The devices for measuring plyometric exercise in field conditions are becoming increasingly prevalent in applied research and practice. However, before the use of a device in an applied setting, the validity and reliability of such an instrument must be determined. The study aimed to assess the validity and reliability of the Output Sport, an inertial measurement unit (IMU), through comparisons with a force plate for research purposes. A repeated measure test-retest study was performed. Reliability was assessed during single-session trials (i.e., intrasession reliability). A total of 34 national/university level athletes (13 females, 21 males) performed three drop jumps with a fall from 30 cm while both devices recorded ground contact time (GCT), flight time (FT), jump height (HJ), and reactive strength index (RSI). T-tests demonstrated that data collected from the IMU device were significantly different to the force platform for all reported variables (all p < 0.01). The intraclass correlation coefficients (ICC) demonstrated good-to-excellent reliability, but with a large range of confidence intervals (CI 95%) for GCT (0.825, 0.291–0.930), FT (0.928, 0.756–0.958), HJ (0.921, 0.773–0.964), and RSI (0.772, 0.151–0.907). The Bland-Altman test showed that the device overestimated contact times and underestimated the other variables. Upon landing, greater ground contact times (i.e., ≥0.355ms) were associated with higher reliability. These results suggest that a single IMU can be used to track changes somewhat accurately and reliably in jump metrics, especially when the GCT is greater than 0.355ms. It is recommended that before practitioners and trainers use the device as a cost-effective solution in the field, further research should be carried out to evaluate a range of data on the type of exercise to be performed.

In recent years, there has been an exponential increase in the number of devices developed to measure or estimate physical exercise. However, before these devices can be used in a practical and research environment, it is necessary to determine their validity and reliability. The purpose of this study is to test the validity and reliability of a load cell sensor-based device (LC) for measuring the peak force (PFr) and the rate of force development (RFD) during the isometric mid-thigh pull (IMTP) test, using a force plate (FP) as the gold standard. Forty-two undergraduate sport science students (male and female) participated in this study. In a single session, they performed three repetitions of the IMTP test, being tested simultaneously with an LC device and a Kistler force platform (FP). The PFr and RFD data were obtained from the force-time curve of the FP and compared with the LC data, provided automatically by the software of the device (Smart Traction device©). The mean difference between the results obtained by the LC device and the gold-standard equipment (FP) was not significantly different (p > 0.05), for both PFr and RFD, which suggests the validity of the ST results. Bland–Altman analysis showed a small mean difference in PFr = 1.69 N, upper bound = 47.88 N, and lower bound = −51.27 N. RFD showed that the mean difference was −5.27 N/s, upper limit = 44.36 N/s, and lower limit = −54.91 N/s. Our results suggest that the LC device can be used in the assessment of the isometric-mid-thigh-pull test as a valid and reliable tool. It is recommended that this device’s users consider these research results before putting the ST into clinical practice.

This systematic review provides critical and propositional information on criteria for determining the volume and intensity of drop jumps during plyometric training programs. Eligibility criteria were defined according to PICOS: Participants: male or female athletes, trained or recreationally active (16–40 years). Intervention duration: more than 4 weeks. Comparators: passive or active control group during a plyometric training program. Outcomes: information on improvement with Drop Jump or Depth Jump, with other jumps, acceleration, sprint, strength, and power output. Design: randomized controlled trials. We searched articles published in PubMed, SPORTDiscus, Web of Science, and Scopus. The search was conducted until 10 September 2022 for English-language articles only. The risk of bias was assessed using Grading of Recommendations, Assessment, Development and Evaluation (GRADE) for randomized controlled studies. We identified 31495 studies, of which only 22 were included. We found that six groups presented results with women, 15 presented results with men, and the remaining four presented mixed studies. Of the 686 people recruited, 329 participants aged 25.79 ± 4.76 years were involved in training. Methodological problems in training intensity, volume distribution, and individualization were noted, but methodological recommendations for their solution are also provided. It is concluded that the drop height should not be understood as the intensity determinant of plyometric training. Intensity is determined by ground reaction forces, power output, and jump height, among other factors. Furthermore, the athletes’ experience level selection should be based on the formulas recommended within this research. These results could be helpful for those who intend to conduct new plyometric training programs and research.

This study aims to verify the validity of the Push Band 2.0 (PB_2.0) device on the reactive strength index (RSI) measurement, using a force plate (FP) and an optical sensor device, OptoJump (OPT), as a reference. Twenty trained athletes performed 60 drop jump trials with a height box of 30 cm. A randomized repeated measures study was conducted during a single session using the PB_2.0, the OPT, and the plate force manually synchronized to obtain RSI data for each jump. Validity was analyzed by contrasting three measures: the intra-class correlation coefficient (ICC), the Bland–Altman test, and R2 coefficient of determination. Bland–Altman analysis showed that RSI and FP for PB2.0 (media = −0.047; IC 93.34%) of all data were within the confidence interval, indicating a statistically reliable result. The RSI measured by the OPT and PB2.0 also provided similar values (media = −0.047). These data are identical to other validity measures (ICC and linear correlation) but differ in the R2 values. The explained variation of PB2.0 measures attained only 29.3% of the FP (R2 = 0.293) and 29.5% (R2 = 0.295) of the OPT assessment, showing a very low determination coefficient. The results of this study point to caution in the use of PB2.0 when measuring RSI in scientific research.

The isometric mid-thigh pull (IMTP) is widely used for assessing maximal force production due to its minimal fatigue impact compared to dynamic strength tests. However, variations in testing protocols, equipment, and athlete characteristics may influence the reproducibility of IMTP-derived variables. Understanding its reliability in youth athletes is crucial for monitoring physical development and optimizing training programs. This systematic review followed PRISMA guidelines. A literature search in four databases (PubMed, SPORTDiscus, Scopus, Web of Science) identified studies on the test-retest reliability of IMTP in youth athletes (≤21 years). Extracted data included participant characteristics, testing protocols, and reliability metrics (intraclass correlation coefficients [ICCs], coefficient of variation [CVs], and standard error of measurement [SEM]). Twenty studies met inclusion criteria (2095 athletes). Peak force reliability was high (ICCs = 0.72–0.99, CVs = 2.0%–8.3%). Early phase force outputs (e.g., force at 50 and 100 ms) showed greater variability (ICCs = 0.73–0.95, CVs = 5.5%–23.3%). IMTP exhibits good-to-excellent reliability for peak force in youth athletes but higher variability in early force measures. Standardizing testing protocols may enhance reliability. Despite methodological differences, IMTP remains a valuable tool for strength monitoring and talent identification in youth athletes.

The reactive strength index (RSI) is a performance measure previously used to assess lower extremity performance; however, this study addresses limitations in its interpretation that need to be readdressed. The purpose of this study is twofold: to test the correlation of a new variable denominated integral reactive strength index (IRSI) with the RSI and to compare the flight time, ground contact time, jump height, RSI, reactive capacity, and IRSI between Olympic athletes in 100 m and 400 m. Ten elite male track and field athletes who qualified for the Olympics participated in this study (age = 24.9 ± 2.42 years; height = 1.75 ± 5.0 cm). They were divided into two groups, the first with five 100 m sprinters and the second group with five 400 m sprinters. The drop jump (DJ) attempts from 0.20 m were performed with the force plate 0.10 m away from the jump box. The DJ 0.30 m and DJ 0.40 m had a 0.15 m separation, and the DJ 0.50 m and DJ 0.60 m had a 0.20 m separation. The correlation analysis showed a high correlation (r = 0.805; p = 0.02) between the RSI and the IRSI. The comparisons between 400 m sprinters versus 100 m sprinters showed that there are no significant differences between the groups for any of the reactive strength variables (p > 0.05). Coaches of these sports’ specialties should take these criteria into account when developing plyometric programs and introduce the IRSI as an accurate measurement for evaluating DJ performance.