Abstract

Abstract
This study presents and applies cross-correlation analysis of lower limb joint angular kinematic signal for coordination assessment during impulse phase of standard Maximum Vertical Jump (MVJ). Standard MVJ has been applied for noninvasive subject specific analysis at Counter Movement Jump (CMJ) and Drop Jump (DJ) with long and short Counter Movement (CM) for comparison with Squat Jump (SJ) and no CM. Long and short CM are intrinsically related to the underlying mechanisms of muscle Stretch–Shortening Cycle (SSC) with the integration of muscular action and synergistic joint coordination an open issue on the contribution for the task to perform. Lower limb joint coordination has thus received increasing research interest as an external observed result of the neuromuscular control mechanisms and the hypotheses of training and repetition contribution for stereotyped coordination with the need of objective tools considering entire time series while avoiding subjective point selection for coordination assessment. The results of maximum cross-correlation (CCr max) and corresponding time delay (t) from entire time series of the Hip (H), the Knee (K) and the Ankle (A) joints angular displacement (?), angular velocities (?) and angular accelerations (a) during a fifty-four trial sample with long, short and no CM performed by a group of healthy untrained subjects conduced to detection of maximum synchrony with null t of the lower limb ? at different conditions, whereas ? and a CCr led to detection of different time delay for CCr max with dominant negative t values corresponding to a proximal–distal coordination sequence at H–K-A. These results point thus for the need to consider entire time series of joint ? and a in addition to joint ? to detect different joint coordination and avoid subjective point selection for coordination assessment. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023.

Abstract
This study presents and applies global metrics for the analysis of the center of pressure (COP) excursion during impulse phases at different standard maximum vertical jump (MVJ) with long, short and no countermovement (CM) at countermovement jump (CMJ), drop jump (DJ) and squat jump (SJ) expanding COP analysis from static to dynamic condition of CM in association with lower limb muscle stretch–shortening cycle (SSC) and complementing previous studies on time structural analysis of COP excursion during impulse phase at standard MVJ. Whereas literature is abundant on COP excursion at gait, run and orthostatic standing position, there is a lack of studies on COP analysis at standard MVJ with an open issue on its contribution to long, short and no CM performance. Fifty-four trial tests were assessed with the selection of the best CMJ, DJ and SJ for each subject based on vertical flight height hflight. During trial tests ground reaction forces (GRF) and force moments were acquired and the COP coordinates were computed during the impulse phases. COP stabilograms and statokinesigrams were plotted and global metrics were computed namely the COPxA antero-posterior and COPyA mediolateral amplitudes of COP excursion, mean radial distance R, the length L of the path and the average velocity v during COP excursion. Statistical significative differences were detected at 5% significance, with higher mean COPxA than COPyA and higher mean COP global metrics at CMJ than SJ both higher than DJ, with DJ higher velocity of COP excursion than CMJ both higher than SJ. Global correlational analysis presented a positive linear association of COP metrics with hflight whereas at segmented MVJ this association wasn’t detected, thus rejecting the negative impact of larger COP excursion on MVJ performance. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023.

Abstract
Due to the growth observed in the wearable market, stretchable strain sensors have been the focus of several studies. However, combining high sensitivity and linearity with low hysteresis presents a difficult challenge. Here, we propose a stretchable strain sensor obtained with off-the-shelf materials by printing a carbon conductive paste into a piece of fabric to be integrated into a smart garment. This process is cheap and easily scalable, allowing its mass production. The sensor developed has a large sensitivity (GF=11.27), high linearity (R-2>0.99), very low hysteresis (gamma(H) = 4.23%) and brings an added value, for example, in sports or rehabilitation monitoring.