Abstract
Background
The Lokomat is a robotic device that has been suggested to make gait therapy easier, more comfortable, and more efficient. In this study, we asked whether the Lokomat promotes physiological muscle activation patterns, a fundamental question when considering motor learning and adaptation.
Methods
We investigated lower limb muscles coordination in terms of muscle activity level, muscle activity pattern similarity, and muscle synergy in 15 healthy participants walking at 3 km/h on either a treadmill or in a Lokomat at various guidance forces (GF: 30, 50 or 70%) and body weight supports (BWS: 30, 50 or 70% of participant’s body weight).
Results
Walking in the Lokomat was associated with a greater activation level of the rectus femoris and vastus medialis (×2–3) compared to treadmill walking. The level of activity tended to be diminished in gastrocnemius and semi-tendinosus, which particularly affected the similarity with treadmill walking (normalized scalar product NSP = 0.7–0.8). GF and BWS independently altered the muscle activation pattern in terms of amplitude and shape. Increasing BWS decreased the level of activity in all but one muscle (the soleus). Increasing GF slightly improved the similarity with treadmill walking for the tibialis anterior and vastus medialis muscles. The muscle synergies (N = 4) were similar (NSP = 0.93–0.97), but a cross-validation procedure revealed an alteration by the Lokomat. The activation of these synergies differed (NSP = 0.74–0.82).
Conclusion
The effects of GF and BWS are modest compared to the effect of the Lokomat itself, suggesting that Lokomat design should be improved to promote more typical muscle activity patterns.
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Abbreviations
- ANOVA:
-
Analysis of variance
- BWS:
-
Body weight support
- C:
-
Synergy activation matrix
- E:
-
EMG matrix
- GF:
-
Guidance force
- IMVC:
-
Isometric maximal voluntary contraction
- M:
-
Number of muscles
- GM:
-
Gastrocnemius medialis
- NNMF:
-
Nonnegative matrix factorization
- NSP:
-
Normalized scalar products
- RF:
-
Rectus femoris
- S:
-
Number of synergies
- SENIAM:
-
Surface EMG for non-invasive assessment of muscles
- SO:
-
Soleus
- SSE:
-
Sum of squared errors
- SST:
-
Total sum of squares
- ST:
-
Semitendinosus
- T:
-
Number of time points
- TA:
-
Tibialis anterior
- VAF:
-
Variation accounted for
- VM:
-
Vastus medialis
- W:
-
Synergy weightings matrix
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The authors would like to acknowledge the participation of all subjects in this study.
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YC: responsible for the study design, data analysis, and interpretation as well as the manuscript writing. MH: responsible for data analysis and interpretation, as well as major revisions of the manuscript. FDM: responsible for the study design, EMG expertise, as well as major revisions of the manuscript. NT: responsible for the study design, supervision of the project, EMG expertise, validation of the main decisions during the study, validation of data interpretation as well as major revisions of the manuscript.
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This study was approved by the Research Ethics Board of UHC Sainte-Justine (2016–831, 4049). All subjects signed informed and written consent before any procedure of the experiments.
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Communicated by Andrew Cresswell.
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Cherni, Y., Hajizadeh, M., Dal Maso, F. et al. Effects of body weight support and guidance force settings on muscle synergy during Lokomat walking. Eur J Appl Physiol 121, 2967–2980 (2021). https://doi.org/10.1007/s00421-021-04762-w
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DOI: https://doi.org/10.1007/s00421-021-04762-w