Role of mechanical power estimates in the O2 cost of walking in children with cerebral palsy

Heart rate responses, agreement and accuracy among persons with severe disabilities participating in the indirect movement program: Team Twin-an observational study

Introduction

Heart rate (HR) monitors are rarely used by people living with disabilities (PLWD), and their accuracy is undocumented. Thus, this study aims to describe the HR response during the Team Twin co-running program and, secondly, to assess the agreement and accuracy of using HR monitors among PLWD.

Methods

This 16-week single-arm observational study included 18 people with various disabilities. During the study, the subjects wore a Garmin Vivosmart 4 watch (wrist). To evaluate the agreement and accuracy we applied Garmin's HRM-DUAL™ chest-worn HR monitors for comparison with the Vivosmart 4. The HR response analysis was performed descriptively and with a mixed regression model. The HR agreement and accuracy procedure was conducted on a subsample of five subjects and analyzed using Lin's concordance analysis, Bland and Altman's limits of agreement, and Cohen's kappa analysis of intensity zone agreement. This study was prospectively registered at Clinical Trials.gov (NCT04536779).

Results

The subjects had a mean age of 35 (±12.6), 61% were male, 72% had cerebral palsy were 85% had GMFCS V-IV. HR was monitored for 202:10:33 (HH:MM:SS), with a mean HR of 90 ± 17 bpm during training and race. A total of 19% of the time was spent in intensity zones between light and moderate (30%-59% HR reserve) and 1% in vigorous (60%-84% HR reserve). The remaining 80% were in the very light intensity zone (<29% HR reserve). HR was highest at the start of race and training and steadily decreased. Inter-rater agreement was high (k = 0.75), limits of agreement were between -16 and 13 bpm, and accuracy was acceptable (Rc = 0.86).

Conclusion

Disability type, individual, and contextual factors will likely affect HR responses and the agreement and accuracy for PLWD. The Vivosmart 4, while overall accurate, had low precision due to high variability in the estimation. These findings implicate the methodical and practical difficulties of utilizing HR monitors to measure HR and thus physical activity in adapted sports activities for severely disabled individuals.

Effect of Lower Extremity Muscle Strength on Aerobic Capacity in Adults with Cerebral Palsy

The purpose of this study is to analyze the effect of lower extremity muscle strength of HIP joint and KNEE joint on the aerobic capacity to provide the basic data for developing an exercise program that can effectively improve the aerobic capacity of adults with cerebral palsy (CP) by identifying the part of the lower extremity muscle. A total of 18 ambulant adults with CP were recruited for this study. Seven ambulant adults with CP were excluded because they did not achieve the criteria of maximal exercise. The data from 11 subjects (11 men) with CP were used for the analysis. The mean (±SD) age, height, weight, and BMI of the subjects were 37.00 ± 12.72 years, 170.45 ± 6.37 cm, 67.02 ± 8.62 kg, and 23.09 ± 2.78 kg/m2, respectively. To measure the muscle strength of HIP joint and KNEE joint in lower extremities, the variables of the isokinetic muscle strength and the muscular endurance were performed using the isokinetic equipment (Biodex Co., Shirley, NY, USA). For the isokinetic muscle strength measurement of HIP joint, the 45°/sprotocol indicating the muscle power and the 300°/s protocol indicating the muscle endurance were used. Additionally, the measurement of KNEE joint was performed once on the left and right side, using the protocol of 60°/s indicating the muscle power and 300°/s indicating the muscular endurance. Progressive exercise tests were conducted on the treadmill (Quinton model—4500) using previously developed protocols targeting CP. The initial protocol speeds were 5 km/h−1 and 2 km/h−1 for the subjects who have been classified as Gross Motor Function Classification System (GMFCS) level I and II, respectively. Using a portable cardiopulmonary indirect breath-by-breath calorimetry system (MetaMax 3B; Cortex Biophysik, Leipzig, Germany), pulmonary ventilation (VE), respiratory exchange ratio (RER), and oxygen uptake (VO2) have been persistently measured. HR monitor (Polar Electro, Kempele, Finland polar Co. RS-800) was used to measure heart rate (HR). A correlation analysis was conducted to find out how the lower extremity muscle strength and aerobic capacity with cerebral palsy are related. Therefore, as a result, VO2peak among aerobic capacity displayed a significant positive correlation in 45° and 300°/s peak torque/BW of HIP joint, and with 60° and 300°/s peak torque/BW of KNEE joint. It was the same with 60°/s Agon/Antag ratio of KNEE Joint (p < 0.05). VEpeak showed a significant positive correlation with 45° and 300°/s peak torque/BW of HIP joint, as well as correlation with 60° and 300°/s peak torque/BW and 60°/s Agon/Antag ratio of KNEE joint (p < 0.05). However, HRpeak showed a significant positive correlation only in 45°/s peak torque/BW of HIP joint (p < 0.05). The result of step-wise analysis was to find out which muscle strength significantly affects VO2peak and HRpeak among aerobic abilities in the lower extremity muscles of those disabled with cerebral palsy. Among the muscle functions of lower extremity muscle strength, 300°/s peak torque/BW of KNEE Joint was found to have the greatest effect on VO2peak (p < 0.001). As a result, 300°/s peak torque/BW of KNEE Joint was found to be the predictable factor that could explain the VO2peak in the disabled people with cerebral palsy at 67% (R2 = 0.661). In particular, among the muscle functions of lower extremity muscle strength at 45°/s peak, torque/BW of HIP Joint was found to have the greatest effect on HRpeak (p < 0.001). As a result, this factor was found to be the predictable factor that could explain the HRpeak in disabled people with cerebral palsy at 39% (R2 = 0.392). In this study, the muscle strength of the lower extremity of CP was closely related to the aerobic capacity, and the muscle endurance of KNEE Joint and the muscle power of HIP Joint were found to be important factors to predict the aerobic capacity of CP.

Energetics of walking in individuals with cerebral palsy and typical development, across severity and age: A systematic review and meta-analysis

BACKGROUND

Individuals with cerebral palsy (CP) report physical fatigue as a main cause of limitation, deterioration and eventually cessation of their walking ability. A consequence of higher level of fatigue in individuals with CP leads to a less efficient and long-distance walking ability.

RESEARCH QUESTION

This systematic review investigates the difference in 1) walking energy expenditure between individuals with CP and age-matched typically developing (TD) individuals; and 2) energetics of walking across Gross Motor Function Classification System (GMFCS) levels and age.

METHODS

Five electronic databases (PubMed, Web of Science, CINAHL, ScienceDirect and Scopus) were searched using search terms related to CP and energetics of walking.

RESULTS

Forty-one studies met inclusion criteria. Thirty-one studies compared energy expenditure between CP and age-matched controls. Twelve studies correlated energy expenditure and oxygen cost across GMFCS levels. Three studies investigated the walking efficiency across different ages or over a time period. A significant increase of energy expenditure and oxygen cost was found in individuals with CP compared to TD age-matched individuals, with a strong relationship across GMFCS levels.

SIGNIFICANCE

Despite significant differences between individuals with CP compared to TD peers, variability in methods and testing protocols may play a confounding role. Analysis suggests oxygen cost being the preferred/unbiased physiological parameter to assess walking efficacy in CP. To date, there is a knowledge gap on age-related changes of walking efficiency across GMFCS levels and wider span of age ranges. Further systematic research looking at longitudinal age-related changes of energetics of walking in this population is warranted.

Associations of inter-segmental coordination and treadmill walking economy in youth with cerebral palsy

This study investigated associations of thigh-shank coordination deficit severity and metabolic demands of walking in youth with cerebral palsy (CP) and their typically developing (TD) peers. Youth (ages 8-18 years) with hemiplegic and diplegic CP [Gross Motor Classification System (GMFCS) I-III] and their age (within 12 months) and sex-matched peers performed a modified six-minute-walk-test on a treadmill. Kinematics (Motion Analysis, USA, 240 Hz) and mass-specific gross metabolic rate (GMR; COSMED, Italy) were analyzed for minute two of treadmill walking. Thigh-shank coordination was determined using continuous relative phase (CRP) analysis. GMR was normalized using participant specific Froude numbers (i.e. GMR_Eq). Maximum and minimum CRP deficit angles (CRP_Max,CRP_Min) were analysed in SPSS (IBM, USA) using paired samples t-tests with Bonferroni correction (p = 0.0125). Associations of knee extension angle deficit (KED_Max) and coordination outcomes with GMR_Eq (log) were assessed using multiple linear regression. Twenty-eight matched pairs were included, demonstrating significantly larger CRP_Max for youth with CP [GMFCS I mean pair difference (98.75%CI) 8.2 (-0.1,16.5), P = 0.013; GMFCS II/III 26.1 (2.3,50.0), P = 0.008]. Joint kinematics and coordination outcomes were significantly associated with GMR_Eq (P < 0.001), primarily due to CRP_Max (P < 0.001), leading to a 1.7 (95%CI; 1.1, 2.4)% increase in GMR_Eq for every degree increase in CRP_Max. These findings indicate an association of thigh-shank coordination deficit severity and increasing metabolic demands of walking in youth with CP. CRP may be a clinically useful predictor of metabolic demands of walking in CP. Future work will evaluate the sensitivity of CRP to coordination and walking economy changes with surgical and non-surgical management.

Mechanisms contributing to gait speed and metabolic cost in children with unilateral cerebral palsy

BACKGROUND

Gait speed and metabolic cost are indicators of functional capacity in children with cerebral palsy. Uncovering their mechanisms helps guide therapeutic actions.

OBJECTIVES

To investigate the contributions of energy-generating and energy-conserving mechanisms to gait speed and metabolic cost of children with unilateral cerebral palsy.

METHODS

Data on eccentric and concentric muscle work, co-contraction, elastic torque and vertical stiffness of the affected-limb, forcing torque of the non-affected limb, gait speed and metabolic cost were collected from 14 children with unilateral cerebral palsy, aged 6-12 years. Analyses included two groups of multiple regression models. The first group of models tested the association between each dependent variable (i.e., speed and metabolic cost) and the independent variables that met the input criteria. The second group verified the contribution of the non-selected biomechanical variables on the predictors of the first model.

RESULTS

Gait speed (R²=0.80) was predicted by elastic torque (β=0.62; 95%CI: 0.60, 0.63), vertical stiffness (β=-0.477; 95%CI: -0.479, -0.474) and knee co-contraction (β=0.27; 95%CI: -1.96, 2.49). The production of eccentric work by the affected limb proved relevant in adjusting the vertical stiffness (R²=0.42; β=-0.64; 95%CI: 0.86, -0.42); elastic torque of the affected-leg was associated with impulsive torque of the non-affected leg (R²=0.31; β=0.55; 95%CI: 0.46, 0.64). Metabolic cost of gait (R²=0.48) was partially predicted by knee co-contraction (β=0.69; 95%CI: 0.685, 0.694).

CONCLUSIONS

The chain of associations revealed by the two steps models helped uncover the mechanisms involved in the locomotion of children with unilateral cerebral palsy. Intervention that changes specific energy conserving and generating mechanisms may improve gait of these children.

Correlating mechanical work with energy consumption during gait throughout pregnancy

BACKGROUND

Measures of mechanical work may be useful in evaluating efficiency of walking during pregnancy. Various adaptations in the body during pregnancy lead to altered gait, consequently contributing to the total energy cost of walking. Measures of metabolic energy expenditure may not be reliable for measuring energetic cost of gait during pregnancy as pregnancy results in numerous metabolic changes resulting from foetal development. Therefore, the aim of this study is to determine if mechanical work prediction equations correlate with the metabolic energy cost of gait during pregnancy.

METHODS

Thirty-five (35) women (27.5 ± 6.1 years) gave informed consent for participation in the study at different weeks of gestation pregnancy. Gas exchange and gait data were recorded while walking at a fixed self-selected walking speed. External (Wext) work was estimated assuming no energy transfer between segments, while internal work (Wint) assumed energy transfer between segments. Hence total energy of the body (Wtot) was calculated based on the segmental changes relative to the surrounding, and relative to the centre of mass of the whole body. Equations for mechanical work were correlated with net and gross O2 rate, and O2 cost.

RESULTS

External, internal and total mechanical energy showed significant positive relationship with gross O2 rate (r = 0.48, r = 0.35; and r = 0.49 respectively), and gross O2 cost (r = 0.42; r = 0.70, and r = 0.62, respectively). In contrast, external, internal and total mechanical energy had no significant relationship with net O2 rate (r = 0.19, r = 0.24, and r = 0.24, respectively). Net O2 cost was significant related Wext (r = 0.49) Wint (r = 0.66) and Wtot (r = 0.62). Energy recovery improved with increase in gait speed.

CONCLUSIONS

Measures of mechanical work, when adjusted for resting energy expenditure, and walking speed may be useful in comparing metabolic energy consumption between women during pregnancy, or assessment or gait changes of the same individual throughout pregnancy.

Analysis of the relationships that body composition and muscular strength have with oxygen cost of walking in children with cerebral palsy

OBJECTIVE

To investigate whether body composition and lower extremity strength relate to oxygen cost of walking in children with cerebral palsy (CP), and to evaluate the relative contributions of these measures to explain variation in oxygen cost seen in this population.

METHODS

A total of 116 children with spastic diplegic CP, Gross Motor Function Classification System levels I-III, aged 8-18 participated. Strength, body composition (body mass index (BMI) and percent body fat) and oxygen cost were recorded. Pearson correlations assessed relationships between variables of body composition and strength to oxygen cost. Forward stepwise linear regression analyzed variance explained by strength and body composition measures. Oxygen data were analyzed by weight status classifications using one-way analysis of variance with significance set at p<0.05.

RESULTS

Total strength (r=-0.27) and total extensor strength (r=-0.27) had fair inverse relationships with oxygen cost. Total extensor strength explained 7.5% (r(2)=0.075, beta=-0.274, p<0.01) of the variance in oxygen cost. Body composition did not explain significant variance in oxygen cost, however significant differences were found in oxygen consumption (p=0.003) and walking velocity (p=0.042) based on BMI weight classifications.

CONCLUSIONS

For ambulatory children with CP, oxygen cost during walking can be partially explained by total extensor strength and not body composition. However, those categorized as obese may adjust to a slower walking speed to keep their oxygen cost sustainable, which may further affect their ability to keep up with typically developing peers and possibly lead to greater fatigue.

Changes in kinematics, metabolic cost and external work during walking with a forward assistive force

We examined how the application of a forward horizontal force applied at the waist alters the metabolic cost, kinematics, and external work of gait. Horizontal assist forces of 4%, 8% and 12% of a subject's body weight were applied via our testing apparatus while subjects walked at comfortable walking speed on a level treadmill. Kinematic and metabolic parameters were measured using motion capture and ergospirometry respectively on a group of 10 healthy male subjects. Changes in kinematic and metabolic parameters were quantified and found similar to walking downhill at varying grades. A horizontal assist force of 8% resulted in the greatest reduction of metabolic cost. Changes in recovery factor, external work, and center of mass (COM) movement did not correlate with changes in metabolic rate and therefore were not driving the observed reductions in cost. The assist force may have performed external work by providing propulsion as well as raising the COM as it pivots over the stance leg. Assist forces may decrease metabolic cost by reducing the concentric work required for propulsion while increasing the eccentric work of braking. These findings on the effects of assist forces suggest novel mobility aids for individuals with gait disorders and training strategies for athletes.

The gait of children with and without cerebral palsy: work, energy, and angular momentum

This paper describes a method to characterize gait pathologies like cerebral palsy using work, energy, and angular momentum. For a group of 24 children, 16 with spastic diplegic cerebral palsy and 8 typically developed, kinematic data were collected at the subjects self selected comfortable walking speed. From the kinematics, the work-internal, external, and whole body; energy-rotational and relative linear; and the angular momentum were calculated. Our findings suggest that internal work represents 53% and 40% respectively of the whole body work in gait for typically developed children and children with cerebral palsy. Analysis of the angular momentum of the whole body, and other subgroupings of body segments, revealed a relationship between increased angular momentum and increased internal work. This relationship allows one to use angular momentum to assist in determining the kinetics and kinematics of gait which contribute to increased internal work. Thus offering insight to interventions which can be applied to increase the efficiency of bipedal locomotion, by reducing internal work which has no direct contribution to center of mass motion, in both normal and pathologic populations.

Detecting Postoperative Change in Children with Cerebral Palsy: Net Nondimensional versus Body Mass Oxygen Normalization

The aim of the study is to investigate whether the net nondimensional oxygen utilization scheme is able to detect postoperative improvement in the energy cost of walking in children with cerebral palsy and to compare it with a body mass normalization scheme. We evaluated 10 children with spastic cerebral palsy before and 9 months after equinus deformity surgery. Participants walked at a given speed of 2 km/hr and 3 km/hr on a treadmill. Oxygen utilization was measured, and mass relative VO2 and net nondimensional VO2 were calculated. Coefficient of variation was used for the description of variability among subjects. Postoperatively, gait kinematics normalized and the mass relative VO2 and net nondimensional VO2 showed significant improvement. Net nondimensional VO2 is able to detect postoperative improvement with smaller variability among subjects than body mass related normalization in children with cerebral palsy.

A comparison of the oxygen cost of locomotion in children with and without developmental coordination disorder

AIM

The aim of this study was to compare the oxygen cost (V(O2)) of walking and running, as well as aerobic fitness, in children with and without developmental coordination disorder (DCD).

METHOD

Thirty-one males (17 with DCD and 14 in a comparison group; mean age 8 y 7 mo, SD 1 y 3 mo and 8 y 5 mo, SD 1 y 2 mo respectively) were tested on two separate occasions at least 1 week apart. On the first visit, motor proficiency was assessed by the McCarron Assessment of Neuromuscular Development instrument, which was followed by the determination of maximal aerobic capacity (V(O2max)). The second visit involved 4-minute bouts of treadmill walking (at 4.3 km/h and 5.8 km/h) and running (at 7.8 km/h and 8.4 km/h). Oxygen consumption, heart rate, respiratory exchange ratio, rating of perceived exertion (RPE), step rate, and qualitative assessment of locomotion were obtained for each speed.

RESULTS

Despite poorer locomotion proficiency, there was no significant difference in the oxygen cost of walking or running between males with and without DCD. However, the DCD group had significantly higher RPE while running at 7.8 km/h (p=0.011) and had greater difficulty achieving V(O2max), resulting in significantly lower scores for aerobic fitness.

INTERPRETATION

The differences in locomotion proficiency between children with and without DCD are not large enough to affect the oxygen cost of locomotion. However, children with DCD are more likely to withdraw from exercising at higher intensities before achieving peak performance.

Mechanical work performed by the legs of children with spastic diplegic cerebral palsy

The purpose of this investigation was to evaluate the work performed on the center of mass by the legs of children with cerebral palsy. 10 children that were diagnosed as having cerebral palsy with spastic diplegia (Age=9.1+/-2 years), and 10 healthy children with no walking disabilities participated (Age=9.4+/-2 years). We collected individual leg ground reaction forces from four force platforms, and calculated the mechanical work performed on the center of mass by the lead and trail legs. The normalized walking speeds were not significantly (p=0.33) different between the children with cerebral palsy (0.26+/-0.07) and the controls (0.28+/-0.06). The children with cerebral palsy performed significantly more negative work by the lead leg during double support (p=0.0004), and significantly less positive work by the trail leg (p<0.00001). During single support, the children with cerebral palsy performed significantly more positive work on the center of mass (p<0.00001). No significant differences were found for the amount of negative work performed by the leg in single support (p=0.84). Children with spastic diplegic cerebral palsy show a diminished ability to appropriately perform mechanical work by the legs to lift and redirect the center of mass. The altered mechanical work performed by the legs on the center of mass may play a role in the higher metabolic cost for walking noted in children with cerebral palsy.

Determination of ankle muscle power in normal gait using an EMG-to-force processing approach

The purpose of this study was to determine the contribution of individual ankle muscles to the net ankle power and to examine each muscle's role in propulsion or support of the body during normal, self-selected-speed walking. An EMG-to-force processing (EFP) model was developed which scaled muscle tendon unit force output to gait EMG, with that muscle's power output being the product of muscle force and contraction velocity. Net EFP power was determined by summing individual ankle muscle power. Net ankle power was also calculated for these subjects via inverse dynamics. Closeness of fit of the power curves of the two methods was used to validate the model. The curves were highly correlated (r(2)=.91), thus the model was deconstructed to analyze the power contribution and role of each ankle muscle during normal gait. Key findings were that the plantar flexors control tibial rotation in single support, and act to propel the entire limb into swing phase. The dorsiflexors provide positive power for swing phase foot clearance, negative power to control early stance phase foot placement, and a second positive power burst to actively advance the tibia in the transition from double to single support. Co-contraction of agonists and antagonists was limited to only a small percentage of the gait cycle.

Between-day variability of net and gross oxygen uptake during graded treadmill walking: effects of different walking intensities on the reliability of locomotion economy

There have been few studies of clinical relevance conducted on the reliability of walking economy. This study was designed to determine if walking economy reproducibility increases as a function of walking intensity, and if there is any advantage in expressing walking economy as net oxygen uptake (VO2) rather than gross VO2 for reproducibility purposes. Sixteen participants (9 males, 7 females; mean age, 22.3 ± 4.3 years) performed resting, submaximal, and maximal protocols on 2 different days, under identical circumstances, within a 7 day period. The submaximal protocol consisted of five 5 min walks (4 km·h–1) at treadmill grades of 0%, 2.5%, 5.0%, 7.5%, and 10%. Findings indicate that increments of 2.5% in treadmill grade effectively increased gross and net VO2 during walks. The reliability of net and gross measures increased as a function of walking relative intensity, reporting intraclass correlation coefficients ranging from 0.89–0.94 and 0.87–0.91, respectively, and mean coefficients of variation (CV) from 7.3%–3.6% and 8.8%–4.4%, respectively. There were no significant differences between the CV for gross and for net VO2 across the spectrum of walking relative intensities. In conclusion, there is no advantage of expressing walking economy as net VO2 instead of gross VO2 for reproducibility purposes, and a single treadmill testing session at a constant speed of 4 km·h–1 is reliable for estimating group and individual walking economy, particularly at higher percent grades.

Mechanical work, energetic cost, and gait efficiency in children with cerebral palsy

Many authors have reported increased energy expenditure during walking in children with hemiplegia. The origin of this increase is not well documented. The aim of our study was to understand better the origin of this increased energy expenditure of walking in children with cerebral palsy (CP) by simultaneously assessing the total mechanical work performed by the muscles and the efficiency of the work production.Twenty independently walking children with spastic, hemiplegic CP and a dynamic foot equinus deformity participated in the study. Instrumented gait analysis, including the analysis of kinematic, mechanical, and energetic variables, was performed. Despite excellent Gross Motor Function Measurement scores (range, 97-99), the energy cost was 1.3 times greater in children with CP than in healthy children. This increase in energy cost was related to an increase in the total positive mechanical work performed by the muscles and not related to a decrease in the efficiency of this work production. This study shows how segmental impairments (foot spastic equinus) increase the total mechanical work performed by the muscles and the energetic cost and how these segmental impairments contribute to the patient's disability. It is useful to associate the clinical examination, classic gait analysis, mechanical work, and energetic assessment to complete the evaluation of the condition of children with CP.

Center of mass motion and the effects of ankle bracing on metabolic cost during submaximal walking trials

The goal of this research was to examine the relationship between center of mass (CoM) motion and metabolic cost and to assess secondarily the effects of equinus gait on metabolic cost during walking trials at various velocities. Twelve (n=12) healthy male adults walked in four brace conditions, including fixed equinus, at three different walking speeds. Metabolic measures and 3D kinematic data were collected during each trial. Significant main effects for velocity were observed on both dependent measures, net O2 cost (p<0.001), and CoM vertical excursion (CoMz) (p<0.01). Correlation analysis showed significant positive correlations between net O2 cost and CoMz that were strongest at fast velocities. Further, analysis revealed the cost of walking at a comfortable speed in the equine position was 28% greater than walking in braces without springs or springs in neutral position and 64% greater than walking in shoes alone. CoMz does correlate with metabolic cost as measured by net O2 cost. Also, normal subjects walking in equinus have an increased net O2 cost and increased CoMz when compared to walking with shoes alone or the other brace conditions at all velocities.

Effect of handrim diameter on manual wheelchair propulsion: mechanical energy and power flow analysis

BACKGROUND

Wheelchair design parameters such as handrim diameter could affect propulsion. The purpose of this study was to examine the effect of handrim size (0.54, 0.43, and 0.32 m) on mechanical energy and power flow during wheelchair propulsion.

METHODS

Twelve young normal male adults (mean age 23.5 years old) were recruited in this study. Both 3-D kinematic and kinetic data of the upper extremity were collected synchronously using a Hi-Res Expert Vision motion system and an instrumented wheel during wheelchair propulsion.

FINDINGS

The kinetic, potential and total mechanical energy of the upper extremity increased as the handrim size increased. For each upper arm segment, the joint translational power and the rotational power of the proximal joint increased with increasing handrim size. The work done during a complete propulsion cycle with the larger handrim size is significantly larger than that using a smaller handrim (P<0.05).

INTERPRETATION

The increased kinetic, potential and total mechanical energy were due to the increased linear velocity and the elevated positions of the upper extremity segments. The shoulder and trunk flexors increased the magnitude of their concentric contractions during propulsion with the large handrim as increased output power is required. By using mechanical energy and power flow analysis techniques, we evaluated the previously-reported effect of handrim size on mechanical cost and provided insight into the relationship between the two.

Center of Mass Movement and Energy Transfer During Walking in Children With Cerebral Palsy

OBJECTIVE

To gain insight into the mechanical inefficiencies of gait patterns used by children with spastic diplegia by analysis of center of mass (COM) movement and energy recovery.

DESIGN

Prospective study using between-group measures to analyze differences between children with cerebral palsy (CP) and age-matched controls without CP.

SETTING

Assessments were performed in a gait laboratory.

PARTICIPANTS

Fifteen children with spastic diplegia and 6 age-matched controls without CP with a mean age of 9.7 years.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Gait data assessed included temporal-distance factors, COM vertical excursion, work done on the COM, and the percentage of energy transferred and relative phase between the potential and kinetic energy.

RESULTS

Children with CP had a 33% smaller energy recovery factor than the controls (P<.001). They also had 60% greater COM vertical excursion (P<.02) and a poorer phasic relation between potential and kinetic energies (P<.02), both of which contributed to greater mechanical work performed (P<.003).

CONCLUSIONS

Compared with the age-matched controls without CP, the children with CP were mechanically less efficient in their gait. Interventions that promote heel contact and roll over and greater knee stability to better utilize the kinetic energy of push-off could improve walking efficiency.

The evolution of clinical gait analysis part III--kinetics and energy assessment

Historically, clinical applications of measurements of force and energy followed electromyography and kinematics in temporal sequence. This sequence is mirrored by the order of topics included in this trilogy on the Evolution of Clinical Gait Analysis, with part I [Sutherland DH. The evolution of clinical gait analysis part I: kinesiological EMG. Gait Posture 2001;14:61-70.] devoted to Kinesiological EMG and part II [Sutherland DH. The evolution of clinical gait analysis part II - kinematics. Gait Posture 2002;16(2):159-179.] to Kinematics. This final review in the series will focus on kinetics as it relates to gait applications. Kinematic measurements give the movements of the body segments, which can be compared with normal controls to identify pathological gait patterns, but they do not deal with the forces controlling the movements. As a major goal of scientifically minded clinicians is to understand the biomechanical forces producing movements, the objective measurement of ground reaction forces is essential. The force plate (platform) is now an indispensable tool in a state-of-the-art motion analysis laboratory. Nonetheless, it is not a stand-alone instrument as both kinematic and EMG measurements are needed for maximum clinical implementation and interpretation of force plate measurements. The subject of energy assessment is also given mention, as there is a compelling interest in whether walking has been made easier with intervention. The goals of this manuscript are to provide a historical background, recognize some of the important contributors, and describe the current multiple uses of the force plate in gait analysis. The widespread use of force plates for postural analyses is an important and more recent application of this technology, but this review will be restricted to measurements of gait rather than balance activities. Finally, this manuscript presents my personal perspective and discusses the developments and contributors that have shaped my thoughts and actions, and which I have found to be particularly noteworthy or intriguing. Just as in parts I and II, emphasis has been placed on the early development. All subtopics and important contributors, in this third and certainly most challenging of the review papers, have not been included. Some may find that my perceptions are incomplete. I accept responsibility for all deficiencies, as none were intended. Letters to selected contributors and their responses reveal how each contributor built on the work of others. The level of cooperation and sharing by these early investigators is extraordinary. Had they wished to withhold information about their own work, clinical gait analysis would have been severely delayed.

Disability Type Influences Heart Rate Response during Power Wheelchair Sport

PURPOSE

The purpose of this study was to determine the influence of disability type on exercise response during power wheelchair competition. The secondary purpose was to determine the extent to which heart rate responses during competition meet cardiorespiratory fitness training intensities for the general population.

METHODS

Forty-eight athletes who had cerebral palsy (CP, N = 31), spinal cord injury (SCI, N = 10), or muscular dystrophy (MD, N = 7), and were competing in the 2003 Power Soccer National Tournament, volunteered to participate. Heart rate was recorded every 5 s throughout pre-game and game conditions by Polar S610 monitors. Average heart rate (HR) values were determined for GAME and RESPONSE (change score between GAME HR and pre-game HR). The Kruskal-Wallis nonparametric test was used to determine whether a significant difference among group medians existed on the dependent measure, RESPONSE (P < 0.05).

RESULTS

A significant difference on RESPONSE (P < 0.05) existed among athletes with CP (29 bpm), SCI (17 bpm), and MD (26 bpm). The median RESPONSE for athletes with CP was 12 bpm higher than athletes with SCI, and this difference was significant (P < 0.01). Further, 22 athletes with CP (71%), 5 athletes with MD (71%), and 1 athlete with SCI (10%) exceeded 55% of estimated HR(max) for at least 30 min during competition.

CONCLUSION

Disability type influences the heart rate response to power wheelchair sport, and may affect the ability to sustain training intensities associated with fitness improvement.

Physical Activity Level is Associated with the O2 Cost of Walking in Cerebral Palsy

PURPOSE

To determine, in children and adolescents with cerebral palsy (CP), the relationship between physical activity level (PAL) and i) oxygen cost of walking, and ii) peak VO2.

METHODS

In 11 subjects (10.6-16.3 yr) with mild CP, PAL, the ratio of total energy expenditure to resting energy expenditure, was determined from 3 d of heart rate (HR) monitoring (field), with individual HR-VO2 calibrations done in the lab. The oxygen cost of walking was measured during three 3-min walks on a treadmill at 60, 75, and 90% of each subject's fastest treadmill walking speed (FWS). Subjects also performed a maximal treadmill exercise test. Alpha was set at 0.05.

RESULTS

One subject was an outlier and eliminated from all simple linear regression analyses. For the remaining 10 subjects, PAL (1.37+/-0.18) was related (r=-0.70 to -0.84) to net VO2 at 60 and 75% FWS (13.1+/-4.1 and 16.2+/-4.2 mL.kg.min), net VO2.m, averaged across the three speeds (0.32+/-0.23 mL.kg.m), and percent peak VO2 at all three speeds (54.5+/-21.5, 63.5+/-20.9, and 75.5+/-15.1%). PAL was not significantly related to net VO2 at 90% FWS (20.8+/-5.3 mL.kg.min) or to peak VO2 (34.0+/-9.2 mL.kg.min).

CONCLUSION

For this population, those with low PAL may also have a high oxygen cost of walking. These individuals' PAL was not related to their peak VO2. Further research is required to determine whether interventions that decrease the oxygen cost of walking also affect PAL and whether changes in PAL affect the oxygen cost of walking.

Responses of children with cerebral palsy to treadmill walking exercise in the heat

PURPOSE

When metabolic rate during arm-cranking in the heat is equated between children and adolescents with cerebral palsy (CP) and matched controls (CON), there are no relevant intergroup differences in heat strain. The metabolic rate, however, is known to be higher in CP during treadmill walking. The purpose of this study was to determine if during treadmill walking in the heat, the higher oxygen uptake (VO2), and thus greater metabolic heat production in those with CP would result in greater heat strain compared with able-bodied, matched CON.

METHODS

Ten boys and girls (10.3-16.3 yr) with spastic CP and 10 individually matched (age, body size, biological maturity, gender, race) healthy CON performed 3 x 10-min treadmill walking bouts in 35 degrees C, 50% RH. Body mass, metabolic variables, heart rate (HR), body temperatures, and rating of perceived exertion (RPE) were periodically measured. Individuals within each CP-CON pair walked at the same speed and slope (0.9 +/- 0.4 m x s(-1), 3.3 +/- 0.6%).

RESULTS

Steady-state VO2 during walking, body temperatures, and HR were all higher in the CP group compared with CON. VO2 was on average 40% higher, rectal temperature was 0.4 degrees C (99% CI = 0.1-0.6 degrees C) higher and HR (during the final minute of each exercise bout) was 37 beats x min(-1) (99% CI = 19-56 beats x min(-1)) higher. There were no differences between the groups in sweating rate (as inferred from body mass changes corrected for fluid intake and output) or in RPE.

CONCLUSION

The subjects with CP demonstrated greater thermal strain than CON during treadmill walking where they require more metabolic energy and thus produce more metabolic heat than CON.

Habitual Physical Activity Levels Are Associated with Biomechanical Walking Economy in Children with Cerebral Palsy

OBJECTIVE

To evaluate in children and adolescents with cerebral palsy the relationship between habitual physical activity and biomechanical treadmill walking economy and whether treadmill belt speed or walking time affect economy.

DESIGN

Physical activity was measured in 11 subjects (10.6-16.3 yrs) with mild cerebral palsy using a triaxial accelerometer. To determine biomechanical walking economy, subjects' stride lengths and vertical sacral excursions were measured during each minute of three 3-min walks on a treadmill (at 60%, 75%, and 90% of individually determined fastest treadmill walking speed).

RESULTS

Biomechanical walking economy at 60%, 75%, and 90% of (their) fastest speed each explained about half of the intersubject variance in daily physical activity (movement counts). A similar relationship was found between these biomechanical walking economy variables and movement counts at or above the 80th and 90th percentile (total minutes per day, number of 5-min bouts per day). Walking economy was 23.9% higher when subjects walked at 90% than when they walked at 60% of their fastest walking speed. No other speed-related effects on economy were found, nor did time affect economy.

CONCLUSIONS

Within this population, those with high biomechanical treadmill walking economy are the more habitually physically active. Treadmill belt speed, but not walking time, affects biomechanical walking economy.

A stair-climbing test for ambulatory assessment of children with cerebral palsy

The purpose of this study was to develop a stair-climbing test to measure energy cost (EC) and mechanical efficiency (ME) in children with cerebral palsy (CP) to evaluate ambulation-related motor function and its changes after intervention or maturation. Five normally developed (ND) and 10 children with CP were tested. The gross ME (MEg) was calculated from the work done (W) and the total energy cost (oxygen consumption) measured while repeatedly ascending and descending four steps for approximately 5 min without subtracting the resting metabolic rate. The MEg was significantly lower in CP than ND (3% versus 20%, P < 0.001). The test was repeated in the 10 children with CP after a 4-month therapy recess. The MEg values correlated with the initial tests, with a small, significant increase of 2%. When calculating net ME (MEn) from W and the energy cost above resting, the correlation of MEn values before and after therapy was inferior to that using MEg values. Similarly, individual ME values obtained by estimating energy cost from the increase in heart rate (HR) during stair-climbing also correlated poorly, with large variability. These results show that MEg may be used to evaluate changes in motor function resulting from age-related development or therapy. MEg is as good or superior to MEn; the extra time required to obtain resting energy cost and heart rate values is not necessary when measurements are desired within the same individual.

Responses of Children with Cerebral Palsy to Arm-Crank Exercise in the Heat

PURPOSE

In response to passive heating, adults with hemispheric brain infarction demonstrate lower skin temperatures (Tsk) and higher sweating rates (SR) on the affected side. It is unknown whether children with similar conditions demonstrate a similar response and whether this response is advantageous to defending body temperature during exercise in the heat. The purpose of this study was to determine whether children with spastic cerebral palsy (CP) demonstrate less thermal strain than healthy peers during short (10 min each) bouts of arm cranking, a mode of exercise where metabolic rate can be matched between the two groups.

METHODS

Eleven young people (8.3-18.3 yr) with spastic CP and 11 individually matched (body size, age, and maturity) healthy controls (CON) performed 3 x 10-min arm-cranking bouts (40 rpm) in 35 degrees C, 50% RH. Body mass, metabolic and heart rate (HR) responses, and body temperatures were periodically measured. Individuals within each CP-CON pair worked at the same intensity (0.55 +/- 0.18 W.kg-1 body mass). Data were analyzed using a repeated measures ANOVA (alpha = 0.05).

RESULTS

Subjects with CP showed no difference from CON in metabolic and HR responses, or SR (as inferred from body mass changes corrected for fluid intake and output). There were also no differences between the groups in the rectal temperature change from room temperature (21-23 degrees C). The increase in Tsk from room temperature, however, was slightly (0.6 degrees C) but significantly lower (P < 0.0001; 95% CI = 0.5-0.7 degrees C) in the subjects with CP compared with CON.

CONCLUSION

Subjects with CP demonstrate thermal strain responses similar to CON during upper-body exercise at relatively low intensities for short duration in a warm climate.

Repeated Treadmill Walks Affect Physiologic Responses in Children with Cerebral Palsy

PURPOSE

To determine whether physiologic responses during treadmill walking in children with cerebral palsy (CP) are affected by repeated walking bouts on different days, and whether effects are different at different speeds.

METHODS

Three girls and five boys (9.2-15.7 yr, 23.3-64.4 kg) with mild CP received 12-15 min of treadmill walking practice and had their fastest walking speed (FWS) determined during an introductory visit. During each of three subsequent visits (day 1, day 2, day 3), subjects walked for 3 min at 60, 75, and 90% FWS. Resting physiologic measures were taken on day 1.

RESULTS

From day 1 to day 3, net ventilation ([OV0312]E), and net heart rate (HR) at 90% FWS decreased by 3.6 L.min-1 and 8 beats.min-1, respectively. There were no differences between day 1 and day 2 or day 1 and day 3 for any other physiologic variable at any speed. Day 3 was less than day 2 for net HR (60% FWS) and, independent of speed, net [OV0312]O2 (per kilogram of body mass and per stride) and net energy expenditure (kJ.min-1). Between-day reliability (R) of physiologic responses was > or = 0.95, except respiratory rate (R = 0.75). Intrasubject, between-day variability for the [OV0312]O2 measures was 7.6-12.9%.

CONCLUSION

Because there were no day 1 to day 3 reductions in metabolic variables, day 1 to day 3 reductions at 90% FWS in net HR may reflect decreased emotional stress over time and reductions in net [OV0312]E, an uncoupling of [OV0312]O2 and [OV0312]E. Despite between-day differences, reliable net physiologic and stable net metabolic variables may be collected in subjects with mild CP after one treadmill walking practice session.

Mechanical energy and power flow of the upper extremity in manual wheelchair propulsion

OBJECTIVE

To investigate the characteristics of mechanical energy and power flow of the upper limb during wheelchair propulsion.

DESIGN

Mechanical energy and power flow of segments were calculated.

BACKGROUND

Very few studies have taken into account the mechanical energy and power flow of the musculoskeletal system during wheelchair propulsion. Mechanical energy and power flow have proven to be useful tools for investigating locomotion disorders during human gait.

METHODS

Twelve healthy male adults (mean age, 23.5 years) were recruited for this study. Three-dimensional kinematic and kinetic data of the upper extremity were collected during wheelchair propulsion using a Hi-Res Expert Vision system and an instrumented wheel, respectively.

RESULTS

During the initiation of the propulsion phase, joint power is generated in the upper arm or is transferred from the trunk downward to the forearm and hand to propel the wheel forward. During terminal propulsion, joint power is transferred upward to the trunk from the forearm and upper arm. The rate of change of mechanical energy and power flow for the forearm and hand have similar patterns, but the upper arm values differ.

CONCLUSIONS

Joint power plays an important role in energy transfer as well as the energy generated and absorbed by muscles spanning the joints during wheelchair propulsion.

RELEVANCE

Energy and power flow information during wheelchair propulsion allows us to gain a better understanding of the coordination of the movement by the musculoskeletal system.

Physical activity, metabolic issues, and assessment

Considering the important health consequences of physical activity and aerobic capacity, current guidelines recommend that all individuals should be physically active all or most days of the week. Relatively little is known about physical activity patterns or aerobic capacity of individuals who have disabilities, but existing data clearly show a disturbing pattern of low levels of physical activity and aerobic capacity in most, if not all, populations who have disabilities. More research is needed on all populations who have disabilities, not only documenting current levels of physical activity and aerobic capacity but also investigating potential strategies for improvement. Unfortunately, the techniques available for measuring physical activity have significant shortcomings. DLW shows considerable promise, but it is expensive and not appropriate for population studies. All other techniques have significant shortcomings in regard to tracking individual physical activity patterns, but they might provide valuable insight regarding group behavior. Although maximal exercise testing is the gold standard for measuring aerobic capacity, this technique is difficult to use in many populations that have disabilities. Few protocols have been validated for use with individuals who have disabilities, and indiscriminant use of protocols developed for nondisabled populations is inappropriate when testing individuals who have disabilities. Submaximal testing could be of considerable utility, but few protocols have been validated. For most populations that have disabilities, submaximal tests designed to predict VO2peak are not valid, given the altered disability-specific physiological responses, which usually result in gross overpredictions. Submaximal tests designed to compare (either intra or inter individual comparisons) physiological responses at predetermined submaximal work rates show considerable promise. Both populations of children who have disabilities that are discussed herein exhibit low levels of physical activity and aerobic capacity, which is consistent with most of the literature for any group that has disabilities. Although the mechanisms for producing lower levels of activity and aerobic capacity differ among children who have mental retardation and children who have CP, the outcome is similar in both populations. Appropriate testing methodology differs between these populations, and the different mechanisms involved demonstrate the disability-specific nature of research in children who have disabilities, which also illustrates the difficulty of producing general guidelines for exercise and physical activity interventions. Current data clearly show the need for improving both physical activity patterns and aerobic capacity in most children who have disabilities. Failure to accomplish this goal will ultimately have considerable negative health outcomes for individuals who have disabilities.

Facts and myths about therapeutic interventions in cerebral palsy: integrated goal development

This article explores a variety of myths and facts about therapy for children who have cerebral palsy. Current evidence is used to refute popular myths and debunk harmful ones. A way of integrating interventions is suggested and a planning process for timing interventions is proposed.

Estimating mechanical cost in subjects with myelomeningocele

An attempt was made to validate a system of calculating mechanical cost using 3-D motion analysis by using Oxygen cost measurements in 26 subjects with myelomeningocele. The three models investigated were (i) vertical excursion of the centre of mass (model 1), (ii) external work done by the centre of mass (CM) (model 2) and (iii) a full body model allowing energy transfers between segments within limbs (model 3). Oxygen cost, and models 1 and 3 all demonstrated significant differences between S1 and L4/L5 level involvement (P=0.001, 0.002 and 0.01, respectively). No significant differences were observed between subjects who had L4 and L5 level involvement. While further analysis showed a moderate correlation between Oxygen cost and the vertical excursion of CM model (R2=0.60), a lack of correlation for the more sophisticated models 2 and 3 questions their use as a method of assessing the energy cost of locomotion in this population.

Reducing the variability of oxygen consumption measurements

The oxygen consumption (O(2)) of 10 able-bodied adults each walking at a variety of cadences and hence speeds was measured. The effect on variability of subtracting the resting oxygen rate from gross measurements and of normalising walking speed to the subject's height was investigated. Both of these were indeed found to reduce variability. A total reduction of more than 40% in the variability of O(2) cost measurements was observed. Using these techniques it was found that, at walking speeds below the average, nett O(2) cost per height was very nearly independent of walking speed.