fig4

Figure 4. P-HMIs for sports coaching. (A) Schematic diagram of smart racket and sensor structure for interactive table tennis coaching. Reproduced with permission from ref.^[74]. Copyright 2019, Elsevier. (B) Photograph of piezoelectric sensor attached to an ice skate blade. (C) Measurement system for mimicking the motion of a knee joint. Reproduced with permission from ref.^[45]. Copyright 2021, MDPI. (D) Schematic diagram of P-HMI system based on a boxing glove. (E) Spatial distribution of force magnitudes obtained from electrodes attached to boxing glove. Reproduced with permission from ref.^[75]. Copyright 2019, Wiley. (F) Schematic diagram of monitoring swimming athlete’s elbow joint angle and heart rate. (G) SEM image of a single ZnO nanowire crossing a pair of electrodes. Scale bar of 10 μm. (H) Waveform of piezoelectric voltage output of butterfly stroke. Reproduced with permission from ref.^[76]. Copyright 2021, MDPI.