The effects of muscle fatigue on knee function during landing

摘要: The human knee acts as a sophisticated shock absorber during landing movements. ability of the to perform this function in real world is remarkable given that context movement may vary widely between performances. For reason, humans must be capable rapidly adjusting mechanical properties under impact load order satisfy many competing demands. However, processes involved regulating these response changing constraints remain poorly understood. In particular, effects muscle fatigue on step are yet fully explored. Fatigue muscles significant for 2 reasons. First, it thought have detrimental act and considered risk factor injury. Second, provides unique opportunity examine mechanisms by which healthy individuals alter function. A review literature revealed effect has been assessed comparing pre postfatigue measurements, with induced voluntary exercise protocol. information limited inconsistent results key measures, such stiffness, showing varying following fatigue, including increased decreased stiffness or failure detect any change some experiments. Further consideration questions validity models used induce measure well pre-post study design, explain lack consensus results. These limitations cast doubt usefulness available identify need investigate alternative approaches. Based review, aims thesis were to: • evaluate methodological procedures validation model adaptation regulation post-impact mechanics repeated landings use new test step-landing task. To address thesis, 3 related experiments conducted collected kinetic, kinematic electromyographic data from separate samples male participants. methodologies optoelectronic motion capture (VICON), isokinetic dynamometry (System3 Pro, BIODEX) wireless surface electromyography (Zerowire, Aurion, Italy). indicators measures each experiment derived data. Study 1 compared reliability repetitive stepping contractions respect quadriceps hamstrings. Fifteen participants performed 50 repetitions twice randomised order, over 4 sessions. Sessions separated minimum week’s rest, ensure full recovery. Validity depended complex interaction protocol, indicator, individual interest. Nevertheless, differences protocols indicated was less effective eliciting valid reliable changes peak power spectral compression, exercise. finding progressed biphasic pattern both exercises. point separating phases, known transition point, demonstrated superior between-test stepping. correction should accurately apply technique landing. examined alterations landings, different sample (N =12) performing 60 consecutive trials. Each trial 1-minute rest periods. provided relation design detecting adjustments significantly pre-impact activity despite environmental task remaining unchanged. This 1st demonstrate without external feedback performance. single-subject analysis more group-level analysis. Finally, trials did not reduce inter-trial variability participants, contrary assumptions underpinning previous studies. studies modify relative research. included modified multiple pre-fatigue measurements singlesubject fatigue-related incorporated analytical approaches fatiguerelated Participants = 16) measured baseline blocks prior model. final block recorded once participant met operational definition identified 1. heavily dependent compensatory individual. continuum responses observed within measure. Overall, preimpact preparation altered highly individualised patterns. Moreover, range active passive strategies adapt fatigue. patterns represented an optimisation based priorities findings regarding functional inducing output compression (sEMG) signals, confounded inter-individual variation, limits sensitivity By addressing limitations, 3rd efficacies experimental observe Consequently, perspectives into conclusion: depend individual, considerable variation present similar physical characteristics. males, postimpact reflects their own demands energy expenditure, joint stability, sensory loading structures. guide future exploration adaptations research area continue reduced emphasis directional population greater focus