Muscle Activation Patterns Are More Constrained and Regular in Treadmill Than in Overground Human Locomotion

Abstract

The use of motorized treadmills as convenient tools for the study of locomotion has been in vogue for many decades. However, despite the widespread presence of these devices in many scientific and clinical environments, a full consensus on their validity to faithfully substitute free overground locomotion is still missing. Specifically, little information is available on whether and how the neural control of movement is affected when humans walk and run on a treadmill as compared to overground. Here, we made use of linear and non-linear analysis tools to extract information from electromyographic recordings during walking and running overground, and on an instrumented treadmill. We extracted synergistic activation patterns from the muscles of the lower limb via non-negative matrix factorization. We then investigated how the motor modules (or time-invariant muscle weightings) were used in the two locomotion environments. Subsequently, we examined the timing of motor primitives (or time-dependent coefficients of muscle synergies) by calculating their duration, the time of main activation, and their Hurst exponent, a non-linear metric derived from fractal analysis. We found that motor modules were not influenced by the locomotion environment, while motor primitives were overall more regular in treadmill than in overground locomotion, with the main activity of the primitive for propulsion shifted earlier in time. Our results suggest that the spatial and sensory constraints imposed by the treadmill environment might have forced the central nervous system to adopt a different neural control strategy than that used for free overground locomotion, a data-driven indication that treadmills could induce perturbations to the neural control of locomotion.

Muscle Synergies in Children Walking and Running on a Treadmill

“…We focused the analysis on all 15 muscles recorded from the lower limb, trunk, and upper limb, but also carried out an analysis on a subset of these muscles in order to confirm the findings from the literature where the main focus is often on the lower limb muscles (Supplementary Material 1). We found that the number of synergies across groups were much lower and comparable to what has previously been found in walking in children and adults (e.g., Dominici et al, 2011;Oliveira et al, 2016;Hinnekens et al, 2020;Mileti et al, 2020;Sylos-Labini et al, 2020) where four synergies is one of the most common findings. The activation patterns and the weighting coefficients were also comparable to what has previously been found in literature.…”

Greater Reliance on Cerebral Palsy-Specific Muscle Synergies During Gait Relates to Poorer Temporal-Spatial Performance Measures

“…This is also confirmed by the addition of a new synergy if an extra voluntary movement, such as kicking, is included in the walking ( Ivanenko et al, 2005 ). Previous studies also demonstrated that treadmill locomotion shares similar muscle synergy structures with overground locomotion ( Oliveira et al, 2016 ; Mileti et al, 2020 ). Similarly, balance-specific muscle synergies were consistently recruited in different types of postural tasks ( Torres-Oviedo and Ting, 2010 ).…”

“…In the study, the muscle synergies were analyzed for treadmill walking. A previous study demonstrated that treadmill locomotion shares similar muscle synergy structures with overground locomotion (Oliveira et al, 2016;Mileti et al, 2020) although synergy activations were more consistent in the treadmill condition (Mileti et al, 2020). Since we classified group-specific synergies based on synergy structures, we assume that walking environment may rarely influence the results.…”

Muscle Synergies in Patients With Multiple Sclerosis Reveal Demand-Specific Alterations in the Modular Organization of Locomotion

“…In addition, the current results were generated only during treadmill walking at a preferred and a fixed speed. There might be slightly differences between treadmill and overground walking; however, muscle synergies have been shown to be generally consistent for both environments (Oliveira et al, 2016 ; Mileti et al, 2020 ).…”