- Email: [email protected]
Daily physical activity and heart rate response in people with a unilateral transtibial amputation for vascular disease1
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Daily Physical Activity and Heart Rate Response in People With a Unilateral Transtibial Amputation for Vascular Disease Johannes B. Bussmann, PhD, Eleonore A. Grootscholten, MD, Henk J. Stam, PhD ABSTRACT. Bussmann JB, Grootscholten EA, Stam HJ. Daily physical activity and hear rate response in people with a unilateral transtibial amputation for vascular disease. Arch Phys Med Rehabil 2004;85:240-4. Objective: To study the activity level and heart rate response, objectively measured during normal daily life, of persons with a unilateral transtibial amputation for vascular disease. Design: Case comparison. Setting: General community, daily life in the Netherlands. Participants: Nine subjects with a unilateral transtibial amputation for vascular disease (convenience sample) and 9 control subjects without known impairments (matched for sex, age, social situation, employment). Interventions: Not applicable. Main Outcome Measures: Duration of dynamic activities, body motility (the intensity of body movement, measured with accelerometry), and heart rate (on 2 consecutive days). Results: Persons with an amputation were less active than the comparison subjects (4.3% vs 11.4% of a 48-h period, P⫽.007). Body motility during walking was lower in the amputee group (.111g vs. .147g, P⫽.003). No differences between groups were found in normalized heart rate during walking. In the amputee group, a strong relationship was found between body motility during walking and the percentage of the day that the subject walked (r⫽.88, P⫽.002). No relationship was found between the percentage of the day that persons with an amputation were active and data from disability questionnaires. Conclusion: Persons with a unilateral transtibial amputation for vascular disease were considerably less active than persons without known impairments. Heart rate response during walking of the amputee group did not differ from the response in the comparison group. Key Words: Amputation; Monitoring; Ambulatory; Physical exertion; Rehabilitation. © 2004 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation N A GLOBAL STUDY OF the incidence of lower-extremity age-adjusted major amputation rates ranged Ifromamputation, 3.7 to 58.7 per 100,000 men and from 0.5 to 32.0 per 100,000 women per year1; in the Netherlands, a rate of 18 to 20
From the Department of Rehabilitation Medicine, Erasmus MC, University Medical Center, Rotterdam, The Netherlands. Presented in part at the 1st World Congress of the International Society of Physical and Rehabilitation Medicine, July 8 –13, 2001, Amsterdam, The Netherlands. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Johannes B. Bussmann, Dept of Rehabilitation Medicine, Erasmus MC, PO Box 2040, 3000 CA Rotterdam, The Netherlands, e-mail: [email protected]. 0003-9993/04/8502-8065$30.00/0 doi:10.1016/S0003-9993(03)00485-4
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per 100,000 persons has been reported.2 After amputation, persons frequently follow a rehabilitation program aimed at optimal functioning with a prosthesis during normal daily life. An important consequence of an amputation is that walking with a prosthesis is less energy efficient, which may result in increased physical strain (expressed as heart rate response or oxygen consumption) during walking.3-11 Another adaptation strategy may be that strenuous activities such as walking are avoided12,13 or that the performance of activities is changed to decrease physical strain.4-6,11 For example, fewer and shorter walking periods and walking slower may counterbalance the decreased efficiency and may result in a comparable or even lower heart rate response and energy cost than in subjects without known impairments. To provide optimal treatment, reliable and valid information about activity level and physical strain during daily life is important. Such information is mostly obtained by means of interviews, questionnaires, and diaries, all of which are based on subjective data from the patient. Gait analysis in a gait laboratory is used to obtain more quantitative and objective data, but these data cannot simply be generalized to actual behavior during normal daily life. Therefore, several studies report the development and use of more objective instruments in persons with an amputation that can be used outside a gait lab. For example, Holden and Fernie14 used an electronic step counter to assess prosthetic use. Stam et al15 developed a similar type of apparatus to assess walking periods during a 7-day measurement period. Armstrong et al16 used an activity monitor to evaluate the activity level of persons at high risk for foot amputation, and the same was done by van Dam et al17 in persons after surgery for a malignant tumor in the leg. However, detailed, combined, and methodologically sound data are still lacking about daily physical activity and physical strain in persons with a unilateral transtibial amputation for vascular disease and about the effect of such amputation on daily physical activity and physical strain. In 1998, Bussmann et al18 reported on the reliability and validity of an accelerometry-based activity monitor in persons with an amputation of the leg. A high percentage of agreement was found between activity monitor output (the automatic detection of mobility-related activities, ie, postures and motions) and analyzed video recordings. Since then, the activity monitor has been validated in several populations, further developed, and applied in several types of research.19-25 Because electrocardiograms (ECGs) can be simultaneously measured with the acceleration signals, the activity monitor allows measurement of both physical activities and heart rate response during normal daily life. The aim of our study was to examine whether, and if so to what extent, people with a unilateral transtibial amputation for vascular disease are less active than persons without known impairments, and whether, and if so to what extent, heart rate response during walking is increased in persons with a unilateral transtibial amputation for vascular disease. Additionally, the relationships between the activity parameters as provided by the activity monitor, on the one hand, and subjective disability measures, on the other, were examined.
PHYSICAL ACTIVITY AND HEART RATE AFTER AMPUTATION, Bussmann
METHODS Participants Our study included 9 persons with an amputation of the lower leg and 9 matched able-bodied comparison subjects. The sample size was based on power analysis by using activity monitor data of a previous study with other subjects as reference.19 Amputees were recruited from patient files of the departments of rehabilitation medicine of Erasmus MC and Zuiderziekenhuis. Inclusion criteria were transtibial amputation, older than 40 years of age, amputation of vascular origin, current use of prosthesis, completion of a rehabilitation program, last treatment less than 3 years before study, and ability to understand and complete the questionnaires. Persons with a bilateral amputation were excluded. Amputees were invited to participate in the study by their rehabilitation specialist. An able-bodied comparison subject was matched to each amputee. Match criteria were sex, age (⫾10y), social situation (living alone, living with a partner), and employment (yes, no; for amputees, the occupational status before amputation was the reference). Comparison subjects with impairments affecting activity level and/or physical strain were excluded. Comparison subjects were recruited from relatives of the participating amputees or from members of the hospital department. The study was approved by the medical ethics committee of University Hospital Rotterdam. All participants signed an informed consent form before measurements were taken. Protocol All participating subjects visited the hospital to receive study information and for placement of the activity monitor (recorder and sensors). They returned home, where they could continue their usual daily activities. Bathing, showering, and swimming were not allowed during the measurement period. Two days later— generally after about 50 hours—a researcher went to the subject’s house to detach the activity monitor and to perform additional measurements on reported limitations in daily functioning (FIM™ instrument, Locomotor Index [LMI]). Instruments and Data Analysis Activity monitor. The rationale for the activity monitor sensor configuration, the subsequent steps of the signal analysis, and the method of activity detection have been described in detail.23 The activity monitor is based on long-term ambulatory measurement of signals from body-fixed ADX202 acceleration sensors.a Uniaxial sensors (sensitive in anteroposterior [AP] direction while standing) were attached at the lateral side of each upper leg, at a level halfway between anterior superior iliac spine and upper side of the patella. A biaxial acceleration sensor was attached at the lower side of the sternum; while standing, the sensor is sensitive in AP direction and in longitudinal direction. The sensors were connected to the activity monitor recorder (15⫻9⫻3.5cm; weight, 500g).a The raw acceleration signals were stored digitally on a PCMCIA flash card with a sample frequency of 32Hz. An ECG (V5 bipolar lead, according to Mason-Likar) was simultaneously recorded on the same recorder, with a sample frequency of 128Hz. After the measurements, the raw signals were downloaded onto a personal computer for analysis. For the automatic detection of mobility-related activities, 3 feature signals are derived from each measured acceleration signal: a low-pass angular feature, a motility feature, and a frequency feature. Based on these features, and by using activity-specific settings in the analysis software and a minimal distance-based detection method, each second of the measure-
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ment, 1 activity from a set of mobility-related activities (static: lying, sitting, standing; dynamic: walking [including climbing stairs], cycling, noncyclic movements, transitions between postures) was automatically detected. The motility feature is the result of calculating the root mean square of the acceleration signal after band-pass filtering (0.3–16Hz, finite impulse response) and downscaling the sample frequency to 1Hz. Motility can be defined as the intensity of body segment movements, measured with accelerometry: the more “dynamic” an activity is, the more variable the accelerometer signals, and the higher the motility of these signals. The 4 motility signals were added and divided by 4, to obtain the body motility signal used in this study. A previous study showed that body motility is closely related to walking speed24 and that this relationship is independent of the walking pattern or efficiency.26 Of the total measurement period with the activity monitor, 48 hours were analyzed. The first hour of the measurement period was not included in the analysis to exclude effects of traveling and habituation to the instrument. The following variables were calculated for the 48-hour period: duration of dynamic activities and duration of walking (both as a percentage of a full day [24h]), mean body motility during walking, and number of sit-to-stand transitions per day. Heart rate was automatically detected from the electrocardiographic signal. The following measures were derived from the heart rate signal: resting heart rate (HRrest, determined from night periods), the absolute heart rate during walking (HRabs, from the last 10s of longer [⬎30s] walking periods), the normalized heart rate during walking (HRnorm, the difference between HRabs and HRrest), and percentage heart rate reserve (%HRR, HRnorm divided by the difference between the maximal heart rate [HRmax] and HRrest). HRmax was derived from the equation: HRmax⫽220⫺age (see, eg, Miller et al27). Because of the known effect of -blockers on heart rate,28-31 heart rate data of non–-blocker users only were used in the analysis. FIM instrument. The FIM instrument32,33 assesses level of independence in daily activities and has 6 domains: self-care, sphincter control, mobility and transfer, moving, communication, and social cognition. The FIM items were assessed by a rehabilitation specialist. For our study, the total (FIM total), the mobility (FIM mobility), and the moving (FIM moving) scores were used. Locomotor Index. The LMI was specifically developed for people with an amputation. The LMI is part of the Prosthetic Profile of the Amputee questionnaire.34,35 The LMI also covers the level of independence of a specific activity and was assessed by the same rehabilitation specialist. Statistics Nonparametric tests (Mann-Whitney U) were used to examine differences between the amputee and comparison groups. The Spearman rank correlation was used to study the relationships between variables. The statistical procedures were performed with SPSS, version 9.1,b for Windows. An ␣ value of .05 was set as the level of significance. RESULTS The characteristics of both groups are given in table 1. There were no significant differences between groups with respect to sex, age, employment, and social status. Three of the 9 persons with a transtibial amputation used -blockers. Amputees were significantly less active than the comparison subjects and walked significantly less (table 2). Body motility during walking was lower in the amputee group, which suggests that amputees walked slower. The difference between Arch Phys Med Rehabil Vol 85, February 2004
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Table 1: Characteristics of the Amputee and Comparison Subjects
Sex (M/F) Age (y) Time since amputation (mo) Time since last therapy session (mo) Use -blockers (yes/no) Work (yes/no) Social status (alone/partner)
Amputee Group
Comparison Group
8/1 55 (44–76) 16 (11–39)
8/1 61 (45–81)
12 (3–34) 3/6 3/6 4/5
0/9 3/6 4/5
NOTE. Values are n or median (range). Abbreviations: F, female; M, male.
groups in the number of sit-to-stand transitions was not significant. HRrest of the 6 amputees not using -blockers showed a tendency to be higher than HRrest of their comparison subjects (9.1bpm, P⫽.06) (table 3). The same phenomenon was found for the HRabs (10bpm, P⫽.15). However, when physical strain during walking was expressed as HRnorm or %HRR, the differences were considerably smaller and evidently not tending to significance. In the amputee group, a strong relationship was found between motility during walking and the percentage of the day that the subject walked (r⫽.88, P⫽.002; fig 1). No relationships were found between the percentage of the day amputees were active and the FIM total (r⫽.31, P⫽.42), FIM mobility (r⫽.58, P⫽.11), FIM moving (r⫽.42, P⫽.26), and LMI (r⫽.51, P⫽.16) scores. FIM and LMI scores were strongly related (r⫽.93, P⫽.00). DISCUSSION We studied the long-term impact of a transtibial amputation on activity level and heart rate response. To our knowledge, this is the first time that activity and physical strain parameters have been simultaneously and objectively measured in detail during normal daily life. Persons with a unilateral transtibial amputation for vascular disease were considerably less active than their able-bodied comparison subjects; a ratio of about 1:2.5 was found. Although this concurs with other studies12,13,17 and with the generally accepted assumption that persons with a vascular amputation are less active, this ratio has never before been provided for this specific group. This ratio does not depend only on data from the amputation group but also on data from the comparison group. Compared with other studies from our department also examining activity patterns of able-bodied subjects, data from the comparison subjects in our study (11.4%) were average; percentages of 11.3% and 12.7% were found previously.19,25 Thus the comparison group in our study was not an exceptionally highly active group.
Table 3: Data on Heart Rate Response Strain of the Amputee and Comparison Subjects
HRrest (bpm) HRabs (bpm) HRnorm (bpm) HRR (%)
Amputee Group
Comparison Group
P Value
69.3⫾9.2 101.5⫾7.7 32.2⫾15.9 34.4⫾16.9
60.2⫾7.8 91.5⫾12.7 31.3⫾10.2 31.6⫾9.2
.06 .15 .87 .87
NOTE. Values are mean ⫾ SD. P values are differences between groups.
In all physical activity measures, the differences between the 2 groups were significant, except for the number of sit-to-stand transitions. One explanation for this latter result is that individuals with an amputation do not have problems with these transfers or are unable to avoid these transfers in normal daily life. Another explanation is more statistical, that is, the variation in the number of sit-to-stand transitions between subjects was relatively large in both groups, so that the considerable between-group difference was not significant. Although not significant compared with the comparison subjects, HRrest tended to be higher in amputees. An elevated HRrest is often considered an indicator of poor health (eg, poor physical fitness)36,37; thus, it seems that our amputee group was less physically fit than the comparison group. This is in line with our expectations: all subjects in the amputee group had amputations because of vascular problems, which was not limited to the distal part of 1 leg. Data on the HRabs during walking seem to indicate that, for our subjects, the physical strain of walking with an amputation is higher than that for the comparison subjects. It has been reported that energy consumption is increased because of the lower efficiency of prosthetic walking.3,4,6-11 However, in our study, when the heart rate data were normalized—that is, corrected for HRrest— only small and nonsignificant differences were found. Therefore, in our view, the most logical and valid interpretation of the heart rate data in our study is that there was no difference in heart rate response during walking. This interpretation is in agreement with other reports: efficiency is assumed to be lower in persons with an amputation. By decreasing walking speed, the energy consumption (and heart rate) of a person with an amputation is similar to that of an able-bodied person.4-6,11 Another interesting finding of our study was the strong relationship in the amputee group between motility during walking and the percentage of the day that the amputee walked (see fig 1). This result suggests that amputees who walk faster also walk for a longer time during the day. Thus, there may be a double gain of an increased walking speed: it corresponds to a longer distance walked— because of the increased walking speed—and to a longer period of walking. However, another explanation may be that people who walk less mainly walk indoors, and people generally walk at a slower speed indoors than outdoors.
Table 2: Data on Physical Activity of the Amputee and Comparison Subjects
Dynamic activities (% of 24h) Walking (% of 24h) Sit-to-stand transitions (n/24h) Body motility during walking (g)
Amputee Group
Comparison Group
P Value
4.3⫾2.6 3.8⫾2.4 43.1⫾16.7 .113⫾.019
11.4⫾5.4 9.7⫾4.2 61.1⫾30.3 .145⫾.014
.007 .007 .20 .003
NOTE. Values are mean ⫾ standard deviation (SD). P values are differences between groups.
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a crucial influence seems not to be likely: the differences in heart rate response data were small, and the currently nonsignificant relationships may become significant but will probably remain weak. CONCLUSIONS The results indicate that persons with a unilateral transtibial amputation for vascular disease are considerably (factor 2.5) less active than matched comparison subjects. In our study, heart rate response during walking in the amputee group did not differ from the response in the comparison group. No relationships were found between the objectively measured activity level during normal daily life and FIM and LMI scores. Acknowledgment: We thank Geertjan Klein Haneveld and KaWing Tsang for their contribution in data collection and data analysis.
Fig 1. Relationship between motility during walking (related to walking speed) and percentage of walking during the 48-hour measurement period in the amputee group.
Newly developed objective activity instruments are sometimes validated by using data from questionnaires as reference, for example, by van Dam et al.17 Although such an approach seems logical, it has an important shortcoming: the fact that different aspects of functioning are measured is, at least partially, neglected. Van Dam reported significant relationships between “activity monitor” measures and functional and quality of life measures; but, in fact, only 3 of the 25 relationships were significant.17 Therefore, in our validation studies of the activity monitor, we considered analyzed video recordings as the best reference method. This line of reasoning is supported by the data of our study: no relationships were found between activity monitor measures and data from the questionnaires. Although this finding may partly be attributed to methodologic shortcomings—for example, significant relationships might have been found with a larger sample size—we believe that our data suggest that the lack of relationship is, at least partly, the result of differences in aspects of the functionality and activity that are measured. Both the FIM and the LMI focus mainly on the level of independence during functional activities, whereas the activity monitor focuses on the level of activities actually performed. Furthermore, the FIM and LMI are questionnaires, which are known to be subjectively influenced by both the subject and the researcher.38 Therefore, when an instrument is to be used in research or clinical practice, it is very important to consider the aspect of activity in which one is interested and the way that aspect can best be measured. Our study also has its limitations. First, it was specifically directed at persons with a unilateral, vascular transtibial amputation. One should, therefore, be careful in generalizing the results to other categories of amputees. For example, whether the results are also valid for people with an upper-leg amputation or for people with an amputation after trauma cannot yet be answered. Future research on other categories of amputees will have to elucidate whether a general mechanism exists. Second, in our study a relatively small sample size was used. The sample size proved to be adequate to show differences between the 2 groups for most activity parameters, but it may have played a role in the (nonsignificant) heart rate data and relationships between activity parameters. This fact must be considered when interpreting the results, but, on the other hand,
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Daily Physical Activity and Heart Rate Response in People With a Unilateral Transtibial Amputation for Vascular Disease Johannes B. Bussmann, PhD, Eleonore A. Grootscholten, MD, Henk J. Stam, PhD ABSTRACT. Bussmann JB, Grootscholten EA, Stam HJ. Daily physical activity and hear rate response in people with a unilateral transtibial amputation for vascular disease. Arch Phys Med Rehabil 2004;85:240-4. Objective: To study the activity level and heart rate response, objectively measured during normal daily life, of persons with a unilateral transtibial amputation for vascular disease. Design: Case comparison. Setting: General community, daily life in the Netherlands. Participants: Nine subjects with a unilateral transtibial amputation for vascular disease (convenience sample) and 9 control subjects without known impairments (matched for sex, age, social situation, employment). Interventions: Not applicable. Main Outcome Measures: Duration of dynamic activities, body motility (the intensity of body movement, measured with accelerometry), and heart rate (on 2 consecutive days). Results: Persons with an amputation were less active than the comparison subjects (4.3% vs 11.4% of a 48-h period, P⫽.007). Body motility during walking was lower in the amputee group (.111g vs. .147g, P⫽.003). No differences between groups were found in normalized heart rate during walking. In the amputee group, a strong relationship was found between body motility during walking and the percentage of the day that the subject walked (r⫽.88, P⫽.002). No relationship was found between the percentage of the day that persons with an amputation were active and data from disability questionnaires. Conclusion: Persons with a unilateral transtibial amputation for vascular disease were considerably less active than persons without known impairments. Heart rate response during walking of the amputee group did not differ from the response in the comparison group. Key Words: Amputation; Monitoring; Ambulatory; Physical exertion; Rehabilitation. © 2004 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation N A GLOBAL STUDY OF the incidence of lower-extremity age-adjusted major amputation rates ranged Ifromamputation, 3.7 to 58.7 per 100,000 men and from 0.5 to 32.0 per 100,000 women per year1; in the Netherlands, a rate of 18 to 20
From the Department of Rehabilitation Medicine, Erasmus MC, University Medical Center, Rotterdam, The Netherlands. Presented in part at the 1st World Congress of the International Society of Physical and Rehabilitation Medicine, July 8 –13, 2001, Amsterdam, The Netherlands. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Johannes B. Bussmann, Dept of Rehabilitation Medicine, Erasmus MC, PO Box 2040, 3000 CA Rotterdam, The Netherlands, e-mail: [email protected]. 0003-9993/04/8502-8065$30.00/0 doi:10.1016/S0003-9993(03)00485-4
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per 100,000 persons has been reported.2 After amputation, persons frequently follow a rehabilitation program aimed at optimal functioning with a prosthesis during normal daily life. An important consequence of an amputation is that walking with a prosthesis is less energy efficient, which may result in increased physical strain (expressed as heart rate response or oxygen consumption) during walking.3-11 Another adaptation strategy may be that strenuous activities such as walking are avoided12,13 or that the performance of activities is changed to decrease physical strain.4-6,11 For example, fewer and shorter walking periods and walking slower may counterbalance the decreased efficiency and may result in a comparable or even lower heart rate response and energy cost than in subjects without known impairments. To provide optimal treatment, reliable and valid information about activity level and physical strain during daily life is important. Such information is mostly obtained by means of interviews, questionnaires, and diaries, all of which are based on subjective data from the patient. Gait analysis in a gait laboratory is used to obtain more quantitative and objective data, but these data cannot simply be generalized to actual behavior during normal daily life. Therefore, several studies report the development and use of more objective instruments in persons with an amputation that can be used outside a gait lab. For example, Holden and Fernie14 used an electronic step counter to assess prosthetic use. Stam et al15 developed a similar type of apparatus to assess walking periods during a 7-day measurement period. Armstrong et al16 used an activity monitor to evaluate the activity level of persons at high risk for foot amputation, and the same was done by van Dam et al17 in persons after surgery for a malignant tumor in the leg. However, detailed, combined, and methodologically sound data are still lacking about daily physical activity and physical strain in persons with a unilateral transtibial amputation for vascular disease and about the effect of such amputation on daily physical activity and physical strain. In 1998, Bussmann et al18 reported on the reliability and validity of an accelerometry-based activity monitor in persons with an amputation of the leg. A high percentage of agreement was found between activity monitor output (the automatic detection of mobility-related activities, ie, postures and motions) and analyzed video recordings. Since then, the activity monitor has been validated in several populations, further developed, and applied in several types of research.19-25 Because electrocardiograms (ECGs) can be simultaneously measured with the acceleration signals, the activity monitor allows measurement of both physical activities and heart rate response during normal daily life. The aim of our study was to examine whether, and if so to what extent, people with a unilateral transtibial amputation for vascular disease are less active than persons without known impairments, and whether, and if so to what extent, heart rate response during walking is increased in persons with a unilateral transtibial amputation for vascular disease. Additionally, the relationships between the activity parameters as provided by the activity monitor, on the one hand, and subjective disability measures, on the other, were examined.
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METHODS Participants Our study included 9 persons with an amputation of the lower leg and 9 matched able-bodied comparison subjects. The sample size was based on power analysis by using activity monitor data of a previous study with other subjects as reference.19 Amputees were recruited from patient files of the departments of rehabilitation medicine of Erasmus MC and Zuiderziekenhuis. Inclusion criteria were transtibial amputation, older than 40 years of age, amputation of vascular origin, current use of prosthesis, completion of a rehabilitation program, last treatment less than 3 years before study, and ability to understand and complete the questionnaires. Persons with a bilateral amputation were excluded. Amputees were invited to participate in the study by their rehabilitation specialist. An able-bodied comparison subject was matched to each amputee. Match criteria were sex, age (⫾10y), social situation (living alone, living with a partner), and employment (yes, no; for amputees, the occupational status before amputation was the reference). Comparison subjects with impairments affecting activity level and/or physical strain were excluded. Comparison subjects were recruited from relatives of the participating amputees or from members of the hospital department. The study was approved by the medical ethics committee of University Hospital Rotterdam. All participants signed an informed consent form before measurements were taken. Protocol All participating subjects visited the hospital to receive study information and for placement of the activity monitor (recorder and sensors). They returned home, where they could continue their usual daily activities. Bathing, showering, and swimming were not allowed during the measurement period. Two days later— generally after about 50 hours—a researcher went to the subject’s house to detach the activity monitor and to perform additional measurements on reported limitations in daily functioning (FIM™ instrument, Locomotor Index [LMI]). Instruments and Data Analysis Activity monitor. The rationale for the activity monitor sensor configuration, the subsequent steps of the signal analysis, and the method of activity detection have been described in detail.23 The activity monitor is based on long-term ambulatory measurement of signals from body-fixed ADX202 acceleration sensors.a Uniaxial sensors (sensitive in anteroposterior [AP] direction while standing) were attached at the lateral side of each upper leg, at a level halfway between anterior superior iliac spine and upper side of the patella. A biaxial acceleration sensor was attached at the lower side of the sternum; while standing, the sensor is sensitive in AP direction and in longitudinal direction. The sensors were connected to the activity monitor recorder (15⫻9⫻3.5cm; weight, 500g).a The raw acceleration signals were stored digitally on a PCMCIA flash card with a sample frequency of 32Hz. An ECG (V5 bipolar lead, according to Mason-Likar) was simultaneously recorded on the same recorder, with a sample frequency of 128Hz. After the measurements, the raw signals were downloaded onto a personal computer for analysis. For the automatic detection of mobility-related activities, 3 feature signals are derived from each measured acceleration signal: a low-pass angular feature, a motility feature, and a frequency feature. Based on these features, and by using activity-specific settings in the analysis software and a minimal distance-based detection method, each second of the measure-
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ment, 1 activity from a set of mobility-related activities (static: lying, sitting, standing; dynamic: walking [including climbing stairs], cycling, noncyclic movements, transitions between postures) was automatically detected. The motility feature is the result of calculating the root mean square of the acceleration signal after band-pass filtering (0.3–16Hz, finite impulse response) and downscaling the sample frequency to 1Hz. Motility can be defined as the intensity of body segment movements, measured with accelerometry: the more “dynamic” an activity is, the more variable the accelerometer signals, and the higher the motility of these signals. The 4 motility signals were added and divided by 4, to obtain the body motility signal used in this study. A previous study showed that body motility is closely related to walking speed24 and that this relationship is independent of the walking pattern or efficiency.26 Of the total measurement period with the activity monitor, 48 hours were analyzed. The first hour of the measurement period was not included in the analysis to exclude effects of traveling and habituation to the instrument. The following variables were calculated for the 48-hour period: duration of dynamic activities and duration of walking (both as a percentage of a full day [24h]), mean body motility during walking, and number of sit-to-stand transitions per day. Heart rate was automatically detected from the electrocardiographic signal. The following measures were derived from the heart rate signal: resting heart rate (HRrest, determined from night periods), the absolute heart rate during walking (HRabs, from the last 10s of longer [⬎30s] walking periods), the normalized heart rate during walking (HRnorm, the difference between HRabs and HRrest), and percentage heart rate reserve (%HRR, HRnorm divided by the difference between the maximal heart rate [HRmax] and HRrest). HRmax was derived from the equation: HRmax⫽220⫺age (see, eg, Miller et al27). Because of the known effect of -blockers on heart rate,28-31 heart rate data of non–-blocker users only were used in the analysis. FIM instrument. The FIM instrument32,33 assesses level of independence in daily activities and has 6 domains: self-care, sphincter control, mobility and transfer, moving, communication, and social cognition. The FIM items were assessed by a rehabilitation specialist. For our study, the total (FIM total), the mobility (FIM mobility), and the moving (FIM moving) scores were used. Locomotor Index. The LMI was specifically developed for people with an amputation. The LMI is part of the Prosthetic Profile of the Amputee questionnaire.34,35 The LMI also covers the level of independence of a specific activity and was assessed by the same rehabilitation specialist. Statistics Nonparametric tests (Mann-Whitney U) were used to examine differences between the amputee and comparison groups. The Spearman rank correlation was used to study the relationships between variables. The statistical procedures were performed with SPSS, version 9.1,b for Windows. An ␣ value of .05 was set as the level of significance. RESULTS The characteristics of both groups are given in table 1. There were no significant differences between groups with respect to sex, age, employment, and social status. Three of the 9 persons with a transtibial amputation used -blockers. Amputees were significantly less active than the comparison subjects and walked significantly less (table 2). Body motility during walking was lower in the amputee group, which suggests that amputees walked slower. The difference between Arch Phys Med Rehabil Vol 85, February 2004
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Table 1: Characteristics of the Amputee and Comparison Subjects
Sex (M/F) Age (y) Time since amputation (mo) Time since last therapy session (mo) Use -blockers (yes/no) Work (yes/no) Social status (alone/partner)
Amputee Group
Comparison Group
8/1 55 (44–76) 16 (11–39)
8/1 61 (45–81)
12 (3–34) 3/6 3/6 4/5
0/9 3/6 4/5
NOTE. Values are n or median (range). Abbreviations: F, female; M, male.
groups in the number of sit-to-stand transitions was not significant. HRrest of the 6 amputees not using -blockers showed a tendency to be higher than HRrest of their comparison subjects (9.1bpm, P⫽.06) (table 3). The same phenomenon was found for the HRabs (10bpm, P⫽.15). However, when physical strain during walking was expressed as HRnorm or %HRR, the differences were considerably smaller and evidently not tending to significance. In the amputee group, a strong relationship was found between motility during walking and the percentage of the day that the subject walked (r⫽.88, P⫽.002; fig 1). No relationships were found between the percentage of the day amputees were active and the FIM total (r⫽.31, P⫽.42), FIM mobility (r⫽.58, P⫽.11), FIM moving (r⫽.42, P⫽.26), and LMI (r⫽.51, P⫽.16) scores. FIM and LMI scores were strongly related (r⫽.93, P⫽.00). DISCUSSION We studied the long-term impact of a transtibial amputation on activity level and heart rate response. To our knowledge, this is the first time that activity and physical strain parameters have been simultaneously and objectively measured in detail during normal daily life. Persons with a unilateral transtibial amputation for vascular disease were considerably less active than their able-bodied comparison subjects; a ratio of about 1:2.5 was found. Although this concurs with other studies12,13,17 and with the generally accepted assumption that persons with a vascular amputation are less active, this ratio has never before been provided for this specific group. This ratio does not depend only on data from the amputation group but also on data from the comparison group. Compared with other studies from our department also examining activity patterns of able-bodied subjects, data from the comparison subjects in our study (11.4%) were average; percentages of 11.3% and 12.7% were found previously.19,25 Thus the comparison group in our study was not an exceptionally highly active group.
Table 3: Data on Heart Rate Response Strain of the Amputee and Comparison Subjects
HRrest (bpm) HRabs (bpm) HRnorm (bpm) HRR (%)
Amputee Group
Comparison Group
P Value
69.3⫾9.2 101.5⫾7.7 32.2⫾15.9 34.4⫾16.9
60.2⫾7.8 91.5⫾12.7 31.3⫾10.2 31.6⫾9.2
.06 .15 .87 .87
NOTE. Values are mean ⫾ SD. P values are differences between groups.
In all physical activity measures, the differences between the 2 groups were significant, except for the number of sit-to-stand transitions. One explanation for this latter result is that individuals with an amputation do not have problems with these transfers or are unable to avoid these transfers in normal daily life. Another explanation is more statistical, that is, the variation in the number of sit-to-stand transitions between subjects was relatively large in both groups, so that the considerable between-group difference was not significant. Although not significant compared with the comparison subjects, HRrest tended to be higher in amputees. An elevated HRrest is often considered an indicator of poor health (eg, poor physical fitness)36,37; thus, it seems that our amputee group was less physically fit than the comparison group. This is in line with our expectations: all subjects in the amputee group had amputations because of vascular problems, which was not limited to the distal part of 1 leg. Data on the HRabs during walking seem to indicate that, for our subjects, the physical strain of walking with an amputation is higher than that for the comparison subjects. It has been reported that energy consumption is increased because of the lower efficiency of prosthetic walking.3,4,6-11 However, in our study, when the heart rate data were normalized—that is, corrected for HRrest— only small and nonsignificant differences were found. Therefore, in our view, the most logical and valid interpretation of the heart rate data in our study is that there was no difference in heart rate response during walking. This interpretation is in agreement with other reports: efficiency is assumed to be lower in persons with an amputation. By decreasing walking speed, the energy consumption (and heart rate) of a person with an amputation is similar to that of an able-bodied person.4-6,11 Another interesting finding of our study was the strong relationship in the amputee group between motility during walking and the percentage of the day that the amputee walked (see fig 1). This result suggests that amputees who walk faster also walk for a longer time during the day. Thus, there may be a double gain of an increased walking speed: it corresponds to a longer distance walked— because of the increased walking speed—and to a longer period of walking. However, another explanation may be that people who walk less mainly walk indoors, and people generally walk at a slower speed indoors than outdoors.
Table 2: Data on Physical Activity of the Amputee and Comparison Subjects
Dynamic activities (% of 24h) Walking (% of 24h) Sit-to-stand transitions (n/24h) Body motility during walking (g)
Amputee Group
Comparison Group
P Value
4.3⫾2.6 3.8⫾2.4 43.1⫾16.7 .113⫾.019
11.4⫾5.4 9.7⫾4.2 61.1⫾30.3 .145⫾.014
.007 .007 .20 .003
NOTE. Values are mean ⫾ standard deviation (SD). P values are differences between groups.
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a crucial influence seems not to be likely: the differences in heart rate response data were small, and the currently nonsignificant relationships may become significant but will probably remain weak. CONCLUSIONS The results indicate that persons with a unilateral transtibial amputation for vascular disease are considerably (factor 2.5) less active than matched comparison subjects. In our study, heart rate response during walking in the amputee group did not differ from the response in the comparison group. No relationships were found between the objectively measured activity level during normal daily life and FIM and LMI scores. Acknowledgment: We thank Geertjan Klein Haneveld and KaWing Tsang for their contribution in data collection and data analysis.
Fig 1. Relationship between motility during walking (related to walking speed) and percentage of walking during the 48-hour measurement period in the amputee group.
Newly developed objective activity instruments are sometimes validated by using data from questionnaires as reference, for example, by van Dam et al.17 Although such an approach seems logical, it has an important shortcoming: the fact that different aspects of functioning are measured is, at least partially, neglected. Van Dam reported significant relationships between “activity monitor” measures and functional and quality of life measures; but, in fact, only 3 of the 25 relationships were significant.17 Therefore, in our validation studies of the activity monitor, we considered analyzed video recordings as the best reference method. This line of reasoning is supported by the data of our study: no relationships were found between activity monitor measures and data from the questionnaires. Although this finding may partly be attributed to methodologic shortcomings—for example, significant relationships might have been found with a larger sample size—we believe that our data suggest that the lack of relationship is, at least partly, the result of differences in aspects of the functionality and activity that are measured. Both the FIM and the LMI focus mainly on the level of independence during functional activities, whereas the activity monitor focuses on the level of activities actually performed. Furthermore, the FIM and LMI are questionnaires, which are known to be subjectively influenced by both the subject and the researcher.38 Therefore, when an instrument is to be used in research or clinical practice, it is very important to consider the aspect of activity in which one is interested and the way that aspect can best be measured. Our study also has its limitations. First, it was specifically directed at persons with a unilateral, vascular transtibial amputation. One should, therefore, be careful in generalizing the results to other categories of amputees. For example, whether the results are also valid for people with an upper-leg amputation or for people with an amputation after trauma cannot yet be answered. Future research on other categories of amputees will have to elucidate whether a general mechanism exists. Second, in our study a relatively small sample size was used. The sample size proved to be adequate to show differences between the 2 groups for most activity parameters, but it may have played a role in the (nonsignificant) heart rate data and relationships between activity parameters. This fact must be considered when interpreting the results, but, on the other hand,
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Suppliers a. Adapted by TEMEC Instruments, PO Box 3011, 6460 HA Kerkrade, the Netherlands. b. SPSS Inc, 233 S Wacker Dr, 11th Fl, Chicago, IL 60606.