- Email: [email protected]
Crutch length: Effect on energy cost and activity intensity in non–weight-bearing ambulation
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Crutch Length: Effect on Energy Cost and Activity Intensity in Non-Weight-Bearing Ambulation Ricky Mullis, MSc, Rebecca M. Dent, BSc ABSTRACT. Mullis R, Dent RM. Crutch length: effect on energy cost and activity intensity in non-weight-bearing ambulation. Arch Phys Med Rehabil 2000;8 1569-72. Objective: To investigate the effect of forearm crutch length on energy cost in three-point, non-weight-bearing (NWB) ambulation. Design: Double-blind repeated measures design using crutch length as the independent variable. Setting: Overland walking circuit at a university campus, Participants: Volunteer, convenience sample of 20 subjects consisting of university students and staff without cardiovascular, respiratory, or orthopedic conditions. Intervention: Subjects used a three-point, NWB gait with forearm crutches set to length using conventional guidelines, and at 2Scm above and below this value. Main Outcome Measures: Oxygen consumption, carbon dioxide production, heart rate, speed of ambulation, and perceived exertion under steady-state conditions. Results: In terms of oxygen cost, ambulation with crutches set to the length recommended in conventional guidelines was not significantly more energy efficient than ambulation with either the longer or shorter crutches. Using crutches set 2Scm longer than conventional,guide,lines produced the lowest respiratory exchange ratio (VCO~NOZ)and the lowest ratings of perceived exertion. However, none of these differences reached statistical significance. Conclusion: Since exact crutch length was not critical in terms of oxygen cost, walking speed, or perceived exertion during NWB ambulation, the importance of rigidly adhering to specific guidelines for setting crutch length was not substantiated in this study. Clinically, consideration of patient preference regarding crutch length (within 2Scm) can be advocated. Key Words: Crutch; Energy cost; Intensity; Rehabilitation. 0 2000 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation
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ALKING AIDS are commonly prescribed when normal ambulation is compromised by pain, impaired balance, weakness, or musculoskeletal abnormality following trauma, surgery, or incapacitating pathology. Although many authors’” have documented specific guidelines for the optimal length of walking aids for individual patients, these guidelines are based primarily on subjective assessmentsof gait quality, rather than considerations of the energy demand or biomechanical efliFrom the Department of Physiotherapy Studies. Keele University, Staffs. United Kingdom. Submitted April 30. 1999. Accepted in revised form August 23. 1999. NO commercial party having a direct financial interest in the results of the research reported in this article has or will confer a benefit upon the authors or any organization with which the authors are associated. Reprint requests to Ricky Mullis. School of Physiotherapy, 2nd Floor Grosvenor Wing. St. Georges Hospital Medical School. London SW17 OQT, UK. 0 2ooO by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation ooO3-9993/00/8105-5622$3.00/O doi: 10.1053/mr.2000.3891
ciency of ambulation. When a three-point non-weight-bearing (NWB) gait is indicated, forearm crutches are frequently the aid of choice issued to patients6 This prescription avoids the risk of axillary artery thrombosis’ and the crutch palsy8 associated with the use of axillary crutches. Previous work9-I2 has shown that ambulation with crutches places a greater energy demand on an individual than unassisted walking. Since altering the length of crutches affects energy costi and biomechanical efficiency around the shoulder girdleI during gait performance, the need to ensure that these aids are set to an optimal length is an important clinical consideration, especially for older persons who may already have impaired muscular strength and lowered exercisetolerance. A substantial number of patients are equipped with walking aids of a length that does not conform to recommendations.‘s~‘6If gait is made less efficient because of this, reduced duration and speed of ambulation and, ultimately, loss of function may result. Paradoxically, adherence to a set of commonly recommended guidelines is counterproductive to metabolic efficiency. I3 The aim of the present work was to establish whether a variation in crutch height of +2.5cm significantly affects energy cost during three-point, NWB ambulation. METHODS A convenience sample of 20 healthy subjects (12 women, 8 men) were selected from university students and staff. The mean age was 22.2 years (SD = 4.85) and mean weight was 68.9kg (SD = 13.3). All were free from cardiovascular, respiratory, or orthopedic conditions. No other exclusion criteria were employed. Approval to proceed with the trial was gained from the University of Keele’s Physiotherapy Studies Departmental Research Ethical Committee. The experimental procedure was fully explained to potential subjects both verbally and by information sheet, and informed written consent was obtained from all participants before they entered the trial. Forearm crutches were used, because they are the most commonly used walking aid in the United Kingdom.6 These were constructed of aluminum with a single upright from which a handgrip extends forward and with a cuff encircling the proximal aspect of the forearm; the crutch was sized initially by means of Mulley’s guide1ines,2which suggest that the distance from floor to handle should equal the height from the ulnar styloid to the ground, with the elbow held in 15” of flexion. We could change crutch length by +2.5cm as required by moving the adjustment hole by one level either way. The dominant leg was established by asking each subject, without prior instruction, to step up onto a bench.13 The nondominant leg was thereafter used as the NWB lib. Before testing, each subject was instructed on how to use a 3-point NWB swing-through gait, and was then allowed 5 to 10 minutes of practice as required. Each subject was also shown the Borg scaleI for rating of perceived exertion (RPE) and instructed on its interpretation and use. Each subject was tested under three separate conditions, walking once with crutches of the correct height, once with crutches set 2.5cm higher, and once with crutches set 2Scm lower than the correct height. The order in which the different Arch
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conditions took place was randomized across subjects to minimize bias from any learning or practice effect. Subjects walked at their preferred speed around a rectangular 62.5meter outdoor track. This mode of activity was chosen over treadmill walking in an attempt to more accurately simulate the customary walking conditions experienced during functional crutch usage. It has been suggested that data collected from subjects walking on a treadmill or at a regulated speed may not accurately reflect the physiological conditions that occurs during more normal, self-determined walking pace.i8 To facilitate the subject’s accustomed pace, ambulatory speed was not controlled acrossthe three trials. Heart rate (HR) was monitored throughout the trial using a PE 3000 Sport TesteP with remote receiver, the accuracy of which has previously been verified.i9 This device allowed us to take readings without affecting the subject’s speed of ambulation. Steady state was considered to have been established when HR variation was less than k5 beats per minute over a full minute (achieved in all subjects within 4 minutes of starting the test). At this point, subjects were fitted with a clean nose clip and mouthpiece that, through a series of two valves connected by flexible hose to a Douglas gas collection bag, allowed collection of all expired gases. Sampling was started when the subject resumed steady-state walking, and gaseswere collected over one complete circuit of the course. We timed the lap by stopwatch, so we could calculate walking speed and rate of oxygen uptake per minute. RPE was obtained by means of the Borg scale” immediately after the subject completed each ambulation mode. The content of the Douglas bag was analyzed by passing a 20-mL sample through a Medgraphics CPX/Db respiratory gas analysis system. This system uses a zirconium oxygen analyzer, which was calibrated to span between 12% and 21% using certified reference gases. The infrared carbon dioxide analyzer was calibrated to span between 0% and 5%. The remaining volume of the Douglas bag was determined by emptying the contents through a digital dry gas meter.cThe temperature of the gas was measured with a thermometer in the gas flow and atmospheric pressure was measured with a barometer. All subsequent volumes were converted to standard dry temperature and pressure. The total inspired volume of air (Vt) was calculated from the change in nitrogen concentration found in the expired sample according to the formula: V, = V, X (P,N, f 79.04) where Vn = expired volume, PzNz = percentage of expired nitrogen, (fraction of inspired nitrogen was taken as 79.04%). The inspired oxygen volume was then calculated from Vt and the amount of oxygen consumed was taken as the difference between the inspired and the expired oxygen volumes. The volume of carbon dioxide (COz) produced was calculated from Vn X the percentage of COz present, since the inspired CO* volume can be considered negligible.20 Subjects rested for a minimum of 10 minutes between each period of ambulation, or until their heart rate returned to resting level if it had not done so within this time. The study was effectively double-blind, since neither the subjects nor the data collector knew the height of the crutch used during each trial. Statistical analysis was carried out using SPSS 6.1 for Microsoft Windows.d Analysis of variance (ANOVA) for repeated measures was used to test for differences between the three conditions in rate of 02 uptake mL/(kg . mitt), 02 cost per meter walked mL/(kg 1m), respiratory exchange ratio (RER = VCOz + VOz), HR. speed (m/set), and RPE (Borg Arch
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score).An alpha level of p < .05 was taken to indicate statistical significance. RESULTS The age-predicted maximal heart rate (APMHR) for each subject was calculated from the equation APMHR = 220 (age in years).‘O The mean steady-state HR during each ambulation for each subject was then expressed as a percentage of that person’s age-predicted maximal value. This figure, along with the RER and RPE, may serve as an indicator of the relative intensity of the activity undertaken (table 1). Differences between the mean values for each outcome measure (table 2) were no greater than 5% across trials, and statistical analysis showed these differences to be nonsignificant (p > .I2 in all cases). Ambulatory speed was not controlled across the three trials; however, the mean speed with conventional length crutches was .87rn/sec (SD .24), which was identical to that with crutches both 2Scm longer and 2.5cm shorter than the conventional crutch (p = .99). In the present study, the order in which the subjects undertook the three walking trials was randomized. A repeatedmeasuresANOVA with trial order as the within-subjects factor was performed on all dependent variables to detect any order effect that may have influenced the outcome. This check established that no significant order effect was evident between trials on any variable (p > .45 in all cases). DISCUSSION In the present study, altering crutch length by ?2.5cm from that recommended in conventional guidelines had no significant effect on either the energy efficiency or the activity intensity of ambulation. The implications for clinical practice are that, within certain guidelines, there should be a move away from rigid adherence to crutch fitting procedures, with more attention being paid to patient preference and comfort. The rate of oxygen uptake and the oxygen cost per meter travelled was lowest when using crutches set at the recommended length, although the difference when compared with the other conditions (less than 5%) was not statistically significant. It may follow that an even greater deviation away from the recommended length would increase these differences in energy efficiency still further, to the point where the functional use of crutches for sustained ambulation becomes limited by energy cost alone. Further research that examines the effect of altering crutch length by a greater amount than was used here would be required to verify this. Clinically it would be expected that a practitioner trained in fitting crutches, adhering to conventional guidelines, would be unlikely to deviate from the “recommended” length by more that one adjustment hole. Therefore, one could argue that the risk of a patient inadvertently receiving (from a reputable source) a crutch that was significantly less energy efficient than one of optimal length is small. Our findings contrast with those of Smith and Enright,i3 Table
1: Energy
Crutch Length Conventional +2.5cm -25cm
Expenditure and Activity Crutch Lengths 02 Rate u’rLlkg/min)
02 Cost tmL/kg/m)
20.9 (3.54) 21.57 (3.06) 21.78 (3.28)
.37 f.09) .39 t.08) .39 t.09)
RER
Intensity
for Different
%APMHR
.96 t.11) 80.8 (9.0) .94 LO81 82.7 (11.4) .95 t.10) 82.5 (10.4)
RPE 12.5 (1.9) 12.4 (1.9) 13.0 (2.1)
Values are means (standard deviation). Abbreviations: 02, oxygen; RER, respiratory exchange ratio; APMHR, age-predicted maximal heart rate; RPE, ratings of perceived exertion.
EFFECT
Table
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LENGTH
2: Summary of Statistical Analysis (Repeated-Measures ANOVA) Between Mean Values of Energy Expenditure and Activity Intensity for Different Crutch Lengths
O2 Rate 02 cost RER %APMHR RPE
ss
df
F
P
8.51 0 0 44.08 4.90
2 2 2 2 2
2.1 1.27 .26 1.46
.14 .29
2.23
.J7 .24 .12
Abbreviations: SS, sum of squares of individual deviations from mean; c/f. degrees of freedom; F, ratio of between-group variance within-group variance; p, probability value.
the to
work showed that oxygen uptake and oxygen cost was when using crutches set at a recommended length, compared with crutches altered by +2&m. Although both studiesexamined the effect of altering crutch length, there were two major differences in the methods employed. In the study by Smith and Enright,i3 gas collection took place while the subjects walked on a powered treadmill using a fixed speed protocol, with the speed determined by walking with crutches of conventional length. Walking speed was held constant over all three trials, and the subjects could not choose their preferred speedon each occasion. The researchersacknowledged that this speed (28rrJmin) was “notably slower than in previous studies,” and we found that the self-selected speed recorded in the present study was considerably faster (52m/min). In the present study the subjects walked around an outdoor track, which more closely replicates customary overland walking conditions.‘* The oxygen cost per meter travelled was less than that recorded by Smith and Enright, I3 but similar to those observed in comparable overland walking reports.10-‘2Furthermore, speed was not controlled and subjects were given the opportunity to walk at their preferred pace on each occasion, as would occur during everyday crutch usage. Interestingly, despite being given this freedom of choice, subject mean speeds were no different when using crutches longer or shorter by 2Scm from that when using recommended length crutches, demonstrating that speed of ambulation was not compromised by changes of this magnitude. It may be that the laboratory-based, controlled walking environment employed by Smith and Enrighti3 is less directly comparable to functional crutch usage than the method used in the present study, and that the difference in findings may have arisen from differences in methods. From a clinical perspective, the relative intensity of ambulation with assistive aids may be of greater concern. Although HR during crutch walking may be disproportionately elevated becauseof the upper extremity component of the activity,2i the %APMHR is still an acceptable index of relative exercise intensity. Extended walking at values greater than 85% APMHR is intolerable for most patients. ii The overall mean APMHR of 82% reported in the present study was similar to that found by Annesley and coworkers,22suggesting that the physical demand of using assistive devices approaches an unacceptable level for many people during ambulation at preferred speed, almost to the point of becoming intolerable. Furthermore, the mean age of the healthy subjects in this study was only 22 years, notably lower than that of many patients who are frequently issued with walking aids. It therefore seems inappropriate that crutches may be issued to elderly persons or to persons with impaired cardiovascular function, without consideration of the physiologic stress of walking with them. Indeed, a safe aerobic conditioning program prescribed for a sedentary but otherwise healthy individual at the age of 40 years would be set at a lower whose greatest
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HR than was observed in this study.23Findings from the present study add further support to previous recommendations made of the need to show caution when issuing aids to these patients.i0.i3.24.25 Conversely, the mean RPE of 12.5 to 13 reported across the three trials in the present study equates with the relatively low intensity of the “somewhat hard” descriptor on the Borg scale. This finding suggests that, despite considerably elevated HRs, the subjects did not perceive their effort to be intolerably intense. This perception is in keeping with the recorded RER values of .94 to .96, which indicate that aerobic metabolism was the major contributor to energy production during ambulation. However, individual variation was considerable, with five subjects’ RERs exceeding 1.00, indicating that an essential degree of anaerobiosis was taking place. This high RER must raise questions about the nature of these five subjects’ steady states during ambulation, even though all appeared to plateau at a constant HR. In the present study, each subject performed only one trial at each of the three crutch heights. However, before the first trial, individual instruction was provided on how to use the crutches in the required fashion. Each subject was then allowed as much practice time as he or she felt necessary (no one needed more than 10 minutes). Excessivepractice before the measured trials may have exacerbated fatigue that may have built up during the measured trials. Statistical analysis showed that no practice effect occurred over the course of the three trials. The subjects did not become more accomplished crutch users (and hence more efficient in their gait action) with their second and third walking trial, regardless of the length of crutch used. This analysis also suggests that the subjects were given sufficient tuition and practice time before data collection took place and adequate rest between trials to negate the effects of fatigue. We believe, therefore, that performing a single trial at each crutch height did not unduly compromise the outcome of the investigation. The blinding procedures were successful to the extent that the gas analysis was accomplished without the equipment operator having knowledge of the crutch height used. During the second and third walks, some subjects stated that they felt aware of whether the crutch height had been increased or decreased since the previous trial. However, because of the objective nature of many of the outcome measures used in the study, we do not believe that this knowledge influenced the results.
CONCLUSION
The present study supports the findings of previous worki3J4 suggesting that the wisdom of rigidly adhering to conventional guidelines for the correct length of crutches is questionable. However, the justification for this conclusion was baaed on evidence that conflicted with previous findings.i3 The data from the present study suggest that, within certain limits, the recommendation of an exact length for elbow crutches is unjustified in terms of the energy cost of ambulation. Walking with crutches of a length within a range defined as being within 2.5cm of the recommended length described by Mulley2 does not significantly affect energy efficiency or speed of ambulation. We therefore suggest that the guidelines given by Mulley2 should be used as a starting point in the crutch fitting procedure, but then consideration should be given to patient feedback and preference to “fine tune” crutch length within these boundaries for each individual. Arch
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5. 6. 7. 8. 9. 10. 11.
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13. 14.
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References Bossingham DH. Wheelchairs and appliances. Clin Rheum Dis 1981;7:395-415. Mulley GP Everyday aids and appliances: walking sticks. BMJ 1988;296:475-6. Smidt GL, editor. Gait in rehabilitation. New York: Churchill Livingstone; 1990. Bauer DM, Fich DC, McGough Kp. Benson CJ, Finsteun K, Allison SC. A comparative analysis of several crutch-lengthestimation techniques. Phys Ther I99 I:7 I :294-300. Jones K, Barker K. Human movement explained. Oxford: Butterworth Heinemann; 1996. Dounis E, Rose GK, Wilson RS, Stevenson RD. J Bone Joint Surg Am 198064~896-9. Plan H. Occlusion of the axillary artery due to pressure by a crutch. Arch Surg 1930;20:314-6. Rudin LN, Levine L. Bilateral compression of the radial nerve. Phys Ther Rev 195 I ;3 I :229-3 I. Andriacchi TP, Ogle JA, Galante JO. Walking speed as a basis for normal and abnormal gait measurements. J Biomech 1977;lO: 261-8. Fisher SV, Patterson RP. Energy cost of ambulation with crutches. Arch Phys Med Rehabil 1981;62:250-6. Nielsen DH, Harris JM, Minton YM, Motley NS, Rowley JL, Wadsworth CT. Energy cost, exercise intensity, and gait efficiency of standard versus rocker-bottom axillary crutch walking. Phys Ther 1990;70:487-93. Holder CG, Haskvitz EM, Weltman A. The effects of assistive devices on the oxygen cost, cardiovascular stress, and perception of nonweight-bearing ambulation. J Orthop Sports Phys Ther 1993;18:537-42. Smith TR, Enright S. Metabolic evaluation of the criteria used to fit elbow crutches by measurement of oxvaen consumption. Arch Phys Med Rehabii 1996;77:70-4. -Crosbie J, Armstrong E, Kempson J. Is walking aid height critical? Aust J Physiother 1992;38:261-6.
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I5 Sainsbury R, Mulley GP. Walking sticks used by the elderley. BMJ 1982;284: I75 I. I6 Simpson C, Pirrie L. Walking sticks: a survey of suitability and supply. Physiother 199 I ;77:23 I-4. 17 Borg GA. Psychophysical bases of perceived exertion. Med Sci Sports Exert 1982;14:377-81. 18. Corcoran PJ, Brengelmann GC. Oxygen uptake in normal and handicapped subjects, in relation to the speed of walking beside velocity~controlled cart. Arch Phys Med Rkhabil 1970;51:?‘8-87. 19. Seaward BL. Sleamaker RH. McAuliffe T. Claoo JF. The orecision and accuracy of a portable heart rate monito;‘Biomed inst Tech 1990;24:37-41. 20. Wasserman K, Hansen JE, Sue DY, Whipp BJ. Principles of exercise testing and interpretation. Philadelphia: Lea & Febiger; 1987. 21. Faria EW, Faria IE. Cardiorespiratory responses to exercise of equal relative intensity distributed between the upper and lower body. J Sports Sci 1988; 16:309- 15. 22. Annesley AL, Almada-Nortleet M. Amall DA, Cornwall MW. Energy expenditure of ambulation using the sure-gait crutch and standard axillary crutch. Phys Ther 1990;70: 18-23. 23. American College of Sports Medicine. Guidelines for exercise testing and prescription. Philadelphia: Williams & Wilkins; 1995. 24. McBeath AA. Bahrke M. Balke B. Efficiency of assisted ambulation determined by oxygen consumption measure. J Bone Joint Surg Am 1974;56:994-1000. 25. Waters RL, Campbell J, Thomas L, Hugos L, Davis P. Energy cost of walking in lower-extremity plaster casts. J Bone Joint Surg Am 1982;64:896-9. Suppliers Polar Electra Oy, Kempele, Finland. Zardiokinetics Ltd., Salford, Lanes, UK. Harvard Apparatus, Edenbridge, Kent, UK. SPSS, Inc., 444 North Michigan Avenue, Chicago, IL 6061 I.
Crutch Length: Effect on Energy Cost and Activity Intensity in Non-Weight-Bearing Ambulation Ricky Mullis, MSc, Rebecca M. Dent, BSc ABSTRACT. Mullis R, Dent RM. Crutch length: effect on energy cost and activity intensity in non-weight-bearing ambulation. Arch Phys Med Rehabil 2000;8 1569-72. Objective: To investigate the effect of forearm crutch length on energy cost in three-point, non-weight-bearing (NWB) ambulation. Design: Double-blind repeated measures design using crutch length as the independent variable. Setting: Overland walking circuit at a university campus, Participants: Volunteer, convenience sample of 20 subjects consisting of university students and staff without cardiovascular, respiratory, or orthopedic conditions. Intervention: Subjects used a three-point, NWB gait with forearm crutches set to length using conventional guidelines, and at 2Scm above and below this value. Main Outcome Measures: Oxygen consumption, carbon dioxide production, heart rate, speed of ambulation, and perceived exertion under steady-state conditions. Results: In terms of oxygen cost, ambulation with crutches set to the length recommended in conventional guidelines was not significantly more energy efficient than ambulation with either the longer or shorter crutches. Using crutches set 2Scm longer than conventional,guide,lines produced the lowest respiratory exchange ratio (VCO~NOZ)and the lowest ratings of perceived exertion. However, none of these differences reached statistical significance. Conclusion: Since exact crutch length was not critical in terms of oxygen cost, walking speed, or perceived exertion during NWB ambulation, the importance of rigidly adhering to specific guidelines for setting crutch length was not substantiated in this study. Clinically, consideration of patient preference regarding crutch length (within 2Scm) can be advocated. Key Words: Crutch; Energy cost; Intensity; Rehabilitation. 0 2000 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation
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ALKING AIDS are commonly prescribed when normal ambulation is compromised by pain, impaired balance, weakness, or musculoskeletal abnormality following trauma, surgery, or incapacitating pathology. Although many authors’” have documented specific guidelines for the optimal length of walking aids for individual patients, these guidelines are based primarily on subjective assessmentsof gait quality, rather than considerations of the energy demand or biomechanical efliFrom the Department of Physiotherapy Studies. Keele University, Staffs. United Kingdom. Submitted April 30. 1999. Accepted in revised form August 23. 1999. NO commercial party having a direct financial interest in the results of the research reported in this article has or will confer a benefit upon the authors or any organization with which the authors are associated. Reprint requests to Ricky Mullis. School of Physiotherapy, 2nd Floor Grosvenor Wing. St. Georges Hospital Medical School. London SW17 OQT, UK. 0 2ooO by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation ooO3-9993/00/8105-5622$3.00/O doi: 10.1053/mr.2000.3891
ciency of ambulation. When a three-point non-weight-bearing (NWB) gait is indicated, forearm crutches are frequently the aid of choice issued to patients6 This prescription avoids the risk of axillary artery thrombosis’ and the crutch palsy8 associated with the use of axillary crutches. Previous work9-I2 has shown that ambulation with crutches places a greater energy demand on an individual than unassisted walking. Since altering the length of crutches affects energy costi and biomechanical efficiency around the shoulder girdleI during gait performance, the need to ensure that these aids are set to an optimal length is an important clinical consideration, especially for older persons who may already have impaired muscular strength and lowered exercisetolerance. A substantial number of patients are equipped with walking aids of a length that does not conform to recommendations.‘s~‘6If gait is made less efficient because of this, reduced duration and speed of ambulation and, ultimately, loss of function may result. Paradoxically, adherence to a set of commonly recommended guidelines is counterproductive to metabolic efficiency. I3 The aim of the present work was to establish whether a variation in crutch height of +2.5cm significantly affects energy cost during three-point, NWB ambulation. METHODS A convenience sample of 20 healthy subjects (12 women, 8 men) were selected from university students and staff. The mean age was 22.2 years (SD = 4.85) and mean weight was 68.9kg (SD = 13.3). All were free from cardiovascular, respiratory, or orthopedic conditions. No other exclusion criteria were employed. Approval to proceed with the trial was gained from the University of Keele’s Physiotherapy Studies Departmental Research Ethical Committee. The experimental procedure was fully explained to potential subjects both verbally and by information sheet, and informed written consent was obtained from all participants before they entered the trial. Forearm crutches were used, because they are the most commonly used walking aid in the United Kingdom.6 These were constructed of aluminum with a single upright from which a handgrip extends forward and with a cuff encircling the proximal aspect of the forearm; the crutch was sized initially by means of Mulley’s guide1ines,2which suggest that the distance from floor to handle should equal the height from the ulnar styloid to the ground, with the elbow held in 15” of flexion. We could change crutch length by +2.5cm as required by moving the adjustment hole by one level either way. The dominant leg was established by asking each subject, without prior instruction, to step up onto a bench.13 The nondominant leg was thereafter used as the NWB lib. Before testing, each subject was instructed on how to use a 3-point NWB swing-through gait, and was then allowed 5 to 10 minutes of practice as required. Each subject was also shown the Borg scaleI for rating of perceived exertion (RPE) and instructed on its interpretation and use. Each subject was tested under three separate conditions, walking once with crutches of the correct height, once with crutches set 2.5cm higher, and once with crutches set 2Scm lower than the correct height. The order in which the different Arch
Phys
Med
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Vol81,
May
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conditions took place was randomized across subjects to minimize bias from any learning or practice effect. Subjects walked at their preferred speed around a rectangular 62.5meter outdoor track. This mode of activity was chosen over treadmill walking in an attempt to more accurately simulate the customary walking conditions experienced during functional crutch usage. It has been suggested that data collected from subjects walking on a treadmill or at a regulated speed may not accurately reflect the physiological conditions that occurs during more normal, self-determined walking pace.i8 To facilitate the subject’s accustomed pace, ambulatory speed was not controlled acrossthe three trials. Heart rate (HR) was monitored throughout the trial using a PE 3000 Sport TesteP with remote receiver, the accuracy of which has previously been verified.i9 This device allowed us to take readings without affecting the subject’s speed of ambulation. Steady state was considered to have been established when HR variation was less than k5 beats per minute over a full minute (achieved in all subjects within 4 minutes of starting the test). At this point, subjects were fitted with a clean nose clip and mouthpiece that, through a series of two valves connected by flexible hose to a Douglas gas collection bag, allowed collection of all expired gases. Sampling was started when the subject resumed steady-state walking, and gaseswere collected over one complete circuit of the course. We timed the lap by stopwatch, so we could calculate walking speed and rate of oxygen uptake per minute. RPE was obtained by means of the Borg scale” immediately after the subject completed each ambulation mode. The content of the Douglas bag was analyzed by passing a 20-mL sample through a Medgraphics CPX/Db respiratory gas analysis system. This system uses a zirconium oxygen analyzer, which was calibrated to span between 12% and 21% using certified reference gases. The infrared carbon dioxide analyzer was calibrated to span between 0% and 5%. The remaining volume of the Douglas bag was determined by emptying the contents through a digital dry gas meter.cThe temperature of the gas was measured with a thermometer in the gas flow and atmospheric pressure was measured with a barometer. All subsequent volumes were converted to standard dry temperature and pressure. The total inspired volume of air (Vt) was calculated from the change in nitrogen concentration found in the expired sample according to the formula: V, = V, X (P,N, f 79.04) where Vn = expired volume, PzNz = percentage of expired nitrogen, (fraction of inspired nitrogen was taken as 79.04%). The inspired oxygen volume was then calculated from Vt and the amount of oxygen consumed was taken as the difference between the inspired and the expired oxygen volumes. The volume of carbon dioxide (COz) produced was calculated from Vn X the percentage of COz present, since the inspired CO* volume can be considered negligible.20 Subjects rested for a minimum of 10 minutes between each period of ambulation, or until their heart rate returned to resting level if it had not done so within this time. The study was effectively double-blind, since neither the subjects nor the data collector knew the height of the crutch used during each trial. Statistical analysis was carried out using SPSS 6.1 for Microsoft Windows.d Analysis of variance (ANOVA) for repeated measures was used to test for differences between the three conditions in rate of 02 uptake mL/(kg . mitt), 02 cost per meter walked mL/(kg 1m), respiratory exchange ratio (RER = VCOz + VOz), HR. speed (m/set), and RPE (Borg Arch
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score).An alpha level of p < .05 was taken to indicate statistical significance. RESULTS The age-predicted maximal heart rate (APMHR) for each subject was calculated from the equation APMHR = 220 (age in years).‘O The mean steady-state HR during each ambulation for each subject was then expressed as a percentage of that person’s age-predicted maximal value. This figure, along with the RER and RPE, may serve as an indicator of the relative intensity of the activity undertaken (table 1). Differences between the mean values for each outcome measure (table 2) were no greater than 5% across trials, and statistical analysis showed these differences to be nonsignificant (p > .I2 in all cases). Ambulatory speed was not controlled across the three trials; however, the mean speed with conventional length crutches was .87rn/sec (SD .24), which was identical to that with crutches both 2Scm longer and 2.5cm shorter than the conventional crutch (p = .99). In the present study, the order in which the subjects undertook the three walking trials was randomized. A repeatedmeasuresANOVA with trial order as the within-subjects factor was performed on all dependent variables to detect any order effect that may have influenced the outcome. This check established that no significant order effect was evident between trials on any variable (p > .45 in all cases). DISCUSSION In the present study, altering crutch length by ?2.5cm from that recommended in conventional guidelines had no significant effect on either the energy efficiency or the activity intensity of ambulation. The implications for clinical practice are that, within certain guidelines, there should be a move away from rigid adherence to crutch fitting procedures, with more attention being paid to patient preference and comfort. The rate of oxygen uptake and the oxygen cost per meter travelled was lowest when using crutches set at the recommended length, although the difference when compared with the other conditions (less than 5%) was not statistically significant. It may follow that an even greater deviation away from the recommended length would increase these differences in energy efficiency still further, to the point where the functional use of crutches for sustained ambulation becomes limited by energy cost alone. Further research that examines the effect of altering crutch length by a greater amount than was used here would be required to verify this. Clinically it would be expected that a practitioner trained in fitting crutches, adhering to conventional guidelines, would be unlikely to deviate from the “recommended” length by more that one adjustment hole. Therefore, one could argue that the risk of a patient inadvertently receiving (from a reputable source) a crutch that was significantly less energy efficient than one of optimal length is small. Our findings contrast with those of Smith and Enright,i3 Table
1: Energy
Crutch Length Conventional +2.5cm -25cm
Expenditure and Activity Crutch Lengths 02 Rate u’rLlkg/min)
02 Cost tmL/kg/m)
20.9 (3.54) 21.57 (3.06) 21.78 (3.28)
.37 f.09) .39 t.08) .39 t.09)
RER
Intensity
for Different
%APMHR
.96 t.11) 80.8 (9.0) .94 LO81 82.7 (11.4) .95 t.10) 82.5 (10.4)
RPE 12.5 (1.9) 12.4 (1.9) 13.0 (2.1)
Values are means (standard deviation). Abbreviations: 02, oxygen; RER, respiratory exchange ratio; APMHR, age-predicted maximal heart rate; RPE, ratings of perceived exertion.
EFFECT
Table
OF CRUTCH
LENGTH
2: Summary of Statistical Analysis (Repeated-Measures ANOVA) Between Mean Values of Energy Expenditure and Activity Intensity for Different Crutch Lengths
O2 Rate 02 cost RER %APMHR RPE
ss
df
F
P
8.51 0 0 44.08 4.90
2 2 2 2 2
2.1 1.27 .26 1.46
.14 .29
2.23
.J7 .24 .12
Abbreviations: SS, sum of squares of individual deviations from mean; c/f. degrees of freedom; F, ratio of between-group variance within-group variance; p, probability value.
the to
work showed that oxygen uptake and oxygen cost was when using crutches set at a recommended length, compared with crutches altered by +2&m. Although both studiesexamined the effect of altering crutch length, there were two major differences in the methods employed. In the study by Smith and Enright,i3 gas collection took place while the subjects walked on a powered treadmill using a fixed speed protocol, with the speed determined by walking with crutches of conventional length. Walking speed was held constant over all three trials, and the subjects could not choose their preferred speedon each occasion. The researchersacknowledged that this speed (28rrJmin) was “notably slower than in previous studies,” and we found that the self-selected speed recorded in the present study was considerably faster (52m/min). In the present study the subjects walked around an outdoor track, which more closely replicates customary overland walking conditions.‘* The oxygen cost per meter travelled was less than that recorded by Smith and Enright, I3 but similar to those observed in comparable overland walking reports.10-‘2Furthermore, speed was not controlled and subjects were given the opportunity to walk at their preferred pace on each occasion, as would occur during everyday crutch usage. Interestingly, despite being given this freedom of choice, subject mean speeds were no different when using crutches longer or shorter by 2Scm from that when using recommended length crutches, demonstrating that speed of ambulation was not compromised by changes of this magnitude. It may be that the laboratory-based, controlled walking environment employed by Smith and Enrighti3 is less directly comparable to functional crutch usage than the method used in the present study, and that the difference in findings may have arisen from differences in methods. From a clinical perspective, the relative intensity of ambulation with assistive aids may be of greater concern. Although HR during crutch walking may be disproportionately elevated becauseof the upper extremity component of the activity,2i the %APMHR is still an acceptable index of relative exercise intensity. Extended walking at values greater than 85% APMHR is intolerable for most patients. ii The overall mean APMHR of 82% reported in the present study was similar to that found by Annesley and coworkers,22suggesting that the physical demand of using assistive devices approaches an unacceptable level for many people during ambulation at preferred speed, almost to the point of becoming intolerable. Furthermore, the mean age of the healthy subjects in this study was only 22 years, notably lower than that of many patients who are frequently issued with walking aids. It therefore seems inappropriate that crutches may be issued to elderly persons or to persons with impaired cardiovascular function, without consideration of the physiologic stress of walking with them. Indeed, a safe aerobic conditioning program prescribed for a sedentary but otherwise healthy individual at the age of 40 years would be set at a lower whose greatest
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HR than was observed in this study.23Findings from the present study add further support to previous recommendations made of the need to show caution when issuing aids to these patients.i0.i3.24.25 Conversely, the mean RPE of 12.5 to 13 reported across the three trials in the present study equates with the relatively low intensity of the “somewhat hard” descriptor on the Borg scale. This finding suggests that, despite considerably elevated HRs, the subjects did not perceive their effort to be intolerably intense. This perception is in keeping with the recorded RER values of .94 to .96, which indicate that aerobic metabolism was the major contributor to energy production during ambulation. However, individual variation was considerable, with five subjects’ RERs exceeding 1.00, indicating that an essential degree of anaerobiosis was taking place. This high RER must raise questions about the nature of these five subjects’ steady states during ambulation, even though all appeared to plateau at a constant HR. In the present study, each subject performed only one trial at each of the three crutch heights. However, before the first trial, individual instruction was provided on how to use the crutches in the required fashion. Each subject was then allowed as much practice time as he or she felt necessary (no one needed more than 10 minutes). Excessivepractice before the measured trials may have exacerbated fatigue that may have built up during the measured trials. Statistical analysis showed that no practice effect occurred over the course of the three trials. The subjects did not become more accomplished crutch users (and hence more efficient in their gait action) with their second and third walking trial, regardless of the length of crutch used. This analysis also suggests that the subjects were given sufficient tuition and practice time before data collection took place and adequate rest between trials to negate the effects of fatigue. We believe, therefore, that performing a single trial at each crutch height did not unduly compromise the outcome of the investigation. The blinding procedures were successful to the extent that the gas analysis was accomplished without the equipment operator having knowledge of the crutch height used. During the second and third walks, some subjects stated that they felt aware of whether the crutch height had been increased or decreased since the previous trial. However, because of the objective nature of many of the outcome measures used in the study, we do not believe that this knowledge influenced the results.
CONCLUSION
The present study supports the findings of previous worki3J4 suggesting that the wisdom of rigidly adhering to conventional guidelines for the correct length of crutches is questionable. However, the justification for this conclusion was baaed on evidence that conflicted with previous findings.i3 The data from the present study suggest that, within certain limits, the recommendation of an exact length for elbow crutches is unjustified in terms of the energy cost of ambulation. Walking with crutches of a length within a range defined as being within 2.5cm of the recommended length described by Mulley2 does not significantly affect energy efficiency or speed of ambulation. We therefore suggest that the guidelines given by Mulley2 should be used as a starting point in the crutch fitting procedure, but then consideration should be given to patient feedback and preference to “fine tune” crutch length within these boundaries for each individual. Arch
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5. 6. 7. 8. 9. 10. 11.
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13. 14.
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