To date, few data are available, but all show a structural and mechanical muscle impact post injections, specifically muscle atrophy which can linger over time. Further studies are necessary to validate this element, and the possibility of change must be taken into account particularly with repeated injections. Thus, in clinical practice, 2D ultrasound and ultrasound elastography are two non-invasive techniques that will help physicians to develop an efficient long term monitoring.

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Lower-limb posture with casting in children has a high level of evidence, but the long-term efficacy of short-leg casting needs to be evaluated. A comparison between the different modalities of casting is missing, and studies specifically devoted to testing the different kinds of casting are needed. Moreover, the delay to casting after BTX injection is not clear. Data on electrical stimulation are not conclusive. Despite the small number of studies, resistance training could be an interesting adjunct therapy notably to avoid loss of strength after BTX injection. Rehabilitation programmes after BTX injection still need to be evaluated.

Whether muscle stiffness is influenced by fatigue remains unclear. Classical methods used to assess muscle stiffness provide a global measure at the joint level. As fatigue may selectively affect specific muscles, a joint-level approach may not be sensitive enough to detect potential changes in muscle stiffness. Taking advantage of ultrasound shear wave elastography, this study aimed to determine the influence of a fatiguing protocol involving intermittent submaximal isometric contractions on muscle shear modulus (an index of stiffness). Methods: Shear modulus was measured on either the vastus lateralis (VL; n=9) or the abductor digiti minimi (ADM; n=10) before and after 15-mins of intermittent submaximal isometric contractions at 60% of maximal voluntary contraction (MVC; 4 s ON, 4 s OFF). An index of active muscle stiffness was estimated PRE and POST-fatigue as the slope of the linear regression established between shear modulus and absolute joint force up to 60% MVC. Results: After the fatiguing exercise, MVC was significantly decreased by 22 ± 7 % and 32 ± 15 % for knee extension and little finger abduction, respectively (p<0.001). When compared to PRE-fatigue, the index of active muscle stiffness was 12 ± 15 % lower for the VL (p < 0.031) and 44 ± 19 % lower for the ADM (p < 0.001) POST-fatigue. Conclusion: Although the present results cannot clearly determine the involved mechanisms, they demonstrate a decreased active muscle stiffness after a fatiguing task involving intermittent submaximal isometric contractions. Further studies should now determine whether this change in stiffness affects performance and risk of injury.