
1.57 + 0.07 (1.43-1.76)
40.5 + 8.8 23.1 +- 4.0 (29-0-68-5)(16.0-31.0)
In an ergonomics laboratory, walking is usually simulated on a treadmill. But in Indian conditions, it involves an extra expenditure to provide such sophisticated instrument in a clinic or in hospital. Besides, it can also affect the walking pattern of normal as well as disabled persons (Garton, 1978; 1979). Previous researchers have also concluded that walking on a road or on a treadmill was identical (Ralston, 1960; Margaria, 1976). Hence, in the present investigation, floor walking on the level was preferred. Analyses of normal and disabled gait during level walking have been made by several researchers (Edwards et al, 1961 ; Murray et al, 1966; Waters et al, 1976) using the method of free and fast chosen pace walking, The subjects were asked to walk along an 11 m long walkway to-and-fro, for 5 min, at first at their free comfortable natural speed and after a sufficient recovery period, they walked faster for the same period. In the case of the post-polio subjects, a slow walk was also registered for about the same period, besides free and fast walking. Hence, the normal subjects were administered free and fast chosen pace walking and the post-polio subjects, slow, free and fast chosen pace walking. This was because the range between free and fast walking speed was not so wide in the post-polio subjects. However, during a pre-test condition, each subject's walking pace was determined by estimating the time taken to cover the 11 m distance. Walking pace of each subject was controlled by a metronome, Laboratory dry bulb (°C) and wet bulb (°C) temperatures in the case of the normal person's experiments were 33-0 -+ 2.5 and 27"2 +- 3"3, and for the post-polio subjects' tests were 32-0 -+ 2"5 and 26-1 -+ 2-8. Speed was measured as the distance covered in 5 min duration which was converted into m/s. The expired gas was collected in a meteorological balloon for the last 2 min period of the 5 min walking event, assuming the last 2 min period as steady state. The gas was analysed in a Lloyd's gas analysis apparatus, and energy expenditure was calculated according to Consolazio et al (1963). The meteorological balloon, instead of a canvas Douglas bag, for collection of expired gas was found suitable for the walking test because it could be hung easily and comfortably on the subject's back (Ghosh et al, 1980). The precautions taken included the careful sealing of the attachment of the 3-way valve to avoid leakage problems and the rapid transfer of the sample from the balloon to the sampling bottle, and the rapid measurement of its volume, to prevent diffusion of the gases and avoid experimental error,
Results
In Fig. 2, the energy expenditure per unit distance travelled (J/kg/m) was plotted against walking speeds (m/s), to determine the optimal speed in case of the post-polio subjects and to compare them with the normal persons. However, in this case, the relationship between energy expenditure per unit distance travelled and walking speed was found to b e , E ' = 7.27V " : - 15-85V+ 12-367 (r =0.928) and El' = 12"V12 - 23-0V1 + 18-6 (r = 0.933) for the normal and post-polio subjects respectively. E ' and El' represent the energy expenditure in J/kg/m and V and V1, the walking speeds in m/s.
Discussion Many scientists have opined that within a short range of walking speed, energy expenditure increased linearly for both 08 oz
Applied Ergonomics
December 1982
:
os _~ "~ 05
o °
.../o
• -.3:'-O-o o i ~ o •/ -
o
o
,,,,e
o I:
Fig. 1
polio
o
~=~i•
~ o2
o o
Post-
//SO
•
~ o.4 e= ~ o.3
I 028
I 056
I I 084 1.12 Speed (m/s)
I 140
I 168
Energy expenditure in relation to walking speed in normal and post-polio subjects
14 12
Q
~ Ic v ~ 8 ~= ~ ~
•
•
. ~ l e •
,~
O
~ 4
e •
e/
~
Post-polio
o
° ~oN°rm°l
0u
o
2 o0 Fig. 2
In Fig. 1, the energy expenditure, expressed in kJ/min/kg were plotted against different walking speeds, expressed in
260
m/s. The relationships between the energy expenditure and walking speed were found to be E = 0-1 V 2 + 0-106V + 6-046 (r =0-901) andEl = 0"181112 + 0"27111 + 0.09 (r = 0"987), for the normal and post-polio subjects respectively. E and E~ represent the energy expenditures in kJ/min/kg and V and V1, the walking speeds in m/s.
I 028
I 0.,56
I I 0.84 1.12 Speed (m/s)
I 1.40
I L68
Energy expenditure per unit distance travelled in relation to walking speed in normal and post-polio subjects
normal (Durnin and Passemore, 1967) and lower extremity handicapped persons (Ganguli et al, 1974c). But within a very wide range of walking speed, energy expenditure does not hold this linearity (Cotes and Meade, 1960; Durnin and Passemore, 1967; Margaria, 1968), instead it is curvilinear in nature. In the present investigation, within a range of 0-28 - 1"26 m/s walking speed, energy expenditure in the case of post-polio subjects increased curvilinearly. However, in the case of normal subjects also, the relationship was curvilinear within a range of 0.56 to 1.68 m/s walking speed. The post-polio subjects expended higher energy than normal people at the obtained range of walking speeds and their degree of demand was higher than for the normal people walking at high speed. At lower speed, the degree of demand was not so high. Previous scientists have demonstrated that some of the lower extremity disabled, such as below-knee and above-knee amputees using prostheses, may consume higher energy than the normal individuals at different walking speeds (Inman and Ralston, 1962; Ganguli et al, 1974c) obviously due to their disabilities, poor prostheses alignment or due to poor training. In a study on crutch-users, Ghosh et al (1980) observed that the crutch-users consumed significantly higher energy than the normal people at walking speeds of 0-56 and 0.84 m/s. But at walking speeds of 1.12 and 1.40 m/s, the energy expenditure of crutch users was not so high above that of normal people to be statistically significant. They concluded that during walking at lower speeds, the crutchusers faced difficulties in maintaining the balance of their body and also maintaining a rhythm. However, they did not face this problem while walking at higher speeds. In the present investigation, the post-polio subjects consumed much higher energy than the normal individuals at the obtained range of walking speeds (Fig. 1). This might have been brought about by the fact that in this study the post-polio subjects had not been using any caliper for a long time. They were rather accustomed to ambulate themselves keeping one hand on the upper part of the affected knee. Probably this way they counter-balanced weak extensors of the knee (quadriceps) and erector muscle of the spine and also partly supported their own torso. Clinical examinations revealed that the disabilities in the post-polio subjects were due to weak muscle power in the hip, thigh and/or calf region, lumber lordosis, abnormal plantar or dorsi-flexion of the ankle joint. In some cases, pelvic tilting during walking was also observed. All these factors were responsible for diminishing the active locomotor muscle mass in the post-polio subjects. Naturally, the metabolic energy output per unit body weight was much higher for these types of disabled persons. Also the above factors may have been responsible for deviating the body's centre of gravity from its normal path, thus demanding higher energy than the normal individuals. The normal subjects consumed minimum energy per unit distance travelled while walking at 1"12 m/s. Below and above this range, energy expenditure was higher. Hence, the optimal speed of walking of normal subjects was found to be 1-12 m/s. This may support the findings of Bard and Ralston (1959), Inman and Ralston (1962), Margaria (1968), and Ghosh et al (1980) on normal individuals. On the other hand, the post-polio subjects consumed minimum energy per unit distance travelled when walking at 0.98 m/s. Hence, obviously, the optimal speed of walking in post-polio subjects.was lower than that of normal individuals. Inman
and Ralston (1962) observed that optimal speed of walking in the case of above-knee amputees using constant friction prostheses was lower than that of the normal individuals. Ganguli et al (1974c) opined that the comfortable speed for walking in case of below knee amputees using patellartendon-bearing prostheses was supposed to be 0.84 m/s, which is obviously lower than that of the normal individuals. Although the optimal speed of walking in post-polio subjects was lower than that of the normal individuals, the metabolic energy demand per unit distance travelled was about 90-0% higher. This high energy demand may be due to the acquired degree of disabilities which may have become severe as a result of not using any assistive aids.
Conclusions The above investigation may conclude the following: (i)
Metabolic energy demand during walking in post-polio subjects was much higher than for normal people. The degree of demand was not so high with low walking speed as in higher walking speed. Lack of use of any assistive devices by post-polio subjects might have incurred severe disabilities which increased the difficulty of normal gait of the post-polio subjects and demanded extra energy for them.
(ii)
The optimal speed of walking in post-polio subjects not using any assistive devices was obviously lower than that of the normal people, but the energy demand per unit distance travelled for post-polio subjects was about 90% higher than the demand on the normal people.
(iii)
Rehabilitation of the post-polio subjects is needed. A suitable ergonomic and economic assistive device is needed for optimum rehabilitation of the postpolio subjects with lower limb affliction so that the energy demands on this group of the physically disabled are not higher than those of normal people.
(iv)
The frequency and cause of damage of the assistive device should be studied, to prevent these disabilities being aggravated.
(v)
For immediate and short term use, auxiliary crutches or elbow crutches should be prescribed to this group of disabled persons. Observations by Ghosh et al (1980) revealed that the optimum speed of walking in normal as well as in auxiliary crutch-users was the same, though the latter group consumed insignificantly higher energy than those of the normal people while walking at the same speed.
Acknowledgements "i'he work reported here is part of the Research Project funded by the Science and Engineering Research Council, Department of Science and Technology, Government of India, New Delhi, India. The authors wish to acknowledge the help and assistance received from their colleagues at the Bioengineering Unit, Department of Orthopaedics, University College of Medicine, Calcutta, and from Mr S. Sethuraman, Superintendent, Vocational Rehabilitation Centre for the Physically Handicapped, Calcutta, India.
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