Analysis of Kinematic and Muscular Fatigue in Long-Distance Swimmers

Article Analysis of Kinematic and Muscular Fatigue in Long-Distance Swimmers Luca Puce 1, Carlo Biz 2,*, Alvise Ruaro 2, Fabiana Mori 2, Andrea Bellofiore 2, Pietro Nicoletti 3, Nicola Luigi Bragazzi 4,* and Pietro Ruggieri 2 1 Department of Neuroscience, Rehabilitation, Ophthalmology, Genetics, Maternal and Child Health (DINOGMI), University of Genoa, 16132 Genoa, Italy; luca1puce@gmail.com 2 Orthopedics and Orthopedic Oncology, Department of Surgery, Oncology and Gastroenterology (DiSCOG), University of Padova, 35128 Padova, Italy; alvise.ruaro@aopd.veneto.it (A.R.); fabiana.mori@studenti.unipd.it (F.M.); andrea.bellofiore@studenti.unipd.it (A.B.); pietro.ruggieri@unipd.it (P.R.) 3 Department of Neurosciences, University of Padova, 35128 Padova, Italy; pietronicoletti.ft@gmail.com 4 Laboratory for Industrial and Applied Mathematics (LIAM), Department of Mathematics and Statistics, York University, Toronto, ON M3J 1P3, Canada * Correspondence: carlo.biz@unipd.it (C.B.); robertobragazzi@gmail.com (N.L.B.) Abstract: Muscle fatigue is a complex phenomenon that is influenced by the type of activity per- formed and often manifests as a decline in motor performance (mechanical failure). The purpose of our study was to investigate the compensatory strategies used to mitigate mechanical failure. A cohort of 21 swimmers underwent a front-crawl swimming task, which required the consistent maintenance of a constant speed for the maximum duration. The evaluation included three phases: non-fatigue, pre-mechanical failure, and mechanical failure. We quantified key kinematic metrics, including velocity, distance travelled, stroke frequency, stroke length, and stroke index. In addition, electromyographic (EMG) metrics, including the Root-Mean-Square amplitude and Mean Fre- quency of the EMG power spectrum, were obtained for 12 muscles to examine the electrical mani- festations of muscle fatigue. Between the first and second phases, the athletes covered a distance of 919.38 ± 147.29 m at an average speed of 1.57 ± 0.08 m/s with an average muscle fatigue level of 12%. Almost all evaluated muscles showed a significant increase (p < 0.001) in their EMG activity, except for the latissimus dorsi, which showed a 17% reduction (ES 0.906, p < 0.001) during the push phase of the stroke cycle. Kinematic parameters showed a 6% decrease in stroke length (ES 0.948, p < 0.001), which was counteracted by a 7% increase in stroke frequency (ES −0.931, p < 0.001). Notably, the stroke index also decreased by 6% (ES 0.965, p < 0.001). In the third phase, characterised by the loss of the ability to maintain the predetermined rhythm, both EMG and kinematic parameters showed reductions compared to the previous two phases. Swimmers employed common compensatory strategies for coping with fatigue; however, the ability to maintain a predetermined motor output proved to be limited at certain levels of fatigue and loss of swimming efficiency (Protocol ID: NCT06069440).