Acute fatigue induced changes the passive and active mechanical properties of the gastrocnemius medialis in individuals with chronic stroke and healthy adults

Abstract Purpose The consequences and underlying mechanisms of neuromuscular fatigue in the plantar flexors in a pathological population such as stroke patients remain poorly understood and have been very little investigated. The aim of this study was to (1) characterise the mechanical properties of the plantar flexors before, immediately after and at a later stage following an isometric fatigue protocol, and (2) compare this response with that of a healthy population. Methods Thirty volunteers took part in a fatigue protocol consisting of 60 isometric contractions, using an ergometer. Torque, shear modulus, stiffness and sEMG were measured under active and passive conditions before (P1), immediately after (P2) and after a 3-minute rest period (P3). Results Under active conditions, both groups exhibited a similar response pattern, with a decrease in torque, shear modulus, RFD and sEMG amplitude immediately following the protocol (P2), followed by incomplete recovery after a 3-minute rest period (P3). In the passive condition, although the shear modulus gradually decreased from P1 to P3 in both groups, overall stiffness did not respond in the same way. The stroke group showed no significant change in stiffness at any measurement time point, whilst the control group’s stiffness gradually increased. Conclusion Fatigue led to mechanical changes in both groups, but with distinct local and global responses. The paretic muscle retains a fatigue response that is relatively comparable to that of a healthy muscle. Thus, the paretic muscle remains capable of relaxing under load despite its chronically elevated stiffness, which could be utilised to achieve clinical functional benefits.