Arm-crank propelled three-wheeled chair: physiological evaluation of the propulsion using one arm and both arm patterns

Disabled people in India frequently use the arm-crank propelled three-wheeled chair (ACWC) for outdoor transportation. Two models of these chairs are commercially available: one is powered by cranking using one arm (ACWC-1) and the other uses both arms (ACWC-2). The purpose of the study was to compare the efficiency of the two types of propulsion with respect to the standard physiological responses and, consequent upon the findings, to recommend the use of a suitable one. The energetics of locomotion of the users at their freely chosen speed (FCS) were measured and compared with changes in the physiological parameters in the within-subject groups. The study was conducted in outdoor settings to simulate the actual locomotive conditions encountered by the users in their practical life. 14 males, who had been regular and proficient users of both propulsion systems for more than last six years and who had a history of paraplegia (below the 10th thoracic vertebra, n=11) and poliomyelitis (n=3) participated in the study. The subjects were required to propel the test chair (a combination of both the propulsion systems built in a single model) on an oval track of 358 m circumference at their FCS for 5 min; ambulatory data were collected during last 3 min of exercise and averaged. The FCS (m/min), heart rates (bpm) and oxygen uptake (l/min) were measured. Physiological cost index (b/m) oxygen consumption (ml/kg/min), oxygen cost (ml/kg/m) and net locomotor energy cost (kcal/kg/km) of the two sets of observations were derived and compared using a t-test for the paired observations. The FCS was significantly higher and the physiological parameters were lower with the ACWC-2 than with ACWC-1, except for heart rate and oxygen consumption, where the difference was not significant . It is concluded that two-arm use is more efficient and less physically demanding than one-arm use in the arm-crank propulsion system and that the former is more suitable for efficient ambulation.     

Oxygen consumption of elderly persons with bilateral below knee amputations: ambulation vs wheelchair propulsion

Elderly bilateral below knee (BK) amputees were tested for oxygen consumption (VO2), heart rate (HR) and velocity (V) during ambulation on a 40m walkway and a stationary wheelchair ergometer. Values obtained from amputees were compared to values obtained from a control population of the same age group. On test day 1 bilateral amputees and normal subjects ambulated at their natural pace on a walkway for approximately 5 minutes. On test day 2 each subject propelled a stationary wheelchair ergometer at their natural rate for the same distance that they ambulated. Measurements of VO2 (ml/m/kg), HR (beats/min), and V (m/min) were obtained during both sessions. Results show that the bilateral BK group required significantly more VO2 (ml/m/kg) (123%), had higher HR (26%), and slower V (36%) than the normal group during ambulation. The energy cost in terms of ml/min/kg during ambulation was similar, suggesting that the amputees ambulated at the same power cost as normals but at lower velocities. During wheelchair propulsion the BK group and normal group showed no significant difference in the 2 criteria. Results suggest that wheelchair propulsion is a more energy efficient mode of mobility for elderly bilateral BK amputees than ambulation. Energy cost and heart rate determinations may be valuable in choosing the course of mobility training and recommended activity levels. Cosmetic, psychosocial, and other clinical factors must be considered in prescribing rehabilitation.     

A multistage field test of wheelchair users for evaluation of fitness and prediction of peak oxygen consumption

An incremental multistage field test (MFT) for wheelchair users was developed to evaluate physical fitness and predict peak oxygen consumption (VO2). Using auditory feedback, the participants (n = 37) were directed to wheel around an octagonal course, increasing their velocity every minute until exhaustion. Wheelchair velocity and metabolic parameters were recorded with the use of a speedometer and a portable spirometer system. The average number of exercise levels performed (MFT score) was 9.17 +/- 5.81, resulting in a peak heart rate (HR) of 99.0 +/- 13.9% of the theoretical maximum. A test-retest analysis (n = 10) showed that the MFT was reliable regarding MFT score, peak VO2, and peak HR reached. Stepwise multiple regression based on individual, wheelchair, propulsion technique, and physiological parameters revealed that the MFT score was the best and only predictor of peak VO2 (mL/min/kg) (= 18.03 + 0.78 MFT score, r(2) = 0.59). The MFT assesses wheelchair mobility and estimates peak VO2 encountered during the test.     

Field test estimation of maximal oxygen consumption in wheelchair users

To develop a field test to estimate maximal oxygen consumption (VO2max) in wheelchair users, 30 men (means age = 34.3 years) were subjected to progressive arm-crank ergometer testing with directly measured VO2max. Additionally, they performed a modified 12-minute wheelchair propulsion test for distance. Field testing was conducted within two weeks of the VO2max determination, using a standardized wheelchair (Quickie II) on a 0.1-mile indoor synthetic running track. Average peak power output and VO2max were 540 kg.m.min-1 and 22.0 ml.kg-1.min-1, respectively. The mean (+/- 1SD) wheelchair propulsion distance was 1.11 +/- 0.24 miles. Correlation of the field test data with the VO2max was highly significant (r = 0.84; p less than .001). The regression of distance in 12 minutes plotted against VO2max yielded the following equation: wheelchair propulsion (miles) = 0.370 + 0.0337 (VO2max, ml.kg-1.min-1), where the standard error of estimate = 0.13. These findings suggest that field testing can provide a good estimate of VO2max in selected wheelchair users.     

Improved upper-body endurance following a 12-week home exercise program for manual wheelchair users

This study determined if a 12-week monitored home exercise program would improve cardiorespiratory endurance in a heterogeneous group of manual wheelchair users, which incorporated subsets of individuals with and without upper-limb impairment. Twenty-seven subjects made up two groups of manual wheelchair users: 20 without upper-limb impairment and 7 with upper-limb impairment. Subjects completed wheelchair ergometer tests using a 1 min JUMP protocol that resulted in volitional exhaustion in 6 to 12 min. Following a recovery period (time > 30 min), subjects completed subsequent constant work rate endurance tests to exhaustion at a power output corresponding to 60% of the maximum attained on the JUMP test. Subjects then underwent 12 weeks of simulated wheelchair rolling exercise using elastic straps positioned to mimic the motion of propulsion. JUMP and constant work rate tests were performed before training and after 6 and 12 weeks of exercise. Oxygen consumption (VO2) increased from rest to peak exercise in both groups and was significantly (p < 0.016) higher at peak for subjects without upper-limb impairment than for those with upper-limb impairment. Heart rate (HR) responses between the groups were similar. No significant differences in peak VO2, anaerobic threshold, or peak HR were observed at 6 or 12 weeks of the training program. Substantial improvement (p < 0.001) in maximum constant work rate tests time (10.37 +/- 2.79 min) was noted at 6 and 12 weeks, with no significant difference between 6 and 12 weeks and no significant intergroup difference. Results of this study indicated that simulated propulsion exercise endurance was improved as a result of the home exercise program.     

Metabolic cost of walking with and without a shoe lift on the contralateral foot of an immobilised extended knee

The purpose of the present study was to determine the metabolic cost of walking with and without a shoe-lift on the contralateral foot of an immobilised extended knee. Eight male subjects were randomly allocated and participated in both the treatment (walking with a 2.5 cm shoe-lift) and control (walking without a shoe-lift) conditions. Cardiac output (Q) and related cardiovascular measurements were analysed to determine the effect of a shoe-lift on central (heart rate (HR); stroke volume (SV)) and peripheral (arteriovenous oxygen difference (a-vO2 diff)) components of oxygen consumption (VO2). A metabolic analyser was used to determine VO2 (ml x kg(-1) x min(-1)), which was converted to oxygen cost (ml x kg(-1) x m(-1)). The shoe-lift had no significant (p > 0.05) effect on VO2 or oxygen cost. There were no significant differences in Q, HR, SV, a-vO2 diff, systemic vascular resistance, carbon dioxide production, respiratory exchange ratio, expired ventilation, tidal volume and respiratory rate between the two walking conditions with and without a shoe-lift. These findings demonstrate that a shoe-lift added to the contralateral foot of an immobilised extended knee does not produce clinically important effects on oxygen cost or efficiency during walking.     

The effect of steering on the physiological energy cost of wheelchair propulsion

Previous studies of the energy cost of wheelchair propulsion have used ergometers or tracks requiring little steering. We have measured minute ventilation (VE), oxygen consumption (VO2), carbon dioxide output (VCO2) and heart rate (HR) during exercise in a two arm, hand-rim propulsion wheelchair on a treadmill, and on three tracks of increasing tortuosity in eight able-bodied subjects. During propulsion at 0.6 m/sec, VE, VO2, and VCO2 were significantly greater on the track with the maximal steering component than on that with the minimal steering component, or on the treadmill with no steering component. Heart rate was significantly higher on the maximal compared to minimal steering component track. Exercise at speeds varying from 0.2 to 1.0 m/sec showed that VO2 and VCO2 were significantly higher on the medium steering component track than on the treadmill at speeds of 0.6 m/sec and above. We conclude that the effort of steering contributes significantly to the energy cost of wheelchair propulsion particularly at higher speeds.     

Reliability of cardiorespiratory measurements during wheelchair ergometry

The purpose of this research was to evaluate the stability of measures of heart rate (HR) and oxygen uptake (VO2) during repeated 30-minute bouts of constant work-rate wheelchair ergometry. Ten able-bodied subjects (seven male; three female) completed three sequential, single-stage wheelchair ergometer propulsion tests, to exhaustion, at least 48 hours apart, to determine the reliability of measurements of HR and VO2. Power output was determined as the resistance required to elicit 75% of the peak V02 attained during a peak graded exercise wheelchair ergometer test, at a propulsion velocity of three miles per hour and a flywheel roll distance of 6.32 meters. The HR and VO2 measurements were averaged over the last 30 seconds of the first (T1) and second (T2) thirds of the tests and at volitional exhaustion (T3). Significant differences were not observed at any of the data points except for HR at exhaustion. The HR at exhaustion was lower for the third test than for the second test. Intraclass correlation coefficients for HR (R=0.92, 0.95, and 0.86) and VO2 (R=0.95, 0.96, and 0.97) were high across the three tests, at all of the data points, respectively. Coefficients of variation were generally low. The results of this study indicated that, with the exception of HR during exercise sustained longer than approximately 30 minutes, VO2 and HR measurements can be made with high reliability during sustained wheelchair ergometer propulsion.     

Effects of wheelchair design on metabolic and heart rate responses during propulsion by persons with paraplegia

The purpose of this study was to investigate the metabolic and heart rate (HR) responses of individuals with paraplegia to propulsion in wheelchairs of different design. Eight male and one female wheelchair-bound adults with paraplegia were studied. Each subject propelled a conventional wheelchair and a sports wheelchair on a level wooden surface at four velocities ranging from 1 to 3 m/sec. Steady-rate oxygen consumption (VO2) and immediate postexercise HR measurements were obtained. A linear regression analysis of VO2 (L/min) as a function of velocity (m/sec) revealed a slope and correlation coefficient of 0.614 and .93, respectively, for the conventional chair, and 0.510 and .96, respectively, for the sports chair. The intercepts of these relationships did not differ between wheelchair designs. The data analysis revealed no difference between chair designs in the relationship between velocity and work rate. Thus, the energy cost of propelling the sports chair at a specific velocity was 17% less than that of the conventional chair. The greater efficiency of the sports chair is attributed to differences in wheelchair design, rather than to the total mass of the device.     

Physical capacity and race performance of handcycle users

The purpose of this study was to determine physical capacity, gross efficiency (GE), and physical strain (PS) of 16 male handcycle users during a 10K race, and to relate these to race performance. All subjects used a handcycle system attached to their own wheelchair and were classified into a group with (A1/A2; N=10) and without (A3; N=6) upper-limb impairments. The PS was defined as the mean heart rate during the race, expressed relative to the heart rate reserve (%HRR). Race performance was defined as the mean race velocity (Vrace). Maximal power output (POmax), VO2peak, and GE (at 28 W) were determined in a graded treadmill exercise test. POmax (55+/-25 versus 129+/-26 W), VO2peak (1.11+/-0.4 versus 2.12+/-0.4 L x min(-1)) and Vrace (13.6+/-3 versus 19.9+/-3 km x hr(-1)) were different between A1/A2 and A3 (p<0.001), whereas PS (80+/-9 versus 88+/-9 %HRR; p=0.12) and GE (10.9+/-1.4 versus 9.7+/-0.9%; p=0.09) were not. POmax, VO2peak, and PS were associated (p<0.05) with Vrace (R=0.91, 0.90, and 0.66). Regression analysis showed that after VO2peak, GE added another 9 percent to the explanation of the variance of Vrace (R2=0.89). In conclusion, attainable handcycling POmax is markedly high and strongly related to race performance. The high PS during the race suggests that handcycling is well suited for aerobic training for most groups of wheelchair users.     

Treadmill training improves fitness reserve in chronic stroke patients.

OBJECTIVE: To investigate the hypothesis that treadmill training will improve peak fitness, while lowering the energy cost of hemiparetic gait in chronic stroke patients. DESIGN: Noncontrolled exercise intervention study with repeated-measures analysis. SETTING: Hospital-based senior exercise research center. PARTICIPANTS: Twenty-three patients (mean age +/- standard deviation [SD] 67 +/- 8 yr) with chronic hemiparetic gait after remote (>6 mo) ischemic stroke. INTERVENTION: Three 40-minute sessions of treadmill exercise weekly for 6 months. MAIN OUTCOME MEASURES: Peak exercise capacity (VO2peak) and rate of oxygen consumption during submaximal effort treadmill walking (economy of gait) by open circuit spirometry and ambulatory workload capacity before and after 3 and 6 months of training. RESULTS: Patients who completed 3 months of training (n = 21) increased their VO2peak +/- SD from 15.4 +/- 2.9 mL x kg(-1) x min(-1) to 17.0 +/- 4.4 mL x kg(-1) x min(-1) (p <.02) and lowered their oxygen demands of submaximal effort ambulation from 9.3 +/- 2 mL x kg(-1) x min(-1) to 7.9 +/- 1.5 mL x kg(-1) x min(-1) (p =.002), which enabled them to perform the same constant-load treadmill task using 20% less of their peak exercise capacity (62.3% +/- 17.2% vs 49.9% +/- 19.3%, p <.002). Gains in VO2peak and economy of gait plateaued by 3 months, while peak ambulatory workload capacity progressively increased by 39% (p <.001) over 6 months. CONCLUSIONS: Treadmill training improves physiologic fitness reserve in chronic stroke patients by increasing VO2peak while lowering the energy cost of hemiparetic gait, and increases peak ambulatory workload capacity. These improvements may enhance functional mobility in chronic stroke patients.     

Energy cost of propulsion in standard and ultralight wheelchairs in people with spinal cord injuries

BACKGROUND AND PURPOSE: Wheelchair- and subject-related factors influence the efficiency of wheelchair propulsion. The purpose of this study was to compare wheelchair propulsion in ultralight and standard wheelchairs in people with different levels of spinal cord injury. SUBJECTS: Seventy-four subjects (mean age=26.2 years, SD=7.14, range=17-50) with spinal cord injury resulting in motor loss (30 with tetraplegia and 44 with paraplegia) were studied. METHOD: Each subject propelled standard and ultralight wheelchairs around an outdoor track at self-selected speeds, while data were collected at 4 predetermined intervals. Speed, distance traveled, and oxygen cost (VO2 mL/kg/m) were compared by wheelchair, group, and over time, using a Bonferroni correction. RESULTS: In the ultralight wheelchair, speed and distance traveled were greater for both subjects with paraplegia and subjects with tetraplegia, whereas VO2 was less only for subjects with paraplegia. Subjects with paraplegia propelled faster and farther than did subjects with tetraplegia. CONCLUSION AND DISCUSSION: The ultralight wheelchair improved the efficiency of propulsion in the tested subjects. Subjects with tetraplegia, especially at the C6 level, are limited in their ability to propel a wheelchair.     

Wheeling à petit pas: Parkinsonism detected by observation of wheelchair propulsion

We present a man with parkinsonism detected by the observation of wheelchair propulsion. His manual wheelchair propulsion technique was observed to include rapid, brief, low-power strokes resembling the marche à petit pas (walking with tiny steps) phenomenon of parkinsonism. We videotaped his wheelchair propulsion and compared him with ten age-, gender-, and diagnosis-matched controls. The patient had a propulsion velocity of 0.14 m/sec compared with a mean (+/- standard deviation) of 0.73 (+/- 0.16) m/sec for the controls, a cadence of 209 strokes/min vs. 60 (+/- 12) strokes/min for the controls, and a mechanical efficiency of 0.04 m/stroke compared with 0.75 (+/- 0.25) m/stroke for the controls. This observation shifted the course of his medical investigations and management as well as his rehabilitation care. This is the first detailed report of how parkinsonian features may affect manual wheelchair propulsion. It suggests that observation of wheelchair mobility should be a routine component of the physical examination of wheelchair users.     

Development of a realistic method to assess wheelchair propulsion by disabled people

Most wheelchair users cannot achieve the steady state of cardio-respiratory performance necessary for standard physiological testing of wheelchair propulsion on ergometers or treadmills. Furthermore "real life" wheelchair utilisation involves short bursts of energy expenditure around furniture and other obstacles. We have developed a method of measuring wheelchair mobility on a test circuit of varying tortuosity and report here our preliminary experience. The parameters of mobility measured included distance; time taken; resting, maximum and final pulses (using a portable monitor); time to recover to stable resting pulse; and perceived exertion using the Borg Scale. Average speed and physiological cost of wheelchair propulsion (PCWP) (the difference between maximum and resting pulse divided by average speed) were calculated. The reproducibility of the components of the method was demonstrated in studies on normal volunteers. The test was also shown to be suitable for use by a sample of disabled people and was used in comparative studies of conventional and a novel arm crank wheelchair in normal volunteers. The method described appears to be an accurate and objective method of assessing wheelchair propulsion suitable for use by disabled people. It can also form the basis of comparative studies of different methods of propulsion of wheelchairs.     

Controllability and physiological evaluation of three unilaterally-propelled wheelchairs for patients with hemiplegia.

OBJECTIVE: To evaluate the controllability of, and physiological responses to, 2 newly designed unilaterally-propelled wheelchairs for patients with hemiplegia. DESIGN: Within-subject comparison. SUBJECTS: A total of 15 patients after stroke were recruited from the rehabilitation centre of Chung Shan Medical University, Taichung, Taiwan. METHODS: Two newly designed wheelchairs (an ankle-propelled wheelchair and a knee-propelled wheelchair) were compared with a commercially available 2-hand-rim propelled wheelchair. Patients propelled the 3 wheelchairs along an oval pathway. Videotapes were made for analysis. The following parameters: total propulsion time, deviation frequency, deviation percentage, physiological cost index (VO2) and rating of perceived exertion were measured and compared. RESULTS: The knee-propelled wheelchair gave the best results for controllability, cardiopulmonary and perceived exertion. However, the gear ratio of this wheelchair's force transmission was fixed, and some patients felt that its propulsion was heavy when starting off. CONCLUSION: The knee-propelled wheelchair showed good controllability and physiological responses for hemiplegic patients. If some details were improved, it would suitable for use by patients with hemiplegia.     

Evaluation of ambulatory performance of the arm propelled three-wheeled chair using heart rate as a control index

PURPOSE: The Arm propelled three wheeled chair (APTWC) is in common use in the economically poor countries for outdoor ambulation, the propulsion force of which is exerted by arm cranking in asynchronous fashion. The purpose of the study was to assess the ambulatory performance of the users of the device using heart rate as a control index, at graded speeds. METHOD: Fifteen regular users of APTWC male with paraplegia and poliomyelitis were ambulated at seven different graded speeds in outdoor settings and the resting and ambulatory heart rate was measured during steady state and then physiological cost index and comfortable speed of propulsion was computed. RESULTS: The physiological strain, linear regression of the relationship between heart rate and speed with correlation coefficient of r = 0.86 (p < 0.001), polynomial regression of the relationship between physiological cost index (PCI) and speed with correlation coefficient of r = 0.83 (p < 0.001) and comfortable speed of propulsion (120 m/min) was reported. CONCLUSIONS: Heart rate can be used to evaluate the ambulatory performance of the device, quantifying energy economy for outcome evaluation and decision making for clinical recommendation.     

Evaluation of ambulatory performance of the arm propelled three-wheeled chair using heart rate as a control index

Purpose : The Arm propelled three wheeled chair (APTWC) is in common use in the economically poor countries for outdoor ambulation, the propulsion force of which is exerted by arm cranking in asynchronous fashion. The purpose of the study was to assess the ambulatory performance of the users of the device using heart rate as a control index, at graded speeds. Method : Fifteen regular users of APTWC male with paraplegia and poliomyelitis were ambulated at seven different graded speeds in outdoor settings and the resting and ambulatory heart rate was measured during steady state and then physiological cost index and comfortable speed of propulsion was computed. Results : The physiological strain, linear regression of the relationship between heart rate and speed with correlation coefficient of r = 0.86 (p < 0.001), polynomial regression of the relationship between physiological cost index (PCI) and speed with correlation coefficient of r = 0.83 (p < 0.001) and comfortable speed of propulsion (120 m/min) was reported. Conclusions : Heart rate can be used to evaluate the ambulatory performance of the device, quantifying energy economy for outcome evaluation and decision making for clinical recommendation.     

Maximal aerobic power in cerebral palsied wheelchair athletes: validity and reliability.

This study examined the validity and reliability of maximal aerobic power (VO2max) during wheelchair ergometry (WE) in wheelchair athletes with cerebral palsy. Six class 3 and class 4 male athletes with cerebral palsy completed two graded exercise tests to volitional fatigue on a wheelchair ergometer mounted on frictionless rollers. Four athletes were also able to complete two tests of bicycle ergometry (BE). Although the reliability coefficients for the VO2max during the two exercise modes were high (.89 and .93 for the WE and BE tests, respectively), the validity coefficients for this variable (ie, the correlations between WE and BE) were poor (.31 and -.24 for trials 1 and 2, respectively). Examination of the individual data indicated that athletes who used wheelchairs as their primary mode of ambulation had higher VO2max values during WE; whereas, those who used canes or no aids for daily ambulation had higher values on BE. Because of the specificity of the, VO2max response, it is recommended that the primary mode of ambulation be considered when deciding on the testing mode for evaluating the cardiorespiratory fitness of athletes with cerebral palsy.     

The reliability and validity of the physiological cost index in healthy subjects while walking on 2 different tracks

OBJECTIVE: To investigate the reliability and validity of the Physiological Cost Index (PCI) scores, as a measure of energy expenditure, when healthy subjects walk on 2 different tracks (20-m and 12-m figure eight tracks). DESIGN: Intra- and interrater reliability and construct validity. SETTING: Physiotherapy division of a university in London, UK. PARTICIPANTS: Forty healthy subjects (15 men, 25 women; mean age +/- standard deviation, 34.5+/-12.6 y). INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Heart rate (in beats/min) and speed (in m/min) were used to calculate the PCI (in beats/m). Rate of oxygen consumption (VO2, in mL x kg(-1) x min(-1)) and oxygen cost (EO2, in mL x kg(-1) x m(-1)) were used as criterion estimates of energy cost EO2. Pearson correlation coefficients between the PCI, components of the PCI, EO2, and VO2 were used to quantify validity. Intrarater reliability was assessed in all participants and interrater reliability was assessed on a subset of 13 subjects using intraclass correlation coefficients and Bland-Altman plots. RESULTS: Intrarater (r=.73, r=.79) and interrater (r=.62, r=.66) reliability were acceptable between PCI scores from 20-m and 12-m tracks, respectively. Correlations between VO2 and EO2 with PCI were weak. PCI scores from the 20-m track were significantly lower than those on the 12-m track (P=.002). Subjects walked significantly faster on the 20-m track (P<.001). Results suggest a large difference in PCI scores would be necessary to indicate a "true" alteration in performance (52% for 20-m track, 43.4% for the 12-m track). CONCLUSIONS: The PCI is reliable but not valid as a measure of the energy cost of walking in healthy subjects, on either track. The 20-m track is recommended for clinical use because it enables subjects to walk at a faster pace.     

Load on the shoulder in low intensity wheelchair propulsion

OBJECTIVE: To assess the mechanical load on the glenohumeral joint and on shoulder muscles during wheelchair propulsion at everyday intensities. DESIGN: Model simulations based on experimental input dataBackground. Virtually nothing is known about the mechanical load on the upper extremity during wheelchair propulsion. Hand rim wheelchair propulsion is a significant risk factor for shoulder pain and injury among wheelchair users. A musculoskeletal model of the upper extremity during wheelchair propulsion will quantify the stresses placed on anatomic structures and may provide insight into the source of symptoms and injuries. METHODS: Three experienced wheelchair users underwent wheelchair exercise tests at combinations of two load levels (10 and 20 W) and two velocities (0.83 and 1.39m.s(-1)) during which input data were collected for a musculoskeletal model of the upper extremity. The model was then used for the estimation of the glenohumeral contact force, as well as individual muscle forces. RESULTS: Peak glenohumeral contact forces were between 800 and 1400 N (100-165% body weight) and differed significantly between load levels. Averaged over the push phase, these forces were 500-850 N. In absolute terms the m. deltoideus and rotator cuff muscles were highly active (>100N). In relative terms the load on the m. supraspinatus was high, with peak values of over 50% of its maximum attainable force. CONCLUSIONS: Low intensity wheelchair propulsion does not appear to lead to high contact forces. The muscle forces in the rotator cuff and especially in the m. supraspinatus are high. This might indicate a risk for muscle damage and the subsequent development of shoulder complaints, such as rotator cuff tears. RELEVANCE: Within the wheelchair user population, there is a high prevalence of upper extremity complaints. Not much is known about the causes of those complaints. Wheelchair propulsion is likely to be a major risk factor. If the (nature of this) mechanical load can be identified, specific exercise programs and/or design changes can be better tuned to prevent overuse injuries.