Purpose During alternate movements across a joint, the changeover from one direction of rotation to the opposite may be influenced by the delay and rate of tension reduction and the compliance to re-lengthening of the previously active muscle group. Given the aging process may affect the above-mentioned factors, this work aimed to compare the dynamics of both the ankle torque decline and muscle re-lengthening, mirrored by mechanomyogram (MMG), in the tibialis anterior because of its important role in gait. Methods During the relaxation phase, after a supramaximal 35 Hz stimulation applied at the superficial motor point, in 20 young (Y) and 20 old (O) subjects, the torque (T) and MMG dynamics characteristics were measured. Results The T and MMG analysis provided: (I) the beginning of the decay after cessation of stimulation (T: 22.51 ± 5.92 ms [Y] and 51.35 ± 15.21 ms [O]; MMG: 27.38 ± 6.93 ms [Y] and 61.41 ± 18.42 ms [O]); (II) the maximum rate of reduction (T: − 110.4 ± 45.56 Nm/s [Y] and − 52.72 ± 32.12 Nm/s [O]; MMG: − 24.47 ± 10.95 mm/s [Y] and − 13.76 ± 6.54 mm/s [O]); (III) the muscle compliance, measuring the MMG reduction of every 10% reduction of torque (bin 20–10%: 15.69 ± 7.5[Y] and 10.8 ± 3.3 [O]; bin 10–0%: 22.12 ± 10.3 [Y] and 17.58 ± 5.6 [O]). Conclusion Muscle relaxation results are different in Y and O and can be monitored by a non-invasive method measuring physiological variables of torque and re-lengthening dynamics at the end of the electromechanical coupling previously induced by the neuromuscular stimulation.

Background Long-term weakness is common in survivors of COVID-19–associated acute respiratory distress syndrome (CARDS). We assessed the predictors of muscle weakness in patients evaluated at 3, 6, and 12 months after intensive care unit discharge with in-person visits. Methods Muscle strength was measured by isometric maximal voluntary contraction (MVC) of the tibialis anterior muscle. Candidate predictors of muscle weakness were follow-up time, sex, age, mechanical ventilation duration, use of steroids in the intensive care unit, compound muscle action potential of the tibialis anterior muscle (CMAP-TA-S100), severe fatigue, depression and anxiety, post-traumatic stress disorder, cognitive assessment, and body mass index. We also compared the clinical tools currently available for the evaluation of muscle strength (handgrip strength, Medical Research Council sum score) and electrical neuromuscular function (simplified peroneal nerve test [PENT]) with more objective and robust measures of force (MVC) and electrophysiological evaluation of the neuromuscular function of the tibialis anterior muscle (CMAP-TA-S100) for its essential role in ankle control. Results MVC improved at 12 months compared with 3 months. Sex (P < 0.001), age (P = 0.012), duration of mechanical ventilation (P = 0.044), and CMAP-TA-S100 (P < 0.001) were independent predictors of MVC. MVC was strongly associated with handgrip strength, whereas CMAP-TA-S100 was strongly associated with PENT. Conclusions Female sex, increasing age, increased duration of mechanical ventilation, and electrical neuromuscular abnormalities are independently associated with reduced MVC and can be used to predict the risk of long-term muscle weakness in CARDS survivors. Trial registration : The present study was registered at ClinicalTrial.gov (NCT: ​​NCT04608994). Registered on October 30, 2020. Retrospectively registered.

IntroductionPatients admitted to the intensive care unit (ICU) following severe acute respiratory syndrome 2 (SARS-CoV-2) infection may have muscle weakness up to 1 year or more following ICU discharge. However, females show greater muscle weakness than males, indicating greater neuromuscular impairment. The objective of this work was to assess sex differences in longitudinal physical functioning following ICU discharge for SARS-CoV-2 infection.MethodsWe performed longitudinal assessment of physical functioning in two groups: 14 participants (7 males, 7 females) in the 3-to-6 month and 28 participants (14 males, 14 females) in the 6-to-12 month group following ICU discharge and assessed differences between the sexes. We examined self-reported fatigue, physical functioning, compound muscle action potential (CMAP) amplitude, maximal strength, and the neural drive to the tibialis anterior muscle.ResultsWe found no sex differences in the assessed parameters in the 3-to-6-month follow-up, indicating significant weakness in both sexes.Sex differences emerged in the 6-to-12-month follow-up. Specifically, females exhibited greater impairments in physical functioning, including lower strength, walking lower distances, and high neural input even 1 year following ICU-discharge.DiscussionFemales infected by SARS-CoV-2 display significant impairments in functional recovery up to 1 year following ICU discharge. The effects of sex should be considered in post-COVID neurorehabilitation.

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