Changes in oxygen uptake, shoulder muscles activity, and propulsion cycle timing during strenuous wheelchair exercise

Differences in muscle coordination between older men and women during brisk walking

Brisk walking is a highly recommended physical activity for healthy community-dwelling older adults. The objective of this study was to examine through principal component analysis (PCA) how muscle coordination differs between older women and men during brisk walking. Thirty-five healthy older adults (65.2 ± 3.0 years old, 18 females, and 17 males) participated in the study. Eight surface electromyographic electrodes were used to record lower extremity muscle activities, and four inertial measurement unit sensors to monitor hip, knee, and ankle motion. Energy expenditure and heart rate were also measured during brisk walking. The effects of a person's sex on muscle coordination were identified through wavelet and PCA analysis of the sEMG signals. The results of energy expenditure and heart rate confirmed that brisk walking exercise is beneficial for older adults. PCA analysis showed that muscle coordination patterns differ between older women and men: during the stance phase a greater co-contraction of tibialis anterior and soleus in the men, and a greater activation of the quadriceps muscles during the loading-response phase in the women. The wavelet and PCA analyses facilitated a quantitative appraisal of sex-specific differences in the muscle coordination patterns of older men and women during brisk walking.

Effect of Manual Wheelchair Type on Mobility Performance, Cardiorespiratory Responses, and Perceived Exertion

This study is aimed at comparing the design and configuration of the most commonly used manual wheelchair models through cardiorespiratory responses, perceived exertion, and mobility performance using two different manual wheelchairs, during mobility tasks. A within-group 2 × 3 × 2 controlled experiment was designed with three independent and four dependent variables. The independent variables included wheelchairs, with the levels active wheelchair with a rigid frame and passive wheelchair with foldable frame; conditions with the levels straight line, slalom, and agility; and speed with levels comfortable and fast. Dependent variables included oxygen uptake (VO₂), distance travelled, speed, and perceived exertion. Results show that the active wheelchair yielded more beneficial characteristics although only the effect of wheelchair type on VO₂ efficiency (oxygen uptake per meter travelled) was statistically significant with a large effect size (F(1, 14) = 118.298, p < 0.001, η² = 0.541). The better VO₂ efficiency was achieved with the active wheelchair under all tested conditions. The effect of wheelchair type on Borg scores was also statistically significant, although with a small effect size (F(1, 14) = 10.340, p = 0.006, η² = 0.119); thus, active wheelchair use had lower Borg scores under all trials and was considered less exhausting than the passive wheelchair. In summary, use of the active wheelchair resulted in the users expending less energy per meter travelled and at the same time experiencing less fatigue. This may benefit overall wheelchair mobility and possibly reduce health complications.

The Effect of Fatigue on Wheelchair Users' Upper Limb Muscle Coordination Patterns in Time-Frequency and Principal Component Analysis

An assessment of shoulder muscle coordination patterns is important to gain insight into muscle fatigue during wheelchair propulsion. The objective of the present study was to quantify muscle coordination changes over time during fatiguing wheelchair propulsion, as the muscles go through distinct levels of fatigue, a) non-fatigued, b) transiting to fatigue and c) fatigued to exhaustion. We recorded surface electromyography (sEMG) signals of the anterior deltoid (AD), middle deltoid (MD), posterior deltoid (PD), infraspinatus (IS), upper trapezius (UT), sternal head of the pectoralis major (PM), biceps brachii (BB), and triceps brachii (TB) during a wheelchair incremental exercise test. Nine wheelchair users with a diagnosis of spina bifida or T6-T12 spinal cord injury volunteered for the study. Oxygen uptake and SmartWheel kinetic parameters were also recorded during the test. EMG signals were processed by wavelet and principal component analysis (PCA), allowing for an assessment of how wheelchair users modify their muscle coordination patterns over time. Analyses of covariance (ANCOVA) were conducted to identify the main effect of fatigue levels on muscle coordination patterns by controlling for the effect of increased workload as covariate. A significant effect of fatigue levels on the PC1 and PC3 loading scores was found after controlling for the effect of increasing workloads (with both cases). In addition, PC3 reflects the most dominant fatigue effect on muscle coordination patterns which are not affected by increased ergometer workload. PC3 indicates muscle imbalance when muscles are fully fatigued and muscle co-contraction when muscles are beginning to fatigue. We conclude that fatigue-related changes in neuromuscular activity during wheelchair propulsion contribute to muscle imbalance and reflect a strategy of stiffening the shoulder joint.

Start-up propulsion biomechanics changes with fatiguing activity in persons with spinal cord injury

Objective: Shoulder pathology is a common condition in wheelchair users that can considerably impact quality of life. Shoulder muscles are prone to fatigue, but it is unclear how fatigue affects start-up propulsion biomechanics. This study determines acute changes in start-up wheelchair propulsion biomechanics at the end of a fatiguing propulsion protocol. Design: Quasi-experimental one-group pretest-postest design. Setting: Biomechanics laboratory. Participants: Twenty-six wheelchair users with spinal cord injury (age: 35.5 ± 9.8 years, sex: 73% males and 73% with a paraplegia). Interventions: Protocol of 15 min including maximum voluntary propulsion, right- and left turns, full stops, start-up propulsion, and rests. Outcome measures: Maximum resultant force, maximum rate of rise of applied force, mean velocity, mean fraction of effective force, and mean contact time at the beginning and end of the protocol during start-up propulsion. Results: There was a significant reduction in maximum resultant force (P < 0.001) and mean velocity (P < 0.001) at the end of the protocol. Also, contact time was reduced in the first stroke of start-up propulsion (P < 0.001). Finally, propelling with a shorter contact time was associated with a greater reduction in performance (maximum velocity) at the end of the protocol. Conclusion: There are clear changes in overground propulsion biomechanics at the end of a fatiguing propulsion protocol. While reduced forces could protect the shoulder, these reduced forces come with shorter contact times and lower velocity. Investigating changes in start-up propulsion biomechanics with fatigue could provide insight into injury risk.

The Effect of Manual Wheelchair Propulsion Speed on Users' Shoulder Muscle Coordination Patterns in Time-Frequency and Principal Component Analysis

A rehabilitation program for wheelchair users should be based on a thorough understanding of shoulder muscle coordination patterns. The objective of the study was to quantify the extent to which the muscle electromyographic (EMG) patterns vary with propulsion speed. A total of 11 wheelchair-dependent participants with a diagnosis of spina bifida or T6-T12 spinal cord injury volunteered for the study. Each participant performed a series of wheelchair propulsion bouts at 1m/s, 1.3 m/s, and 1.6m/s. EMG signals of 8 shoulder muscles as well as the physiological and kinetic variables were recorded. Propulsion at 1.6m/s generated significantly higher EMG intensities in biceps brachii, anterior deltoid, pectoralis major, and middle deltoid than at 1m/s and 1.3m/s. The combined wavelet and principal component analysis showed that the faster propulsion speed requires higher push muscle activity in the early push phase and in the phase transitions between alternating push and recovery. Training to strengthen the shoulder flexors to achieve smoother phase transitions could improve rehabilitation outcomes by increasing functional speed while lessening shoulder strain.

Development and validation of an automated step ergometer

Laboratory ergometers have high costs, becoming inaccessible for most of the population, hence, it is imperative to develop affordable devices making evaluations like cardiorespiratory fitness feasible and easier. The objective of this study was to develop and validate an Automated Step Ergometer (ASE), adjusted according to the height of the subject, for predicting VO2max through a progressive test. The development process was comprised by three steps, the theoretical part, the prototype assembly and further validation. The ASE consists in an elevating platform that makes the step at a higher or lower level as required for testing. The ASE validation was obtained by comparing the values of predicted VO2max (equation) and direct gas analysis on the prototype and on a, treadmill. For the validation process 167 subjects with average age of 31.24 ± 14.38 years, of both genders and different degrees of cardiorespiratory fitness, were randomized and divided by gender and training condition, into untrained (n=106), active (n=24) and trained (n=37) subjects. Each participant performed a progressive test on which the ASE started at the same height (20 cm) for all. Then, according to the subject's height, it varied to a maximum of 45 cm. Time in each stage and rhythm was chosen in accordance with training condition from lowest to highest (60-180 s; 116-160 bpm, respectively). Data was compared with the student's t test and ANOVA; correlations were tested with Pearson's r. The value of α was set at 0.05. No differences were found between the predicted VO2max and the direct gas analysis VO2max, nor between the ASE and treadmill VO2max (p= 0.365) with high correlation between ergometers (r= 0.974). The values for repeatability, reproducibility, and reliability of male and female groups measures were, respectively, 4.08 and 5.02; 0.50 and 1.11; 4.11 and 5.15. The values of internal consistency (Cronbach's alpha) among measures were all >0.90. It was verified that the ASE prototype was appropriate for a step test, provided valid measures of VO2max and could therefore, be used as an ergometer to measure cardiorespiratory fitness.

Comparison of metabolic cost, performance, and efficiency of propulsion using an ergonomic hand drive mechanism and a conventional manual wheelchair

OBJECTIVE

To compare the metabolic cost (oxygen uptake per unit time [V˙o2 consumption], heart rate, and number of pushes), performance (velocity and distance traveled), and efficiency (oxygen uptake per distance traveled [Vo2 efficiency]) of propulsion using a novel ergonomic hand drive mechanism (EHDM) and a conventional manual wheelchair (CMW).

DESIGN

Repeated-measures crossover design.

SETTING

Semicircular track.

PARTICIPANTS

Adult full-time manual wheelchair users with spinal cord injuries (N=12; mean age ± SD, 38.8±12.4y; mean body mass ± SD, 73.7±13.3kg; mean height ± SD, 173.6±11.1cm) who were medically and functionally stable and at least 6 months postinjury.

INTERVENTION

Participants propelled themselves for 3.5 minutes at a self-selected pace in a CMW and in the same chair fitted with the EHDM.

MAIN OUTCOME MEASURES

Velocity, distance traveled, number of pushes, V˙o2 consumption, Vo2 efficiency, and heart rate were compared by wheelchair condition for the last 30 seconds of each trial using paired t tests (α=.01).

RESULTS

The CMW condition resulted in more distance traveled (33.6±10.8m vs 22.4±7.8m; P=.001), greater velocity (1.12±0.4m/s vs .75±.30m/s; P=.001), and better Vo2 efficiency (.10±.03mL·kg(-1)·m(-1) vs .15±.03mL·kg(-1)·m(-1); P<.001) than the EHDM condition, respectively. No significant differences were found between the 2 conditions for number of pushes (27.5±5.7 vs 25.7±5.4; P=.366), V˙o2 consumption (6.43±1.9mL·kg(-1)·min(-1) vs 6.19±1.7mL·kg(-1)·min(-1); P=.573), or heart rate (100.5±14.5 beats per minute vs 97.4±20.2 beats per minute; P=.42).

CONCLUSIONS

The results demonstrate that metabolic costs did not differ significantly; however, performance and efficiency were sacrificed with the EHDM. Modifications to the EHDM (eg, addition of gearing) could rectify the performance and efficiency decrements while maintaining similar metabolic costs. Although not an ideal technology, the EHDM can be considered as an alternative mode of mobility by wheelchair users and rehabilitation specialists.

Patterns of shoulder muscle coordination vary between wheelchair propulsion techniques

This study investigated changes in the coordination patterns of shoulder muscles and wheelchair kinetics with different propulsion techniques by comparing wheelchair users' self-selected propulsion patterns with a semicircular pattern adopted after instruction. Wheelchair kinetics data were recorded by Smart(Wheel) on an ergometer, while EMG activity of seven muscles was recorded with surface electrodes on 15 able-bodied inexperienced participants. The performance data in two sessions, first using a self-selected and then the learned semicircular pattern, were compared with a paired t-test. Muscle coordination patterns across seven muscles were analyzed by principal component analysis. The semicircular pattern was characterized by significantly lower push frequency, significantly longer push length, push duration and push distance (p < 0.05, all cases) without a significant increase in push force, when compared with the self-selected pattern. In addition, our results show that in the semicircular propulsion technique, synergistic muscles were recruited in distinct phases and displayed a clearer separation between activities in the push phase and recovery phase muscles. An instruction session in semicircular propulsion technique is recommended for the initial use of a wheelchair after an injury.

Comparison of shoulder load during power-assisted and purely hand-rim wheelchair propulsion

BACKGROUND

Repetitive forces and moments are among the work requirements of hand-rim wheelchair propulsion that are related to shoulder injuries. No previous research has been published about the influence of power-assisted wheelchair propulsion on these work requirements. The purpose of our study was therefore to determine the influence of power-assisted propulsion on shoulder biomechanics and muscle activation patterns. We also explored the theoretical framework for the effectiveness of power-assisted propulsion in preventing shoulder injuries by decreasing the work requirements of hand-rim wheelchair propulsion.

METHODS

Nine non-wheelchair users propelled a hand-rim wheelchair on a treadmill at 0.9 m/s. Shoulder biomechanics, and muscle activation patterns, were compared between propulsion with and without power-assist.

FINDINGS

Propulsion frequency did not differ significantly between the two conditions (Wilcoxon Signed Rank test/significance level/effect size:4/.314/-.34). During power-assisted propulsion we found significantly decreased maximum shoulder flexion and internal rotation angles (1/.015/-.81 and 0/.008/-.89) and decreased peak force on the rim (0/.008/-.89). This resulted in decreased shoulder flexion, adduction and internal rotation moments (2/.021/-.77; 0/.008/-.89 and 1/.011/-.85) and decreased forces at the shoulder in the posterior, superior and lateral directions (2/.021/-.77; 2/.008/-.89 and 2/.024/-.75). Muscle activation in the pectoralis major, posterior deltoid and triceps brachii was also decreased (2/.038/-.69; 1/.015/-.81 and 1/.021/-.77).

INTERPRETATION

Power-assist influenced the work requirements of hand-rim wheelchair propulsion by healthy subjects. It was primarily the kinetics at rim and shoulder which were influenced by power-assisted propulsion. Additional research with actual hand-rim wheelchair users is required before extrapolation to routine clinical practice.