Integrated Timing of Stroking, Breathing, and Kicking in Front-Crawl Swimming: A Novel Stroke-by-Stroke Approach Using Wearable Inertial Sensors

Abstract

Quantitative evaluation of synergic action among the different body segments is fundamental to swimming performance. The aim of the present study was to develop an easy-to-use tool for stroke-by-stroke evaluation of a swimmer’s integrated timing of stroking, kicking, and breathing. Twelve swimmers were evaluated during one trial of 100 m front-crawl swimming at self-selected speed. Five three-axial inertial sensors were mounted on the head, wrists, and ankles. Algorithms for the wrist entry into the water, the lower limb beat during the downward action, and the exit/entry of the face from/into the water were developed. Temporal events identified by video-based technique, using one sagittal moving camera, were assumed as the gold standard. The performance was evaluated in terms of the root-mean-square error, 90th percentile of absolute error, coefficient of variation, Bland–Altman plots, and correlation analysis. Results of all temporal events showed high agreement with the gold standard, confirmed by a root-mean-square error of less than 0.05 s for absolute temporal parameters and less than 0.7% for the percentages of the stroke cycle duration, and with correlation coefficients higher than 0.856. The protocol proposed was not only accurate and reliable, but also user-friendly and as unobtrusive as possible for the swimmer, allowing a stroke-by-stroke analysis during the training session.

Wearables in Swimming for Real-Time Feedback: A Systematic Review

“…Four articles recruited elite-level swimmers (22.2%) [ 29 , 32 , 34 , 37 ], two articles recruited international-level participants (11.1%) [ 33 , 35 ], four articles recruited national-level/semi-professional participants (22.2%) [ 22 , 28 , 35 , 38 ], one article recruited local-level participants (5.5%) [ 31 ], and three articles recruited local/non-expert swimmers (16.7%) [ 22 , 25 , 36 ]. Conversely, six articles (33.3%) [ 21 , 23 , 24 , 26 , 27 , 30 ] did not report the swimmers’ competitive level.…”

“…Table 2 summarizes the aims of the studies, the participants´ demographics, and the swim strokes. From the 18 articles included for qualitative synthesis, eight (44.4%) [ 21 , 23 , 24 , 25 , 30 , 31 , 34 , 38 ] assessed wearables exclusively in front crawl, six (33.3%) [ 26 , 27 , 29 , 32 , 33 , 35 ] assessed wearables exclusively in all four swim strokes, two assessed wearables for the tumble turn in front crawl (11.1%) [ 36 , 37 ], one just assessed wearables in breaststroke (5.5%) [ 22 ], and another one assessed wearables in butterfly stroke (5.5%) [ 28 ]. Overall, 177 swimmers were recruited in all studies (103 males, 62 females, and 12 that the authors failed to note the sex of the participants).…”

“…Table 3 consolidates the details on the assessed sensor, the anatomical landmark where it was placed, variables analyzed, and the main findings of the studies. Fourteen studied accelerometers (77.8%) [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 29 , 32 , 33 , 35 , 36 , 37 , 38 ], seven studied microcontroller units (MCUs) (38.9%) [ 22 , 25 , 26 , 27 , 28 , 29 , 37 ], six studied IMUs (33.3%) [ 21 , 22 , 23 , 24 , 28 , 31 ], three studied visual feedback (16.7%) [ 25 , 26 , 27 ], and just one studied a gyroscope (5.5%) [ 34 ].…”

“…About the anatomical landmark, eight studies placed the wearable on the lower back (44.4%) [ 21 , 22 , 23 , 29 , 34 , 36 , 37 , 38 ], seven on the head (38.9%) [ 24 , 25 , 26 , 27 , 28 , 33 , 35 ], and five on the wrist (27.8%) [ 21 , 25 , 26 , 27 , 30 ] ( Table 3 ). Overall, the articles identified and/or measured variables related to kinematics and kinetics (e.g., duration of the stroke, stroke count, stroke rate, speed) during the arm stroke.…”

“…Figure 1 depicts the PRISMA flow diagram for identifying, screening, and checking eligibility, which then helps to determine inclusion of the articles. A total of 18 articles [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ] were included in the qualitative synthesis.…”