Exercise-induced fatigue in young people: advances and future perspectives

This is the author accepted manuscript. The final version is available from Springer Verlag via the DOI in this record.PURPOSE: In recent decades, the interest for exercise-induced fatigue in youth has substantially increased, and the effects of growth on the peripheral (muscular) and central (neural) mechanisms underpinning differences in neuromuscular fatigue between healthy children and adults have been described more extensively. The purpose of this review is to retrieve, report, and analyse the findings of studies comparing neuromuscular fatigue between children and adults. Objective measures of the evaluation of the physiological mechanisms are discussed. METHOD: Major databases (PubMed, Ovid, Scopus and Web of Science) were systematically searched and limited to English language from inception to September 2017. RESULT: Collectively, the analyzed studies indicate that children experience less muscular and potentially more neural fatigue than adults. However, there are still many unknown aspects of fatigue regarding neural (supraspinal and spinal) and peripheral mechanisms that should be more thoroughly examined in children. CONCLUSION: Suitable methods, such as transcranial magnetic stimulation, transcranial electrical stimulation, functional magnetic resonance imaging, near-infrared spectroscopy, tendon vibration, H-reflex, and ultrasound are recommended in the research field of fatigue in youth. By designing studies that test the fatigue effects in movements that replicate daily activities, new knowledge will be acquired. The linkage and interaction between physiological, cognitive, and psychological aspects of human performance remain to be resolved in young people. This can only be successful if research is based on a foundation of basic research focused on the mechanisms of fatigue while measuring all three above aspects

Altered drop jump landing biomechanics following eccentric exercise-induced muscle damage

© 2021 The Authors. Published by MDPI. This is an open access article available under a Creative Commons licence. The published version can be accessed at the following link on the publisher’s website: https://doi.org/10.3390/sports9020024Limited research exists in the literature regarding the biomechanics of the jump-landing sequence in individuals that experience symptoms of muscle damage. The present study investigated the effects of knee localized muscle damage on sagittal plane landing biomechanics during drop vertical jump (DVJ). Thirteen regional level athletes performed five sets of 15 maximal eccentric voluntary contractions of the knee extensors of both legs at 60◦/s. Pelvic and lower body kinematics and kinetics were measured preand 48 h post-eccentric exercise. The examination of muscle damage indicators included isometric torque, muscle soreness, and serum creatine kinase (CK) activity. The results revealed that all indicators changed significantly following eccentric exercise (p< 0.05). Peak knee and hip joint flexion as well as peak anterior pelvic tilt significantly increased, whereas vertical ground reaction force (GRF), internal knee extension moment, and knee joint stiffness significantly decreased during landing (p< 0.05). Therefore, the participants displayed a softer landing pattern following knee-localized eccentric exercise while being in a muscle-damaged state. This observation provides new insights on how the DVJ landing kinematics and kinetics alter to compensate the impaired function of the knee extensors following exercise-induced muscle damage (EIMD) and residual muscle soreness 48 h post-exercise.This research was supported by the postdoctoral scholarship program implemented by University of Thessaly (Greece) and funded by the Stavros Niarchos Foundation, grant number 5394.02.02Published versio

sEMG-based evaluation of muscle recruitment variability during walking in terms of activation length and occurrence frequency

Surface electromyography (sEMG) is commonly used in gait analysis for detecting muscle activity in a non-invasive way, preserving the normal mobility of the subject. The purpose of the study was to assess the variability of sEMG signals acquired from lower-limb muscles during walking. To this aim, a statistical analysis of sEMG signals from a large number (hundreds) of strides per subject was performed in twenty-two healthy young caucasian volunteers. Tibialis Anterior, Gastrocnemius Lateralis, Rectus Femoris, Biceps Femoris and Vastus Lateralis were selected to represent both proximal and distal leg segments. Besides the muscular activation onset-offset instants, the study was aimed to analysed the occurrence frequency of muscle recruitment, a parameter seldom considered because of the low number of strides usually analysed in classic EMG studies. Findings illustrated that a single muscle showed a different number of activation intervals in different strides of the same walking. The number of times when muscle activates during a single gait cycle defined the modality of muscle recruitment, that in the present study was referred to as activation modality, i.e. n-activation modality consists of n-activation intervals for the considered muscle, during a single gait cycle. For each of the selected muscles, five activation modalities were detected. Each of these activation modalities is characterized by a different occurrence frequency and by different onset-offset activation instants. Concomitance of these results indicates a large variability in onset-offset muscular activation and occurrence frequency, which should be considered in discriminating pathological from physiological behaviour and for designing focused gait studies

European consensus on the concepts and measurement of the pathophysiological neuromuscular responses to passive muscle stretch

BACKGROUND AND PURPOSE: To support clinical decision-making in central neurological disorders, a physical examination is used to assess responses to passive muscle stretch. However, what exactly is being assessed is expressed and interpreted in different ways. A clear diagnostic framework is lacking. Therefore, the aim was to arrive at unambiguous terminology about the concepts and measurement around pathophysiological neuromuscular response to passive muscle stretch. METHODS: During two consensus meetings, 37 experts from 12 European countries filled online questionnaires based on a Delphi approach, followed by plenary discussion after rounds. Consensus was reached for agreement ≥75%. RESULTS: The term hyper-resistance should be used to describe the phenomenon of impaired neuromuscular response during passive stretch, instead of for example 'spasticity' or 'hypertonia'. From there, it is essential to distinguish non-neural (tissue-related) from neural (central nervous system related) contributions to hyper-resistance. Tissue contributions are elasticity, viscosity and muscle shortening. Neural contributions are velocity dependent stretch hyperreflexia and non-velocity dependent involuntary background activation. The term 'spasticity' should only be used next to stretch hyperreflexia, and 'stiffness' next to passive tissue contributions. When joint angle, moment and electromyography are recorded, components of hyper-resistance within the framework can be quantitatively assessed. CONCLUSIONS: A conceptual framework of pathophysiological responses to passive muscle stretch is defined. This framework can be used in clinical assessment of hyper-resistance and will improve communication between clinicians. Components within the framework are defined by objective parameters from instrumented assessment. These parameters need experimental validation in order to develop treatment algorithms based on the aetiology of the clinical phenomena.status: publishe