The agreement between EV-CO and TOE-CO is clinically acceptable, and these two techniques can be used interchangeably.

Wearables are commonly used in practice for measuring and monitoring performance in high-level sports. That being said, they are often designed and intended for use during sports conducted on rigid surfaces. As such, sports that are conducted on sand, e.g. beach volleyball, lack equipment that can be specifically applied in the field. Therefore, the aim of this study was to develop and validate an inertial measurement unit (IMU)-based system for automatic jump detection and jump height measurement in sand. The system consists of two IMUs, which were attached to different parts of the athletes’ bodies. For validation under laboratory conditions, 20 subjects each performed five jumps on two consecutive days in a sandbox placed on force plates. Afterwards, five beach volleyball athletes performed complex combinations of beach volleyball-specific movements and jumps wearing the IMUs whilst being video recorded simultaneously. This was conducted in an ecologically valid setting to determine the validity of the IMU to correctly detect jumping actions. The results of the laboratory tests show excellent day-to-day reliability (intraclass correlation coefficient [ICC] = 0.937, two-way mixed effects, single measurement, consistency) and excellent concurrent validity (ICC = 0.946, two-way mixed effects, single rater, absolute agreement) compared to the gold standard (force plates). The accuracy in jump detection of the IMU was 100 and 97.5% in the laboratory and ecologically valid settings, respectively. Although there are still some aspects to consider when using such devices, the current findings provide recommendations regarding best practice when using such a device on a variable and unstable surface. Collectively, such a device could be applied in the field to provide coaches and practitioners with direct feedback to monitor training or match play.

Beach handball athletes experience an overlap during their preparation phase for the beach and the indoor season for several weeks. This transition phase from playing on an indoor surface to a sand surface is crucial for players’ performance levels both on the sand and indoor surfaces, but coaches and athletes alike are concerned about possible performance impairments when training on a sand surface while still playing indoors. Therefore, we aimed to evaluate the effects of a specific transition phase from the indoor to the beach season in elite beach handball athletes. With 29 elite athletes participating in the study, we evaluated their jumping (countermovement and drop jump) and sprinting (5–10–20 m) performances and conducted a handball-specific agility test on both rigid and sand surfaces. In addition, we evaluated a drop long jump on a sand surface. Vertical jumping performance was analyzed using a 3D marker-based system on both rigid and sand surfaces under standardized laboratory conditions. All tests took place directly before and after a 6-week intervention program. The results showed that athletes in the intervention group significantly improved their performance in jumping (countermovement and drop long jump) compared to the control group. Furthermore, performance on a rigid surface was not only maintained for all tests but also significantly increased for the countermovement jump. Therefore, the intervention program is effective at improving performance during the transition from indoor to beach seasons without impairing indoor performance.

The echocardiographic measurement of SV or CO at the level of the AV has to be reconsidered.