Analysis of Kinematic and Muscular Fatigue in Long-Distance Swimmers

Abstract

Muscle fatigue is a complex phenomenon that is influenced by the type of activity performed 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 Frequency of the EMG power spectrum, were obtained for 12 muscles to examine the electrical manifestations 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).

Keywords: electromyography; muscle coordination; swimming; task failure.

Figure 1

The figure illustrates the conditions under which the swimmer is involved in the study. In situation A, corresponding to the non-fatiguing and pre-mechanical failure phases, the swimmer’s face is perpendicular to the flickering light used for rhythm control. In situation B, representing the mechanical failure phase, the swimmer’s face is no longer aligned with the flashing light. In addition, the different phases of the stroke cycles are outlined.

Figure 2

The figure shows the temporal evolution of the electrical manifestations of fatigue from the initial moment of the test (non-fatigue phase) to the moment immediately preceding the loss of the ability to maintain the predetermined speed (pre-mechanical failure). Abbreviations: FCR = Flexor Carpi Radialis; BB = Biceps Brachii; TB = Triceps Brachii caput lateralis; DL = Deltoideus Lateralis; LD = Latissimus Dorsi; ST = Superior Trapezius; ES = Erector Spinae; PM = Pectoralis Major pars clavicularis; RF = Rectus Femoris; BF = Biceps Femoris.

Figure 3

Comparison of muscle profiles at 100% of a stroke cycle across different phases and muscles studied. Data were obtained by calculating the average muscle profile of all participants.