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Estimating Energy Expenditure for Different Assistive Devices in the School Setting

Lephart, Kim PT, DPT, MBA, PCS; Utsey, Carolyn PT, PhD; Wild, Dana L. PT, PhD, PCS; Fisher, Steve R. PT, PhD

doi: 10.1097/PEP.0000000000000047
Case Report

Purpose: This case report describes a simple means of estimating energy costs for a child with cerebral palsy using different assistive devices within a school setting.

Key Points: A 9-year-old boy, Gross Motor Function Classification Scale level III, was assessed over 8 ambulation trials using a posterior walker and using forearm crutches. Each trial was followed by a fine motor accuracy task. An energy expenditure index (EEI) was calculated for each device. For the posterior walker, EEI was 47% higher overall compared with forearm crutches. Fine motor accuracy and task completion time were similar for both devices.

Conclusion: EEI was a straightforward method of estimating the energy costs of different assistive devices. Measurement procedures described in this case were time efficient in the field and provided a reasonable estimation of energy expenditure to help decide objectively which assistive device would best fit the needs of the student.

Video Abstract: For more insights from the authors, see Supplemental Digital Content 1, available at

Supplemental Digital Content is Available in the Text.Measurement procedures described in this case report were time efficient in the field and provided a reasonable estimation of energy expenditure to help decide objectively which assistive device would best fit the needs of the student.

Physical Therapy Department, University of Texas, Medical Branch, Galveston, Texas.

Correspondence: Kim Lephart, PT, MBA, 924 Langdale Court, Culpeper, VA 22701 (

At the time this article was written, Kim Lephart was a tDPT student at the University of Texas, Medical Branch Galveston, Texas.

Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Web site (

The authors declare no conflicts of interest.

Children with cerebral palsy (CP) spend 2 to 3 times more energy when walking in comparison with children of the same age who are not disabled.1–5 This increased energy expenditure, sometimes called energy costs, accounts for an added tendency for children with CP to fatigue at low walking velocities and may affect their academic performance.3,6 A goal of school-based physical therapy is to assist students in being as functionally independent as possible while identifying means for each student to conserve energy to concentrate on their academic tasks and achieve their individualized educational plan (IEP) goals.7 Assistive devices are frequently used to accomplish this objective. Physical therapists in schools are often responsible for making clinical decisions regarding which assistive devices are most appropriate and energy-efficient for their students.

Several methods are available to determine energy expenditure. Double-labeled water and indirect and direct calorimetry are considered the “reference standard” but are expensive and not practical for use in the school setting.8 Other techniques, including activity logs, questionnaires, heart rate, or accelerometers, are less expensive and less technically demanding.5,9–13 These less expensive and more accessible energy expenditure estimation techniques are better suited for the school setting and can provide useful information to inform the clinician's decision making.

One such technique, as studied by Rose and associates,4 uses an energy expenditure index (EEI) based on oxygen uptake and heart rate. The EEI is calculated by subtracting the resting heart rate from the postwalking heart rate and by dividing the difference by the walking speed. Johnston et al5 found that heart rate was an accurate measure of energy expenditure in children with CP. Though not the “reference standard,” EEI is easily obtained in the field,4 and is a reasonable measure of energy expenditure in the school setting. The EEI, in combination with other considerations such as posture and safety, can provide school-based physical therapists with objective data to more accurately evaluate assistive devices.

Understanding energy costs is important for clinical decision making related to assistive devices.14 Several types of assistive devices are available and commonly used in school settings, including posterior walkers, forward walkers, quad-based canes, and crutches. Decisions to recommend a posterior walker versus a forward walker have been based on studies that found that the use of a posterior walker resulted in an upright posture and more energy efficient walking for children with CP.14 These results are refuted by Mattsson and Andersson,15 who found no difference in energy cost in children with CP between the 2 walker designs. However, a posterior walker has an added safety benefit of allowing the child to use protective extension should he or she fall forward.

Rose et al16 investigated the energy cost of using a wheeled walker versus bilateral quad canes in 12 children with quadriplegic or diplegic spastic CP. Some children had less energy expended with quad canes and other children had less energy expenditure with forward walkers.16 Other researchers have examined the energy cost associated with ambulating with axillary crutches versus a forward walker.17 Although that study included adults, they suggested that less energy was expended while ambulating with crutches, and these results may be applicable to school-aged children with CP.

Physical therapists working in schools have the responsibility to understand the amount of energy a child with CP may expend when ambulating in school using an assistive device. Franks and colleagues18 found that increased energy expenditure when ambulating with an assistive device might have potentially negative effects on certain aspects of educational performance, especially visual motor accuracy as measured by fine motor tasks. The purpose of this case report is to describe the use of a clinical measurement procedure to estimate energy costs of different assistive devices within the school setting in a child with spastic diplegic CP.

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The child was a 9-year-old boy in the fourth grade with a diagnosis of spastic diplegic CP, level III on the Gross Motor Function Classification Scale, who was left handed. He underwent selective dorsal rhizotomy 3 years prior to this examination of energy expenditure and started the school year using a posterior walker and bilateral ankle-foot orthoses. No comorbidities or intellectual impairments were noted. The student functioned in a regular fourth-grade class with weekly special education support for assistance with organization.

The family's goal was for him to use his forearm crutches at school as well as at home. The student preferred to use the forearm crutches in school as he stated that “it is the next step, because then comes walking without crutches.” Teachers reported that the student often appeared fatigued, frequently resting his head on the desk, and was unable to complete his academic workload after ambulating with his forearm crutches. Thus, teachers preferred that he use his posterior walker. The student received monthly consultative school-based occupational therapy to address his IEP goal of producing legible written work within the fourth-grade parameters. He demonstrated difficulty with fine motor tasks, specifically writing activities, and in the past had used a slant board and weighted pencil to accommodate. At the time of this report, the student refused to use these accommodations, as he did not want to appear to be different with respect to his peers. The student did use the accommodation of shortened writing assignments, as when fatigued with writing, his penmanship became illegible.

Although the student had difficulty with writing tasks, he was independent with dressing and hygiene related to toileting. He received monthly consultative school-based physical therapy to address his IEP goal of exiting the school building to a designated area, a distance of approximately 400 ft, while keeping pace with his peers, within the allotted time required by the school division. At the time of this case report, the student used forearm crutches and ankle-foot orthoses to access his school environment and a posterior walker during physical education, recess, and toileting activities.

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Given the student's preference for forearm crutches and the teacher's preference for him to use his walker, the physical therapist sought objective data to support the decision regarding which assistive device would be more energy efficient and allow the student increased participation in educational tasks. The primary outcome measure chosen for this determination was the EEI.4 Secondary measures included the Pictorial Children's Effort Rating Table (PCERT),19 Distal Finger Control Task20 (a fine motor accuracy task), and 55-m walk time.

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This case report focused on 4 outcome measures, the EEI, PCERT, Distal Finger Control Task, and time to walk 55 m, selected to measure the student's effort through using quantitative and qualitative measures of exertion. The EEI is a method to quantify and compare walking energy expenditure in the field for children and adolescents, and it is calculated according to the protocol put forth by Rose et al.4 Briefly, EEI is determined by subtracting resting heart from the heart rate obtained after a 55-m walk at a comfortable pace and then dividing the sum by walking speed for the 55 m (postwalking heart rate − resting heart rate / walking speed). The EEI has a reliability coefficient ranging from greater than 0.81 to 0.94 at comfortable and fast walking speeds.21,22 Researchers have demonstrated concurrent validity of EEI and oxygen consumption of children with CP (r = 0.61),12,13 making this outcome measure potentially valuable in determining energy costs when the student ambulates with different assistive devices. The student's average resting heart rate was 81.75 ± 4.61 beats per minute; he was not being treated with any medications that could interfere with heart rate measurement; and he expressed appropriate understanding of the testing procedure.

The PCERT is a quick and efficient visual analog scale used to rate perceived exertion intensity level.19 Scores range from 1 to 10, with higher scores indicating increased difficulty completing the activity due to the effort required. The PCERT test-retest reliability has an ICC of 0.77 with concurrent and construct validity promoting its use among children aged 9 to 15 years,19,23 as such, the PCERT was deemed suitable as an outcome measure for this student. The student's resting PCERT score was 1, suggesting that he understood the concept of the test and could appropriately report.

The teacher was concerned that the student could not keep up with written tasks when using his forearm crutches and 1 of his IEP goals was legibility of his writing; therefore, a fine motor accuracy task was chosen as an additional outcome measure. The Distal Finger Control Task assesses fine motor accuracy using outlined circles of graduated sizes (1/4″–5/8″) within which the student must complete a loop. It is frequently used by occupational therapists in the school setting to determine fine motor accuracy.20 Scores range from 0 to 42 points with higher scores for better performance. He was able to manipulate all task components and expressed an understanding of the test procedure.

The second IEP goal was for the student to keep pace with his peers when evacuating the school building during fire drills. Therefore, the time taken to complete the 55-m walk was used as an additional outcome measure. Based on these examination data, the measurement procedures were considered appropriate for the student

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The outcome measures EEI, PCERT, Distal Finger Control Task, and 55-m walk time were used to inform objectively the physical therapist which assistive device would be most appropriate for the student. Should an assistive device require less energy expenditure, then that device would be preferred to conserve the student's energy for educational tasks. One of the student's IEP goals was to keep pace with his peers. Should results indicate that the student could ambulate faster with a specific assistive device, then that assistive device would be appropriate to assist the student in achieving his IEP goal. Another of the student's IEP goals was to write legibly. Should the results demonstrate that an assistive device had a lesser effect on the legibility or accuracy of the fine motor task, then that assistive device would be more appropriate in assisting the student to achieve his IEP goal. In the event of a conflict between the different outcome measures indicating which assistive device would best to assist the student to achieve his IEP goals, the student's preference for an assistive device would balance the physical therapist's decision.

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The student participated in 8 sessions of 2 ambulation trials, for a total of 16 trials. The EEI was calculated for each trial, for each assistive device. The student walked first with the posterior walker for all odd numbered sessions. He walked first with the forearm crutches for all even numbered sessions. After each trial, when the student's heart rate returned to his resting heart rate, he completed the Distal Finger Control Task.20 This information was used to ascertain whether the assistive device affected his fine motor skills, as suggested by Franks et al.18

For each of the 16 trials, the student ambulated 55 m at a self-selected pace using a posterior walker or forearm crutches. Time to complete the 55 m was recorded in seconds (to the nearest 0.01 second) using a hand-held stop watch. The assistive device used first for each session was alternated for each trial. For session 1, he first used a posterior walker followed by forearm crutches. Between each trial, he rested for at least 3 minutes, until his heart rate was within ±5 beats per minute of his initial resting heart rate.4 Resting heart rate was assessed while sitting and standing using a digital fingertip pulse oximeter (Beijing Choice Electronic Tech. Co). Postwalking heart rate was assessed immediately following the 55-m walk using the digital fingertip pulse oximeter. At the end of each walking trial, the student pointed to or said the corresponding numerical value to rate his exertion level on the PCERT. The sessions took place over a 5-week period, with 2 sessions per week and at least 1 day of rest between sessions.

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Mean EEI for the forearm crutches across 8 trials was 0.48 ± 0.22 beats per meter. Mean EEI for the posterior walker was 0.66 ± 0.33 beats per meter. EEI for the posterior walker was overall 47% higher compared to forearm crutches. According to Rose et al,4 an EEI of 0.71 ± 0.32 beats per meter demonstrates increased energy expenditure or poor economy, whereas an EEI of 0.47 ± 0.31 beats per meter demonstrates decreased energy expenditure or maximum economy. Figure 1 shows EEI for the 8 sessions with the posterior walker and forearm crutches. The figure shows a generally decreased EEI for 5 of 8 trials using the forearm crutches.

Fig. 1

Fig. 1

The mean PCERT for forearm crutches was 1.69 ± 0.88; the mean PCERT for the posterior walker was 1.56 ± 0.73. Figure 2 shows the PCERT scores for the posterior walker and forearm crutches across each of the 3 sessions. In 3 of 8 sessions (38%), he reported exerting the same amount of energy for both assistive devices. In addition, for 50% of the trials, the student believed that he put more effort into walking during the second ambulation trial, regardless of which assistive device was used.

Fig. 2

Fig. 2

The mean score on the Distal Finger Control Task for forearm crutches was 25.0 ± 2.45; the mean for the posterior walker was 27.5 ± 4.28. Figure 3 shows the Fine Motor Scores across all 8 sessions; for 10 of 16 trials (62.5%), fine motor accuracy was higher after ambulating with the posterior walker. For 4 of 16 trials (25%), fine motor accuracy scores were the same for both the posterior walker and the forearm crutches.

Fig. 3

Fig. 3

The mean time to complete the Distal Finger Control Task following the use of forearm crutches was 212.13 ± 20.57 seconds. The mean time for the posterior walker was 214.0 ± 46 seconds. After the student ambulated with the posterior walker, he took less time to complete the fine motor task in 5 of the 8 sessions (62.5%). Figure 4 shows time to complete task across each trial. The student was observed to rest his head on his right arm while completing the test with his left hand. He appeared to do this to stabilize his trunk, as he only had to control his left wrist and fingers. This was the behavior his teachers frequently noted and reported as “fatigue.”

Fig. 4

Fig. 4

The mean walking time over the 55 m for the forearm crutches was 65.98 ± 5.68 seconds; mean walking time for the posterior walker was 63.11 ± 5.90 seconds. Overall, it took 2.87 seconds or 4.4% longer for the student to ambulate the 55 m using his forearm crutches compared with the posterior walker. Although ambulating 55 m with 2 seconds variability is not clinically significant, when extrapolated for a student required to change classes frequently or walk more than 55 m, this time difference may become important.

For this student, one of his IEP goals focused on the distance traveled (400 ft); as such, forearm crutches would likely be the most appropriate assistive device as they conserved the most energy. Another important consideration is this student's preference for using the forearm crutches as he felt crutches were more socially acceptable than his posterior walker.

Although the differences in walking time and fine motor activity could potentially be important, on the basis of these data, the decision was made to recommend forearm crutches. The therapist decided that the lower energy cost should be less fatiguing and would ultimately allow the student increased participation in educational tasks. This decision also took into consideration the student's preferences.

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Physical therapists choose assistive devices within the school setting on the basis of safety, the school environment, energy-level requirements, and the psychosocial effect of the device, with the ultimate goal for the student to fully and successfully participate in his educational program. This case report describes a clinically efficient means of estimating energy costs of 2 different assistive devices within the school setting for a 9-year-old student with spastic diplegic CP. The EEI and PCERT were found to be straightforward and useful ways for physical therapists working in schools to compare the energy costs of 2 different assistive devices. In this case, forearm crutches required less energy expenditure than the posterior walker.

These findings are in accord with previous research concluding that interventions focused on improving biomechanics can decrease the energy cost of ambulation in a child with CP.6 Although little change was reported for the PCERT, it did provide important feedback about the student's feelings of exertion with each trial.

Franks et al18 investigated children with spina bifida and not children with CP and found that increased energy consumption when walking with assistive devices might have a possible adverse effect on fine motor accuracy. They compared assistive devices used for walking and wheelchairs. In our case, the student performed better on the fine motor accuracy task in 5 of 8 sessions (62.5%) with the posterior walker, which had a higher energy cost, compared with forearm crutches. Yet, the overall differences in fine motor accuracy between the posterior walker and forearm crutches were small.

He also ambulated several seconds faster, using the posterior walker compared with forearm crutches. During the school year when this report was developed, the student used both assistive devices during the day; in previous school years, he used the posterior walker exclusively. Park et al14 suggested that increased familiarity with a posterior walker often accounts for faster walking time with this assistive device.

This case report has limitations. While our EEI findings are consistent with the literature, caution should be exercised when using the EEI, as heart rate can be influenced by external factors such as emotional stress10 and the student's age.24 For example, Furukawa et al24 found that deterioration of walking endurance in children with CP as they age may be due to difficulty with walking coordination and stability from joint deformity, spasm, or muscle weakness as opposed to a reduction of pulmonary-cardiac function. This limitation is naturally mitigated when testing single subjects over short time periods, but further consideration should be given to the effect of age when comparing results of multiple subjects over an extended period.

Although the fine motor accuracy task allows clinicians to determine how the use of an assistive device can potentially affect a student's academic performance, a more sensitive fine motor accuracy test may be necessary to assist in further defining the effect a specific assistive device could have on a student's fine motor accuracy. Finally, some scores for the measures used in this case were not markedly different between the 2 assistive devices. The information the measures provided was, nevertheless, helpful in the field for supporting a frequently encountered clinical decision. We believe that this particular approach can be useful in the school setting for adding objectivity to what can sometimes be a subjective endeavor. Further study of a student's fatigue with an assistive device after several consecutive trials of walking could also help pediatric physical therapists determine the effect of endurance with an assistive device on a student's participation in his educational program.

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Physical therapists generally accept that it is appropriate for a student to use an assistive device requiring the least amount of energy5,14,16 so they can more fully participate in the school environment. School-based therapists should be cognizant that ambulating with an assistive device may have potentially negative effects on certain aspects of a student's educational performance, including fine motor accuracy tasks. This case report demonstrates that the EEI and PCERT are time-efficient, effective in the field, and are reasonable measures of energy expenditure in the school setting to objectively decide which assistive device would best fit the needs of a student.

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The authors thank the student, family, teachers, and the school that graciously agreed to participate in this case report. We also thank Derek Thrall and Elizabeth Manus for their review of this manuscript.

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ambulation; assistive devices; case report; cerebral palsy; child; energy expenditure

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