Comparison of elliptical training, stationary cycling, treadmill walking and overground walking
Introduction
Promoting, maintaining and enhancing gait function are common therapeutic goals in neurorehabilitation, with the recent proliferation of devices to assist patients and clinicians towards achievement of those goals. While these devices may facilitate practice of the locomotor pattern, their superiority in enhancing gait outcomes remains uncertain [1]. Comparative evaluation of the biomechanical and coordinative aspects of various device-driven locomotor training tasks may provide some insights into their potential effectiveness in improving overground ambulation. Multiple studies have compared treadmill to overground gait kinematics, some including kinetic and electromyographic (EMG) data as well. Some small kinematic differences have been identified across these modalities, but are generally considered inconsequential [2], [3]. Riley and colleagues [4] demonstrated the “essential equivalence” of treadmill and overground walking, showing differences in 12/22 kinematic parameters in 33 healthy adults, with all but one less than 2° in magnitude. Lee and Hidler [5] confirmed the similarity in kinematic patterns, but noted more pronounced EMG differences responsible for preserving the nearly identical motions. Some studies have reported contradictory directions of differences, for example, increased [6] or decreased [4] peak hip flexion on the treadmill. Some differences may be attributed to the novelty of the treadmill for some subjects which often dissipate with a short practice (less than 10 min) [7]. Some clinical populations, e.g. the elderly [8], may have more difficulty accommodating to the treadmill and require additional practice.
Far less research has evaluated the biomechanical similarity of other lower extremity device-augmented training tasks to walking. Elliptical training was recently compared to overground walking in 15 healthy young males with a primary focus on joint loading; however, three-dimensional kinematic differences were also reported [9]. Excursions were similar at the knee and hip, but the curves were shifted into greater flexion at each joint particularly for the second half of the cycle with the elliptical. Kinematic differences from overground walking were also identified in the frontal and transverse planes. These findings were largely replicated by Burnfield and colleagues [10] who additionally demonstrated that not all elliptical trainers are ‘equal’ with some more closely resembling walking kinematics and kinetics.
In addition to the degree of biomechanical similarity other considerations for choice of a device include relative differences in joint stress which are important if repeated use of a training device is indicated. Degree of similarity in the coordinative aspects of the movements in the device including the degree of interlimb reciprocation versus synchrony and of intralimb coupling versus isolated control may also affect the degree of transfer. For example, walking involves reciprocal movements of the legs and arms, in contrast to a task such as rowing which involves bilaterally synchronous motions. Persons with disorders such as stroke or cerebral palsy often demonstrate more synergistic or constrained movement patterns within a limb such as massed flexion or extension during gait. These impair selective motor control or the ability of joints to move independently of each other [11], [12], [13]. The extent to which selective control may be required or reinforced may differ across tasks, especially for tasks like cycling and elliptical stepping which constrain motion to a pre-set arc, is also as yet unknown. The degree of ankle and knee intralimb coupling during gait in 78 children from ages 3 to 13 years without disability was −0.70 [14]. This indicated that these joints tended to move in opposition; whereas in 34 children with CP of similar ages, the correlation was +0.70 indicating a high and significantly greater (p < 0.05) degree of synergism. Additionally, to enhance training and neuroplastic effects, there should be an underlying rhythm or pattern but it should optimally be variable and flexible rather than rigid [15].
Our goals were to compare lower extremity kinematics of cycling, elliptical training, overground and treadmill walking in healthy adults, and to provide greater justification for further exploration of the use of these tasks and other exercise tasks or robotic devices in gait rehabilitation. We hypothesized that elliptical kinematics would more closely resemble walking than does cycling and therefore may have greater transfer to overground gait patterns. We further hypothesized that both elliptical training and cycling would show a similar or greater degree of interlimb coordination than treadmill or overground walking due to the interlimb coupling inherent in those devices.
Section snippets
Participants
Ten healthy young adults (6 males) participated. Mean age was 22.7 ± 2.9 years (range 20–29 years), mean height was 173.5 ± 9.8 cm (range 155–191 cm), and mean mass was 69.5 ± 9.8 kg (range 49.5–79.1 kg). The protocol was approved by our Human Subjects Institutional Review Board and written informed consent was obtained from all individuals.
Procedures
Three-dimensional lower extremity kinematics were collected with a ten-camera motion capture system (Vicon, Lake Forest, CA), at a sampling rate of 120 Hz. For the
Results
Cadence was higher during T than W (p < 0.001) and E (p < 0.024) (Table 1). Sagittal plane kinematic plots are shown in Fig. 1. These indicated that T excursion, position, and variability were very similar to those of W as reported previously. The only difference was greater hip rotation excursion during W. When comparing all four conditions, knee excursion was the only parameter that showed no differences. E and C showed unique patterns of differences from W. E showed higher values on all but two
Discussion
The primary goal here was to explore potential locomotor training alternatives to the treadmill by evaluating their kinematic similarity. As has been shown previously, nearly complete kinematic similarity between treadmill and overground walking was demonstrated here by evaluation of individual joint positions and excursions and, for the first time, by a composite value based on principal components analysis, the GDI. In contrast, the patterns for the two other locomotor tasks studied here were
Conclusion
As exercise and robotic devices are increasing employed for gait training in patient populations, their individual and relative effectiveness compared to conventional gait training must be evaluated. Our data reinforce the kinematic and coordinative similarity of treadmill and overground walking. Cycling showed the largest GDI difference from overground, with elliptical closer but still a significant distance from all three. If kinematic similarity was the sole determinant of skill transfer,
Acknowledgement
This work was funded by the intramural research program at the NIH Clinical Center.
Conflict of interest
None of the authors on this manuscript have any financial or personal relationships with other people or organisations that could inappropriately influence (bias) their work.
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