Traditional coaching techniques and methods are being challenged by new approaches supported by advances in science and technology. Augmented biofeedback applications are one such example. They enable accelerated motor learning and offer additional information to coaches. Our motivation is the use of wearable wireless inertial sensor devices that provide real-time swimming motion data to coaches. Wireless communication in the water environment is a challenging task because radio waves do not

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... etrate the water well. Our solution uses Wi-Fi communication modules in conjunction with an application layer communication protocol that ensures reliable sensor signals and data transmissions during swimming when the communication channel is cyclically unavailable. We first measured the conditions of the swimming environment in terms of channel availability and then designed a block-selective repeat protocol that ensures reliable real-time data transmission. We have carried out a series of measurements in the swimming pool with young professional swimmers. The results prove the correct functioning of our protocol. We also present some basic protocol features, such as protocol efficiency. The presented work is used in the current development of a coach-based augmented biofeedback application in swimming. Abstract Traditional coaching techniques and methods are being challenged by new approaches supported by advances in science and technology. Augmented biofeedback applications are one such example. They enable accelerated motor learning and offer additional information to coaches. Our motivation is the use of wearable wireless inertial sensor devices that provide real-time swimming motion data to coaches. Wireless communication in the water environment is a challenging task because radio waves do not penetrate the water well. Our solution uses Wi-Fi communication modules in conjunction with an application layer communication protocol that ensures reliable sensor signals and data transmissions during swimming when the communication channel is cyclically unavailable. We first measured the conditions of the swimming environment in terms of channel availability and then designed a block-selective repeat protocol that ensures reliable real-time data transmission. We have carried out a series of measurements in the swimming pool with young professional swimmers. The results prove the correct functioning of our protocol. We also present some basic protocol features, such as protocol efficiency. The presented work is used in the current development of a coach-based augmented biofeedback application in swimming.